Panel Voltage is different than battery voltage?

[jbinbi]

Trying to help a friend debug a battery issue, that I now think might be a windlass issue. See https://www.cruisersforum.com/forums...ng-243084.html

When he runs his windlass on seawind cat, 4 yr old agms, his electronics reset. Originally thought it was his battery, and he bought a load tester, but not the correct type. Following some advice of the group here, I lent him my multimeter and told him to read V at the battery while running the windlass.

He had the leads across the front battery. I am assuming this is his house. He has 3 of these, and can add in the 3d via a switch (has outboards so normally leaves all 3 combined as he can pull start the engines if needed).

I told him to turn off solar and bat charger. Let rest for a bit. Panel was reading in the mid 12s, but multimeter was reading 13.05 at the battery?!? BTW, connections all look very good.

Then he ran windlass, dropped 25' of chain. Panel was showing 11.8, but multimeter still 13.02?!?!

Ran the windlass again, and it shut down everything in a second?

So now I am thinking it is the windlass that has an issue. Possibly loose connection somewhere, or he mentioned the foot switch by the windlass doesn't work, he runs the windlass from the helm switch. Possibly something wrong there.

I am going there on Thu, but wondering if collective group's wisdom has some thoughts. Thanks.

[sailorboy1]

The panel voltage reading would depend on where in the system it measures. If the voltage right at the battery isnt dropping it isnt the battery.

I bet there is a bad connection somewhere between the battery and the panel and when you run the windlass (big load) it drops the voltage and everything turns off (we know it does).

[Jim Cate]

Actually, if the battery voltage remains constant when a big load is applied, well, I wonder if the multimeter is connected to the correct battery? There should be some drop in voltage. Also, if they are lead acid batteries and are not being charged, 13.05 V is kinda high, so I wonder if all is as described.

Jim

[Dsanduril]

Originally Posted by Jim Cate

Actually, if the battery voltage remains constant when a big load is applied, well, I wonder if the multimeter is connected to the correct battery? There should be some drop in voltage. Also, if they are lead acid batteries and are not being charged, 13.05 V is kinda high, so I wonder if all is as described.

Jim

+1. If the battery voltage measured at the terminals isn't dropping when running the windlass then most likely this isn't the battery that is running the windlass. Battery switch not in the right position? Or faulty? Fuse?

For more tools, the next step would be a clamp on DC ammeter (they make them that can connect to your voltmeter or stand-alone). See how much current the windlass is drawing from the battery - guessing that if you put it on the same batteries it won't be any.

[jbinbi]

Originally Posted by Jim Cate

Actually, if the battery voltage remains constant when a big load is applied, well, I wonder if the multimeter is connected to the correct battery? There should be some drop in voltage. Also, if they are lead acid batteries and are not being charged, 13.05 V is kinda high, so I wonder if all is as described.

Jim

Yes, wondered about that it wasn't the correct battery running it.

[MikeFL]

Is it an analog voltmeter on the panel? It may need calibrating - I'd go with the multimeter. Properly sized and proper wiring to the windlass? Is the circuit to the windlass protected with the correct breaker size and type? What does "shut down everything" mean?

[rejas]

I would bring a jump start cable to combine the batteries in order to find out if they really are combined by the switch(es).

[markcouz]

If you fully charge an AGM, and then remove the charge source with no load applied then above 13v would be a very normal measurement (called surface charge). Apply a load and then this with very quickly drop to the normal +_ 12.8v where it will stabilize as surface charge is bled off.

If no load is being applied when measuring 13v at the battery then the panel meter should be measuring the same - the difference could be as a result of 1) dodgy meter 2)bad cable or connection 3) not measuring same battery.

Use the multimeter to test at the same point as the panel meter to verify panel meter accuracy.

If meter is accurate then check whether difference is as a result of different source or bad connection.

If source is correct then voltage drop must be the cause - test using voltage meter on (+) cable from source to panel and then (-) cable from source to panel - one of these cables should reflect the 2v drop experienced and that is the cable requiring attention.

[wholybee]

This really seems like a bad connection to me. In fact, the primary symptom of a bad connection is a large voltage drop when a load is applied(sometimes it can be to zero volts), that would only be measured on one side of the bad connection. The voltage would remain fine at the voltage source. If all the connections were good, I would expect to see a drop at the battery.

It's possible you are looking at the wrong battery, but that isn't my first guess. Measure the voltage while the load is applied at every connection and junction until you fine where the drop occurs, starting at the battery and working to the windless. If you are looking at the wrong battery, you should discover that in the process.

[jbinbi]

Well, I went to the boat today to do measurements myself and try somethings out.

Attached is a pic of the switches and the meter at the panel. It is a smart meter that will show amps going in and out and V. Assuming this is across a shunt and with a microprocessor. (This pic was taken after the system shut down and was rebooting, the V comes up.)

Battery V was pretty much always at 13 with multimeter at the battery, yet panel V would change as the windlass ran dropping from 13 to 12.x .

Panel would shut down as I am assuming the electronics turns on at roughly 11s , so this is the 'reboot' he was talking about. The panel would turn off when V dropped below panel electrical turn on V, then when we stopped windlass and turned switch on and off, the V would be high enough to re enable the panel.

We ran the windlass with the house bank turned on, and got it to shut down with engines running (though they are outboards and meter says they are putting in about 5A).

If we turn on the combiner (yellow switch) for the start battery to add it in with the 2 others making up the house, then the system did not shutdown.

My conclusions, but asking for opinions here: I think the house bank needs replacing. Adding in the 3d battery has enough capacity to run the windlass, but the 2 batteries in the house bank themselves do not. Even with the engine running.

I am still mystified why the multimeter reads differently directly at the battery than the panel with a load. Unless there is a lag of a minute or so at the battery itself? But more concerned if we should just be replacing at least 2 batteries, and possibly the start itself?

[Dsanduril]

Use the same voltmeter to measure at the panel and at the batteries. Does the voltmeter show a difference between measurements at the batteries and measurements at the panel? If yes then it's time to start tracing through the connections and see why there's a difference. If no then one instrument is wrong.