Help please selecting a relay?

involves

current

Tim,

In the first position, what is turned 'on' (if anything) before you move through to the second position and pull the contactor in. If nothing then surely the two positions are redundant and a single one would give the same logical function

AWEM

Andrew

Not so. The first position switches on the supply to the contactor, the second energises it (& it latches on). Think of it in terms of on & off contactor push-buttons. The first position is the NC 'off' button, the second is the NO 'on' button. Moving the lever to the central 'off' position has the same effect as pressing the stop button. I *could* just wire the first position switch direct to the inverter, but it would be rather too easy to switch the thing on when you didn't really want to. Much safer to have to push it against a stop before something happens. Also I have a near-identical machine which will still be on the original controls, & would prefer to keep them as similar as possible in operation to avoid confusing my tired old brain

Cheers Tim

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As the signal to the inverter drive will be low voltage mAmp, why not fit a judiciously placed microswitch to do the reversing?

Tom

This may not be the best solution, but it is one:-

RS Stock no. 256-5262 DPCO multimode relay,10A 230Vac coil in a RS Stock no. 215-5433 8pin DIN & surface socket for MT2 relay

Wire the first set of contacts on the switch between the live and the common of one of the pairs of contacts. Wire the Normally open contact to one side of the coil. Wire the other side of the coil to neutral.

Wire the second set of contacts on the switch across the Normally open contacts.

This means that the relay will close when you push the switch to the second position and will hold closed until you go back to the central position.

Use the second set of contacts to talk to the inverter. Lather, rinse and repeat for the other direction.

Mount the relays and holders in the existing control box or in a DIN rail switch box from RS or your local sparky supplier.

You may also be able to do exactly the same thing by going to your local electrical or heating wholesalers and getting a couple of DPCO mains relays.

Mark Rand RTFM

Work for a company with defence contracts by any chance, Mark? :-)

Tom

We have built the odd power station :-)

But this setup is not that much different to my domestic central heating system (give or take the odd 120 tons of slightly enriched uranium :-)

Mark Rand RTFM

Going on what one hears about UK domestic central heating systems, reliability and/or efficacy are seldom mentioned in the same sentence..:-)

Tom

Thanks Mark, exactly the sort of thing I was after. I didn't find those or anything similar, despite trying several different searches on RS.

There's space on the panel beside the inverter. The whole lot *should* just about go onto the original panel inside the back of the lathe base, by dint of replacing the original 2" long standoffs with 1/2". I'll have to put some louvres inthe (cast iron) door, though, to allow cooling.

I'll ask at the electrical place this morning, I'm going there anyway.

Cheers Tim

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There's nothing wrong with the existing, properly engineered, switch, except that it doesn't send the right signal to the inverter. I don't think replacing it with a microswitch would help.

Cheers Tim

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Andrew,I think this is Tim`s CVA lathe.If so the first position of the switch acts as a stop button would.i.e. it makes the holding circuit and the second part of the switch travel acts as the start button. I know you will understand but others may not. The first position of the switch feeds power to the NO auxillary contact on the motor contactor,the second part gives a momentary signal to the coil thus closing the contactor and making the holding circuit throgh the now closed NO contact. Mark.

"There's nothing wrong with the existing, properly engineered, switch, except....." Perhaps you might elaborate on what sort of "signal" your drive needs?

Looking at the manual of my drives:

"Detail of Remote Connection. (24v control max load = 200mA.) .... Terminal 7 "Forward/Reverse control input. Direction of motor rotation is reversed when this terminal is opened/closed. Change may be initiated while motor is running. This causes ramp down, change of direction and ramp up to set speed."

My suggestion only involves obtaining reverse and in this manner my brother's Mascot has been operating for about 3 years now. His is the older model that had direct online starting. I suppose it's about WSYL.

Tom

Not an option (so far as I can see) with my drive. There are two inputs, one for forward, the other for reverse. Yes I could arrange to switch directly between the two, I could just put an extra switch on the control panel to do that, but as I said before I wish to retain the functionality of the original controls.

WSYL??? What Starts Your Lathe??

Thanks Tim

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Tim,

I have a number of mains (coil) relays, if you haven't got one (or two) yet I can bring them up on Saturday.

Cheers

Peter

D*mn!! I've just got in from collecting some from the local wholesalers. Looks like the same item, give or take, that Mark suggested from RS, and pretty much the same price.

Re the other thread on converting motors - I went to the rewind people yesterday to try to scrounge/buy some suitable wire & sleeving, they offered to do the job for 30 squid. Deflation in action, it was 50 about 6 years ago! I decided to leave it with them. Collected this afternoon, they reported that, despite being clearly labelled as star wound, it was *already* in delta but with one phase reversed. This is original Crompton wiring, apparantly the original motor fitted to the lathe circa 1978. Very strange. I don't know what happens if you wire a motor with one phase reversed onto the mains, but I know they don't like it when connected to an inverter. It was prone to tripping the breaker when trying to start in top gear (3000 rpm), which my other lathe doesn't, but that has a completely different control board to this one. I'll report later as to what happens when I connect it to the drive!

Thanks for the offer

Tim

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