BMS & Dumb Charger or no BMS & Balance Charger?

[SteveAndBelle]

Hi all.

Just about to build my first LiPO pack but really want to keep the on-bike size down. It'll be a 14S 5AH pack built from inexpensive 25C RC Zippy packs powering a very bog standard 48V 750W BBS02 for easy short commuting to & from work so wont be under much load. The main 25A fuse is still intact so I guess that proves current draw isn't really an issue. Using an in-pack BMS and Balance Charger combo would obviously be the ultimate way to go as you'd have full control over charging and discharging but of course that results in lots of expensive redundancy in that the BMS can do exactly what a balance charger can do during a charge cycle. The way I see it I should be able to get away with using one or the other so what are peoples thoughts on the following scenarios:

1. Build a BMS into the battery pack and just use a 'dumb' 48V Charger
2. No BMS but use a nice 14S Balance Charger

I assume No.1 would be the pick as the BMS will monitor both charge & discharge but as I already know I wont be pushing the pack very hard plus I plan to include a system voltage monitor I'm wondering if No.2 would also be a viable option? A BMS is far cheaper than a fully blown 14S balance charger so from a cost perspective the BMS & 'dumb' charger would be the obvious choice but I really do want to keep the pack as minimal as possible so I'm swaying towards running without a BMS.

Any tips or suggestions would be appreciated, thanks.

 

[Ykick]

My 1st suggestion would be to avoid Zippy brand packs. Turnigy has always done me right while Zippy have always failed in some way shape or form.

I would suggest BMS w/dumb charger along with a small cheap RC charger more for troubleshooting, minor balancing. I use my RC charger to bring up a single cell through the balance leads for a different way of balancing. Usually much faster than the regular balance functions.

 

[SteveAndBelle]

My 1st suggestion would be to avoid Zippy brand packs. Turnigy has always done me right while Zippy have always failed in some way shape or form.

Cool, thanks for the advice but unfortunately I already have the Zippy packs Cost next to nothing at $15 each so I'm not too worried if they fail. Sure, it'll be disappointing but not the end of the world.

Sounds like an in-pack/on-bike BMS is the way to go. Bugger. Back to the drawing board!

 

[motomech]

There are lot's of bulk charging options for 12S, but not so many for 14S.

If I were you, I would just buy this because in the long run, you are likely to spend as much fooling around with lesser options that won't work well in the long run.
That's actually a good price for that charger.

http://www.ebay.com/itm/like/301809862602?ul_noapp=true&chn=ps&lpid=82
What's you plan for a LVC?
Does your controller have one and if so, at what Voltage?
I.M.O., a hard and fast LVC is a neccessity for Lipo.

 

[SteveAndBelle]

There are lot's of bulk charging options for 12S, but not so many for 14S.

If I were you, I would just buy this because in the long run, you are likely to spend as much fooling around with lesser options that won't work well in the long run.
That's actually a good price for that charger.

http://www.ebay.com/itm/like/301809862602?ul_noapp=true&chn=ps&lpid=82
What's you plan for a LVC?
Does your controller have one and if so, at what Voltage?
I.M.O., a hard and fast LVC is a neccessity for Lipo.

Exactly the charger I have in my eBay Watch List. I'll probably get one in a week or two. Actually yes! I forgot that the BBS02 has a built-in LVC which is set to 41V (I think) but I'll be programming to 43V as per some others running a similar setup. I suppose the 14S charger and the LVC would free me from having to include a BMS, yay! Cheers Mototech

 

[motomech]

43V is rather low for 14S. It will yield a cell V of 3.10 V.
Healthy Lipo can be brought back with care, but it is still risky to go that low. 13S would yield a cell V of 3.30, better, but still not quite right.
The LVC for my 12S, for example, is 3.65 V, perfect as this is the point where the cells start to stray.
You will need to use an Alarm and not let your packs fall as low as 43 V.
Still, it's better than nothing.
One last thing, I ran/run 5 Ah capacity for a long time and I often found it very useful to carry an extra 5 Ah pack. At least till you are sure of the range you will have and also on longer rides or rides where I'm just exploring.
Once the first pack was depleted, I would swap them and turn around for home.

 

[dogman dan]

? no bulk chargers for 14s? tons of them out there. But more of them for 13s.

Whats rare is balance chargers for 14s.

Bulk charger and bms would be easiest. Don't do what I do, I just bulk charge no bms. Or rather, I'm the bms. I have many ways to balance the pack when needed.

 

[Wheazel]

I have used both methods and what I can draw from my experience is that I really value userfriendlyness and ease of use in the long run.
I want it to be fast and easy to charge my batteries. I have had hobby lipo cells dying after a while but I am yet to experience this with 18650 cells.
Have charged ebikepacks built from 12s 16ah out of 8ah zippys with a hyperion 1420 charger. (can do 14s as the name hints)
Connecting the balanceleads and selecting the right program gets old quick, plus it increases the risk of error.

So for me the obvious choice when building batteries for ebikes nowadays is some 18650cell suitable for my application and a bms, and a silent bulkcharger.
I am currently using a meanwell hlg320 (adjustable voltage and current) for all my 12s in house charging. Silent and very plug and play.
Only the cargobike is charged with a fanequipped eaton powerupply, but that one is always charged in a garage or outside as the battery is stationary in the bike and the bms is integrated with the controller.

My vote is on quality cells + bms. (not counting rc lipo to this)
If I would be forced to go the rc charger route again I would spend some time on making the connection for the charging a "one connector for everything" to further eliminate the risk of wrong connections and also make it more trivial to use. I would have to live with the hyperions fan noise and not having a low voltage cutoff.

 

[SteveAndBelle]

Great info guys. I think I've made up my mind.... I'll invest in a decent balance charger to charge & care for the entire pack in one go as that will assist both during initial pack/bike setup and also if I need to troubleshoot any cell/pack problems later on. The LCD on the charger (versus absolutely nothing on a BMS) will be a big bonus so I think I'll go down the Hyperion or Thunder Power 14S Balance Charger route. This means I can leave the pack BMS free but just keep an eye on overall voltage via the throttle volts display I'm yet to get plus setup the BBS02s LVC appropriately to avoid a catastrophic failure. Current draw isn't so much a problem as I'll have 125A on tap so I wont be putting too much strain on the Zippys.

Excellent! I'll be charging the bike outside but under cover and may even look into building a solar charging station so fan noise etc. isn't going to be a problem. Fingers crossed these Zippys are all OK and keep me going for a while without any big problems. Still, if not then it's not the end of the world as I purposely wanted to start at the lowest common denominator and work up from there if required.

Thanks for the help/advice. This eBike thing is great fun and forums like this just add to the enjoyment of the build. I'll post some pics in coming weeks once I get it all sorted out.

 

[motomech]

What Hyperion??
You mean the defective 1420i?
That model was pulled when most of them started blowing smoke.
I know I lost $150 on that POS.

The Thunder should be a good rig.
I had a 1220 that gave good service for 4 years and when it did blow, it was because the Power supply failed.

You do understand you will need a power supply for the Thunder?
And a serious one at that, min. of 400 Watts!
Probably the least expensive way to do that is to buy two used server power supplies on Ebay and join them is series w/ the chasis isolation mod.

The problem with 13S and 14S is not finding a bulk charger per se, but finding a way the balance the cells(MY Mean Well LED PS will adjust the top charge to 59.2 V). The Battery Medics I use only handle up to 6 cells, although I suppose two of them could be spliced onto a single 8 pin JST extension. But buying 4 BM's is $100.That's why 12S is so much easier.
Perhaps Dogman will chime in on how to inexpensively balance 14S

 

[SteveAndBelle]

What Hyperion??
You mean the defective 1420i?
That model was pulled when most of them started blowing smoke.
I know I lost $150 on that POS.

The Thunder should be a good rig.
I had a 1220 that gave good service for 4 years and when it did blow, it was because the Power supply failed.

You do understand you will need a power supply for the Thunder?
And a serious one at that, min. of 400 Watts!

Yeah, I can't really find any Hyperions (& now I know why!) so the Thunder Power is really the only choice anyway. I have a 12V 60A (720W) Power Supply at home so that should do the trick. I wont need to charge at a high rate as I'll have all night and would prefer to keep the batteries happy with a slower, low-current charge plus I'd like to look into a solar storage charging rig in the longer term so wont need the Power Supply anyway as the Thunder power will connect direct to the storage battery (whatever that will be). Good points though, thanks!

 

[Ykick]

The easiest and simplest way to balance multiple cells of any number is to merely charge low cells through the balance lead/connector. A simple pin-dongle and 1S charger is all you need.

Don’t even need high amps since you shouldn’t push more than 2-4A through majority balance wires.

That’s why I suggested bulk charger with a BMS (for charge/discharge protection) plus a cheap small RC Charger for balancing if/when needed.

Of course, when balancing is frequently required there’s probably something wrong with a cell/group? But a small RC Charger can help dig deep enough to identify potentially duff cells.

Once you become used to the concept of charging single cells through balance wires you may discover more options such as scavenging cellphone BMS and using USB port for cheap, easy, protected 1S charger…. I used the later with one of my USB device power bricks for touching up a low cell group without any AC grid power available. That was cool…