Please help me trouble shoot my electrical issue

[Hoosierdoc]

I thought I was good to go, then two problems. First my charge controller (renogy PWM) was simply passing full voltage to batteries. About 15.7V for a few days from a 100W panel. Batteries are T-105 x 2. I swapped controller for the victron MPPT with BT.

I provide that info in case it matters for the real issue. I put a watt meter in between battery disconnect switch and my breaker panel. Or I thought I did. When I brought boat to marina today the batteries shifted a bit (will fix that later) and a negative wire came loose on the watt meter. It was behind a wall and I couldn’t see it. I turned on the switch and my panel dimly read 3.2V. All battery connections were intact and the only loose wire I could find was the disconnected negative off the watt meter, which I thought would have disconnected the circuit entirely. There was enough power to run my LED lights but not the radio. The solar panel was disconnected at this point.

Prior to bringing the boat down setup was working fine. Any thoughts on how i’m getting 3.2V? Makes me think I have it setup incorrectly. When using the 2A USB port to charge my iPhone it is registering 0.85A draw, if that helps.

I’ll need to map everything out and post it if the answer isn’t obvious. Thanks!

[Spot]

Have you tried checking each battery by itself? Are those the 6v golf cart style ones?

[Hoosierdoc]

Yes, they are 6v golf cart batteries.

Sorry, I forgot a key piece. I Hve another watt meter between my charge controller and my batteries. That shows 12.7v from the battery. So the batteries seem good, just not sure how i’m Showing 3.2v at the breaker panel.

I do have a multi meter on the boat I can use

[markbarendt]

Missing or poor grounding is often a fault on machinery. When that happens electricity tries to find any way it can to complete the circuit and that can mean back-feeding through ‘harder paths’ like say lighting fixtures and other electrical items to find a ground. Diminished voltage is normal when that happens.

Start disconnecting things. Easy stuff first like turning off the lights/light breakers, unplugging blenders... Do one thing at a time and retest then another...

[sainted]

Here's what you need to do:

Disconnect your battery from any charging source (solar panels, battery charger) and load.

Check the acid level in the batteries. Top the acid up with distilled water to the bottom of the fill rings if they are low. If the plates are not completely covered when you check and the batteries take a lot of water, the batteries are likely toast.

Use your multimeter to measure the battery's voltage at the battery. If it's in the 12V range, move on to the next step. If it's really low, like 3.2 volts, you probably killed the batteries by over charging them.

If the batteries have a decent charge, turn everything on the panel off and turn the house battery switch on. Leave the solar panels, etc, disconnected. Measure the voltage at the panel between the main positive bus and the ground bus that should be adjacent, usually behind, the panel. You should get 12 Volts or whatever it is that you measured at the batteries. If that's not what you get, measure between the positive bus on the panel, and the negative terminal on the battery. If you get 12 Volts, then you know you have a bad ground connection. If you get the same voyage as you measured at the panel, measure between the panel ground bus and the positive terminal of the battery. If you get 12 Volts, you have a bad battery switch or other poor positive contribution to the panel.

If you don't understand any of this, call an electrician.

Good luck.

[hellosailor]

15.7 VDC would be above the equalizing voltage, and that's just supposed to be applied for a short time. Several days of it should have definitely boiled out some electrolyte, so that level needs to be checked & corrected, but don't be surprised if the batteries have been killed. It is possible they'll show a 12.7 volt capacity under no load, and then drop very rapidly if any load is connected.

The loose negative behind the watt meter (which is why you always need positive physical connections and secured wiring) may have been on the side away from the batteries, so it would have still be a "hot" ground connection to them. If it contacted anything else, that could have pulled the batteries down. Hard to say, but you need to start by assuming the first controller either is broken, or was accidentally pushed into an equalizing mode. (Perhaps on a monthly cycle that's in the docs but often not read?).

You've got to be logical to find these problems. Check controller, check wiring, check batteries...and make sure to load test the batteries. Don't assume anything is "right" until you've gone down a checklist and made sure of it. And of course, see about sending that first controller to Renogy for a service check.

[Hoosierdoc]

Thanks guys. I’ll work through it all Tuesday when I get back down there

I tossed the old controller. It was four years old and came with the panel kit. Was a pwm one. It had same voltage on panel input and battery output side

[roland stockham]

Another point to watch for is tha a lot of 12v equipment has an absolute voltage limit of 15v so if you have been at 15.7 for a few days you need to check anything electronic (ie containing a circuit board) that was connected. I have lost a set of batteries due to a failed chatge controller before and now always turn off all charging sources when leaving the boat for a while on hard standing. I.e if I don't need the pumps!

[laika]

The equalize voltage of Trojan flooded 12v is 16.2, so if you check and the battery plates aren't exposed they might be ok. I've equalized Trojan batteries for extended periods at 15.5v bc my battery charger will not go higher. At least in my case, at 15.5v there was hardly any offgassing. Fwiw