Snubber Circuit?

Thread Starter

Rangerover

Joined Aug 18, 2018
31
HI Everyone,
so, i have upgraded my kids power wheels with DC motors and a controller out of an ebike/scooter running at 18v which has been working really well. after a while we loose reverse in the car. After some troubleshooting, the dpdt switch was blown so i would just replace the switch. After some time, the same thing would happen.
After doing some research im learning about snubber circuits, and while i think they are easy to make, i have no idea how to read a wiring diagram so i have no idea what to solder where etc.
i have had a look at some youtube clips although they are all theory clips and no practical clips ie no one actually soldering components.

Does anyone know of a clip to save me looking through every single youtube clip?
Also, as its a dpdt switch, do i need 1 or 2 snubber circuit and on what pins? my guess is i need 2 circuits on pins 1 & 2, is that correct?

appreciate any help and support
thanks
Sam
 

ebeowulf17

Joined Aug 12, 2014
3,274
Could you share a schematic (hand drawn wiring diagram is fine) so we can see how you've got things set up right now? Often DC circuits can be protected with a flyback (or freewheeling) diode, but with the motor being reversible that may not be an option. The devil is in the details!

Assuming you need RC snubber(s) instead of diode(s) it may be easier to buy pre-made snubbers than to make your own. Quencharc snubbers have worked well for me in the past and are readily available through many electronics suppliers.

Anyway, we need more info. If you can provide a wiring diagram, and probably also some specs on the motor (current and/or wattage specs at least, and the more info the better,) you'll get more detailed answers. If you're lucky, someone who knows this stuff way better than me will help out once you add the relevant details!
 

crutschow

Joined Mar 14, 2008
24,953
In general, if the DC motors are in a H-bridge type configuration where the voltage is reversed to reverse the motors, then 4 diodes can be used to protect whatever switches/circuitry is driving the motor.

Connect a diode from each side of the motor to the battery plus side (cathode to battery), and a diode from each side to the battery minus side (anode to battery).
Diagram below.
The diodes should probably be rated for 3-5A., 50V.
That will conduct any motor spikes in either direction back to the battery, and limited to the battery voltage.
1580371716386.png
 

Thread Starter

Rangerover

Joined Aug 18, 2018
31
ebeowulf17 - i havent been able to find specs on the motor, although they are Traxxas 550 12t. i do have Quencharc (diff brand) off the motor (i have w DC motors, one on each rear wheel)

attached is my diagram, i know its very basic although i hope it gives you enough detail

crutschow - will the diodes stop the spike on the battery or to the dpdt or both?

appreciate the support
 

Attachments

ebeowulf17

Joined Aug 12, 2014
3,274
In general, if the DC motors are in a H-bridge type configuration where the voltage is reversed to reverse the motors, then 4 diodes can be used to protect whatever switches/circuitry is driving the motor.

Connect a diode from each side of the motor to the battery plus side (cathode to battery), and a diode from each side to the battery minus side (anode to battery).
Diagram below.
The diodes should probably be rated for 3-5A., 50V.
That will conduct any motor spikes in either direction back to the battery, and limited to the battery voltage.
View attachment 197874
That's really cool! I must've read several dozen threads where this would've been useful and I've never seen it come up before. I'm surprised this is my first time seeing it, cause it looks brilliant!

Based on the thread starter's diagram, it looks like it's not an H-bridge in this case, but rather a motor speed controller followed by a DPDT switch wired as a forward/reverse control. That doesn't change the validity of your solution, it just makes the implementation look a little different than I first pictured.

When I first read your post I imagined that the easy implementation of your suggestion would simply place all 4 diodes across various terminals at the switch, but then I realized that would be connecting to the + and - outputs of the motor controller, not the battery. I only bring it up in case someone else reads it and makes the same mistake I did. If I'm understanding this correctly, it's critical that the diodes connect from the two motor wires to the two battery wires (as you stated,) bypassing both the motor controller and DPDT switch.
 

ebeowulf17

Joined Aug 12, 2014
3,274
ebeowulf17 - i havent been able to find specs on the motor, although they are Traxxas 550 12t. i do have Quencharc (diff brand) off the motor (i have w DC motors, one on each rear wheel)

attached is my diagram, i know its very basic although i hope it gives you enough detail

crutschow - will the diodes stop the spike on the battery or to the dpdt or both?

appreciate the support
It took me a minute to sort through the switch pin numbers and visualize it, but I've got it now. Thanks for the details. Without knowing more about the motors, I wouldn't be confident sizing/spec'ing parts myself. However, @crutschow really knows his stuff, so I'd bet that if you follow his advice you'll be in good shape.
 

KeithWalker

Joined Jul 10, 2017
890
From the information you have given, I suspect the switch is failing when direction is changed while the car is in motion. That will cause arcing across the contacts. Ideally the direction should only be changed when the motors are at rest. You need some kind of interlock to stop this happening.
Regards,
Keith
 

Thread Starter

Rangerover

Joined Aug 18, 2018
31
Keith, thats exactly what i was thinking. Issue is when the kids are driving the cars and racing etc they tell me they "forget". hence why im trying to see if there is a fix for this.

In saying that, crutschow, your way would stop this from happening?
 
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