Unused wires on mep 803a

[SalmonSlayer]

Just curious if one was only using the gen on single phase 120/240 if any of the wires on the big ass switch on the back wall can be eliminated for simplicity. Same for the AM/VM switch on the front. ( I want to say s7 but could be wrong). Keep getting short circuit alarm when it rains and I spray them both with deoxit and cycle switches which does seem to help but if I decided to take it all apart and clean it thoroughly I wondered if any of the wires could be omitted
Thanks

 

[Digger556]

There is a lot that COULD be eliminated. The engine is very basic at its core, requiring only pressurized fuel and and a quick spin (starter) to get it running.

The gen-head is a standard 12 wire with a field coil. The 12 wires could be permanently wired in 120/240v configuration. You could bypass the CTs, the contactor, the mode switch etc., it is just a matter of looking at the wiring diagrams to understand HOW to bypass those components.

Same goes for the AM/VM switch. You could hardwire an output directly to the volt meter or from the CT to the load meter.

 

[Guyfang]

Well, its better to have, and not need, then to need, and not have. Sure you can do that. But if for any reason later on in life you need 3 phase, you will not have it.

 

[2Pbfeet]

Just curious if one was only using the gen on single phase 120/240 if any of the wires on the big ass switch on the back wall can be eliminated for simplicity. Same for the AM/VM switch on the front. ( I want to say s7 but could be wrong). Keep getting short circuit alarm when it rains and I spray them both with deoxit and cycle switches which does seem to help but if I decided to take it all apart and clean it thoroughly I wondered if any of the wires could be omitted
Thanks

I agree with @Guyfang on this one as well. Unless you go all in, stripping this down to an engine and a gen head with AVR, you are going to have a lot of wires, so the odds that removing the wires will solve the short issue is much less than one in three in my book. If you want a stripped down generator, why not swap this one for one built that way?

Personally, I'd spend the effort double checking terminal cleanliness, screw tightness, wire integrity, getting vibrating wires away from metal, and giving every single conductor end a shot of De-Oxit, not just the switches, though that's great too.

You didn't mention where in Alaska you are, so this is just a guess. If your generator is in a damp area, or an area exposed to humidity, like being on damp soil, there is going to be condensation on metal surfaces such as terminal strips and switches. A residual coating of De-Oxit will help keep water off the wires and contacts. Even better would be getting the generator under cover, and in an insulated enclosure.

All the best,

2Pbfeet

 

[Ray70]

I'm not all that well versed in how the burden resistors work, but I think there could also be a possibility of a damaged or cracked resistor, or a poor solder joint on one of them that could be causing your issue, if Detoxit in the switches isn't helping at all.
@kloppk is 100X better at explaining the resistor / overload / short circuit function than I am....

 

[kloppk]

Since you are experiencing "SHORT CIRCUIT" I suspect @Ray70 suspicion or something like it may be causing the faults.
From the symptoms it sounds like it might be a bad connection or cracked resistor.

A short circuit fault gets tripped when the K8 Overload/Short Circuit relay thinks there is a SHORT CIRCUIT condition.
Details in a bit..

For each leg of the genset there is essentially a CT and Burden resistor which generate an AC voltage proportional to the load on each leg.
Each of teh 3 voltages are supplied to K8 so it can monitor for any Overload or Short Circuit conditions
Normally the AC voltage generated is between 0 and 5.6 volts AC. This represent 0 to 100% load on the corresponding leg.
At 133% Load the AC voltage is 7.5 volts.
A load of 130% will cause K8 to trigger an Overload after 8 +/- 2 minutes. If the overload is greater than 130% K8 will trigger an Overload fault quicker.
The time delay of the overload fault is inversely proportional to the amount of overload.

A SHORT CIRCUIT fault is triggered when sensed CT voltage is 23.9 volts, which is way more than the 7.3 volts of a minor overload.

The voltages above are generated by the CT and Burden resistor circuit. The CT outputs an AC Current which gets applied across the Burden resistor. That resulting current flow across the resistor creates the AC voltage across the resistor that K8 monitors.

If a Burden resistor or associated wiring, connectors or switch contacts result in the Burden resistors resistance to no longer be in parallel with the CT the resulting voltage will skyrocket causing K8 to throw a Short Circuit fault.

Here is a diagram showing the interconnect of the CT's and the Burden resistors. It does not show specifically all the wires and connectors that connect everything together. With the set in 120/240 mode CT3 gets both R12 and R13 applied in parallel across CT3 by way of a set of contacts in S8.

 

[Guyfang]

On several sets I found that the Short Circuit fault light on, and it was the wires to the burden resisters in the left rear corner of the control cube. They had worn through, due to vibrations, against the side of the control cube. I like to look for shorts by opening all doors and take off the top of the gen set. Wait until dark and start the set up. In the dark. Look for a faint spark.