Batteries again.... sorry :(

[Fordulike]

I understand that a battery prefers a low discharge rate over a long period, so what is a safe C rating to aim for when calculating a bike setup?

 

[Vikki]

Not absolutely sure about this but I'm pretty sure that batteries are reasonably happy to discharge quite heavy currents until they are discharged or near discharged. Depth of discharge can affect a batteries longevity.

Lead acid, SLA and Lithium batteries were developed because they could discharge high currents safely. Obviously there is a safe limit and, without looking it up I couldn't give a figure, but any discharge rate that causes a battery to go above its safe working temperature is a bad thing. I wouldn't want to take a battery anywhere near it's maximum safe temperature as this also has the effect of shortening its life span.

To calculate what size battery you would need is probably best left to the more knowledgeable amongst us but a rule of thumb is more Ahr = more miles.

That would be down to the rating of the motor and the efficiency at which the system works. My Wisper easily gives me 30+ miles on an 18 month old 36V, 14Ah battery.

I think Flecc would have some figures on Watts per mile under certain circumstances. You could judge battery size on that.

I read somewhere that more batteries die through bad charging than almost any other abuse.

Just a thought, but C rating is the capacity rating and this affects range.

Best regards.

Vikki.

 

[eddieo]

I understand that a battery prefers a low discharge rate over a long period, so what is a safe C rating to aim for when calculating a bike setup?

did you get another replacement battery?

 

[flecc]

The discharge rate directly affects the battery's life. I remember one LiFePO4 battery manufacturer quoting 70% of capacity after 3000 charge cycles when used at a 1C discharge rate, but the 70% after 1000 cycles when used at a 2C rate.
.

 

[Fordulike]

Yep eddieo, they sent a new one. Old one must have been knackered.
The reason for my battery question is that i'm going to build a bike from scratch for next summer.
When i say scratch, i mean buying a fully assembled bike and adding a kit.
I thought that buying a large capacity battery not only meant more miles, but put less strain on it when drawing current.
My intention, if funds permit, is for a 36v Ping with a 500w hub motor.
Looking at some various spec sheets, it looks like these motors can draw up to 800w. I assume the average power is 500w though.
Doing some calculations it could draw up to 22 amps.
If it was working at the max all the time, i assume it would discharge a 20Ah battery at close to the 1C rate and all other times less than 1C.
Please correct me if i have calculated wrong
So is a 1C maximum discharge rate or less something to aim for from a battery?

 

[Oxygen Bicycles]

C rating explained

.
Doing some calculations it could draw up to 22 amps.
If it was working at the max all the time, i assume it would discharge a 20Ah battery at close to the 1C rate and all other times less than 1C.
Please correct me if i have calculated wrong
So is a 1C maximum discharge rate or less something to aim for from a battery?

Hi Fordulike,

Yes you calculated it right, 22amps continuously drawn from 20Ah will give a rating of just above 1C. What you need is to have a battery that continuously will accept a 1C discharge rate and approx 4C in bursts.

To those who aren't familiar with the C discharge rating please see below example:

Battery with 36V and 10Ah capacity - if discharged during slight hill climbing may be drawn at 10A continuously. If this battery will be discharged within period of 1 hour at 10A then the discharge rate will be exactly 1C.

Normally the discharge rates with most 250W bikes are just under 0.5C. We use greater current of even 16A during sharp hill climbing but that normally takes only few minutes. During the start we also drain battery with fairly high currents of approx 15A but that's only a burst that takes few seconds so the batteries are capable of coping with that.

Also to give an example the battery 36V 10Ah being ridden for 2 hours until flat has been discharged with the 0.5C rate. Hope that helps to those who weren't familiar with it.

All the best

Andrew
Oxygen Bicycles