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Old 02-12-2019, 16:52   #1
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Voltage drop with electric winch

Hi- on our Hanse 388 we have electric halyard/sheet winches. House batteries are two Mastervolt Lithium 200Ahr, cabling looks huge- not sure exact AWG.

When we use a deck winch, eg to trim main, voltage alarm on B&G Zeus system routinely signals low voltage, I.e. “ Alarm- low CAN bus voltage” below 10 volts. For as fast as Li batteries receive charge (80Amps continuous) , it seems odd that drawing current drops volts so much. Any advice/ opinions appreciated.
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Old 02-12-2019, 17:34   #2
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Re: Voltage drop with electric winch

Welcome to the forum.

A DC motor, such as on a winch, draws maximum current at zero RPM, such as when the winch has pulled a line tight and has progressed to the line stretch mode.

It may be that all is good and that all is normal, but there are tests that will verify the condition.

The easiest test is to configure for line stretch mode and use the DC voltage meter that should be part of your tool arsenal.

Measure: unloaded battery voltage; line stretching battery voltage and voltage drops on winch circuit. Easiest way is to clamp the negative lead on the battery then touch the positive lead to each point in the circuit. Note it is possible to locate a defective crimp by carefully touching the wire conductor or by touching the lug.

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Old 02-12-2019, 19:17   #3
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Re: Voltage drop with electric winch

"Line stretch mode"? Is that what happens just before you pull the rig down? That's not really how one uses a sheet trimming winch...

The problem here is not in the winch circuit wiring, because the voltage drop is being reported by the sailing instruments, which I assume are much further back into the wiring system..

Dropping below ten volts would be odd. Those winches do not draw that much power. I draw over 400 amps when running my bow thruster, and don't see a voltage drop of that magnitude--and that's with AGM batteries.

First, we want to see if the problem is the battery or the wiring. Run the winch with a volt meter directly across the battery terminals. If the battery terminals show the same voltage drop, then the batteries are the issue. I bet you will see a much lower voltage drop at the batteries. That would indicate a problem with a high resistance connection somewhere in the wiring.

Look closely at ALL the connections from the battery terminals on out. I suspect a loose or corroded connection somewhere. It is important to find it. High resistance connections get hot. Sometimes VERY hot. They can start fires even at amp draws far below that needed to blow a fuse.
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Old 02-12-2019, 22:37   #4
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Re: Voltage drop with electric winch

Wow- thank you for those comments. I've relayed to electrician to examine all points.
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Old 03-12-2019, 04:05   #5
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Re: Voltage drop with electric winch

Greetings and welcome aboard the CF, Mike.
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Old 03-12-2019, 05:55   #6
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Re: Voltage drop with electric winch

The most likely issues are either a bad connection or incorrect power distribution. Winches should always be powered from a feed directly from batteries. Winch current should never flow through same wires as the instrument panel supply. At least that’s a rule I have adopted. Winch circuits get their own breaker/disconnect.

Many boats use a 1/2/all/off switch and route all power from batteries through that switch. If this is your scenario consider the bad connection possibility or perhaps the wiring from batteries to the switch is too small or too long.

A wiring diagram of your boat would help diagnose the possible cause.
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Old 03-12-2019, 17:09   #7
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Re: Voltage drop with electric winch

We have/had a similar issue. After we replaced our windlass, we would routinely get a "Lo Voltage Alarm" on our chartplotter when we raised the anchor. Our 6-Trojan T-105s are only 2 years old, but because our boat is 30 years old and made in Taiwan (where shortcuts were frequent), we elected to replace all the battery cables. We bought a 50' spool of black 2/0 and a 50' spool of red 2/0, a Harbor Freight hydraulic squeezer, and a 25-pack of 2/0 x 5/16" lugs. We are just now completing the install, but the old cable was stiff-to-rigid, and lots of ends that looked really bad. We had to abandon some cable-we just couldn't get to it, and I've got about 5' left off each spool. We'll know soon if it was worth the effort...but it can't be any worse than it was!

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