Exploding capacitors problem when DC motors are running

Thread Starter

Wahhe

Joined Apr 22, 2020
7
I am trying to make a Radio Flyer Tesla for kids into remote controlled. So, I have bought several components (see list below) and hooked everything according to the schematic provided from the ESC (electronic speed controller). However, every time I open the throttle the wheels start to turn as expected, but after a few second one of the capacitors of the DC motors explodes. The capacitors are 47 uF 16V. The battery is a 4s battery which states that it provides 14.4 V. However, measuring the output voltage of the battery gives 16.4 V approximately. In the attached pictures the capacitor is shown just before the explosion. The second picture shows it during the explosion. The last picture shows how I connected the ESC and all the other components together.

So, does anyone know what is going wrong and why the capacitors explode every time? And how do I fix it?

Component list
  1. ESC: QUICRUN WP 880 Dual Brushed ESC (2-4S)
  2. Remote controller: Microzone MC6C
  3. Receiver: Microzone MC7RB
  4. 35kg servo (to control the steering with the remote controller)
 

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Thread Starter

Wahhe

Joined Apr 22, 2020
7

Thread Starter

Wahhe

Joined Apr 22, 2020
7
Electrolytic capacitor can explode because of: higher voltage, short circuit or change polarity.
Yes I am aware of higher voltage and change of polarity explode capacitors, that's why i never used full throttle on my remote controller. As you can see in the picture I allowed around 3 V to the motor and the wheels did turn but after turning a few second then the capacitor exploded. That is what I found very strange.
 

Bobes

Joined Mar 19, 2020
51
Yes I am aware of higher voltage and change of polarity explode capacitors, that's why i never used full throttle on my remote controller. As you can see in the picture I allowed around 3 V to the motor and the wheels did turn but after turning a few second then the capacitor exploded. That is what I found very strange.
Motor is very high load. Therefore, electrolytics are never used in parallel to it.
 

Janis59

Joined Aug 21, 2017
1,179
Caps may explode exclusively for THREE reasons
1) wrong polarity for electrolytics
2) overvoltage for any cap
3) excessive current via this cap translated via tan(delta) to thermal flux. Formula of max reactive power says circulated reactive power multiplied to tan(delta) is thermal flux. For example - 100V 100A the circulating power is 100*100=10 000 W. Then at (I guess) tan(delta)=0,05 have the thermal flux 10 000*0,05=500 W. Its safe-explanatory, that few cm2 object may not sink so grand thermal power. By the way, especially for slow type casps like electrolytes, at higher frequencies that tan(delta) may grow very rapid
 

Alec_t

Joined Sep 17, 2013
11,285
If the controller can reverse the motor then a polarised electrolytic cap connected directly across the motor WILL definitely be destroyed. If the caps came with the controller or motor, presumably there are instructions for their use? What do the instructions say?
 
Last edited:

dendad

Joined Feb 20, 2016
3,528
I would expect the capacitors supplied were not to be installed across the motors, but on the power input to the controller. That is, across the battery connection.
Adding caps across the motor is not correct.
 

Bobes

Joined Mar 19, 2020
51
I would expect the capacitors supplied were not to be installed across the motors, but on the power input to the controller. That is, across the battery connection.
Adding caps across the motor is not correct.
It can be done, but NEVER electrolytics! Just ceramics, or film capacitors, which aren't normally made of value more than 1uF.
 

Thread Starter

Wahhe

Joined Apr 22, 2020
7
The capacitors are connected as shown in the attached pictures out of the box. When one of the original caps exploded, I connected a new capacitor (polarized which I understand is wrong) at the exact location as the original. The original capacitors are non polarized.

I know someone who has done this same project with success and the only difference is that is uses an ESC which provides a max current of 60A while mine does 80A. He uses Hobbywing QuicRun WP 860 Dual Brushed 60A ESC‎.

The original caps look like electrolytic capacitors, am I right?

What types of caps do you suggest and I should probably replace all of them to prevent exploding the other ones as well right?
 

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dendad

Joined Feb 20, 2016
3,528
The hint is the "NP" on the caps.
That is Non Polarized"
They do seem to be a higher value that I would expect. As mentioned above, normally they would be low value ceramic caps.
These may have died because of excess ripple current. If you have the motors loaded down, that current will go up. Look for Low ESR, NP caps, at least twice the battery voltage.
 

Thread Starter

Wahhe

Joined Apr 22, 2020
7
The hint is the "NP" on the caps.
That is Non Polarized"
They do seem to be a higher value that I would expect. As mentioned above, normally they would be low value ceramic caps.
These may have died because of excess ripple current. If you have the motors loaded down, that current will go up. Look for Low ESR, NP caps, at least twice the battery voltage.
I can only find Aluminium Electrolytic Capacitors which are non polarized 47uF and at least over 16V. I found this capacitor : ECEA1VN470U CAP, ALU ELEC, 47UF, 35V, RAD PANASONIC at https://sinuss.nl/componenten/passieve-componenten/condensatoren/aluminium-electrolytic/aluminium-electrolytic-capacitors-leaded/2326038-ecea1vn470u-cap-47f-35v-20-panasonic . This should work right?
 

MaxHeadRoom

Joined Jul 18, 2013
20,695
You could always use motor start capacitors, designed for AC and are bi-polar, these should never blow with the lower voltage across them. :cool:
Max.
 
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