Onan MDJE stopped making power

[Duvie]

After getting the Solace in the water this Spring I started the Onan generator and was only getting 15 volts output. After going through the troubleshooting steps in the YD service manual it seemed as though I had a bad voltage regulator.

I bench tested a spare voltage regulator board I had as well as the one that came out of the generator. The spare tested somewhat good but it seemed as though one of the pots was corroded or something as the output flickered a LOT. When I bench tested the unit that came out of the Solace it smoked instantly! This confirmed my previous beliefs.

A new or rebuilt board on line was several hundred dollars. After doing some research on Smokstak it seems as though many have used an SX460 regulator to replace the stock unit. These SX460 regulators can be had for around 30 dollars on many sites and need to see a field resistance of over 15 ohms. I had to add a 5 ohm resistor for my MDJE to meet this spec.


After installing the SX460 and resistor the unit made electricity like a champ. I completed a quick voltage and stability adjustment and all is good. Total cost of repair was 38 dollars.

Picture on top is the new board with resistor and field circuit breaker. Picture on the bottom is the old set up. I had to make up an aluminum adapter plate to bolt in the new board.

Thought I would share as it might help someone out with one of these older Onans.

 

[Ski in NC]

Very nice!!!

 

[edisonescandon]

hello DUVIE. the resistance is put at the 110volt input or output to the rotor brushes.

 

[Duvie]

The SX460 wants to see at least 15 ohms on the field This is where you want to add a resistor not the 120 volt sensing terminals.

Measure your field resistance with an ohm meter. It will probably be around 8 to 10 ohms. Add the appropriate amount of resistance to get the total over 15 ohms. Take a look at the Smokestak website. There are several threads on the site that cover the SX460 such as this one...…

https://www.smokstak.com/forum/threads/sx460-voltage-regulator-for-old-onan-generators.139868/

 

[edisonescandon]

Thank you so much.

 

[CharlieJ]

Duvie: Beautiful job and very innovative. Well done.

As a further enhancement, I have an Onan MDJF and went through a couple of boards early on. I solved this about 20 years ago by remotely mounting the control box, so it is not subject to the engine's inherent vibration. Has worked ever since.

 

[edisonescandon]

updated 07/11/2021.

I made a few changes to my onan MDJE 7.5KW marine diesel generator 1971. -AVR GB 160 -(ESD5500E speed controller -MSP6729 Magnetic Speed Sensor -ADC120 actuator) -DSE704 Generator AMF Controlle.


I put a honda radiator on the generator to cool the engine and use it when the electricity goes out in my house. I don't know how to put photos of the modifications.

 

[Lepke]

There's a number of people and companies online that repair circuit boards. They do it by testing the components and replacing them as needed. Not recent, but I've had a number of boards repaired from a washer to old nav instruments. Cost is usually $50-100. Not as cheap as Duvie's, but a way to avoid overpriced replacement boards for us electronic illiterates.

 

[zigzag930]

I'm curious as to why the SX460 needs a resistor. What is the value and rating of the resistor you have used?

I installed the SX460 on both M673 and M843 generators and did not use a resistor. Both gensets appear to be working fine after a hundred+ hours.

Would love any input on this....

 

[Duvie]

Zigzag, the specifications on the regulator is that it wants to see a field resistance of 15 ohms. So if your field resistance of your genny is 10 ohms you will need to add a 5 ohm resistor in series to meet the input spec.

This specification probably has something to do with limiting current through the regulator. Also note you will need to use a power resistor. As I recall I used one in the 10 to 50 watt range. Ebay is your friend. Leon

 

[Mischief Managed]

Thanks for this! I have a 1992 MDKD that this would be ideal for. I just ordered an SX460 for it on that jungle website for 24 bucks. I also ordered a set of four 2.5 ohm 50 watt resistors for 13 bucks on ebay. I can use one or more of them in parallel or series to make a ballast resister array from .625 ohms to 10 ohms.