Why? Lights dim & fans stop every 18 minutes

[KrazySailing]

Hi


1991 Moorings 500 (a Beneteau Oceanis 510 to Moorings specifications) with original wiring. Every 18 minutes the halogen ceiling lights dim (several circuits) and the 12V cabin fans stop. The lights stay dim for 5 to say 15 seconds. We are in Marina Mazatlan, Mazatlan, MX.



Tried:
- turned off battery charger, problem persists

- domestic water pump cycles as needed and no effect.
- no radios, laptop on/off no effect
- cell chargers, no effect
- no electric toilets.


Not successful getting a voltage reading when dim.


There are 3 common ground terminals in a DIM rack, about 15 wire per DIM

Think I will move to terminal strips.


Looking for ideas or advice.


Thx

[Tin Tin]

Fridge/freezer?

[glenn.225]

That sounds like a unique problem and I don't have aspecific answer, but I have found over the years when dealing with electrical problems, the first thing to do is check your grounds. I have seen some pretty weird problems caused by bad grounds. Hope this helps.

[sailorboy1]

Only time that happened to me was when the batteries were dying. When the freezer started it would drop the voltage

[Wotname]

I have seen electronic light dimmers trigger when an electronic water level sensor activates an auto bilge pump.

Independently the electronic light dimmers worked OK and independently the electronic water level sensor auto bilge pump work OK but they would not play nice together. I think the problem was solved by some serious RFI measures but I dunno the details.

Just another point to consider!

[KrazySailing]

120V fridge with freezer on shore power. Problem persists with batter charger off.


I said circuits get power and gound on a DIM rail. I'm a little dim, I meant a DIN rail.

[Jerry Woodward]

Something similar happened to me last year. It was due to a poor connection at the positive bus for the house feed. When I measured the voltage at the house panel, it was considerably less than the battery voltage...classical voltage drop. You have enough voltage at the house panel to run things, but when a load turns on, eg a refrigerator compressor, the lights dim because the voltage dips. Open the house breaker panel and measure the voltage at the main positive feed to the panel. If it is significantly less than your house battery bank voltage, then it is your panel feed or ground. If you put a load on your house panel, you can often find where the voltage drop is by touching the various cable connections. The connection where the voltage drop is happening will be hot.

[wholybee]

I assume because you specified 18 minutes it is 18 minutes every time, never 17 or 19 minutes? That is your best clue.

I would not jump to replacing the DIN rail connections yet. You are only guessing, and if wrong you might make the issue worse or more difficult to troubleshoot.

Here is how I would go about it.
You can safely assume the voltage is dropping on the lights and fans without measuring it. The question is where? You said several circuits were involved. Does that mean separate circuit breakers? I would want to isolate them. You could try just turning everything off, but I might go as far as physically disconnecting all the other circuits. Does this happen when every other circuit is not only turned off but disconnected. Don't forget any always on circuits, like bilge pumps.
I would also want to know what is going on at the battery while this happens. You will need a DMM with a current meter, not just a panel meter. And also measure voltage at the same time. What you are looking for is a voltage drop at the battery, or a current spike, or anything unusual.
Then repeat that on other circuits, not the lights, but everything else. Is there a surge of current to a bilge pump circuit when this happens?

Thinking about it, some auto bilge pumps work by turning on for a few seconds at a predetermined interval. If they pump water, they stay on. If not, they turn off. Maybe that sort of thing is happening. Perhaps a bilge pump is jammed so for a few seconds it pulls tons of current, but not long enough to blow a fuse. Just a guess.

[OldGreyB]

Interesting problem, here is something to try and or comment back on:

You state the vessel is original Moorings Charter standard and you have a 120Vac fridge freezer. I assume if original Moorings Charter standard of that year it also has a generator. IF the 120Vac fridge freezer is original equipment installation, then for charter operation it would be wired to be fed by shore power OR generator OR inverter from batteries.

The cycling described is a standard period and of a duration that is similar to current draw time of a refrigerant motor starting as others have suggested.

Potentially if you are on shore power and have a corroded or loose terminal on the main board feed or shore power lead on the 120Vac side, when the refrigerant motor is starting, it could be drawing 120Vac power via the load shearing of the inverter / batteries to have sufficient start current. The batteries may not be holding up due to age, ( or not being fully charged due to battery charger also being effected by corroded or loose terminal on the 120Vac side. ) You are seeing the resultant in the lights and fans dropping down for the motor start period.

Try turning off the 120Vac fridge freezer by directly unplugging it for an hour to observe if the light & fan cycling still happens.

[KrazySailing]

Problem solved.

12 V deep cycle house batteries had several cells each almost empty of fluid. Caretaker did not check over the Mexican winter!

Changed over to starter battery and now no dimming.

Thx for the advice.