18650 based 24V battery: Ok to series connect for 48V?

[hobbes1069]

I wound up getting two of these from work which were part of a recall. These models had no actual instance of catching fire but the company is replacing all batteries out of an abundance of caution (i.e.: liability).

https://wstech.dk/wp-content/uploads/2020/11/ADL24LINMC-39AH-50A-CB.V2.3.pdf

The data sheet doesn't say other than to not exceed the max voltage, but when connecting batteries in series they only see the step in voltage, no?

24V is about useless for me. I can't use it on my ham radios since they need 12V and if you're going to do anything else, you might as well go 48V to keep the wire gauge down.

Thoughts?

Thanks,
Richard

 

[sunshine_eggo]

They are NMC, which isn't quite as bad as NCA (Tesla), but is nowhere near as good as LFP.

Unfortunately, I can't answer the question. Putting in series depends on the BMS. Essentially if ONE battery goes into protection, the other BMS may need to be able to handle the full bank voltage. In most cases, they can. In some they can't. If you can open them up and determine what BMS they have, you may be able to get there. You might also be able to find deeper support info for those batteries.

This 2021 user manual from that same company makes cautions against putting them in series:

https://wstech.dk/downloads/Documents/WST.User.Manual.November.2021.pdf

Given that the BMS is CAN communication capable with documentation, I'd like to believe it was designed to handle higher voltage and would be fine in series.

Maybe email them?

If series turns out to be a no-go, you have the option of 24V-12V conversion.

Operation between 3.5V and 3.92V is about 20-80% SoC. This is generally very safe and can vastly extend cycle life.

If you need to series them, I would get a BMV-712 or smartshunt to monitor the 48V and the mid-point 24V. Both can log selected data for 46 days.

You might need to periodically break the bank down, parallel them and than charge to peak voltage to re-balance.

Peak charge: 27.44 *2
Deepest discharge: 24.5 *2

The BMV is more spendy, but it has the following advantages:
1) external display that can also program
2) BT is in the display and has notably better range.
3) Has a control relay that can be commanded to open or close based on SoC and/or Voltage.

Me and NMC get along pretty well, so if you can get more, I would.

 

[hobbes1069]

Yeah, I popped the top since it's only held in with screws, but the case is welded stainless steel where the opening has a "lip". There's no way to remove the BMS without pulling the cells first and I'm not sure I'm willing to go that far. I can see the mosfets but there's not enough clearance to get a shot with my phone camera.

If one BMS were to shut down it should break the circuit right? I guess there could be an instantaneous voltage/amp spike that could harm the BMS though.

I try to stay away from DC voltage conversions for two reasons, one my radios can draw up to 30 amps, so I need a good one, and second it's another point of failure.

Since I got these for free I'm not too worried about the number of cycles I get, plus unless I cycle them daily calendar aging will likely get them first.

These are my first 24V batteries (or NMC outside of cell phones / pocket chargers) so I don't have a charger for it so I've very carefully topping them off with my adjustable power supply. They were at a very low state of charge and I didn't want to risk them "going to sleep".

I need to do some research but I wonder how easy it would be to get the CANBUS working on both. That way I could monitor both. If I can get that going in Node Red I can make a custom dashboard for monitoring and even add custom logic to shut it down if the cells get too out of wack.

Thanks,
Richard

 

[sunshine_eggo]

Yeah, I popped the top since it's only held in with screws, but the case is welded stainless steel where the opening has a "lip". There's no way to remove the BMS without pulling the cells first and I'm not sure I'm willing to go that far. I can see the mosfets but there's not enough clearance to get a shot with my phone camera.

If one BMS were to shut down it should break the circuit right? I guess there could be an instantaneous voltage/amp spike that could harm the BMS though.

That's the idea. It's generally low probability, and you just lose the BMS. Replacing BMS is also an option.

I try to stay away from DC voltage conversions for two reasons, one my radios can draw up to 30 amps, so I need a good one, and second it's another point of failure.

Go overkill... 60A... https://www.amazon.com/uxcell-High-Power-Converter-Regulator-Transformer/dp/B01LZJ9MGF

I have 1X 48V to 12V converters 2X 8-40V-12V converter, and a 12 to 5V converter. The 48 to 12V is pretty critical for network/comm components. I'm okay with it.

Since I got these for free I'm not too worried about the number of cycles I get, plus unless I cycle them daily calendar aging will likely get them first.

True. It's also about staying well away from the voltage limits for safety.

These are my first 24V batteries (or NMC outside of cell phones / pocket chargers) so I don't have a charger for it so I've very carefully topping them off with my adjustable power supply. They were at a very low state of charge and I didn't want to risk them "going to sleep".

Nice.

I need to do some research but I wonder how easy it would be to get the CANBUS working on both. That way I could monitor both. If I can get that going in Node Red I can make a custom dashboard for monitoring and even add custom logic to shut it down if the cells get too out of wack.

You ham radio folks are pretty clever, I'm sure you'll get it figured out in no time...

https://wstech.dk/downloads/Documents/WST.CANBus.Specification.V4.5.pdf

 

[hobbes1069]

I'm going to stick to the data sheets recommendations, 21V-28.8V.

I found this converter (it's a bit more) that does 13.8V which is what ham radio equipment is actually designed for (typical vehicle alternator output).

https://www.amazon.com/dp/B097XTKND7

The only concern is how noisy the conversion is. Radios inherently are trying to pick up very weak signals so noise coming in over the power inputs can be an issue. I haven't noted any issues with my Victron solar charge controller and my 12V battery I built from CALB cells. I got them years ago before the good cheap batteries were available when just about your only option of BattleBorn or similar

 

[hobbes1069]

I found a low noise converter!

Inexpensive ultra low noise linear 24 volt to 12 volt 30 Amp DC/DC converters (regulated) 360 Watts for marine radio, ham radio, 13.5V.

linear low noise 24 volt to 12 volt 25amp 340 watt DC-DC reducers suitable for automobile, heavy vehicle, and marine electronics.

www.powerstream.com

Only it's 49% efficient and $205... I think it's "low noise" by throwing away half the power instead of bucking it...

I also looked at a 2-3kW all-in-one solar inverter but they recommend at least 200Ah and I'm at about 80.

The search continues for a purpose for these batteries!