7.6BTD Blowing 8A Fuse Part 2

[dtfeld]

I bypassed the high temp switch this morning in order to finish an oil change, impeller change and a new belt. Got it all done and fired the generator up and put a full load on it. Was working great for about 20 minutes, then it died again.

Blew the 8A fuse again!

I replaced the fuse and this time, the fuse blew as soon as I hit the preheat switch (as opposed to the start switch yesterday).

I opened the on generator control box and I could smell acrid electrical smoke. I looked at the wire looms, but could not identify a chafed/shorted wire. About the only other thing in that box are the K1 and K2 relay. The only other things in that circuit are the other temp and pressure switches. Might they all been fried at the same time??

Ran out of time, but something is shorting out that circuit...could be out on the wire loom, but the smell was prominent as I opened the control box.

Hmmm.

Ideas?

 

[LMBoat]

I would try to bypass the other safety senders (oil & coolant) and see what happens. Easy/cheap to do. You could have had another one fail. Possibly the new one is bad? I had a similar issue and it was the coolant sender.

 

[dtfeld]

I bought 2 new relays, that’s about the only thing in the box brside wires, so I’ll replace those and the start bypassing the other switches...

 

[ttmott]

David - I don't remember any "fuse" in the generator's circuits; at least on a 2000 400DA with the Westerbeke 7.6BTD. Seems there were three circuit breakers on my generator; two in the DC wiring and one for the AC feed. On the DC side there is a 20A main circuit breaker and then a 10A self resetting for the controls. Item 13 below is the 20A and Item 25 is the 10A.

 

[ttmott]

These are the two circuit breakers:

 

[dtfeld]

Factory manual has 2 versions. One with an 8A fuse, another without. Manual says it protects the control box. I think another difference is the plug on the wiring harness...I have a 3x5 pin plug, the other is 2x4.

Here’s the schematic I’ve been working off of and seems to match what is in the boat. Not sure why the difference.

 

[dtfeld]

Snapped this today, unfortunately too busy boating to do any further troubleshooting

Looks like they changed this at some point from a 10A cicuit breaker to a 8A fuse...

 

[dtfeld]

So finally diagnosed the issue. I think I had a double component failure. The water temp switch was shorted to ground and the control relay for the preheat solenoid is also problematic. I knew the water switch was grounded and replaced that, but still blowing fuses.

I noticed that the preheat solenoid was getting unusually hot, and pulled the "S" contact off. Generator now running just fine, albeit without the glow plugs, so obviously the preheat solenoid is pulling way to much current. I'm going to order a new one and I expect to be back up and running shortly.

My guess is the temp switch failed to ground and that caused an issue with the preheat solenoid.

 

[dtfeld]

Upon further review...

I have now replaced the coolant temp switch that had failed to ground, both the K1 and K2 relays ( I dont think they were bad) and finally the preheat solenoid. Started it up, everything works as its supposed to...except the preheat solenoid is now made all the (glow plugs on all the time) and the preheat solenoid was unusually hot.

Looking at the schematic, that solenoid should only close when the preheat switch is depressed. However there is a diode that feeds the K2 and K1 relay. I'm wondering if that diode isn't bad??? Possible failed closed due to over voltage.

How else could that circuit be hot??

Also anybody have a specification on that diode? I'd like to buy one for the next trip to the boat in case that is the failure.

 

[Ben1553]

Did you ever figure this out? I'm having the same issue.

Upon further review...

I have now replaced the coolant temp switch that had failed to ground, both the K1 and K2 relays ( I dont think they were bad) and finally the preheat solenoid. Started it up, everything works as its supposed to...except the preheat solenoid is now made all the (glow plugs on all the time) and the preheat solenoid was unusually hot.

Looking at the schematic, that solenoid should only close when the preheat switch is depressed. However there is a diode that feeds the K2 and K1 relay. I'm wondering if that diode isn't bad??? Possible failed closed due to over voltage.

How else could that circuit be hot??

Also anybody have a specification on that diode? I'd like to buy one for the next trip to the boat in case that is the failure.

View attachment 73401

 

[dtfeld]

Did you ever figure this out? I'm having the same issue.

That diode circled in red needs replacing...

It may have taken out some of the safety switches as well.

 

[TRG]

So finally diagnosed the issue. I think I had a double component failure. The water temp switch was shorted to ground and the control relay for the preheat solenoid is also problematic. I knew the water switch was grounded and replaced that, but still blowing fuses.

I noticed that the preheat solenoid was getting unusually hot, and pulled the "S" contact off. Generator now running just fine, albeit without the glow plugs, so obviously the preheat solenoid is pulling way to much current. I'm going to order a new one and I expect to be back up and running shortly.

My guess is the temp switch failed to ground and that caused an issue with the preheat solenoid.

I have a 8.0 btd but have the same issue blowing the 8 amp fuse. How do you check to tell if the oil, water, or exhaust switches are shorting to ground. I have a hunch one of the 3 is the problem but not sure how to test to tell which switch has the ground issue.

 

[dtfeld]

I have a 8.0 btd but have the same issue blowing the 8 amp fuse. How do you check to tell if the oil, water, or exhaust switches are shorting to ground. I have a hunch one of the 3 is the problem but not sure how to test to tell which switch has the ground issue.

I saw your other post, and responded. There is a Part 3 to this saga, but long story short, the first thing is diode circled in red above needs to be replaced.

you may have a bad switch, and you can use a small wire to jump the individual switches (or all 3 for that matter) to eliminate them for diagnostic purposes.