How to limit the current on a battery

[future55]

Hello everyone.

I bought an electric scooter 24v 450w motor with SLA batteries that were too heavy to transport and going bad so I replaced them with Lithium Iron Phosphates. My power controller wouldn't shut off under any load so I bought another charge controller that broke altogether. I then bout a 60v 1000w power controller thinking that this would solve all problems, but it does the same thing.

I'm pretty sure it's the battery current that is shorting out the charge controller, but what do you think?

 

[Audioguru]

When an electric motor starts running it draws a very high current because it is stalled. Maybe the original battery could not supply the very high amount of stalled current but the new battery can do it. If you lengthen the startup time of the motor a little then its peak current will be reduced.
Adding a very low value resistor in series with the motor will reduce its peak current.

Please post a video of you riding the scooter at maximum speed that you can not control.:shock:

 

[D.A.(Tony)Stewart]

any mismatched charger can fail. Read battery charge requirement specs 1st before buying charger. Without current limit on charger, batteries will appear as short circuit.

 

[Audioguru]

Sorry, before I did not understand that the charger circuit failed.
A Lead-acid battery is completely different to a Lithium battery. You need a charger that is made to charge your new Lithium battery.
It will limit the voltage and current and shut off when it detects that the battery is fully charged.

Maybe the Lithium battery was voltage discharged too low or was charged too high and is now destroyed.
You must add a circuit to disconnect the Lithium battery from the scooter when its voltage drops to its minimum allowed voltage.

 

[future55]

Well the charger is works fine with the new batteries, it is the device that throttles the power from the batteries to the motor that is the issue.

So you understood correctly.

Can you recommend a resistor?

Thank you all very much.

 

[Audioguru]

A resistor can be calculated when the unknown spec's for the battery are known and the stalled current of the motor.

 

[future55]

A resistor can be calculated when the unknown spec's for the battery are known and the stalled current of the motor.

Of course:

Specifications:
Nominal Voltage
12.8V
Capacity
Nominal 4600 mAh
Minimum 4500 mAh
Charging Voltage
14.6±0.05 V
Charging method
CC-CV
Temperature Range
Charge 5~60˚C
Discharge -20~60˚C
Storage
-25~30˚C (3 months)
End Voltage of Discharge
9.2 V
High power that goes up to 20A discharge current.

https://www.amazon.com/Tenergy-12-8...F8&qid=1416329664&sr=8-1&keywords=12.8v+4.5ah

though in researching these I noted this:
*Note: These "Lead-Acid replacement" LiFePO4 batteries are not designed to be connected in series or in parallel when in use. Such configurations exceed the usage parameters the battery components are designed for. Doing so may cause the cells inside to become unbalanced, and impose additional strain on the battery components, leading to battery damage and/or fire.

Though now that I have them, any thoughts?

 

[Audioguru]

The multi-cell lithium batteries for radio-controlled model airplanes have extra connections so that a charger can properly balance-charge them.
Many of the cheap Chinese Tenergy Lithium airplane batteries are garbage. Their chargers are also garbage.

 

[future55]

Well these are sealed box units, but noted.