AVR-Chat

Steven Hodge Wrote
>Yes, my application is (sort of) automotive.  Specifically it is a boat
>environment, which is 12 VDC.  My guess is that in some respects it's not
>quite as harsh as automotive, but in others, eg, high power RF
transmissions
>and need to shield magnetic compasses from EM fields, it is far worse.    
I
>have many uses for uC's but the specific one that the post was about is
that
>I have put in a "bow thruster", which is a huge 5.0 KW, 12 VDC motor that
>draws about 400 A (which is another story).   This needs to be run from its
>own local 12 V battery (an Optima AGM starting type) because to run it from

Maybe not your best choice of battery.  What's your on time and frequency
look like?

>the main boat's bank in the aft part of the boat, the voltage drops even in
>large 4/0 cable would kill a lot of the motor's thrust.   

That would be why you run the local battery in parallel with the remote. 

How far are you from your main battery bank?  Inductance may be as big a
problem as resistance.  Actually I rather expect your battery resistance is
comparable to your cable resistance.

>Regarding voltage divider current drains, my assumption is that from the
>data sheets the analog ADC input likes to see 10 Kohms maximum impedance.
>For a maximum input to the ADC of Vcc = 3V this implies a current drain
>through the divider, regardless of amount of dividing, of 0.3 mA.   

You've forgotten your local capacitor an/or buffer op-amp.  You could
easily run a 10M resistor divider and follow it with a voltage follower to
bring the effective impedance down.  

You can also power the circuit only when it needs to be (the whole thing,
not just the voltage divider).

Robert


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> >I have put in a "bow thruster", which is a huge 5.0 KW, 12 VDC motor that
> >draws about 400 A (which is another story).   This needs to be run from its
> >own local 12 V battery (an Optima AGM starting type) because to run it from
>
> Maybe not your best choice of battery.  What's your on time and frequency
> look like?

12V?  I^2R losses will eat you alive!  48V would be better, but I'll
assume you're stuck with it.
Turning off this monster will be interesting.


> You've forgotten your local capacitor an/or buffer op-amp.  You could
> easily run a 10M resistor divider and follow it with a voltage follower to
> bring the effective impedance down.

You need to check the opamp's input offset before using such large
input resistors too.
The input offset current into 10M could yield a large error.

> You can also power the circuit only when it needs to be (the whole thing,
> not just the voltage divider).

True.


For a telco application, I needed to see the voltage across the pair.
The part 68 spec didn't allow us enough current to light up an
optoisolator in constant mode, but what we ended up doing was to
sample the line momentarily, which sort of falls through a hole in the
spec. There's many millions of them out there now, and no country's
telco approval has objected..  Instead of trying to draw less than a
microamp, we draw about a milliamp, but only for a few millisec.

>12V? I^2R losses will eat you alive! 48V would be better, but I'll
>assume you're stuck with it.

You got it.   Boat electrical is moving (very slowly) to higher voltages,
but I'm stuck with the legacy 12 V.

>Turning off this monster will be interesting.

Well, the actual thruster control circuitry which came with the unit does
this.  It uses solenoids and handles the actual turning on/off of the motor.
All I have to do is provide 2 active-low signals, one for each direction
(port or starboard).   And, as I said, protect those solenoids from
(literally) melt-down.

However, I separately need to have, for safety reasons, a remote means of
enabling/disabling the local thruster battery power, ie, a "battery
disconnect switch".   This is the "other story" I mentioned.    I could use
a commercial mechanical switch but these cost around $100 and, more
important, it would be difficult to access.  Hence the "remote" part.

This switch only has to carry the 400 A, not make or break it.   One can buy
from the thruster company a remote switch to do this, but it costs around
$800  (yes, that is no typo).   Commercial solenoids that can carry 400 A
continuous do not exist insofar as I can tell.  The best I have found is 250
A, so two of these in parallel would work, but the cost would still be $250
for two of them.   Thus I'm making my own using eight IRF2804 mosfets in
parallel.  I've used one of these quite successfully for a few years now for
a 45 A load.  These mosfets can carry up to 75 A continuous and have an
incredibly low on-resistance of only 2 milliohms.   These babies hardly get
warm at all with 45 A flowing through them.  I put heat sinks on but I'm not
convinced they are necessary.  I use Micrel 5014/5015 drivers with them.

Thanks for everyone's help.   This forum is looking to be very helpful, like
the boat ones I am on.  I hope I can reciprocate sometime.

Steve



[Non-text portions of this message have been removed]

Would a heavy duty starter solenoid from a diesel truck do the job for you?
I had a project a few years ago where the truck part was less than 1/4 the
cost of the commercial part.

-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Steven Hodge
Sent: Friday, December 14, 2007 9:54 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Re: ADC Vref

 

>12V? I^2R losses will eat you alive! 48V would be better, but I'll
>assume you're stuck with it.

You got it.   Boat electrical is moving (very slowly) to higher voltages,
but I'm stuck with the legacy 12 V.

>Turning off this monster will be interesting.

Well, the actual thruster control circuitry which came with the unit does
this.  It uses solenoids and handles the actual turning on/off of the motor.
All I have to do is provide 2 active-low signals, one for each direction
(port or starboard).   And, as I said, protect those solenoids from
(literally) melt-down.

However, I separately need to have, for safety reasons, a remote means of
enabling/disabling the local thruster battery power, ie, a "battery
disconnect switch".   This is the "other story" I mentioned.    I could use
a commercial mechanical switch but these cost around $100 and, more
important, it would be difficult to access.  Hence the "remote" part.

This switch only has to carry the 400 A, not make or break it.   One can buy
from the thruster company a remote switch to do this, but it costs around
$800  (yes, that is no typo).   Commercial solenoids that can carry 400 A
continuous do not exist insofar as I can tell.  The best I have found is 250
A, so two of these in parallel would work, but the cost would still be $250
for two of them.   Thus I'm making my own using eight IRF2804 mosfets in
parallel.  I've used one of these quite successfully for a few years now for
a 45 A load.  These mosfets can carry up to 75 A continuous and have an
incredibly low on-resistance of only 2 milliohms.   These babies hardly get
warm at all with 45 A flowing through them.  I put heat sinks on but I'm not
convinced they are necessary.  I use Micrel 5014/5015 drivers with them.

Thanks for everyone's help.   This forum is looking to be very helpful, like
the boat ones I am on.  I hope I can reciprocate sometime.

Steve



[Non-text portions of this message have been removed]



 
Yahoo! Groups Links






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11:29 AM

On Dec 14, 2007 1:33 PM, Philippe Habib <phabib@well.com> wrote:
> Would a heavy duty starter solenoid from a diesel truck do the job for you?
> I had a project a few years ago where the truck part was less than 1/4 the
> cost of the commercial part.


I was wondering the same thing.

It would take four of them for a polarity reversing switch, and the
drive to them isn't insignificant either, but a smallish relay could
drive each pair, and I'd want some safety logic to prevent a
shoot-thru, which could be rather entertaining in this application.

Well the gotcha seems to be the continuous part.   Starter relays in cars or
trucks are only designed for a few seconds of continuous use.   The thruster
is limited in total use to something like 5-7 minutes, but it is also
required, and is designed for, being able to be actually on continuously for
a good chunk, if not all, of that 5-7 minutes.  It's like a huge starter
motor that is actually required to be on continuously for periods of up to a
few minutes.   Web searches seem to come up with many in the 200 A ballpark,
but not 400 A.   

 

Besides that the IRF2804's cost less than $4 each.   Steve

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Philippe Habib
Sent: Friday, December 14, 2007 10:34 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Re: ADC Vref

 

Would a heavy duty starter solenoid from a diesel truck do the job for you?
I had a project a few years ago where the truck part was less than 1/4 the
cost of the commercial part.

-----Original Message-----
From: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>
[mailto:AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> ] On
Behalf
Of Steven Hodge
Sent: Friday, December 14, 2007 9:54 AM
To: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> 
Subject: RE: [AVR-Chat] Re: ADC Vref

>12V? I^2R losses will eat you alive! 48V would be better, but I'll
>assume you're stuck with it.

You got it. Boat electrical is moving (very slowly) to higher voltages,
but I'm stuck with the legacy 12 V.

>Turning off this monster will be interesting.

Well, the actual thruster control circuitry which came with the unit does
this. It uses solenoids and handles the actual turning on/off of the motor.
All I have to do is provide 2 active-low signals, one for each direction
(port or starboard). And, as I said, protect those solenoids from
(literally) melt-down.

However, I separately need to have, for safety reasons, a remote means of
enabling/disabling the local thruster battery power, ie, a "battery
disconnect switch". This is the "other story" I mentioned. I could use
a commercial mechanical switch but these cost around $100 and, more
important, it would be difficult to access. Hence the "remote" part.

This switch only has to carry the 400 A, not make or break it. One can buy
from the thruster company a remote switch to do this, but it costs around
$800 (yes, that is no typo). Commercial solenoids that can carry 400 A
continuous do not exist insofar as I can tell. The best I have found is 250
A, so two of these in parallel would work, but the cost would still be $250
for two of them. Thus I'm making my own using eight IRF2804 mosfets in
parallel. I've used one of these quite successfully for a few years now for
a 45 A load. These mosfets can carry up to 75 A continuous and have an
incredibly low on-resistance of only 2 milliohms. These babies hardly get
warm at all with 45 A flowing through them. I put heat sinks on but I'm not
convinced they are necessary. I use Micrel 5014/5015 drivers with them.

Thanks for everyone's help. This forum is looking to be very helpful, like
the boat ones I am on. I hope I can reciprocate sometime.

Steve

[Non-text portions of this message have been removed]

Yahoo! Groups Links

-- 
No virus found in this incoming message.
Checked by AVG Free Edition. 
Version: 7.5.503 / Virus Database: 269.17.2/1184 - Release Date: 12/14/2007
11:29 AM

 

__________ NOD32 2724 (20071214) Information __________

This message was checked by NOD32 antivirus system.
http://www.eset.com



[Non-text portions of this message have been removed]

On Dec 14, 2007 2:13 PM, Steven Hodge <stevehodge@speakeasy.net> wrote:
> Well the gotcha seems to be the continuous part.   Starter relays in cars or
> trucks are only designed for a few seconds of continuous use.   The thruster
> is limited in total use to something like 5-7 minutes, but it is also
> required, and is designed for, being able to be actually on continuously for
> a good chunk, if not all, of that 5-7 minutes.  It's like a huge starter
> motor that is actually required to be on continuously for periods of up to a
> few minutes.   Web searches seem to come up with many in the 200 A ballpark,
> but not 400 A.

Ouch.

Can the battery actually deliver 400A for 5 minutes?
A large deep cycle should be about 4500 Amp/min, but the puckert
effect says SIGNIFICANTLY less under that fast a drain.

My application was for a hydraulic pump that only needed to run for a few
seconds every few minutes.

-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Steven Hodge
Sent: Friday, December 14, 2007 11:14 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Re: ADC Vref

Well the gotcha seems to be the continuous part.   Starter relays in cars or
trucks are only designed for a few seconds of continuous use.   The thruster
is limited in total use to something like 5-7 minutes, but it is also
required, and is designed for, being able to be actually on continuously for
a good chunk, if not all, of that 5-7 minutes.  It's like a huge starter
motor that is actually required to be on continuously for periods of up to a
few minutes.   Web searches seem to come up with many in the 200 A ballpark,
but not 400 A.   

 

Besides that the IRF2804's cost less than $4 each.   Steve

 

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Philippe Habib
Sent: Friday, December 14, 2007 10:34 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Re: ADC Vref

 

Would a heavy duty starter solenoid from a diesel truck do the job for you?
I had a project a few years ago where the truck part was less than 1/4 the
cost of the commercial part.

-----Original Message-----
From: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>
[mailto:AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> ] On
Behalf
Of Steven Hodge
Sent: Friday, December 14, 2007 9:54 AM
To: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> 
Subject: RE: [AVR-Chat] Re: ADC Vref

>12V? I^2R losses will eat you alive! 48V would be better, but I'll
>assume you're stuck with it.

You got it. Boat electrical is moving (very slowly) to higher voltages,
but I'm stuck with the legacy 12 V.

>Turning off this monster will be interesting.

Well, the actual thruster control circuitry which came with the unit does
this. It uses solenoids and handles the actual turning on/off of the motor.
All I have to do is provide 2 active-low signals, one for each direction
(port or starboard). And, as I said, protect those solenoids from
(literally) melt-down.

However, I separately need to have, for safety reasons, a remote means of
enabling/disabling the local thruster battery power, ie, a "battery
disconnect switch". This is the "other story" I mentioned. I could use
a commercial mechanical switch but these cost around $100 and, more
important, it would be difficult to access. Hence the "remote" part.

This switch only has to carry the 400 A, not make or break it. One can buy
from the thruster company a remote switch to do this, but it costs around
$800 (yes, that is no typo). Commercial solenoids that can carry 400 A
continuous do not exist insofar as I can tell. The best I have found is 250
A, so two of these in parallel would work, but the cost would still be $250
for two of them. Thus I'm making my own using eight IRF2804 mosfets in
parallel. I've used one of these quite successfully for a few years now for
a 45 A load. These mosfets can carry up to 75 A continuous and have an
incredibly low on-resistance of only 2 milliohms. These babies hardly get
warm at all with 45 A flowing through them. I put heat sinks on but I'm not
convinced they are necessary. I use Micrel 5014/5015 drivers with them.

Thanks for everyone's help. This forum is looking to be very helpful, like
the boat ones I am on. I hope I can reciprocate sometime.

Steve

[Non-text portions of this message have been removed]

Yahoo! Groups Links

-- 
No virus found in this incoming message.
Checked by AVG Free Edition. 
Version: 7.5.503 / Virus Database: 269.17.2/1184 - Release Date: 12/14/2007
11:29 AM

 

__________ NOD32 2724 (20071214) Information __________

This message was checked by NOD32 antivirus system.
http://www.eset.com



[Non-text portions of this message have been removed]



 
Yahoo! Groups Links






-- 
No virus found in this incoming message.
Checked by AVG Free Edition. 
Version: 7.5.503 / Virus Database: 269.17.2/1184 - Release Date: 12/14/2007
11:29 AM

>Ouch.

>Can the battery actually deliver 400A for 5 minutes?
>A large deep cycle should be about 4500 Amp/min, but the puckert
>effect says SIGNIFICANTLY less under that fast a drain

It should be able to.  The Optima battery that I will be using is a starting
type of battery, not a deep cycle, with a CCA (cold cranking amps) of 1100 A
(model D31T).  It is one that is specifically recommended by commercial
installers of my make/model of thruster.  Optima "spiral-wound" AGM
(absorbed glass matt) batteries are pretty amazing batteries.  They hold
their charge for months on end without having to be float charged.   (But
they are easily destroyed by over-charging or over-voltage.)

In practice, operation of a thruster is usually bursts of power lasting
10-30 seconds.    Periods of minutes are very unusual.but can occur.

Steve

 

 

 

 



[Non-text portions of this message have been removed]

> It should be able to.  The Optima battery that I will be using is a starting
> type of battery, not a deep cycle, with a CCA (cold cranking amps) of 1100 A
> (model D31T).

Right, but I'm sure there's a finite time limit to that.

http://en.wikipedia.org/wiki/Car_battery    Wikipedia says it's 30 seconds.


> In practice, operation of a thruster is usually bursts of power lasting
> 10-30 seconds.    Periods of minutes are very unusual.but can occur.

Well, it looks wimpy to me, but if the thruster guys say it's ok, then
I guess....
I've never played with a thruster before.

At 09:53 AM 12/14/2007 -0800, Steven Hodge wrote:
>
>
> >12V? I^2R losses will eat you alive! 48V would be better, but I'll
> >assume you're stuck with it.
>
>You got it.   Boat electrical is moving (very slowly) to higher voltages,
>but I'm stuck with the legacy 12 V.
>
> >Turning off this monster will be interesting.
>
>Well, the actual thruster control circuitry which came with the unit does
>this.  It uses solenoids and handles the actual turning on/off of the motor.
>All I have to do is provide 2 active-low signals, one for each direction
>(port or starboard).   And, as I said, protect those solenoids from
>(literally) melt-down.
>
>However, I separately need to have, for safety reasons, a remote means of
>enabling/disabling the local thruster battery power, ie, a "battery
>disconnect switch".   This is the "other story" I mentioned.    I could use
>a commercial mechanical switch but these cost around $100 and, more
>important, it would be difficult to access.  Hence the "remote" part.
>
>This switch only has to carry the 400 A, not make or break it.   One can buy
>from the thruster company a remote switch to do this, but it costs around
>$800  (yes, that is no typo).   Commercial solenoids that can carry 400 A
>continuous do not exist insofar as I can tell.

Actually they are fairly common.  You are just using the wrong 
keywords.  What you want is a contactor.  For this kind of work I prefer 
Albright.  Unlike many companies they actually provide specifications for 
their contactors

For example

An SW200
         - 250A continuous
         - 450A 30% duty cycle, ~360second on time.  They would likely 
consider this intermittent duty if I recall correctly
         - breaking current 1500A at 48V
         - < $150

An SW500 is rated to 500A, that's a telecom unit so you may have to special 
order to get a 12V coil.

I really like their SD250 which combine a line contactor with an emergency 
disconnect.

I've had good luck with Tecknowledgey

http://www.tecknowledgey.com/catalog/default.php?cPath=57

Knowledgeable and good service.  They asked me a number of questions and 
then let me specify exactly what I needed once they realized I knew what I 
was talking about when I asked for what I asked for.

>The best I have found is 250
>A, so two of these in parallel would work, but the cost would still be $250
>for two of them.

If they are automotive I wouldn't trust them.  They are almost certainly 
less capable than their rating, probably a good deal less.  I've had bad 
experiences with people putting an automotive solenoid where a proper 
contactor should be used in order to save money.  Also they don't parallel 
well under arcing conditions.  I am seriously NOT impressed when it comes 
to automotive ratings on electrical power devices, when you can find 
ratings they are usually seriously close to the edge of the devices 
capability at best.

>Thus I'm making my own using eight IRF2804 mosfets in
>parallel.  I've used one of these quite successfully for a few years now for
>a 45 A load.  These mosfets can carry up to 75 A continuous and have an
>incredibly low on-resistance of only 2 milliohms.   These babies hardly get
>warm at all with 45 A flowing through them.  I put heat sinks on but I'm not
>convinced they are necessary.

Umm, paralleling MOSFETs to carry current is not a trivial 
task.  Especially for turn on/turn off.  They are also a LOT more sensitive 
to inductive kickback than contactors. There are all sorts of interesting 
traps here.

Robert

http://www.aeolusdevelopment.com/

 From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time?  37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live.... we 
currently have stock."

Robert, thank you for your valuable comments.   "Contactor"!   I had never
heard that terminology.   All that is ever used in the marine world is
"solenoid", or sometimes "relay".  But you are right, searching on that term
does the trick.  I am very rapidly converging on using the SW500.  It's $10
cheaper than the SW200 and is higher rated and continuous duty.   I looked
at the SD402 but for $25 I can just add a standard marine manual battery
disconnect switch (meeting the amp requirements) to the SW500 to accomplish
the same.     

 

As for the mosfet idea, your post prompted me to estimate the cost of the
parts to make it (mosfets, copper bus bars, pcb manufacture, and other) and
it came to roughly the same as the SW500.  So that made things a no-brainer.
Even though now a dead idea, I do, however, want to comment that my existing
single-mosfet board which carries 45 A is operating two motors that are
switched on/off externally.   So it presumably gets hit with inductive
spikes.  I do have protection diodes on it.   Admittedly currents are much
less than 400, but I have never had any problems with it.

 

I would not use automotive stuff either.   Equipment rated for marine use
has very stringent specs, especially electrical.   A fire on a boat is an
extremely serious event.

 

As for the battery, well, what can I say?   It was recommended by a person
who installs about 60 thrusters a year in boats.   The thruster specs only
call for a minimum of 800 CCA and this is 1100.   There are probably 3
issues that play into this.  The first is that typical use, as I said, is
one to a few bursts each lasting 5-15 seconds or so.   Continuously on for
periods of one to a few minutes are the exception.  The second is that the
thruster does not get used anywhere near as frequently as a normal starting
battery.   In a year, in my case, maybe a couple of dozen times.   The third
is that weight in the bow of any boat (where this necessarily has to be,
because it moves the bow sideways) is to be avoided as much as possible.
Thus it's better to live with under-rating it for the extreme circumstances
rather than have to always suffer the negative consequences of the extra
weight of an additional or larger battery.  (The thruster itself weights 60
lbs.)

 

Once again, thanks for your help.

 

Steve

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Robert Adsett
Sent: Friday, December 14, 2007 4:46 PM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Re: ADC Vref

Actually they are fairly common. You are just using the wrong 
keywords. What you want is a contactor. For this kind of work I prefer 
Albright. Unlike many companies they actually provide specifications for 
their contactors

For example

An SW200
- 250A continuous
- 450A 30% duty cycle, ~360second on time. They would likely 
consider this intermittent duty if I recall correctly
- breaking current 1500A at 48V
- < $150

An SW500 is rated to 500A, that's a telecom unit so you may have to special 
order to get a 12V coil.

I really like their SD250 which combine a line contactor with an emergency 
disconnect.

I've had good luck with Tecknowledgey

http://www.tecknowledgey.com/catalog/default.php?cPath=57

Knowledgeable and good service. They asked me a number of questions and 
then let me specify exactly what I needed once they realized I knew what I 
was talking about when I asked for what I asked for.

>The best I have found is 250
>A, so two of these in parallel would work, but the cost would still be $250
>for two of them.

If they are automotive I wouldn't trust them. They are almost certainly 
less capable than their rating, probably a good deal less. I've had bad 
experiences with people putting an automotive solenoid where a proper 
contactor should be used in order to save money. Also they don't parallel 
well under arcing conditions. I am seriously NOT impressed when it comes 
to automotive ratings on electrical power devices, when you can find 
ratings they are usually seriously close to the edge of the devices 
capability at best.

>Thus I'm making my own using eight IRF2804 mosfets in
>parallel. I've used one of these quite successfully for a few years now for
>a 45 A load. These mosfets can carry up to 75 A continuous and have an
>incredibly low on-resistance of only 2 milliohms. These babies hardly get
>warm at all with 45 A flowing through them. I put heat sinks on but I'm not
>convinced they are necessary.

Umm, paralleling MOSFETs to carry current is not a trivial 
task. Especially for turn on/turn off. They are also a LOT more sensitive 
to inductive kickback than contactors. There are all sorts of interesting 
traps here.

Robert

http://www.aeolusdevelopment.com/

From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time? 37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live.... we 
currently have stock."

 

__________ NOD32 2724 (20071214) Information __________

This message was checked by NOD32 antivirus system.
http://www.eset.com



[Non-text portions of this message have been removed]

At 07:49 AM 12/15/2007 -0800, Steven Hodge wrote:
>Robert, thank you for your valuable comments.   "Contactor"!   I had never
>heard that terminology.   All that is ever used in the marine world is
>"solenoid", or sometimes "relay".  But you are right, searching on that term
>does the trick.  I am very rapidly converging on using the SW500.  It's $10
>cheaper than the SW200 and is higher rated and continuous duty.   I looked
>at the SD402 but for $25 I can just add a standard marine manual battery
>disconnect switch (meeting the amp requirements) to the SW500 to accomplish
>the same.

Welcome to my world.  It's a bit of an industry separator.  In the EV 
industry relays are low current devices and solenoids are used to open and 
close hydraulic valves.

The SW500 is probably overkill for you but that's not a bad thing.

>As for the mosfet idea, your post prompted me to estimate the cost of the
>parts to make it (mosfets, copper bus bars, pcb manufacture, and other) and
>it came to roughly the same as the SW500.  So that made things a no-brainer.
>Even though now a dead idea, I do, however, want to comment that my existing
>single-mosfet board which carries 45 A is operating two motors that are
>switched on/off externally.   So it presumably gets hit with inductive
>spikes.  I do have protection diodes on it.   Admittedly currents are much
>less than 400, but I have never had any problems with it.

Yep, but here is a big jump in complexity once you start paralleling 
(larger than is immediately apparent).   With a 12V but you are probably a 
lot further away from breakdown than I usually am but keep in mind that 
even uS pulses will short a MOSFET after which it will either fuse due to 
the very high current or just act as a wire.

>I would not use automotive stuff either.   Equipment rated for marine use
>has very stringent specs, especially electrical.   A fire on a boat is an
>extremely serious event.

Speaking of which, remember these are open contactors.  If you need to 
avoid sparks you may need to enclose them.

>As for the battery, well, what can I say?   It was recommended by a person
>who installs about 60 thrusters a year in boats.   The thruster specs only
>call for a minimum of 800 CCA and this is 1100.   There are probably 3
>issues that play into this.  The first is that typical use, as I said, is
>one to a few bursts each lasting 5-15 seconds or so.

  That does make a difference.  It's only a few multiple of automotive 
start times.

>Continuously on for
>periods of one to a few minutes are the exception.

That's the one that was worrying me.  Discharging at (a guess) > 4C is not 
a good thing to do to a battery.  At the short duration though that is what 
automotive batteries are optimized for.

>The second is that the
>thruster does not get used anywhere near as frequently as a normal starting
>battery.   In a year, in my case, maybe a couple of dozen times.   The third
>is that weight in the bow of any boat (where this necessarily has to be,
>because it moves the bow sideways) is to be avoided as much as possible.
>Thus it's better to live with under-rating it for the extreme circumstances
>rather than have to always suffer the negative consequences of the extra
>weight of an additional or larger battery.  (The thruster itself weights 60
>lbs.)

That leads me to think a DC/DC from your main battery bank might be 
worthwhile.  It would keep the thruster battery charged up but the current 
draw would be minimal.


>Once again, thanks for your help.

Not a problem.

A couple of items to keep in mind

To Albright an intermittent duty coil is used on direction contactors and 
is expected to run some thing like 40-60% on with 10's of seconds to 
minutes between direction changes.    Continuous can handle more but an 
intermittent coil may well work for you.

The SW500 is a telecom contactor so a 12V coil may take extra lead time.  I 
expect it will be available but it might be uncommon.

Tek will probably question you on your selection to make sure you are 
making the right choice.  They seem quite knowledgeable from my contact 
with them and they don't do much second guessing once it's clear you know 
what you are doing.  I've had the same issue with a number of contactor 
manufacturing companies, they don't want to provide specifications they 
want the details of your application so they can pick the contactor for 
you.  It's one big reason I like Albright.

Good Fortune.

Robert

http://www.aeolusdevelopment.com/

 From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time?  37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live.... we 
currently have stock."

Welcome to my world. It's a bit of an industry separator. In the EV 
industry relays are low current devices and solenoids are used to open and 
close hydraulic valves.

Ø    I’ve encountered that use of “solenoid” as well.  (Does “EV” stand for
Electric Vehicles?  I just bought a Prius.)

The SW500 is probably overkill for you but that's not a bad thing.

Ø    Agreed.

Speaking of which, remember these are open contactors. If you need to 
avoid sparks you may need to enclose them.

Ø    Good point, but probably not necessary for 2 reasons.   First it is at
the other end of the boat from the engine, propane, fuel, etc, but, more
important, the contactor does not make/break the 400 A.  It only has to
carry it.  Thus there should not be any sparks.  Nonetheless, I’ll mention
it when I talk to Teknowledgey.

That leads me to think a DC/DC from your main battery bank might be 
worthwhile. It would keep the thruster battery charged up but the current 
draw would be minimal.

> To charge the thruster battery I  have a marine-grade “Automatic Charge
Relay” (there’s that term again, even though it handles up to 60 A!).   This
automatically connects to the main boat bank whenever that bank is being
charged, and disconnects when not.   The main bank always uses a “smart”
charger, either from shore power (120 VAC source) or the engine.   This is
SOP on boats.  The thruster battery thus automatically gets charged every
time the boat is on shore power or the engine is used, regardless of whether
or not the thruster has been used (the same as the engine start battery).
The Optima batteries hold their charge so well that the battery can go weeks
or even months without being used and not float charged in the interim.  I
use an Optima for the engine start battery.   

> Also, the thruster is only used when the engine is running.   In practice
the engine will have typically been running for many tens of minutes, often
an hour or more, before the thruster is actually used.  Thus the thruster
battery will always get charged immediately before being used in almost all
cases.  (I should add that this is a sailboat, so the engine is not
necessarily on all the time when the boat is underway.)

> I have a third Optima on the boat, a deep cycle one.  This is used for the
source of that 45 A current that I mentioned with the mosfet business.
This gets used on a pretty steady basis and needs to be kept as charged as
possible all the time, whether or not an external charging source is
present.  In this case, I do use a DC/DC arrangement to keep it charged from
the main bank.

To Albright an intermittent duty coil is used on direction contactors and 
is expected to run some thing like 40-60% on with 10's of seconds to 
minutes between direction changes. Continuous can handle more but an 
intermittent coil may well work for you.

The SW500 is a telecom contactor so a 12V coil may take extra lead time. I 
expect it will be available but it might be uncommon.

Ø    Thanks for the tip.  I’m ok with up to a couple of months.

Tek will probably question you on your selection to make sure you are 
making the right choice. They seem quite knowledgeable from my contact 
with them and they don't do much second guessing once it's clear you know 
what you are doing. I've had the same issue with a number of contactor 
manufacturing companies, they don't want to provide specifications they 
want the details of your application so they can pick the contactor for 
you. It's one big reason I like Albright.

> I’ll do as you suggest and talk to Teknowledgy and let them guide my final
decision.

> Steve



[Non-text portions of this message have been removed]

At 09:57 AM 12/15/2007 -0800, Steven Hodge wrote:
>Welcome to my world. It's a bit of an industry separator. In the EV
>industry relays are low current devices and solenoids are used to open and
>close hydraulic valves.
>
>Ø    I’ve encountered that use of “solenoid” as well.  (Does “EV” stand for
>Electric Vehicles?  I just bought a Prius.)

That's right.  I generally have worked with 'real' EVs rather than 
automobiles although at a previous employer we did some stuff with Feel 
Good Cars.  There are a lot more electric vehicle out there than most 
people realize.  One line at one OEM we worked with was probably running 
5-10K per year.  And then there are companies whose output is measured in 
low double digits per year.

The other usages aren't wrong but usage in the EV industry has generally 
developed a connotation to the various terms.

Every transport you see running down the highway probably had an EV 
involved in at least one of loading or unloading it.


>Speaking of which, remember these are open contactors. If you need to
>avoid sparks you may need to enclose them.
>
>Ø    Good point, but probably not necessary for 2 reasons.   First it is at
>the other end of the boat from the engine, propane, fuel, etc, but, more
>important, the contactor does not make/break the 400 A.  It only has to
>carry it.  Thus there should not be any sparks.  Nonetheless, I’ll mention
>it when I talk to Teknowledgey.

Well it might have to break 400A if something goes wrong down 
stream.  Hopefully that's unlikely but that's what the breaking current has 
to be specified to meet.

Note, if you are truly cold switching (no current, thus no arc) you can run 
into problems keeping the contactor tips clean.   That caused me a trip to 
a customer site one time (vehicle wouldn't move because the tips had a thin 
and non-visible layer of contaminants).

Robert

Another sign of the end of civilization, our technical magazines are 
getting chatty
 From an EETimes product descriptions 2006/08/09
".... systems that can sample gobs of inputs simultaneously"
Now just what is the technical definition for gobs again?
http://www.aeolusdevelopment.com/

"Speaking of which, remember these are open contactors.  If you need to 
avoid sparks you may need to enclose them."

Remember, too, that if there are combustible fumes you'll need more than 
just an enclosed contactor.

How about your batteries, Steve?  Are they in an enclosed space?  If so, 
you might want to have some sort of air exchange to ensure you don't 
have a buildup of gas in the enclosure.  An AGM battery, although 
"sealed" will still produce gas at the end of its charge cycle and if 
the internal vapor pressure gets too high due to a high charge voltage 
they'll vent...and that's hydrogen.

If you're reversing, you might also want to make sure you bring your 
motor to a full stop before reversing polarity of drive.  That can be 
accomplished by using a slight delay between forward and reverse and 
some breaking resistors in the circuit, and an auxiliary contact on your 
contactors.  If you try to "plug reverse" it'll probably peg your fun 
meter, but in the wrong direction.


REB


Robert Adsett wrote:

>At 07:49 AM 12/15/2007 -0800, Steven Hodge wrote:
>  
>
>>Robert, thank you for your valuable comments.   "Contactor"!   I had never
>>heard that terminology.   All that is ever used in the marine world is
>>"solenoid", or sometimes "relay".  But you are right, searching on that term
>>does the trick.  I am very rapidly converging on using the SW500.  It's $10
>>cheaper than the SW200 and is higher rated and continuous duty.   I looked
>>at the SD402 but for $25 I can just add a standard marine manual battery
>>disconnect switch (meeting the amp requirements) to the SW500 to accomplish
>>the same.
>>    
>>
>
>Welcome to my world.  It's a bit of an industry separator.  In the EV 
>industry relays are low current devices and solenoids are used to open and 
>close hydraulic valves.
>
>The SW500 is probably overkill for you but that's not a bad thing.
>
>  
>
>>As for the mosfet idea, your post prompted me to estimate the cost of the
>>parts to make it (mosfets, copper bus bars, pcb manufacture, and other) and
>>it came to roughly the same as the SW500.  So that made things a no-brainer.
>>Even though now a dead idea, I do, however, want to comment that my existing
>>single-mosfet board which carries 45 A is operating two motors that are
>>switched on/off externally.   So it presumably gets hit with inductive
>>spikes.  I do have protection diodes on it.   Admittedly currents are much
>>less than 400, but I have never had any problems with it.
>>    
>>
>
>Yep, but here is a big jump in complexity once you start paralleling 
>(larger than is immediately apparent).   With a 12V but you are probably a 
>lot further away from breakdown than I usually am but keep in mind that 
>even uS pulses will short a MOSFET after which it will either fuse due to 
>the very high current or just act as a wire.
>
>  
>
>>I would not use automotive stuff either.   Equipment rated for marine use
>>has very stringent specs, especially electrical.   A fire on a boat is an
>>extremely serious event.
>>    
>>
>
>Speaking of which, remember these are open contactors.  If you need to 
>avoid sparks you may need to enclose them.
>
>  
>


[Non-text portions of this message have been removed]

The thruster battery will be in a naturally-vented compartment.   However,
one of the task's of the uC will be to monitor charge currents and turn on a
fan when they are high.   The main boat batteries (750 amp-hours) are in
their own compartment with a similar venting fan.   The need to vent
charging batteries is a well-known issue on boats.

 

The uC will "pre-process" the two port/starboard direction signals that
actually cause the motor to turn on in the desired direction.   One task of
the uC is, in fact, to introduce the delay you mention.  It will be a delay
that suppresses both "on" signals for a short time after either signal goes
from "on" to "off", but not from "off" to "on".  That way if the operator
naturally pauses between directions an additional (annoying) delay will not
be imposed.

 

The actual thruster unit has the reversing solenoids.  I don't need to deal
with them.  All I need to do is provide the two active-low signals that
cause it to go one direction or the other.

 

Steve

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Roy E. Burrage
Sent: Saturday, December 15, 2007 10:42 AM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Re: ADC Vref

 

"Speaking of which, remember these are open contactors. If you need to 
avoid sparks you may need to enclose them."

Remember, too, that if there are combustible fumes you'll need more than 
just an enclosed contactor.

How about your batteries, Steve? Are they in an enclosed space? If so, 
you might want to have some sort of air exchange to ensure you don't 
have a buildup of gas in the enclosure. An AGM battery, although 
"sealed" will still produce gas at the end of its charge cycle and if 
the internal vapor pressure gets too high due to a high charge voltage 
they'll vent...and that's hydrogen.

If you're reversing, you might also want to make sure you bring your 
motor to a full stop before reversing polarity of drive. That can be 
accomplished by using a slight delay between forward and reverse and 
some breaking resistors in the circuit, and an auxiliary contact on your 
contactors. If you try to "plug reverse" it'll probably peg your fun 
meter, but in the wrong direction.

REB

Robert Adsett wrote:

>At 07:49 AM 12/15/2007 -0800, Steven Hodge wrote:
> 
>
>>Robert, thank you for your valuable comments. "Contactor"! I had never
>>heard that terminology. All that is ever used in the marine world is
>>"solenoid", or sometimes "relay". But you are right, searching on that
term
>>does the trick. I am very rapidly converging on using the SW500. It's $10
>>cheaper than the SW200 and is higher rated and continuous duty. I looked
>>at the SD402 but for $25 I can just add a standard marine manual battery
>>disconnect switch (meeting the amp requirements) to the SW500 to
accomplish
>>the same.
>> 
>>
>
>Welcome to my world. It's a bit of an industry separator. In the EV 
>industry relays are low current devices and solenoids are used to open and 
>close hydraulic valves.
>
>The SW500 is probably overkill for you but that's not a bad thing.
>
> 
>
>>As for the mosfet idea, your post prompted me to estimate the cost of the
>>parts to make it (mosfets, copper bus bars, pcb manufacture, and other)
and
>>it came to roughly the same as the SW500. So that made things a
no-brainer.
>>Even though now a dead idea, I do, however, want to comment that my
existing
>>single-mosfet board which carries 45 A is operating two motors that are
>>switched on/off externally. So it presumably gets hit with inductive
>>spikes. I do have protection diodes on it. Admittedly currents are much
>>less than 400, but I have never had any problems with it.
>> 
>>
>
>Yep, but here is a big jump in complexity once you start paralleling 
>(larger than is immediately apparent). With a 12V but you are probably a 
>lot further away from breakdown than I usually am but keep in mind that 
>even uS pulses will short a MOSFET after which it will either fuse due to 
>the very high current or just act as a wire.
>
> 
>
>>I would not use automotive stuff either. Equipment rated for marine use
>>has very stringent specs, especially electrical. A fire on a boat is an
>>extremely serious event.
>> 
>>
>
>Speaking of which, remember these are open contactors. If you need to 
>avoid sparks you may need to enclose them.
>
> 
>

[Non-text portions of this message have been removed]

 

__________ NOD32 2726 (20071217) Information __________

This message was checked by NOD32 antivirus system.
http://www.eset.com



[Non-text portions of this message have been removed]

On Dec 17, 2007 10:18 AM, Steven Hodge <stevehodge@speakeasy.net> wrote:
> The thruster battery will be in a naturally-vented compartment.   However,
> one of the task's of the uC will be to monitor charge currents and turn on a
> fan when they are high.   The main boat batteries (750 amp-hours) are in
> their own compartment with a similar venting fan.   The need to vent
> charging batteries is a well-known issue on boats.

Brushless fans, I hope :)

Of course J

> their own compartment with a similar venting fan. The need to vent
> charging batteries is a well-known issue on boats.

Brushless fans, I hope :)



[Non-text portions of this message have been removed]