Using AA cells for an e-bike battery.

[flecc]

One of the regular "What if" questions is what would happen if cheap consumer rechargeable NiMh cells were used to make up an e-bike battery at low cost. Some while ago A to B magazine did just this with 20 cells to make an add-on back-up battery for a Giant Lafree Comfort, which gave up to five extra miles range, albeit at a slightly reduced performance.

But what if a full size battery was made, what if it was used with a much more powerful motor, what would happen when using a standard charger on these? So I concluded it was time to do a range of tests in an eZee battery shell with eZee's most powerful motor to give some answers to those questions, and there are some surprising results.

These two paragraphs are repeated on the web page.

Here's the link to this.
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[flecc]

Update on my AA battery

Some of you may recall I left the battery case as a half full 5 Ah one with 64 cells, and that gave a quarter range of just about 5 miles. However, after using it for some while, the cells have bedded down and I now easily get at least six miles from this half weight battery.

It's now the battery used in the Q bike for 4 mile round trips to the local Selsdon shopping centre, uphill nearly all the way there and with one short steep climb going and two of them on the return trip, after which the meter is still on green.

At the recelling cost of £64, it's proved to be a cheap light battery for doing short trips, the only penalty being a slight reduction in power, not a problem on the Q bike with plenty of performance in reserve.
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[skoolrun]

Some of you may recall I left the battery case as a half full 5 Ah one with 64 cells, and that gave a quarter range of just about 5 miles. However, after using it for some while, the cells have bedded down and I now easily get at least six miles from this half weight battery.


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That’s encouraging news flecc, I read your original thread with interest and following in the footsteps of others I have a draw full of Lidl cells waiting to be assembled into a 5Ah battery. Are you still charging with the Li-ion charger? Also, what is the advice on the inclusion of barrier diodes in the charge/ discharge circuits?

 

[flecc]

I found the Li-ion charger wasn't consistently getting enough into it as it ran in, so I'm charging with the eZee NiMh charger now. I also left the Schottky diodes out and just charge the two banks in parallel now, and the cells are self equalising ok. There is a risk in doing that though, but if you include the diodes, they're only necessary in the charging line. When drawing current to drive the motor, running in parallel is perfectly ok.

Let us know how you get on with those Lidl cells when you get round to trying them, but initially best to use the Li-ion charger as that will run the cells in without pushing them too hard at first.

I also think it safest not to run the AA cells right out to empty as it stresses them, so once the range settles, best to keep within it most of the time. That's why I don't know the exact full range with mine and keep it to around 4 mile trips, knowing that it's still on green and with plenty in reserve.
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[skoolrun]

Many thanks for the guidance, I will certainly post information on the results achieved with the Lidl cells, but it may be a few weeks before I get a chance to do the work.

 

[Jeremy]

Thanks for posting details of this experiment, it's set me thinking. Looking at all of the various NiMH cell options, it looks like some of the sub-C ones offer the best mix of capacity, internal resistance and price, particularly if purchased as RC model packs (although I can't quite see why packs are cheaper than bulk individual cells).

Looking around, I've found some decent looking packs that look promising, 3.7AHr at 9.6V, with a 30A max discharge. Ten of these, arranged as two strings of 5 (48V at 7.4 AHr), charged separately but discharged together, look as if they might do. This would give about 350 W/Hr for a weight of around 5.44kg and a price of £146.

Compared to AA cells these sub-Cs look good, as despite the modest cell capacity increase they seem to have a much lower internal resistance, at just 4 mohms per cell when charged, compared with about 25 mohms for high capacity AA cells. I believe that this should allow the pack to deliver more useful power, with less internal losses and heating at high discharge currents.

I'll experiment with my small SLAs first, but am inclined to think about making up a pack from these RC batteries, if only because it seems fairly easy to do for the probable performance.

Jeremy

 

[flecc]

I agree Jeremy, both C and sub C are better for the job, they'd have much better discharge characteristics. My AA experiment was mainly prompted by the very low prices easily available for those, and also just plain curiosity.

And it's a handy bit of extra range now for minimal extra weight carried.
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[alanwarwic]

Thought I would resurrect this thread as I had he idea of using 30 of the Aldi or Lidl C cells which I assume rate at 4AH. (D at 4.5AH)
Lidl ones are seasonal so maybe the Aldi ones are better quality?

This does looks a good way of making an around town/emergency pack that maybe also lighten the feel of bike. Methinks they are now at £2.80 so at 15 packs it now comes to £42.

Any tales to tell guys?

 

[flecc]

Yes, member Fecn used Aldi C cells to build himself a pack. You can read all about it in several posts he made in the following thread, starting with this post.
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[alanwarwic]

An interesting thread.

I wonder how things have evolved for both Fecn and mkc1.

 

[flecc]

Fecn lives a little way from me and when I last saw him he had a load of the C cells which he was thinking of building into another pack, I don't remember what for though. The first pack you read about was a range extender for his Kalkhoff Agattu. He still pops into the forum from time to time so may see this and come into the thread with an update.
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