Convert LiFePO4 to Li-ion

[rich110]

I have a Sunrunner ebike that I got as non-working/dead battery.

The original battery is 24v 6Ah lifepo4 which I assume is 8s4p.

24v 10Ah lifepo4 is gonna cost £300, any smaller Ah don't provide enough current. 24v 10ah liion is £125

Can I buy a 24v 10ah li-ion standard battery and just drop in?

lifepo4 8s would operate 20.0v - 27.2v voltage range
liion 7s would be 21v - 29.4v

Is there a chance that would blow the controller? Does the controller run at reduced speed because it senses the battery voltage, which might give me issues because of the different voltage profiles of the cells?

I hooked it up to 21.8v and it operates the motor at low speed on the throttle, at 25.4v it went a little faster. This is with no load (wheel in the air) and running from nimh AAs just to test if it's worth spending more money on as I don't have an existing battery to test with.

 

[E-HP]

24v 10Ah lifepo4 is gonna cost £300, any smaller Ah don't provide enough current. 24v 10ah liion is £125

Can I buy a 24v 10ah li-ion standard battery and just drop in?

lifepo4 8s would operate 20.0v - 27.2v voltage range
liion 7s would be 21v - 29.4v

Is there a chance that would blow the controller? Does the controller run at reduced speed because it senses the battery voltage, which might give me issues because of the different voltage profiles of the cells?

Controller should be fine, and LVC for the 8S lifepo4 and 7S liion are pretty close.

The missing information needed to answer your question is the current output of the stock battery.

"24v 10Ah lifepo4 is gonna cost £300, any smaller Ah don't provide enough current."

The 10Ah doesn't provide information on the current output, but indicates the energy available, which would equate to range, so if you are saying 10Ah wouldn't provide enough energy/range, then you should clarify that. If you are talking about power (acceleration, hill climbing), then you need to provide the current specs of the stock battery (or enough information about the cells to make that determination).

Assuming the you have 8S4P, and even generic lifepo4 26650 cells can output 10A, then the pack might be able to output 40A. For a 7S4P lithium ion pack to work, the cells would need to be capable of 10A output each, which would be pretty high end 18650 cells (not cheap), but possible. 4P of Samsung 25R cells would provide 10Ah of capacity, and 80A output, for instance, so there are definitely combos that would work.

You could find a combination of liion cells that will work for you, but you have to pay attention to the output current to make sure it meets your requirements.

EDIT: Looking at these bikes online, the motors don't consume much, so it looks like a conversion wouldn't be a problem. It would still be good to choose a battery with decent cells, but you have a lot of options.

 

[rich110]

The original pack is made of 32 cells 18650 PHET EP1600 which are rated at 1.5-2.25A/cell 1500/1600mah (2 different data sheets from 2003!)

The pack doesn't have a current rating printed on it anywhere.

I found this lifepo4 which is similar spec but only rated at 5A continuous 15A pulse (<3m) available for <£100
https://ultramax.co.uk/pub/media/sebwite/productdownloads//s/l/slaumxli6-24-tech-v1k21.pdf

Would that be adequate to run a (I assume) 250w motor? Probably seems a bit under-spec. The motor doesn't have a power rating anywhere.

I just took apart the controller and it has caps rated at 35v but reveals the motor is brushed - 2 wires going to motor and a small relay that you can hear click in when you apply throttle and it drops out a couple of seconds after you stop throttle. It has some semiconductors on the back heatsink so what purpose is the relay?

http://www.tti.com.tw/en/relay/Automotive-tr20.cfm

12V coil. 25A/30A 16VDC

The controller appears to have LVC at 21.0v

It has;
green - throttle button.
brown/black/blue - pedal sensor
red/white - brake switches