Pot Question

[Damifino]

:laughing: I know guess how many views vrs replies, I have a Delta GR450 bench grinder. I purchased new and liked the variable speed control. 1725 - 3450 rpm.

Went to sharpen some tools and it ran at 3450 or higher, when I try to adjust speed control, no difference.

Took it apart and the pot (potentiometer) fell apart. It's a 3 wire that goes to a black box inside the grinder.

Checked all over online for a replacement delta pot, no longer available. With that being said ebay has quite a few with different ratings and am not sure which I would need.

Motor is 5 amp. Induction motor so am stuck with getting a replacement pot if possible.

 

[cjoffutt]

This place claims they can get it:

Delta Sensor #DEL-908960 - Tool Parts and Accessories - PartsWarehouse

might be worth calling to see if it's accurate or not.

 

[radios1]

take a picture so you know where the wires go, unsolder the pot, and measure the resistance on the outside terminals with an ohmmeter, that will give you the value you need for the new pot..

 

[workinonit]

Does the pot have a number on it or a resistance value. You need to know the resistance and wattage and you can get a replacement if all else fails.

 

[Damifino]

This place claims they can get it:

Delta Sensor #DEL-908960 - Tool Parts and Accessories - PartsWarehouse

might be worth calling to see if it's accurate or not.

Thanks... I called them and what I understand that would be for the whole thing, I only need the pot, he's going to check if that's available The one's I saw on ebay are around 5.00 or less

 

[Damifino]

Does the pot have a number on it or a resistance value. You need to know the resistance and wattage and you can get a replacement if all else fails.

No numbers anywhere.

 

[Damifino]

take a picture so you know where the wires go, unsolder the pot, and measure the resistance on the outside terminals with an ohmmeter, that will give you the value you need for the new pot..

It's in 2 pieces, don't think I could get a value.

 

[workinonit]

Does it go to some sort of board or electrical device or is it in line with the power that goes to the motor? Some pics would be good.

 

[Damifino]

Does it go to some sort of board or electrical device or is it in line with the power that goes to the motor? Some pics would be good.

Yes it goes into a circuit board inside of unit, I haven't removed that because when I took front panel off to access the pot it came out in 2 pieces. This would tell me it's the pot that needs replacing.

Will take some pics and post a little later, I really like this grinder but can't sharpen tools at 3450 without that dreaded blue steel color.

 

[workinonit]

If it goes to a circuit board it's a low wattage pot. Probably small. just need to figure out the resistance. If it's still intact enough you can measure it.

 

[workinonit]

Definitely low wattage. I would think there would be some number on that shell somewhere. If not you will need to locate a drawing for that grinder.

 

[Damifino]

I have looked all over pot...no numbers, nothing. I guess my next move is to gut it out and see if any values are on pcb. I cut the wires on the back half and tabbed together. Got nothing throughout range.

Next step is guttin it out, will keep you posted and thanks for everyone's guidance.

 

[CobyRupert]

Can you measure the speed pots resistance?
If near zero, it’s probably used with AC voltage. If, not near zero, and variable, it could be ac or dc.
Last ditch would be, with 3 wires unhooked, to start up machine and measure what the voltages are between the 3 wires.
Or look to see what voltage the power supply to the circuit board is.
I think 0-5vdc, 0-10vdc, 24vdc, 24vac are common “control” signal voltages.

 

[Damifino]

Got the pcb out, the connector from the pot plugs in as shown, no values shown that I saw.

 

[CobyRupert]

I should of said what is the voltage supply ON the circuit board, instead of TO the CB. It’s probably not 110V.
I mean the voltage in the wire to the pot.
Typically you can think of a pot as an impedance (~resistor) connected across 2 wires. For example: Let’s say one wire is 10 volts, the other is 0 volts (a ground reference). The impedance of the potentiometer now has 10 volts across it. The potentiometer moves/connects (“taps”) the third wire somewhere between the two ends of that impedance depending on where you turn the dial.
So with the dial turned all the way down, the third wire sees 10 volts. With it turned all the way up, third wire sees the 0volts. With dial turned in the middle, 3rd wire sees 5 volts, 1/4 turn =2.5 volts, 3/4 turn = 7.5 volts etc.. Always between 0-100% of the “control voltage” being used.
So, in this example, the input to the circuit board on the third wire is somewhere between 0-10V. The other two wires supply the 10V and 0V reference.
You need a potentiometer rated for the correct control voltage.
If you have that, almost any potentiometer will give you the 0-100% input on the 3rd wire.

 

[CobyRupert]

What I call the third wire is called “(2)” in this diagram

 

[Damifino]

Thanks Coby, so if I do what your post #14 instructs, this should be the info I need?

 

[CobyRupert]

Well...without specific info on the existing potentiometer or the circuit board (do you have any info on the circuit board / variable speed drive?), it’s the only way I can think of to get information that gets you closer to a replacement.
Short answer: yes.

 

[CobyRupert]

Do you think your grinder uses same pc board and pot as this one?:

http://s3.amazonaws.com/dpec/assets...96/23-196 6-Inch Grinder Parts List Rev 9.pdf