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Single phase to 3 phase motor conversion.

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Rodney Markham30/05/2020 17:50:22
8 forum posts
4 photos

Thanks Dave,

I'll dig out some lamps and connect in star (I presume)

Rodney Markham03/06/2020 17:58:02
8 forum posts
4 photos

circuit diagram.jpg

Rodney Markham03/06/2020 18:07:58
8 forum posts
4 photos

Above is the circuit diagram, very basic bit of kit.

The Clarke converter pointed out by Dave, looks to like the converter starts up with one set of capacitors and then switches over to more or whatever.

I have connected 3no. 60Wh filament bulbs, 1 gets over 300v the other about 85v (according to my multi meter)

The 100 -124 Mf capacitor is a motor start, my multi meter on capacitance range only gives me a nF reading, the 8Mf read about 7 and a bit.

I haven't put my meter across all the other capacitors, has anybody got any better suggestions?

Robert Atkinson 203/06/2020 18:42:02
644 forum posts
16 photos

Well that circuit applies 180 degrees to two phases (should be 120) and about 90 to the other. not an ideal situation.
The capacitor that reads in nF range is faulty. The 8uF are about right, tolerace is tpically +- 10% and normally under. Note that it's not just capacitance and basic voltage rating that matter when replacing. It must be rated for motor starting applications.

Robert G8RPI.

Rodney Markham03/06/2020 20:30:56
8 forum posts
4 photos

That's helpful Robert, the capacitor that reads nF is only brought into circuit when the boost button is pressed.

This capacitor has the following no. 092A100B250BD4A, they are on ebay for £50.00! if I was sure it's the solution I'd go for it

Rodney Markham03/06/2020 20:55:08
8 forum posts
4 photos

Farnell part no. 2759872 is a 100uF 220vAC for £4.74 would that work?

Still confused that this is only in circuit when he Boost button is pressed

Clive Foster03/06/2020 20:58:10
2204 forum posts
73 photos

Boost button forces a large phase shift on one leg to get the motor moving against a load. Off load the motor may well be able to start without the extra capacitor in circuit.  Even with the boost such converters are usually only able to start the motor under modest loads.

£50 sounds a lot for a start capacitor. £15 - £20 is more usual.

But these converters are brutally hard on the start capacitors. Especially if they don't have an automatic control relay to bring the start capacitor into and out of circuit. Robert probably has the figures but modern, affordable, ones are very short term rated, maybe 30-40 seconds from turn on to pop.

Short term runs with lots of stops & starts is going to kill one quite quickly.

Time to pull the plate off the motor and investigate if it can be re-wired from star to delta. If it can invest in a VFD and unload the converter "spares-repair" via E-Bay.

Eaton DE-1 is easiest VFD to do a basic install on if you just want to run the motor at its set speed (or can do without a spiffy display) as it basically just works off a switch like the usual contactor controls. Anything with an Inverter Drive Supermarkets easy set-up guide is nearly as easy to install but you will probably need some extra bits.


Edited By Clive Foster on 03/06/2020 21:16:43

Rodney Markham04/06/2020 07:03:25
8 forum posts
4 photos

The task in-hand is to run a little milling machine from a single phase supply, attached photos may help.

Robert Atkinson 204/06/2020 08:21:40
644 forum posts
16 photos
Posted by Rodney Markham on 03/06/2020 20:55:08:

Farnell part no. 2759872 is a 100uF 220vAC for £4.74 would that work?

Still confused that this is only in circuit when he Boost button is pressed



That capacitor is maginally rated on Voltage, 3 minutes on 220 V or 1 minute at 300V. UK mains is nearer 240V than 220V depending were you are. As Clive says they have very short life. Ideally the capacitor should be non polarised but these are larger and more expensive. The one you linked is effectiviely two 200uF polarised (electrolytic) capacitors conneted in series positive to negative.

A better choice wold be a film capacitor 100uF 450 V at £25

Better again would be two 60 uF 450 V at £17.50 each wired in parallel (more capacitiance, less current through each capacitior.

Best of allis wire for Delta, fit a VRD and weigh the transformer from the old converter in for scrap.

Robert G8RPI.

Edited By Robert Atkinson 2 on 04/06/2020 08:22:31

Clive Foster04/06/2020 09:57:49
2204 forum posts
73 photos

Thats a nice little milling machine, AEW Viceroy / Horizon. The motor in your pictures will convert to delta for a VFD just fine.

I see why a converter was used. Two motors. 2 hp on the spindle and 1/3 rd hp on the power feed I think.

Conventional wisdom is that VFD boxes should be used one per motor to avoid large power variations, switching issues and things likely to get their electronic knickers in a twist. More so with modern ones which tune themselves to the motor as an effective way of improving the speed range over which the power holds up well.

However I think it possible that my favourite, for simple installations, Eaton DE1 series can cope with two motors as they are supplied as a simple alternative to old style contactor controls and are more tolerant of "less than ideal" fitting. Its possible that the 2.2 kW version (£140) has the overload capability to handle the power feed motor being switched in with the main motor running otherwise you'd need the 1.5 kW version (£121) for the main motor and the 0.25 kW (£65) version for the power feed. Always assuming the feed motor can be connected delta too.

See **LINK** for the Eaton range.

I'd contact Inverter Drive Supermarket and ask what they suggest. I've no affiliation but have had good service myself and they have a stellar reputation for helping folks who don't know much about such things to make a good choice.

If going for two VFD boxes you may be able to do it more cheaply but best to avoid anything that doesn't have a proper English manual or UK native back up. IDS do wonderful easy set-up guides for some of the ones they sell.


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