Need Help Hacking Bosch 36v 400 10A battery pack

[Alan2000]

I was given a Bosch battery pack that appears to have a faulty BMS. The pack was putting out an error code and would not run on the Bosch bike. However, the charger would charge the pack. I pulled it apart and decided to simply bypass the BMS to use it with my Bafang 36v 500w conversion kit. Runs fine! Basically I tapped into the power leads before they enter into the BMS.

Now here are my questions...

1) How should I charge it without spending $200 for a Bosch battery charger?
2) Can I use the charger I use for my RC LiPo batteries to charge it? It's a higher end RC charger.
3) If I use my RC charger, what type of battery do I select? Pack has Samsung INR18650 cells. https://www.powerstream.com/p/INR18650-25R-datasheet.pdf
4) There is no balancing plug on the pack like you find on RC Lipo packs, does that matter?
5) What voltage should the pack be charged to?
6) What low voltage cutoff should I set on my bike's controller to prevent damage to the pack?

I left the BMS connected as that way I can still us the button on the pack to see power level. I also assume that the BMS balances the cells. I'm used to a balance lead for each cell on a RC LiPo pack and don't understand how e-bike 18650 packs get balanced. Any info about that would be great.

 

[dogman dan]

To use the pack naked, the first thing I'd do would be to remove the bms, and put jst plugs on the sense wires.

I'm not sure exactly how to use your RC charger to charge it, but you'd essentially be looking at two 5s sections, to charge it with most chargers. If your charger does 10s, then perfect. If not, you'd have to create a pack with some extra wires coming out allowing you to charge and balance it as two 5s packs.

Use the lipo setting, to charge it to 4.2v per cell.

Look up cell specs to figure out where to set your LVC. But you also need to bear in mind that you want to stop at a certain point under load, which varies,,, This is the tricky bit about running a naked pack. Look up the lowest possible cut off point by finding specs for that cell.

Best option for charging and running this pack on other bikes than the bosch could be to replace the bosch bms with a generic one, then charge with a generic 36v charger.

 

[Alan2000]

My RC charger will charge 10s packs. For now until I get a real pack I have been using a 10S RC LiPo pack I made. (Only good for about 10 miles but could not wait to try my bike so I have been using that pack for now.) It has a balancing plug for the 10 cells. Are you saying to run this Bosch pack raw I would need to break the pack down into 4 packs each with a 10 cell balance plug in order to keep them balanced?

I was hoping I could just tap into the charge port already on the existing BMS to charge it since it does charge the pack when using the Bosch charger. I'm not too concerned about over discharging as the bike controller will cut off at whatever safe predetermined cutoff I set it too.

 

[dogman dan]

Ahh, I see, it's still charging and balancing right, just not running on the bosch bike.

In that case, if you are just careful about DOD, do exactly that. Charge through the bms, bypass it to discharge on the non bosch bike. Sounds great to me, that way you still get a nice balance charge. And since either way you run the same risk on the discharge, no difference there.

 

[Voltron]

Just bear in mind that the Bosch system is pretty low power, so the 4p set up can't sustain much of a C rate, so you'll have to watch it on something with higher draw.

Now if you had two, that you could parallel for 36v and higher draw, or series for being a booster pack on your 72v 30ah pack... hmmmmm.

 

[Hwy89]

I think you should tap into the balance wires and install a 10S balancing plug outside of the battery case. Then you would be able to check from time to time to see if that BMS is really keeping the cells balanced. You could also charge it on your RC balance charger. If the BMS is faulty in one aspect do you want to trust it to balance?

 

[Alan2000]

I need to do more research on ebike packs. Normally in RC airplanes and such there is a balance lead for each cell. On the eBike pack such as this Bosch you don't have 40 balancing leads, one for each cell. I'm guessing perhaps it's broken down in 4 packs for balancing purposes and each of the 4 packs balance as if they are 4 separate 36v batteries running in parallel?

@Voltron - The spec sheet for the batteries says 20A continuous discharge rate. Wouldn't that mean that the Bosch 36v pack with 40 batteries could put out up to 80A continuos? The max draw on my bike is 25A. So I think I am fine or am I totally missing something? (I'm bypassing the BMS output lead so if the BMS is limited in amps it can crank out, that would not be a problem.)

The sheet says 2.5v low voltage cutoff for the cells? I8650 go down with 2.5V? I guess that must be right as some of the BMS units I've been looking at list 2.5v for LVC. But to keep cells from getting abused, what is the recommend LCV to program in the bike's controller?

@Hwy89 - Very good point. I think the BMS output was intentionally disable by Bosch as it was some type of customer demo pack. Would be easy to run a balance plug outside. I just need to figure our exactly what I'm balancing, etc. I'm confused because when I'm charging RC stuff normally I charge through the main leads and the balance cable is just to balance, and not charge. So if I have a 10s balance plug on the Bosch pack, that is only balancing 1 of the 4 packs rights? Or do I run 4 of the 10s balance plugs and alternate using each of the balance plugs? For example, use the one to balance pack1 on first charge and then next time I charge the pack use the balance plug for pack 2, etc?

@DogMan - I'd like to keep it as simple as possible and thought using the existing BMS but tapping into power before the BMS would do just that. Hopefully the balancing feature is working. I can always pull it open after a few charges and test the voltage of the cells. But it also would not be hard to solder a balance plug once I know where to solder the leads. LOL

BTW, what's the deal with the $933 MSRP for a Bosch battery? I didn't see 24K gold strips connecting the batteries or anything special looking in the pack.

 

[Hwy89]

From your pictures it appears to be a 4P 10S battery pack. Each group of four paralleled cells effectively become one for balancing purposes. They are connected together positive to positive and negative to negative and each of the four will always have the same voltage. The four cell "blocks" are then connected on series ( negative of one to positive of the next) and their voltages add up to the pack voltage.
The balancing leads can be seen in your second picture. They are the small multi colored wires soldered to the blocks. There should be ten or eleven of these small wires leading to your BMS. Sometimes the first wire (usually black) is not there because the BMS will get that directly from the negative power lead.
The easiest way to add a balancing plug would be to solder your own wires to the places where the existing balance wires are soldered leaving the existing wires in place.
Wire the plug with the first wire coming from B- or pack negative and each successive wire wire coming from the next block of cells with the 11th wire coming off B+ or pack positive.
With nothing plugged into the balancing plug this will have no effect on the operation of the BMS but will allow you to check cell balance without opening the case.
My opinion on low voltage cut off is to keep it above 3.5. Below that there isn't enough capacity left to warrant the risk of damaging the cells.

 

[Alan2000]

Ok, thanks. I'll run a balance plug out of the case so I can monitor each of the packs to make sure the BMS is keeping them balanced. Just did a quick ride with the Bosch pack after swapping out the Bafang 44T chainring to a RaceRace 34T chainring. My top speed is still the same 27MPH in high gear (11T cog) w/out pedaling. The 44T chainring must really be lugging the motor and putting quite a load on the batteries and gears for mountain bike use. Glad I swapped it out. Could probably even go with a smaller chainring, but that's another topic...

Here are pics of both side. I'll just piggyback onto the existing balance wires as you pointed out and run an 11 pin connector out of the case. (10 leads plus ground wire.)

 

[Hwy89]

Less chance of shorting something out if you have the balance plug already wired. Then to keep the sequence correct use a marker to number each spot where you will be soldering. Solder one wire at a time and keep the rest of them isolated.

 

[Alan2000]

I ordered these to make the balance plug:

http://www.progressiverc.com/balance-extensions.html

The local shops did not have balance plugs for 10s.

 

[Voltron]

Congrats on the ride... I was a little worried about the amp draw because I'm still used to lower c-rate cells, and the fact that my own 25 amp controller was actually drawing close to 50 during hard riding when I metered it, and heating up the battery until I paralleled more in.

 

[Ykick]

I’ve kinda skim-read here but a couple things jump out to me.

Those JST adapters appear to be 9-wire or 8S each? For 10S, check here if these will work - http://www.buddyrc.com/pigtail-10s-male-jst-xh-blance-connector.html

The other thing I would suggest if/when you get a tap on each 4P series group is to perform simple IR test of the cells. That would provide a good indication of their ability to deliver higher load power.

Minimum tools for IR testing would be watt/amp/power meter and voltage monitoring (JST plug) for each series string. Record starting voltage of each series string, apply a known value load (It doesn’t need to be large load but bike under way is always good).

Load for about 10-20 seconds, jot down the series string (cell) voltage drop under that load (I sometimes just snap a picture on my phone if connected to RC Charger or CellLog). Then it’s just an Ohm’s law math problem. Divide voltage drop by Amp load, multiply by 1000 = mOhm (yes, that’s milli, not Meg)

Any pack much above 20mOhm is gonna struggle to deliver 30A or more, IMO.

You’ll also immediately see if some group is way of outta whack from the others.

 

[Alan2000]

The plug I ordered is 11 wire for 10s. There is a dropdown menu on the order page to select the # of leads. I ordered 1 set which is 2 cables. Maybe I should have ordered a second set so I could have one for each group? I'm still green to running packs in parallel. In my years of LiPo hobby use I have not had a need to run packs in parallel so I'm still figuring out how it plays out when you have a pack permanently connected in parallel, etc. I connected my battery logger on the trip yesterday. No time to download the data to see how much power I was pulling and the corresponding voltage. The battery lever meter dropped more under full load than when I am using my temporary RC battery back. But it bounced right back up after reducing the load. Have about 13 miles now on the pack and the built in battery meter is showing 80%. When I get some some I'll pull the data from the logger and post info.

 

[irq]

Sorry for Hijacking.

do you probably sell the bms? dead or alive, doesnt matter for me

Hijacking over

 

[999zip999]

If you have samsung 25r in that pack it could discharge 40amps safe and ez. 1600watts. Most bosch packs came with 29e which is a 4amp cell not 20a Samsung 25r . Nice to have sense wires for a cellog 8s or less like two 5s sense wires. What are your plans for the pack ? Run parallel when needed for range. What motor, controller setup do you have ?

 

[Alan2000]

@ Irg - For now I plan to leave the original Bosch BMS in there, despite the fact I'm bypassing it for power to the bike. I'm hoping the BMS is working to keep the cells balanced. (The Bosch bike it was going to be used on did not like the pack and gave an error code. I think the BMS was intentionally deactivated.)

@ 999zip999 - I am using the Bafang BBS02 36V 500W setup. I changed the 44T chainring to a 35T as I plan to use it mostly on mountain trails. I have the Bafang programmed now to cap out at 24amps just to feel that I am not pushing it to full 25A capacity. I download the data from the last ride. Peak amps was 23.73 and max watts 843. Ride was about an hour and went 11 miles and used 5015mAh. Had about 2 miles on the pack before this ride. Seems like the Bosch pack should be fine with this setup. When I had the 44T chainring it would pull close to 1000W.

Made mount for the battery and she is all ready to go now without Gorilla tape holding it on! LOL.

 

[Alan2000]

I was wondering why the watts were peaking so often after looking at the data in the chart. I reviewed all the settings in the BBS02 controller and found out the Pedal Assist Start Current was set to 100%! Yikes! Should be around 25%. So every time I started to pedal it was putting out 100% power on startup. No wonder all the spikes. Changed it to 25% and still drives nice and with a lot less strain on system.

 

[Voltron]

Well, you got me motivated to do something with my Bosch packs..... Now they're 72v booster pack. Thx for the reminder to do something with them!

 

[Alan B]

Just to confirm what was already stated, because the OP seems to have doubts.

Once cells are connected in parallel, they act as a single cell. They have the same voltage, they effectively become one larger cell. You cannot tell them apart, you cannot monitor them separately (except for individual cell temperature) due to the hardwired parallel connection. So wire up a single 10S balance connector and pretend your pack is 10S1P -- but with four times larger cells.

 

[Pkal@1234]

I have a doubt regarding the BMS, what is the interface offered between the BMS and the Motor Controller?