Small Ah BMS?

HRTKD

Boondocker
I'm considering building a 20 Ah 8s 24v battery. This is for an electric lawnmower. Space is very limited in the battery box.

Should I get the Overkill Solar/JBD 8s BMS or is there another BMS that is closer to the 20Ah rating of the battery that I should use instead? The Overkill Solar BMS will fit within the battery box, just barely.

I'm spoiled in that I've been using the Overkill Solar 4s BMS for almost a year and it's been working great and was easy to configure and use.

The charger that came with the mower is 30v/2.0 amp. If I can use the charger that would be a nice to have. But not critical. If I use the charger, I think I would need to create a 9s battery because the 30v charge would exceed what the 8s battery can handle. A ninth battery would require a BMS that works with a range of cells not just 8s.
 

Gazoo

Dumb Dumb
How much current is the motor going to draw when cutting light grass and possibly heavy grass? The charger will overcharge the cells and you will need to rely on the BMS to cut off the charge which is ok IMO for that application. Since we, and I say we because I use an 8S overkill, and we know how reliable they are, personally that's what I would use. As you know it has many settings and you can configure it to match the C rate the cells are capable of, so you will have proper over current disconnect. That's my free 2 cents. :)
 

HRTKD

Boondocker
The charger that came with the mower would put out 30+ volts. My thought is that is too much for an 8s 3.2v battery. The max volts for a typical 8s LiFePO4 battery should 29.2v (3.65v x 8).

The specification label on the charger says 30 volts at 2.0 amps. But without a load on it, I measured 33.8 volts. (I have to wonder if that's why the SLA batteries died.) With such a high voltage, I would expect an 8s BMS to hit the high voltage limit right away and cut off charging. If I had a 9s BMS with 9 cells, I could charge up to 32.85v. That's still less than the charger is putting out, so maybe adding a cell and using the charger is a waste of time.

You're right that the motor in the mower could pull more current than I was thinking. The SLA batteries were only 12 amp, wired in series to get 24v. I have no specs on the motor, unfortunately.
 

chrisski

Photon Sorcerer
Have you decided on a small BMS yet?

This is a link to a small 20 amp BMS I am considering off E-Bay:


I’m working on a project that would build a 24 volt small battery pack of 25 ah cells which I would want to charge at 10 amps. Looks like dealing with wires that small, they’re supposed to be soldered on.
 

HRTKD

Boondocker
Have you decided on a small BMS yet?

This is a link to a small 20 amp BMS I am considering off E-Bay:

I’m working on a project that would build a 24 volt small battery pack of 25 ah cells which I would want to charge at 10 amps. Looks like dealing with wires that small, they’re supposed to be soldered on.

No, I have not committed to anything yet. The point above that the mower will likely have a good size surge, is making me rethink this.
 
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