BMS for lots of hoverboard packs in parallel?

Batteries, Chargers, and Battery Management Systems.
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BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 02 2017 1:14pm

Is there a bms that will handle lots of 36v hoverboard battery packs? I know usually bms's only handle a few volts per channel. I want to get like 20 hoverboard packs and parallel them and throw them into my e-bike trailer.

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Re: BMS for lots of hoverboard packs in parallel?

Post by Telemachus » Oct 02 2017 6:23pm

The hoverboard Packs will come with their own BMS. You can parallel them to get power out of them, but it might be better to charge them individually.

Alternatively, you could just use 1 bms (from anyone of the packs) and run hard wires to tie them all together as 1 "battery."

Most hoverboard batteries are going to be 10s2P, or about 4400mah at 36V nominal, 42V fully charged.

If you were to cut the BMS off of the other backs, and tie the wires altogether to a single BMS, as well as tie the power and grounds together, you would essentially have a 36V, 10S2(n)P battery n(4400mah) battery, where n is the number of packs you tie together.

Assuming you can find a 10S charger that will charge at 3-4 amps, it would take about an hour per pack to charge.

So if you string 5 together in parallel, and rely on a single BMS, you would have a 22 amp hour battery, and it would take somewhere around 5-6 hours to charge at 3-4 amps.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 02 2017 9:47pm

I'm not so sure I want to go cutting them open if I can avoid it.
My official plan is to buy 20 of them for a 3168W battery + the 1kw one I already have and then throw 2 100w panels on top of the trailer with a charge controller. With any luck that will allow me to have an official car replacement.
I suppose you have a point though, I don't know how the bms's do their balancing but it would be reasonable to assume you can't use a bms to handle other bms's.
You seem to be implying that I can parallel them up front without fear though?

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Re: BMS for lots of hoverboard packs in parallel?

Post by flat tire » Oct 02 2017 9:55pm

That sounds like a bad and poorly though out idea. Just buy brand name cells and enjoy good times as opposed to using crappy batteries with crappy (and dangerous) bms.

“The bitterness of poor quality remains long after the sweetness of low price is forgotten”

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 02 2017 10:20pm

As far as I understand the whole exploding hoverboard battery thing was just a misrepresentation by the media because of some people with knock of packs.
I'm certainly not going to spend over 4 times the price on an equivalent pack using diy cells.
The packs I'm getting use LG FK-16758 cells from a US seller.

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Re: BMS for lots of hoverboard packs in parallel?

Post by flat tire » Oct 03 2017 1:34am

Ha wow you don't even know what batteries it's using. The part number you mention is for the whole pack. The cells are claimed to be LG MF1. Who knows if they're counterfeit? Ebay guarantees are not worth much there. The current capacity of those cells isn't too good either but I guess it's not too bad if you're putting so many together. Anyway, your math is off because the cost of those packs is similar ($316/kWh) to 25R and 30Q ($324 - $360 / kWh). And those prices are from a US vender. If you're gonna drop $1K it's probably best not to drop it on crap packs like these. The worst part is the BMS. You can be 100% assured it is the cheapest possible part for the job and in a configuration like yours will only make the battery vastly less reliable.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 03 2017 9:19am

Alright, you've convinced me. What BMS do you recommend? I'm thinking about getting a batch of 200 Sanyo NCR18650GA cells.

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Re: BMS for lots of hoverboard packs in parallel?

Post by flat tire » Oct 03 2017 12:47pm

Yeah that's a way better choice. What voltage are you running and how much power? Only 36V? Just make sure the cells are way below their maximum current rating at peak power for best results. If you ran 10S for ~36v nominal, you would have 20P and about 200 amps nominal discharge from 200 cells. Just make sure your current draw is well below that to keep the cells happy.

I dont use a BMS myself I don't have a very good opinion of them unless you spend a lot of $$$$. You're much better off getting a 10S RC Charger for balance. I use a iCharger 3010b. That baby will balance or bulk charge 10S at 500W on 12v and 1000W on 24v+. You won't actually need to balance your pack except very occasionally if you're careful not to fully charge it (I like 4.12 per cell) and never fully discharge (try keeping at least 20-25% capacity in the cells, don't ever run them flat.) If you do those things and use new cells the pack should stay in excellent balance.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 03 2017 3:10pm

My goal is to use 2 100W solar panels over the trailer to charge the batteries. You think a solar charge controller should be enough?
I'm looking at this one https://genasun.com/all-products/solar- ... ontroller/
It's a 48v charge controller but it says it has a float/CV voltage of 56.8V which I assume means that's the actual charge voltage which would be about 80% of a 52v battery bank charge if I'm not mistaken.
What do you think?

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Re: BMS for lots of hoverboard packs in parallel?

Post by flat tire » Oct 03 2017 8:42pm

That means the termination voltage is 56.8v. That works out to 4.05v / cell with a 14s config. That's fine, cuz keep in mind charging to full 4.2v / cell will reduce longevity, increase risk of a "bad event" in the case of imbalanced cells, and give you barely any more range than 4.05. It looks like they'll configure that charger however you want though. Also charging from 2 100w (they won't put out that much, btw) solar panels will be terrifically slow even if you have full sun in a clear sky at high noon--meaning you will gain barely any range for the effort and cost expended. It would make way more sense to put the money toward a plugin charger unless you're gonna ride this thing out where you can't plug it in. Keep in mind with a plugin charger often you can charge for free (or a cup of coffee if it's starbucks or whatever) and the cost is extremely low even if you charge off your own power.

How many cells do you intend to run in series and what is the motor?

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 03 2017 9:37pm

I want to be able to ride from CT to Florida, or maybe even to Cali on a single charge, at least that's the end goal. I know it's been done before.
Although that was with a 250w motor.

I'm using an e-bike simulator from here http://www.ebikes.ca/tools/simulator.html? after playing around with it I learned that I should be able to get several hundred miles out of a single charge if I keep the speed at or under 20mph using such a pack as I have planned.

I don't really know how the 200w panel will play in practically but the person who went from LA to DC on a single charge said the battery never went below 70% or something.
I'm going to have to buy the panels first to see how they extend my range and then add batteries after, else I end up with more then I need if there is such a thing.

I want to use pedal assist but I think it's garbage, dangerously poor response. I'd probably go with a torque sensor or just throttle the current so I'm forced to pedal.

I'm leaning toward a 52v pack since my lunacycle one that I currently have is 52v. Which would mean 14s.
The motor is cyclone 3000.

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Re: BMS for lots of hoverboard packs in parallel?

Post by amberwolf » Oct 03 2017 10:20pm

Just a bit of a math check:

There's about 2500Wh in 200 of those cells, assuming you get the full 3.5Ah out of each one at a nominal voltage of 3.7v. (meaning, fully charging them to 4.2v and running them down to manufacturer specified LVC)

A quick google indicates it's about 1200 miles from Connecticut to Florida (depending on origin and destination points, as well as route).

So you'd have to have an efficiency of about 2Wh/mile to do that in a single charge. If you're only using it for just assist at certain portions of a ride, and otherwise are providing all the motive power yourself by pedalling, that might be possible. It'd be much more typical to get 10Wh/mile+, even just riding on the flats, presuming a typical speed something between 15-20MPH and a regular bicycle.

Otherwise, you'd need to stop and recharge periodically, or you'd have to carry some other source of energy (like solar or generator on a trailer). (by definition all of these make it no longer "on a single charge")



CT to CA googles at about 3000 miles, so you'd have to have an efficiency of about 0.83Wh/mile to do it in one charge. Given all the mountains along the way, I think that's extremely unlikely to be possible.


Could you post the URL you get when you setup the simulator? (it contains everything needed for someone else to see the same simulation you do). It might help show how you're seeing the high range you get out of it.

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Re: BMS for lots of hoverboard packs in parallel?

Post by flat tire » Oct 03 2017 10:27pm

amberwolf, I think he intends to charge the bike from solar while he rides.

OK, long distance is a cool goal.

You will probably get lower power consumption with a properly specced direct drive hub motor than a Cyclone 3k. That motor runs thru a planetary reduction + your bike's drivetrain, so even though those losses will not be very high at 20mph, you are riding a long ways so it adds up.

You will need really big solar panels to actually get 200w. At least 1 square meter in theory, in practice probably a lot more in practice if you want to sustain 200w. Also you will need optimized aero and motor / battery if you want to pull 200w at 20mph.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 03 2017 10:37pm

The bike needs to double as my winter commute bike in the new england winter so I bought a mid drive and put it on a mountain bike. Not the most optimal long distance bike for sure, but I figure in a worst case scenario I load up the trailer with as many batteries as I need. If I get anywhere near the 70% maintained battery as that lady that went from LA to DC did I should be okay.

I'm currently looking at these batteries http://www.ebay.com/itm/201916138726
At first I thought it was a scam but there are quite a few people on youtube that have done thorough tests on these packs and claim they are legit. The price is difficult to resist.

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Re: BMS for lots of hoverboard packs in parallel?

Post by Telemachus » Oct 04 2017 11:22am

So now we are back to the hoverboard batteries. Lol.

There is no doubt that those cells are well price, and there are reports of many people enjoying them. Just keep in mind that you are going to have to separate the cells and either solder on to the nickel tabs, or remove the tabs entirely to spot weld the new ones on.

Alternatively, if you have a trailer, you could just load up on several of these batteries and parallel a few of them, at a time. Change your batteries every several hours.

When you stop for the night, charge them all up. Hoverboard chargers and power strips or extremely cheap.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 04 2017 12:00pm

Why not just parallel them all into a single battery and throw them in a trailer? Why only a few?

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Re: BMS for lots of hoverboard packs in parallel?

Post by flat tire » Oct 04 2017 1:17pm

coinmaster wrote:Why not just parallel them all into a single battery and throw them in a trailer? Why only a few?
Correct.

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Re: BMS for lots of hoverboard packs in parallel?

Post by Telemachus » Oct 04 2017 3:26pm

I guess I was assuming the trailer was for storage, and the batteries were physically on the bike. If you are okay running a tether cord to the trailer, then by all means parallel all of them. We have returned full circle to your idea in the beginning. :-)

As far is charging them, by far the easiest way to charge them would be to get several hoverboard chargers, and plug them into a power strip.

Unless of course if we go back to what I had stated previously. It would not be too difficult at all the bypass the other bms and rely on a single BMS to charge all of them.

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Re: BMS for lots of hoverboard packs in parallel?

Post by docw009 » Oct 06 2017 1:43pm

Just a small fry here. I put two of those hoverboard batteries in parallel and can get 8AH out of the pair. I charge them in parallel too, which saves some fuss and allows for equal voltages. I use them as singles to run my low power ebikes. They have a 20A limit so I run two in parallel on my bigger motor. Yes, there's not a lot of AH, but I don't use a lot at one time.

I also bought a hoverboard charger. It's 42.3 volts with no adjustments possible. My ebike charger is 42.0 volts. A battery that's indicating full charge and zero current on the latter charger will happily accept a little more from the former. I'm not sure what that means. I expected the BMS to shut off. Maybe my meter is off. Maybe it means hover board chargers might not be trust worthy.

One BMS with 20 batteries likely has more failure points from the wiring shutting down the whole unit. A battery with an individual BMS could shut down though and the array still works. Might be worth it for safety to put in shottky diodes. The OP will have to balance time vs charge current.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 07 2017 4:30pm

At minimal I'm going to be paralleling 20 of those batteries. Should be about 87AH.
Given their price, the limiting factor for me is their weight or I'd get like 10 KW worth.
87AH should be around a 40-50 LB trailer, sadly a 10kw pack would be about 140 LB, electric or not that can't be good.

I bought one of these for charging https://lunacycle.com/luna-charger-36v- ... e-charger/
Batteries aren't my area of expertise, I don't know much about their failure modes.
I'm considering putting a fuse between each pack and the bus bar, what benefit would the diode be over a fuse?

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Re: BMS for lots of hoverboard packs in parallel?

Post by docw009 » Oct 07 2017 9:30pm

Suppose one of your many batteries in parallel develops some kind of fault and it drops down to 33 volts, and because it's a fault, the onboard BMS is not doing anything. All the other batteries at 36volts could start flowing current into it. A diode pointing toward the load will prevent currrent backflow when this happens.

So where's the diodes in my parallel arrangement of two batteries? Not using one yet. Maybe I ought to buy some. Tradeoff with a diode is that it would prevent charging of the battery array thru the output plug. These batteries only have one plug.

Do you have to hook up all 20 at once? Four arrays of 5 packs each would be 20AH. You ought to get 40 miles in three hours from 20 AH plodding along at bike speeds. Then swap to the next set of batteries,

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 07 2017 11:34pm

Preventing charging is kind of a pain.
I could separate the batteries into smaller groups but they are going to be connected to a bus bar anyway, I could disconnect any one of them any time I want.
Last edited by coinmaster on Oct 07 2017 11:37pm, edited 1 time in total.

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Re: BMS for lots of hoverboard packs in parallel?

Post by Telemachus » Oct 07 2017 11:36pm

I don't understand paralleling more than just a few, either. That way you'll be able to know if/when one of them fails.

Take some labels with you to label them if needed.

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Re: BMS for lots of hoverboard packs in parallel?

Post by coinmaster » Oct 07 2017 11:40pm

I ordered these for the connection http://www.ebay.com/itm/172796933289
I'll be able to connect/disconnect whatever pack I want at any time. Each pack should be capable of a max of 10A, so if I use a fuse of a bit less than that it should trip the fuse if one of them fails.

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Re: BMS for lots of hoverboard packs in parallel?

Post by docw009 » Oct 08 2017 11:06am

FYI, these packs should put out 20A on a consistent basis. Mine do.

I'm curious. What's your model for solar based riding?

I admit that I'm completely clueless on solar. Here's my first shot at it. On amazon, a $200 panel seems to be rated for 100W, and is bigger than you want to carry on a trailer, but let's say you do that . Maybe you can rig a a 42V charger with 80% efficiency. That will be 2A. One of these 4AH packs will take 2 hours to charge. I'll guess you have six hours during the summer where there's enough light hitting the top of the trailer. You can charge 3, maybe 4 batteries a day. On my bike, I could get 20 miles out of one battery, but only for slow speed pedal assist riding ( I think PAS works fine). I would think your solar range is under 50 miles a day if you're on throttle only. Now if you stop at noon, take lunch, maybe a nap, now you can fold out six panels and do better.

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