Building a small A123 Battery Pack

[jerrysimon]

Ah now I understand.

Up until I got home the max current draw was around 13amps. I am not sure where the 17amp draw occured, but when it happened it must have been very short given I have a 15amp quick blow fuse in there

I guess I need to do some more tests.

PS Herb thanks for the explanation. The battery is not my design many have done it before me. I have read a lot about people using 10 cells but in nearly all cases they later seem to add another 2.


Regards

Jerry

 

[daniel.weck]

Up until I got home the max current draw was around 13amps. I am not sure where the 17amp draw occured, but when it happened it must have been very short given I have a 15amp quick blow fuse in there

There's a big condensator in the controller, which charges-up when you plug the battery or when you use the switch to let the current flow. This may induce high Amps for a limited time, thus the reading picked-up by the power meter. My Cycle Analyst registers a peak Amps value that is higher than what I see when I climb the most serious hill...so it must be related. I read that some high-power applications require the use of a MOSFET in addition to a regular physical switch, to avoid the high-amp spark when connecting the battery.

++Dan
(still under 25cm snow)

 

[jerrysimon]

Ah Dan so it may have occured when I switch off ?

I will check it again next time before I switch off. Maybe I should put a MOSFET thingy (sorry I am not an electrician) in the circuit.

I am currently charging the battery with the cheap charger and I have Turnigy connected in line so will be interesting to see how much it puts back into the battery. All exciting stuff lol

Regards

Jerry

 

[daniel.weck]

I think the peak occurs when the condensator charges, i.e. when the battery gets connected to the controller. Worth trying different patterns though.
Dan

 

[jerrysimon]

I think the peak occurs when the condensator charges...

Yes that makes sense, though I am certain that mid way through my journey it was not higher than 13amp max. As you say more tests required

Regards

Jerry

 

[Herb]

I think we can concur that the battery is indeed not undersized for its proposed duty.

It will probably have a range of 8 miles, a figure than compares to my own 2.6ah 36v Bosch lithium battery.

It is also be a good modular approach using the latest technology to anybody wishing to build a battery of 2.3, 4.6 or any multiple up to and above the 10Ah that a lot of riders perceive as the normal capacity of a electric bike.

I need one.

Herb

 

[jerrysimon]

Herb it seems so, but I think if you want a battery for regular longer distances it might make more sense to buy a 10Ah one given that the equivalent 4 of these would cost about £240 for just the new cells plus the build.

The real advantage of these for me is to be able to keep weight down for my short journey plus I wanted to make my Brompton as light as possible so I could carry it into work when I get there. Again I travel mainly on a flat route with a few small inclines. I may build a second pack as a spare/backup and as I say will probably just use one for work and get a second charger to keep there.

Battery charger has currently put 0.94Ah back in and still going


Regards

Jerry

 

[jerrysimon]

Cheap ebay charger put 1.594Ah back into the battery. Interestingly its rated at 1.6amps but it never charged at higher than 1.1amps. I guess there are some losses with the Turnigy meter in the circuit as well. Seems to confirm the charger is doing its job and cuts out at the right place.

Will be interesting to do a full discharge ride to see how many miles I get, how many Ah are used and how much goes back in to the battery on a full charge.

Regards

Jerry

 

[jerrysimon]

The battery should have a capacity of 2.3 (Ah) times the voltage (say 37V - a figure in between the actual of 39.6 and the lowest 33.74)

2.3 x 37 = 85.1 wh

so you have probably used two thirds of your battery capacity

The penny begins to drop

Freedom E quotes 91 Whr for these batteries so that must be based on the nominal voltage of 39.6v for 12 cells.

I need to fit my trip computer so I can get some distance figures too. Lets hope the thaw remains here and I can get out again this week.

Regards

Jerry

 

[NRG]

I think we can concur that the battery is indeed not undersized for its proposed duty.

It will probably have a range of 8 miles, a figure than compares to my own 2.6ah 36v Bosch lithium battery.

It is also be a good modular approach using the latest technology to anybody wishing to build a battery of 2.3, 4.6 or any multiple up to and above the 10Ah that a lot of riders perceive as the normal capacity of a electric bike.

I need one.

Herb

We'll have to agree to disagree At 2.3Ah and even at a 13amp peak draw discharge is still high at 5.5C maybe it will be fine for short journeys while the cells are new but given the heavy load they will age faster and die sooner, better would be 5Ah to get under 3C and stress the cells less.

 

[jerrysimon]

NRG these A123 cells have a 30C (69 amps) rating for continuous discharge and over 4C (10 amps) rating for charging if you choose!

So 13amps average discharge (probably a lot less over the full ride) and 1.6amps charging is not really stretching them. At 10C they are quoted as having a 1000cycle life.

A123 Single Cell ANR26650M1 3.3v - electricwingman

Anyway we will see what happends after I have used them for a few months. I plan to monitor them closely.

Regards

Jerry

 

[Herb]

We'll have to agree to disagree

NRG in the interest of forum harmony

I propose the following

I need one.

Herb

You on the other hand need two – keep your discharge rate down.

The upside of this compromise is a good battery for me.
The ability to run a small E-Bike factory with the spare battery capacity for you.

Herb



Edit, Did I write that ! This may seem harsh comment, but consider - one of the reasons we are able to debate is because of your expert knowlege and past record in batteries.

 

[NRG]

NRG these A123 cells have a 30C (69 amps) rating for continuous discharge and over 4C (10 amps) rating for charging if you choose!

So 13amps average discharge (probably a lot less over the full ride) and 1.6amps charging is not really stretching them. At 10C they are quoted as having a 1000cycle life.

A123 Single Cell ANR26650M1 3.3v - electricwingman

Anyway we will see what happends after I have used them for a few months. I plan to monitor them closely.

Regards

Jerry

My apologies! For some reason I assumed NiMh...

For reference here's the manufactures page for these cells:

A123Systems :: Products

Still....if it where me I'd go for double the Ah....OK I'll get me coat....

Herb: no problem, when do we start the new factory?

 

[trepo]

Ah now I understand.

Up until I got home the max current draw was around 13amps. I am not sure where the 17amp draw occured, but when it happened it must have been very short given I have a 15amp quick blow fuse in there

I guess I need to do some more tests.

PS Herb thanks for the explanation. The battery is not my design many have done it before me. I have read a lot about people using 10 cells but in nearly all cases they later seem to add another 2.


Regards

Jerry

I have a different brand of motor myself, maybe you remember the youtube video of winter driving I linked a week or two ago...

Anyway that kit blew fuse a few times, and when it happened I was always accelerating from slow speed. The controller is a 12A model, and it even blew a 20A fuse once!

That problem disappeared after I got the MMC box installed and the seller commented that it smooths out high current spikes that may have been caused by turning throttle fast.

Since then I have also installed the same Turnigy meter as you and it shows max. 13.7 amps which is very well in line with the controller used. I know this is a different kit but one possible explanation...

Regards

Taisto

 

[jerrysimon]

That problem disappeared after I got the MMC box installed and the seller commented that it smooths out high current spikes that may have been caused by turning throttle fast.

Thanks Taisto,

What is a MMC box ?

Regards

Jerry

 

[eddieo]

So are we going to piece something together, representative of the forums views? or just write in individually..........

I know we are probably split between pedelec and crank owner/users, but surely we all agree on the main issues.

maybe it is time to leave Europe

 

[jerrysimon]

Wrong post replied to I think eddieo, I think you want the next one down

Jerry

 

[trepo]

Thanks Taisto,

What is a MMC box ?

Regards

Jerry

MMC box is an additional "controller" box to be connected between the battery, throttle, pedal sensor and normal motor controller. It's main use is to make throttle legal in most European countries if you use elfkw ebike kit (not available for other makes, at least at the moment). It just detects when you pedal and the throttle operates only at those periods of time. Of course some motor controllers have this feature built-in without need for any additional electronics.

You see, at least here in Finland ebike motor can only operate legally in the same time you pedal. Otherwise your ebike is considered as electric moped and you have to go through expensive type registration process etc. and it costs several thousand euros on top of the fine police gives you.

That is something I don't want although I have to admit it is a very unlikely to happen.

Sorry for my tangled english but hope you get what I mean.

Regards

Taisto

 

[shemozzle999]

They are larger than I expected. I am use to using Sub C cells for my RC models here is a comparison of the two. The Sub C cell is a 3000 mAh NiMh cell. In fact I had thought of using NiMh cells in 3 packs of 12v connected in series. The problem is they are heavier and I would probably have to charge all three packs seperately. They do however go up to I think 4600mAh now so it certainly worth thinking about.





Just saw these on ebay from a UK based supplier and wonder if they could do the job?

4600mAh SubC SC NiMH rechargeable with tab Vapextech on eBay (end time 18-Jan-10 09:52:10 GMT)

 

[jerrysimon]

I don't see why they wouldn't work as they seem to be able to cope with 30amps draw.

You would need 33 cells to match the 39.6v of the A123 pack in this thread. Two of my packs would give you about the same capacity and you would need 24 cells which would work out cheaper.

For charging the NiMh cells in a 33 cell pack you would need a dedicated charger capable of detecting temp change i.e. you would need to incorporate a thermister into your pack.

The alternative is to buy 3 of their 12v packs but again that would only give you 36v in series. You could then charge the three packs seperately without a thermistor, like we do in the RC environment, but you would have the hassle associated with splitting them up everytime to charge and the charger would probably be more expensive than the ebay one I am using here to charge the A123 packs in their series form.

Horses for courses really. I thought about it, but the A123s offer a better, simpler and more managable solution in my opinion.

Regards

Jerry