Author Topic: Extending the Bafang motor to battery cable.  (Read 417 times)

Extending the Bafang motor to battery cable.
« on: June 15, 2020, 08:48:11 am »
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?
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Torslanda

  • Professional Gobshite
  • Just a tart for retro kit . . .
    • John's Bikes
Re: Extending the Bafang motor to battery cable.
« Reply #1 on: June 16, 2020, 10:53:29 am »
I think when we did cycleman's it was 2-core mains. Soldered using a 'lineman's joint'.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Extending the Bafang motor to battery cable.
« Reply #2 on: June 16, 2020, 11:38:21 am »
It needs to be able to carry 7 amps. I’d look for 13 amp rating or higher myself.

Re: Extending the Bafang motor to battery cable.
« Reply #3 on: June 16, 2020, 03:02:27 pm »
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?
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Valiant

  • aka Sam
    • Radiance Audio
Re: Extending the Bafang motor to battery cable.
« Reply #4 on: June 16, 2020, 06:13:56 pm »
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.
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Re: Extending the Bafang motor to battery cable.
« Reply #5 on: June 16, 2020, 11:36:04 pm »
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

Re: Extending the Bafang motor to battery cable.
« Reply #6 on: June 17, 2020, 06:14:34 am »
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
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Re: Extending the Bafang motor to battery cable.
« Reply #7 on: June 17, 2020, 08:00:31 am »
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.

Re: Extending the Bafang motor to battery cable.
« Reply #8 on: June 17, 2020, 08:17:36 am »
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.
Never knowingly under caffeinated

Torslanda

  • Professional Gobshite
  • Just a tart for retro kit . . .
    • John's Bikes
Re: Extending the Bafang motor to battery cable.
« Reply #9 on: June 18, 2020, 06:00:02 pm »
I should point out that Redshift carefully matched the cross section to the original Bafang cable on the motor.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Extending the Bafang motor to battery cable.
« Reply #10 on: June 18, 2020, 09:31:56 pm »
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
Never knowingly under caffeinated