Can a 24V 30A Dimmer Switch Handle the Starting Current of a 500W 24V Motor?

[sam charlton]

Hello,
I'm currently constructing an electric bicycle using a 500w 24v motor, 2X24v 7ah batteries (maybe 4 later on). I bought a 24v 30a dimmer switch to use as a "throttle". During the intitial test (on a table, not on the bike!) It worked absolutely fine for 2 minutes, but then began to smoke and gave out completely leaving the motor to run at full power. i purchased the same dimmer switch again, but can anyone think of a reason why it happened and how i can prevent the circuit from ruining the new switch?
Here is a list of links to the parts I'm using:
https://www.ebay.co.uk/itm/DC-12v-24v-30a-led-switch-dimmer-controller-for-led-strip-single-color-black-GY/292378969377?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

http://www.ebay.co.uk/itm/ZY1020-Electric-Motor-24v-500w-Brushed-E-Bike-Scooter-24-Volt-500-Watt-6mm-Chain/192391102611?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

https://www.ebay.co.uk/itm/TWO-x-DynoEurope-12V-7-5Ah-VRLA-SLA-RECHARGEABLE-SEALED-BATTERIES/162621571240?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649Thanks!

Sam :)

EDIT: i have seen posts saying this circuit would not work because the motor is not controlled by voltage, but by frquency. regardless, i don't see why this would cause the switch to smoke and give out.

 

[Alloymouse]

Hi Sam, welcome to PF!

It seems that there's a possibility that the dimmer switch you got might not exactly work as advertised... my recommendation is to get a better dimmer switch or some sort of variable resistor that can handle higher currents and with better heat dissipation. The battery and motor seem fine (I've worked with those exact parts before, so I trust them.)

 

[sam charlton]

hello,

thanks for your reply, it's good to know you have used the batteries and motor haha!
the first switch i got was from china so am not even going to bother sending them a message. the new switch is from a uk distributor so if i encounter the same problem in my next test i will definitely message them. i am starting to look into the use of motor speed controllers rather than a dimmer switch. it is hard to know you need something when you don't know they exist!Thanks again, Sam.

 

[Asymptotic]

Was the dimmer hot after it smoked out?

24V at 30A is 720 watt dimmer rating, and at first glance ought to be enough for a 500W DC motor, but it is in a very small case. If the dimmer case (BTW - the fine-print claims the dimmer is a PWM controller) isn't bolted to an appropriately large heat sink, the power semiconductor(s) will overheat and burn up.

i have seen posts saying this circuit would not work because the motor is not controlled by voltage, but by frquency. regardless, i don't see why this would cause the switch to smoke and give out.

Photo shows a red and black lead, and description says it is "brushed", so it looks like it is a permanent magnet DC motor. PMDC motor speed is varied by adjusting armature voltage.

If this were a three-phase AC motor, then frequency control is half correct - both frequency and voltage must be varied in proportion with one another.

 

[wirenut]

If you look at the info in the link, you may be overloading the dimmer:
Output: 1 Channel 360W 12-24V (0-30A)

 

[Svein]

Using a dimmer as a throttle on a motor? The spikes from the motor will certainly kill it!

Run your motor in a dark room and watch the sparks fly around the brushes.

 

[Asymptotic]

If you look at the info in the link, you may be overloading the dimmer:
Output: 1 Channel 360W 12-24V (0-30A)

Good catch

 

[jim hardy]

DC motors draw several times rated current while starting. So overcurrent might be killing the controller .
but since it ran for a minute or two,
more likely Svein has the answer - the motor's inductance applies reverse polarity overvoltage to your PWM controller.

Try feeding the motor through a full wave bridge rectifier rated 40 amps or more. That'll absorb reverse polarity 'spikes' .
https://www.ebay.co.uk/itm/KBPC5006-50A-600V-Metal-Case-Power-Diode-Bridge-Rectifier-Control-Single-phase/382380804493?hash=item5907ac098d:g:TbgAAOSwvktaaXt3

An inexpensive experiment...