Blew 110 AMP fuse. Pump resistance 2 ohms

Rhadley · Jun 27, 2010

I blew the 110 amp fuse on my 1984, 120HP mercruiser with low pressure hydraulic trim pump. Solenoids seem ok--they operate when I disconnect wires to the pump. Resistance thru the pump voltage input wires to ground is 1.7 ohms. Is my pump gone? I don't see what else could pull that current in that circuit.
Thanks

RRitt · Jun 28, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

10 amps isn't that much. lots of trim motors will melt that kind of fuse.
110 amps is enough to catch your boat on fire and kill all fish within 100yards. You sure it was 110amps?

Rhadley · Jun 28, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

That's what the manual says it is, and by the looks of it I believe it. This is a large copper/insulated connection between the +12V cable going to the pump solenoids and the solenoids. I'm sure you have it also.

Icefire55 · Jun 28, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

1.7 ohm should get 7 amps to it, on 12 volts. one thing you should look is to see if the + side is grounded somewhere, like a bad wire.

Rhadley · Jun 28, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

If it was grounded, the resistance would be zero. Although conditions could change when the pump pulls current.

Icefire55 · Jun 28, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

it depends where he tested it. if he disconnected the pump and checked the resistance at the pump, the wire from the solenoid to the pump can be grounded.

There is a short somewhere because to blew a 110A fuse @ 12v, you need a minimum of 0.11 Ohms or less

RRitt · Jun 29, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

Rhadley said:
That's what the manual says it is, and by the looks of it I believe it. This is a large copper/insulated connection between the +12V cable going to the pump solenoids and the solenoids. I'm sure you have it also.

my boat has a 20A circuit breaker between starter battery+ and relay solenoid. It doesn't even begin to make sense installing a 110A fuse to protect a 15A device.

Icefire55 · Jun 29, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

the 110A fuse probably protect the whole battery in case of a direct short no to blow the battery apart.

Bt Doctur · Jun 29, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

A starter/alt shop can rebuild it, check there first

Rhadley · Jun 29, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

The 15 or 20A in-line fuse is to the wire that goes out to the trim sensor or limit switch. That is not what I am talking about. And yes, I disconnected the pump wires from the solenoids. The pump should have a known, good resistance to it; that is what I need to know.

Bt Doctur · Jun 29, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

That fuse is what powers the wire going to the control box handle to power the up and down solenoids, nothing to do with anything else.Does the pump run when connected to a battery?

Rhadley · Jul 2, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

Nope. I was leery of putting a hard-wired connection knowing it might pull a ton of current, but when I touch 12V to it quickly, it sparks and does not turn over the pump at all.

stonyloam · Jul 2, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

From the book. Diagram shows the 110 amp fuse protecting the up solenoid.

Electrical Specification
Pump Amperage Draw
115 Amps at
2200-2600 P.S.l.
(15173-17932 kPa)

Howard Sterndrive · Jul 2, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

a fuse that size seems whacky, but my math says it is right.

Those little trim pumps flow just over 1 gallon per minute. I used the formula for hydraulic horsepower:

2600 psi X 1 GPM /1714 = 1.5HP

1.5HPx 746 = 1131 watts

1131W/12V= 94 amps

when we take into account the energy lost in the conversion to hydraulics I can see 110A no problem

Icefire55 · Jul 2, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

Gee, 110Amps for a little trim pump!

Well if it's indeed 110A, than the resistance is wrong and should be lower. a car starter have abou 0.04 and can crank up 300Amps.

I would remove the motor for the pump if possible in case of a blocage and try it.

Howard Sterndrive · Jul 3, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

12V and 100 A = .12 ohms

of course motors (and most loads) read quite a different resistance value on the bench than they represent in the circuit when it is operating

Rhadley · Jul 4, 2010

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

Took off the motor from the pump and applied power. Spins free. Insides look fine.

Solenoids work and do not short to ground when activated. Pump seems to turn fine; used screwdriver to turn it with motor off. I've uploaded a picture of the fuse. About ready to just get a new fuse and see if it was a fluke..

tm3912 · Aug 27, 2012

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

Rhadley I know this is an old post but wondering if you had any luck with your problem. I have a 110A fuse exactly like yours. My trim won't work, although I can hear the solenoids clicking the motor will not engage. When I test the fuse, per the manual I get 12V on the bottom side of the fuse but only 2 volts on the top side. Knowing nothing about electrical stuff I don't know if this is right or wrong.
Anyways can you tell me if you changed out the fuse and if that worked. Thanks.

Don S · Aug 27, 2012

Re: Blew 110 AMP fuse. Pump resistance 2 ohms

tm3912, you need to start a thread of your own, with your engine and drive information. This thread is about Rhadley's problem.

Blew 110 AMP fuse. Pump resistance 2 ohms

Petty Officer 1st Class

Captain

Petty Officer 1st Class

Seaman Apprentice

Petty Officer 1st Class

Seaman Apprentice

Captain

Seaman Apprentice

Supreme Mariner

Petty Officer 1st Class

Supreme Mariner

Petty Officer 1st Class

Vice Admiral

Rear Admiral

Seaman Apprentice

Rear Admiral

Petty Officer 1st Class

Attachments

Cadet

Honorary Moderator Emeritus