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Old 06-05-2008, 14:35   #1
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Blowing fuses in the bilge system

Pop, Pop, Pop, Pop. We sure have consumed a lot of fuses trying to get the bilge pumping system working.

We installed the pump with a fuse, no problems, worked fine !

Then we installed a float switch (Sure Bail), in series. That works until we pour salt water in the bilge to test it and Pop, goes the fuse !

All joints are above the water line and are sealed with resin heat shrink. All componenets test fine with the multimeter when not in use.

Very simple circuit, tripple checked Batt>fuse>switch>sure bail>pump>ground

Can the salt water be shorting out the system enough to pop the fuse, and if so why would the pump work alone.

Any suggestions ?
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Old 06-05-2008, 14:41   #2
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Sounds like your float switch may have lost it's water tight integrity and be shorting out to the water.
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Old 06-05-2008, 14:56   #3
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Originally Posted by ribbony View Post

Can the salt water be shorting out the system enough to pop the fuse, and if so why would the pump work alone.

Any suggestions ?
Perhaps if the Sure Bail switch is faulty or if the Sure Bail float switch was designed to go in the ground side of the pump wiring (unlikely). I am not familiar with this switch but it should be fairly easy to troubleshoot the system.
Try measuring the resistance to ground from the load side of the main switch (with the main switch turned off) with everything else connected and salt water in bilge. Or you could take the same measurement from the load side of the fuse (with fuse removed and main switch turned on).
This should tell what current the circuit will draw (ohms law). Any faults (i.e. resistance too low) can be found by continuing to take measurements further "downstream" in the circuit until you find the short to ground.

BTW, you haven't done something silly like wired up the float switch in parallel with the pump by mistake. This would pop the fuse only when water is added to bilge or when float switch is manually operated - if the Sure Bail can be hand operated that is.

Good luck.
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Old 06-05-2008, 18:39   #4
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Bilge pump wiring can be very confusing...

I found wiring up the bilge pump to be very confusing. Just when I thought that I had it all worked out I'd find that an active wire was common or something.

Try drawing out your wiring diagram neatly and carefully. Check and then study it closely. Maybe even get a friend to help.

Now check that your wiring is done exactly in accord with your diagram.

If it still does not work after that go through and check everything with a multimeter.
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Old 06-05-2008, 21:43   #5
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Can I clarify a point. Are you saying that the float switch runs the pump OK by manually lifting the switch, but as soon as you put water in, the fuse blows???
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Old 06-05-2008, 22:34   #6
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I just mention this in case it helps the trouble shooting, but I generally agree with the others.

We use a Sure Bail make float switch for automatic pumping of grey water. My understanding of these switches is that the float part with the mercury switch in (and I believe they still use a mercury switch) is foam filled to prevent water ingress. So no point shaking it to see if any splashing sounds and while possible it may be unlikely to be water ingress into that. But, of course, is easy to check for other than open circuit with a multimeter when the float is in lowered position.
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Old 06-05-2008, 23:11   #7
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I am doubting the float switch as such. The float switch is not switching Neg and Pos, but just one of those. So only one polarity will be going through the switch. Normally Pos, although either is fine. Unless it has been wired incorrectly, the only other thing I can think of is a nick in the cable insulation of a wire in the water. But then there has to be two nicks, one in the Pos and one in Neg. So that is hard to believe.
My thoughts are,
Both Pos and Neg are wired across the float switch.
Pump has a short
Too small a fuse when the load comes on the pump.
A short in the cable somewhere between the fuse and the pump, especially is the cable is twin cored so as both lines are close together.
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Old 06-05-2008, 23:22   #8
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I agree Alan. There would have to be two faults for the switch itself to be implicated - one a cabling one and the other the switch itself .
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Old 06-05-2008, 23:24   #9
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Guys, I think Rib's bilge pump system worked fine until he added the float switch in series with the pump. We don't know if the fuse blows when the switch is manually operated (but it would be handy to know); however we know that when salt water is added to the bilge, the fuse blows. We also don't know what happens if fresh water is added and again, this would be nice to know.
It is hard to imagine that the salt water by itself could create a low enough resistance to ground to blow the fuse but maybe it is possible.
So most likely faults are wiring error (even though it has been rechecked - but rechecked perhaps the same person who made the original error).
This could easily be proved by manually lifting the float switch with the bilge dry - if the fuse blows then the salt water is a red herring (I just had to add that!!).
If not, then try adding fresh water instead of salt water to see if it is just the fact that it is salt water (i.e. low resistance) that is causing the problem.
More I think about it, I gotta go for a wiring error (sorry ribbony )
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Old 07-05-2008, 15:05   #10
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Hi All

Switch is brand new, straight out of the packaging. It has dual black wires with no polarity identification.

The switch can be manually operated. I will try a fresh water test when we go out to the boat and let you know the result.

Also, had better check my wires again !

I can see the merits of circuit breakers after a session of fuse popping !
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Old 07-05-2008, 15:57   #11
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Did I miss something here or has nobody asked what size fuse you are using? Are you sure you have the correct value fuse?
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Old 07-05-2008, 16:43   #12
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Quote:
or has nobody asked what size fuse
Yep I suggested wrong fuse.
But I also suggest it is a wiring issue. I think something is crossed up somewhere.
Ribbony, I assume the swtich is a three position. On/Off/Auto. It is also possible there is an indicator light which needs a neg feed. Make sure you haven't crossed something up there. Also if you are using Auto, you need more wires run to the bilge than just Pos and neg. One set switches out the float switch. So check you haven't screwed up there as well. Plus as I said earlier, one polarity ONLY (normaly Pos) runs through the float switch. You do not have both going to the float switch.
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Old 07-05-2008, 16:57   #13
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Quote:
has nobody asked what size fuse you are using?
Quote:
Yep I suggested wrong fuse.
He did say in the first post that
Quote:
We installed the pump with a fuse, no problems, worked fine !

Then we installed a float switch (Sure Bail), in series. That works until we pour salt water in the bilge to test it and Pop, goes the fuse !
I still vote for a bad float switch.
Is the amp draw really that different between a bilge pump running dry and bilge pump moving water?
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Old 07-05-2008, 23:31   #14
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Is the amp draw really that different between a bilge pump running dry and bilge pump moving water?
Absolutely! Centrifugal pumps draw the greatest current at highest volume. Head makes no difference. It is mass of water being spun through the impeller. The bigger the flow, the more the current drawn.

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I still vote for a bad float switch.
There is no possible way a bad switch is going to short the system. The short must be between Pos & Neg. Even if the switch has a fault and was live to the salt water, the Neg must also be live to the water. And even then, no enough current can be drawn through the water to blow a fuse. However, the bare wires will fizz and turn green in minutes and the connection will be eatin away. So a short to water will be very obvious very quickly.
nup, the fault simply has to be the way it is wired.
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Old 08-05-2008, 09:32   #15
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There is no possible way a bad switch is going to short the system. The short must be between Pos & Neg. Even if the switch has a fault and was live to the salt water, the Neg must also be live to the water. And even then, no enough current can be drawn through the water to blow a fuse.
nup, the fault simply has to be the way it is wired.
I hate to be so pedantic, but we'll just have to disagree. I think that an excited electron placed into the saltwater in the bilge of a steel boat will have a pretty easy time finding its way back to the negative post of a battery. I have been wrong once or twice before though
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