Westerbeke 8.0 BTDA kicking my arse

[ZZ13]

Ok. I just took a bike ride to S Hutchinson island to noodle on this. I think the problem is with the fuel delivery circuitry for the following reasons:

1. Fuse blows while preheat is held down and starter is cranking. Sometimes it actually just starts but it now always blows with the preheat engaged. That rules out the shutdown switches and the start relay/starter.

2. Bypassing the shutdown switches with jumpers makes no difference. Another data point in support of #1.

3. The point of shutdown varies. Sometimes it actually started and ran for a few seconds. Sometimes it shuts down as soon as it tries to start.

My next idea is to systematically disconnect the fuel delivery circuitry and hope I get to a point where the starter keeps on cranking without blowing the 8 amp fuse.

 

[ttmott]

I'm confused on the 8 amp fuse. That fuse isn't big enough to drive anything on the generator except for the relay in the TB. Did you pull the relay to see if the fuse still blew? I just can't seem to find an 8 amp fuse on any of the WB schematics.....

Edit - I found it. Pull the two relays and see if it still blows the fuse.

 

[ZZ13]

I'm confused on the 8 amp fuse. That fuse isn't big enough to drive anything on the generator except for the relay in the TB. Did you pull the relay to see if the fuse still blew? I just can't seem to find an 8 amp fuse on any of the WB schematics.....

Edit - I found it. Pull the two relays and see if it still blows the fuse.

Pull all the wires on the relay or just the input power wire? Start relay and run relay. Should I pull them one at a time? Run relay first? I think the preheat switch activates the run relay. I can hear it click when I depress it.

 

[ttmott]

Pull all the wires on the relay or just the input power wire? Start relay and run relay. Should I pull them one at a time? Run relay first?

No those Bosch style relays in the J-box. They should pull right out of their sockets. They are about an inch cube.
If one has failed and shorted, it will definitely blow that fuse.

 

[ZZ13]

No those Bosch style relays in the J-box. They should pull right out of their sockets. They are about an inch cube.
If one has failed and shorted, it will definitely blow that fuse.

Sorry Tom but I’m confused. Are these in addition to the K1 and K2 relays that are connected by wires with spade connectors? If so where is this J Box? I didn’t see any socketed relays in the box behind the gauge panel.

 

[ttmott]

Sorry you are right K1 and K2. I had assumed they were in standard relay sockets.
So, pull the wires off of terminal 86 on both relays and insulate the wire if needed. 86 is the relay coil +12V that ends back at the 8 amp fuse. The generator will not run but at least you can see if it still blows the fuse when preheat is pressed.

 

[ZZ13]

Sorry you are right K1 and K2. I had assumed they were in standard relay sockets.
So, pull the wires off of terminal 86 on both relays and insulate the wire if needed. 86 is the relay coil +12V that ends back at the 8 amp fuse. The generator will not run but at least you can see if it still blows the fuse when preheat is pressed.

Roger that. I’m down to 4 fuses out of the 15 I started this with. I just ordered 30 more. Ha!

 

[km1125]

I'd be tempted to replace those diodes with one rated for a higher current than the fuse. and replace the fuse with a circuit breaker that could be reset when things go south. However, finding what is shorted to ground is the real culprit. If I read correctly, one of the issues was one of the gauges shorted to ground internally. What were the other issues?

 

[ttmott]

Roger that. I’m down to 4 fuses out of the 15 I started this with. I just ordered 30 more. Ha!

Here you go this test is for the circuit in red -

 

[ttmott]

If the fuse still blows when you press preheat then leave the relays disconnected and disconnect the wire going into the oil pressure switch which should be a black with white stripe. This will remove the OP switch and the daisy chain of sensors from the equation. Here I highlited the test circuit in blue

 

[ttmott]

Then it still the fuse blows then disconnect the preheat solenoid coil wire (purple with white stripe) with still all the others disconnected and run the test again. Here in Green
This covers everything on that fuse related to pressing the preheat button

 

[ZZ13]

Thanks Tom. One clarification. Preheat alone does not blow the fuse. Pressing start while holding preheat blows the fuse. Sometimes it blows while cranking, before it starts. Sometimes it actually starts but then blows almost right away after that.

 

[ttmott]

Thanks Tom. One clarification. Preheat alone does not blow the fuse. Pressing start while holding preheat blows the fuse. Sometimes it blows while cranking, before it starts. Sometimes it actually starts but then blows almost right away after that.

Oh OK - still go through the test regiment above. Quite possibly a combination of things that are adding up to more current and taking out that tiny fuse.
So, if the above testing doesn't net anything then put a 10 amp fuse in then try again.
There are only a few things that draw current on that fuse.
The only thing the start switch powers is Relay K1 coil.
I'm beginning to think that the preheat solenoid may be having problems. We can set it up to start and run the generator without the preheat solenoid in the loop - another test later.

 

[ZZ13]

Oh OK - still go through the test regiment above. Quite possibly a combination of things that are adding up to more current and taking out that tiny fuse.
So, if the above testing doesn't net anything then put a 10 amp fuse in then try again.
There are only a few things that draw current on that fuse.
The only thing the start switch powers is Relay K1 coil.
I'm beginning to think that the preheat solenoid may be having problems. We can set it up to start and run the generator without the preheat solenoid in the loop - another test later.

Looks like you nailed it again, Tom. I left the relays connected and went straight to disconnecting the shutdown sensors and preheat solenoid. Doesn’t blow. I reconnected the shutdown sensors and still doesn’t blow. So looks like it’s the preheat solenoid like you suspected. I’ll order a new one (or two). Only $35.

Thanks a bunch. I owe you. Looks like I’ll go sponsor CSR again. I’ve been really down on it for that group of posters that want to keep turning it into a site for emotional non boating topics.

 

[ttmott]

Good news! I would be concerned with that tiny fuse regardless; if it were mine I be using a 10 amp fuse there. It seems with the preheat solenoid and two relays all on at the same time that it is very close to the 8 amps.

 

[ZZ13]

Good news! I would be concerned with that tiny fuse regardless; if it were mine I be using a 10 amp fuse there. It seems with the preheat solenoid and two relays all on at the same time that it is very close to the 8 amps.

I’ll check into that. So in summary there are only four things (6 individual items) that draw current through that fuse. The two relays, the group of three shutdown switches and the preheat solenoid. Wish Westerbeke had this and your debug steps in their manual.

So did the failed diode take out the solenoid? Or did the solenoid take out the diode? I’m guessing the diode was the root cause.

 

[ttmott]

I’ll check into that. So in summary there are only four things (6 individual items) that draw current through that fuse. The two relays, the group of three shutdown switches and the preheat solenoid. Wish Westerbeke had this and your debug steps in their manual.

So did the failed diode take out the solenoid? Or did the solenoid take out the diode? I’m guessing the diode was the root cause.

The switches don't consume current they only pass it; no different than a length of wire.
The diode good or bad will not affect anything other than the generator will not start if it fails; it'll crank but not start because the oil pressure isn't up during cranking. That diode is there to allow relay K2 to close when preheat is pressed and the generator to run until oil pressure is up and that oil pressure switch closes. Then after it starts, oil pressure is up, and preheat switch released the current to keep K2 energized comes through the three sensors rather than through the diode.

The diode is a check valve. If there is a dead short to ground on the anode side of the diode and +12V on the cathode side the diode may break down eventually and fail but I'm not yet convinced. Regardless if there was a dead short on one side you couldn't start the unit anyway because that fuse would continuously blow. Conversely if you have a dead short on the cathode side of the diode it will fry every time. A picture I clipped of a web site -

 

[km1125]

It wouldn't take a dead short one one side of the diode to fry it, just more current than it's rated for. If it's a 4 Amp diode and you're drawing 4 Amps though it, you're running on borrowed time. If half of the current flowing through the fuse was going through that diode, then the diode would fail around the same rate as the fuse would.

The other thing that can fry a diode is "back EMF" from something like a relay coil. When the current flow to a relay coil is interrupted, the magnetic field around the coil collapses. When this happens a spike of voltage is sent out both ends of the relay coil. It's like a micro-sized ignition coil and can cause a spike of hundreds or even perhaps a thousand volts. If the diode is not rated to handle this spike, then it will fail when the spike arrives at the diode's leads. A small capacitor to ground can eliminate this spike before it becomes a problem.

 

[ZZ13]

One last question. Slow blow or fast blow fuse? My replacements are all fast blow which means a startup spike gets it. I think I read factory fuse is slow blow.

 

[km1125]

You probably want a regular or slo-blo fuse for that. A fast blow fuse is really to protect sensitive electronics and you really don't have any of that in the circuit. As I noted before, I'd be MUCH more inclined to replace it with a circuit breaker anyways.