Author Topic: Wheelchair motor break question  (Read 1033 times)

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Offline AncosicTopic starter

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Wheelchair motor break question
« on: January 23, 2013, 01:12:18 AM »
old question... but I didn't really understand the answer...


I've purchased a pair of wheelchair motors (Jazzy Pride 1121) and I understand there needs to be 24V to lift the brakes. It has been previously suggested to just remove them- but wouldn't that be risky? having a motor without some sort of failsafe? (is it there for any other reason? it's not used in normal function right?)

if I remove them, should I install some other stopping mechanism? is it risky? I don't expect much momentum, it's pretty much just going to be a mobile platform... or moving table...

if I leave them in place, how should I supply the power? I have two deep cycle batteries to run the motor, but I can't just put this in parallel right?

Offline briselec

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Re: Wheelchair motor break question
« Reply #1 on: January 23, 2013, 01:38:08 AM »
They have an electric brake for the same reason a car has brakes.
Just power them thru a suitable size relay.
In assembly language no one can hear you scream

Offline AncosicTopic starter

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Re: Wheelchair motor break question
« Reply #2 on: January 23, 2013, 08:59:28 AM »
I was under the impression that the wheelchair motor brakes (the ones built into the motor) were only on/off and not part of normal function. So if I take them out it wouldn't effect the normal operation, but the in-case scenario of losing power....?


and I don't mean to be repetitive, but I'm not well versed in electronics... you suggested a power relay to control the brake circuit: can I run it parallel to my motor circuit (the hookup between my batteries and motors), would I risk putting too much current through this? does the power relay limit the draw?

I saw some tutorials in power regulation- but both the motor and the brakes are 24V. I don't think the brakes run off as much amperage, I 'm afraid if I hook them up together I'll fry the brakes.... should I be concerned about limiting amperage into the brake circuit?


Offline jwatte

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Re: Wheelchair motor break question
« Reply #3 on: January 23, 2013, 10:56:42 AM »
When you say "can I just parallel it" it's unclear what "it" means.

Typically, you will have some kind of speed control for the motors. You don't want speed control for the brakes. (Note: "brake" not "break!")

A typical wiring diagram would be:

Two batteries in series -> on-switch and fuse -> brake circuit -> back to batteries
Two batteries in series -> on-switch and fuse -> motor controller -> motor circuit -> motor controller -> back to batteries
Two batteries in series -> on-switch and fuse -> voltage regulator -> control logic -> back to batteries

So, in this sense, the three pieces (brakes, motor, and contol) are "in parallel." For high-current systems, "on-switch" is either a relay with a small signal switch for the coil, or something like a few parallel high-performance MOSFET transistors and a small signal switch for the gates.

Offline AncosicTopic starter

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Re: Wheelchair motor break question
« Reply #4 on: January 23, 2013, 02:38:31 PM »
thank you =P

would this be ok? this' what I had meant by parallel... there'd be a supplied 24 V to the brakes- are there any electrical risks associated with this?


Offline jwatte

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Re: Wheelchair motor break question
« Reply #5 on: January 24, 2013, 12:08:37 PM »
That looks fine to me, assuming the controller and brakes are rated for 24V. The brakes may be implemented as some kind of coil with a spring; if that's the case, you may want to add a kickback reduction diode across the brakes, and perhaps a capacitor. Else, when you cut power, the kickback from the coil may give enough voltage as a short spike on the electrical line to damage your controller. You can probably measure this with a good oscilloscope if you worry about it.

 


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