Help with Battery specs please

Hey guys, hoping someone can help as I am new to all this and a little confused.

Looking for a suitable battery after buying a kit that has the following specs:

High power brushless front hub motor that allows up to 25 MPH top speed.
* 48V Brushless Front Hub Motor can reach up to 900W.
* Prewired Speed Controller Unit with 26 Amp current limit.
* This Controller can be powered by any 48v voltage battery pack with a min. 30A peak discharging drain current. Other control voltages suitable.

I want to go with a 48v 15ah battery as I have limited space to work with (250mm x 160mm x 80mm)
Most 15ah Im looking at (cheaper end) seem to have a 15a or 20a BMS built in.
What would happen if I used a battery like above with the kit controller that has a higher rating?

Thanks !

Puffy said:

Hey guys, hoping someone can help as I am new to all this and a little confused.

Looking for a suitable battery after buying a kit that has the following specs:

High power brushless front hub motor that allows up to 25 MPH top speed.
* 48V Brushless Front Hub Motor can reach up to 900W.
* Prewired Speed Controller Unit with 26 Amp current limit.
* This Controller can be powered by any 48v voltage battery pack with a min. 30A peak discharging drain current. Other control voltages suitable.

I want to go with a 48v 15ah battery as I have limited space to work with (250mm x 160mm x 80mm)
Most 15ah Im looking at (cheaper end) seem to have a 15a or 20a BMS built in.
What would happen if I used a battery like above with the kit controller that has a higher rating?

Thanks !

Click to expand...

When you open the throttle too much the battery BMS will likely cut-off power to the system.

That said, many BMS will be rated “continuous power” and they may very well handle peaks approaching double the continuous rated power.

15-20A continuous rated BMS might work, but might not? 30A continuous rated BMS would most certainly work fine for that kit.

Thank you for you help...... its what I feared would happen.
So the BMS will likely cut all power if its exceeded and not just limit it?

Puffy said:

Thank you for you help...... its what I feared would happen.
So the BMS will likely cut all power if its exceeded and not just limit it?

Click to expand...

Yes, cuts all power when over current discharge occurs. BMS generally reset when the load is removed momentarily but that's no way to enjoy an eBike.

Trying to get across a busy intersection and lose power, ugh...

It's impossible to say if a 15Ah battery that has a 20a bms will be ok for you or not (approx 26A max), but chances are, you'll likely be ok, if you are using the power moderately, most of the time.

Cheap suppliers (expensive 1s can do this too) will generally tend to state specs that are optimistic and at the upper end (or above) what the battery can reasonably deliver. Not all specs are created equally

Generally a bms will have a continous rating and have a trip limit that is higher, maybe much higher than the contionuous rating, but who knows how it will perform in advance, or how good the bms is, or the suze/rating of the cables used to link it all together. The cheapest packs will scrimp on EVERYTHING and if you get under that (not) plush exterior will likely look like it was constructed by a 5 year old in art class
Frankly, if you have some idea about electrics and are handy, by all means get a really cheap battery, BUT, be prepared to find out, it isn't great and may need a BMS swap, or possibly more down the road. Also be prepared that it may take a looong time to arrive, as you can't get a heavy battery shipped half way around the world for peanuts. Also, be prepared to find out in a few months or less that the battery is unusable. If you couldn't deal with all that, better to get a battery from a supplier with a good reputation for their product and service.
Don't think that the only difference between that super cheap battery on Ebay and something significantly more expensive from a good supplier/manufacturer is their profit margin (but granted, the professional operation is unlikely to be willing to supply/support for the scraps that a low level back street operation would be willing to accept). The cells used are important, but that isn't the whole story. The way it has been constructed, the bms used, the way the cables are routed, the additional safety features that might be used, are equally as important, if not moreso.
A pack with good cells, can still fail prematurely, or even be dangerous. So don't think that a certain wonder cell is the whole story, it's not.

Buy a couple of 10C 6s rc lipo packs and don't worry about them cutting off on you. Maybe 2 16ah packs in series. 10C ones would be rated for 160A.

You need to look for a battery that comes with a 30 amps bms. (amp limit cutoff) In 15 ah size, it shouldn't take that great cells to provide that. It can be 20 amps continuous, because 25 mph will take you about 18 amps.

The ones you have been looking at suck, really bad, which is why a 15 ah battery can't handle more than a 20 amps bms.

Thanks guys for the great advice.... Didn't know RC batteries were an option.
If I wired two of these in series 22.2v each = 44.4v will that be enough for the 48v kit?

Seems like a viable option, is there anything to be mindful of when using these batteries. Guess I'll need a suitable charger but do I need to wire a bms / balance... anything like that?


http://www.hobbyking.com/hobbyking/store/__74096__MultiStar_High_Capacity_6S_12000mAh_Multi_Rotor_Lipo_Pack.html

Minimum Capacity: 12000mAh
Configuration: 6S1P / 22.2V / 6Cell
Constant Discharge: 10C
Peak Discharge (10sec): 20C
Pack Weight: 1525g
Pack Size: 180 x 70 x 55mm
Charge Plug: JST-XH
Discharge Plug: XT90

Yes, those will be perfect for 48V controllers with a typical 42V LVC.

Wesnewell, could you recommend a good charger for a pair of 12000mah.

Cheers !

There are many ways to charge a 12s pack. Any 12s rc charger will work to charge the whole pack together. You could parallel charge them as 6s packs with any 6s charger. You could bulk charge them as a 12s pack and use 2 6s battery medics. Just depends on how you want to do it and how much you want to spend on charging equipment. And how fast you want to charge them.You could even use a bms and bulk charger. The options are almost limitless. This charger will take ~4 hours for a full charge at 300W.
http://www.hobbypartz.com/75p-1220-charger.html?gclid=CNa3z9_N57ICFayPPAod10MAPw
Or you could bulk charge in ~1 hour with an emc-1200 bulk charger using a couple of battery medics.
http://ecitypower.com/index.php/joomla/contentall-comcontent-views

If you burn your house down having been told to use RC batteries, you won't be the first to come here and do just that. Nearly all the fires are caused by using RC batteries. This is why at RC meets they are charged outside in flame proof bags.

It's not the battery at fault in most cases. It's simply not been used safely. You seem to recognise the need for a bms and so I don't need to say much here. Just that doing it properly with a 30a bms and simple bulk charge is both the cheapest and best option. About $100 delivered from bmsbattery or the likes. The RC bargain cells are the 5Ah 4s hardcase type which will likely save you enough on batteries to buy the charging kit. About $25 a brick iirc.

A 15ah commercial pack with 20a bms may only contain 1.5C cells. Making 22.5A the max draw and limiting lifespan at that.

I have read up on the dangers... we have an empty silo on our property where I will charge them so the house will be safe :wink:

Plenty of fires these days, from other types of bike batteries.

Use some common sense where you put the bike to charge it, or where you put the battery to charge and store it.

On top of the pile of old newspapers, up against the curtains of the babies room, aint it. Lots of ways to make the top of a wood table fire resistant. piece of large tile, etc.