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Old 28-07-2016, 06:06   #1
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Macerator pump - voltage drops from 12.9v to 6.5v

I installed a brand new Jabsco 18590-2092 macerator pump on our boat. it is connected to a switch and then to an approximately 15' run of 14 gauge wire to the breaker panel. When I measure the voltage at the switch it reads 12.9v, but the moment I turn it on the voltage drops to 6.4v and the pump sounds very labored. After 5-10 seconds the breakers trips.

As it's a brand new pump hooked to brand new hoses and a brand new holding tank, I'm pretty confident that it's not a blockage of any sort. The only thing that isn't new is the wiring, as that was left over from when a macerator was previously installed. I should note that the last owner removed the macerator, so I do not know whether there was a similar problem before or not.

Any ideas before I start ripping everything apart?
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Old 28-07-2016, 06:16   #2
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

Check the current draw of the pump or at least look at the name plate current. 14 gauge wire is probably way too small for the current. Look at the entire run of wire from the battery to the pump and verify the size and length. Then refer to a wire size chart and select the proper size wire for 10% voltage drop.
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Old 28-07-2016, 06:24   #3
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

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Originally Posted by transmitterdan View Post
Check the current draw of the pump or at least look at the name plate current. 14 gauge wire is probably way too small for the current. Look at the entire run of wire from the battery to the pump and verify the size and length. Then refer to a wire size chart and select the proper size wire for 10% voltage drop.

Yes, all what he said. Also check for corrosion on any connections, crimps or terminals. But I also think 14 gauge may be too small for the pump.
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Old 28-07-2016, 07:12   #4
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

Also check if a PO made a splice some where in that 14 gauge run.
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Old 28-07-2016, 07:33   #5
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

My macerator draws about 10 amps and uses 10 awg wire. For a 14 awg wire that would be 6-8% voltage drop, which is pretty high. But you are getting 50% drop and even 18 awg should only have around 22%. So you have a wire or connection problem. Don't forget the ground wire as it has to be be in good condition also.
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Old 28-07-2016, 07:49   #6
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

Quote:
Originally Posted by MondayNever View Post
I installed a brand new Jabsco 18590-2092 macerator pump on our boat. it is connected to a switch and then to an approximately 15' run of 14 gauge wire to the breaker panel. When I measure the voltage at the switch it reads 12.9v, but the moment I turn it on the voltage drops to 6.4v and the pump sounds very labored. After 5-10 seconds the breakers trips.

As it's a brand new pump hooked to brand new hoses and a brand new holding tank, I'm pretty confident that it's not a blockage of any sort. The only thing that isn't new is the wiring, as that was left over from when a macerator was previously installed. I should note that the last owner removed the macerator, so I do not know whether there was a similar problem before or not.

Any ideas before I start ripping everything apart?
Your macerator, after the in-rush, will settle out at about 14-17A of current depending upon head, effluent thickness, and voltage applied at the pump end.

The optimal situation for best performance is to aim for a voltage drop of about 3% - 4% this will clear the tank faster, bust through thick effluent easier, and help account for any battery voltage sag on top of the wiring voltage drop. The in-rush current to get that motor turning can easily exceed 35-40A.

At a bare minimum you'll really want a breaker of about 20-25A because if the impeller stalls or bogs down with solids the current will increase beyond the nominal 14-17A range. Jabsco and many others assume ideal conditions, which rarely ever happen in the real world, and a nominal current. Bog down one of these pumps with effluent and the current will trip a 20A fuse or breaker pretty easily.

For a 15' circuit, or round trip wire length of 30', you are really looking at 8GA or 10GA at a minimum for the best performance of the pump.

That said your voltage drop is excessive even for 14GA wire...
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Old 28-07-2016, 08:31   #7
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

Lots of good information and advice already about wire sizes and connections, but for that kind of voltage drop I'd also check the voltage across the battery terminals while the pump is running or trying to run. If the voltage drop also occurs across the battery terminals, you probably have one or more weak cells in the battery, which can't handle their part of the load.


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Old 28-07-2016, 08:32   #8
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

I agree with the integrity of the wires being an issue. Once corrected, it seems a, "Start Capacitor," at the unit, would be prudent. Any thoughts?

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Old 28-07-2016, 08:58   #9
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

The inrush of current when starting is causing a large voltage drop across your supply line.
the resistance of the supply line and/or its connectors is a place to check.
Until the motor is able to attain operating speed it is not able to produce back emf and therefore appears as a dead short and trips the breaker.
Anything that will prevent the motor from reaching operating speed could cause the problem, including thick sludge.
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Old 28-07-2016, 09:18   #10
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

My gut says 14 ga is too small, but I had the same thing happen all the time with a macerator that only had a 3-4 ft run of wire. Sometimes when I turned the switch the pump would hum and move a couple turns, eventually breaking free and operating, although it often sounded a bit labored most all the time. There were no lumps in the water flowing thru either. Are all these pumps that way? Does urine attack the seal or something?
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Old 28-07-2016, 09:20   #11
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

8 or 10 gauge depending on the length of the run. All new marine grade connectors properly crimped. And remember the fuse is there to protect the wire. 40 amps for #8, 30 amps for #10. Forget the capacitor on a DC motor. Capacitors are used on AC motor starting because they go from zero to full RPM immediately. Electric motors, at a given voltage, will draw maximum current at zero RPM. Trying to run your pump at half voltage, is like lugging a car engine - amperage goes way up. Rewire it correctly and your problem will disappear.
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Old 28-07-2016, 09:27   #12
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

Quote:
Originally Posted by lonesoldier0408 View Post
I agree with the integrity of the wires being an issue. Once corrected, it seems a, "Start Capacitor," at the unit, would be prudent. Any thoughts?

Sent from my VK810 4G using Cruisers Sailing Forum mobile app
Start capacitor on a DC motor? New one on me. Please provide details.
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Old 28-07-2016, 09:41   #13
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

Quote:
Originally Posted by MondayNever View Post
I installed a brand new Jabsco 18590-2092 macerator pump on our boat. it is connected to a switch and then to an approximately 15' run of 14 gauge wire to the breaker panel. When I measure the voltage at the switch it reads 12.9v, but the moment I turn it on the voltage drops to 6.4v and the pump sounds very labored. After 5-10 seconds the breakers trips.

As it's a brand new pump hooked to brand new hoses and a brand new holding tank, I'm pretty confident that it's not a blockage of any sort. The only thing that isn't new is the wiring, as that was left over from when a macerator was previously installed. I should note that the last owner removed the macerator, so I do not know whether there was a similar problem before or not.

Any ideas before I start ripping everything apart?
14AWG sounds small to me.
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Old 28-07-2016, 09:55   #14
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

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Start capacitor on a DC motor? New one on me. Please provide details.

I'm attempting to learn from the forum. I have seen capacitors in Stereo Amplification systems, DC.
I'm no electrical engineer, just asking, "What if.?"


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Old 28-07-2016, 10:23   #15
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Re: Macerator pump - voltage drops from 12.9v to 6.5v

A capacitor in a dc circuit is seen as a dead short. Once the capacitor has reached its full charge it is a short. The only reason it works on AC is it is continuously being charged and discharged on every cycle.
I would suggest a minimum of #10AWG for any high draw motor loads.
If you measure the static resistance of the pump with an ohmeter you can calculate the start up current. once you have the start up current you can determine the wire size.
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