electrical noob needs a potentiometer help

road

road

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My Craftex mini lathe uses a 4.7 k pot with a switch for speed control.
The splined post broke off the pot.
So I need to change it.

Being as cheep as I am,, A local electronic shop has 5k pots w switch for $3.99 & no shipping costs.

would there be any concernable difference in the 5k as to the 4.7k ?

As long as a 5k keeps the rpm stable from low to mid range, even if the rpm ramps up quicker at the hi end of the 5k it should be within range.. I hope..

I hope I stated that right..

lmao
 
Road you are only talking about a 6% increase in resistance. It may not be as sensitive as it was with the 4.7K,(instead of 1 rpm change with a tiny turn, maybe 1.5 rpm) but will function quite nicely.
 
I think most electrical circuits and components have a design tolerance like +- 5 or 10%. I imagine you are well within the tolerance of a new part. I am no EE though :)



bedwards
 
If you consider how a pot is normally connected to the circuit, I wouldn't expect any noticeable difference. In a 3-wire connection, one side is connected to positive power, possibly 5 VDC. The opposite end of the resistance is connected to the board ground, or 0 VDC. The middle terminal is the wiper. It slides around the resistance, but it isn't measuring resistance. It's sending a variable voltage into the circuit to control the speed.

The only difference from using a slightly higher overall resistance will be a slightly lower available current. If the circuit is set up to respond to voltage, not current, it should respond exactly as before. In a linear pot (not audio taper), turning the pot 50% will pass 50% of the available voltage into the circuit, whether it is a 4.7k or a 10k. Make sure you get linear.
 
The difference in maximum resistance should be insignificant. Be aware that potentiometers commonly have two different characteristic responses. An audio taper is logarithmic while a linear taper is, er, linear. It's most likely the original is a linear taper. Getting a replacement with a different taper will work but will change the "ramp rate" you referred to.

The replacement should have at least the same power capability (measured in watts) as the original.
 
The 5 K will be just fine. If you really wanted to be exact you could just add an additional resustor and drop it to 4.7, but whats the point. As long as it is rated for the wattage or above you will be just fine with no discernable difference in how it works. Good call to check befpre you butched just in case it wouldn't work for some reason or other.

Bob
 
Got my new 5k pot today.
I got 3 for $7.00 (future project in mind)

I had it all rewired before dinner.
It works even better than before, nice n smooth.

While I had the control box off I made a plastic cover for the board to protect it from swarf n chips and added some cooling holes too.
 
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