EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: dglad4 on May 17, 2016, 02:16:34 pm
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Hey guys, does anyone know of a good solution to a low power cutout for lead acids?
I want to buy a new deep cycle for camping and previously with using low voltage disconnects to protect from overdischarge annoyingly is voltage sagging on a heavy load causing the LVD to trip before remaining power gets to the desired point. Of course trip voltage could be set lower to allow for this but when light loads sip away the battery can get discharged too far.
Is there a 'smart' LVD out there or design which isn't effected by dropping supply voltage on load? My thoughts are there would be one that can monitor current and make a cutout voltage adjustment based on how heavily the battery is being drawn from, if this would work that is.
Thoughts?
Thanks for your help in advance.
PS: I'm an electronics hobbyist, so I can build circuits from scratch based on a design But I couldn't figure out how to design one like I need. I'm happy to look at products for sale and just buy one if they're available and reasonably priced.
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I'm working on a similar project involving a lead acid battery, solar panel, inverter and12v cig lighter outlets for camping and was going to use an automotive relay, but at 130ma draw I felt it was quite high. Opted for a latching relay, not as high capacity but ok for my needs. A microcontroller will monitor voltage and disconnect power if it's too low. There will be a "start" button to turn relay back on.
I'm curious to see what other solutions others come up with though as mine may be more complicated than it has to be.
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If the idea were to convert an existing low voltage cutout then.
You'd need to add current as a factor for the input voltage divider, eg add Opamps.
basic idea is
V => VxI = Watts.
Another way would be to quickly sample the voltage when the load is switched out (and running of it's smoothing caps).
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Not at all hard with something like this:
https://www.maximintegrated.com/en/products/power/supervisors-voltage-monitors-sequencers/ICL7665.html (https://www.maximintegrated.com/en/products/power/supervisors-voltage-monitors-sequencers/ICL7665.html)
They're getting on a bit now but at the time they were very low current requirement.
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Add some low pass filtering so a momentary dip will not trigger it.