RE: [AVR-Chat] Timer Counter
2006-10-05 by kholt@sonic.net
Or is the solenoid an intermittant-duty, and the locked on period too long for the IR dissipation? Maybe spikes are a red herring. It's bad to have a system where a SW glitch can kill an expensive part. For a solar system of this type, where you can carefully specify all the components, you might be able to reduce the amp-hour capacity of the battery so that it would discharge before the solenoid fried. Or current limit the battery into a supercap, to allow the short term current surge to the solenoid. Or any other simple method that allows a short term(50ms)burst of current followed by a long term lower hold current.
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> Thank you all for the replies. > > I normally put a 1N4004 diode across the inductor and a BZY18 Zener diode > across the 12 volt supply with a 2Amp fuse before the Zener diode on my > own > designs. > > I have not designed these boards myself and have only seen a couple of the > boards not the installation, there is a diode across the driver FET on the > board but I now suspect that there may not be any across the solenoid > coils. > > I think that perhaps I had better go and have a look at the installation > take my Tektronix THS720 scope with me and do a few measurements. > > Just done a test with a 12Volt SLA battery and a 12Volt relay coil to > prove > the point, 20Volt spike across the battery with a 1N4004 diode across the > coil, 600Volt spike across the battery without the diode, looks like the > original designer may have been expecting the battery to absorb the > spike!! > Or ??? > > > > Thanking You, > > Owen. > > > > > > All outgoing emails scanned by Trend Micro > > -----Original Message----- > From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf > Of Roy E. Burrage > Sent: Thursday, October 05, 2006 2:12 PM > To: AVR-Chat@yahoogroups.com > Subject: Re: [AVR-Chat] Timer Counter > > > > You might want to go back and add diodes across those solenoids, Owen. > > Transients on the power line can cause you all sorts of problems that a > > 3 cent diode will solve. > > > > We once had a customer who had us modifying some control modules that > > they sent all over the world. They had a problem with something letting > > all the smoke out of the power drivers and warranty repairs were killing > > us. I went over to their place and did some system evaluation and found > > the problem to be coming from transients generated by a clutch/brake > > assembly. With a high voltage scope probe and Tektronix 465 scope, all > > I could see of the transient was about 1,000 volts...and it was way off > > the display so I never could see what the peak values were. These > > transients were also several microseconds in duration. A 1N4004 across > > the coil of the clutch/brake cured the problem...and we made money from > > then on. > > > > The clutch/brake was drawing less than half an amp at 24 volts DC so it > > doesn't take a lot of current or voltage to generate humongous > > transients. All it takes is a lot of ampere turns. Diodes should be > > physically mounted as close to the solenoids as possible. > > > > > > REB > > > > > > > > OWEN-A wrote: > > > >> > >> > >> > >> > >>>I am trying to modifying a PIC program to get a shift register to work > >>> > >>> > >> > >> > >> > >>>properly, toggle the clear pin on the shift register to force all >>> outputs > >>> > >>> > >> > >> > >> > >>>to > >>> > >>> > >> > >> > >> > >>>"0" to prevent it from holding the data for too long and burning out an > >>> > >>> > >> > >> > >> > >>>expensive solenoid. > >>> > >>> > >> > >> > >> > >> > >> > >> > >>>The shift register is a 74HC595 and will occasionally lock an output on > >>> > >>> > >> > >> > >> > >>>for > >>> > >>> > >> > >> > >> > >>>a long enough period to destroy a solenoid. > >>> > >>> > >> > >> > >> > >> > >> > >> > >>>These solenoids are $350-00 each and they burn out around 40 to 50 a >>> year > >>> > >>> > >> > >> > >> > >>>on > >>> > >>> > >> > >> > >> > >>>the system. > >>> > >>> > >> > >> > >> > >> > >> > >> > >>>Have tried a PIC group but have not received any replies. > >>> > >>> > >> > >> > >> > >> > >> > >> > >>>I normally use AVR's with a C compiler the more that I see of the PIC >>> the > >>> > >>> > >> > >> > >> > >>>more I dislike them! > >>> > >>> > >> > >> > >> > >>Sounds like a problem with a transient on the supply. Something like an >> AVX > > >> > >>TransGuard will cure the problem. > >> > >> > >> > >>Leon > >> > >> > >> > >>These units are in the field on 12 volt battery supply with solar panel > >>charging system (no mains supply) the 12 volt solenoid's are driven by > >>VNP5N07 Fully protected power mosfets (ST Microelectronics devices) > >>switching one end of the solenoid to V- the other end of the solenoid is > >>connected the battery V+ . > >> > >>The 1N4004 protection diodes are across the mosfets "not the solenoids" >> (no > >>diodes across the solenoids). > >> > >>I had not noticed this before but perhaps the internal resistance of the > >>batteries may be high enough that the ringing of the solenoid coil could >> be > >>causing a spike on the supply??? > >> > >>Sorry for the HTML! > >> > >>Thanking You, > >> > >>Owen. > >> > >> > >> > >>[Non-text portions of this message have been removed] > >> > >> > >> > >> > >>Yahoo! Groups Links > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > > > > > > [Non-text portions of this message have been removed] > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > (Yahoo! ID required) > > > > > mailto:AVR-Chat-fullfeatured@yahoogroups.com > > > > > > > > > > > > > > > > > > [Non-text portions of this message have been removed] > >