Building my first ebike battery

[Cobblers66]

Hello all. I'm just ordering all the parts to build my first ebike battery.

So far I've ordered 40 LG m29 cells rated at 10a continuous discharge, and a 20a continuous balancing bms.

I'm going to make a 36v 10s4p pack to replace the battery in my missus powabyke Milan 2.

The current pack is 10s3p and very tired badly needing replacing.


The bike has a 250w brushless hub motor 120deg without hall sensors.

The speed controller is a acw36e-22x01a.

Is it worth upgrading the speed controller to a higher amp rated model get a little more power or is the only way to get more power from the motor running it at a higher voltage.

Cheers

 

[Nealh]

Power comes via current and not voltage.
Looks like your controller is 22a +/- 1a which is more then most bikes but brushed motors often demand more current.

How do you plan on connecting parallel and series connections and what material for the buss bar/interconnectors.
The P ones don't have to carry much current but the S ones do so you need interconnector material ideally that can take the whole 10a current load of each cell, some might divide the max controller current of 23a divide by four and use a buss/interconnect just to cover this, but if a cell fails or becomes weak the other busses then will be over worked for the current load.

Pure nickel 1mm2 is capable of 4.459a current load/ampacity optimally and 6.619a is max acceptable.
Copper is approx. 4 x more capable and 1mm2 16a optimally.

 

[Cobblers66]

I've ordered some 0.2mm 8mm nickel strip and was going to double up the series connections.

From the info I've found online the controller is rated at 15a and and it says 250w however a max or 540w.

Sorry the bike is a powa cycle Milan 2 not a powa byke.

On there website they say it has a 200w motor I cannot find any markings on the motor but its definitely a 3 wire non sensor brushless hub motor

 

[Sturmey]

.... all the parts to build my first ebike battery.

I would recommend buying the spacers as they give strength to the pack and reduce the likelihood of strips/balance wires breaking or shorting. They also help cooling.
I would also make up a dummy load and do a full charge and then discharge to 30 volt on battery, observing the group voltages, which should remain in balance to 0.01 v for new cells. If you measure the current and/or load resistance, you can also estimate the actual working ah capacity doing this, which should be a bit better than 90% of the nominal capacity.

 

[Cobblers66]

Roughly how much do these spacers increase the pack size. I want to keep the pack inside the existing battery holder and I'm already going from a 3p pack to a 4p pack which there is space for inside the holder if I remove some of the foam packers that are around the existing pack. I've seen 2 types of spacers, some are lock together squares and other types are offset cylinders. The square type look a little bulky.

I will do a load test once built, hopefully the cells will be OK, I've bought them from a UK wholesale supplier I didn't fancy risking it with ebay cells

 

[Sturmey]

Roughly how much do these spacers increase the pack size. I want to keep the pack inside the existing battery holder and I'm already going from a 3p pack to a 4p pack which there is space for inside the holder if I remove some of the foam packers that are around the existing pack. I've seen 2 types of spacers, some are lock together squares and other types are offset cylinders. The square type look a little bulky.

I will do a load test once built, hopefully the cells will be OK, I've bought them from a UK wholesale supplier I didn't fancy risking it with ebay cells

I used the square type that lock together. I think they add an extra 1mm all around. 10X 4 rows of 18650 would normally be 180 X 72mm, but with spacers would be 200 X 80. plus a little extra on the height.
I suppose the main thing is that the battery is mechanically robust, however way you achieve that.

 

[Cobblers66]

Well I received my cells this morning, 24hr uk delivery so really good. I've tested all 42 I bought and they are all sat at 3.6v exactly. Before I start building the pack I'm going to fully charge them individually. I've just got to wait for my nickel strip

 

[Sturmey]

...... Before I start building the pack I'm going to fully charge them individually.

Warning! Don't charge the cells individually. I will give two reasons. When you are assembling the pack, its very easy to accidentally put on short circuits. For example, I was soldering balance wires using a roll of solder and one part of solder roll came in contact with adjacent cell and there was sparks and solder melted. For this reason, its better and safer if batteries are only partially charged (e.g 3.5v) when assembling packs.
The second reason is that you may knock the cells out of balance. Ideally, a good battery has identical cells (from the same batch/manufacture date) and all cells are subject to the same charge/discharge currents during its lifetime. A well built battery with good cells (even without a balancing BMS) will often keep in perfect balance for many months.

 

[Nealh]

Build the pack with the cells at the factory voltage they arrived at.
Which vendor did you use, Fogstar ?

 

[Cobblers66]

Build the pack with the cells at the factory voltage they arrived at.
Which vendor did you use, Fogstar ?

Yes fogstar

Ive already started charging, should a discharge the 8 I've done so far back to 3.6?

 

[Sturmey]

Ive already started charging, should a discharge the 8 I've done so far back to 3.6?

I think you should and within 0.01 volts. This can be a tedious job as after discharge to 3.6v, the battery volts may rise a little after a period of time (to perhaps 3.63v) and you will need to discharge slightly again and recheck again after a few hours.
But again, it is necessary as the battery needs to be kept balanced and it would be dangerous to assemble a battery with fully charged cells.

 

[Cobblers66]

OK I've sorted the cells out now and they are all equal.

I decided to go with the square type cell holders as there is enough space for them, I carnt build the pack yet as I'm still waiting for the nickel strips the cell holders. I think the bms will arrive today but I've also bought so braided sheath for the balance cables.

What did arrive yesterday was the new speed control. Its a brainpower model with Lcd display. I connected it all up last night and also made a discovery. I believed the motor was a sensorless motor as it only had the 3 thick wires.

I chopped the end off the motor cable ready to be re terminated with new plugs and the end of the cable has been heatshrinked. Once it cut it off I found the hall sensor wires were all there hidden behind the heat shrink.

The controller I bought was supposed to be dual mode for sensors or sensorless. I hooked up the sensor cables and did the self learn sequence and it works a treat. I get a speed readout on the lcd display so I'm happy with that, and everything else works like it should.

The only thing there isn't a connector for on the new controller is the hand throttle kill switch that is mounted on the handlebar.

Would it be possible to just wire this switch in series with the signal wire from the hand throttle or would this cause a error of some sort. Missus only really uses pedal assist and its handy being able to disconnect the hand throttle.

 

[Cobblers66]

Well I got tired of waiting for the cell holders to be delivered and went ahead last night with glue and heat shrink.

Started at 10pm and finished around 5am

Did have a few brews though and also wasted time having to find a wiring diagram for my bms. Also had to wait for the bodged up spot welder I had made to cool down quite frequently.

I found it to be a easy job that just needs you to concentrate and be methodical.

Most annoying part was the cutting of the 72 series connection nickal strips.

Total cost ended up at under £130 for a 36v 11.6ah pack.

Missus didn't want to wait for a load test she told me to get it in the bike and she would test it.

Anyway after a full charge she went out for a quick 6 mile ride on the return the pack was sitting a 4.07 volts.

She is very happy with it. She says it has loads more power so we will just have to see how it goes now. Thanks for the help

 

[Gliggsy]

Hi there fella, I'm in the process of building my own pack using boston swing 5300 cells, Purchased 21 of them to make a 7s 3p 24 volt pack, I have all the bits except one bms although I am a little concerned that the bms that I ordered are for 7s and there is a wiring diagram on e bay where they came from but there's only 7 wires, I would have thought it should be 8 as most are, wondered if you had any thoughts on cells or concerns with 7 wire bms... Glyn

 

[Cobblers66]

Sorry I'm a newbie with this sort of stuff I would have to check the wiring diagram to see if it was suitable. I think my bms had 11 thin cables 1 negative and 10 positive also plus a ihad to solder on the battery negative negative output and and negative charger cable

 

[Nealh]

Hi there fella, I'm in the process of building my own pack using boston swing 5300 cells, Purchased 21 of them to make a 7s 3p 24 volt pack, I have all the bits except one bms although I am a little concerned that the bms that I ordered are for 7s and there is a wiring diagram on e bay where they came from but there's only 7 wires, I would have thought it should be 8 as most are, wondered if you had any thoughts on cells or concerns with 7 wire bms... Glyn

Show us a link to the BMS, some don't use the the extra wire as the b-.

 

[Gliggsy]

6S/7S Li-ion Lithium Battery Protection Board 60/30A 25.2V 24V 29.4V lipo BMS. Hopefully this is the link

 

[Gliggsy]

https://www.google.com/url?sa=t&source=web&rct=j&url=[URL]https://h5.aliexpress.com/item/33029952396.html&ved=2ahUKEwiol-3a5tzpAhVOQhUIHRQbDg4QFjANegQIBBAC&usg=AOvVaw3JLuqX2vh-wm9m5bgnCt5Q&ampcf=1

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