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Old 12-25-2013, 12:29 PM   #1
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Blown 15 amp inline fuse on freshwater pressure pump

Merry Christmas everyone. The other day we found there was no running water in the galley and discovered a blown 15 amp inline fuze on freshwater pressure pump. I replaced it and water pressure returned but I noticed yesterday that the fuze had blown again. A colleague suspects it's a load issue which suggests the pump is the issue. The system groans when the pump is operating. Are there other possible causes for this? I do have a spare pump, BTW.

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Old 12-25-2013, 02:45 PM   #2
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Your pump is probably binding due to trash in the impeller, bad bearing, ? and is pulling enough current to blow the fuse. Pull the pump and replace and it should be fine.

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Old 12-25-2013, 02:53 PM   #3
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Check your filter(s)- they could be clogged enough to cause this.
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Old 12-25-2013, 02:57 PM   #4
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Good suggestions from David.
It also could be the pressure switch, the pump should shut off b/4 it draws more than 10-12 amps. If it "groans" just b/4 shutting off but not while the water tap is full on, I would say pressure switch. Some are adjustable, some not, If adjustable lower the shut-off pressure (CCW on the screw or nut) in the pressure switch.
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Old 12-25-2013, 03:01 PM   #5
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Thanks so much. I'm a newbie boat owner and am continuing on my learning curve. Is the pressure switch on the pump or elsewhere in the system?

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Old 12-25-2013, 03:11 PM   #6
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Usually it's on the pump, depending on the manufacturer.
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Old 12-25-2013, 07:33 PM   #7
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If replacing the pump solves the problem, you might be able to rebuild the old pump economically and use it as your spare.
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Old 12-25-2013, 07:44 PM   #8
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Jim

Depending upon the sound insulation in your Krogen 42 you may not be able to hear the fresh water pump running. Before you replace the pump, replace the fuse once more and then listen to whether or not it turns off or is it running 24/7. If it is running then you either have a malfunctioning pressure switch or an air leak.


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Old 12-25-2013, 08:57 PM   #9
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also check your wiring..... too small wire in the system or corrosion could be the culprit by increasing the amperage draw....
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Old 12-26-2013, 06:55 AM   #10
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Fuses come in many styles , some are ,slow blow, that will allow a slight overload as a motor starts, some are very fast blow , to protect delicate electronics .

Slow blow for motors is worth the effort, although I would measure the pressure at the faucet to see if its normal..
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Old 12-26-2013, 07:01 AM   #11
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Small wires and corroded connections equal high resistance and high resistance in a DC system means lower voltage and current.

Too small cross section of wire and a corroded connection gets hot because the power per unit of area may be very high, not because the amount of power has increased.

Increasing resistance in order to reduce voltage and current is the oldest method of controlling the speed and power of brushed DC motors. When you increase resistance you decrease voltage and that reduces the speed the motor turns. The slower it turns the less power it produces and the less current it draws.

If the load on the motor increases (say it's a positive displacement pump and the discharge is blocked) and voltage remains the same, then yes, the current will increase and the fuse may blow.

But, when electrical input to the motor is decreased by resistance, the current required to run the motor is also decreased and the fuse will not blow.
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Old 12-26-2013, 07:10 AM   #12
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Quote:
Originally Posted by RickB View Post
Small wires and corroded connections equal high resistance and high resistance in a DC system means lower voltage and current.

Too small cross section of wire and a corroded connection gets hot because the power per unit of area may be very high, not because the amount of power has increased.

Increasing resistance in order to reduce voltage and current is the oldest method of controlling the speed and power of brushed DC motors. When you increase resistance you decrease voltage and that reduces the speed the motor turns. The slower it turns the less power it produces and the less current it draws.

If the load on the motor increases (say it's a positive displacement pump and the discharge is blocked) and voltage remains the same, then yes, the current will increase and the fuse may blow.

But, when electrical input to the motor is decreased by resistance, the current required to run the motor is also decreased and the fuse will not blow.
Thanks for the explanation....
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Old 12-26-2013, 08:14 AM   #13
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Good advise from psneed and RickB! Spot on!
I suggest this book or one like it for anyone not understanding all the systems on their boat. After teaching electrical and diesel and a career in the automotive industry I am amazed at the myths of electricity that are given as gospel by even experienced cruisers.

Boatowner's Mechanical and Electrical Manual : How to Maintain, Repair, and Improve Your Boat's Essential Systems: How to Maintain, Repair, and Improve Your Boat's Essential Systems, Edition 3
Nigel Calder - May 31, 2005
McGraw Hill Professional - Publisher
$49.95 $27.47 Buy Goolge play store

Hope this Helps
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Old 12-26-2013, 12:36 PM   #14
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Thanks again all. I've got the e version of Calder's book on my iPad and have even reviewing this section on water pumps etc. it seems the pump may or may not have the switch. This will be a. Winter project.

Jim, Sent from my iPad using Trawler
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Old 12-26-2013, 06:07 PM   #15
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Which water pump mfgr & model and maybe you will get more specific answers? Maybe not but usually it helps us help you.
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Old 12-30-2013, 09:10 AM   #16
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Why not start with the simple things first? Check the strainer or filter on the inlet side of the pump. Make sure it's not partially clogged. Clean it and reinstall it.

Is the fuse that's blowing the correct fuse for the pump? Check the installation instructions or the manufacturer's website. A previous owner may have used the incorrect fuse. Something like a pump would do well with a "slow blow" fuse because of the current surge when the pump starts up.

Why is there an inline fuse in the first place? Isn't the circuit protected by a circuit breaker (or fuse) in the electrical panel?
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Old 12-30-2013, 11:59 AM   #17
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I haven't been back to the boat since Christmas Eve so cannot comment further to you questions, except to say that I don't know why this is protected by an inline fuse.

I am concerned however that I may have either drain the water tanks prior to working on this pump or have a bung (or two) at the ready to control the water flow while I work on the pump. I'm worried the system will siphon otherwise. I don't believe there is a shutoff on the tank side of the pump.

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Old 12-30-2013, 12:02 PM   #18
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You need a fuse/breaker for the circuit and you should have one for the device, hence the inline.
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Old 12-30-2013, 12:37 PM   #19
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Quote:
Originally Posted by Xsbank View Post
You need a fuse/breaker for the circuit and you should have one for the device, hence the inline.
I don't think a second fuse is usually required...as long as the wire from a fused/breaker panel to the device is protected and the device doesn't need special protection (never had a pump that did)...no need that I know of.

http://www.shurflo.com/files/RV-Inst...0003_0013_.pdf
.

unless there are other devices on that circuit.
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Old 12-30-2013, 12:46 PM   #20
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I should have clarified. I understand the need for the fuze/breaker, but don't know why the pump wasn't wired into the breaker panel.

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