Login Join Maker Pro

# problem with 48vdc motor destroys relay

#### Bluejets

Oct 5, 2014
6,920
I working on a 48vdc motor but every time I turn it off with a relay ,the relay gets destroys.
As Minder has quoted, use an automotive relay .
Being 24v coil, most truck relays should suffice.

I imagine the motor is on load when switching on and off........if so, they can draw quite an amount of startup current, at least 4 times full load.
Given that, I would tend to use a starter solenoid, however there may be some restrictions on duty cycle.
Alternative would be a 100A contactor.
That should stop it's monkeying around, although could cost a few hundred bucks.

One additional query though, why use such a motor in the first instance?
Perhaps if you describe what you need to achieve, there may be better alternative drives.

#### Delta Prime

Jul 29, 2020
1,966
I would tend to use a starter solenoid, however there may be some restrictions on duty cycle.
Alternative would be a 100A contactor
We used an oscilloscopes math function FFT( Fast Fourier Transform)That is an algorithm that reduces the calculation time of the DFT (Discrete Fourier Transform) which is an analysis tool that lets you view the acquired time domain (amplitude vs. time) data in the frequency domain (amplitude and phase vs. frequency)
And we have seen current spikes along with in Rush current of 200 amps in the milliseconds with the e-bike on throttle alone no pedal assist, flat out,which is a very long time for relays and these guys can handle it. Workable service life time of the relay must be derated of course.

#### Bluejets

Oct 5, 2014
6,920
We used an oscilloscopes math function FFT( Fast Fourier Transform)That is an algorithm that reduces the calculation time of the DFT (Discrete Fourier Transform) which is an analysis tool that lets you view the acquired time domain (amplitude vs. time) data in the frequency domain (amplitude and phase vs. frequency)
And we have seen current spikes along with in Rush current of 200 amps in the milliseconds with the e-bike on throttle alone no pedal assist, flat out,which is a very long time for relays and these guys can handle it. Workable service life time of the relay must be derated of course.
Yeah, well, many times this approach gets blown out of the water with the "suck it and see method based on experience".

#### Delta Prime

Jul 29, 2020
1,966
the measurements we made were based on theory & was all real time.
I never heard that expression though I think you fine-tuned it just for me. And I'm happy to see I'm not on your ignored list. That was my motivation not helping anybody.

#### Delta Prime

Jul 29, 2020
1,966
Off topic;
What was the price of your engagement ring?? HeHe
Was it an inductive ringing? Or did you just give her your snubber... Circuit?
Hehe...

#### mrNobody

Jul 1, 2023
7
This is just an example!this is the one my friend purchased for his e-bike which is a 2000 Watt DC motor
The coil can come in different voltages and as stated by
Mr. @Martaine2005 you need an external diode for Reverse EMF. Protection!
View attachment 59670
All the above is just an example of how you would connect you can configure it any way you wish it'll work just the same. Gives us wiring diagram of how you have everything connected or would like to have it connected.
This wire colored diagram one shows a 12 relay but what it doesn't show it's connected to the same 12 volt source along with the switch on the relay coil and I would put fuses in there on the positive rail. it depends on your skill set! But I'm pretty sure we are all more happy to help you.
View attachment 59671
And another thing people are probably going to give you crap cuz it says China right on your relay. They used to say same thing about U.S. products right after world war II. Cheap and unreliable. Just buy from a known good vendor. But I'm glad we're not speaking German or Japanese in the U.S.A.
Happy 4th of July everyone! You want some...Get Some!! Hoorah!!
Thanks for replying. And happy 4th July, I don't hav the parts no before tomorrow but it will look like this

And it's the "k1" contacts that's stil together every time I shut down the motor, it's a school project it's a vacuum pump that's just need to start when s1 is closest and stop when s1 is open but the relay Keeps failing så thankful for all the help from all of you

#### Delta Prime

Jul 29, 2020
1,966
it's a school project i
Oh hell your thread should be in homework help we've all said too much. I'm out of here.

Replies
0
Views
68
Replies
2
Views
143
Replies
15
Views
457
Replies
23
Views
704
Replies
10
Views
441