Can a 12s BMS be charged by 55V or 58V charger?

[baltimorebiker]

A bestech bms suchs as this one:

http://www.bestechpower.com/444v12spcmbmspcbforli-ionli-polymerbatterypack/PCB-D105.html

or one of ebay like this:

http://www.ebay.com/itm/44V-48V-50-4V-12S-60A-Lithium-ion-Li-ion-LiPo-Li-Polymer-Battery-BMS-PCB-System-/221644780045?ssPageName=ADME:X:RTQ:US:1123


They both state to charge at 50.4V but these chargers are hard to come by and expensive. Its easy to find 55V or 58V chargers. Can I use a 55V or 58V charger on the BMS? Shouldn't the BMS protect from over voltage? Is heat dissipation the issue or something like that?

As a side note, I'm going to run 12 nissan leaf lipos with one of those BMS I linked above. Thanks.

If the BMS won't accept 55V or 58V, I would rather use a 12s balance charger and go without a bms. And use this charger.

http://www.hobbypartz.com/75p-1220-charger.html

 

[Ykick]

In a perfect world you should okay using somewhat higher charge voltage than specified. In fact, that’s often the only way to achieve balancing mode. I tend to avoid that if I can but as long as the BMS is functioning properly it should be protected. Many charger output voltages can be adjusted as well.

eBay BMS has double the FETs and rated much higher current handling than the Bestechpower D105. I’ve used eBay BMS before (and several Bestetchpower, not D105 however) and the eBay BMS is somewhat lower build quality but very functional as long as you only expect about half the labelled current capability.

And you should verify with Bestechpower if that D105 model is still available? In the past I’ve found many BMS on their site which are no longer available.

 

[baltimorebiker]

Thanks for the advice. I think I will go with a 12s bms with 55V charger and just try not to leave it plugged it for long periods when done charging.

I plan on using a 45 ah battery and drawing 40A to 50A. Do you think its worth it to pay $30 extra for this bms:

http://www.ebay.com/itm/44V-48V-50-4V-12S-80A-Lithium-ion-Li-ion-LiPo-Li-Polymer-Battery-BMS-PCB-System-/321741686412?pt=LH_DefaultDomain_0&hash=item4ae94c868c

This model appears to have only 6 FETS but with a humongous heat sink.

 

[dnmun]

you can buy whatever you want but it won't matter if you have decided to use the wrong charging voltage for the battery. nothing can compensate for common sense.

 

[riba2233]

There you go...

http://www.aliexpress.com/store/product/12S-48V-50-4V-CV-4amp-Li-ion-LiPoly-Battery-Charger-Aluminum-Casing-Electric-Bicycle-Charger/313864_32220991084.html

If you want higher current, buy stronger charger and adjust voltage, or ask greentime to adjust it for you.

 

[amberwolf]

As a side note, I'm going to run 12 nissan leaf lipos with one of those BMS I linked above.

First question you need to ask yourself is:

What is the max charge voltage per cell that they should be charged to?

Next is to do the math:

What is that voltage times the number of cells in series?

I don't know what those cells are meant to take, but if you use 55V on 12 series cells, you end up with almost 4.6V per cell!

If you use 58V, you end up with more than 4.8V per cell!

I think you're heading for trouble doing this.

Assuming your cells are meant for 4.2V max per cell, then 12s gives you 50.4V. I wouldn't wanna have a charger that goes any higher than that.

If those cells are like my EIG NMC cells, they they only go to 4.15V max, and that's only 49.8V for 12s.

So with a 58V charger you'd be going almost 9v, almost 20%, above what it should be.



If your 50.4V BMS is meant to shut off the whole input to it once it reaches that HVC, then maybe it could protect the pack from the overvoltage you'd be giving it on every charge otherwise.

If it only has a cell-level HVC, but still cuts off teh whole nput to it if any cell goes too high, then again maybe it could protect the pack.

If it does not cut off teh input to the whole pack, but instead simply tries to shunt current around the cells, you are still applying too high a voltage to the pack, and if the shunt current is not enough to load the charger down to the 50.4V (or whatever max it should have) then it will apply a higher voltage to the pack, and do whatever damage that does to the cells.

Also...what happens to your pack if the BMS FETs fail shorted? Or something else goes wrong that prevents it from shutting off input voltage? your pack will then charge to the full voltage of the charger...and I expect that's bad news at 55V or 58V.


You don't need a higher voltage to balance your pack. You just need time for that to happen with the correct voltage, as the BMS shunts current around the other cells. Higher voltage just means more chance to overcharge your pack.


Keep in mind that the chargers typically reduce current because of the decreasing voltage difference between the pack and the charger output. If the difference is larger (because of the wrong charger voltage) then the current will be higher, and it may be much too high for the shunts in the BMS to bypass all of it around the already full cells, and if that happens they will continue to charge. Being already full, that means overcharge.


If you are relying on yourself to disconnect the charger after teh pack is full, then you don't need a BMS in the first place, and the BMS won't do the job of balancing that is one main reason to have one. But worse, if you forget or are distracted or otherwise dont' remove it in time, and any of the above things happens, you'll be overcharging your pack.





If you get a higher voltage charger and it turns out to be adjustable, then you could tune it down to your correct pack voltage HVC...but if it's not adjsutable and you use it anyway, well, it's *your* pack and I guess you can abuse it anyway you like.

 

[baltimorebiker]

Thanks for all the input.

I decided to get a Thunder 1220 - 12s lipo balance charger for $95. That's less than the $75 bms and $50 50.4v charger. I will also have no current limit, and more control over my voltage. (will probably charge only to 4.15V to prolong life).

I already have a 360 watt PC power supply so I can easily transition into using a 12s lipo charger . I am already familiar with using 6s lipo chargers for my 24v pocket bike. I will be using a watts up meter, so I can monitor voltage and energy while I ride.

 

[baltimorebiker]

Update:

The thunder rc charger works great with the nissan leaf battery. The nissan leaf battery actually came with a wire harness that was internally connected to each cell, so it was easy to connect to 2 x 6s jst connectors to the wire harness which easily interfaced with the 12s charging from the thunder rc charger.

2000 whr battery weights about 40 lbs and its huge, so the biggest problem right now is finding a place to mount the battery. I am thinking of using a battery bag, and stuffing it into the main triangle frame. This would largely impede pedaling, but with 2000 whr, I don't think I will ever need to pedal. I just don't want an uncomfortable riding position. Comfort and handling is a big factor for me, so putting in in the main frame will reduce comfort, while putting it in the rear will reduce handling. I have an XL steel frame bike, so putting battery in main triangle might not be too uncomfortable for me because I can wedge it pretty far forward away from my legs.

Quick question: the thunder charger has a max charge capacity of 20 ah. Given that I have a 45 ah battery, I don't know if the charger will be able to fully charge my battery. I'm thinking that the charger might shut down once 20 ah has been dispensed, and I will have to restart the charger again to get it to go up further. Or maybe, entering battery capacity is just the chargers way of preventing users from putting extremely high charge C rates on small batteries? I don't know which is the case, but I will find out eventually through testing, and update here. Testing may take a while because battery takes over 10 hours to charge, and I would need to ride at least 100 miles to fully discharge. My watt meter will give me the answers I want.

 

[dnmun]

maybe you can get a backpack frame and mount the battery on the backpack frame as though it was a backpack battery. that would make it easy to carry into the house where the little RC charger is.

 

[baltimorebiker]

Frame backpack would probably be very uncomfortable with a 40 lb battery in it. It's probably also bad for my back for long periods. And it would probably get pretty hot. It might be the only option though if it doesn't fit in the main triangle. Only way a frame backpack might be viable is if I can somehow let the backpack hang low, so that the rear rack can support some of the weight of the backpack. I have made huge grocery runs (50 + lbs) on bikes and being able to rest on the rear rack makes a huge difference. Center of gravity would be pretty high, and it would be making bike further off balance by putting more weight at the rear.

 

[dogman dan]

Sounds like a huge pack. Consider two sections, and two chargers. One section, would be what fits in the triangle.

Or get a bulk charger that can be adjusted to 12s use with the bms. I found my 5 amps 36v charger could be turned up to that high a voltage, but then you turn the amps down enough to not overheat it, keep it at 250w or so.

 

[dnmun]

Frame backpack would probably be very uncomfortable with a 40 lb battery in it. It's probably also bad for my back for long periods. And it would probably get pretty hot. It might be the only option though if it doesn't fit in the main triangle. Only way a frame backpack might be viable is if I can somehow let the backpack hang low, so that the rear rack can support some of the weight of the backpack. I have made huge grocery runs (50 + lbs) on bikes and being able to rest on the rear rack makes a huge difference. Center of gravity would be pretty high, and it would be making bike further off balance by putting more weight at the rear.

yep, the point is that these huge cells are very hard to use on an ebike. even if you can split it and hang it on each side in back in panniers it is a huge load imo.

 

[docnjoj]

I charged AMP20 A123 cells for 2 years with the Thunder 1220 using the 20 amp cut of but never actually experimented with batteries that were larger Amp/hours. You can cut the time to not shut off, so it may be possible to charge a bigger pack. I have nothing to experiment with as I am now trying (very carefully) 16 a/h Lipo. You could certainly see if your charger will exceed 20 a/h. It might?
otherDoc

 

[baltimorebiker]

I have decided that the best course of action is to completely remove the pedal drive train. This includes removing front and rear derailleur, shifters, and all 3 chain rings. This saves a bit of weight and gives the bike a clean look like a fixie. Most importantly, removing the chainrings makes it easy to drop the huge EV battery into the bottom of the main triangle. It is hard to pedal, but I took out the pedal drive train, so it doesn't matter. I can still "clown pedal" so I don't look too illegal. I left pedals and rear cassette so I can just say its internally geared lol.

I figured with a 2000 whr battery, I wouldn't need to pedal at all.

Pics to come when done

 

[baltimorebiker]

Here are some pics of what I went with:

Complete bike, battery was stuffed into main triangle:

https://www.dropbox.com/s/p5k56bipcvrfjx4/2015-06-06%2000.01.59.jpg?dl=0

Charging set up, using thunder charger, 12 jst balancer wired to stock wire harness:

https://www.dropbox.com/s/j6zot3wu782veb6/2015-06-07%2022.10.13.jpg?dl=0

Over all, bike handles great. You barely notice the 45 lb battery, because its nearly at dead center of the bike. It surprisingly doesn't impede pedaling that much, but I took out pedal drive train so it doesn't matter. I typically go full throttle all the time which draws about 1600w, going about 30-35 mph. I use about 33 whr/mile because I can't pedal and go full throttle all the time. Have yet to test the full capacity of the 2000 whr battery. The most I have used is 750 whrs, but I will try to do a full discharge test eventually. Biggest problem is that the frame does not fit me. Its a 22 in frame and I am only 5 ft 9 in. This makes it a little uncomfortable to ride, and very uncomfortable at stop lights because I can't reach both feet to the ground. Might consider going to a smaller frame, but I don't know if I can find a bike, and I don't think the huge battery will fit in the triangle.

 

[wompus]

That battery doesn't look as huge as I imagined from your description.

Not sure i'd like the pedals having no resistance whatsoever. Those brakes also seem like they might be a bit on the sketchy side for 30-35?

Looks like you are local-ish to me. I'm pretty new to the E-bike community but have been building and fabicating stuff for a while. if you need any help designing/building a battery box, let me know I might be able to help.

Here's my first build. You won't find me in the city, but more likely riding around Harford county.

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