Excessive voltage drop and heating when charging

[BlueSmoke]

Hi everyone,

I'm working through a batch of EVE 280Ah cells from Docan Technology. I built up a 12v pack with 4 of the cells today and connected a 12v OverkillSolar BMS. That went perfect.

I don't have a 12v dedicated lithium battery charger and planned to use my existing Samlex 12v charger that I use for FLA batteries. It's set for 14.4v absorption and 13.5v float, so it should work well enough for charging this pack. Spoiler alert, it's not working like I had hoped.

I have 10 gauge leads coming from the charger terminated with 45 amp Anderson power pole connectors. I have ring connectors bolted to the BMS and battery main positive stud with 10 gauge wire terminated with 45 amp Anderson power pole connectors.

The BMS is seeing 13.4 volts from the charger, confirmed by multimeter. The charger has 3 outputs. The two outputs that I am not using are running at 14.4 volts, confirmed by multimeter. The output I am using is running 14.0 volts, confirmed by multimeter. The charger is getting very warm. I can smell the glue inside of it liquifying again and the heat sink fins are very warm. The bottom of the charger is too hot to handle.

It looks like I'm getting 0.4 volts voltage drop at the charger and another 0.6 volts drop across the Anderson connector. The Anderson connector is also warm to the touch. The wire close to the connector is heating, but close to the battery it is still cool as you would expect. I'm only passing 15 amps, so 10 gauge wire less than 5' total length should not be heating like this. The BMS says that the cells are charging and my multimeter shows the polarity is ok, so I don't think have something reversed and am back feeding the charger.

I have used this charger extensively to charge FLA batteries and have never had anything like this happen. Does anyone have any idea of what could be going wrong here? I can remove the Anderson connector, but I was just charging an FLA yesterday with the same exact cable and there was no problem same as every other time in the last 6 years.

Here's a picture of what I'm working with.

 

[mikefitz]

What charge current is the BMS reporting?

The poor charger is having to work overtime. Add extra lengths of cable in the charge path to drop the volts a little.

I'm only passing 15 amps

Via the BMS app or on the charger meter?

My guess is that the charger has a simple current limit circuit that is not able to tolerate the high current being accepted by the battery.

Has the fan turned on?

Try setting the unit to 13.5 volts, both DIP switches to of,f and see what happens.

Mike

 

[BlueSmoke]

BMS is seeing between 15.0 and 15.4 amps. The ammeter on the charger is showing it pegged at 15 amps which is what it does for hours with FLA batteries. It is a passively cooled unit, so no fan.

I set the dip switches to off so it would do 13.5 volt constant voltage charge. The voltage drop was less, but it was only pushing 3 amps due to the voltage being seen at the BMS not being enough to do any serious charging.

 

[Brett V]

I see two sets of wires. Is there something else connected besides the battery and charger?

 

[BlueSmoke]

I see two sets of wires. Is there something else connected besides the battery and charger?

There's a 12v female cigarette lighter connector attached, but there's nothing plugged into it.

 

[Brett V]

Not sure why the charger is heating up so much. Looking at that connector, there's no way it will survive 45 amps. It's getting warm and has a high loss at 15amps so that's your first problem. Were these cells top balanced before you assembled the battery? If they're at a low SOC, they will pull everything that charger can pump out.

 

[BlueSmoke]

Not sure why the charger is heating up so much. Looking at that connector, there's no way it will survive 45 amps. It's getting warm and has a high loss at 15amps so that's your first problem. Were these cells top balanced before you assembled the battery? If they're at a low SOC, they will pull everything that charger can pump out.

The cells have not been top balanced yet. I'm charging them up in preparation for top balancing. The cells are at a low state of charge and I expect them to be pulling the charger's full rated output.

 

[Brett V]

With what you have on hand, I don't know how you limit the current being drawn from your charger and I'm sure you're concerned with frying it...
I would be. Check and see if there is a dip switch setting that supplies a lower charge voltage.

 

[mikefitz]

Mount the charger vertically and if you have a computer fan, use to help cooling. You are correct about no internal fan, only the more powerful Samlex units have internal fans.

Mike

 

[NPhil]

My wild guess is that it could have something to do with 280AH of LiFePO4 being a very different kind of load than the lead-acid that the charger was designed for.

 

[BlueSmoke]

My wild guess is that it could have something to do with 280AH of LiFePO4 being a very different kind of load than the lead-acid that the charger was designed for.

This is my guess too but I don't understand why it would make much of a difference. A load is a load. Except when it's not. I bought a progressive dynamics lithium charger which should solve the problem and is significantly more powerful.

 

[Smokin]

Add a 10' wire from charger to battery let her rip. Put a leaf blower on it to cool it

 

[NPhil]

This is my guess too but I don't understand why it would make much of a difference. A load is a load. Except when it's not. I bought a progressive dynamics lithium charger which should solve the problem and is significantly more powerful.

I don't know, but I guess a way to test would be to run the charger into a dead short (assuming the manual doesn't say you can't do that), which a lithium ion battery is closer to than a lead acid battery, and see if it heats up the same way, or perhaps a little worse. If the manual says you can't do that, probably you have your answer.

 

[BlueSmoke]

I got the new charger today. The same thing happened with this one! The big difference though was I had 2 gauge wire in the charger lugs and crimped ring terminals bolted to the battery and BMS. This time I noticed that my BMS was reporting one cell as 0.05V higher than the others. My multimeter showed the voltage across the cell studs to be lower and inline with the other cells, but higher at the ring connector for the BMS. Turns out that the positive lead from the charger had loosened. This was causing a high voltage reading on that cell plus excess heating in the wire. I tightened that down again and the wire was much cooler when I checked on it 15 minutes later.

So the excessive heating in the FLA charger may have been caused by a similar problem. Something loosened in the Anderson connector is my guess. Either way, I've got a pretty sweet charger now. It's currently putting 90 amps into the cells, so it is literally 6 of the other charger.