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Onan MDJE - How can you tell what is T1, T2, T3 or T4?


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Old 12-19-2017, 04:39:56 AM
NomadAU NomadAU is offline
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Default Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Hi,

I've now got the engine part of my Onan (MDJE-53CR) up and running - got the missing rear oil seal from Cummins here in Oz, so a good win there!
I'm now looking at the generation side, and with the unit fully built, I have a few questions. I'll ask each on a different post so as not to confuse too much.

So, my first question is how do I tell what the 4 T wires are from the stator? I've identified the 2 field wires (F1 and F2) and the 2 12v battery charging wires, so I'm now left with the 4 T wires. So far as I can see, none of them have any labeling - maybe this was removed by previous owner/technician/etc.

As the attached image shows, they are all covered in a sort of woven sleeve (maybe a heat resistant sleeve?). I've peeled one off to see if there were any markings underneath on the insulation sleeve, but can't see any.

My Operators manual provides a selection of configurations - I need 240V at 50Hz. In order to configure my output, I need to identify each of the T wires. I'm guessing there's a way of doing this without the wires being labeled?

Thanks for your help
Mike
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Old 12-19-2017, 09:04:47 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Onan used black marker on the outside of the wires. About every 2 inches. Can be very hard to see.
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Old 12-19-2017, 09:54:37 AM
Graycenphil Graycenphil is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

What Billy said. I had an old MDJE, I must have looked at the wires fifty different times with different lights before I found it. Itís hard to see, but itís there. Once you see it, itís much harder not to see.
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Old 12-19-2017, 10:14:09 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

You could try one of those cheater glasses. They really come in handy for us old folks. Once you find one end the rest are simple.
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Old 12-19-2017, 10:16:54 AM
Tim0477 Tim0477 is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Maybe someone else can better explain this, but basically you are going to have to use a meter to determine which wires are part of the same winding. You should have 2 pairs of wires which should show continuity (one pair for each winding). Once you have identified your 2 pairs, leave them disconnected and get the set running. If all is well, you should get about 120V when reading across either pair of wires. Now you have to get the phasing right. Take one wire from each pair and temporarily connect them together. Get the set running again and measure between the two wires left disconnected. If it is correct, you should see about 240V. If you see next to nothing or some odd reading, reverse ONE of the pairs and try again. This would give you 120 - 240 single phase. The two wires connected together become your neutral and the two wires left disconnected become your hot leads. Once you have it working correctly, compare what you have to the correct wiring diagram and label accordingly.

Tim
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Old 12-19-2017, 10:25:44 AM
armandh armandh is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

similar to above but without running

you have two windings with four leads [two each]

find what are winding pairs with an ohm meter and connect in series
if one wire is grounded be sure that is in the center.
[if you cannot differentiate between two that are near ground pick one for now]
feed one winding with a low ac voltage
[use an old train transformer or 6.3 filament transformer, or doorbell transformer, or AC wall wart]
measure the voltage at each winding; the un-fed winding will be lower.
measure across both of the windings in series

if you get the sum of the voltages they are phased correctly
if you have a voltage between center neutral and ground reverse both pairs.

if you get the difference of the voltages reverse one pair's connection;
the grounded pair if there is a voltage between neutral and ground
the un-grounded pair if there is no voltage between neutral and ground

re measure for the sum of the two voltages and no voltage between neutral and ground

when running and regulated correctly you should have 120-0-120
and no voltage between center neutral and ground
label, reconnect as needed.

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YMMV

use all necessary precautions when measuring lethal voltages
by using this free advise, you, your heirs, etc absolve and hold harmless the advisor.

Last edited by armandh; 12-20-2017 at 09:44:35 AM.
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Old 12-19-2017, 11:21:42 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

The generator end has two windings, T1&T2, and T3&T4. T2 is USUALLY grounded to the frame inside the generator. The windings will measure somewhere around 0.1 ohm, so unless you have a milliohm meter or a Kelvin meter, they will appear to be a direct short.

Start by measuring resistance from one wire to the other three. You should find one of the other T leads will show a low resistance on the order of 0.1 ohm. This will define one winding. The other two wires should also show a low resistance connection between them. This will identify the other winding. There should be infinite resistance between the two windings.

One of the sets of windings will usually show a low resistance to ground. This will identify the T1-T2 pair. Follow these two wires back into the generator end, and you should find one of them has a jumper to ground. This is the T2 lead. The other of the pair is the T1 lead.

Do you need 240 volts with one side grounded, or do you need the more common (in America) 120-neutral-120 volt connection?
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Old 12-19-2017, 01:57:13 PM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Do you have a magnaciter?
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Old 12-19-2017, 02:29:43 PM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

You can identify the pairs of output wires by checking continuity with the gen stopped. With all wires disconnected from each other T1 will have continuity with T2 and T3 will have continuity with T4. Also the smaller sampling wires which go to the voltage regulator will have continuity with T1-T2 as well. If you then hook one wire of each pair together with one of the opposite pair and start the generator , measure the voltage from the non connected wires if you get 220V then that is the correct orientation, if you get 0V or a very low voltage , less than 20v between then you need to switch one wire. If you can find markings on at least one of the 4 wires the rest is just logic. The markings can be very hard to find but they are there on the cloth sleeve not on the inner plastic insulation. Cheers Dan
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Old 12-20-2017, 01:49:21 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Quote:
Originally Posted by Billy J Shafer View Post
Onan used black marker on the outside of the wires. About every 2 inches. Can be very hard to see.
I'll pull the wires out a bit and see if I can find the markings. That's got to be the first thing I try!

But Kevin K has thrown me a curved ball with his question
Quote:
Originally Posted by Kevin K View Post
Do you need 240 volts with one side grounded, or do you need the more common (in America) 120-neutral-120 volt connection?
I don't know the answer, but what I do know is that here in Oz we have 3 wires for our domestic (and boat) 240v power.
  1. Active
  2. Neutral
  3. Earth
The 240V is between the Active and Neutral...the Earth is there to ground the current if/when something goes wrong with the appliance. So, I'm inclined to think I need the 240 volts with one side grounded, but I'm happy to be corrected.

Cheers,
Mike
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