I am ready to start my education on my battery charger. I have a starter battery and two house batteries - all 4D. I have a Guest 2530A charger. There is only one red light titled "DC Power Available."
That is an an older ferroresonant charger from the late 80's / early 90's. They do make a humming noise. The problem with them is FR chargers have a tough time doing finishing charges and float stages. They need to switch on and off because they don't do very low currents well. The newer switch mode chargers handle low current output far better and can be left on for weeks or months on end where a low end FR tends to not do nice things when left on for long periods..
The charger never shuts off. My house batteries were drained down to 4.3V the other night (that may be a different discussion), so I plugged in the charger and connected to one of the house battery terminals. It has been charging for 36 hours and still buzzing. Now, the panel voltmeter reads 13.7 or so. (And the switch is on house.) Handheld voltmeter reads 12.89.
They are not intended to shut off but instead go into "float mode" where they maintain a lower voltage. Many older chargers don't do this stage as well as newer ones and with an FR charger you will likely hear it humming along..
First, why the difference in readings?
Analog panel volt meters can be notoriously inaccurate. We also don't know where it is sensing voltage or where your charger ties in or what the voltage drop may be in the system. The only reading that matters is at the batteries. 12.89 is barely above static resting voltage for a full bank? What was the voltage with the system loads off?.....
Is it supposed to stop buzzing? The charger says finished charge at 13.8V and it is there or very close according to panel voltmeter.
It likely won't stop buzzing....
Is 36 hours an obscene amount of time to charge?
Yes but you should be in float not bulk or absorption so the buzzing is likely normal for that charger even in float.
Can I check the water lever while it is charging?
Usually best to check it when they are resting. Heat can cause the electrolyte to expand slightly and make them look more full than they are. Should be about 1/8" below the lower edge of the fill "well" but not touching the well at all..
The batteries don't feel hot and they are obviously not boiling over. Is it dangerous to keep charging them?
I am not a fan of leaving an FR chargers on charge any longer than is necessary. With a newer switch mode charger that's fine but with many older chargers I feel it an be safer to err on the side of caution.
Wiring charger to the battery switch.
The negative is grounded - no problem there. Intuition tells me to wire the positive to the "Both" terminal on the battery. That way I could charge the starter batt or the house batts or both. The alternator feeds the starter, then to the "Both" terminal. But for some reason, during one of those half conversations with my mechanic, he said I should wire in to the "House" terminal so that I could charge the house or both.
I would not advise that. This means you will need to leave the battery switch in the ON or BOTH position when you leave the boat and also introduce a few more connection points to corrode and cause voltage drop. A better approach would be to get a newer switch mode charger with dual outputs or add an ACR (voltage sensitive combining relay) or an Echo charger. You then run the charger direct to the house bank and the automatic charge managing device takes over keeping the second bank charged.
What is the proper terminal on the battery switch for the battery charger?
None for me, but if you have to, direct to the #1 or #2 post. If not willing to invest in a new charger or a charge managing device then you will need to go to the "C" post and leave it set to BOTH, or what ever bank you want charged.