Possibly dumb question - Page 1
Forum section: electronics / beginners

author: Connecteur
author_rank: Frequent Contributor
timestamp: July 26, 2021, 05:15:45 pm
content: Is there such a thing as a flat plate resistor? One that you could tuck between an AA battery and the battery contact (in a battery holder) to reduce current? I'm trying to reduce the speed of an electric shaver.

author: AmnevaR
author_rank: Contributor
timestamp: July 26, 2021, 05:36:26 pm
content: Haven't seen anything like this. Perhaps you can cobble together a flat resistor using a little bit of nichrome wire between kapton tape?DIY kapton flex PCB

author: bob91343
author_rank: Super Contributor
timestamp: July 26, 2021, 05:37:32 pm
content: Or a diode?

author: tooki
author_rank: Super Contributor
timestamp: July 26, 2021, 05:50:13 pm
content: Bear in mind that in many modern devices, the power isn't connected directly to the motor, so putting a resistor inline may or may not have the desired effect.Also consider the power dissipation in the resistor, since a motor may be pulling significant current.

author: Connecteur
author_rank: Frequent Contributor
timestamp: July 26, 2021, 06:50:50 pm
content: Quote from: tooki on July 26, 2021, 05:50:13 pmI'm sure it's just a direct connection. There is only a slide switch and no indicators. I suppose a quarter-watt resistor inline with the motor would work.

author: gbaddeley
author_rank: Regular Contributor
timestamp: July 28, 2021, 11:44:45 am
content: How about a small piece of thin double sided pcb, with a leaded resistor soldered across each side?

author: Zero999
author_rank: Super Contributor
timestamp: July 28, 2021, 12:43:31 pm
content: Quote from: gbaddeley on July 28, 2021, 11:44:45 amOr a hole drilled in it, with a 603, or 402 resistor inside, connecting the two layers. You will probably need several, to keep the power dissipation per resistor low enough.

author: Circlotron
author_rank: Super Contributor
timestamp: July 28, 2021, 12:49:56 pm
content: Or maybe a 1.2V NiMH battery instead of a 1.5V alkaline?

author: Zero999
author_rank: Super Contributor
timestamp: July 28, 2021, 01:27:28 pm
content: Quote from: Circlotron on July 28, 2021, 12:49:56 pmThat's unlikely to make any difference in a high current application, because NiMH cells have a much lower impedance, than alkaline, so will drop much less voltage under load. You'll probably find the voltage across an alkaline and Ni-MH cell are very similar, given a decent load current.

author: Connecteur
author_rank: Frequent Contributor
timestamp: July 28, 2021, 03:29:51 pm
content: Quote from: Circlotron on July 28, 2021, 12:49:56 pmIt's actually a lithium AA with a nominal voltage of 4.2V. The trimmer was running too slowly and stalling when using the 1.5V alkaline it was designed for. I wanted to boost the torque and speed with a lithium cell, but it's running a bit too aggressively and I want to reduce it's running speed to about half.

author: Zero999
author_rank: Super Contributor
timestamp: July 28, 2021, 03:39:24 pm
content: Quote from: Connecteur on July 28, 2021, 03:29:51 pmCrack it open and put a PWM circuit inside it. Job done.

author: Circlotron
author_rank: Super Contributor
timestamp: July 28, 2021, 09:55:14 pm
content: A batterizer with a buck converter instead of the boost converter would be just the thing here!

author: james_s
author_rank: Super Contributor
timestamp: July 29, 2021, 04:26:57 am
content: Quote from: Connecteur on July 26, 2021, 06:50:50 pmI doubt it, not without burning up. The motor in a shaver if it was designed to run from 1.5V is probably going to draw close to an amp if not more. PWM is the way to go if you want to control the speed of a DC motor. Personally I would probably shop for a better shaver.

author: Zero999
author_rank: Super Contributor
timestamp: July 29, 2021, 07:32:54 am
content: Quote from: james_s on July 29, 2021, 04:26:57 amIt's possible the motor is designed to work up to a much higher voltage than 1.5V. It's quite common to see motors rated for 1.5V to 4.5V operation, especialyl the cheap ones used in toys, like the product linked below.https://www.rapidonline.com/trumotion-3v-12200-rpm-miniature-motor-37-0146If so, running at a higher voltage is likely to shorten the life of the gears and blades, rather than the motor.A PWM circuit can be made with a cheap microcontroller or couple of logic gates, a transistor and a freewheeling diode.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 29, 2021, 07:35:44 am
content: put a diode or 2 or whatever you need series with that motorfor the resistor, first you need to calculate resistor value and power, otherwise you will got a heating platelet's say you wanna reduce at half the motor power, that means that power goes into the resistor, what wattage you get for him? do the math first