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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #11  
Old 07-25-2011
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If one battery is unable to start the engine do not switch to both, switch to the good battery. There is no good reason to combine a good battery with a close to dead one.
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  #12  
Old 07-25-2011
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Originally Posted by MarkSF View Post
Obviously when overnighting, you'll want to drain the deep cycle battery (2?), keeping the starting battery (1) for reserve. In that case the next morning select 1, start the engine, run for 10 mins, then switch to 2.

Mark,

If you need to select #1 to start the motor then you're drawing the house bank far to low and ideally need a bigger bank. You should never need to switch off the house bank. If you do need to then there is a bank size issue or the battery is getting long in the tooth..

Even 50% SOC a single group 24, 27 or 31 should easily start most small Yanmar, Universal, Beta, Nani or Westerbeke's...

A single group 24 bank leaves you with just 37.5 Ah's to use from a 100% full charge. When working off the alternator and only ever getting charged back to about 80% of full. Then you have only 22.5 Ah's to use before hitting the 50% DOD longevity threshold.

22.5 Ah's is far to little capacity for a weekend on most 25-36 +/- footers if you use the devices and lights most use...
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  #13  
Old 07-25-2011
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This question comes up so many times, that I've developed an Electrical 101 thread with links to many discussions about this very topic, which includes replies from many of the folks who have chimed in here.

http://c34.org/bbs/index.php/topic,5977.0.html

See reply #2 for a very succinct summary of what to do. Get you alternator output off the CV post of the 1-2-B switch and follow btrayfors, Brian's and Maine Sail's advice.

All the best,

Stu
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Old 07-25-2011
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mac, there are many answers because there are many difference kinds of equipment out there and they are not all built to the same spec. For instance:

IF your battery switch is a make-before-break type, and IF it has not worn out so that feature fails, then yes, it is safe to switch while running. (Notice, two IFs.)

The problem is that conventional alternators are wired up (IF you have a conventional alternator and IF it is wired up conventionally, two more IFs) so that the feedback to the alternator is designed to cause more power to be generated when there is less (i.e. no) power coming back form the battery. Normally that's a good thing, low battery means give it more power. Except, if you break the connection, the alternator says "Gee, that poor battery really is dead, I'd better run flat out" and 15-30 seconds of that can be enough to burn out an alternator.

Except ...some of the new alternators have protection built into them, and they don't care about a momentary blink/loss in the feedback. Some of them have spike and surge protection built in too. Others will shut down if the battery voltage drops to ~10.5V and won't let you recharge the battery until someone gives you a jump to reset them.

More protections, more "brains".

Some battery switches (odds are yours isn't) don't just use "make before break" but they also use a second set of contacts for "field sense" lead to make sure that feedback wire is switched to whatever battery you are using.

Confused yet? That's why there's a lot of different advice, you need to know exactly what equipment you have, what it can accept, how it is wired, and then verify that it IS actually wired and working correctly.

The alternative is to always assume the worst, and never switch batteries while the engine is running. That way, no matter what the equipment is or whether it is malfunctioning, you can't hurt it.

As to why your starting battery isn't always getting charged...that's a whole other issue to pursue. Could be a bad diode, a diode isolator was installed, a bad cable or corrosion...I'd use and run JUST on that battery, while troubleshooting just that battery, to see if it isn't something "local" in just that part of the wiring. (Which could include the connection to the battery switch, or a thinner longer cable, or an older one that's rotting inside...all sorts of simple things.)
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Old 07-26-2011
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Not necessarily true, and that's why so many of us have been suggesting that you remove the alternator output from the switch and wire it to your house bank. Done that way, you could turn the switch OFF and still not cause any issues with the alternator.
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Old 07-26-2011
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The only reason most manufacturers wired the alternator output through the 1,2,both switch in the past (some still do) is it is the cheapest way to charge 2 banks - not the best.
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Old 07-26-2011
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"remove the alternator output from the switch and wire it to your house bank. Done that way,"
Stu, presumably you also mean with an echo charger or West/andina Combiner added in, so the house bank will in turn charge the starter battery.
More stuff. (Good stuff, but more stuff, for the folks who aren't running it yet.)
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Old 07-26-2011
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Quote:
Originally Posted by hellosailor View Post
"remove the alternator output from the switch and wire it to your house bank. Done that way,"
Stu, presumably you also mean with an echo charger or West/andina Combiner added in, so the house bank will in turn charge the starter battery.
More stuff. (Good stuff, but more stuff, for the folks who aren't running it yet.)
You can add one but it is not 100% necessary with a 1/2/BOTH switch if the owner is on a strict budget. Just use BOTH when charging and your doing the same thing as when the alt ran to the "C" post of the switch and you selected both. You will NOT however be able to charge the second bank while the switch is in that position so an ACR or Echo is very wise and an expense any owner should be talked into when moving the alt from the "C" post to the house bank..

I personally would much prefer a voltage sensitive relay or an Echo type device as it makes the system a lot easier to use. A Blue Seas ACR is about $70.00 and an Echo can be had for about $130.00..

Just had another fried diode situation a couple of weeks ago and may have one I am looking at on Friday. This is not an uncommon problem and is the reason a good battery switch like the 1/2/BOTH/OFF gets an undeserved bad rap....
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  #19  
Old 07-26-2011
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Quote:
Originally Posted by hellosailor View Post
"remove the alternator output from the switch and wire it to your house bank. Done that way,"
Stu, presumably you also mean with an echo charger or West/andina Combiner added in, so the house bank will in turn charge the starter battery.
More stuff. (Good stuff, but more stuff, for the folks who aren't running it yet.)
Yes.

And I must take this opportunity to congratulate Maine Sail, Brian, Bill and a bunch of others for retyping answers to this same question, over and over again. I understand there are new folks. That's why I developed the 101 topic, which links to a lot of what has been described many times before, on this and other forums. Each of the questions has merit, since the poster is new and is asking what is a basic, but highly important question.
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Old 07-26-2011
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I appreciate all the input and my plan is set.

1. At some point I will install an Echo or similar regulator and change up my wiring configuration. I completely rewired the boat a couple of years ago adding new wiring, fuses and a breaker panel etc and took great care to try and do it right. This never came up so will fix that.
2. In the meantime I will just adjust how I function. I have an analog voltmeter which was starting to show roughly 12.2 values. I thought it was supposed to be up near 13 but did not pay it much mind. Never again. I am on a river and have a roughly 30 minute motor to get to the end of the channel. Going down the river will start/run off battery 1 and going up the river will start/run off battery 2. This way both batteries will get full attention for at least 30 minutes per trip. Until I get the regulator this is probably the best I can do.

I will also pay more attention to the batteries in the off season and bring them in to get tested. The last thing I want is to not be able to start my engine when I have to get back to my mooring against an outgoing tide. I have SeaTow but would rather not have to call them. I am also planning to get an electric trolling motor and battery for my dinghy which will serve as a nice backup if needed.
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