Potentiometer resistor has me confused - Page 1
Forum section: electronics / beginners

author: imisswaves
author_rank: Newbie
timestamp: December 03, 2017, 07:55:14 pm
content: Here is the schematic. Sorry if it's messy. I'm new to this.If that doesn't help, here is a picture of the potentiometer:I've been playing with electronics a little bit and I know my way around like a beginner. I'd really like to understand more and I had this old trolling motor fall into my lap, so what greater time than now to join eevblog and ask you all my questions that I've never asked (but have probably been asked umpteen times).So the main switch failed in the circuit and I'll have to replace that, but the 10 OHM resistor is blown. The thing is, I can bypass the main switch and give power to the motor. When I do this everything works just fine (actuating the potentiometer regulates motor speed), even with that ceramic resistor blown out. So my initial question is what is the point of the 10 OHM resistor? I don't understand its usefulness but I have a feeling if I just use it without that resistor then I'll be hurting something.And while we are here, concerning the element labeled "unsure of what this is". What could this be? It's mounted on the front of the motor, which would be submersed in water. Im assuming it requires a lot of heat sinking, but it's potted in there and I'd probably ruin it trying to get to it. Anyone have an idea of what it could be?

author: Ian.M
author_rank: Super Contributor
timestamp: December 03, 2017, 08:32:16 pm
content: The potted module is the speed controller. Its got electronics in there, probably to rapidly chop the motor power to vary the speed, which is why it needs cooling.Without a schematic for the speed controller it is impossible to know what the 10R resistor is for. However it *may* be part of a protection circuit, so I would find a replacement of the same type, value and wattage. If you don't knoew the wattage, find the same value but physically larger.

author: StillTrying
author_rank: Super Contributor
timestamp: December 03, 2017, 09:22:59 pm
content: With such hefty resistors maybe X is a simple power device, take your pick which device or type!

author: imisswaves
author_rank: Newbie
timestamp: December 03, 2017, 09:46:39 pm
content: Quote from: Ian.M on December 03, 2017, 08:32:16 pmAaah, I figured that was it but I thought the potentiometer was doing the speed controlling but now I see how thoughtless that is! The potentiometer is just sending the speed controller a voltage which it is translating into a motor speed, right? So the speed controller is just intermittently pulsing the battery power to the motor based on that voltage. That makes way more sense I knew I was missing something.Now another question.. if it is a protection circuit, how does that work?When the motor is switched on, doesn't current always flow through that resistor? So say the speed controller dies, the motor would still run without it right?

author: Ian.M
author_rank: Super Contributor
timestamp: December 03, 2017, 09:49:51 pm
content: The resistor may be there so that if the pot goes momentarily open circuit (e.g. due to a worn or contaminated spot in its track), the motor doesn't go to full speed. Unless you suspect it was a hack job by a previous owner, you should reinstate it as it was.

author: imisswaves
author_rank: Newbie
timestamp: December 04, 2017, 02:55:11 am
content: Thanks so much for the breakdown Ian.M everything makes much more sense.I will be replacing with a like resistor

author: mikerj
author_rank: Super Contributor
timestamp: December 04, 2017, 09:14:43 am
content: What's the resistance of the potentiometer (at full scale)?