Lithium battery question

[Dak77]

Do you have space for a 6p battery? If so, buy a couple vruzend kits and make your own. You'll know exactly what you have and trouble shooting will be much less bullcrap. Forget the bms garbage and check the voltage of each parallel group once a week. https://www.18650batterystore.com/18650-Battery-p/lg-m29.htm in the US sells LG m29 for about $3 a piece for 50qty . If you only charge it to 32.8 volts (4.1v per cell) , you don't have to sweat too much about perfect balance. But unless you abuse the crap out of it, balance won't be an issue for a long time and when it does become an issue, order some balance leads and use a hobby charger to balance it in 2 sections. Take your time ensuring your connections are secure, and that it's encased and protected from touching metal and you will have a much much better battery than these premade chinese crap packs. Also consider a meanwell LED powersupply to charge it. An ELG-150-36a runs about $35 and has adjustable voltage and current.

 

[fechter]

Thanks again for all the responses. I don't need to go fast just want scooter to work. It sounds like i need a better battery rated for higher amps. Again i dont need to go full throttle all these time i just want it to work. Where is the best place to get such a battery?

I would get a new BMS and just try the battery you have. What else would you do with it anyway. If the battery overheats or dies early, then look for a new battery. The battery will be able to handle current over it's rating for short bursts like accelerating from a stop. Going full throttle up a long hill is where you would need to be careful. If you get it running, you do a test ride then open the deck and feel the battery temp (or rig up a thermometer for testing).

 

[eMark]

AGREE! :thumb:

Even though twilloug's EVE battery may be overrated at 30.6 amps max continuous discharge it's still good for short bursts of 30A (15-30 sec). The previous suggestion of connecting a 7S balance lead ... https://www.amazon.com/uxcell-Balance-Connector-Extension-Charger/dp/B07GN7S7BM/ref=pd_sbs_263_4/139-5157333-5670654?_encoding=UTF8&pd_rd_i=B07GN7S7BM&pd_rd_r=c9b97065-057c-47d4-a550-cc6ba93ed94c&pd_rd_w=s7Eyi&pd_rd_wg=wehBw&pf_rd_p=7cd8f929-4345-4bf2-a554-7d7588b3dd5f&pf_rd_r=CNQVA8SDF4Y1BQXQM538&psc=1&refRID=CNQVA8SDF4Y1BQXQM538 ... (although U only need 1 not 5) is even more justified with your 7S4P Chinese EVE battery with cells of questionable quality.

Then get yourself: A Cell log alarm ... https://www.commonsenserc.com/product_info.php?products_id=2862 ... , Tenergy 5-in-1- 7S Intelligent Cell Meter and/or the iSDT BattGO 8S that is more accurate and capable of discharge balancing besides other handy features. You may also want to wire in series (red positive discharge wire) a waterproof marine Inline Fuse Holder. You need a BMS(BPS) for protection even though it may not discharge balance your P-groups unless the variance is more than 30mV ... thus the reason for using a BattGO-8S for closer monitoring-balancing cells of questionable quality.

It's my experience that you can have both a 7S balance lead and 7S BMS connected to cells. Connect the 7S BMS leads to one set of your 7S4P cells and your 7S balance leads to another set of your 7S4P cells if easier that way. Use the iSDT BattGO for balance discharging (if necessary) when the EVE is resting (e.g. bottom and/or top discharge balancing). However, when bulk charging you can use the BG-8S for monitoring cells, the Tenergy 7S monitor and the Cell log 8S monitor. Keep that CS Spy Alarm cell monitor plugged into the 7S balance lead set at say 3.5V or 3.4V when riding your Scoot e-scooter for extra safety warning protection.

 

[john61ct]

I have no idea what you intend to mean by this, afaik there is only one "set" of cells here.

Connect the 7S BMS leads to one set of your 7S4P cells and your 7S balance leads to another set of your 7S4P cells if easier that way.

If multiple cell-level devices need to be connected at the same time, they and the BMS can all be wired into the same set of leads.

I hope you aren't suggesting four at a time though?

> get yourself: A Cell log alarm

There are many dozens of per-cell voltage checkers with a low voltage alarm,

The CellLog, celllog/cell log device was a specific one, that also allowed for wiring in an LVC rather than just sounding a buzzer.

Probably best to avoid confusion, to not use that brand name as a generic term

 

[jordanjozsef]

I have a question about the BMS, but I couldn't find a straight answer. The BMS's rated current is 60A, but my controller is able to draw 100A. I don't think I'll ever use over 60A continous, because that means 6000W, and that would mean really high speed. But the 100A would be great when accelerating. I don't know how the BMS will behave. Will it smoke at 100A? Will it shut down? Will it do anything at all? The peak discharge current is 200A, but I don't belive it's true, since I already smoked one, when I directly connected a brushed DC motor, so it must have drawn lots of current to burn it out. So what does 'peak' mean? A second? 30 seconds? A minute? The cell's continous discharge current is 10A, so they would handle it (28s10p), the 3kW motor too, I'm only worried about the BMS.

 

[fechter]

The actual rating is dependent on temperature. The BMS is supposed to trip when it exceeds the “peak “ rating. How long you can go over the continuous rating depends on cooling.

It’s possible the one you fried was defective or rated higher than it was really capable of.

 

[john61ct]

I have a question about the BMS, but I couldn't find a straight answer. The BMS's rated current is 60A, but my controller is able to draw 100A.

Please link to the specs or source page for the specific BMS you are referring to.

Many do not limit current but just shut down operations or burn at some point above their rating.

The owner / builder really should make sure the controller or CA or maybe a fuse/CB keeps the current below spec.

BMS is only for last-ditch protection when primary fails.

If you can and need to use 100A, then get a bigger BMS.

> So what does 'peak' mean? A second? 30 seconds? A minute?

Ratings for devices built by renowned firms employing top engineers will be precisely spec'd. Cheap Chinese stuff's ratings are usually grossly "optimistic", so pushing up to even half the rating will cause stress and reduce lifespan and reliability.

> The cell's continous discharge current is 10A, so they would handle it (28s10p)

Have you actually tested that?

 

[amberwolf]

since I already smoked one, when I directly connected a brushed DC motor, so it must have drawn lots of current to burn it out.

a brushed dc motor makes a crapload of rf from it's brushes (you can see the arcing that does this if you run it in a dark room, if you can see inside it thru air vents). so it doesnt' have to be current that destroys fets connected to it--rf contains energy at all sorts of frequencies, that the bms fets probably arent' protected from (not really a need to design them to be).

arcing upon connection to a load also causes rf, but this usually lasts so short a time it's not that big a deal, compared to the continuous rf of a brushed motor.


if a brushed motor is low enough resistance, and high enough load on it, then it could draw *huuuuuge* currents for a short time trying to start spinning, till it gets fast enough to lower that current draw (via back-emf; you can look that up if interested). those currents could be in the hundreds of amps in some situations, and may be so high that the fets in the bms simply can't take it *at all*.


that's one reason a motor controller is used, so it can limit current draw on stalled motors, and so it's capacitance can help absorb some (most) of that rf from the brushes, among other reasons.

 

[jordanjozsef]

The BMS is unavailable, but it was a CLRD BMS 14s 60A rated. The brushed motor was a test, no load was applied at all, it didn't spin fast. It stopped for a short time, so I disconnected the battery and when I connected again it started rotating again and the BMS started to smoke. The motor's cable melted inside, the brushes were damaged too, so I guess it was shorted, before the BMS blew up. I should never do stupid things like that, connecting 120V DC to a 48 V brushed motor is not a good idea.

There's a load test on YouTube if you type Lanzhd 18650, the voltage drop is acceptable at 10A (from 4,2V to 3,2V), they just need cooling. I have used them for a year at 50A maximum current (5A / cell), and they didn't lose much capacity (around 200 mAh) . The voltage drop remained the same. And they were soldered, hot glued together, wrapped around with polyfoam, and put them in a thick black wooden box without any cooling. Probably the worst thing I could do. Now they will be tested, put in brackets, spot welded and temperature monitored with a fan so it turns on when it's necessary.

 

[amberwolf]

The brushed motor was a test, no load was applied at all, it didn't spin fast. It stopped for a short time, so I disconnected the battery and when I connected again it started rotating again and the BMS started to smoke. The motor's cable melted inside, the brushes were damaged too, so I guess it was shorted, before the BMS blew up. I should never do stupid things like that, connecting 120V DC to a 48 V brushed motor is not a good idea.

a brushed motor, unlike a brushless, has a definite rpm limit, and thus a definite voltage limit. if you exceed the rated speed of the motor, you risk the commutator (the copper bars around the armature that the brushes ride on to transfer power to the windings) physically disintegrating and breaking the brushes, shorting stuff out, etc. it's even possible in severe cases for commutator segments to "grenade" out of the motor casing and fly around as shrapnel.

i don't know if that's what happened in your case, but you can open the motor to find out if you like.


another thing that happens is that at higher voltages, currents are higher, so arcing is greater. at some point, arc welding can occur between commutator segments, or inside the brushholders, etc. 120vdc is nearly three times 48vdc, so the currents would be that much higher.


if the motor stopped, by itself, then that means the bms's output had already shut off, to try to protect the bms from whatever overload the motor was presenting it.

reconnecting the bms presented the overload to it again, but this time apparently it couldn't react fast enough to protect itself, or the overload was beyond it's ability to do so, with further damage to the motor both before and after the bms failed.

 

[jordanjozsef]

The brushes were crushed, and was impossible to turn, so you are right. The cells survived, so the bms protected the battery pack after all.

 

[twilloug]

The Escooter has been on the back burner for a while. Got back to getting it running.

I have not replaced the bms on the battery yet but i did some more testing. The motor operates when the charger is plugged in and throttle applied. I also got the motor to operate without the charger plugged in and a jumper wire for negative cable that bypasses bms.

I tried resetting bms as well by unplugging bms, plugging charger in and then reconnecting. That didn't seem to work.