MEP-003a Charging System - Higher Than Normal

[ckesey]

I have a MEP-003A that isn't charging the batteries. According to the testing article here (and TB) I have a bad regulator. I also had a open stator which has recently been replace.

After stator replacment, I'm getting 56v AC between the two stator wires while it's running (and wires disconnected from the terminal block) . The TB says 30-35v AC.

When I test the stator without it running (wires disconnected) I get 0.8ohms (close to the 0.6 in the TB test for being good.

The gen is dialed in at 1800 rpm and the main AC voltage is 122v on each leg. What would cause me to get this much output voltage on the charging stator?

 

[Triple Jim]

If I remember right, the 30-35 VAC is with the stator connected to a working regulator. When open circuited it can get higher.

When you measured 0.8 ohms, did you account for the meter lead resistance? Touch the leads together and read the resistance. Then subtract that value from the reading of the stator resistance.

 

[ckesey]

So there is 0.2 ohms in my test leads which puts this even closer to what the manual says is normal.

I checked and it says to conduct this test with the leads disconnected (open). I just don't want to kill a new rectifier if this isn't normal incoming voltage.

Looking at this I don't see how it can't be normal. What else is there? There is a magnet (that's visually appears to be in good shape) a stator which I just replaced with NOS that ohms out to what the manual reads and its turning at a fixed speed which results in 60.2 htz AC output voltage 120/240v (which would indicate the engine RPM is correct).

I guess I could put a aftermarket battery charger on it but I would really like to make it orginal.

Thanks for any input

 

[Triple Jim]

I doubt if there is anything abnormal going on. Maybe your meter is not a true RMS type.

 

[ckesey]

I'm using a Fluke 79 which says on the front it's a true RMS meter. I don't want to overthink this but I really don't want to set a match to $100 on hooking up a new rectifier to it either. I don't get any output on the current rectifier.

 

[Guyfang]

Are you sure its the right Stator? Did it come in the original package? Was the package closed and the right part # and NSN were on the box?

 

[ckesey]

I can't say for sure as the box and paperwork has been discarded. The purchase was for a 003a but can't say for sure that's what I received/installed.

This morning I purchased another as a spare that I'll installed and compare results.

There is simple and easier fix to charge the battery but I really want to retain it as orginal.

Thanks

 

[Guyfang]

Look at both Stators for a part number/NSN. This kind of thing happens, sometimes.

 

[ckesey]

I bought a spare stator and installed it yesterday. It tested good according to the ohm reading. It gives me the same 51-52 AC volts and the previous one. Not exactly where to go from here. Will this kill a replacement rectifier with this voltage?

 

[Ray70]

Lets go back to the beginning.... Are or were you having a charging system failure and if so what was happening?
I suspect you have 2 good stators and possibly either a measurement error or yet another mistake in the TM!
I'm pretty sure I've seen about 50VAC at the stator wires with everything disconnected on most all stators I've tested.
With the stator connected I think 30-35V is probably typical.
I know this contradicts the TM and 80% of the Sticky, but it's not the first error we've seen in the documentation.
If you aren't charging your batteries at 27+VDC I'd say your regulator is most likely the issue, not the stator.
Once you connect the stator to a good VR I bet your voltage will drop closer to 30 -32 on the stator leads and 28 out of the VR to the batteries.

 

[ckesey]

Yes I have had charging issues (not charging) since I bought the unit. When I first started troubleshooting it I had 0v from the output of the stator when running. I ohm the old stator and it was open. I ordered a replacement for it. When I first installed the new one I was getting 30-35v but still nothing on the output of the rectifier.

Discouraged, I put a battery charger on the batteries and pushed it off another day.

Fast forward to "another day" 1-2 years from then, I was determined I wasn't going to get beat and started my checks (according to the TM) from scratch. When I pulled the 2 stator wires off off the TB and checked them with my Fluke, I'm now getting 50-56v AC. I wasn't expect this since last time I checked it it was 30-35v AC. When I ohm it, it was 0.6 ohms (reading 0.8 ohms but shorted the leads show 0.2 ohms).

Not really sure what else it could be, I found another stator at a discount that had been removed from a working unit. I bought it as a spare to have another test point. That used stator also ohms at 0.6 and produces the same 50-56v AC when installed.

I'm fairly confident at this point I also have a bad rectifier, however I don't want to installed a new one and kill it immediately if the stator is producing voltage that isn't correct.

 

[peapvp]

When these TM's were written in the 1970's, the most common test equipment was a analog AC / DC Meter

The average internal resistance in the AC Volt range was 10,000 Ohm per Volt

If the manual stated: 35 VAC and the meter was set to the correct range, then the internal resistance was app 350,000 Ohm or 350 K Ohm

These numbers were important to know, as one had to determine the load the test equipment would post to the to be tested circuited. Otherwise your test results were garbage.

Today's Digital Meter have a internal resistance off app 10,000,000 Ohm or 10 MOhm or higher.
This is practically infinite Ohm and the meter does not pose a load to the test circuit. Hence the meter no longer poses a load to the test circuit.

If you get 50 to 56 VAC with a digital meter, then you will get most likely 30 to 35 VAC with a analog meter, as both meters load the coil differently.

Add a 350 KOhm resister across both wires and then retest the output voltage with your DMM

 

[ckesey]

Thank you for the info and incite. We had an old analog meter here at work that I'll try and locate. I would be intresting to see what the old analog meter shows. I will try and locate a 350 kOhm resistor to take reading from with my DMM for comparison.

I'm just trying to keep the smoke in on new rectifier I just order.

Thanks again!

 

[Guyfang]

Ray may have something concerning TM error. Has anyone compared the work passage of the MEP-002A and the MEP-003A? Sometimes it was right in one TM and in the other wrong. Would be easy enough to check.

 

[peapvp]

Ray may have something concerning TM error. Has anyone compared the work passage of the MEP-002A and the MEP-003A? Sometimes it was right in one TM and in the other wrong. Would be easy enough to check.

Guy,
The two TM’s ending in -12, for the 002A and 003A, published in the Generator TM section of this forum, show the same required test results to pass stator as good

002A



003A

 

[Guyfang]

Its what I assumed, but until someone looks, its always an unknown. To quote Sir Arthur Conan Doyle,
“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”

 

[Ray70]

When these TM's were written in the 1970's, the most common test equipment was a analog AC / DC Meter

The average internal resistance in the AC Volt range was 10,000 Ohm per Volt

If the manual stated: 35 VAC and the meter was set to the correct range, then the internal resistance was app 350,000 Ohm or 350 K Ohm

These numbers were important to know, as one had to determine the load the test equipment would post to the to be tested circuited. Otherwise your test results were garbage.

Today's Digital Meter have a internal resistance off app 10,000,000 Ohm or 10 MOhm or higher.
This is practically infinite Ohm and the meter does not pose a load to the test circuit. Hence the meter no longer poses a load to the test circuit.

If you get 50 to 56 VAC with a digital meter, then you will get most likely 30 to 35 VAC with a analog meter, as both meters load the coil differently.

Add a 350 KOhm resister across both wires and then retest the output voltage with your DMM

Very interesting! and indeed when I've tested them in the past I always had a DMM. The results with an analog meter or with the resistor will be interesting to see!