AVR-Chat

Hi guys,

I am designing a university project, a hand-held printer using the 
AVR and a small thermal printer. For portability I want to use 4 x 
2300mAh AA batteries in serial/parallel to provide me with 3V.

The printer runs on 5V but consumes over 3.5A peak, so I require a DC-
DC converter circuit (or at least a starting point) to provide 3V at 
5A peak.

Has anyone designed anything like this, or can give me some advice? 
Maybe someone has an idea for a better battery for me to use?

Cheers
Col

At 09:16 AM 7/30/2004, C Sizer wrote:

>Hi guys,
>
>I am designing a university project, a hand-held printer using the 
>AVR and a small thermal printer. For portability I want to use 4 x 
>2300mAh AA batteries in serial/parallel to provide me with 3V.

Shuttle or line mech?  Line is much faster, and much more demanding.
You need roughly the same horsepower as a laser printer of the same size would.

>The printer runs on 5V but consumes over 3.5A peak, so I require a DC-
>DC converter circuit (or at least a starting point) to provide 3V at 
>5A peak.
>
>Has anyone designed anything like this, or can give me some advice? 
>Maybe someone has an idea for a better battery for me to use?

You'd be far better off to put your batteries in series, and then buck regulate the 3V.
There are pulse-skipping converters that are very efficient. If the current is low enough, you can win with analog again..  Then again, why not run on 5V?

Also, do the math on burn energy, you'll find that the faster you print, the less energy you spend.  A significant amount of your print energy goes into heating up the printhead mass.  Wake up, go like hell, shut down.

Dedicate a timer to the stepper, and another to the burn.
Use the burn timer like an alarm clock, interrupting you when the first head group is done, then reload for the remainder of the burn on the second group, etc.

You can start the burn pulse with a nominal value, do the calculations (FMULT is your friend) and then change the timer setting to the calculated burn width.

The stepper will need to be accelerated, and decelerated, depending on how much rasterized data you have built up. 

The SPI port is great at blowing out data to the head at high speed. 

I did one early this year, using a Mega-8 with on-chip osc, and a stepper driver IC.
It was capable of running the mech at full speed, which ended up to be faster than the 1.7 GHz laptop could send the data out.

You'll find the details of getting this going properly, quite interesting.

--- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:

> ... I want to use 4 x 2300mAh AA
> batteries in serial/parallel to
> provide me with 3V.

Sounds like alkaline cells at 1.5 volts each.

> The printer runs on 5V but consumes
> over 3.5A peak, so I require a DC-
> DC converter circuit... to provide
> 3V at 5A peak.

You mean to provide 5V/3.5A, which will suck six amps or more from 
your 3V battery. I don't think this will work. The internal 
resistance of alkaline cells will be too high and your 3 volts will 
sag something terrible.

Like everyone else, I suggest you switch batteries.  Use four NiMH AA 
cells to get 5V and regulate down to 3V. I don't think you'll need to 
buck down, just use a linear regulator, unless you're taking a lot of 
current at 3V. Although the capacity of the NiMH cells won't be 2300 
mA.h (I use 1800 mA.h cells but I think now you can do a bit better) 
I think they will actually last longer. This is because the alkaline 
cells will never give you full capacity at such a high discharge rate 
and you're avoiding power loss in the boost converter. High quality 
cells will be able to keep the voltage up because NiMH cells have a 
low internal resistance. For example, the 7.2 volt 6.5 A.h modules in 
my car have an internal resistance just a bit over 10 milliohms. I 
can get 60 amps or more from the 300 volt battery and the voltage 
stays up at 275 volts.

Graham.

4 NiMH batteries is a good starting point, but remember that you'll
only get 4.4 - 4.6V (series total) over most of the discharge curve.


At 06:17 PM 7/30/2004 -0000, you wrote:

>--- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:
>
>> ... I want to use 4 x 2300mAh AA
>> batteries in serial/parallel to
>> provide me with 3V.
>
>Sounds like alkaline cells at 1.5 volts each.
>
>> The printer runs on 5V but consumes
>> over 3.5A peak, so I require a DC-
>> DC converter circuit... to provide
>> 3V at 5A peak.
>
>You mean to provide 5V/3.5A, which will suck six amps or more from 
>your 3V battery. I don't think this will work. The internal 
>resistance of alkaline cells will be too high and your 3 volts will 
>sag something terrible.
>
>Like everyone else, I suggest you switch batteries.  Use four NiMH AA 
>cells to get 5V and regulate down to 3V. I don't think you'll need to 
>buck down, just use a linear regulator, unless you're taking a lot of 
>current at 3V. Although the capacity of the NiMH cells won't be 2300 
>mA.h (I use 1800 mA.h cells but I think now you can do a bit better) 
>I think they will actually last longer. This is because the alkaline 
>cells will never give you full capacity at such a high discharge rate 
>and you're avoiding power loss in the boost converter. High quality 
>cells will be able to keep the voltage up because NiMH cells have a 
>low internal resistance. For example, the 7.2 volt 6.5 A.h modules in 
>my car have an internal resistance just a bit over 10 milliohms. I 
>can get 60 amps or more from the 300 volt battery and the voltage 
>stays up at 275 volts.
>
>Graham.
>
>
>
>
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>

At 02:17 PM 7/30/2004, Ken Holt wrote:


>4 NiMH batteries is a good starting point, but remember that you'll
>only get 4.4 - 4.6V (series total) over most of the discharge curve.

Actually, they are dead, for this app, at 1V/Cell, so 4V.
An additional cell wouldn't be a bad idea, if the head can take the max voltage.
If the charger is connected while the head is connected, that can be 1.6V/Cell, or 8V.
If you D/C the head while charging (and you need to have than mechanism in place anyway) then you only have to withstand about 1.3V/Cell or 6.5V.

On Jul 30, 2004, at 1:17 PM, Graham Davies wrote:

> --- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:
>
>> ... I want to use 4 x 2300mAh AA
>> batteries in serial/parallel to
>> provide me with 3V.
>
> Sounds like alkaline cells at 1.5 volts each.

He needs a supply voltage of 3V, not batteries that add up to that much.
As he states below, he needs a converter:

>
>> The printer runs on 5V but consumes
>> over 3.5A peak, so I require a DC-
>> DC converter circuit... to provide
>> 3V at 5A peak.
>
> You mean to provide 5V/3.5A, which will suck six amps or more from
> your 3V battery. I don't think this will work. The internal
> resistance of alkaline cells will be too high and your 3 volts will
> sag something terrible.
>
> Like everyone else, I suggest you switch batteries.  Use four NiMH AA
> cells to get 5V and regulate down to 3V. I don't think you'll need to
> buck down, just use a linear regulator, unless you're taking a lot of
> current at 3V. Although the capacity of the NiMH cells won't be 2300
> mA.h (I use 1800 mA.h cells but I think now you can do a bit better)
> I think they will actually last longer. This is because the alkaline
> cells will never give you full capacity at such a high discharge rate
> and you're avoiding power loss in the boost converter. High quality
> cells will be able to keep the voltage up because NiMH cells have a
> low internal resistance. For example, the 7.2 volt 6.5 A.h modules in
> my car have an internal resistance just a bit over 10 milliohms. I
> can get 60 amps or more from the 300 volt battery and the voltage
> stays up at 275 volts.

Unfortunately with a linear regulator, the current required from the
battery is still 3.5A.  With 4 NiMH cells in series and a DC-DC
converter with 90 percent efficiency, you could get the peak current
draw down to about 2.4A.   A linear regulator under the same
conditions is wasting 5 W *more* power than the switcher. That's
a lot of extra power and heat when you're operating off of batteries.

Mike

At 08:07 PM 7/30/2004, Mike Murphree wrote:


>On Jul 30, 2004, at 1:17 PM, Graham Davies wrote:
>
>> --- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:
>>
>>> ... I want to use 4 x 2300mAh AA
>>> batteries in serial/parallel to
>>> provide me with 3V.
>>
>> Sounds like alkaline cells at 1.5 volts each.
>
>He needs a supply voltage of 3V, not batteries that add up to that much.
>As he states below, he needs a converter:


Just so we understand here, the printer is 5V, and it's stepper is 5V, but you're thinking of using 3V logic to drive it, right?

--- In AVR-Chat@yahoogroups.com, David VanHorn <dvanhorn@c...> wrote:
> At 09:16 AM 7/30/2004, C Sizer wrote:
> 
> >Hi guys,
> >
> >I am designing a university project, a hand-held printer using the 
> >AVR and a small thermal printer. For portability I want to use 4 x 
> >2300mAh AA batteries in serial/parallel to provide me with 3V.
> 
> Shuttle or line mech?  Line is much faster, and much more demanding.
> You need roughly the same horsepower as a laser printer of the same 
size would.
> 
> >The printer runs on 5V but consumes over 3.5A peak, so I require a 
DC-
> >DC converter circuit (or at least a starting point) to provide 3V 
at 
> >5A peak.
> >
> >Has anyone designed anything like this, or can give me some 
advice? 
> >Maybe someone has an idea for a better battery for me to use?
> 
> You'd be far better off to put your batteries in series, and then 
buck regulate the 3V.
> There are pulse-skipping converters that are very efficient. If the 
current is low enough, you can win with analog again..  Then again, 
why not run on 5V?
> 
> Also, do the math on burn energy, you'll find that the faster you 
print, the less energy you spend.  A significant amount of your print 
energy goes into heating up the printhead mass.  Wake up, go like 
hell, shut down.
> 
> Dedicate a timer to the stepper, and another to the burn.
> Use the burn timer like an alarm clock, interrupting you when the 
first head group is done, then reload for the remainder of the burn 
on the second group, etc.
> 
> You can start the burn pulse with a nominal value, do the 
calculations (FMULT is your friend) and then change the timer setting 
to the calculated burn width.
> 
> The stepper will need to be accelerated, and decelerated, depending 
on how much rasterized data you have built up. 
> 
> The SPI port is great at blowing out data to the head at high 
speed. 
> 
> I did one early this year, using a Mega-8 with on-chip osc, and a 
stepper driver IC.
> It was capable of running the mech at full speed, which ended up to 
be faster than the 1.7 GHz laptop could send the data out.

> 
> You'll find the details of getting this going properly, quite 
interesting.

Hi David,

thanks for the input.

I did make a mistake in my email, I want the output of the converter 
to be 5V not 3V.

The printer is an OEM module complete with controller etc. I am only 
interfacing it to the Atmel via RS232. The time I have to develop 
this project would not allow me to go to the lengths you describe 
here, although as you say it would be an interesting exercise. The 
printer can be configured for optimal speed/power, I am not 
interested in speed but low power consumption for my design is to be 
hand held. The printer is a line thermal using 60mm wide paper.

My concerns are size, weight and power consumption. If you know of 
any more suitable battery/powersupply combinations I would be 
greatful for your input.

Cheers
Col

--- In AVR-Chat@yahoogroups.com, "Graham Davies" <YahooGroups@e...> 
wrote:
> --- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:
> 
> > ... I want to use 4 x 2300mAh AA
> > batteries in serial/parallel to
> > provide me with 3V.
> 
> Sounds like alkaline cells at 1.5 volts each.
> 
> > The printer runs on 5V but consumes
> > over 3.5A peak, so I require a DC-
> > DC converter circuit... to provide
> > 3V at 5A peak.
> 
> You mean to provide 5V/3.5A, which will suck six amps or more from 
> your 3V battery. I don't think this will work. The internal 
> resistance of alkaline cells will be too high and your 3 volts will 
> sag something terrible.
> 
> Like everyone else, I suggest you switch batteries.  Use four NiMH 
AA 
> cells to get 5V and regulate down to 3V. I don't think you'll need 
to 
> buck down, just use a linear regulator, unless you're taking a lot 
of 
> current at 3V. Although the capacity of the NiMH cells won't be 
2300 
> mA.h (I use 1800 mA.h cells but I think now you can do a bit 
better) 
> I think they will actually last longer. This is because the 
alkaline 
> cells will never give you full capacity at such a high discharge 
rate 
> and you're avoiding power loss in the boost converter. High quality 
> cells will be able to keep the voltage up because NiMH cells have a 
> low internal resistance. For example, the 7.2 volt 6.5 A.h modules 
in 
> my car have an internal resistance just a bit over 10 milliohms. I 
> can get 60 amps or more from the 300 volt battery and the voltage 
> stays up at 275 volts.
> 
> Graham.

Thanks Graham 

yes, you are right, I did mean for the converter to output 5V.

As this is to be a hand held device I was going for light weight, and 
reasonable power consumption. The thought was to connect the 
batteries in 2 pairs of 2 batteries in series (to give 3V) then 
connect these in parallel to increase capacity and reduce the drain. 
I had not considered the internal resistance issue, but of course 
NiMH will only give me around 2.4V in this configuation. Now that I 
think it out, there isn't any way I can get the sort of life out of 
the batteries I was after.

Looks like it's back to the drawing board for me :-)

Cheers
Col

Thanks Ken,

In the series/parallel combination I was looking at I will be looking 
at about 2.2 - 2.3V then, that means around 4A being drawn from each 
series combination - yikes!!!!!

Cheers
Col

--- In AVR-Chat@yahoogroups.com, Ken Holt <kholt@m...> wrote:
> 
> 4 NiMH batteries is a good starting point, but remember that you'll
> only get 4.4 - 4.6V (series total) over most of the discharge curve.
> 
> 
> At 06:17 PM 7/30/2004 -0000, you wrote:
> >--- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> 
wrote:
> >
> >> ... I want to use 4 x 2300mAh AA
> >> batteries in serial/parallel to
> >> provide me with 3V.
> >
> >Sounds like alkaline cells at 1.5 volts each.
> >
> >> The printer runs on 5V but consumes
> >> over 3.5A peak, so I require a DC-
> >> DC converter circuit... to provide
> >> 3V at 5A peak.
> >
> >You mean to provide 5V/3.5A, which will suck six amps or more from 
> >your 3V battery. I don't think this will work. The internal 
> >resistance of alkaline cells will be too high and your 3 volts 
will 
> >sag something terrible.
> >
> >Like everyone else, I suggest you switch batteries.  Use four NiMH 
AA 
> >cells to get 5V and regulate down to 3V. I don't think you'll need 
to 
> >buck down, just use a linear regulator, unless you're taking a lot 
of 
> >current at 3V. Although the capacity of the NiMH cells won't be 
2300 
> >mA.h (I use 1800 mA.h cells but I think now you can do a bit 
better) 
> >I think they will actually last longer. This is because the 
alkaline 
> >cells will never give you full capacity at such a high discharge 
rate 
> >and you're avoiding power loss in the boost converter. High 
quality 
> >cells will be able to keep the voltage up because NiMH cells have 
a 
> >low internal resistance. For example, the 7.2 volt 6.5 A.h modules 
in 

> >my car have an internal resistance just a bit over 10 milliohms. I 
> >can get 60 amps or more from the 300 volt battery and the voltage 
> >stays up at 275 volts.
> >
> >Graham.
> >
> >
> >
> >
> >
> > 
> >Yahoo! Groups Links
> >
> >
> >
> > 
> >
> >

--- In AVR-Chat@yahoogroups.com, David VanHorn <dvanhorn@c...> wrote:
> At 08:07 PM 7/30/2004, Mike Murphree wrote:
> 
> 
> >On Jul 30, 2004, at 1:17 PM, Graham Davies wrote:
> >
> >> --- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> 
wrote:
> >>
> >>> ... I want to use 4 x 2300mAh AA
> >>> batteries in serial/parallel to
> >>> provide me with 3V.
> >>
> >> Sounds like alkaline cells at 1.5 volts each.
> >
> >He needs a supply voltage of 3V, not batteries that add up to that 
much.
> >As he states below, he needs a converter:
> 
> 
> Just so we understand here, the printer is 5V, and it's stepper is 
5V, but you're thinking of using 3V logic to drive it, right?

Sorry for the confusion,

the printer mechanism and controller both operate from 5V. I am not 
intending to directly drive the logic, but to interface to the 
printer controller by RS232.

Cheers
Col

>
>the printer mechanism and controller both operate from 5V. I am not 
>intending to directly drive the logic, but to interface to the 
>printer controller by RS232.


Ok, I understand.

You can probably find something at your local model airplane shop, in Lithium Polymer batteries, that will fit. They aren't cheap, but they offer huge output power, and you get >7V with two cells.  Then you just need a buck reg for your logic.  Your printhead should be able to operate here. 

The primary determinant here will be the printhead's operating range. 
Look for the "do not exceed" numbers in the data sheet.

Dave -
The question of adding an extra cell to an NiMH stack is one that is
vexing me at the moment.  I hope that this battery discussion isn't
too much off-topic, I appreciate getting people's battery experience
dumped once in a while.  Also, it's on-topic because so many AVR
projects involve portability and battery efficiency.
For those of us living off-the-grid, NiMH is a new promising improvement
over the ancient lead-acid technology and the troublesome NiCad.
I am trying to develop a modular portable power system based on
a unit of 10 or 11 NiMH F cells to replace the common 10 NiCad or
6 lead acid.  Use of 11 NiMH cells would give about 12 V at the low end,
which would be an improvement, and would only be too high (>15V) when
charging.  However, charging may be done out of the load system, and
in any case, most 12V inverters, lights, etc now can handle 15-16 volts 
because the recommended lead-acid equalizing charge in now up to 15.5V 
(although it still doesn't help extend battery life).
I'll be using the lightweight 12V modules in series and parallel
configurations
to power electric scooters, in-the-field 120VAC power packs, etc, and as house
back-up.  They can be charged anywhere where there is a temporary excess
of power.  And of course, the smarts for their interconnectivity,
manintenance, etc
will come from AVR!

Ken




At 02:50 PM 7/30/2004 -0500, you wrote:
>At 02:17 PM 7/30/2004, Ken Holt wrote:
>
>
>>4 NiMH batteries is a good starting point, but remember that you'll
>>only get 4.4 - 4.6V (series total) over most of the discharge curve.
>
>Actually, they are dead, for this app, at 1V/Cell, so 4V.
>An additional cell wouldn't be a bad idea, if the head can take the max
voltage.
>If the charger is connected while the head is connected, that can be
1.6V/Cell, or 8V.
>If you D/C the head while charging (and you need to have than mechanism in
place anyway) then you only have to withstand about 1.3V/Cell or 6.5V.

>
>
>
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>

>
>I am trying to develop a modular portable power system based on
>a unit of 10 or 11 NiMH F cells to replace the common 10 NiCad or
>6 lead acid.  Use of 11 NiMH cells would give about 12 V at the low end,
>which would be an improvement, and would only be too high (>15V) when
>charging. 

Check your specs, I've seen as high as 1.6V as "ok" under 1C charge, for an old cell.

> However, charging may be done out of the load system, and
>in any case, most 12V inverters, lights, etc now can handle 15-16 volts 
>because the recommended lead-acid equalizing charge in now up to 15.5V 
>(although it still doesn't help extend battery life).
>I'll be using the lightweight 12V modules in series and parallel
>configurations
>to power electric scooters, in-the-field 120VAC power packs, etc, and as house
>back-up.  They can be charged anywhere where there is a temporary excess
>of power.  And of course, the smarts for their interconnectivity,
>manintenance, etc
>will come from AVR!

I can't hand you the code, but I can help you with the design of a charger. 
BTDT.  We used the tiny-26's PWM output to control the current, but if you know the charge rates you want, a buck switcher altered to be a constant current output, would be a lot easier to control.  You'll want to be able to turn it off rapidly.

You'll also want the ability to put a LARGE (>15C) discharge on the cells, for just a moment. Don't rely totally on firmware to limit the pulse duration. I favor a large electrolytic that is discharged by a parallel resistor, and charging the cap is what does the discharge pulse.  A kick-ass mosfet on the ground side controls it.

Ken Holt wrote:

> Dave -
> The question of adding an extra cell to an NiMH stack is one that is
> vexing me at the moment.  I hope that this battery discussion isn't
> too much off-topic,

<LISTMOM HAT ON>

As previously stated, anything electronics goes here, as what is an AVR 
without the support electronics ?

The only things I would consider off topic is Religion and Politics ;) 
other than that, I can not see why *most* other things can not be talked 
about.

</LISTMOM HAT ON>

;)

Regards,

Kat. (the one with many hats)

-- 
---------------------------------------------------------------
K.A.Q. Electronics	Website: www.kaqelectronics.dyndns.org
IM: Yahoo: PinkyDwaggy  MSN: katinka@kaqelectronics.dyndns.org
For Everything Electronics     Phone: 0419 923 731
---------------------------------------------------------------

Hi,

lithium polymer battery is does not like sourcing high
currents. NiCad's and NiMh's do. May be its better you
start with rechargable battery tecnologies and decide
the mode of voltage regulation after that. series
connection of batteries during charging seems to me
more appropriate too.

Murat



--- David VanHorn <dvanhorn@cedar.net> wrote:

> 
> >
> >the printer mechanism and controller both operate
> from 5V. I am not 
> >intending to directly drive the logic, but to
> interface to the 
> >printer controller by RS232.
> 
> 
> Ok, I understand.
> 
> You can probably find something at your local model
> airplane shop, in Lithium Polymer batteries, that
> will fit. They aren't cheap, but they offer huge
> output power, and you get >7V with two cells.  Then
> you just need a buck reg for your logic.  Your
> printhead should be able to operate here. 
> 
> The primary determinant here will be the printhead's
> operating range. 
> Look for the "do not exceed" numbers in the data
> sheet. 
> 
> 



		
__________________________________
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At 06:17 AM 8/1/2004, MuRaT KaRaDeNiZ wrote:

>Hi,
>
>lithium polymer battery is does not like sourcing high
>currents.

The model aircraft world is using them in high drain apps without much problem.
You don't want to discharge them more than 2C, but with such a small printer, that won't be a problem

> NiCad's and NiMh's do. May be its better you
>start with rechargable battery tecnologies and decide
>the mode of voltage regulation after that. series
>connection of batteries during charging seems to me
>more appropriate too.

Nicads are more tolerant of abuse in charging, and they have a larger operating temperature range.  Sanyo "C" type NIMH's are a lot like Nicads, with the large capacity of NIMH.

--- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:

> ... of course NiMH will only give
> me around 2.4V in this configuation.

Col, I think this thread has got confused by people not reading your 
original post and disagreeing with perfectly workable solutions.

Four NiMH cells in series will give you 5V if they are fully charged. 
This will sag a bit when the printer draws off 3.5A and also as the 
cells discharge. I would hope that the printer continues to work down 
to some lower voltage, but you will have to find that out.

Your series/parallel idea to increase capacity is really not such a 
good idea if you have to boost convert to a higher voltage. The extra 
capacity is lost to converter inefficiency.

Think again about my proposal.

Graham.

Hi guys,

thanks to everyone who has responded, it has been truely helpful. 
There were a number of considerations raised I had not though of at 
all.

I will go back to the drawing board and analyse all the current 
demands of my design before making a final decision.

Cheers, and again thanks

Col

--- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:
> Hi guys,
> 
> I am designing a university project, a hand-held printer using the 
> AVR and a small thermal printer. For portability I want to use 4 x 
> 2300mAh AA batteries in serial/parallel to provide me with 3V.
> 
> The printer runs on 5V but consumes over 3.5A peak, so I require a 
DC-
> DC converter circuit (or at least a starting point) to provide 3V 
at 

> 5A peak.
> 
> Has anyone designed anything like this, or can give me some advice? 
> Maybe someone has an idea for a better battery for me to use?
> 
> Cheers
> Col