Alternator, Battery Switches and Monitors

[Tkenopic]

Hello all,
Last fall I found that my alternator was over-charging the batteries. I just got back from taking it to an repair shop and indeed it looks as though the regulator failed. He's ordered the part and will replace it and retest it. He also tested the batteries and were ok (only 2 years old - identical Group 27 Deep Cycle).

We started talking about possible causes of regulator failure and I mentioned I had read here on the forum somewhere that accidentally switching the battery switch to 'off' while the engine is running could kill the regulator. He said for sure that would do it, but so would just switching from 1 to 2 or 'All' (I have the typical red dial switch). Even the split second of switching from any of those, over time, would over-load the regulator.

Our practice for the last 3 years that we've owned the boat was suggested by the previous owner and other friends:
-Start the boat with the switch on 1 to use that as the starting battery
-Once the engine is running, turn switch to 'All' to make sure both batteries are being charged
-Once the engine is off, turn switch to 2 for use as the house battery

So I'm wondering a couple of things from the experienced users here:
1) What is your battery switching 'best practice'? Do I have it wrong? Do I need to start and run the boat on 'All' all the time when the engine's running?

2) Is this true that switching between 1, 2, or All could ruin the regulator? If so, is there a way to wire the switch so that doesn't happen?

3) I have an ammeter in the cockpit, but I'm now wondering if a battery monitor, wired next to the switch inside might be a good idea to keep an eye on battery health and give me an advanced warning about over-charging or other issues. Does anyone have one they like?

Thanks,
Trevor

[Sam]

Well, about 10 yrs ago I changed out an original 40 yr old battery selector switch which required 360 degree rotation through #2 -both - #1- off. When I installed a new design alternator with an internal regulator I managed to fry it by going to "off" with the old switch just before crew in cockpit turned off ignition. The new switch is a red Perko with a short throw covering "2-both-1-off" in about 70 degrees. The research I did at that time was that the new switch design always has a contact" load" in between all battery selections except for "off. Switching battery settings, except for "off" while the A4 is running should not cause a problem. However, I DO NOT DO IT. My SOP is simple, start on 1 and motor out of harbor, sails up and switch to 2 and use to motor back when needed. One of my Optima blue top AGM dual purpose batteries is now 10 seasons old [sits in heated garage in winter with occasional "maintainer'] and I would not be surprised if it is still viable. FYI, boat is on a mooring can and all power is off except for 2 auto bilge pumps.

[alcodiesel]

I start mine on 2 and leave it on 2. Both batts charge regardless of switch position. I figure if 2 dies whilst out sailing I have 1 for starting.

[romantic comedy]

My switch says that switching between batteries is ok. The switch keeps a connection thru the cycle.

I usually start on the engine battery then switch to house battery after a few minutes.

[joe_db]

There are a LOT of variables here.
The guiding principle is the alternator field cannot change instantly. Therefore if you disconnect it from the battery(s), the regulator cannot cut the field current fast enough to not have the voltage rise quite high. The usual result of this is burning out one or more diodes and getting LESS output. Damaging the regulator is a bit unusual.
I use a 16 volt zener diode on my alternator to help prevent this.
Now on to switching:
It helps a lot to have a diagram of what goes where and know what kind of switches you have. On my own boat the alternator runs through a circuit breaker to the house battery, so no combination of switching will damage it. On the usual old boat factory setup, a 1-2-BOTH-OFF switch controls everything. If it is a "make before break" switch, you can switch between 1,2 or both while the engine is running as long as you don't turn it past off. If it is not make before break, you cannot switch it at all.

[ndutton]

Trevor, it sounds to me like your alternator repairman is not up to speed on the function of a marine battery switch so any advice coming from him on the subject is suspect. I'm not disparaging him, it's just that he is unfamiliar.

I've been switching batteries with the engine running for 45 years and never a problem - - - and NEVER through the OFF position.

[Tkenopic]

Thanks for the info everyone!

[TomG]

I have an ammeter in the cockpit, but I'm now wondering if a battery monitor, wired next to the switch inside might be a good idea to keep an eye on battery health and give me an advanced warning about over-charging or other issues. Does anyone have one they like?

At the risk of being labelled a heretic, I use and like my Blue Sea Automatic Charging Relay. I don't do extended cruising or have exotic electrical demands, so simple is better for me. One switch, turn it on, leave it on until I'm ready to leave the boat, turn it off. So simple a caveman sailor could do it!

Blue Sea ACR with Starter Interrupt

[sailhog]

We start with "All." Sails up, we go to "2," the house bank. It stays at "2" at anchor, and then back to "All" to start. A 50 watt solar panel charges the house bank.

[Administrator]

At the risk of being labelled a heretic, I use and like my Blue Sea Automatic Charging Relay. I don't do extended cruising or have exotic electrical demands, so simple is better for me. One switch, turn it on, leave it on until I'm ready to leave the boat, turn it off. So simple a caveman sailor could do it!

Blue Sea ACR with Starter Interrupt

+1 for the heretics. Me, too.

Bill

[wristwister]

I start mine on 2 and leave it on 2. Both batts charge regardless of switch position. I figure if 2 dies whilst out sailing I have 1 for starting.

Same here. Alternator charges both batteries regardless of switch position. Same thing with the charger (dual battery output). The switch only governs which battery(s) the juice flows out of. Therefore, I don't see how flipping the switch between 1-2-all would have any affect on the alternator.

... but then again, I'm one of those "simple caveman sailors" spoken of in this thread.

[Marian Claire]

"My switch says that switching between batteries is ok. The switch keeps a connection thru the cycle." Post # 4.
That is my understanding. The switch "makes" a second connection before it "breaks" the first. Make before break. I have switched back and forth between 1, both and 2 hundreds of times. Never "thru" off with the engine running. No issues.
Dan
S/V Marian Claire

[ndutton]

Why hasn't this been done already?

I would like to see a 1-2-ALL battery switch with a mechanical OFF gateway. The switch would turn normally through positions 1, 2 and ALL but to attain OFF the user would have to push the handle in to allow it to turn further.

[joe_db]

I would like to see a 1-2-ALL battery switch with a mechanical OFF gateway. The switch would turn normally through positions 1, 2 and ALL but to attain OFF the user would have to push the handle in to allow it to turn further.

I haven't seen that, but I have seem them with field interrupt connections that turn the alternator off when the switch turns off.

[ndutton]

That works Joe provided you have access to the field connections. My alternator is a single wire, modified self excite with internal regulator. As delivered there is one connection, the output.