very tough circuit breaker question on Volvo 5.7GS

[scott76310]

I think I will do a back flip if someone can figure this one out!! I have a 1996 Glastron with the fuel injected 5.7GS volvo penta engine. On the right exhaust riser is 3 circuit breakers. The biggest one is a 60 amp and it is the one I am having problems with. The breaker only trips when I turn off the ignition. It is very intermittent. It may go a couple weekends with no trips or it may trip once or twice a weekend or it may trip several times in a row. It only does it when you turn the key off!!! Never ever has it tripped while running or turning on (when you would think the load is greatest). I know it trips at the exact second you turn it off because I have the radio running off of an accessory switch on the dash and it kills power to it at the same time. I have no way that I can think of to test it. I know the circuit breaker is good. The only possible thing I could think of that would cause that was possibly a faulty ignition switch that had a short in it when turning off but I left the switch on once and killed it by pulling the safety lanyard by the throttle to kill the engine and it still tripped the breaker. I think everything on the boat runs off of this circuit because nothing works when it is tripped. Please help!

 

[HT32BSX115]

Re: very tough circuit breaker question on Volvo 5.7GS

Howdy,

In general 2 things could be happening. You *could* have something going in the switch internally that is occasionally shorting the switch out or the actual circuit breaker is/has become defective and is getting hot but not quite hot enough all the time to trip. DC circuit breakers don't really fail that often. especially when they are not being used as a switch themselves.

I would have a very close look at the wiring behind the dash near the ign switch. It's possible that the switch itself is turning ever-so slightly when you turn it off allowing the "hot" side to contact something grounded. THat would trip the breaker pretty quickly.


Regards,

Rick

 

[Reel Poor]

Re: very tough circuit breaker question on Volvo 5.7GS

Just a guess.....But maybe someone has replaced the switch with an older model outboard switch. They ground the ignition system to kill the engine.

 

[wire2]

Re: very tough circuit breaker question on Volvo 5.7GS

I expect you can access the back of the ignition switch? Try leaving the key on and removing just the ignition wire. That will narrow it down to the key switch or somewhere else.

Or, place a hand compass over the ign. wire and watch when you switch off. If there is a current spike then, the needle will sense it and deflect hard. It works like a non-calibrated ammeter.

Let us know what you find.

 

[Dunaruna]

Re: very tough circuit breaker question on Volvo 5.7GS

Test the alternator output, your problem could be a faulty regulator.

 

[scott76310]

Re: very tough circuit breaker question on Volvo 5.7GS

Thanks for the reply's everyone!! You guys question the ignition switch shorting out and that was also my first thought. I know its not an outboard switch because it is very intermittent and that would trip it everytime. I don't think it is possible now that it is the switch because as I stated in my first post. I have killed it by using the safety switch lanyard that goes around your wrist and it still did it so that pretty much eliminated any possibility of a short in the ignition switch because I killed the motor without touching it. I also thought it was a bad breaker even though that made no sense whatsoever as to why it would only trip when I shut off the ignition. I wired a large 60 amp fuse to the back of the breaker and the last time it tripped I just left it tripped and installed the 60amp fuse. It worked for most of the day like that and then it eventually blew the fuse so I just reset the circuit breaker again and it worked for the rest of the day. Its weird because sometimes it will last for a couple weeks and sometimes I have to push it every time I kill it!!!! I can't think of any way to test it but testing the alternator as stated above did cross my mind but I was actually wondering what on the boat could cause a large power draw when you kill the power to it. Thanks again for the reply's, I would be thrilled to get any more ideas!

 

[Don S]

Re: very tough circuit breaker question on Volvo 5.7GS

I doubt you are getting a 60+ amp power draw. You could get a clamp on meter or one that just sits on the wire and actually test the amperage, but my guess is the breaker is faulty. I have replaced a couple of those style breakers because the pop at times for no reason, but not when shutting off the engine.

 

[Mischief Managed]

Re: very tough circuit breaker question on Volvo 5.7GS

Since the fuse blew too, I'd rule out the breaker as a problem. Thinking you have a floating ground that's forcing current in odd directions, kind of like when a wire is broken in trailer a trailer light harness and the lights "work", but in a really weird manner. I'd check the negative battery connections on the engine and the bonding wires on the rest of the boat.

 

[wire2]

Re: very tough circuit breaker question on Volvo 5.7GS

You did blow the 60 amp fuse in parallel, so there must be a current spike at turnoff.

There are only a few circuits that can draw that much, (other than a short). The starter, trim pump, and possibly the alternator.

The starter shouldn't be using that circuit.

The trim circuit *might* energize both up & down at once but very unlikely. You could verify by removing the wires from the solenoids and turn engine off.

If not the trim, test the alternator by removing the large wire and turn key off.

Do you have a vom or digital voltmeter? Place the + lead on a breaker terminal and - to ground. Does the voltage jump up at key off?

 

[Don S]

Re: very tough circuit breaker question on Volvo 5.7GS

What is the FULL model number of your engine?
A 5.7GS is a carbed engine, also need the letters following what I assume will be 5.7GSi

 

[scott76310]

Re: very tough circuit breaker question on Volvo 5.7GS

Don S. I really thought it must be a faulty circuit breaker too but it still makes no sense why it would only do it when I turn it off and yes 60 amps is a bunch so I feel like there is a direct short when I kill the switch so the only really logical answer is the switch has a short in it but then we go back to when I killed the boat using the emergency kill switch and didn't touch the ignition switch and it did the same thing. I have checked the grounds to the engine and have even completely changed all the battery cables even though everything looked like new even the connections where it is bolted to the block looks new. There is no rust or corrosion or anything like that on the engine anywhere. At this point I am wondering about a bad ground somewhere even though I don't understand how that causes that when I turn the switch off or maybe something in the alternator???? Is there something in the alternator that would cause a large draw, short or voltage spike when I kill the power to it but it is still spinning (because the engine is still turning a short time before it stops running)?? Would a votage spike even cause a problem? I can't imagine a 60 amp draw but I don't understand what would cause a short when you kill the power either???? I really appreciate all the feedback I have got so far!

 

[scott76310]

Re: very tough circuit breaker question on Volvo 5.7GS

Don S. It may be the GSi. I can't tell you for sure because I have the boat at the storage building right now and I can't run and check it today but it defenitily isn't the carbed model. Its a 96 glastron with the 5.7 and a throttle body injection.

 

[scott76310]

Re: very tough circuit breaker question on Volvo 5.7GS

You did blow the 60 amp fuse in parallel, so there must be a current spike at turnoff.

There are only a few circuits that can draw that much, (other than a short). The starter, trim pump, and possibly the alternator.

The starter shouldn't be using that circuit.

The trim circuit *might* energize both up & down at once but very unlikely. You could verify by removing the wires from the solenoids and turn engine off.

If not the trim, test the alternator by removing the large wire and turn key off.

Do you have a vom or digital voltmeter? Place the + lead on a breaker terminal and - to ground. Does the voltage jump up at key off?

Wire2 thanks for the input. I was wondering if I could just disconnect the alternator but then I am right back to the part where it does it very randomly. It may go 2 weeks without tripping the breaker or it may trip it once or twice on a weekend or sometimes it trips it several times in a row but it is so erratic. It is rare that it does it over and over again!! I do have a digital voltmeter. So you are saying I can put one probe on the circuit breaker (still wired up) and the other to ground. When its running I am going to assume that this number will be 13-14 volts. When I turn the key off then there may be a possibility that this number will jump up and if so how much and what would be abnormal. I am assuming that any increase would be abnormal. Does this mean that a voltage spike would cause the breaker to trip?

 

[wire2]

Re: very tough circuit breaker question on Volvo 5.7GS

Yes, any voltage rise with key off is odd. It should remain at ~12v or drop to 0 with key off, depending on where the CB is connected in the harness.
The alternator field is dropped with key off, so there should be no output, even though it's still spinning.

An increase in voltage will typically cause a corresponding increase in current. (Ohm's law)


Your dash voltmeter gets disconnected with the key so it won't show a spike.

Intermittent faults are challenging, keep feeding us info, we'll try to narrow it down.

 

[bruceb58]

Re: very tough circuit breaker question on Volvo 5.7GS

You verified that you are indeed getting a current draw by installing the 60A fuse and having it blow.

Might be necessary to start isolating things to find the culprit. A guess is going to be that it is the alternator.

Just as a sanity check, check to see that the wire that comes off the breaker is not rubbing against the engine somewhere. It is possible that the insulation has worn through and the shaking of the engine as its shutting down causes a momentary short.

A loose ground will not be causing your problem. It would actually prevent the breaker from tripping..

 

[bruceb58]

Re: very tough circuit breaker question on Volvo 5.7GS

Yes, any voltage rise with key off is odd.

Actually not odd at all. You can have a back EMF if there are any inductive loads when turning off power.

 

[scott76310]

Re: very tough circuit breaker question on Volvo 5.7GS

You verified that you are indeed getting a current draw by installing the 60A fuse and having it blow.

Might be necessary to start isolating things to find the culprit. A guess is going to be that it is the alternator.

Just as a sanity check, check to see that the wire that comes off the breaker is not rubbing against the engine somewhere. It is possible that the insulation has worn through and the shaking of the engine as its shutting down causes a momentary short.

A loose ground will not be causing your problem. It would actually prevent the breaker from tripping..

Thanks for the replys. I did check the wires going to the breaker when I had it off and there are no worn insulation spots or anything like that and I am pretty certain there are no shorts of that type because I have been is some very rough water and have had the boat rocking in every direction and it Never ever has tripped while it was running or driving only at the exact second the ignition is turned off either by the key switch or using the lanyard kill switch.

My next question to everyone was going to be if a loose ground would cause something like this to happen. I know the one from the battery to the block and the computer to the block are good. If there is a loose ground I have no idea where it would be or how I would find it. I haven't found one so far and I have been all over that boat. I have had someone tell me to look for a loose ground and now you say it will not cause that. I think sometimes when there is a weird electrical problem people are quick to say "look for a loose ground" I know that can cause weird things and I am really curious as to who is right on that one. Bruceb58 you seem like you know what you are talking about so unless someone can give me a reason then I will assume right now that maybe its not a ground issue.

I guess that right now I will look at the alternator a little closer but then again it is so hard to check because it is so random. Could an alternator shop determine it as a fault even being so intermittent?

Ok, you got me on the back EMF. I don't know that much about that and what kind of problems that could cause. Could this be the problem and what is to high of a voltage?

Thanks again everyone for all of the feedback. I really do appreciate it.

 

[wire2]

Re: very tough circuit breaker question on Volvo 5.7GS

"Back EMF" (electromotive force) is the result of an applied voltage causing a current in a coil and inducing current in adjacent turns. The induced current opposes the applied voltage and slows the initial inrush of power.

The point is, in DC circuits, it's always in the opposite direction, so would tend to reduce voltage, not spike it up.

The only inductive load on at "run" will be the blower

Most industrial DC controls have a diode across relay coils to absorb the induced energy. It's connected in reverse and does nothing when DC is applied, only when it's removed and a spike is induced.

 

[bruceb58]

Re: very tough circuit breaker question on Volvo 5.7GS

The point is, in DC circuits, it's always in the opposite direction, so would tend to reduce voltage, not spike it up.

The current may be in the opposite direction...you will certainly get a voltage spike. That is why diodes are put across relays. The back EMF is large enough to blow the outputs of circuits driving the relays.

Back EMF is a very short duration of current though...not enough to trip a relay since the relay relys on the heating effect to trip the realy and it needs high current over a longer period of time.

 

[scott76310]

Re: very tough circuit breaker question on Volvo 5.7GS

The current may be in the opposite direction...you will certainly get a voltage spike. That is why diodes are put across relays. The back EMF is large enough to blow the outputs of circuits driving the relays.

Back EMF is a very short duration of current though...not enough to trip a relay since the relay relys on the heating effect to trip the realy and it needs high current over a longer period of time.

So you are saying Back EMF will not cause my problem? Wire2 said the blower is the only inductive load at run. Would the electric fuel pumps fall into that catagory also? I think my boat has 2 electric pumps on it so I guess they could cause back EMF because it has done it with the blower off also. If what you say is true then checking the wire on the breaker with a volt meter wouldnt do any good.

You also said it wouldn't be a ground.

All that leaves is a short or large load and if that is the case then I would need an amp meter and not a voltage meter. Have you ever used or do they even have an amp meter with the little clamp that checks dc voltage. If they do make them how well do they work? I am thinking that if I use one of these to check the amperage and not the voltage going to the circuit breaker to determine the load. Maybe it is near capacity and that is why it trips periodically (as I am writing this I can't help but think that if it was that near capacity then it would trip when I turned on lights, the blower, stereo etc but that never happens) Ok, I have already talked myself out of that, I guess I could still use the amp meter and look for large loads to occur while turning off the ignition and then start removing items from the circuit until it quits?????

Thank you guys so much for keeping the replies coming.