Wiring 240V motor

[garrardgfgParticipant @garrardgfg]

I’m after some help understanding the wiring of a 240v ½ HP electric motor which doesn’t behave quite the way I was expecting.

I recently dug out an old small ¼ inch chuck pillar drill which I bought second hand as a stop gap about 30 years ago while renovating another small pillar drill. I’ve used it occasionally ever since, but recently decided to clean it up and put it to a new use. The motor is about ½ HP and I would guess is about 60-70 years old and painted a standard grey. Unfortunately, the motor has no plate on it or any markings at all. The wiring and plug needed replacing and when uncoiling the insulating tape over the connections I noted that there were 4 wires coming out of the housing in two twisted pairs.

Yellow and Black (These were originally connected to 240V and used for years and Red and Black (These were unconnected and insulated)

There is no external capacitor or evidence of a capacitor in the casing and when switched on with the yellow and black connected to 240V the spindle historically always rotated clockwise (looking at spindle) from a static start. There is no sound of a centrifugal switch operating.

I put a meter across the two pairs of wires to try to understand what was going on and got the following

Yellow – Black = 14.5 ohms

Red – Black = 21.0 ohms

So two independent windings as there was no continuity between the two windings or with the chassis.

I connected the yellow – black to 240v again and checked the rotation speed = 1490 +/- 3 RPM in clockwise direction, but I also found that I could get it to rotate in either direction if I spun the motor first.

I connected the red – black to 240v and measured a rotation speed of 1490 +/- 3 RPM. However, I stopped the test quickly as there was a smell of hot windings and the casing was warm to touch. When it had cooled down I quickly checked rotation direction and could get it to rotate in either direction if I spun the motor first.

Ideally, I want the motor to be reversible and ultimately, I want to put some speed control on. Can anyone tell me what type of motor I have? Why it runs on just two wires with no apparent capacitor or use of a start coil? What the red-black terminals are (?120V?)? if the hot winding smell on the red-black winding is just 70 years of non-use? Whether I could make it reversing and which terminals I should be connecting? If there is likely to be something missing on the motor.

[Robert Atkinson 2Participant @robertatkinson2]

Sounds like he red-black pair are a start or run winding. Were you getting adequate torque when running on the Yellow black pair?

As it is a non load start you could use a small, say 4uF, capacitor in series with the red black pair to ensure starting in a given direction. Reversing the connection of the start connection will reverse the direction.
This is completely sub-optimal but it does not appear that your application is perfomance critical.

Robert.

[SillyOldDufferModerator @sillyoldduffer]

If the black wire on the yellow winding is dark blue, and the motor is British, then this is probably a “capacitor start and run” motor.   (Guessing: there are at least 5 different types of single-phase motor.)

Try this circuit:

The 4uF capacitor is as suggested by Robert.  The optimum value depends on the motor and is unknown, so a guess is necessary.   Reversing done as he said.

Early single-phase motors didn’t bother with start windings.  Instead the operator pulled a rope wound round the pulley to start the motor, in either direction. Went out of fashion because rope starts are inconvenient and hazardous to both operator and motor, but it works.

I’m worried why the start winding was disconnected and insulated.  Maybe, in the past, the capacitor failed short circuit and burned out the start winding.  Then someone kept it going by disconnecting the damaged winding – a bodge.   If so, I’d replace the motor – without the start winding, it won’t start reliably or reverse.

Old motors can be dangerous because ancient faulty insulation causes shocks and fires. Replace if the motor gets hot or causes ‘tingles’. Ideally test with a megger – ordinary multimeters can’t detect leakage.

Good luck,

Dave

 

 

[Clive FosterParticipant @clivefoster55965]

The wiring suggested by Dave is for a permanently connected capacitor motor. Different animal to a Capacitor Start and Run which has two capacitors, one for start and one for run.

As I understand things the run capacitor effectively turns it into a “sort of” two phase motor and is usefully more efficient than a common single phase motor at its rated speed and load.

Unfortunately the fixed single capacitor variety are usually tightly tuned to a specific speed. Generally they don’t like varying loads or speeds. Starting torque isn’t great either. The permanently installed capacitor is tuned to give a phase shift for maximum efficiency at the operating rpm, not to boost start.

Usually found on fans and similar devices with predictable loads and modest starting torque needs.

I’ve run a couple on drill presses before and found they tend to get very hot if the speed and load shifts outside its rated value. Melted the second one when I left it running (bad boy!) off load for a couple of minutes whilst distracted. Got way too hot to touch and never worked well again. Shame because it was really nicely engineered with a smart cylindrical body and spider mount. Clearly a fan motor. Very cheap from Bulls surplus in Croydon.

Clive

[noel shelleyParticipant @noelshelley55608]

As has been said, one colour standard was as shown by Dave, red/black run windings + blue /yellow start windings. The start runs it up and dictates rotation,then the run keeps it going. What you have there sounds suspect ! for light (1/4″) work it may have worked.

I think I would give up now and find another motor.  Noel.

[duncan webster 1Participant @duncanwebster1]

I once had a motor with a burned out centrifugal switch, so I wired it up with 2 contactors, while the start button was held down both start and run windings were energised, when released the run winding continued until the stop button was pressed. The run contactor was a start/run with overload protection.

The first post implies that the motor self starts without the presumed start winding connected, which I don’t understand

[duncan webster 1Participant @duncanwebster1]

I also put a capacitor in series with the start, value advised by Crompton Parkinson who supplied the motor. It was so old only one of their chaps knew anything about it, but they actually sent me a cap gratis. You don’t get customer service like that from China

[garrardgfgParticipant @garrardgfg]

Thanks for all your comments. Your questions made me look again at the wire colours, and I can’t see any hint of blue, they both look black to me unless the colour has oxidised over the years (see picture).

 

 

 

However, in the bright sunlight I did notice very feint inscriptions on the casing. (Only goes to show you can never look at something long enough!). I finally managed to read these as follows:

General Electric

Model 5KH29 GG16A     HP1/3    PH1

CY 60/50   Volts 230    Amps 1.5/1.85

Temp Rise 40C          RPM 1725/1425

Time Rating Cont                   CODE R/S

PTU      GFJ 1445                 Made in USA

I did a quick google search and found the following:

 

5KH29GK6845 Marathon Electric Thermally Protected AC Motor (Motor looks very similar to mine with 4 wires red, black, yellow, blue)

The Marathon Electric 5KH Series Thermally Protected AC Motors come in a variety of shapes and sizes. This series offers several different horsepower options, as well as thermal protection. The 5KH series comes with permanently lubricated bearings.

The GK6845 is 1/8HP 125V so not the same., but the series looks identical in construction and appear to be obsolete

So with respect to my motor

– its got all the power I need on its starter winding for what its used for.

– With it rated as 240V it suggests its not dual voltage so ‘over heating’ may be non-use of main winding for years? or possible internal wiring issue?

– Do any of the new facts change the advice you have all helpfully given me?

– Presumably if I wired is as the very helpful diagram, but left out the run? capacitor for the present it should run OK if its going to run (assuming I might need to give it a bit of rotation.

– Is it OK that there is no start capacitor? ,

– is it OK there is no centrifugal switch to take out the start winding once its rotating?

Many thanks

 

[Robert Atkinson 2Participant @robertatkinson2]

Looks like it was designed for a centrifugal switch. You must have either a switch (could be a manual pushbutton) or a capacitor in series with the start winding or it will burn out. A timer is is also a possibility for the start winding switch.

A new (old) motor might be easier.

[MacolmParticipant @macolm]

Another configuration sometimes encountered is a start contactor, which usually has a solenoid of a few turns in series with the main winding. Due to a strong spring, only the initial “not yet” running current can move the armature. This presses a contact transiently to energise the start winding.

It avoids the need for a centrifugal switch, but no idea if any are readily available. Most likely used on (larger) refrigeration compressors.

[BazyleParticipant @bazyle]

The purpose of the (small) capacitor in some motors is just to give it a nudge in the right direction and does not contribute significant power when running. Applying the capacitor to the other end of the winding will nudge it in the other direction. Residual magnetism in the rotor can provide the bias that is currently causing it to self start.

[Macolm]

On Macolm Said:

Another configuration sometimes encountered is a start contactor, which usually has a solenoid of a few turns in series with the main winding. Due to a strong spring, only the initial “not yet” running current can move the armature. This presses a contact transiently to energise the start winding.

It avoids the need for a centrifugal switch, but no idea if any are readily available. Most likely used on (larger) refrigeration compressors.

Good point Malcolm, I’d forgotten about those. This is a random example from ebay:
https://www.ebay.co.uk/itm/226800138059
As you can see they are available for smaller motors.
Be wary of the modern “PTC” versions. These connect in series with the start winding only. PTC stands for positive temperature coefficient and describes a type of temperature dependent resistor a.k.a thermistor. When cold they have low resistance so in this case allows starting current to flow. The current heats the thermistor and the resistance goes up. reducing the current. The current reduces proportionally with the resistance but the power and thus heating increases with the square of the current so the device quickly reaches an equilibrium at much lwer current. So far so good. The problem is that it has to cool down to reset between stopping and starting. This is not good for frequent stop start operations liek a drill. There is also an issue with the intended application in fridges and freezers. If you gat a short power interruption when the compressor is running the PTC does not cool and the motor stalls when power comes back on.

Robert.

 

[Richard SimpsonParticipant @richardsimpson88330]

Just to mention out of interest rather than offering any form of advice, I remember in my college days discussing the Star-Delta starter.  This was for three phase systems.  The motor started up with the coils connected in a Star configuration, which gave better torque characteristics but then, when up to speed, the starter unit changed over to connecting the coils in a Delta configuration, which gave a more efficient characteristic for normal running.

As I said for three phase supply but just an interesting aside.

[garrardgfg]

On garrardgfg Said:

… 

So with respect to my motor

– its got all the power I need on its starter winding for what its used for.

Correct, and it’s continuously rated (able to deliver power without needing to stop periodically to cool down.)   Except substitute “run winding” for “starter winding”,

– With it rated as 240V it suggests its not dual voltage so ‘over heating’ may be non-use of main winding for years? or possible internal wiring issue?

over-heating is always bad.  Either due to being wired incorrectly (missing or wrong capacitor), more likely due to internal damage – burnt insulation, insulation failed due to old age or chafed, stuck centrifugal switch (if fitted)

– Do any of the new facts change the advice you have all helpfully given me?

Not so far.  But, we don’t know for sure what sort of motor this is, and there are several possibilities.  I don’t understand why the yellow/black winding was disconnected:  either the start winding is faulty, in which case rewind or replace it.  Or it has a jambed centrifugal switch, which it might be possible to restore or replace.  Given this is an elderly US made motor, spares might be unobtainium in the UK.

– Presumably if I wired is as the very helpful diagram, but left out the run? capacitor for the present it should run OK if its going to run (assuming I might need to give it a bit of rotation.

I expect so, but only you are in a position to find out.  As the exact type of motor hasn’t been identified, we can only guess.  As I said, rope-starting single-phase motors used to be a thing, but it died out because it can catch the operator, and, if he’s too slow, cook the motor.  Also a time-waster – much more convenient if the motor starts automatically when switched on.  But it’s and option if you want to keep a damaged motor in service: personally, I’d cough up and replace the motor.

– Is it OK that there is no start capacitor? ,

Not really.

– is it OK there is no centrifugal switch to take out the start winding once its rotating?

Maybe, see objections to rope-starting above, but it should work.  We don’t know if this motor has a centrifugal switch or not.  If present it will be fairly obvious at the back-end of the motor if the casing is removed, and might be visible through the cooling slots:

 

…

 

Unfortunately, I couldn’t find any information as to the exact type of motor or how it is wired.  Closest is this blurred diagram:

Which I think translates to this, but let me emphasise this is more guesswork:

And a problem with the diagram it causes overheating.  Could be because the diagram is wrong, or, the motor’s start winding is burnt out.

Mucho confusion about single-phase motors!  Clive picked me up for saying I thought you have a “Capacitor Start and Run” motor,  If so, my book is wrong!  “Capacitor Start and Run” is not the same as “Capacitor Start and Capacitor Run”!  Modern parlance may be clearer: what I call “Capacitor Start and Run” is a PCM (Permanent Capacitor Motor),

I prefer to understand and explain, if I can, rather than rely on hazy memory and experience.  Electric motors rely on two magnetic fields repelling or attracting at the right time so that a rotor turns.   Quite easy to arrange with a DC motor, or a 3-phase AC motor, rather difficult in a single-phase motor.  A single electromagnet flips North/South 50 times per second so the rotor doesn’t move, even though the electromagnet induces current in the rotor coil.  The two currents are in phase, and unless something unbalances it, the rotor just vibrates slightly and gets hot!  By imbalance I mean “shifts the phase / relative timing of two magnetic fields”.

Spinning the rotor mechanically creates the necessary imbalance: once the rotor is moving, the magnet fields are out of phase, and attraction/repulsion occurs.   Rotor speed is locked, with some slip, to the AC frequency of the power source, hence 1725rpm @ 60Hz, and 1425rpm @ 50Hz.

There are several ways of creating the imbalance needed to start a single-phase motor, and it may also help to reinforce the imbalance even after the motor is running.

Here’s 4 different examples, note the basic similarity.   They all have a run winding and a start winding.  The start winding is arranged inside the motor at an angle to the run winding.  This creates the necessary imbalance, but exactly how the start winding is managed varies considerably:

 

Top left: run and start windings both connected permanently, no capacitor or centrifugal switch.  Simple, reliable, inefficient, and low torque.  The start winding needs a lot of Copper.

Top right: run and start both connected permanently, with the start winding fed by a capacitor.  The capacitor provides the phase-shift needed to unbalance the magnetic fields,  and maintains it when the motor is turning.  The capacitor reduces reliability, but the motor is more efficient, with more torque, and a smaller start winding.

Bottom left: only run is connected permanently.  The start winding is connected to line via a centrifugal switch until the motor is reaches about 70% of full speed, after which the start winding is disconnected.   Less reliable because of the switch, but the start winding can be much thinner.

Bottom right: this common arrangement provides better torque and reasonable efficiency, the cost is reduced reliability.   The run winding is always connected to line.   As is the start winding via a capacitor.   But this capacitor only trickles power into the start winding to help maintain torque: it is not enough to start the motor.   The beefy start capacitor is only connected to the winding by a centrifugal switch whilst the motor accelerates up to speed, then it’s disconnected.   The start winding is on the thin side, and powering permanently soon overheats it.   This type is unreliable because it depends on two capacitors and a mechanical switch.

Single-phase motors are far from ideal – the design is always a compromise, and they all vibrate.

Though they look similar, different types of single-phase motor are not the same inside.  They are each arranged mechanically to optimise the necessary magnetic effects for their intended usage; coil positions, wire gauges, gaps, core metal etc.  A mass of devil in the detail and the design maths is well beyond me!

Anyway, in practice, connecting a bottom right type motor as if it were a top left type will probably burn out the start winding.  But adding a capacitor to a top left type won’t cause any damage – the motor will just have reduced power and torque.  Likewise, using the wrong sized capacitor, at least too small, won’t do any damage, which is probably why Robert suggested 4uF.

If a motor needs capacitors they are usually mounted on the case.  Not the law though – some designs put the capacitor in a separate box, or inside the control unit.   Without the spec, the best we can do is guess.

These days, a good way of sorting a duff single-phase motor is to replace it with a VFD & 3-phase, or – even better – brushless motor with controller.  Chinese sewing machine motors are popular – powerful and cheap.  They’re industrial, not to be compared with the dinky Universal motors found on grannies Singer!

Dave

 

 

 

[noel shelleyParticipant @noelshelley55608]

Malcolm and Robert have both referred to the devices used to get motors started, both common on fridges at various times. The PTC or solid state starter was a cheap method which as Robert has said had a serious flaw that ruined many a fridge.

My thought is that if the OP wants to use this motor, then dismantle it and see what you have, test it’s electrics and if all is sound then go from there. Does the spec not tell how it starts ? Has the centrifugal switch got stuck ? I have a similar motor in the shed I will have a look at it. Noel

[MacolmParticipant @macolm]

As Robert said, avoid the PTC type of refrigerator starter. One with a winding such as the ebay example should be OK as long as it matches the motor, not necessarily easy to determine. Integrated (but separate function) thermal overload seems usually to be a bimetal belleville washer heated by the motor current with a resistor, that snaps off and on in a relaxation cycle – fairly dreadful, but might save burnout.

[garrardgfgParticipant @garrardgfg]

Thank you all for your contributions, very informative and helpful, and easy to understand.

To close out the post, I followed the suggested advice and connected a 4microfarad capacitor in series with the start winding. I tried the red/black pair as the start winding to start with and found that the motor overheated very quickly (smoke!) within about a minute. Because the red/black wires had a higher resistance than the yellow/black pair I thought maybe the red/black pair were the start winding rather than the ‘standard’ yellow /blue or in my case yellow/black. So I changed the circuit assuming the windings / colours were reversed and tried again.

Using the yellow/black as the run windings and the red/black as the start winding the motor runs fine, but does get a bit hot after about 6min (but just hot to touch – no smoke). It also reverses as it should when the start windings are reversed, so I suspect were getting there.

Am I right in thinking a different capacitor is unlikely to stop the overheating? What I have understood / read suggests that a bigger capacitor could cause faster overheating and a smaller capacitor may not give sufficient phase shift for the starter winding and also cause overheating?

As the use I have for the motor is very limited, and when I need it it’s for much less than 6min, I will probably live with it for the moment as it is. I think the next step (as suggested) would be to disassemble it to see if there is a centrifugal switch that’s stuck on. If not I suspect it could be a damaged winding? I also realised (a bit late in life!) that with an induction motor I cant easily get speed control as the phase cycle governs the speed not voltage.

Finally, I would like to thank Dave for pointing me at ‘cheap Chinese sewing machine motors’ I’ve had another project (BCA Jig borer) that has been stalled for 15 years on motor/gearbox/speed issues and Dave’s comment sent me off doing more research in an area that I hadn’t thought of. I managed to pick up a 1Hp servo motor with controller at reasonable cost which I think should do the job very nicely, or at least keep me out of trouble for a week. What a great place this forum is! – sincerely, thanks to you all. I’ve been a subscriber to MEW since Issue 1, but had never seriously engaged with the online side.

[Robert Atkinson 2Participant @robertatkinson2]

A smaller capacitor may help the over-heating but it indicates that it may need some kind of switch in the start circuit.

Robert.

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