Author Topic: wheelchair motor voltage?  (Read 2480 times)

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Offline BANETopic starter

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wheelchair motor voltage?
« on: May 31, 2011, 10:17:09 PM »
Hello all,
I just wanted a second opinion on wheelchair motor voltage.  24v is nominal for a standard 24v wheelchair motor, however, people have told me you can put up to 36v for about 5 mins and get about 50% more performance.  Does anyone see any issues with this besides the obvious one of over heating?  

Here is a webpage i found supporting the 36v.
http://www.robotmarketplace.com/products/NPC-B82HT.html

thanks in advance,

Offline marto

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Re: wheelchair motor voltage?
« Reply #1 on: June 01, 2011, 01:21:18 AM »
Wheel chair motors are made to last so 36V will probably work fine for an extended period of time. You can probably get away with up to 48V but really depends on motor.  Other main thing to consider is the brushes too much voltage/current and you may just destroy them.

As with anything its designed to run on 24V so you should run it on that. 36V+ will probably work and give you 2.25 times the power but don't be surprised if you significantly shorten the life span of the motor or destroy it.

That being said I run 12V drills on 24V in my combat robots and they are fine most of the time but I kill a lot more than I would expect to @ 12V.

Steve

Offline Soeren

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Re: wheelchair motor voltage?
« Reply #2 on: June 01, 2011, 06:49:47 AM »
Hi,

I just wanted a second opinion on wheelchair motor voltage.  24v is nominal for a standard 24v wheelchair motor, however, people have told me you can put up to 36v for about 5 mins and get about 50% more performance.  Does anyone see any issues with this besides the obvious one of over heating?  

Here is a webpage i found supporting the 36v.
http://www.robotmarketplace.com/products/NPC-B82HT.html

First off, motors are constructed differently. Some will be better at getting rid of heat than others, some will be wound differently and with different gauges and lacquer.
The motor was designed to work reliably at 24V - going 50% over voltage is asking for trouble in some form.

'That aside... Like so many other components, limits are not absolutes and will depend on design parameters and use pattern.
The best way you can find out, if your particular motors will cope resonably well with a higher voltage, is to test it with a temperature sensor bolted to the chassis, preferably at a place near where the windings transfer the heat out.

First run it at the nominal 24V (loaded with a belt brake if possible) for at least 30 minutes, or until the temperature has stabilized (a PC controlled setup would really make it easy). Take notes like "24V, nn°C(or °F)".
Increase the voltage to 26V and wait another 30 mins or until temp. is stable. Note down, increase by 2V and repeat.

As long as the chassis stays below 50°C you should be in the green, but it's hard to put numbers on it, so don't go over say a 20% temperature rise (above the 24V derived temp).

You can then turn things around a bit and stabilize the temp at 24V, then crank it up to 36V and see how long it takes to reach a 20% higher temp.
If you wanna repeat it, allow plenty of time to settle back to the 24V temperature.


When guesstimating, try to err on the conservative side if possible (like 30 minutes may be more than needed at each step up). The temperature rise will take some time to get from the windings to the chassis (hence the 30 minutes to stabilize the temperature) and unless you know the specs of the exact lacquer used on the magnet wire, don't assume it will keep up much above 80°C.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline BANETopic starter

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Re: wheelchair motor voltage?
« Reply #3 on: June 02, 2011, 11:21:19 AM »
thanks for the input guys,
I just ordered some more batteries for 36v. 
Quote
First off, motors are constructed differently. Some will be better at getting rid of heat than others, some will be wound differently and with different gauges and lacquer.
these are standard merit motors; however, ive compared the coils to my various other wheel chair motors and they look to be a heaver gauge.

Quote
First run it at the nominal 24V (loaded with a belt brake if possible) for at least 30 minutes, or until the temperature has stabilized (a PC controlled setup would really make it easy). Take notes like "24V, nn°C(or °F)".
Increase the voltage to 26V and wait another 30 mins or until temp. is stable. Note down, increase by 2V and repeat.
you are a mind reader.  :D I got a temperature sense a while back and i going to try to use the axon as a datalogger and do some testing

Offline Billy

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Re: wheelchair motor voltage?
« Reply #4 on: June 06, 2011, 12:58:53 PM »
these are standard merit motors; however, ive compared the coils to my various other wheel chair motors and they look to be a heaver gauge.

Besides the heating of the coils, you may want to consider heating of the bearings. Running no-load will keep the current down which may give you a feeling that 36V is OK, but overheating of the bearings will lead to early failure. I've seen bearing races that have changed color they gotten so hot, and thats when used within spec. If you burn the lubricant out of the bearings during your test, it may not be possible to relube.

I'd say do the test as you're planning, but see if you can find a way to monitor bearing temp as well. It's probably low risk though. At worst, your motors don't last as long as they otherwise would.

Offline Soeren

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Re: wheelchair motor voltage?
« Reply #5 on: June 06, 2011, 02:05:14 PM »
Given the time to stabilize the temp, a raise in bearing temperature and whatever else may contribute (like eg. poor venting) will reflect in the total - that's the entire point in the stabilizing time.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Daanii

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Re: wheelchair motor voltage?
« Reply #6 on: June 06, 2011, 05:16:54 PM »
I don't think boosting the voltage from 24 V to 36 V is going to have any effect on the temperature of the bearings.

 


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