Harrison M300 The rebuild

[ford34/2]

Harrison Manual 300

Free manual on Harrison Lathe user group. Has wiring about page 67/68 but doubt if its any good for you, sorry
Stan


http://f1.grp.yahoofs.com/v1/MA1VT3...f7inweWpgom2/Harrison_M300_Machine_Manual.pdf

 

[Tractor Man]

Were the old caps of a higher or lower value - if they were higher then that would account for the load voltage drop.

The pictures show that in your RPC the voltage is increased from 240v to 415v using a transformer. The transformer output provides 2 of the phases and then a start cap provides the third phase on start up, this cuts out and a run cap maintains the third phase.

So in theory unlike other RPC's that use a delta star switching system to step up the voltage within the motor (more complicated but no transformer needed) the L1 to L2 voltage (or transformer output) should stay at around 415v no matter the load (wihin operating limits of course!). However at 290v something seems very wrong!

Have you checked the transformer output voltage before it goes into the motor (on the transformer terminal block) just to insure the transformer is operating correctly.

I also see that there is a thermal overload in the RPC it might also be worth checking this as sometimes they can become faulty.

 

[Shox Dr]

Cheers Stan, unfortunately, there seems to be many different wiring layouts, The Pic Hareng posted of his board is similar but that's about it. And is different again to my wiring diagram

 

[ford34/2]

M300

in the unlikly event you aint got a manual, then its worth the download and 69 pages to print it off, all as you expect, + exploded diagrams.

Hope you get there.-- I know you will

Stan

 

[Shox Dr]

OK from the start. The RPC was bought with a fault, when I called transwave they said to replace the Caps as matter of coarse. This was done, it was then found someone had turned up the voltage on the timer. Also the contactor on the far right was faultly. After I'd done this it run the lathe no problem.

Old cap values

1x 35uf
2x 27.4uf

New

1x 35uf
2x 25uf

 

[Tractor Man]

Those cap values seem ok - the 2 x 25uf are obviously a bit low compared with the originals but would probaly not cause a huge voltage drop.

Thats interesting about the timer - what is it set at? Usually the start cap should cut out after about 2 to 10 seconds - if it stays on longer than this then the motor would get too much voltage on the 3rd phase which could cause it to heat up and ultimately fry the windings.

Is there an adjustment between minutes and seconds on the timer - is it set to minutes instead of seconds?

 

[Shox Dr]

It's a relay and shows voltage, and it's set for just over 200v. trips after less than 5secs

 

[Tractor Man]

That time period sounds about right. What is the range of voltages the relay can be set to?

Does the RPC start up correctly - how long roghly does it take for the idle motor to get up to speed?

 

[Shox Dr]

100v to 500v. Less than a second for the relay to trip, the contactor

 

[Tractor Man]

I'm just wondering if the RPC has some kind of voltage boost circuit - i.e when the RPC is under load from a starting motor a voltage sensing relay subs in another cap and providing a voltage 'boost'. The timer and relay combined sugests this is its function and that the start cap is just cut out by the releasing of the 'start' button'.

In the 10 to 15 seconds the lathes runs for does it get up to full speed - If it doesn't then it could be that this 'boost' circuit is not on for long enough.

You could try changing the voltage on the relay timer - start by turning it down a bit - if the problem is worse then that could be the issue. I wouln't turn it up first just incase something goes pop!

 

[Tractor Man]

Just had another idea!

You said the lathe slows down then the RPC trips - this could be due to the thermal overload in the converter being set wrong (bimetalic strip heats up and slowly breaks the connection - could cause slowing then trip!)

Make sure the amp rating on the overload matches that of the idle motor - should be around 10.5amps.

 

[Shox Dr]

Just reset it to 9.5amp, same thing, RPC vibrates, lathe slows, the then the RPC trips out

 

[Tractor Man]

I really can't think of anything else - I'm starting to get a feeling that the problem is in the lathe wiring not the RPC - something could be creating a short.

Is there an MCB or RCD fitted to the RPC output? You could measure the amps the lathe is drawing at the output of the RPC - if this is anything over around 5amps after startup there is a problem with the lathe wiring.

Have you any other 3 phase machines to test the RPC on and see if it works and the problem is with the lathe?

 

[Shox Dr]

Sorry no other 3ph gear. No MCB or RCD fitted. I've a clamp meter, do I need to be measuring each phase or all together

 

[Tractor Man]

Measure each phase to phase ampergage individually and see what the reading is - ideally they should be almost equal.

Fitting an MCB on the RPC output would provide a good indication if too many amps were being drawn and would trip before the motor heats up and the RPC trips = better protection

A 10 amp 3 phase MCB would be fine.

 

[Tractor Man]

Sorry, should have said you need to measure the amperage of each individual phase - not phase to phase...

 

[Shox Dr]

No Load
L1-L2 5.3amp
L1-L3 5.7
L2-L3 5.29

Underload

L1-L2 4.49amp
L1-L3 5.3
L2-L3 5.29


OK I've just just run the lathe, while taking the measurements the lathe slowed and stopped. RPC still runs all voltages and amps as listed. The lathe motor was warm.

Iam thinking the same as you, it's the lathe wiring?

 

[Shox Dr]

Sorry, should have said you need to measure the amperage of each individual phase - not phase to phase...

OK how do you do that then. If you hadn't guessed leccy is the work of the devil

 

[ford34/2]

Amps per phase

will your clamp on meter not measure each phase individually?

Or is it possible to wire direct into the drive motor, by passing all the lathe electrics??

Stan

 

[Tractor Man]

It seems like you've made the correct measurements anyway!! - sometimes depends on the clamp meter you using.

Those amp readings seem good - all very near to 5amps.

I agree that the problem sounds like it is with the lathe wiring as the RPC seems to be running at near constant amp values which suggests it is ok.

I think the next stage is to address the lathes wiring, I find the best way to work on machine wiring is to start with each individual parts of the circuit - motor, switches, contactors, isolators and supply feed. Then start with the supply input, work back and join everything together checking that everything works as you go.

You can test that all the contactors, microswitches etc are operating properly on the lathe bafore actually connecting the motor - this may help to locate any problems easier.

Also if possible I would replace the contectors on the lathe just incase there is a small underlying problem with them.

Like you say leccy really is the work of the devil