Lithium battery an unexpected aspect

W

William_H

Well-Known Member
Joined
28 Jul 2003
Messages
14,403
Location
West Australia
Visit site
I have a Shoprider mobility scooter which very efficiently tows my aluminium dinghy (tender) down to the water from home. 2x 12v Lead aid batteries got tired and it turned out I could buy 2x 12v Lithum 50AH https://au.litime.com/products/liti...ium-ion-battery?_pos=1&_psq=50AH&_ss=e&_v=1.0 cheaper and lighter than LA. So I fitted them. My charger is a pair of 10w solar panels. So fairly slow charging. But apparently I have finally fully charged the lithium as charge current cut off.
Now beetling down the hill the primary braking for the Shoprider is regenerative braking. ie the motor is turned in to a generator and tries to charge the battery and in the process slows the Shoprider. Turns out if the battery is fully charged the BMS says no don't want any more and immediately cuts power resulting in the brake on the motor bringing every thing to a halt. Shut down and start again all ok until speed builds up happens all over again. A decent run on flat ground discharges the battery sufficiently to make room for charging from regeneration. A lesson learnt that full charge has problems in my case. ol'will
 
Chiara’s slave said:
Sounds like the thing needs a software upgrade. Electric cars simply don’t brake with regeneration when charged to 100%. Its another good reason to do that as rarely as possible.
Click to expand...
Ha ha, soft ware uprade? It is a very old gopher. No access to microprocessor if indeed it has one. It is a case of software made for LA battery and I fitted lithium with BMS.
Simple answer is to not be so keen to keep it on charge continually and if it is fully charged to go for spin on flat land before going down hill.
Yes I am sure electric cars resolve this problem in regenerative braking perhaps turning off BMS charge cut off in regeneration. The power from regen braking must go somewhere. Perhaps a resistor though I doubt it. ol'will
 
Presumably radiated off as heat, in a car. You have to use the actual brakes to slow down when you’re fully charged, its a real novelty for me, I do it so rarely. The software update was tongue in cheek, clearly its not that sophisticated. For you, I’d try not to fully charge.
 
William_H said:
Yes I am sure electric cars resolve this problem in regenerative braking perhaps turning off BMS charge cut off in regeneration. The power from regen braking must go somewhere. Perhaps a resistor though I doubt it. ol'will
Click to expand...
You don't disable the charge cut off in the BMS, for any reason. It's there to prevent overcharged cells which will become permanently damaged.
Yes the energy has to go somewhere, a heating element would be the easiest. But in your case, can you change your charger settings so that the lithium battery isn't actually reaching full charge?
How are you charging it anyway? It needs a different voltage profile.
 
Sea Change said:
You don't disable the charge cut off in the BMS, for any reason. It's there to prevent overcharged cells which will become permanently damaged.
Yes the energy has to go somewhere, a heating element would be the easiest. But in your case, can you change your charger settings so that the lithium battery isn't actually reaching full charge?
How are you charging it anyway? It needs a different voltage profile.
Click to expand...
Will has previously posted that he has a pair of 10W solar panels, with no controller, relying on the BMS to block the charge when the batteries are fully charged.

Don't try this at home.
 
ProDave said:
I thought you were going to say because the Li batteries were lighter than the La you didn't have enough traction to pull the tender back up the slipway.....
Click to expand...
Funny you should say that. The "slipway" is in fact grass with a step from sand beach yes it does need a bit of a help up because of traction issues. I don't know whether to sit on the gopher to add weight on back wheels or not sit on it to reduce overall weight. Mostly I don't sit on to traverse the grass but is is only 5 metres slope up to a concrete path.
A s to Paul Rainbow's comments re charging. Charge at exactly 15v per battery as per battery maker's spec. (30v 2 in series) But charge profile of BMS is not accessible. Problem of full charge is overcome by running for a while on flat ground to discharge before going down the hill. But I am also tending not to charge so often. ol'will
 
William_H said:
A s to Paul Rainbow's comments re charging. Charge at exactly 15v per battery as per battery maker's spec. (30v 2 in series) But charge profile of BMS is not accessible. Problem of full charge is overcome by running for a while on flat ground to discharge before going down the hill. But I am also tending not to charge so often. ol'will
Click to expand...
The spec may say 15V, but it isn't a constant 15V, the charger should reduce or stop charging when the battery is charged. The BMS doesn't have a charge profile, that's the job of the charger. The BMS is a last line defence, it will block charging if the cells are fully charged, but as a safeguard, you're supposed to have a charge profile in the first instance.

I just hope that no-one reading this thinks it's a good way to install LFP on a boat.
 
You must log in or register to reply here.

Share this page

Top