Electrical crisis

[j24sailor]

We are having a bit of an electrical crisis on Hound's Hollow. We had her hauled out last week for three days to change the zincs etc, and she was put back in the water on Wednesday. The only 12V things turned on were the bilge pump, the AM/FM radio in standby (can't turn it off completely) and the AIS transmitter. Nothing was done to the electrical system. We unfortunately couldn't be there but went today to check on things and the low voltage alarm was going off. The original battery meter was reading 10.4V and the Blue sea meter was measuring 2-3V (little, no big panic). The blue sea meter said the batteries were 100% and there was about 0.3A going in and out. The solar panels said the batteries were fully charged. I took the volt meter to every battery (which are three years old, and were holding at 13.1V in January even off shore power overnight) and thankfully they were reading 14.4V and then around 13.6V when I turned the battery charger off at the panel. I opened up the panel and across both busses it was reading 10.4V so there is power getting to the panel but there is a 2-4V drop from the batteries so I think there is some sort of loss on the battery end as I know the Blue sea monitor shunt is by the batteries. I unplugged the solar panels and the results were about the same so I plugged them back in again as I think they are helping keeping the batteries charged. I did notice on the battery isolator the two outside pins were ready 13.6V and the two inside ones 10.6V both with the battery charger on and off. This is where it became really interesting. I had turned on the lights in the galley when this first happened to see if they were dim (before pulling out the battery meter). When I turned off the power to the boat at the switch in the back lazarette everything was fine. When we actually unplugged the boat physically the lights went off. So the 12V system from the batteries is not working at all, yet the 110V system is feeding the lights (and 12V system) even with the breaker turned off which is really weird. In the end I unplugged the boat and turned everything off including the two breakers for the engine battery and the house battery. I couldn't find any corroded connections either at the battery or at the panel and all the connections were good. There is some green discolouration on the onshore plug, but the shoreside plug was just replaced last year.

As a bit of a side note our two year old radar died in January and was replaced under warranty, but we did have a few problems with the new one as well turning itself off in February and I wonder if this has been going on for a bit and a voltage drop was causing it to turn off, the the battery meters were both giving me good numbers both plugged in and unplugged to shore power.

I wasn't able to trace the wire today all the way from the battery to the panel but it is behind panels and protected. Any ideas especially on why I have 12V power only when plugged in to shorepower but even when the shorepower is turned off on the boat breaker back where it comes into the boat. There is a galvanic isolator there but that shouldn't make a difference.

Thanks James

[sitara]

Hi James,

I had strange electrical symptoms on my boat that was diagnosed as a faulty battery isolator. Lights were staying on even when the house bank was turned off. It turned out the cable between the alternator and starter motor had not been removed on installation so the isolator was seeing 12 volts whenever the start battery was switched on and so not isolating the batteries. So don't assume the original wiring is correct.

If everything was normal before slipping it sounds like there is a problem somewhere in the earthing, especially if you are getting a 2-3 volt drop from the battery to the I assume Schreiber panel. Check the supply behind the panel to ensure it is not the panel meter.

I would disconnect all inputs to the batteries (solar and shore power) and start checking all systems from there. And maybe disconnect each battery physically to check that there are no dead batteries.

No doubt some of the more experienced electrical experts will have some good ideas.

Good luck, Rob

[Trevor]

Hi James,

You may have a couple of things slightly odd here but just to get the boat to work properly again, the critical part of your story is "I did notice on the battery isolator the two outside pins were ready 13.6V and the two inside ones 10.6V both with the battery charger on and off."

The battery isolator should have the same voltage on one side as the other unless it is turned off. I suggest vigorously switching it on and off and see if that fixes your problem at least temporarily. If that switch has a high resistance it will cause the problem you describe. It has happened on my boat and can be quite annoying as the voltage presented to the switch panel reduces with every device you turn on. That is because as you draw more current the voltage drop across the switch increases and makes the problem worse.

If the switch does not improve by working it on and off, simply jumper the switch with a piece of wire and the fault should be fixed. Then at least you will know the switch is faulty and needs replacing.

I hope this helps,

Good description of the symptoms by the way.

Regards,

Trevor

[ForGrinsToo]

If all that was done was to haul out, replace zincs, touch up the bottom paint, it does not seem likely you have developed a continuity problem (leading to low voltage) except for the battery isolator. So now you have three votes against the battery isolator. One would reasonably expect it to be relatively immune to voltage spikes, but....

Geoff

[rene460]

Hi James, I have reread your initial post a few times since it first appeared, and also think that isolator switch is a problem, but as Trevor observes, there seems to be a few things going on.

I would check that switch and the battery wiring by starting with your positive lead of a digital volt meter on the actual positive battery post, not the clamp, and poke along the positive wire to the switch and the accessible connections beyond until you find that volt drop.  You will need some lights on to be sure there is current flowing to see the volt loss.  Then do the same for the negative lead, but this time starting with the negative lead of the coltmeter on the battery negative terminal post.  I will be surprised if you have to go beyond the battery and switch compartments.

Once you identify that issue, if it is the switch, working it on and off a few times might help, otherwise replace it.  If not the actual switch it could be the clamp to post contact area needing cleaning or a faulty connection of the actual copper wire into the clamp, but the switch is my first guess.  A bit of corrosion due to dampness is a more than adequate explanation.

Then other issues.  Twelve volt power apparently from the battery charger even while the isolation switch in the back locker is off?  Sounds like the charger is connected to the wrong side of the switch.  Seems strange, and worth chasing down, but at least you can isolate by unplugging, but be well aware of the issue until you get it checked out and if necessary fixed.

Once you have a faulty connection you can get strange things happening through alternative circuits as other respondents have mentioned.  These are also worth checking out just in case there is something waiting quietly to cause grief another time.  But first, you need the full battery voltage all the way from the battery to the switchboard.

With some luck, you will track it down relatively easily, and have a more reliable system as a result.

rene460

[j24sailor]

Thank you everyone, just a quick update. I did get a marine electrician to come in as I don't like fooling around with electricity too much and I had to be at work. Of course he turned on the 12V system and it worked completely and all the battery monitors read perfectly. Because it was working and he was doing me a favour coming today he didn't have a chance to explore further but is going to take a better look on Friday. Isn't it always the way. If he doesn't find anything then I will take everyone's suggestions. Thanks James