BMS Testing.

[Ypedal]

I am bench testing my LiMn packs for the Chaos, and beleive i have a defective BMS.

This is a 10cell BMS with ballancing, but since the cell voltages are all over the place, the ballancing is not happening properly.

By manually draining some of the higher voltage cells i've taken the back back to within 0.04v of each other but would like to test the BMS, problem is i have no clue how.

 

[Ypedal]

It has a " Max Amp " value of 35, that will trigger the bms to shut you down at the slightest bit over.

This feature still works.

But the ballancing seems to be buggered.

Look on the right side. brown and red, they look a bit too close for comfort..

and the potting compound looks bubbly in the middle of the board.

 

[Ypedal]

Now my current plan is to run leads to bypass the BMS, but still use it to give me a visual signal of " LVC ".

If i run the motor directly, and an LED to the discharge wires from the BMS, i can draw 40 amps without having to reset the bms when it trips.

 

[Ypedal]

Or upgrade the fets ?

 

[marty]

Ypedal,
This is batteries you describe at Topic 36v 20ah LiMn Battery Update.
?
See a blue and yellow packs over there? Why don't you switch the BMS on blue and yellow batteries?

I got the same gbp-battery. Mine is blue 48V 20Ah. Go here to see GBP Battery Co / 48V 20Ah Li-ion Watching your battery experiments very closely. Hope to have a bike and motor to test mine on real soon. Looking at bikes now.

 

[Ypedal]

them's the ones.. the pictures above are from the green pack.

 

[marty]

them's the ones.. the pictures above are from the green pack.

Ok do look GREEN not YELLOW

Just switch BMSs Thats how I fix things. When replacing parts - Don't test, guess :lol:

 

[mvadventure]

In Ypedals defense, not that he needs defending, even under warranty changing stuff out on this LiPO4 stuff ain't all that easy. Unless of course your supplier has spare parts and thus far that's not happening a lot. It's got to come from China and we all know how slow that boat can be.

My LiPO4's are uglier than Ypedals and my Lithium charger doesn't work. I'm waiting for the supplier to come back from China! Fortunately my old SLA charger works 95% as good delivering 55 volts instead of the potential 57.6.

However, ugly or not, defective charger or not (since my BMS is working fine) I ain't never going back to SLA. Zane of Aten Energy spent a lot of time on the phone bragging about the BMS and so far, now that I understand a little about what it is and what it does, it's pretty much perfect.

Mike

 

[Beagle123]

Ypedal: Why would you want a BMS that is sketchy to even touch your batteries? If I were you, I'd remove it. Just attach a voltmeter to your handlebars, and if the overall voltage drops below 2.8v per cell, just stop riding.

I don't understand why people think they're safer with a BMS. The most dangerous set-up is a BMS that malfunctions. But if you can see the voltage with your own eyes, its like constantly testing your BMS to make sure its correct. And since your using LiFePo4, you're not even in any danger anyway.

The downside is that you may want to use individual chargers so you're not charging at higher voltage.

Also, those FETs and wires will just add more resistance/inefficiency to your bike.

 

[Ypedal]

These packs are Lithium-Manganese .. not LiFePo4.

The LiFe are the foil pouch cells.. other headache all together.

A BMS is important for most packs, and should be present. a Quality bms is a valuable item to have. Unfortunately they are not very popular.

Peak pack voltage is not that great a way to monitor cells when you have a 72v system.. i agree that one can become very familiar with state of charges status. but when going thru traffic , keeping your eyes on the road is important.

A BMS that monitors independant cells voltage can save you big $$$ by preventing catastrophic failures.


A charger failure can be another big problem, i'm more worried about that than bms failure.

 

[Beagle123]

Peak pack voltage is not that great a way to monitor cells when you have a 72v system.. i agree that one can become very familiar with state of charges status. but when going thru traffic , keeping your eyes on the road is important.

A BMS that monitors independant cells voltage can save you big $$$ by preventing catastrophic failures.

Hi Ypedal: I'm using LiMn too, and I"m planning on using no BMS. You can see the voltmeter and ampmeter on my build page. I agree that a good BMS would be a helpful thing to have, but I don't trust them. Even if I installed a BMS, I would want to monitor the batteries anyway to make sure the BMS is working.

I disagree that the BMS would save you big $$$ by preventing catastrophic failures because it would only be saving the bad cells anyway. I'm planning on testing individual cell voltages every couple of weeks. Unless something goes really bad all of a sudden, I should be able to detect any problem cells. I think that cells would deteriorate slowly, so they would easily be found. If there are some bad cells in the pack, I think I'd notice that the bike isn't performing well, and if they fry, that's fine because they were bad anyway.

My ideal solution is making a voltmeter that cycles through all the individual cells, and reports the lowest voltages. That would be the most reliable solution.

Good luck.

 

[fechter]

Seems like you could test the BMS by measuring all the cell voltages while charging.

You might be able to completely disconnect the battery from the BMS, then feed it with charging voltage and see what the voltages are. If you do this, you should probably limit the supply current, since there aren't any batteries to absorb the power. You could just put a resistor in series with the charger.

This way you can tell immediately if one section is screwed up. If its working properly, all the voltages should be the same.

I don't think the two wires look so bad, but the bubbled potting compound looks bad.

 

[kbarrett]

I don't think the two wires look so bad, but the bubbled potting compound looks bad.

Having electronics emit smoke is usually a bad sign.