Has anybody come across this BMS?

[Smart]

After trouble shooting my bikes failure to work in the technical forum with help from some very knowledgeable forum members I was advised to start a new thread to see if anybody has come across this BMS and if anybody has any experience in repairing a faulty one.

It has come from a battery pack on this bike http://www.barnesandrobinson.com/ba...enix-electric-mountain-bike---br005-455-p.asp

 

[dnmun]

you should take a better picture of that side of the BMS with the yellow plastic off so we can follow the traces across the upper part where those mosfets are and where those little sot23 transistors are.

you will need to rig up a space heater to discharge the pack into. one without a fan, like an oil filled electric radiator or radiant heating element but no fan.

then you can discharge the battery into the heater and measure the cell voltages on the cells as the battery discharges.

it would be neat if you had a 11 pin XT extension so you could have the BMS separate from the pack and be able to measure the voltages on the traces on the side facing down against the top of the pouches. take the nuts free on the mosfets and unscrew that plate and pull the plate off the mosfets so we can measure the voltages on the mosfet gate legs.

you would need a voltmeter to use the 10A scale for the discharge, and another voltmeter to measure the voltages. but it sounds like it will shut down immediately so the cell may stand out if one cell is bad and the ammeter is not needed, just the voltmeter.

but you need to see what the voltage is on the gate leg of those mosfets and what turns it on and off. it does turn on to charge, what happens on discharge is the question.

 

[Jeremy Harris]

I've had a good dig around and can't find that exact BMS anywhere. Some Chinese sites call these things "Protection Circuit Modules" (PCM) so I had a search for that as well.

The advice dnmun has given is good, if we can get a better look at it we may be able to guess the next thing to check.

Out of interest, where in the UK are you? It may be that there's someone here fairly near to you who may be able to help.

 

[Smart]

I'm in crystal palace.
I will take the battery apart again today and take pics of the BMS. I'm not so sure I can get hold of a space heater to separate the BMS fully but I'll try.
I've emailed the bikes manufacturer and the uk distributor but haven't had a reply (about a week ago).
One thing I did notice after putting the battery back together temporarily was that the lights on the handlebar display behaved differently when I pushed the power button. Now there is one solid light indicating low battery that only stays on for a few seconds and then all the lights go on in sequence and then off again. The only thing I have done differently is to cover a small piece of exposed wire that comes from the BMS with some tape as it was extremely close to the metal layer screwed on top of the BMS. I don't know if that's made a difference but I thought I'd better mention it.

 

[Smart]

Here's one with the film removed

 

[Smart]

here's another with the wire directions to the best I could explain
4 of those big screws to the left have mosfets under them

 

[dnmun]

you have two wires labeled 'to capacitor'. where is that capacitor and what does it look like?

you can use a buncha big wattage light bulbs to discharge the battery too if you don't have a space heater. you will need jumpers with alligator clips on the ends to make the connections too.

i doubt if the people who sold or imported it have a clue so don't expect much. i doubt if they will tell you if they have a manufacturing defect either. but if we can establish that the cells will function under load when we discharge, then we can look elsewhere than the cells.

the BMS is curious too. looks like it is missing an entire row of little SOT 23 transistors across the bottom and their base and emitter resistors.

 

[Smart]

you have two wires labeled 'to capacitor'. where is that capacitor and what does it look like?

The capacitor is tucked away in the top of the battery case lid next to the ignition, I'm presuming its a capacitor as I can't get it out but it is cylindrical in shape. one of those wires runs to the neg coming off the BMS and the other is going to the positive off the BMS even though they are both black wires.

i doubt if the people who sold or imported it have a clue so don't expect much.

Thats what I feared. Just random people shipping cheap bikes in fro china and marking them up for profit with no knowledge of the product.


If I bypass the BMS and hook straight to the controller from the cell +/- bolts will this also indicate wether or not the cells function under load?

 

[dnmun]

you need to be able to measure the cell voltages on those pins when the battery is discharging. we have not established that the problem is not with a bad cell even thought they are all fully charged it seems. one of the tabs under that connecting plate could be damaged, but not too likely. so discharging in a controlled manner while you measure the voltages is the best way for me to see that.

i am curious about how that end cap is wired up now that i know there is a big cap in there too.

 

[Smart]

you need to be able to measure the cell voltages on those pins when the battery is discharging. we have not established that the problem is not with a bad cell even thought they are all fully charged it seems. one of the tabs under that connecting plate could be damaged, but not too likely. so discharging in a controlled manner while you measure the voltages is the best way for me to see that.

Ok, I'll have to give it a go at some point during the week as I don't have the resources lying around to do this

i am curious about how that end cap is wired up now that i know there is a big cap in there too.

I'll take another pic with some light shining on the capacitor area in the lid

 

[Smart]

Eureka!!
If I apply pressure to the area marked in the pic (one of the connections from the ignigtion must be loose) then I get 41.7v through to the bikes controller and the bike seems to work! (havn't tested fully)
I stumbled upon this whilst checking various voltages of wires coming from the bms a moment ago.

 

[Smart]

Just wanted to say thanks for all the help in these forums..
Turns out the problem wasn't the Controller or the BMS, it was the ignition.
I desoldered the wiring for the ignition and cleaned it up and then re-soldered the wires and the fault still seems to happen but its the actual switch inside the ignition.
If I turn it to the ON position and don't firmly apply pressure as if i'm trying to snap the key then the switch doesn't work.
So I guess I'll have to remember to force the key every time I use the bike.

 

[Jeremy Harris]

That's good news that it's something so straightforward, good bit of detective work in finding it!

You may be able to find a replacement switch that would fit, as often they are a fairly standard size. Alternatively, if you can take the switch out, then you may find that you can tighten up the crimped-in plate at the back. Sometimes these switches are poorly assembled and from your description of pressure fixing it it sounds as if the rear plate may not be fully home.

 

[dnmun]

way cool, it did not seem like the BMS was dead. i would chop out all that stuff, the switch, the cap, the fuse, and to turn the battery on and off put a switch between the source leg and the gate leg on the mosfets. it could be a tiny switch, just enuff to turn off the mosfets and it won't burn up from switching the controller current.

turn the switch on and the battery is off, turn the switch off and the battery is on.

 

[Smart]

I did contemplate replacing the ignition for a switch (ignition barrell seems like a bit of overkill for a mountain bike) but I'll probably leave it as it is until it really starts acting up.
My next task is to fit a throttle/thumb throttle just not sure which of the wires on my controller are for the throttle and which throttle to buy.
Do I just need to look for a 36v compatible throttle?
I'm surprised nobody has come across this BMS before though, it seems to be an almost identical battery packs to ones manufactured by Advanced electronics Energy out of guangdong.

 

[dnmun]

i think those limn2o4 BMSs are common. i thought it was a super efficient use of the space.

the throttle is the same for all the motors. you don't wanna get a throttle with the voltage indicators built in. when they get wet the high voltage can leak onto the throttle signal and punch the bike into uncontrolled WOT. use a cycle analyst from justin at ebikes.ca or get a watt meter to keep track of your charge levels. there is no other way that works.

i don't like those switches and fuses in the high current lines. i like to just turn off the output mosfet. that is what they do best.

 

[Smart]

The pedelec control display on the handlebars already shows a battery gauge so I think I just want want a basic thumb throttle.
I've seen a few that have 2 wires and some with 3 wires coming from the throttle.
How can I determine which wires from the controller are for the throttle and will the throttle automatically override the pedelec?

Sorry for taking this off topic.

 

[Jeremy Harris]

BTW, the key switch/battery pack mechanical catch looks to be available cheaply on it's own: http://www.greenbikekit.com/index.php/accessories/key-lock-ignition-for-e-bike-rear-rack-battery-case.html should you decide to replace it.

A basic throttle, either twist grip or thumb, will have three wires, usually either red, black and green or sometimes red, black and blue. You should find three throttle wires coming from the controller with those colours that aren't connected to anything. It can be confusing with pedelec as well, as often the pedelec wires are the same colours as the throttle wires. If a throttle is fitted then it will normally over ride the pedelec.

 

[Smart]

Thanks Jeremy, I had looked for a replacement barrel but couldn't find one. I think I will buy the one you suggested.
I'm now trying to find a reasonably priced thumb throttle that ships from the UK, I've seen one on eBay that I will probably buy. My only concern is the fact my bike has a grip shift and I don't want to have the thumb throttle in a position that may be uncomfortable to use but I guess I'll just buy it anyway as its only £12.99