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Old 09-24-2008, 03:25 PM   #1
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direct wire to house batteries from alternator?

I've got a .6 volt drop between my alternator output and my batteries and was thinking about running a direct line to the house batteries while leaving all the other standard connections in place, any reason to not do this? The panels and accessories would still have selective switching through the battery selector switch but the house bank would receive it's main charge directly from the alternator and regulator. In the case of my set up ie: alternator-selector switch-panels-batteries does this mean if a battery isn't selected then it isn't receiving a charge like in the case of the starting batteries which I never select to run panel loads? My selector switch is for house/start/both. I do not have a combiner.
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Old 09-24-2008, 06:12 PM   #2
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RE: direct wire to house batteries from alternator?

If there is an isolator then it's invisible. The Alt puts out 14.3 and the batteries are getting 13.7 volts. How and or does the not selected battery receive a charge?
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Old 09-24-2008, 10:01 PM   #3
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RE: direct wire to house batteries from alternator?

You could do the direct line, and as you suspect, it would always charge the house bank and only charge the start bank if you place the switch to the "both" position.

But the first thing to do might be to check where exactly you're getting the voltage drop.* As oldfishboat points out, your drop does sound suspiciously like an isolator (I think he meant 0.7 volts, which is the standard drop of*a silicon diode).* If the drop is in the wire between the alternator and the selector, then changing the destination to the house bank won't change anything... you'll have the same drop there.* If the drop is in the path between the selector,electrical panels,*and the batteries, then you have a major problem in that circuit which really needs to be fixed.

If the drop is in the alternator to selector wire, you might want to beef that wire up ... these are frequently only #12 or #10 wires, and making them a #6 or a #4 will take care of the problem.* If that's not*practical to do, another option is to use a remote sensing regulator - you have the voltage regulator sense at the far end of the wire, so that the alternator output is made high enough to compensate for the drop across the wire.* There's a little danger here, however - if the sensing wire becomes disconnected from the alternator output, the regulator will force the alternator to full output.* The high end regulators that are designed for remote sensing (Balmar and such) will also limit the alternator voltage output to a resonable value if the sense line shows much lower voltage.

In any case, I'd suggest connecting a voltmeter between each point in the alternator-to-battery chain to try to determine where the voltage drop is happening, and plan a fix accordingly.*
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Old 09-25-2008, 12:33 PM   #4
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RE: direct wire to house batteries from alternator?

The alt is 70amp and the only recent changes I made was a smaller pulley on the alt to get more rpm as I'm, like many, cruising at a low rpm (1600).* I think my problem is the undersized wires and several connections involved in this boat's 25 year old setup and thought the direct route of a 2awg for the 5' would solve the voltage drop without rewiring the whole system.

-- Edited by Daddyo at 13:35, 2008-09-25
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Old 09-25-2008, 04:27 PM   #5
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RE: direct wire to house batteries from alternator?

Well I ran a 2awg 5' cable direct to the house bank and my voltage jumped to 14.18V from 13.73V so for the $20 I'm very pleased.
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Old 09-25-2008, 08:51 PM   #6
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RE: direct wire to house batteries from alternator?

Daddyo -

Do you know where the regulator sense voltage is taken from?* It sounds like it's probably at the alternator (possibly an internal regulator), but the one danger of connecting the output directly to the house bank is if the sense is on the other side of the battery selector switch - if you have the other bank selected, now the sense is no longer connected to the output of the alternator.* So the regulator will put full field voltage on the alternator, and your voltage on the house bank*will go up - up - up.

Otherwise, sounds like you found your problem.
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Old 09-25-2008, 09:53 PM   #7
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RE: direct wire to house batteries from alternator?

It's the original Motorola unit with internal regulator so I've got to assume the sensor is from the alt itself and should not be hampered with the direct setup. The other factor is the connection to the bank on the otherside of the selector is still in place. Also I will never select the start battery on the selector anyway.
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Old 09-26-2008, 05:18 AM   #8
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RE: direct wire to house batteries from alternator?

I usually prefer to do what would be called "Auto" style in terms of the basic setup.

With a large diesel very few if any Rotary switches can pass the big amps required to start a cold diesel with no block heater.

For HOUSE system I prefer the rotary switch to allow the loads to be selectivly put on the house or start batts.

Normal operation is House all night , and combining to BOTH (to charge house batt) after anchor up and warm up to 180F.

The switch will handle 150A , the alts rated cap , so it has no problem feeding a Trace inverter to run a rooftop air cond all day , with the engine on.

Pretty seamless , and never a problem IF you remember to de combine as part of shutdown check list.

A Std RV solenoid would work with ZERO effort (actuated by run position on key switch) , but the solenoids would berequired to handle 150A , so 3 would have to be ganged ($18 each).
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Old 01-27-2009, 12:21 AM   #9
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RE: direct wire to house batteries from alternator?

all wires in a charging system should be the same size...use an external 3 step regulator...i like amplepowers, next, and V3 regs...i have the V3...it`s the best i`ve seen...had a lot of problems with balmar...my B+/charge wire from the alterator goes directly to the house, then an ample power eliminator charges the start batt...connected from the house to the start batt...only switch is to combine house/start...also switches have losses...fittings are important...use good ones, and a good crimper...solder if necessary...solder should never be used to hold a wire to a fitting, only to keep it in place after it`s crimped correctly...internally regulated alternators take a long time to charge batts...if they are set to a low voltage, the amps wont be hi enuf, and if set hi, over 14v, they will use water...that`s why the 3 step is a good idea. (my opinion) my system is set up in a very similar fashon, and has been running hands off for 15 yrs...except to add water...clyde
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Old 01-27-2009, 10:57 AM   #10
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RE: direct wire to house batteries from alternator?

The danger here is that if an alternator diode shorts out, you have no way to disconnect the alternator from the battery. A friend lost his boat from this the other year. He could put the resulting fire out, but it kept reigniting beacuse the battery was dumping itself into the shorted alternator.

FWIW.
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Old 01-30-2009, 04:52 AM   #11
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RE: direct wire to house batteries from alternator?

The danger here is that if an alternator diode shorts out, you have no way to disconnect the alternator from the battery.

If someone is actually worried about this a slow blow fuse or melting wire (auto style ) would be a safety.

The fuse blowing by accident underway might cause the diodes in the alt to need replacing.

For a worry wort , simply selecting a large truck or bus alternator that carries the diodes on a simple to replace exterior plate would solve that hassle.
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Old 01-30-2009, 08:20 AM   #12
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direct wire to house batteries from alternator?

The charging system should be fused near the battery regardless of how it is connected. The proper size fuse or breaker is important. This will eliminate the fire danger and allow direct connection to the battery which is the preferred method. This is a problem with multi-banks and using isolators to connect multiple batteries will result in insufficient charging since there will be a voltage loss through the isolators. Battery charging combiners do work better but you will still have some voltage loss. Fuses should be used on the alternator cable to prevent accidental switching in the off position and breakers do go bad.

-- Edited by Capn Chuck at 09:23, 2009-01-30
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Old 01-31-2009, 04:49 AM   #13
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RE: direct wire to house batteries from alternator?

For most installations running the Alt output directly to the starter feed is closest and require least Volts loss.

There is NO CHANCE of protecting anything by fusing a starter batt lead.

" Battery charging combiners do work better but you will still have some voltage loss."

I do not think the voltage loss with a proper simple ($20) solenoid could be measured with out lab grade equipment.

"" Fuses should be used on the alternator cable to prevent accidental switching in the off position and breakers do go bad.""


????????????


Should someone desire to actually move the alt output many batt switches have a field cutoff built in should it accedentally get switched to OFF,, and are "make before break", on changing batt selection.

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