Extending the Bafang motor to battery cable.

[nobby]

My Bafang BBSO1b motor 36v 250W is powered by a 36v 15Ah battery.
I need to lengthen the cable between motor and battery shoe for my Trice.
What cable do I need to do that, please?

[Torslanda]

I think when we did cycleman's it was 2-core mains. Soldered using a 'lineman's joint'.

[sojournermike]

It needs to be able to carry 7 amps. I’d look for 13 amp rating or higher myself.

[nobby]

Thank you both Torslanda and sojournermike.

The shop that supplied the motor finally got back to me and they use 32A cable!

Is the 7A from VA=W so 36V x 7A = 252W the rating of the motor and 13A for a safety margin?

[Valiant]

You'll be fine with 13a mains cable. Not sure why they are using 32a unless they use the same cable for all systems ie upto 1500w. Just make sure any fuses are matched.

[aidan.f]

Cables should be oversized to minimise Voltage drop. Peak current may be a lot  higher than the simple maths predicts. This is not so much of a problem with a relatively high Voltage battery but still I would go for 2 mm sq.  Rated around 20 amps

[nobby]

Thank you Valiant and aidan.f

I have a length of the 32A (14AWG and 2.5mm squared) on its way and when it arrives if it is too thick I'll order 16 AWG 1MM squared rated at 21A.

Thanks for the help all

[sojournermike]

Thank you both Torslanda and sojournermike.

The shop that supplied the motor finally got back to me and they use 32A cable!

Is the 7A from VA=W so 36V x 7A = 252W the rating of the motor and 13A for a safety margin?

Yes, but as rightly pointed out the peak current may be higher depending on it’s controlled. I did think about voltage drop too, but assume it’s a short cable run which will help with that. Also, that the cable won’t be buried in a wall, but will benefit from passing airflow!

2.5mm² is rated for a 32 amp ring main, when there are two runs of cable. A spur needs 6.5mm² usually. I recently did the calls for 3 long armoured cable runs to a pair of ev chargepoints (7kW each) and the shed. Even with 6.5mm there is a fair voltage drop on the run. On a related point 2.5mm will run warm if it’s connecting a 3kW immersion heater.

[nobby]

Thank you both Torslanda and sojournermike.

The shop that supplied the motor finally got back to me and they use 32A cable!

Is the 7A from VA=W so 36V x 7A = 252W the rating of the motor and 13A for a safety margin?

Yes, but as rightly pointed out the peak current may be higher depending on it’s controlled. I did think about voltage drop too, but assume it’s a short cable run which will help with that. Also, that the cable won’t be buried in a wall, but will benefit from passing airflow!

2.5mm² is rated for a 32 amp ring main, when there are two runs of cable. A spur needs 6.5mm² usually. I recently did the calls for 3 long armoured cable runs to a pair of ev chargepoints (7kW each) and the shed. Even with 6.5mm there is a fair voltage drop on the run. On a related point 2.5mm will run warm if it’s connecting a 3kW immersion heater.

Cheers. Thanks again for the help. Much appreciated.

[Torslanda]

I should point out that Redshift carefully matched the cross section to the original Bafang cable on the motor.

[nobby]

I should point out that Redshift carefully matched the cross section to the original Bafang cable on the motor.

The 32A cable arrived today and it seems to be the same size as the original ends and the same type with silicon outer.
Just waiting on the correct sized seals for the Delphi weatherpack connector