e-bike power pack question - Fuel Economy, Hypermiling, EcoModding News and Forum

Lazarus · 02-18-2008, 07:19 PM

I have an e-bike with a 600w hub motor Kit. The power supply is 3- 12v/12ah batteries and 50 amp controller. I'm trying to extend the range and have a few questions. I'm not looking for more top end just longer range. I have a unlimited supply of SLA batteries so I need to stick with that.

I don't have the room for the next step up in batteries size to 12v/18ah or to have 2 sets of 3 12v/12ah batteries in parallel. I do have room to go with a 48v and just maybe a 60 volt pack. Right now I have a sweet spot of about 300w that seems to work well. So here where I need input.

If w=V*A then increasing the pack voltage should increase the range if I continue the commute at the same speed and not just blast at full throttle?

Will the motor only draw what it's maximum wattage is or can I burn the motor up if I increase the voltage? Same question for the controller.

Any input is appreciated.

NoCO2 · 02-18-2008, 09:05 PM

Do you have one of those baskets that fits over the rear wheel and hangs down with baskets on either side? If you don't, look into those they can give you some more battery room.

As for anything else, I'll be watching what people say. I'll be looking to do this when I get making my e-bike.

MetroMPG · 02-18-2008, 11:24 PM

The motor will draw more than its rated for, if the controller will let it. So if you upped the voltage, you would have to be careful you weren't asking it to do more work than it already can on its stock voltage (ie. top speed, or rate of acceleration) or you could theoretically heat it up and damage it.

EDIT: of course, now that I think of it, the real answer is "it depends". Some motors are more tolerant than others of being over-volted. It's also possible that you could raise the voltage and run it flat out with no ill effects.

AndrewJ · 02-18-2008, 11:59 PM

Quote:

Originally Posted by NoCO2

Do you have one of those baskets that fits over the rear wheel and hangs down with baskets on either side? If you don't, look into those they can give you some more battery room.

One of these?

I think every bike shop in existence carries wald baskets, and they're cheap too

NoCO2 · 02-19-2008, 11:25 AM

Sweet, I'm getting one of those. I've been looking to get some baskets for my bike so I can actually carry other things then what's on my back when I go to work and the grocery store.

jjackstone · 02-19-2008, 12:27 PM

Lazarus,
As Darin says, it depends. Normally the higher voltage won't harm the motor at all. I would be a bit more concerned with the controller. Those are normally built for a specific range. Call the distributor or manufacturer if possible and see what they say.
JJ

Ryland · 02-19-2008, 12:30 PM

I say get a better battery, but you say you can get lead acid batteries for free? then first off make sure they are good so you don't have dead weight from a dead cell, a bad battery will add resistance to your string of cells and brring it all down.
2nd make sure that your voltage drop is not slowing you down, put a volt meter on your bike and check the readings as you accelerate, if your 36v pack is droping to 30v, then you need more capasity, this will bring your range up as well.
another thing is to keep your weight low, this will make the bike handle better.

Lazarus · 02-21-2008, 03:59 PM

Quote:

Originally Posted by Ryland

2nd make sure that your voltage drop is not slowing you down, put a volt meter on your bike and check the readings as you accelerate, if your 36v pack is droping to 30v, then you need more capasity, this will bring your range up as well.
another thing is to keep your weight low, this will make the bike handle better.

How do you arrive at the 30v?

MetroMPG · 02-21-2008, 04:13 PM

I'm not sure what the specs are for sealed batteries, but with the flooded batts in the ForkenSwift, you are supposed to avoid drawing the voltage down below 1.75v per cell (5.25v per 6v battery, 10.5v per 12v battery).

Anything below that risks cell reversal, which if it happens will, as Ryland says, ruin the battery and dramatically reduce range & performance of the remaining batteries.

Following those rules, you shouldn't draw a 36v pack below 31.5v. Now, as I said, sealed may have a different threshold. I'm not sure.

Lazarus · 02-21-2008, 05:53 PM

That seems way to low. Although they are a 3 12v battery the voltage is really 13.1_ per battery so it's almost 40 volts. I would think it would be somewhere around 35-36 volts. I'll have to see if i can find some data on it. Thanks for the in put everyone.