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Author Topic: Fusing brushless motors  (Read 1315 times)

AlisterL

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Fusing brushless motors
« on: July 24, 2012, 05:31:33 AM »

On my normal brushed installs I generally try to get a fuse on both sides of the ESC - that is between the motor and the ESC and also between the ESC and the battery.

How would I fuse the motor to ESC side on a brushless setup? I presume that fusing just one of the three leads would still be sufficient (on the basis that the full current draw will be across each of the three wires at some point), but it might need two, if not all three fused?
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Alister

nick_75au

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Re: Fusing brushless motors
« Reply #1 on: July 24, 2012, 06:54:52 AM »

One fuse in the battery positive is all that is required, don't fuse any of the motor leads, if it blows you may actually damage the ESC.

Please take this as a General comment, not aimed at you personally :-)
I've never understood the fuse the motor wires as well as the positive for brushed set-ups, its just adding unessential fusing, all the current has to flow through the battery Positive lead anyway, The ESC is a switch, does your household circuit have fuses before and after the switch?, the exception would be if running 2 motors in parallel, then I would fuse each motor.

Nick
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AlisterL

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Re: Fusing brushless motors
« Reply #2 on: July 24, 2012, 10:13:15 PM »

Hi Nick,

thanks for your reply and I didn't take that personally.

In answer to your question, I fuse between the motor and ESC to protect the ESC from excessive current draw.
WRT the brushless motors, it seems to me that some of the maximum current draw numbers can be quite large - but I would not expect that in normal operation to get anywhere near them. So using an ESC with a rating lower than the max of the motor would be possible as long as I could protect the ESC in some way - making the overall solution cheaper. From what you say, that the ESC could be damaged if a fuse between the motor and ESC blew, this approach may not be possible and I would need to use an ESC with a max current rating higher than that recommended for the motor. But this figure is not necessarily the stall current I would guess?
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malcolmfrary

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Re: Fusing brushless motors
« Reply #3 on: July 24, 2012, 10:46:32 PM »

The hope is that the ESC should carry its own over current protection, so fuses between motor and ESC are surplus to requirements.  The purpose of the fuse in the battery lead is to protect the boat from damage should a fault in either the wiring or ESC cause a large current to flow and heat up the wiring or ESC.  A sudden disconnection of one of the phases could cause unexpected back EMF spikes to appear on the remaining phases.  These could be absorbed, or they could have unpredictable, but probably bad effects on the ESC.  Given that the wiring between motor and ESC should be as short as possible, extending it to include an extra fault liability seems counter productive.  The same applies to brushed motors and their ESCs as well.
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AlisterL

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Re: Fusing brushless motors
« Reply #4 on: July 24, 2012, 11:33:21 PM »

Thanks Malcolm,

the note to self is to verify that the ESC has the necessary functionality to prevent overcurrent or shutdown the motor etc. Umm, I guess this is the thermal overload bit maybe?
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nick_75au

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Re: Fusing brushless motors
« Reply #5 on: July 25, 2012, 06:43:04 AM »

All the current has to pass through the positive(or negative) battery lead regardless of the ESC, so a over current fault anywhere in the system will cause the fuse to blow, the maximum current draw of any motor can be very large, the lower voltage Speed 700's have a stall current of 100+ amps, but there is no way a 100 amp esc or fuse is required, more in the order of 20 amps.

Fuse to just over the normal maximum amps of the system under load, not what the motor is capable of, this will protect the ESC and motor from any short circuit or stall fault.

Nick
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AlisterL

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Re: Fusing brushless motors
« Reply #6 on: July 25, 2012, 08:46:36 AM »

Ahh.  Of course Nick that is correct - maybe I should have thought that through a bit further - thanks chaps..
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