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ssullivan 11-03-2006 10:13

Good god... I'm losing it. Battery switches??
Yet another electrical question. Sorry.....

I have two of those large, round switches that allow you to select 1, 2, or all batteries. You know... they say on them not to turn to off when the engine is running? (to avoid damage to the diodes/alternator)

One of the round switches is for the house bank. The other is for the starting battery. Would it be acceptable to have the house bank in the "off" position while I start and run the engine? I would have the starting battery in the "on" position during the entire exercise.

I ask because I'm working on my starter issue (bendix doesn't engage flywheel) and I need to isolate the starting battery system from the house system.

Seems whenever I bring the old, crappy Interstate house batteries into the circuit, they drag the voltage on my starting battery down to 13.2V, which I think is what's causing my starter problem (not enough power getting to starter).

So can I run the engine with only one of my battery switches in the "on" position?

Jon D 11-03-2006 11:29


Without a wiring diagram I can't say for sure but you should be able to. In effect you have the alternator pointed at the starter bank only. That should not be an issue. The big caution is not to switch while running as that can potentially cause an issue with the alternator.

ssullivan 11-03-2006 13:03

Thanks, Jon. That is what I suspected, but somehow... due to very little rest... I'm losing it! :)

Could not recall if the alternator somehow needed to see 2 banks on it, or if just the starting battery was sufficient.


Rick 11-03-2006 14:28

Separating the myth from facts
Internally regulated alternators ALL have built-in "load-dump" transient protection which absorbs the energy stored in the alternator stator winding (as well as the energy transformer coupled from the field winding). By the time that the "load dump" caused by opening all of the alternator load (inadvertently or advertently) is absorbed by the protection device the internal regulator has time to cut down the field winding current and no damage occurs either to the alternator diodes or other components designed to tolerate load dump transients.

Externally regulated alternators, however, need external load dump transient protection (called Zap-Stop devices sold by Ample Power, Cruising Equipment (now owned by Xantrex) and THEY need to be slo-blow fuse protected with blown-fuse indicators. This alone is insufficient protection for more than several hundred milliseconds before the field winding must be disconnected else damage will occur to some circuit elements.

For that reason I recommend that externally regulated alternators which, in general, have a voltage sense line connected to a specific battery, never be wired so that the alternator output can be disconnected from the battery with the voltage sense wire. In addition, ALL alternators are, by their very nature, current limited and, therefore, do not ever need fuses directly on their outputs as long as the output wire size is sufficiently rated to carry maximum current (why would anyone do otherwise?).

At the battery end of the wire one could argue that a fuse is needed and, in that case, I recommend that a single diode rated to carry maximum alternator current be placed in parallel with that fuse so under all conditions your electrical system is protected from damage (also with a blown fuse indicator). This is often overlooked.

Using battery disconnect switches with field disconnect switching is not ultimately reliable as a solution to prevent damage to the alternator output diodes.

capt lar 11-03-2006 14:35

Hey Sean - you guys need a day off and a dinner out. You have been hard at it for months. Remind your wife that this is not sailing - this is a major construction project.
Usually a "Guest" type switch would be used with position 1 for one bank and position 2 for the second bank. Unusual that you have 2 separate switches, each with the ability to control 2 banks (plus "all" and "off"). My point is you seem to have the capability for 4 banks. Some boats have separate bank for windlass and some for another major 12V appliance like refrigeration. You might want to run down those feeds to figure out if some other equipment is isolated. i would also be curious to understand how those two swiches are interconnected, if they are. This may lead you toward your initial problem.
My boat has a weird set-up. The previous owner could not remember to put switch to "all" so he never charged his house bank. He changed, at considerable expense, to a single bank system with 3 separate switches (house, engine and parallel) so the alternator always charges all 3 batteries (one bank) but the switches control which batteries are feeding to the main panel.
As to your question, if there is juice to the starter, you are good to go. I think size of alternator and output and if there is a regulator would determine if you could overcharge one bank, but this is a dark hole for me as well.


Jon D 11-03-2006 14:49


One other thought came to me when I was at my boat. You might consider changing your wiring a hair.

Set it up so the starter draws directly off battery bank 1[start bank]. Buy an Echo charge or equivalent and install across the back of the switch as instruction say. Set the selector so alternator is seeing bank 2[house bank]. This will allow the alternator to charge the depleted house bank according to its needs and the echo charge will top off the start battery. This should solve your 1/2/both issue and allow for better charging...


capt lar 11-03-2006 15:03

Jon - Do you have any idea why he would have 2 Perko or Guest battery switches, each with two bank positions, with only 2 banks of batteries ?


ssullivan 11-03-2006 15:42

I'll elaborate on the dual switches:
For the sake of where the thread is headed, I want to take the time to elaborate on the 2 switches:

They are twin Perko switches, sitting side by side. One switch is solely for the starting battery. The other switch is for a house bank that currently consists of two junky Interstate batteries. (got the Trojans to replace just the other day)

So... I wanted to just turn the starter battery on by itself to see if I could isolate some things as the pertain to my starter problem. (Starter motor spins, but does not engage flywheel)

I tried starting the engine with just the starter battery switch on (and the house bank off). Well... I couldn't have blown anything since the enging never started! :) :)

Just a big whirr as the starter motor spun up and didn't engage the flywheel.

I carefully measured voltages at the starting battery, at the solenoid, ignition, and starter posts. All measured the same voltage (13.8) so I have no voltage drop (dirty connections) between the batt and the starter. At least one thing is ruled out.

Next, I'm in the process of pulling the starter to try and lube up the Bendix, as has been suggested to me as a possible solution.

Someday... we'll be sailing. :) Just as Larry says... we desperately need a day off. We plan to keep on pushing through until May, then maybe have a couple weeks off before the summer season starts. To those thinking about chartering as something to do in retirement: FORGET IT! Unless you want to work full time. :)

capt lar 11-03-2006 16:00

Gotcha Sean - I misunderstood the configuration.

CaptainK 11-03-2006 17:43

Hey Sean.

I know you hell bent on getting that boat of yours "up-n-ready" for sailing season.

But, dude!! I really think you need a day or two off. I have seen people in the past, make mistakes. And even make their work harder on themselves. Due to not getting enough rest!! I have even done that, to myself in the past!!

You still have plenty of time on your hands to finish the remainder of your boat tasks til next season.

How much more work do you really have. Til "you" consider it all complete?

GordMay 11-03-2006 17:46

Simle answer:
House Battery 'Off' & Start Battery 'On' - NO possible damage to alternator.

ssullivan 12-03-2006 08:36

Captain K.... you know... you are totally right!

I think we'll give ourselves an extra month to get all the other "details" finished. You make a good point about making mistakes as fatigue sets in.

What's really misleading is that I keep thinking that this boat is like my old 30 footer. Just spend a couple weeks, and you can re-fit everything. Not the case anymore. Plus... everything is to a much higher standard for charter.

Thanks for the input. I'm taking it to heart and saying "screw it!" We'll get the basics done for our early season (April) charter that's booked, then work on the boat some more during april to be ready for May. We are already book up for May. Wow!


CaptainK once whispered in the wind:
Hey Sean.

I know you hell bent on getting that boat of yours "up-n-ready" for sailing season.

But, dude!! I really think you need a day or two off. I have seen people in the past, make mistakes. And even make their work harder on themselves. Due to not getting enough rest!! I have even done that, to myself in the past!!

You still have plenty of time on your hands to finish the remainder of your boat tasks til next season.

How much more work do you really have. Til "you" consider it all complete?

CaptainK 12-03-2006 08:40

No problem Sean.

Just looking after my fellow yachtsmen. That's all!!

Besides, you're not 20-something anymore. Just thought I'd give you a reality check!!:D

Also, you and you're lovely wife needs to spend some quality time out on the town. Go watch a movie. Or if ya into sports. Go catch a game. And see who's playing. If there are any bars, with any live music. Go out and hang out there. Relax!!:cheers:

CaptainK 12-03-2006 08:49

Oh yeah Sean.

Congratulations on having your first two months booked!!

You never did tell me how much more work you got left on your boat?

ssullivan 12-03-2006 10:07

I'm not sure how much we have left.... ha ha ha

It's hard to tell. Now that you have the new boat, you know what I mean. There's a list of things you "must do" to be seaworthy. There's a list of things you "want to do" to make it more comfortable, and then there's a list of "gee... it's be nice to have" things.

Here are my lists:


1) Get the starter working
2) Get genset/chargers/Trojan batts all running
3) Bolt in u-bolts to dinghy/dink so it can be lifted higher out of the water on the davits
4) Put sails back up - they are down for winter
5) Check anchors, etc...
6) Engine tune up
7) Get mast boot ordered / installed
8) Get Johnson 9.9 cooling pump kit and fix that

Must do for Charter:

1) Finish up master head/ceiling in there
2) Install new cabin sole
3) Install lighting in cockpit
4) Wax topsides/deck/etc...spring work
5) Bottom paint (could go in the seaworthy list, but could be put off until after April charter)
6) Install new refrigeration
7) Re-bed ports that run along salon/galley - they were done by an amateur last time - silicon everywhere!

Nice to do:

Well.... this list could go on forever... ha ha ha

That's where I'm at. Since there is only one early charter in April, I plan to squeak by without getting 100% of this stuff done. Then, using your advice... I'll take the rest of April to do this stuff. May is booked with chaters, and we'll be ready to go. I had been trying to get all this done by April 1st. Looks like no way that would happen.

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