£20 Ebike Battery

[jerrysimon]

Ok as promised this is my thread on a £20 DIY ebike battery.

I have been thinking about making one of these for a while. Just to remind you of my current DIY battery setup, see details here

My current battery is based around A123, 3.3v, 2.3Ah cells. Its a 12s1p pack made up of two packs of 6s1p connected in series which provides me with 36v, 2.3Ah of power. The pack is over two years old, has 3300 miles on it with some 700 charge cycles. I did abuse it a little and had to change two cells a few months ago but its been fine since then. This packs costs about £80 to make.

A123 also do some lower capacity batteries 3.3v 1.1Ah. The prompt to try these was when I received one of the new small/mini controllers. I thought hey, I could put all this in a very small package on one of my light portable setups. Post to follow.

I did some tests on my commute and confirmed my outbound commute could be reduced to 400-600mAh if I used more physical effort. My return commute is even better using only 300mAh. My commute is a 12.5 miles round trip and the batteries can be charged at work before I return the 5.25 miles home.

Ok here are the two pack types. As I said I buy them pre made up, glued together with the associated connector strips spot welded to the battery terminals.

The original 6s1p pack using 3.3v, 2.3Ah cells

The new 6s1p pack using 3.3v 1.1Ah cells. Note for a 12s1p pack you need two of these.

Physically they are half the size and half the weight. Here is the first 6s1p with balance taps and power leads.

All the details of how to do this are in my DIY battery build link above. Finally the completed battery shown next to its bigger brother. A sort of mini-me of the orignal.

Note there is a 15amp car blade fuse fittted in the circuit for safety.

Top original battery weighs around 1kg and new mini-me one weighs 0.5kg.

Regards

Jerry

 

[jerrysimon]

But does it work ?

Both cells are rated at 30c constant and 60c peak. For the larger pack that's 69amps constant and 138amps peak/burst!

The new pack again can draw 33amps constant and 66amps peak/constant. More than enough for my Tongxin which averages around 5amps and ocassionaly might draw 10-12amps.

I tested it on my Brompton this morning and it performed faultlessly. There may have been a slight reduction in power over my regular battery, but that was probably my perception. When I got to work I had used 485mAh so less than half the capacity of the battery. This is good as I know I can afford to put in less effort and still get to work. On the way home I will put my cellog on and monitor voltage to make sure I have no voltage sag.

Again, to emphasise, I commute across Cambridge city centre and my ride is pretty flat so this battery has a very limited application. Perfect for me though it seems, once I start my summer commute on my Moulton and put in more effort in an attempt to get fitter.

The battery might make a good backup for your regular battery and at £20 who cares.

So I hope I have proved that in the right application, a £20 ebike battery is feasable

Regards

Jerry

 

[jerrysimon]

I guess I should have started this post with a Geek Alert

Regards

Jerry

 

[amigafan2003]

What are you using to spot weld Jerry?

 

[jerrysimon]

What are you using to spot weld Jerry?

I don't, the supplier spot welds them for me

Regards

Jerry

 

[KirstinS]

Brilliant post Jerry

If I can find someone to supply a tongxin, controller and throttle/button this would be ideal solution for my commute

 

[jerrysimon]

Thanks Kirstin, I will post some pics of the minimalist fit I am doing on my Moulton, for lazy day summer commutes later.

Regards

 

[jerrysimon]

Just cycled home and was a bit more generous with my throttle usage. Home is easier anyway and I used 416mAh.

***major geek alert***

I monitored each cell voltage of one of the 6s1p packs using my cellog (details in the other thread linked) and there was no major sag over my larger battery and each cell sagged the same.

One thing I have noticed with these packs, as all batteries I guess, is not to regularly discharge them completely. I did that with my original pack for the first twelve months which is probably why I lost a couple of cells after two years. I think I could happily pull 6-700mAh out of these without abuse and as I said for £20 if they fail after a year or so who cares!

Regards

Jerry

 

[jhruk]

I did some tests on my commute and confirmed my outbound commute could be reduced to 400-600mAh if I used more physical effort. My return commute is even better using only 300mAh. My commute is a 12.5 miles round trip and the batteries can be charged at work before I return the 5.25 miles home.

Again, to emphasise, I commute across Cambridge city centre and my ride is pretty flat so this battery has a very limited application. Perfect for me though it seems, once I start my summer commute on my Moulton and put in more effort in an attempt to get fitter.

With your present minimal battery use it looks as if you get any fitter you won’t need electrical assist at all.

I rather hope that doesn’t happen as I find your posts most informative.

 

[jerrysimon]

Thanks lol

I guarantee when the autumn/winter wind and rain is back, I will be back on my Brompton using nearer 1.5Ah each way

Ebikes have transformed my working day, there is just no way I would ever have got to using a bike for much more than the odd short ride in the summer. Now I use it every day except in snow and ice.

I am 51 and was diagnosed an type 1 insulin dependent diabetic in my early 30s. Just knowing I have a little bit of help if I need it, makes all the difference. Annoyingly this means I have to carry orange juice (extra weight) on every ride for those physical induced hypos

Ps the other advantage of this battery is charging is complete in about 20mins!

Regards

Jerry

 

[jhruk]

Thanks lol

I guarantee when the autumn/winter wind and rain is back, I will be back on my Brompton using nearer 1.5Ah each way

Ebikes have transformed my working day, there is just no way I would ever have got to using a bike for much more than the odd short ride in the summer. Now I use it every day except in snow and ice.

I am 51 and was diagnosed an type 1 insulin dependent diabetic in my early 30s. Just knowing I have a little bit of help if I need it, makes all the difference. Annoyingly this means I have to carry orange juice (extra weight) on every ride for those physical induced hypos

Ps the other advantage of this battery is charging is complete in about 20mins!

Regards

Jerry

Very sorry to hear about the diabetes, that’s no fun at all.

I do know exactly what you mean by ‘just knowing I have a little bit of help if I need it’ though. I live at the top of a hill and the thought of having to climb it to get home, when I was most tired, was starting to put me off going out for unassisted rides. E-bikes mean I don’t have to worry about it and I go out much more now.

I hope to have a go at making one of your ‘special batteries’ soon, so keep posting.

 

[jerrysimon]

Here is the link on ebay for the 6s1p packs welded up. You need to add balance taps and power lead etc.

If you order them one at a time its below the import duty limit and you can be certain it will get through

If you want to make the larger 2.3Ah ones then get the packs ready made up with taps and lead here as its just not worth doing yourself for this money. I have just ordered one from them instead (in fact they may be the same people just off ebay) and waiting to see if it comes through ok. They do some of the smaller packs as ready made up as well, which would save some hassle but they seem a little more expensive than the ebay ones, plus I had spare taps and power leads to use up.

You will then need a series lead for the two 6s1p packs. All in my DIY battery build thread linked earlier.

Also you will need a cheap RC balance/charger for initial/occasional balancing. A cheap ebay SLA 36v charger can then be used to safely bulk charge them. I have one at home and one at work.

Regards

Jerry

 

[jhruk]

Here is the link on ebay for the 6s1p packs welded up. You need to add balance taps and power lead etc.

If you order them one at a time its below the import duty limit and you can be certain it will get through

If you want to make the larger 2.3Ah ones then get the packs ready made up with taps and lead here as its just not worth doing yourself for this money. I have just ordered one from them instead (in fact they may be the same people just off ebay) and waiting to see if it comes through ok. They do some of the smaller packs as ready made up as well, which would save some hassle but they seem a little more expensive than the ebay ones, plus I had spare taps and power leads to use up.

You will then need a series lead for the two 6s1p packs. All in my DIY battery build thread linked earlier.

Also you will need a cheap RC balance/charger for initial/occasional balancing. A cheap ebay SLA 36v charger can then be used to safely bulk charge them. I have one at home and one at work.

Regards

Jerry

Thanks for that - I'll probably try the 2.3Ah one first.

 

[Caph]

It's very interesting to hear about these lithium batteries which I'm assuming are what makes up our big proprietary battery units. Thanks for the info Jerry.

Am I right in thinking that this would also work with 16 Duracell rechargable AA nimh batteries also for about £20 which would be about 3 times as bulky but weigh a bit less overall and have over double the capacity at a very similar 20V?

 

[jerrysimon]

It's very interesting to hear about these lithium batteries which I'm assuming are what makes up our big proprietary battery units. Thanks for the info Jerry.

Am I right in thinking that this would also work with 16 Duracell rechargable AA nimh batteries also for about £20 which would be about 3 times as bulky but weigh a bit less overall and have over double the capacity at a very similar 20V?

These cylindrical cells (the larger ones) are used almost exclusively in 36v DeWalt drill packs and not in the larger ebike batteries you see, which require a BMS (battery management system) to keep the cells in balance. The larger capacity ebike batteries also parallel them up to enable higher current draws. The beauty of these A123 cells is that a singe series cell can cope with a constant current draw of 30C+

Domestic re-chargeable AA NiMH batteries would be useless in that any attempt to pull the currents needed for a hub motor, would result in major voltage sag. I don't even want to think about how hot they would get if you tried!

I have now done several commutes/charge cycles with this pack and am astounded by how well they are performing. I will do a write up of the new bike fit I am using them on later.

Regards

Jerry

 

[flecc]

Domestic re-chargeable AA NiMH batteries would be useless in that any attempt to pull the currents needed for a hub motor, would result in major voltage sag. I don't even want to think about how hot they would get if you tried!

Been there, done that! Account on this link

 

[Caph]

Domestic re-chargeable AA NiMH batteries would be useless in that any attempt to pull the currents needed for a hub motor, would result in major voltage sag. I don't even want to think about how hot they would get if you tried!

I had a sneaky feeling it wouldn't be that simple. Good job I didn't start a fire trying it out!

How do you charge these Lithium batteries?

 

[Caph]

Been there, done that! Account on this link

Wow Flecc, that's some thorough testing. Conclusive proof it isn't really up to the job, though interestingly it could get you back home if needed.

 

[cwah]

Jerry, obviously you're very handy being able to do that

Why don't you get a lipo setup? It would be lighter and because you won't use a lot of amps you should have several hundred of cycles out of it.

The zippy compact from hobby king have now up to 168wh/kg!!
HobbyKing R/C Hobby Store : LiPo, LiFe, NiMH Battery>ZIPPY Compact

 

[jerrysimon]

How do you charge these Lithium batteries?

All the details are in this link

These batteries are dealt with in exactly the same way as the larger capacity ones.

Regards

Jerry