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


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  #11  
Old 12-20-2017, 03:05:32 AM
NomadAU NomadAU is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

I got lucky...out of the 4 wires, I found 2 wires where I could read the markings, got T4 and T2...so figuring out the rest was childs play. I must say that the markings are definitely well hidden, and without being told that the wires are marked, I would never have looked more closely.
On to the next problem...or do I mean 'challenge'.
Thanks all for the guidance.
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Old 12-20-2017, 09:40:55 AM
armandh armandh is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Quote:
Originally Posted by NomadAU View Post
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

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
oops; did not notice OP's location
yes that is correct for 240 volt only connection.
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  #13  
Old 12-20-2017, 04:36:07 PM
len k len k is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

From your 2nd pic in post 1 looks like T2 always is the lead to ground to gen frame. This becomes important if your gen has a magnaciter AC voltage reg. Has to do with providing a return current path for magnaciter 12VDC flashing current that starts the bootstrap process of making AC.
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Old 12-20-2017, 05:05:57 PM
NomadAU NomadAU is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

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Originally Posted by len k View Post
From your 2nd pic in post 1 looks like T2 always is the lead to ground to gen frame. This becomes important if your gen has a magnaciter AC voltage reg. Has to do with providing a return current path for magnaciter 12VDC flashing current that starts the bootstrap process of making AC.
I'm pretty sure I don't have a magnacitor on this. I'm basing this on the fact that my MDJE has a rotating exciter coil complete with rotating diodes. Also it has no brushes. From what I understand this means it doesn't have a magnecitor.
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Old 12-20-2017, 05:14:53 PM
len k len k is offline
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Sounds like a YD genhead with electronic votlage reg in the penthouse above control box, no magnaciter.

I have same in a JB. Genhead should have a small permement magnet in it so does not need flashing, so no need to worry about providing a return current path for fashing. My spec AA makes ~ 20VAC at no load without reg hooked up. That's enough for reg to bootstrap it's way up to 120V/240.

With a YD genhead should be able to use a sx460 type reg , they have China knock offs for ~$20 , people here have used china version with sucess. Beleive only issue is sx460 needs a field resistance of 15 ohms min, but YD feild is ~ 12 ohms, so need to add 3-4 ohms of extra resistance in series with feild.
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Old 12-21-2017, 04:04:12 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

Now that I've identified the T wires, I am still a bit unsure about how to wire them to an output power cable.

I believe the attached schematic relates to the configuration I need, but I still need to confirm what the actual connections should be.

So here in Australia, we have 3 wires in our 240V supply, Active, Neutral and Earth. I believe the 240V is across the Active and Neutral but I'm pretty sure that most devices still work if you swap the Neutral and Earth, however, this is not correct wiring, and things like Residual Current Detectors (RCDs) will trip if you do this. So I think that I need to wire up my output in the following way.

Just join T1 and T4 using a simple cable connector.

On the output cable, join the Active (Red) to T3.
Join the Neutral (Blue) to T2.

That leaves the Earth (Green/Yellow) which I think should go to the chassis? There is a nut/bolt in the genset distribution box that I can attach this to.
I'm a bit puzzled by the schematic which shows T2 being also wired to ground. Does this mean that my Earth and Neutral are both wired to the chassis? This doesn't seem correct.

Can anyone confirm how I should wire the output.

Cheers,
Mike
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  #17  
Old 12-21-2017, 09:24:34 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

for 240V only that is correct
for powering an un-bonded load in the field [the load has no neutral/earth connection]
with a ground rod to the generator frame
this is what keeps the neutral near ground potential.
the residual current [we call it ground fault interrupt] wont trip because
all the power going through the active is coming back on the neutral.
but a ground to the neutral; returns some of the current over the safety ground [earth] [or you]
then it should, we hope, trip


powering your house if/where there is a neutral/earth bond
is a bit more complicated

if the active/neutral load you are transferring has no neutral/earth bond
and you are transferring both active and neutral then the generator ground stays
but is disconnected if only transferring the active wire, relying on an existing bond.

this prevents any static charge build-up in the otherwise isolated system
your electrical codes may be different, consult someone locally with generator electrical instillation experience
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Last edited by armandh; 12-21-2017 at 10:00:09 AM.
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Old 12-21-2017, 12:19:09 PM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

I believe your "earth" wire is what we call ground wire (green).

Little overview.....Here electric code only allows ONE (active) neutral/ground (N/G) bond (connection).

-- If gen is alone out in the field that is done at the gen.

-- If gen is connected to a house that is feed by utility then usually you use house N/G bond and don't connect gen neutral to gen frame ( connection between those 2 occures at house's N/G bond. ) To protect against shocks off gen frame have to run wire from house N/G bond to gen frame.

Alternately, here can have N/G bond in house AND gen , BUT must use a transfer switch that also switches the neutral ( so only one N/G bond is active at any time)
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Old 02-08-2018, 04:02:15 AM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

In my Onan MDL3 the T1 and T4 are attached to the main breaker on the unit itself. The T2 and T3 are bonded together and grounded to the panel box on the unit. How do I determine which of the two wires T2 and T3 is the neutral.
Thanks, Iver
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  #20  
Old 02-08-2018, 02:52:34 PM
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Default Re: Onan MDJE - How can you tell what is T1, T2, T3 or T4?

The connection between T2 T3 is the neutral not one or the other. Your generator is wired correctly for normal useage. Cheers Dan
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