home brewed

[daniel.weck]

Both Freedom, and the Electric Wheel Company, are supplying the controller made by:

<http://www.lsdzs.com/>

I see. My Tongxin 80mm 180W 190rpm motor from Frank ( Das Elektrorad von Frank Scheftlein: Komplette Pedelec- / Elektrofahrrad Umbausätze und Ersatzteile von Bafang, Puma (eZee), Tongxin u.a. ) comes with a custom controller supplied by e-Crazyman / Keywin Ge (units manufactured by Shenzhen Sucteam). It's obviously a brushless and sensorless controller, with a 3-level power switch (nice feature) and Pedal Assist Sensor input. It's programmable using the ParameterDesigner.exe application (available via Frank with the data cable, or from the Endless-Sphere forums).

Regarding the A123 battery, I am looking forward to hearing more about these prismatic units !

Green Car Congress: A123Systems Prismatic Cell Lineup: Up to 5,300 W/kg in High Power Cell, 20 Ah Cell for PHEVs

A123Systems :: Products

Full size image: http://img26.imageshack.us/img26/2289/a12320ah.jpg

Cheers, Dan

 

[Sir_Bob]

tat

I use to like the youngs brew kit. 40pints for only a tenner.

thx

Bob

 

[wurly]

Missed your question about the balancing circuit....

Dead cheap/simple. Used the higher accuracy version of the TL431 (5mV), with 0.1% resistors for the two setting the reference point. The rest are non critical, except that the main load resistor, needs to be able to handle 0.3W. Draws about 90mA, when the cell voltage gets above just on 4.2v. Far cheaper than any alternative I've seen, and seems to work OK.....

Best Wishes

Hi Roger
Welcome to the forum
I have a question (or two) about your balancing circuit diagram. I want to make my own battery pack with a balancing circuit and your diagram has given me a few ideas.
Am i right in thinking the reference voltage depends on the state of the cell voltage in the first place? I can see that the load resister stops the cell overcharging when it reaches 4.2V. How does the circuit behave when cell voltage is less than 4.2V, for instance, during discharge with regards to the reference point? Will the circuit still balance cells in a pack during discharge or is your circuit designed for balancing during charging?

Mel

 

[wurly]

Nice looking bikes. was wondering how did you deal with fitting motors....are forks alloy or steel? and did the motors fit or did you need to stretch the forks?

Hi Eddieo
Fitting the Tongxin was easy. I just filed out the slots in the steel forks, made the slot a little deeper (to make sure the v brakes lined up with the rims). Both bikes had 100mm wide legs, so no cleareance problems.
Battery choice is rearing it's head again. 7ah SLA's have been fine for our short journeys to work, but mine are showing the signs deterioration after 7 months of use. Trying to weigh up building my own pack or buying a small LifePo4 pack.
l like the idea of DIY and 'home brewed' ebikes even if my first attempts at designing/building fail.
I have never laced a wheel before. It took 5 attempts following a good wheel building book. The next one i did was easy/easier. Stripping apart a Tongxin motor isn't a problem either, now i know how to fix and maintain them. It is an enjoyable learning curve.

 

[Fecn]

Hi Roger
Welcome to the forum
I have a question (or two) about your balancing circuit diagram. I want to make my own battery pack with a balancing circuit and your diagram has given me a few ideas.
Am i right in thinking the reference voltage depends on the state of the cell voltage in the first place? I can see that the load resister stops the cell overcharging when it reaches 4.2V. How does the circuit behave when cell voltage is less than 4.2V, for instance, during discharge with regards to the reference point? Will the circuit still balance cells in a pack during discharge or is your circuit designed for balancing during charging?

Mel

The TL431 regulator used on Roger's circuit has a built in reference voltage generator producing 2.5v. That voltage reference is compared with the input voltage from the R1-R2 resistor network to determine when to switch the current through R3 and R4+D1 on. When the voltage is less than 4.2v, the TL431 regulator will be switched off and no form of cell balancing will occur - arguably cell balancing during discharge is pretty pointless as long as you have a per-cell low voltage cut-off function.

In addition to the low voltage cut-off function, the other shortcoming with this circuit is that it does not have the ability to disconnect the charge current to prevent cells from reaching too-high a voltage - merely to drain a small current should the voltage exceed a pre-set level. For example, imagine a pack with 2 cells, one fully charged, and one fully discharged (at 3.0V). A two cell charger would need to charge to 2x4.2v=8.4v. As soon as we switch the charger on, the fully-charged cell exceeds 4.2v and the cell balancer starts to burn off extra energy at around 250mA... However, the charger is pouring on the extra charge at 2500mA so the cell voltage still rises to extreme levels. I've seen this solved on some BMSes where if a single cell rises above 4.3v then the charger is temporarily disconnected until the BMS has the chance to burn off some joules.

Although it's a cell-balancer, it's not a full-featured BMS solution.

 

[Straylight]

Regarding the A123 battery, I am looking forward to hearing more about these prismatic units !

And in the post prismatic future.....? This?

 

[jerrysimon]

Stripping apart a Tongxin motor isn't a problem either, now i know how to fix and maintain them. It is an enjoyable learning curve.

Interesting care to share ?

What about getting parts ?

Regards

Jerry

 

[Orraman]

Could this be of interest?

Dave

This balancer would be the circuit for 1 cell. One would have to be built for each cell in the pack to be balanced. Although normally balancing current would be very small to keep a battery pack in balance, this balancer is capable of sinking 2 amps (or higher) with an appropriate heat sink. It is intended as an external balancer to be used while charging the battery pack.

simple high current balancer - RC Groups

 

[Roger Hamlett]

Balancing cicuit

Hi Eddieo
Fitting the Tongxin was easy. I just filed out the slots in the steel forks, made the slot a little deeper (to make sure the v brakes lined up with the rims). Both bikes had 100mm wide legs, so no cleareance problems.
Battery choice is rearing it's head again. 7ah SLA's have been fine for our short journeys to work, but mine are showing the signs deterioration after 7 months of use. Trying to weigh up building my own pack or buying a small LifePo4 pack.
l like the idea of DIY and 'home brewed' ebikes even if my first attempts at designing/building fail.
I have never laced a wheel before. It took 5 attempts following a good wheel building book. The next one i did was easy/easier. Stripping apart a Tongxin motor isn't a problem either, now i know how to fix and maintain them. It is an enjoyable learning curve.

It is basically just a precision Zener.
The problem is that on these cells, the resistance remains low as the cell voltage rises, and a a critical voltage (I think it is 4.235v on a Li-Po cell), the chemistry starts to go really haywire, with the cell overheating, and potentially exploding!....
If you are charging several cells in series, and one fully charges before another, the charger still sees the total voltage as 'below target', and keeps delivering power, and the fully charged cell voltage can creep up towards this danger level. What you want, is a circuit that draws almost nothing when the cell is below the 'charged' voltage, and draws enough current to prevent the cell voltage rising much further, as the cell reaches the dully charged level.
Most chargers help you, by switching from their 'high current' mode, down to what is effectively a 'trickle charge' mode, when the voltage gets up to about 4v/cell.
The nominal 'zener voltage' of the circuit is 4.188v, and every example built has been within a couple of mV of this. Below the 'switch point', the circuit only draws about 1mA,while above this shoots up to just on 80mA.
It is not the circuit to use to re-balance a badly imbalanced pack on fast charge, but I have used it on a few helicopter packs, where ater a day's use, one gives them a slow charge at home, and in each case the pack has balanced up after a short time. The 'point' was that it is very cheap compared to the published circuits doing this!....

Best Wishes