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AEI motor wiring for rescued lathe

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Mike Wood 124/05/2013 10:43:28
2 forum posts
3 photos

Hi, I've recently rescued a slightly beaten-up ML7 (from a cowshed, in Ohakune). There's a motor attached but there's no cable wired in.

The motor's nameplate says it's a single-phase 1/3HP 1425rpm Associated Electrical Industries Ltd one


It looks to have 4 terminals in the terminal block, labelled A1, A2, T2 and T3. I don't see a T1!


There are helpful wiring instructions underneath the wiring cover as well, suggesting the following (not sure the photo's come out all that clearly...)

Connect mains - to A1 & A2, but if overload device fitted - to A1 & T3

Connect capacitor (if fitted) to A1 & T2

To reverse rotation interchange leads from inside motor to A1 & A2

wiring cover

The motor spins if I connect power to A1 & A2 (like it says, although I've only tried it unloaded while it was clamped on the bench). It mentions a capacitor though - would this have been a start capacitor? Possibly missing with the cable or switch etc if it was originally there.

Anyway, I wondered if anyone was familiar with these motors, and...

- if it's ok to use the motor on the lathe as-is, just connecting mains from my switch to A1 & A2 (or is it likely to need a capacitor)?

- if it needs a capacitor, is there a ballpark size for a motor like this? Hunting on google brought me to a rule-of-thumb calculation of

Cap size (uF) = (2650 x Full load amps ) divided by supply Voltage, which comes out to about 28uF for me -- (2650 x 2.5) / 240

thanks for any advice anyway

Robbo28/05/2013 10:12:18
1504 forum posts
142 photos

Hi Mike,

Clever cows you have in NZ, ours in UK only eat grass and wander about, never heard of one using a lathe.

This is the old problem of identifying an old motor, and it's a long time since I saw an AEI.

One of the problems is that makers tended to use the same casings and covers for differently wound motors, and used a stick-on label to identify them. This of course fell off quite quickly. On some capacitor motors the cap. was not attached to the body of the motor as is current practice. This enabled the motor to fit in a smaller space with the cap at the end of it's wires somewhere nearby.

The terminal arrangement is typical of AEI and is used on reversible and capacitor motors among others. There is also another type known as a "split phase", which only uses 2 terminals, but has 2 wires per terminal, 1 for the run winding and 1 for the start winding. As we can only see 2 wires in yours, would suggest these are the start winding connections, as the motor is reversible by changing them over. Perhaps the connections to the run winding are underneath the terminal plate, as they never change polarity.

If it starts readily and runs up to speed then I would suggest a split-phase.

Run it for increasing lengths of time and see what happens, and check that the torque is OK.

If nothing untoward happens then go ahead and use it, bearing in mind that there may be some insulation problems because of age.

Sorry to be so vague, but at least this post will ,bring you back to the top of the list, where someone more knowledgable might see it.


jason udall29/05/2013 12:43:09
2031 forum posts
41 photos

As has been said same case many motors hence the ambigous labling,,which throws us back to first principles.

A quick prod with ohm meter might tell if t1 t2 go anywhere.. if not then these are "spare" and you can treat them as a red herring..

If the motor runs /starts nicely then you don't need a start cap... that said insultion/ shorted turns are still a possibilty ...

good luck

john fletcher 129/05/2013 14:51:15
804 forum posts

I have BTH/AEI circuit diagram.If your motor has not got a capacitor fitted, then as some one says its a split phase motor.That being the case, the run winding will be connected to terminals A1 & A2, the short time rated start winding will also be connected to A1 & A2. If you want to make the motor reversable then that is possible, however it will mean a complete motor dismantle. Using a scriber or some other sharp instrument scribe across both motor end shields, two marks on the non drive end one on the drive end, righr across, these are alignment aids for re assembly. This motor is elderly so proceded with care, remove the 4 through bolts, and using a mallet give the stator a sharp tap on both ends, it should fall apart.When removing the rotor be very careful not to scratch the windings, DONT lay the stator on its windings, a sure way to ruin a good motor. Inside of the non drive end is the centrifugal switch, to which one end of the start winding is attached, the other end of the winding is connected to A1. Using a big iron unsolder the two wire. The start winding is the thinner of the two and has a much higher resistance than the run winding. Once dis connected the start winding should be connected to terminals T1 & T2 via the switch. To give the motor a much better starting torque a proper AC electrolytic capacitor of around 60 or so micro farads can be safely fitted. To reverse the motor is is necessary to reverse either the start winding or run winding one not both.So a double pole double throw change over switch preferably with centre off and a proper motor starter with non volt release.If you need any more help then contact me. By the way the formula regard cap value is correct for 60Hz 2650, different for us on 50, 3200 near enough if anyone is interested.Ted

Les Jones 129/05/2013 16:36:44
2261 forum posts
156 photos

Hi John,
I am not familiar with this particular motor but do you think it is worth Mike disconnecting the two wires that are connected to terminals A1 and A2 an then measuring the resistance between these two terminals in case the start winding (Via the centrifugal switch.) is connected to the underside of the terminals. If that was the case just swapping over the two wires would reverse the motor. This could be the meaning of the text "To reverse rotation interchange leads from inside motor to A1 & A2" on the plate.


Nicholas Farr30/05/2013 06:51:11
3413 forum posts
1586 photos

Hi Mike, I have an AEI motor of the same type as yours except that it is a 1/4 HP. It has exactly the same instructions on the cover and exactly the same connection plate inside with the same two wires on A1 and A2 and swapping these round reverses the direction of the motor. There is no start or run capacitor on mine, switching is done by the internal centrifugal switch.

Regards Nick.

Mike Wood 130/05/2013 10:11:48
2 forum posts
3 photos

Hi, and thanks very much for all your helpful advice.

As suggested, I've had a quick go at attacking it (fairly gently - it looks pretty old) with an ohmmeter to see if I could add anything in the way of useful information.

I first disconnected the black wire and red wire that you can see coming from underneath the terminal plate to terminals A1 and A2.

Measuring the resistance from the free end of the black wire to the free end of the red one gave me a reading of 6.2 ohms.

The resistance between terminals A1 and A2 was now 15.8 ohms.

Neither terminal T2 nor T3 seemed to be connected to anything else - they were both open circuit to A1, A2 and each other.



Ady106/05/2016 16:17:54
5159 forum posts
738 photos

I found this thread because I've been reversing an AEI motor today and I thought I'd share

Simply reversing the mains didn't work, it just spun in the same direction, which was the wrong one for me

originally A was connected to C and B to D, like in mikes photo

So I swapped them over into an X shape and rewired the mains. The black cable on the left is the capacitor, which is simply left in place whichever way round things are


Andy Holdaway06/05/2016 16:30:33
167 forum posts
15 photos

I may be wrong, but you appear to have earthed one end of the capacitor? That can't be right!

Ady106/05/2016 16:39:17
5159 forum posts
738 photos

It was like that when I got it and had a "safety sticker" from the auction house

(Anyway, before each startup I was tucked safely behind my shaper)

Works fine now and there's no zappy bits if you touch it while its running

Edited By Ady1 on 06/05/2016 16:41:21

Robbo06/05/2016 18:45:24
1504 forum posts
142 photos

You haven't earthed the capacitor, but you obviously use a different cable colour code from us in the UK.

However, there doesn't seem to be any earth connection at all!

Mark Chapman 127/08/2018 22:21:40
2 forum posts

ive got the same motor and it turns nice and strong - i find the resistance of the coils varies from one motor to another

i could photograph the original wiring - the earth should go to the case definately

my rcd would trip out otherwise


Mark Wallis 116/12/2018 13:06:35
1 forum posts

Hi all, Im new here and have just got a lathe with the same motor as above. It all seems to be working fine and using the Forward/Reverse switch works as it should, but I have noticed that when the motor starts and the centrifugal switch clicks on, you get a good spark. Now i'm assuming that as it doesn't have a capacitor it doesnt need it for start or run, but would it help with reducing the initial startup load and hence reduce or even eliminate the sparking from the centrifugal switch contacts.

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