Converting to larger battery

[tbonephile]

I am new to this forum and had a question that I wasn't able to find via search. I have a electric scooter that has a 48V 20ah sla battery right now. Can I simply replace the 48v 20ah with a 48v 40ah battery? I am planning on going with a lifepo4. Main goals are for more consistent current (can never reach top speed after I've used more then 25% of the charge on my sla and improved range) Also I've heard simple replacing a 20ah sla with a 20ah lifepo4 will give me better range. Any idea how much of a difference it would be? MY the motor is a 400 watt rearhub and the controller came with and is built into the scooter. Thanks in advance for the help.

 

[Link]

Whoa, a 40Ah lithium pack would be some serious range.

Yeah, if you get a complete lithium pack, it's pretty much a drop-in replacement (though you'll probably have to redo some connectors).

Replacing 20Ah of SLA with 20Ah of lithium would likely increase your range by 40-60%, depending on the quality of the original SLAs. 40Ah would probably triple it or more.

 

[dogman dan]

Fitting 40 ah of Lifepo4 in that scoot would be fairly easy. Fitting it in the budget is another story. A 48v 20 ah ping pack would be a good place to start. lighten you up so much, you may not need any more.

 

[Anonymous]

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[Link]

Since he can fit 4 20Ah SLAs in there (the pack on the left), I'd say he has enough room for 40Ah of LiFePO4. And 4 of those 20Ah SLAs will weigh 52lbs; 40Ah of LiFe will only weigh 40. He'll still have a reduction in weight with a 40Ah pack.

Granted, a 1,920Whr battery pack will cost about $1,500 even at Ping's prices...

What sort of range are you getting with the SLA, BTW?

 

[tbonephile]

This is a link to my ride

http://www.china-phillips.com/ProView.asp?id=304&TypeID=102

I am actually based in China so that scooter only cost around 550 USD! I get about 60km range from it riding at a topspeed (built in controller limit) of 40km (Beijing has 0 hills) although 60km means draining the entire battery so realistically around 45km. However I use this scooter as my only means of transportation since I've located to Beijing so sometimes I need something that will go further...or recharge in 3 hours or can be completely drained for range so I am looking forward to lifepo4. The batteries are in the footwell. Ideally I would like a solution that can fit in the stock battery case. Ironically being based in China there are no dealers that sell units for domestic use. I have been trying to get in touch with Ping although I haven't been able to get a response from him via email.

 

[Link]

Ping would be a good choice. He can make you a custom-shaped pack if you give him dimensions, so I'm told.

LiFePO4 does suffer a bit when drained all the way, but it's not even close to being as bad as it is to SLA. 180km of range would be very enviable, indeed.

 

[tbonephile]

Any idea how long it takes to charge a Ping battery?

 

[Link]

He usually supplies a 2A charger, so a 40Ah pack would take 20 hours after it's well balanced. :?

The cells themselves, however, are specced to be charged at up to 1C (I think). 40A in the case of a 40Ah pack. So, assuming you could find a big enough charger, they could be done in an hour. But, I'd only use a 20A charger (two hours to charge the pack) to preserve their cycle life.

 

[tbonephile]

Link,

Thanks for all the help, any idea where I could get a "power" charger and also is it true that with lifepo4 that you don't lose current like you do with SLA? IE as the charge is used, the current is less and so is the top speed. This is what I would really like to change with my SLA.

 

[Link]

I don't know where to get an uber-charger like that, but I do know it'll cost you a pretty penny. Very high amperage chargers like that don't come cheap. We're probably talking about a $300 charger here. :? You might find that a smaller charger (say 4 or 5A) will work for your needs, though. How far per day do you expect to go?

You mean sag? Yeah, LiFePO4 holds its voltage very well under load until it's dead. My old 48V SLA pack would sag down as low as 30V. My new LiFe pack hasn't gone below 47V, and it has to supply more current than the other pack.

 

[dogman dan]

According to Ping's specs his battery can charge up to 5 amps. I'm using a 4 amp sla charger at work so I can get in a full charge by quitting time. With my 20ah battery a fully drained battery takes about 12 hours with the 2 amp charger. With a 40, you should be able to make it home to charge, but the night might be too short at 2 amps. Two 20 ah packs and two chargers would take half the time also.

 

[kbarrett]

Agreed ... that would be the cheaper solution. Get two 20Ah batts, and two chargers.

Use the batts one at a time, or, if you can get your hands on a schottky diode, parallel them into one 40Ah batt.