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Old 06-29-2014, 06:11 PM   #1
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Bilge pump voltage

One of the bilge pumps on my DF 44 was working perfectly until it stopped. When I put a meter on the circuit, it was only getting 3 volts. What's the most likely cause, circuit breaker? Thanks.
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Old 06-29-2014, 06:23 PM   #2
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The most likely cause is a loose or corroded connection somewhere, either in the positive or the negative parts of the circuit. If you think the circuit breaker is the problem (I doubt it) measure the voltage at the load side of the circuit breaker. If it's low, measure the line side and see if it's the same. If it is the problem is in the circuit before the circuit breaker.

None of these measurements mean anything unless the pump is trying to run so activate the float switch.
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Old 06-29-2014, 06:28 PM   #3
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. . . What's the most likely cause, circuit breaker?
Probably not, unless the connections on the back of it are loose or corroded.

First look at the connections on the battery that supplies power to the pump.

Assuming the pump is controlled by a float switch, check that second.

Then check the wires from switch/pump to power supply - be suspicious of any lump wrapped in electrician's tape.

Good luck and, as always, let us know what it turns out to be.
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Old 06-29-2014, 06:32 PM   #4
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be suspicious of any lump wrapped in electrician's tape.
Yup. They can turn the most interesting shades of green. Sometimes one of those "Oh, I'm just going to do a quick fix here, and will come back later and do it right" things. Five years later . . .
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Old 06-29-2014, 06:34 PM   #5
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All good suggestions.
If you have to replace any wiring, make sure the new stuff is tinned
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Old 06-29-2014, 06:35 PM   #6
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I have seen many inoperable bilge pumps have corroded crimp connectors mainly on the ground side, why? I have no idea but I have repaired many at our marina and for some reason the ground or -12VDC is usually the culprit. Also many times the wrong style of butt splice connector is used. Most failures seem to be the non sealing blue style. The heat shrink type butt connectors should be used along with heat shrink tubing. When making the repair make sure you cut the wire back beyond where the silver center conductor has changed colors from overheating.
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Old 06-29-2014, 06:47 PM   #7
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Thank you all for the quick replies! I too was suspicious of the bundle of wires near the pump, so I forced the meter probes into the two main wires that presumably come from the breaker box. That's where I'm seeing 2-3 volts. Ron, I'll see if I can get to the back of the panel. Thank you, sir.
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Old 06-29-2014, 07:07 PM   #8
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I assume you have float switch. Check the voltage that feeds the switch/pump where the switch/pump wires split off from the DC feed usually within 18" of the pump. Just drop one of the legs. If you have 12 VDC +/- then reconnect and activate/monitor the voltage. If it drops to the 3 volts, take the switch out of the system and see what happens. I would suspect either the pump or the float switch since they are in the bilge in a less than ideal environment.
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Old 06-29-2014, 08:31 PM   #9
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+1 Ron, None of these measurements mean anything unless the pump is trying to run so activate the float switch.

I suspect bad connections to the float switch or the pump in the damp bilge. Either way poking meter leads into unknown wires can give false readings.
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Old 06-29-2014, 08:34 PM   #10
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I suspect bad connections to the float switch or the pump. Either way poking meter leads into unknown wires can give false readings.
Bill
Worse than that, it leaves holes in the insulation for moisture to enter.
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Old 06-29-2014, 09:40 PM   #11
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I must not be understanding. Would there not be 12 volts across the two wires feeding the float switch? If I probe the wires upstream of the float switch, wouldn't that take a faulty switch out of the picture?

I do plan to replace punctured wires.
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Old 06-29-2014, 11:26 PM   #12
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I must not be understanding. Would there not be 12 volts across the two wires feeding the float switch? .
No, probing the two wires going to the switch should show you no voltage since neither of the two wires is a ground. You need to find a good ground to put you negative probe on then start testing the wires for voltage. And you need to check the ground wire as well. And even them you might not get a true voltage reading without pulling a load on the wires.
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Old 06-30-2014, 08:18 AM   #13
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I must not be understanding. Would there not be 12 volts across the two wires feeding the float switch? If I probe the wires upstream of the float switch, wouldn't that take a faulty switch out of the picture?

I do plan to replace punctured wires.
Not if the float switch is on the negative side of the pump? There are too many variables here, take the entire lump or group of wires apart. Find the +12 VDC plus and the -12 VDC or negative. Start from there and then check continuity through the float switch.
This is simply basic logical troubleshooting.
1 You have one 12 VDC device not working (the bilge pump in question)
2 Find and check the main voltage feed (verify you have + and - 12VDC at the bilge pump. If you don't have the proper voltage at this point work your way backwards to the negative buss feeding the pump and the positive supply check any fuses or breaker that is in the 12 VDC feed circuit.
3 Check the float switch for continuity
4 If everything looks good then take the + and - 12VDC and temporarily bypass the float switch does it work then? If not replace the pump and repeat this step.
5 If the answer to #4 is yes then re-install the float switch, manually operate it does it working now?
6 If not bypass the float switch wires by connecting them does it work?
7 If bypassing the float switch works replace the float switch.
8 Problem solved
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Old 06-30-2014, 08:37 AM   #14
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I must not be understanding. Would there not be 12 volts across the two wires feeding the float switch? .......
If everything else is working and wired properly, you should read 12 volts across the float switch when it is in the "off" position and zero volts when it is in the on position.

Trying to read the voltage across the switch tells you nothing.

The bilge pump circuit is no different than a lighting circuit. Power is supplied from the positive side battery through a fuse or circuit breaker, then a switch, the pump motor, and back to the negative terminal of the battery. There may be more than one switch. A power switch and a float switch.
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Old 06-30-2014, 09:13 AM   #15
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If everything else is working and wired properly, you should read 12 volts across the float switch when it is in the "off" position and zero volts when it is in the on position.

Trying to read the voltage across the switch tells you nothing.

The bilge pump circuit is no different than a lighting circuit. Power is supplied from the positive side battery through a fuse or circuit breaker, then a switch, the pump motor, and back to the negative terminal of the battery. There may be more than one switch. A power switch and a float switch.
I agree Ron the circuit isn't that complicated.
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Old 07-01-2014, 10:17 AM   #16
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I was putting the probes on the two switch wires, but was getting only a couple of volts whether the switch was on or off.

In any event, I'm having other work done at a yard and will have the electrician have a look. I'll post whatever I find out.

Thanks for the great feedback.
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Old 07-01-2014, 12:47 PM   #17
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I was putting the probes on the two switch wires, but was getting only a couple of volts whether the switch was on or off.

In any event, I'm having other work done at a yard and will have the electrician have a look. I'll post whatever I find out.

Thanks for the great feedback.
That will tell you nothing about voltage to the pump. Both those wires are hot or positive wires. One should have power to it at all times and the other only when the switch is on. You test those by grounding the negative probe and checking each switch wire with your positive probe.

You need to get a book on basic marine DC and AC systems before you try to test anything else. So you'll know and understand what you're doing.
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Old 07-02-2014, 10:18 AM   #18
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That will tell you nothing about voltage to the pump. Both those wires are hot or positive wires. One should have power to it at all times and the other only when the switch is on. You test those by grounding the negative probe and checking each switch wire with your positive probe.

You need to get a book on basic marine DC and AC systems before you try to test anything else. So you'll know and understand what you're doing.
Hey, Bill, thanks for the lecture! I'll certainly keep those books in mind to add to the 3 on 12-volt DC I already own.

It turns out the two primary wires feeding the bilge pump and switch are, in fact, positive and negative, exactly as they appear to be. The reason the pump stopped working is that the PO wired it to an unmarked breaker that someone had shut off by mistake. I didn't notice it had been switched off, which was clearly my mistake.

Sorry to waste everybody's time on this but I do appreciate all the constructive feedback.
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Old 07-02-2014, 10:54 AM   #19
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Hey, Bill, thanks for the lecture! I'll certainly keep those books in mind to add to the 3 on 12-volt DC I already own.

It turns out the two primary wires feeding the bilge pump and switch are, in fact, positive and negative, exactly as they appear to be. The reason the pump stopped working is that the PO wired it to an unmarked breaker that someone had shut off by mistake. I didn't notice it had been switched off, which was clearly my mistake.

Sorry to waste everybody's time on this but I do appreciate all the constructive feedback.
It wasn't intended as a lecture. It was just based on your posts it sounded like you were unsure of what you were doing and how you should do it. So I was merely suggesting you do some research before you come to any incorrect conclusions as to what the problem was.

Glad it turned out to be something simple.
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Old 07-02-2014, 11:00 AM   #20
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Should a bilge pump even be on a switched source? Fuse protected for sure but not switched.
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