Bridgeport VFD Suitable Speed Pot

Keith, 10k linear is ideal although a bit either way won't cause a problem (4.7K, 22K).

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That seems like it might be something that's useful to know. Does a

9-wire single-speed have centre-tapped windings? How is it wired for star or delta?

Dave

The 9 wire motors are a US abomination due to their supply being part

110volt, part 220 volts and part run off 139 U2 batteries in series.

No joking, part is centre tapped and the other part are separate coils to allow them to use all these voltages. Judging by the posts from the States about letting the magic smoke out, usually all three voltages together.

Selection of these correct connections is like trying to guess the away draws in the Scottish Premier league.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

Duncan, many thanks for the information and luckily it appears I already have a suitable pot here so a few pence saved.

Dave, I don't know much (anything!) about electrics at all so can't answer your question other than point you in the same direction that John pointed me. The link to wire these 9 wire motors from a low voltage VFD is here:

My wires are similarly marked so hopefully it will just be a wire up and switch on job. I hope the "magic smoke" that John talks about stays where it should be as I feel it could be expensive if it escapes.

Best regards

Keith

Never done it with a mill, but have done it with a lathe. Hopefully not teaching granny, but I'd get a ten turn pot if you can - a single turn job is too sensitive.

Norman, thanks, certainly not "teaching Granny" here, I know very little about electrics. Looking at the RS page they bring in another complication of ?W, I assume that a low power requirement would be OK for this application? I see they do 3W 10 turn 10K linear for about =A38 if one of those will do I'll pick it up tomorrow with the VFD.

Thanks again Norman

Best regards

Keith

jontom snipped-for-privacy@hotmail.com wrote: ... snipped

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Thanks Keith! I need to draw that out, but it looks like they parallel windings for delta and put them in series for star; not too strange really. Mmm, is "sudspumpwater" the new name for M1J25? :-)

Dave

The thing to bear in mind with a multiple turn pot is that you don't know what it's set to just by looking at it. I debated this one with myself when converting my lathe. My mill has an ordinary single turn pot, it does the job OK, but the lathe speed seems more critical - plus I have the drive set for a wider speed range than on the mill. I decided to go for a 5-turn pot (less common), as it's not too tedious to wind it to one end before starting. I'm happy so far with that arrangement

Cheers Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

Take a look at Dial Mechanisms in the aRSoles catalogue - they do a whole range of them: typically RS 509-973. They also have the advantage of being able to lock in position.

Bob

Tim, Bob thanks for the comments I hadn't thought of the starting setting at all. I am considering the need for a spindle rpm gauge if I can find a suitable (cheap) system but that won't help if I don't know what I'm going to get when I push the start button. I still remember the thickear I got from my (politically incorrect but very effective) instructor when I had started a Bridgeport at top speed with a large flycutter set up. One of my "friends" had decided I needed top speed when I was having a break (long one no doubt). The wind (fence blown down) and rain has kept me from RS so still got time to think about what I need.

Best regards

Keith

You can get knobs that are geared so you use a single-turn pot but you have to turn the knob five, eight or ten times in order to cover the range of the pot. They usually also have an arrow or pointer or something to indicate the setting of the pot.

You can also get ones with (mechanical) digital displays inbuilt, but they would probably not be suitable.

One other possible advantage of a multi-turn pot is that they tend to be more robust than single-turn pots - but a higher wattage (say 2W plus) pot will also tend to be robust.

Peter, thanks another point the old brain hadn't clicked to this morning, 10 turn pot and 10 turn knob would make for some very sore fingers!! I will really need to try and wake up these days.

Best regards

Keith

Why was a 10 turn pot suggested I missed that !

I've always used single turn, but made sure the knob fitted to it was a large enough diameter to give not too coarse an adjustment.

Just don't use a LOG pot! That would be fun.

Wayne...