# Which supercapacitor range is needed to run a 48V DC motor?

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1. Sep 12, 2016

### Durga Raj Kumar B

I'm doing a project where I need to hand power for dc motor (12V or 24V) and charge a super capacitor, and then use it to drive another 48V dc motor. I want to know which Super capacitor will be suitable?

Please give suggestions for Super capacitor specifications for both 12V and 24V that will help me get the most efficiency out of such a system?

2. Sep 12, 2016

### Staff: Mentor

Super capacitors are pretty efficient. But many of them come in voltages much below 12V. You will have to string several in series before connecting to 12 or 24 V supply, and a different number in series to power the 48 v motor.

Also, capacitors are not like batteries. When 50% of the energy is used, the capacitor voltage drops to 50%. You need to know the maximum and minimum voltages for the 48V motor.

More important, how much energy (measured in watt-hours) do you need to store? That is the most important parameter. For example, if the 48V motor is rated at 12 watt, and you run it for one hour, that is 48 watt-hours. Go find out how many watts the motor needs, then decide for how long you need to run it, then return here with those answers.

Also, be aware that high energy charged super capacitors can be unsafe if not handled properly. If the PF mentor is not satisfied that you have the background to do it safely, he may close this thread.

3. Sep 12, 2016

### CraigHB

The main problem with what you want to do is you don't see super capacitors much over 2.7V tolerance and if you can find them higher they get crazy expensive. As mentioned you have to string a bunch in series to get to a 48V tolerance, like 20 of them. The problem with putting them in series is capacitance reduces similar to resistors in parallel. So after you put 20 of them in series to get that 48V tolerance you end up with a 20th the capacitance which will be a problem driving a motor any length of time.

The reason super capacitors can be dangerous is they have very low internal impedance so very large instantaneous currents can occur if terminals are shorted. It can be a rather explosive event. You do have to be careful with them when charged. Also you have to be careful about over-charging them or they can break down internally resulting in the same event. So yeah the PF moderators may shut down the thread if they feel it's an overly hazardous topic.

Curious why a Li-Ion battery can not do the job for you. They have their hazards as well, but still a lot safer. A 12S Li-Ion battery could do the job with a nominal 44.4V. You can get a couple small 6S hobby style LiPo batteries off the shelf fairly cheap and run them in series.