803a trips DC breaker in AUX fuel position

[BDenmark92]

DC circuit breaker trips as soon as the master switch is in the AUX fuel position.
I can reset the breaker when the switch reaches the main fuel supply position and the generator will start and run fine from there. I found a little box by the fuel pumps that has four wires on each side of it. If I unplug that box, the circuit breaker does not trip. What is the function of this box and where can I find one?
Sorry for the low quality picture, I was hoping these numbers could provide some information. I can provide a better one tomorrow

 

[jamawieb]

Hard to find new but you may find one through Delks Army Surplus. They are really simple and you maybe able to fix the problem if you remove the circuit board from the box and do some testing.

 

[Guyfang]

First, is this a new gen set to you?
Have you ever seen it work right?
Have you downloaded the TM's?
Now, stop and think. The gen set will work, in the normal start and run S1 position? If so, then think about what is different between the normal start and run, and AUX? The E1, (Aux fuel pump). Open up the cover to the fuel tank, and disconnect the plug to the E1. Then start the set normaly. Then place the S1 in the AUX position. Did the CB1 pop? If not, then you might just try testing the E1, to see if it works OUTSIDE of the normal operating circuit. You can do that with two pieces of wire. Go from, (and its good to have help here) the + and - side of a 24 VDC power source, like the slave recpt or the battery's. Will the pump run or not. If the pump runs, then start looking at the A9 (float switch module).

 

[BDenmark92]

First, is this a new gen set to you?
Have you ever seen it work right?
Have you downloaded the TM's?
Now, stop and think. The gen set will work, in the normal start and run S1 position? If so, then think about what is different between the normal start and run, and AUX? The E1, (Aux fuel pump). Open up the cover to the fuel tank, and disconnect the plug to the E1. Then start the set normaly. Then place the S1 in the AUX position. Did the CB1 pop? If not, then you might just try testing the E1, to see if it works OUTSIDE of the normal operating circuit. You can do that with two pieces of wire. Go from, (and its good to have help here) the + and - side of a 24 VDC power source, like the slave recpt or the battery's. Will the pump run or not. If the pump runs, then start looking at the A9 (float switch module).

I am a heavy diesel field mechanic that has never touched one of these generators before.
This was my first interaction with this piece of equipment
The hour meter shows 31hrs and there is a sealed document showing it was placed in storage not long after manufacturing.
My customer bought this unit along with an 804a and hired me to check both generators.
I have not returned to the generators since I first inspected them.

In the field I did not have the TM's available but already narrowed down the issue down to what I now believe is the "Float Switch Module", if that is what the little box under the fuel tank cover, bolted to the side panel is. When it is unplugged the breaker will not trip. Unplugging anything else has no positive effects.

My main reason for this post is positively identifying what that little box is and finding a replacement or repairing it.

 

[kloppk]

According to the TM internally there are a couple of relays and possibly other components.
There is one available on ebay. Search for 88-20492

 

[Guyfang]

The A9 is what controls the E1. So, naturly if you unplug it, the E1, (if it were shorted) would pop the CB1. Dosnt cost a dime to first unplug the E1 and see what happens.

 

[Ray70]

I agree with Guy, unplug your Aux. pump and see what happens first. IF the float module happens to end up being the problem there are only a handful of components in it. It may be easier to repair than find a replacement, however it is unlikely that the module is causing the breaker to pop. My money is on a shorted pump.... seen it before....
Usually when the float modules go bad the pump doesn't get power and won't run. Unplug the pump, if the DC breaker no longer pops ( and you have under 3/4 tank of fuel ) check for 24V on the pump wires when in AUX position on S1, if you do, replace the pump. There are Airtex pumps available for under $50. Tons of info all over this forum for the pump PN's that work best.

 

[BDenmark92]

I appreciate the input guys, Ill have to be more specific of my troubleshooting process in the future. The first thing I did was unplug the fuel pump, then worked my way up toward the key switch.
Anyway I found the issue with my float module. There's an internal component that is mounted against the case (I assume to use it as a heat sink) that was shorting out. I placed a non conductive thermal pad between the component and the case and the issue is resolved.

By the way, Thank you Guyfang for posting all those TMs. Saved the day on another genset I worked on.

 

[Ray70]

Good work tracking down the problem, but I have a bit of a concern with the repair. I believe the item in question is a voltage regulator. It is mounted to the aluminum case which does act as a heat sink. Given that the component has shorted internally, I would be concerned that is would fail completely at any point. By isolating it from the heat sink you may speed up it's final demise. If you look at it under magnification it should have markings that will identify it and you could buy a replacement for a couple bucks. Might be worth fixing it correctly rather than risk having if fail at the worst possible moment! If you can't find any markings, I have a bad module in my parts pile, I can take a look and figure out what you would need.

 

[BDenmark92]

I suppose I should add as a disclaimer for anyone that stumbles upon this thread in the future, I consider what I did as more of a proof of concept rather than a repair. I agree the voltage regulator, if that is indeed what it is, needs to be replaced. The pad I used is a thermal conductive pad, but not electrically conductive so if anything it aids in the transfer of heat, not hinders.

 

[Guyfang]

Post a picture.

 

[rpjuneau]

Ok just reading these post trying to trouble shoot my mep002a. Was and has been a great gen set. Have 52R walmart batteries that keep failing every 2 to 3 months. Needles to say did load test and batteries failed again. Pulled boat battery and another battery, she cranked right up, made mistake of disconnecting jumper between batteries while running, DC breaker tripped. Turn master off reset switch, turn to aux and instant trip. What do I need to check for to replace. Thinking diode, resistor. Need insight. Thanks

 

[rpjuneau]

Ok just reading these post trying to trouble shoot my mep002a. Was and has been a great gen set. Have 52R walmart batteries that keep failing every 2 to 3 months. Needles to say did load test and batteries failed again. Pulled boat battery and another battery, she cranked right up, made mistake of disconnecting jumper between batteries while running, DC breaker tripped. Turn master off reset switch, turn to aux and instant trip. What do I need to check for to replace. Thinking diode, resistor. Need insight. Thanks

Meant 51R batteries

 

[Light in the Dark]

You really should ask this question in a separate thread, just for your topic.

 

[doghead]

Most likely one of the fuel pump capacitors failed(common when you unhook battery while running).

Snip it out of the circuit, it’s not needed.