Is there a digital potentiometer that can handle higher voltage/current?

[JerryG]

I was using a digital rheostat to control a certain device. However, the current seemed to be a bit too much for the rheostat. All was working fine for about 5 minutes until the resistance started to fluctuate a little bit and a few minutes later, the digital rheostat became an open circuit. The chip I was using was a microchip MCP4162-103E/P which gives a resistance up to 10 k ohms. Does anyone know of a digital pot/rheostat that can handle more voltage/current? Or should I try putting several of these chips in series or parallel? Or is there a better way to digitally control a variable resistance?

 

[MATLABdude]

What application are you using this in (i.e. how much current / voltage are you putting through this)? Most of this type are generally only meant for low-voltage / current applications (like controlling amplifier gain or voltage dividers)

 

[JerryG]

I am using it to control an electric outboard motor on a boat. The motor has a built in rheostat that ranges from 220 - 5500 ohms. I have put a digital rheostat in its place to be controlled by a micro controller. At 220 ohms, the current was 1 mA and at 5500 ohms, the voltage reached 3.6 V which is equal to the absolute max voltage according to the datasheet. I thought it would fall withing the part's specs, but I guess not since normal operation lead to failure.

 

[MATLABdude]

Unfortunately, they're not strictly resistive nor is it "isolated" from the input / power rails (hence maximum voltage that you can use on the potentiometer side). I'm also guessing that the outboard motor's power quality isn't the greatest, in terms of spikes and electrical noise.

Do you happen to have a schematic for the motor? In other words, what's the rheostat actually doing, and how does it control the motor?

 

[JerryG]

No schematic or datasheet for the motor. I can't tell you how it actually controls the motor since it just leads to a sort of "black box" motor controller. And since it's a boat motor, I doubt any effort has been made to reduce noise.

I can say that the circuit I have setup runs on a separate battery, so the power rails are completely isolated from the motor's power source.

I was thinking next, I could get four of those same chips. Put two pairs in parallel and put those two pairs in series, thus giving the same overall resistance, but dividing power dissipation between them. I'm just not sure if there would be a better way of going about this. You think it would be better to setup a jfet as a voltage controlled resistor?

 

[MATLABdude]

I'd try to figure out how much power is going through it at the low and high settings--use a DMM in-line with the (original) potentiometer to measure the current and then measure the voltage across the potentiometer at both these settings. If it's purely a matter of power dissipation, your solution (or one capable of dissipating more power) will work. If it's spikes or voltages outside the acceptable range, you'll have to use something else.

Here's a something else--Bourns motorized potentiometer:
http://ca.mouser.com/ProductDetail/Bourns/PRM162-K420K-103B1/?qs=sGAEpiMZZMsEGgLEzQVydkrAXCSDHgZNhAu%252bWQAc3qU%3d

The two potentiometers should be isolated from one another as well as the motor, allowing you to control the outboard as well as measuring the potentiometer setting.