Battery Charging . . . again !! - SailNet Community
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Battery Charging . . . again !!

Hi, I'm a bit of a novice and have been trying to get my head around what I should do for a new battery setup on my Compass 29 (yes I'm in Australia !).

I've been reading some very interesting posts about VSRs and battery combiners and shuch like, and its finally sinking in, but there is still one thing I haven't figred out yet. In fact, I haven't even seen any info on it, so maybe its a non-issue. Hopefully the experts can help.

Assumption: a charging source (lets keep it simple and make it one charging source), reduces its output dependant on the charge (voltage ?) in the battery being charged. This is good for battery life.

Hypothetical: I have a 1 smallish starting battery and 1 largish house battery bank. I'm out for the weekend and have run my house bank down very low over night powering the ESKY My starting battery is all but fully charged as its only started the engine once on the way out. I start the engine in the morning and the alternator kicks in.

Questions : Regardless of how my batteries are combined the alternator will at some point be charging 1 almost full battery and 1 almost empty battery bank, so what charge level (voltage?) does it use to determine its output ?

Taking this to the nth degree, would it be possible/better to have a regulator/controler for each battery bank, rather than for each charging source ?

All throughts appreciated.

Kind regards,
Greg.
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Quote:
Originally Posted by MrSeaDragon View Post
Hi, I'm a bit of a novice and have been trying to get my head around what I should do for a new battery setup on my Compass 29 (yes I'm in Australia !).
Compass 29.. a nice boat. Welcome to Sailnet, Greg.

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...
Hypothetical: I have a 1 smallish starting battery and 1 largish house battery bank. I'm out for the weekend and have run my house bank down very low over night powering the ESKY My starting battery is all but fully charged as its only started the engine once on the way out. I start the engine in the morning and the alternator kicks in.

Questions : Regardless of how my batteries are combined the alternator will at some point be charging 1 almost full battery and 1 almost empty battery bank, so what charge level (voltage?) does it use to determine its output ?

Taking this to the nth degree, would it be possible/better to have a regulator/controler for each battery bank, rather than for each charging source ?
To answer your question directly: it depends how you have the charging set up. The simplest setup usually has a couple of diodes connected - one to each battery - allowing current to flow to each with the most discharged getting the benefit, as Jody pointed out. The problem with this sort of setup is that there is not really anything stopping the full battery being overcharged.

A better setup would be to have a regulator/controller for each bank. This allows the regulator to either trickle-charge or float-charge each battery independently. Have a look at the Blue Seas web site for ideas.

Hope this helps.

-
"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"
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Jody-

I'd have to disagree. If you've got an ACR, it really does little to prevent or prohibit you from draining down your start battery. You really need to read about the capabilities of the ACR again. You're attributing capabilities to it that it simply does not have.

If the main battery switch is in the ALL or BOTH position, whatever loads you have on the system will draw down BOTH BATTERY BANKS. THE ACR CAN'T PREVENT THE RESULTS OF USER ERROR.

All an ACR does is eliminate the need to put the Main Battery Switch into the BOTH or ALL position to charge both battery banks when a charging source is present. It does not prevent batteries from being discharged if you have the battery switch set incorrectly—it merely reduces the possibility of that occurring by removing the need to change the setting on the switch from the 1 or 2 position to the BOTH or ALL position to charge both banks, and since you don't change to the BOTH or ALL position, you don't have to remember to change back when not charging.

The newer, more compact squarish ACR will sense charging level voltages on either bank and combine if it is detected. The older, longer retangular one would detect a charging source on the primary bank and connect both banks for charging when a charging level voltage was detected, but needed an optional "sense" wire connected to do so for both banks.

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Now if you are severely depleted, the cool thing about an ACR is that it will prohibit usage of the cranking source in luie of say amping out your stereo for some fireworks display... to be used..

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Last edited by sailingdog; 07-11-2008 at 08:23 AM.
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Ahhh... Did Jody say something, SD?

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just goes to show a little knowledge can be a dangerous thing.

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Ahhh... Did Jody say something, SD?

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Aww... no fair retracting post Jody...You cant be right all the time you know...it helps some of us lessor's feel better ya know...
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I'm a bit lost here with the missing piece. What is an ACR?

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I'm a bit lost here with the missing piece. What is an ACR?
An "Automatic Charging Relay". See the Blue Seas web site here for more info.

Not sure that it's what I'd use, but some people do..

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I use one one charger and one 3-step regulator, and switch manually. Protect your alternator diodes with a battery master designed to disable the alternator field wire before you switch.
It is simple and it works fine.
Battery internal RESISTANCE determines the battery draw when charging. A discharged battery has less resistance, and so draws more current, slowly falling off as the battery resistance recovers.
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Basically it is a relay that closes when it detects charging level voltage on one of the two sides. Some will only detect charging level voltage on the primary side, and need a sense wire connected to detected it on the secondary side. Others, like the newer ACR that is squarish, will automatically detect it on either side.

They're very convenient in that you can start your engine and as soon as the alternator output is detected,it will combine the batteries so that both banks are being charged while the alternator is running, without you having to do anything. This makes it far less likely that you'll leave the main battery switch in the "BOTH/ALL" position and kill both battery banks when you're sitting at anchor after the engine shuts off.

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I'm a bit lost here with the missing piece. What is an ACR?

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—Cpt. Mal Reynolds, Serenity (edited)

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