DC Motor on fire -> nearly exploded :((

Hi electronic friends,

I need some help. I have connected these following two parts together and had let them run. While running I went to toilet, and when I came back, the DC Motor catched fire. My home was stinking badly, I even could not breath. I connected this two parts:

DC-Motor, 24V, 4650 U/Min, 51W max. | eBay ( regarding to eBay maximum 51 WATTS)

LED Trafo 24V DC Mean Well LRS-100-24 Schaltnetzteil case 24 V/DC/0-4,5/ 108W | eBay (4,5 Ampere Current)

What did I wrong ? And how can I fix this ? Any solutions ?

Maybe a prof could say: stupid questions, but as my nickname suggest, I am an absolute beginner :smiley: so sorry for that.

First tell your prof the only stupid question is the one you don't ask.

I can see no reason for the motor to burn up.

My only thoughts are:

  1. some foreign material got into the motor (through the openings) and caused the motor to stall then burn up.
    Can you spin the rotor (even though it is already damaged).

  2. The bearings seized due to running at high speed with no load.


  • The power supply failed and put too much voltage on the battery.
  • The motor was mismarked and is really a 12V motor

I would contact the eBay seller, even if the return window is closed.

An absolute beginner would have made a block diagram showing exactly how you had all this connected together. Since you expect someone on the internet to know how you connected it all, you are before an absolute beginner.
Please start over so someone can perhaps help you figure out what you did and what the problem was.
By the way connecting what you described cannot possible heat up or catch fire. You obviously had some sort of power supply connected. What is it?

Hi thanks. I have connected all cables as it should be. I will show you a complete wiring tomorrow. Right now I am at work.

A couple of thoughts:

  1. Some motors aren't designed to run without a load and will over-speed if you try (a bit like putting you car in neutral and then flooring the gas pedal - whereas different story when you're in gear).

  2. From my radio controlled helicopter days I know that some motors rely on external components for cooling (a bit like a car needs a radiator fan).

Regardless, since you've "smoked" that motor, it's toast - so you might like to have a think about whether it's the best option before buying another one.

That's a series-wound motor you're thinking of - not relevant here as the motor is a permanent magnet DC motor (PMDC).

Most DC motors are perfectly happy run no-load at rated voltage continuously - the power dissipation is much greater under load,
so I suspect the motor was loaded or seized - usually a motor's
internal fan is plenty for no-load.

Bearings in a new motor would not seize by them selves.

Did you have any load on the motor? I.e. was the spindle connected to anything? Did you measure the actual current that it was taking?

Hi there,

I just uploaded a YoutubeVideo to explain you everything again. Maybe it could help for finding the problem:


It seems you ended up with a 30V supply powering a 24 volt motor with no load. Left it running for some period of time.

What likely happened is the motor increased in speed to generate enough emf to keep the current low.

I can't tell by your motor like but it looks like the bearings are simple "pressed bronze" bearings. If dry could cause an issue.

Have you tried to turn to armature since it burned up?


What 30V supply?

Tom.... :smiley: :+1: :coffee: :australia:

Hi Tom,

Looking at the OP's video his 24 volt supply is measuring 30V. Could be the supply could be the meter is wrong could be.......

There is an adjustment control on the Meanwell supply.
Tom... :smiley: :+1: :coffee: :australia:

Wow! I didn't see that, thank you. I had the same problem as absoltue_beginner

@ JohnRob What does "armature" mean ?

The volt meter is absolute okay. Please anser these:

  1. could the 30V voltage damage the DC ?

  2. I allways knew that the power supply allways should have more current output than the DC or etc... again, I am a beginner, so again a stupid question: could it be that the 4,5A Output current damage the DC ? I know certainly that the maximim current input for the DC is 2,1Amps (51 Watts). So should I use a power supply with 2,1Amps ??? <-- maybe it is a stupid question :smiley:

How it usually works is that the motor - at any given voltage - will try to draw a certain amount of current ... so the power supply needs to be CAPABLE of supplying that amount of current.

So if 24v is the correct voltage for the motor - and it draws, say, 2 amps at 24 volts then all that matters is that the power supply is capable of supplying at least 2 amps at 24 volts. So long as it's 24volts then the power supply could be capable of delivering 20000 amps and it would still be fine.

Okay, and what happens with the amps when the supply has a 30V voltage ? Maybe with 30V the amps going to the DC is higher than 2amps ?

Ohms law tells us that for a given resistance, current (and power) will increase in proportion to the voltage.

So lets put that in the context of your motor;

It's supposed to run on 24v and dissipate a maximum of 51 watts. p/v=i (p = power, v = voltage, i = current) so 51 watts divided by 24 volts equals 2.13 amps.

v=i*r ... so v/i = r (with r being resistance). So 24 volts divided by 2.13 amps = 11.29 ohms.

Assuming that the motor load is purely resistive and doesn't change (don't ask!) then at 30 volts it'll be drawing 30 volts / 11.29 ohms = 2.66 amps.

And 30 volts at 2.66 amps would be a power dissipation of 30 * 2.66 = 79.72 watts - which would be 56.31% over it's rated maximum.

But having just said all that, what the motor ACTUALLY draws (thus how huch heat it puts out - thus how hot it gets for a given amount of cooling) is also going to depend on it's load.

So in the context of your project:

  1. you can probably throw that motor away since it's been smoked (it'll have damaged insulation and will probably fail again)

  2. You need to decide if you want to take a chance on another one the same (but only feed it a maximum of 24v) or re-think it and use something else. From my experience with high-power RC helicopter motors it's to be expected that they'll get hot if run under load for a few minutes ... but the difference is that (a) they have fans built in to pull air through and (b) they're designed to take it (they can be far too hot to touch right after a flight). Other than that I probably can't help a lot unfortunately.

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@CJSouthern <--- what a great explaination !!! Thanks. Everything you calculated sounds consistand and smart! okay, I have to put a fan to cool it down. Because, the motor will run for 8 hours a day. Maybe I will use resistors to pull down the amps (because I do not need such a speed). As example, this:

With this I would drop 10 WATTS ?

Thanks - feel free to "reward me" by using the like button (so the system thinks I'm wonderful) :wink:

Adding resistors are probably not the way to go; you'll still end up dissipating a lot of heat - it'll just be spread over the motor and resistor instead of just the motor.

I think the fastest way forward is probably to start by taking 3 steps back and make some better design choices. Plenty here who can help with that but first of all we need enough information to "fill in the blanks" - so perhaps you could start by telling us exactly what you're trying to achieve?

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Yes the most importamt thing is what do you want to achieve runming a motor 8 hours per day?

Running a motor is not a selfpurpose.
So tell us what is the FINAL purpose.
best regards Stefan