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 Post subject: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:11 pm 
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Joined: Wed May 12, 2010 3:07 am
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Location: Spring TX
OK, I need some help understanding sum'n about a battery A/B switch. On my Mastercraft (I know it ain't a wood boat but most of the internal running hardware are the same ;-) I had an issue with leaving a switch on and the battree run flat. So a buddy of mine gave me a nice A/B switch. It didn't have any instructions with it. Now I did do a search on teh forum and came up with several wiring diagrams. Bill had some nice ones posted... I installed it before I left home and yes I even soldiered the terminals and everything. Nice job I thought. I only have one battery right now but I do plan on installing a second one later on after the bunk board fix. My question is about the swich, it had of course, "Batt 1", Batt 2", and to Engine post. It also had 2 lil smaller post that said "Field" on it. Uhhh what am I supposed to hook up to the field post (two of them, kinda in and out)? I suppose it has something to do with electrolysis????

Ya see I have a Switch on my ole skiff and it's kinda a 1 stop shop, last thing I do is kill the power from the battery then the battery is always ready to go when you are, nome sain

OK that was question 1 so we'll see how this goes before I post Question 2. I like to keep them seperate as then it makes it easier for others to find when doing a search.

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NO PICS, I'M IN OZ. lol


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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:18 pm 
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Location: Owasso, Oklahoma
See here:

http://www.perko.com/images/catalog/pdf/Fig%208501-8504%20Inst%20(8500INS1).pdf
I'm assuming it's a 1, 2, off, or both switch. The field hookups are normally for alternator fields. Hope that helps.

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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:24 pm 
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Location: Owasso, Oklahoma
Looks to me like the field grounds are only for unregulated alternators.

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I told my wife we needed a three-car garage for my projects...she told me to ask her for permission next time before I buy a house.
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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:30 pm 
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Location: Spring TX
Yep it sure did. I'm assume'n I don't have such a thing as those wire weren't present in the battery compartment. I'll have to do some more investigating when I get home of course, but I don't think it's relevant in my case... ***edited***And as your second post says it seems to be over my head and I'll have to look closer at the alternator when I get home. I don't think it applies in my situation. I'm assuming mine is regulated??? sheesh electrics kick my b***

Thanks fer the speedy response. I guess I should have took pics of the install but I didn't. I was there that day in storage doing that and getting a broken bolt out of the block. After I bought the boat I had noticed that the alternator bracket was broken so I took it off and took it home. I had some 1/4" plate and I used my plasma cutter to make a new one. It turns out the there was a bolt on the lower portion of that bracket that has broke off in the block. So I drilled it, and then was VERY lucky to get it out with an easy out. With all of that going on I didn't think I was gunna have time to take pics. It went WAY easier than I thought...

Thanks fer your help Bill.


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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:34 pm 
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Location: Spring TX
So if I read it correctly it breaks the field current in the alternator if you switch it to the off position so it will kill the engine? And you would want to do this so you're not running the engine solely on the alternator???


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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:36 pm 
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Location: Birmingham, AL, USA
Bill

Sorry, can't help. Neither of my boats' switches have the field terminals you mention.

Don't know.

Bill

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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:40 pm 
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Location: Owasso, Oklahoma
Anytime. Most, not all, but most newer alternators are regulated according to the self-proclaimed know-it-all marine mechanic here at hand. Apparently this is an issue more on older twin engine boats especially when the battery switch is set to "both" as heat build up and generator phases can cause bad things to happen.

I'm not the expert on this one but that's what the neighbor is telling me.

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I told my wife we needed a three-car garage for my projects...she told me to ask her for permission next time before I buy a house.
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 Post subject: Re: Battery A/B Switch
PostPosted: Sat Jan 15, 2011 6:48 pm 
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Location: Orange CA
Do a search for battery shutoff switch and include AFD automatic field dis connect you may also be able to find a wiring diagram

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 Post subject: Re: Battery A/B Switch
PostPosted: Sun Jan 16, 2011 6:35 am 
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Location: Puyallup, WA
PB

The field connections are for alternators with external regulators only. They prevent the diodes in the rectifier from being burnt up when turning the battery switch to the off position while the alternator is charging.

Blue Sea has a good explanation where I got the picture form http://bluesea.com/viewresource/91.

Hope that helps.

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 Post subject: Re: Battery A/B Switch
PostPosted: Sun Jan 16, 2011 4:44 pm 
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Location: Spring TX
Awesome guys! Thank you fer taking the time ta post this. It helped me and I'm sure it'll help others.

I'm not at home right now but I reckon this won't apply to my set up... When I get home it'll be close to time to get her out of winterize mode. :wink: Yep, all that for 6 weeks of storage! lol I'm gunna be replacing the raw wader intake hoses and installing a Sherwood strainer. I'm gunna take pics of all this and I reckon I should post them even though she's not a wood boat. ;-) Well she does have some wood on the stern. The swim platform it beautiful teak. hehehe

Thank again!
Blair


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 Post subject: Re: Battery A/B Switch
PostPosted: Tue Jan 18, 2011 10:55 pm 
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Location: Battle Point, Leech Lake... tundrasota
Only really applies to a diesel powerplant with an old electromechanical regulator. Is of questionable value even then, but entirely not needed on any of today's modern internally regulated alternators.

Way back (in Bill's day :wink: ) the relay-style regulators wouldn't react fast enough when the load was suddenly pulled from the alternator, the output voltage would spike well over 30 volts. The ancient selenium diodes were easily destroyed by high reverse voltage. Modern diodes can easily handle that type of spiking (I know of a fellow operating a ghetto-engineered-wind-turbine running over 90 volts through a stock GM 120 amp bridge.) Modern regulators clamp the field fast enough to make the problem a thing of the past. RV and OHV's have been using dual battery switches with no field-kill for years with no problems, but if you are really worried about it, shunting the alternator output to ground through a 16(ish) volt high power zener like the old motorola 2535 diode will do the job properly, and not add to the confusion in the electrical system.

Some alternators should never have the field killed while the alternator is working. That crappy Dulcier alternator that was floating around in the mid '80's will let the magic-smoke out of the regulator pack if you kill the field winding. (they called the sensor/feedback circuit "field" who knows what made that seem like a good idea.)

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