Lithium battery protection

somewhereinusa

Solar Enthusiast
Since the lithium batteries I'm using (Valence) don't have any protection built in (only cell balancing), I've designed a protection system. It will totally disconnect the battery bank from everything if things go awry. It will also turn on a compartment cooling fan or turn on a heat pad if called for.
I have it bread boarded and the code written. For you coders out there, mine is probably a bit clunky but, it works. Not really necessary but nice for a bit of bling I'm working on a screen to see what temps and voltages are. The voltage dividers I'm are only good for 25V but my system is 12V. I've read that you can modify them for higher voltages. This is made to read one module (12 volt battery) and will work for major catastrophe.

49153111003_5f80a315aa_o.jpg
 

Craig

Watts are Watts!
Staff member
Moderator
What are you using for relay #1 is it a "Latching relay" or just a normal solenoid?
 

kringineering

New Member
That looks nice. What happens when the battery is less than 11 volts and the charger is disconnected? Can you manually override it to charge?
 

April

Solar Enthusiast
I think they are wondering if a latching relay would save on power.
Why the need for a 4 relay board which then operates 30 Amp relays?
The voltage dividers you talk about are they on the temp sensing board ,the 4.7K ?
Can I have a look at your code ? I might be able to suggest mods .
 

somewhereinusa

Solar Enthusiast
That looks nice. What happens when the battery is less than 11 volts and the charger is disconnected? Can you manually override it to charge?
If all goes as intended the batteries never get below 11V that's one of the conditions that will disconnect them. Yes there is a manual override.
 

somewhereinusa

Solar Enthusiast
I think they are wondering if a latching relay would save on power.
Why the need for a 4 relay board which then operates 30 Amp relays?
The voltage dividers you talk about are they on the temp sensing board ,the 4.7K ?
Can I have a look at your code ? I might be able to suggest mods .
I currently have a latching relay in that position, I just this minute figured out how to wire it so that once tripped to only be reset manually.
The 4 relay board is because I couldn't find any relays that would operate with 5V and handle the 30A 12V. I just found some solid state relays that will do it so when they arrive we'll see how they work. That will replace 7 relays with 4.
The voltage dividers are the two small boards on the right. I found them to be very inaccurate. I have since replaced them with one board that will sence 3 voltages and seems to be accurate to 3mV. Working on a diagram that shows all of this. The 4.7K is pullup to make the sensors work.
My code, along with some revisions that have helped a lot, is here. Github, all help is appreciated. I'm terrible at coding.
 

April

Solar Enthusiast
Code looks pretty good to me . Not an Adafruit fan . The temp sensors can be up to 2 degrees out I have found.
best to get it to a solder point asap because after a month of weather the connectors give corrosion mis-reads
But it all looks good ,seems you have it well under way . Ill follow.
 

somewhereinusa

Solar Enthusiast
Code looks pretty good to me . Not an Adafruit fan . The temp sensors can be up to 2 degrees out I have found.
best to get it to a solder point asap because after a month of weather the connectors give corrosion mis-reads
But it all looks good ,seems you have it well under way . Ill follow.
Not much left that is Adafruit except the screen driver. I'm working on final solder up of the things I can. The four temp sensors are within about .5 degrees of each other. Nothing terribly critical on the temps except freezing I'm using 38° to turn the heat on and 34° for total disconnect. If the heat works I don't have to worry about freezing. I think those figures should account for temp errors. I may even add a separate digital thermostat for that cold cut off just to be safe.
Thanks for the comments. Always good to have a second set of eyes. I have no one around here to bounce ideas off of.
 

somewhereinusa

Solar Enthusiast
I think the cathode side of the diode on the 500A relay should be connected across the coil. Move the cathode to the purple wire.
Good catch.
It turns out this may not be the final diagram. I think I have figured out how to use my original latching contactor by removint SSR #1 and replacing it with a TB6612FNG motor controller.
 
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