Is it feasible to build a battery?

[John F]

A new 15 amp battery will cost me over £300. Is it an option for a guy like me, who likes building stuff and tinkering, to build my own?

 

[Arbol]

I am thinking about doing the same.

Apart from what the experts may tell you, what I have found out so far is there are two levels of complexity:

1. Soldering: in this case, you can solder "bricks" in series to build your own battery (plus a BMS, plus a fuse, plus a switch, at least). You can accomplish this with big cells having enough capacity for your usage
2. Spot welding: in this case, in addition to soldering "bricks" in series, you spot weld cells in parallel, until you accomplish your desired capacity. You can use then 18650 cells, which are relatively widely available. You can also get whatever shape you want

I want to do (2). So it will be great to hear additional comments.

 

[John F]

I am thinking about doing the same.

Apart from what the experts may tell you, what I have found out so far is there are two levels of complexity:

1. Soldering: in this case, you can solder "bricks" in series to build your own battery (plus a BMS, plus a fuse, plus a switch, at least). You can accomplish this with big cells having enough capacity for your usage
2. Spot welding: in this case, in addition to soldering "bricks" in series, you spot weld cells in parallel, until you accomplish your desired capacity. You can use then 18650 cells, which are relatively widely available. You can also get whatever shape you want

I want to do (2). So it will be great to hear additional comments.

You know more than me! I can solder fine, what do mean spot welding? Like they build cars?!

 

[KirstinS]

Spot welding is infinitely neater than soldering unless you are really rather skilled IMHO

That translates into the pack will bigger than a spot welded one

How much bigger depends

My soldering is effective but not neat - I reckon it adds an extra 10% over spot welding

I'm not fussed but FYI in case you are !

Cheers

 

[Deleted member 4366]

The easiest and cheapest way to make a battery is using Hobbyking lipos. A 10aH 36v or 44v battery costs about £120 for the cells, a few quid for wires and connectors, £20 to £60 for a charger, and $5 to £20 for monitoring equipment

 

[smee]

Spot welding is infinitely neater than soldering unless you are really rather skilled IMHO

I'd like to say, just for a different perspective on it, that it doesn't take much practice to be able to solder a neat joint. I suspect many, like me, have a soldering iron, but not a spot welder, in their kit, so I would be soldering.

 

[trex]

it is doable to build your own battery but commercially suicidal if you want to start a small business doing this. As d8veh said, simplest way is to buy cheap ready made 'bricks' and join them together and add a monitoring circuitry. You won't save much making your battery this way though.
3 bricks of 36V 4.5AH cost $240 from Hobby King, you need to add charger + case + monitor.
Sometimes e-bike suppliers have dead batteries to give away because they cost them to dispose of. If you can get hold of this free material, learn to fix them.
http://www.wooshbikes.co.uk/?batteries
Image of BMS
Battery wiring diagram

 

[drsolly]

14.4v, 5AH costs £16 at Hobbyking (go for the 20C hardcase 4s). So a 36v 10AH needs 6 of these, costing £96 (and you'll get 43v, which will make your motor happier).

http://hobbyking.com/hobbyking/store/__26801__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack_UK_Warehouse_.html

A 4s balance charger costs £6, a power supply is £9, monitors £1.43 (you'll need one per brick).

I think you save a bundle by making your battery this way, and Lipos are lighter. But you do need to read up on how to handle Lipos.

 

[trex]

john F has a Santana CDL with 36V 15AH battery - a new one costs £300 from Woosh. He'd need 9 14.4V 5AH bricks, plus 9 Y-pieces, plus monitor, plus inline fuses, plus DC power supply, plus balance chargers plus case plus firebag to make a replacement. Not much cheaper than a ready made one.
The case for LIPO is to put just one small and cheap £60 10s 5AH brick in a saddle bag that can power a BPM kit over 10-12 miles.
This is what may happen if you leave the charger on unattended:

 

[smee]

14.4v, 5AH costs £16 at Hobbyking (go for the 20C hardcase 4s). So a 36v 10AH needs 6 of these, costing £96 (and you'll get 43v, which will make your motor happier).

How is it that we can safely use a higher voltage? Isn't the motor (and driver electronics) designed for a particular voltage?

 

[KirstinS]

I'd like to say, just for a different perspective on it, that it doesn't take much practice to be able to solder a neat joint. I suspect many, like me, have a soldering iron, but not a spot welder, in their kit, so I would be soldering.

If you use nickel strips to solder instead of wire then it's much neater also

 

[Deleted member 4366]

How is it that we can safely use a higher voltage? Isn't the motor (and driver electronics) designed for a particular voltage?

The controller is designed for 36v, but I've never found one that can't work happily with 44V lipos (actually about 48v). The motors can run at any voltage. You can run a 36v motor at 100v if you want. Changing the voltage changes the speed in direct proportion, but it also affects the speed at which it has good efficiency. A 250w motor is rated at 250w, so as you increase the voltage, you need to reduce the current. Different motors can handle different amounts of power, so it's difficult to make a rule for the maximum. Nearly all will manage 700w max, and some 1000w or more.

The only real problems you get with over-volting is the battery display will always show full, and the controller will no longer protect your battery against over-discharge. Hence, the need fir a monitoring system.

 

[Arbol]

it is doable to build your own battery but commercially suicidal if you want to start a small business doing this.

Sorry for the naive question, but why would it be commercially suicidal to do that?

Naively, I see in forums many people would like to have their battery inside the frame, alongside the controller, all protected from "outside".

So, somebody offering a battery to fit a given frame would provide a service many people would want.

Also, batteries are scarce and / or expensive, at least in Europe.