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dryan

SPDT Switches

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Will some one make sure this circuit I've created will allow me to run each of the motors forwards and backwards? (Top two buttons control MOT1, bottom two control MOT2). Make sure there is no problem with pushing more than one button at once (make sure I won't short anything out).

Why do people solder ceramic capacitors across the leads of a motor?

spdt.gif

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Why do people solder ceramic capacitors across the leads of a motor?

 

This is usually for interference suppression.

 

Your circuit looks good. I personally would install an interlock that holds the paired switches from being operated independently and add a stop switch in series with each motor for an off fuction. This allows single function control and prevents two off postions from existing. :cool:

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yeah, the ceramics work as back EMF dampers, nothing more, in fact putting several (about 6 or 8) turns of wire in a loop around a ferrite material and put that inline with your motor will also stop alot of high frequency noise from the brush contacts in your motor :)

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Thanks for your input, though I'm not going to mess with the interlocks - the switches are momentary anyway; I can maybe see how it would help if they were the "push on, push off" type. I will probably add an shutoff switch in there though.

 

For the ceramic, the denomination doesn't matter much, as long as it is small... less than a micro-ohm?

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I've got cordless screwdriver motor (which has good torque), and when I connect the leads to my 6v power I get a fair number of sparks. Would a cap shorting the leads of the motor take care of this, or does the cap only affect the EMF/noise?

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it`ll only effect back emf at high frequencies.

you could try a ferrite choke coil, that will help a little :)

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just as an after thought, should you really be using 6v on an electric screwdriver motor? most are only rated at 3V max.

 

anyway, your spark problem, since your ctc diag shows that motors will be operated in both directions, if you use 2 diodes per motor, soldered back to back or front to front (makes no dif) and put that across the motor terminals, it`ll reduce the sparking considerably :)

I suggest a pair of IN4001`s per motor: T2------->]----[<-------T2 like that.

 

if you can get the ferrite choke for each motor, even better. but if not, the IN4001 PIV and FB will eliminate most of the back EMF for you :)

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http://www.right-tool.com/bldeas6valsc.html 6v Alkaline, 130rpm, 20in*LBs torque. :)

Though most other models have more torque, this screwdriver costs $8 at Walmart. It is cheaper because the manufacturer doesn't have to include rechargeble batteries and a charger. It does come with 4 Alkaline batteries, though.

 

My other Black & Decker screwdriver has 40in*LBs on 3.6v NiCad for ~$20.

DeWalt has 80in*LBs, but costs over $100; it runs on 7.2v.

 

Now that I see a picture of the 1N4001, I have plenty of those that I can desolder off some dissected electronics.

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fair enough then, it`s just most I`ve seen are about 2.4v or 3.6, and I`ve never seen one that takes AA alkaline sort? Coolness :)

 

well the back to back diodes will certainly do the trick for you anyway :)

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