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Mecc Alte Spa Generator

Charlin

Registered
I have a Mecc Alte Spa generator Model# Xm1622000N wired single phase that is only putting out 44 volts (22 per leg). An internet search brought me
here, to a thread where another person with the same gen was having the same problem. My situation is about the same as theirs, low hours, bought
from Central Main Diesel in 2005. This is a link to that thread https://www.smokstak.com/forum/thre...28-1l-4-15kw-output-only-55-volts-max.185749/ The only difference is I think that one was wired 3 phase.

The AVR is an SR7-2G http://bdsar.com/wp-content/uploads/2016/09/avr-sr7.pdf The first thing I tried was to excite with 12 volt battery and the output only
jumped to 46 volts and that is where it is at now. I followed the testing advice from the other thread and this is my results.

Ohms between red wires on AVR 1.8, Ohms between black and green 0.3 disconnected from AVR. Voltage on red wires 33, voltage on black and green wires 23
and voltage on blue and yellow 1.3 all while connected to AVR. All this is AC voltage. Someone I was talking to said that there should be some DC voltage
on the regulator somewhere but I have no idea where to test for that.

The person in the other thread was able to rewire the regulator and got back up and running, but I don't think that would solve this one as they had full
output while exciting, I don't. If anybody has any suggestions on what to check next it would be greatly appreciated. I can't find anyplace around here
that works on this make, so I would not have even known where to start if it wasn't for the info here.
 

Birken Vogt

Registered
The regulator puts off DC voltage onto blue and yellow in response to lowering generator voltage. The lower the voltage output the higher the DC voltage on blue and yellow. In practice the differences will be small, you will normally see somewhere between 15 and 30 volts DC on blue and yellow operating.

http://bdsar.com/wp-content/uploads/2016/09/avr-sr7.pdf

Probably the next thing to check is the diodes on the end of the generator.
 

Charlin

Registered
I started thinking about it a little while ago and went out and checked the blue and yellow for DC voltage, there was none.
I will pull the front off tomorrow and check the diodes. Thanks for the help.
 

Birken Vogt

Registered
Better check again. If you have no DC voltage on blue and yellow it is unlikely you will be getting that much voltage on the other windings. 5-10 volts AC output is all I would expect from residual DC.
 

Charlin

Registered
Do you mean on the terminals where I should be getting 240? or on the other wires on the AVR? If you are talking about the output
on the main terminals, I did check again when I tested the blue and yellow for DC. It read 46 volts on the output terminals, and 0 DC
on the blue and yellow wires. I did have 1.2 volts AC on the blue and yellow wires. I think I will wait to pull the diodes out until I hear
back from you, just in case that may not be an issue. I also can check all the wires on the AVR again for resistance and voltage
if you think it is necessary.
 

Birken Vogt

Registered
Measure again the output voltage AC with the blue and yellow disconnected. Make sure nothing disconnected touches anything else when testing as some of these generators have one end of this and another end of that winding connected in common for some reason. The Italians did things different. If you still have the same voltage with blue and yellow not connected then I guess you just have a high residual voltage and that is OK.

What does not make sense is that if you have good residual voltage of 5 VAC or more when running and no DC on blue-yellow then that would indicate a bad regulator. But if you feed 12 volts into blue and yellow and you have no output that would indicate a generator problem. Hard to believe that both things broke at the same time. Usually problems of this nature are an error in measurement instead.

I literally just finished working on one of these yesterday so lucky for you it is still fresh in my mind. I had pretty much forgotten about the old thread.
 

Charlin

Registered
Tested again with blue and yellow disconnected. 43.86 AC output on main terminals. 0 volts DC on blue and yellow. You stated that it seems
like it be could be a regulator or generator problem. Do you think something happened internally and then messed up the regulator?

How this began was I started up the generator and was checking output before putting a load on it, and the voltage dropped from 250 volts
down to 44 volts while I was looking at it. What I noticed different is the voltage was bouncing around between 249.2 to 251.7. I have never seen
it do that much variation before.

I don't know if that means anything to help figure out the problem or not. The voltage is also down a few volts from when I excited it. It
went from 44 to 46 after excitation. It seems like it tried to excite but something is wrong. So what do you think now?

I figured you did this professionally from the help you gave in the other thread. You and Wayne 440 both seemed to really know about this stuff.
I really appreciate the help with this.

Main_Terminals.jpg Blue_Yellow_Wires.jpg
 

Zeromedic

Subscriber
Last Subscription Date
03/08/2020
When meter readings are afu, double and triple check your meter(s).

Failing batteries and borken'd test leads have caused me much lost time over the years.

Steve
 

Birken Vogt

Registered
The blue and yellow wires receive power from the voltage regulator so there is no need to measure them disconnected. They are an input, not an output.

What is the voltage on red-red (I think) while all this is happening?
 

Charlin

Registered
I thought about a meter problem so I checked the dryer outlet in my garage, it was spot on. Voltage and frequency. I know the generator
isn't putting out power because the governor freaked out, engine revving up and down.

The governor gets a signal from the final output and adjusts the speed of the engine accordingly. I had to disconnect the governor and
manually adjust the engine RPM to get the correct frequency.
 

Charlin

Registered
I didn't get DC on the blue and yellow connected either. Red wires had 33 volts, and green and black had 23 volts.
 

Birken Vogt

Registered
When the VR gets fed AC voltage from the green and black, and red-red, it puts out corresponding DC voltage on terminals 1 and 3. I think you measured 1-3 for DC with it running but just want to confirm. Just for kicks do it with the wires disconnected, maybe there is a short in the exciter field or something. When you apply power to the exciter field, not much should happen when you connect the wires, but when you disconnect it should draw a pretty noticeable DC arc due to inductance.
 

Charlin

Registered
Yes, I measured 1-3 running. Not sure I follow, do you want me to test the 1-3 terminals on VR with the wires disconnected?
Or do you mean test 1-3 terminals with red-red and green-black disconnected?
 

Charlin

Registered
You nailed that one! I reread your post and it sunk in, sometimes I read stuff fast and don't catch it all. The key word I missed was
inductance. Blue-Yellow disconnected I have 36.64 DC, connected almost nothing.

So now what do I dig into? I really appreciate this Birken Vogt, I would have pulled out what little hair I have left if it wasn't for you.
AVR_BL_Yel_Discon.jpgAVR_BL_Yel_Conn.jpg
 

Birken Vogt

Registered
So it sounds like your exciter field coil may be shorted. If it pulls the regulator down to almost nothing.

How many ohms across blue-yellow? And what is it supposed to be (I don't know)? IIRC the one I just finished was 20 ohms give or take but I could be wrong. It was about a 50 kw machine. Maybe you can find the manual for yours, they are kind of hit and miss and I don't know if they supply that info anyway. But it should not be the 1 ohm like on a main coil.
 

Charlin

Registered
I have 11 ohms across blue-yellow. Nothing to ground, I didn't know if that was relevant or not. The generator is a 15 KW. There is nothing
on the data sticker I see that looked like it would be helpful, maybe you will recognize something.

There is nothing in the manual I can find, I will go back through it. The place I bought it from stuck that data info over the original plate.
I peeled it off to see if there was anything on the original that would be useful, but it pretty much pulled all the info off. It was printed on
another sticker, not stamped on a plate like I thought it would be.

In this thread: https://www.smokstak.com/forum/thre...28-1l-4-15kw-output-only-55-volts-max.185749/
that is the same generator as mine. He was able to get the sellers sticker off but I still don't see any info that might help.
Data_Tag.jpg
 

Charlin

Registered
Thanks, I will check that now. Those pages aren't in the manual that came with the generator. I feel a little better now, I was afraid the
exciter would have to be replaced.
 

Charlin

Registered
All diodes tested good unless I missed one. There were 6 the best I could tell. That rear bracket didn't want to come off very easy so I
left it alone and worked through it. Do you normally use a puller to remove those? It seemed like I could get a three jaw around that
center piece.
 

Birken Vogt

Registered
I just worked through the end bell but bigger units are easier to work on, I don't know how yours is set up.

Here is how I did it. With the diode packs removed you should have the 3 exciter rotor phase wires loose. That is the center terminal on each diode pack.

First test the resistance per that sheet. Then clip your meter to all 3 combinations of these and tap the exciter stator blue/yellow with a battery. You should see a pulse in your meter each time you do this on the exciter rotor wires, all 3 combinations. This gives reasonable suspicion that the exciter is good but is far from a foolproof test. Then check the wires that tie all 3 positives and all 3 negatives to the actual red/black (green?) that go up to the main field.

Test the ohms of the main field. Also repeat the test I showed above only now you are zapping battery onto the main field and looking for pulses on the generator output.
 

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