eBay battery's

[Dano]

Hello new to this site, been looking in to doing a bike conversion for a long time now. I work with electric motors so pritty clued up in that area. Only thing that I get lost on is battery's. Been looking through eBay and would really like 48v 20ah battery. This is only for a hobbie not to go to work or anything like that.

http://pages.ebay.com/link/?nav=item.view&alt=web&id=252009862360&globalID=EBAY-GB

This is first battery.

http://pages.ebay.com/link/?nav=item.view&alt=web&id=371360240453&globalID=EBAY-GB

Here is second.

Any help input would be good thank you. I've brought nothing yet so just looking for some feed back.

 

[Deleted member 4366]

Where will you put it? Make a cardboard box the same size to see where it will go. 7 to 8 kg is massive. Not many racks will cope with that. Also, that weight on the back of your bike with a rear motor will make it unrideable.

 

[Dano]

Yeah I'm yet to mesaure it up. If not it be going in a back pack. At least it couldn't be stolen that way. Was more concerned if they are any good? Thanks.

 

[Deleted member 4366]

Get a backpack. Put 8 litres of water in it. See how far you can ride.

 

[Dano]

Good point. I'll have a measure up see where I can fit things.

 

[Alan Quay]

I agree with D8veh, those are heavy.

What are you trying to accomplish exactly? Do you need lots of power, lots of range, both?

How much do you weigh, how much do you want to pedal?

What terrain?

 

[Dano]

I don't need lots of power but it's good to have. But I'd like 20-30 miles with as little effort as possible. 90kgs at a guess. Mainly road I got quite an exspensive car to run about 25p per mile so if I do enough miles on it should pay for its self. Thanks

 

[Alan Quay]

Sorry, forgot to ask how fast you want to go....

 

[Dano]

Long as I can sit at around 15mph be okay. Was aiming for the 1kw hub.

 

[Alan Quay]

Most of those eBay 1kw hub motors are direct drive. Fast, but with little torque.

From your description you need high torque.

I suggest 36v/15ah (540wh) battery, 15-20a controller, geared hub motor (Bafang BPM or CST are good examples).

You don't need a 48v x 20ah (960wh) monster battery for this.

 

[Deleted member 4366]

A 48v rear Q128 motor wheel with a 48v 11.6 Ah 09 bottle battery with the included 20A controller kit will give you everything you want. It will have better hill-climbing than a 1000w DD motor, but less speed (19mph). Your bike will still be light enough to handle and pedal like a bicycle.

 

[Dano]

Okay yeah I understand I'll have a look into it thanks guys.

 

[Nealh]

36v/15ah battery 350w BPM @20A does up to 55 miles @ 16 -21 mph.

 

[Dano]

Yeah I'd like more power. Had a measure up and that battery is huge. Not even sure if I'd fit the bottle type in. Have to buy one and see how it goes.

 

[selrahc1992]

Most of those eBay 1kw hub motors are direct drive. Fast, but with little torque.

From your description you need high torque.

I suggest 36v/15ah (540wh) battery, 15-20a controller, geared hub motor (Bafang BPM or CST are good examples).

You don't need a 48v x 20ah (960wh) monster battery for this.

as an aside, does anyone know how much torque a direct drive motor like that produces? if a kalkhoff impulse 2 produces 70nm, a BPM something like 60 with 36V/20A, a TCM something like 50 (these are just my half-baked guesses, feel free to correct), where would a direct drive motor be? many thanks

 

[Deleted member 4366]

It depends how many amps you give it. At 48v 25A, you'd get about 40 NM of useable torque at the back wheel, maybe a little more if you let it start to overheat. A 500wBPM under the same conditions would give about 50NM.

It's difficult to compare that with a crank-drive motor because it's unclear where the torque is measured. It should be at he crank, but Bosch use a small sprocket now. How can it have a similar torque to one with a large sprocket? Normally, with a crank-drive, the torque would be less at the back wheel, depending on the gearing. Say you had a 44T chainwheel and a 34T bottom gear, 50Nm at the crank becomes 38.6Nm at the back wheel. In top gear, you only get 12.5Nm.

 

[Dano]

Surely a geared motor would use more power making it not go as far?

 

[selrahc1992]

It depends how many amps you give it. At 48v 25A, you'd get about 40 NM of useable torque at the back wheel, maybe a little more if you let it start to overheat. A 500wBPM under the same conditions would give about 50NM.

It's difficult to compare that with a crank-drive motor because it's unclear where the torque is measured. It should be at he crank, but Bosch use a small sprocket now. How can it have a similar torque to one with a large sprocket? Normally, with a crank-drive, the torque would be less at the back wheel, depending on the gearing. Say you had a 44T chainwheel and a 34T bottom gear, 50Nm at the crank becomes 38.6Nm at the back wheel. In top gear, you only get 12.5Nm.

many thanks, I guess that means if one stuck an s12sh (45A) one could get enough torque from it, though one would get more from a bpm, so no point really, wont wade back into any hub versus crank dichotomy, but it may explain (hub giving similar torque across wider range in real life scenario) why I get up most hills faster on a hub drive with less amps

 

[stevenatleven]

this is interesting because a friend just bought one of these 20 Ah/48v batteries and has just built a bike up with a 2 speed Xiongda motor.
On a out first outing yeaterday it seemed to go okay but locating the battery in the frame will take a bit of work.

 

[Fordulike]

Thank god the Chinese came up with this design of battery



They are light enough to carry a spare one in a back pack