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36V solar CC that can tolerate having the battery disconnected?

boondox

Chief Engineer, RedNeckTech Industries
Joined
Mar 1, 2020
Messages
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Howdy All,

I am upgrading my golf cart, which is the hardest working golf cart in the country, to LFP. I have the battery on the way and I need to figure out a charge controller. It is a 36V cart and is charged from a small 350 watt dedicated array.

The problem is finding a charge controller that doesn't mind the battery being disconnected while the solar is still plugged in. The old charger never minded this but it does not support LFP. It seems like the new chargers all warn of disconnecting the battery while the solar is plugged in.

The way the cart is used the charging cable is hooked up unless it is being used. When you need it, pull the charge cable and go. Could I put a big cap on the output? Or is there a CC that doesn't mind having the battery disconnected?

I could see some kludgy work-arounds but it needs to be idiot proof as a number of people use the cart and relying on them to disconnect the solar first with be problematic.

Thanks!
 
I would also be concerned with inrush current when plugged back in which would be a regular occurrence.

How about having a second parallel battery always connected to the charge controller? This would solve both battery disconnect and reconnect issues.

In regards to 36V, I know many of the Victron units have really wide voltage setting ranges that include ~36V.
 
I would also be concerned with inrush current when plugged back in which would be a regular occurrence.

How about having a second parallel battery always connected to the charge controller? This would solve both battery disconnect and reconnect issues.

In regards to 36V, I know many of the Victron units have really wide voltage setting ranges that include ~36V.

Problem is being 36 volts that would be an at least minor PITA. There are plenty of 36 volt CC's so no problem there.

I suppose I could see some make before break type relay situation or something but that would be a bit of a dog and pony show.
 
Sorry I was unclear.

Yes, a second battery would work but then I would need to get a second 36V LFP battery. This might be the simpler solution but probably not cheap.

My other idea is to make a relay system that would disconnect the solar from the CC before disconnecting the battery. I'd have to work out how to exactly do that. The main thing is it needs to be automatic. I can't trust everyone who uses the cart to do a proper sequence.
 
This might be the simpler solution but probably not cheap.
I don’t know much about these but here’s one for 40 bucks:


After thinking more about this, implementing an A, A+B, B switch, you could keep at least one battery connected (both momentarily in the switching process).
I am not a fan of mixing chemistries so this would keep them distinct and keep continuous power to your SCC (which I think is very important).

And I do understand and appreciate your desire for a foolproof mechanism with several people having to be able to do the switching. You know what they say about making things foolproof…

Just some ideas. Hopefully helpful or a stepping stone for improvement.
 
I don’t know much about these but here’s one for 40 bucks:


After thinking more about this, implementing an A, A+B, B switch, you could keep at least one battery connected (both momentarily in the switching process).
I am not a fan of mixing chemistries so this would keep them distinct and keep continuous power to your SCC (which I think is very important).

And I do understand and appreciate your desire for a foolproof mechanism with several people having to be able to do the switching. You know what they say about making things foolproof…

Just some ideas. Hopefully helpful or a stepping stone for improvement.
Sadly, that is for just the case and you need 52 X 18650 batteries to go in it. The point is well taken though, I will search around.

I can think of a control system but it would need a custom plug/adapter that broke the solar input before the battery was disconnected. I'll have to think of something as my LFP battery is on the way.
 
Well, I think I am going to go with this:

Use a 4 pin, 220VAC type of twist lock plug on the cart. Two wire will of course bring power to the battery. The other two will operate a relay that will connect and disconnect the panels to the CC. I can use a 10 second time delay relay so that the battery is properly connected before solar gets connected. Put a big cap on the output of the CC so that it has something there until the relay kicks off the panels.

I don't think I need a cap pre-charge as there is no inverter.
 
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