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Old 02-09-2010, 05:46   #1
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Charging a Dedicated Starter Battery and House Bank

I'm wondering if anyone can provide some advice on how I'd best keep 1 dedicated starter battery and a house bank of 2 deep cycles charged (considering I live 1.5 hours from my boat and use it every few weeks for day trips and occasional weekends out at anchor)?

Obviously I'd use the starter battery to start the engine. Then could I keep the battery switch on the starter battery while we were motoring out to the river (about a 25 minute motor)? Would that be enough to recharge the starter battery? (engine displacment- 27 cubic inches; alternator- 35A, battery- 550CCA &140 min at 23A)

Then, if we shut off the engine and want to run the radio and lights, I could switch to the house bank. And I could use the engine or the battery charger to recharge the house bank?

Then, assuming we got everything charged back on the dock, I was thinking I could set the battery switch to both and hook up the trickle charger, to keep them all topped off.

Does this seem like a good plan? Any recommendations for another way to do it?
Thanks
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Old 02-09-2010, 06:05   #2
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Yes, that will work OK, but is not optimum, because when you combine the house bank and the start battery it requires you to physically turn the switch to "BOTH", and it then electrically links all the batteries together. Depending on the state of charge (SOC) of the batteries, this can cause an inrush of current to the relatively depleted batteries, and a corresponding outrush of current from the battery(ies) with the higher voltage.

This may or may not cause a problem downstream.

The preferred way to deal with a house bank and a separate starter battery these days is to use a voltage follower device like an EchoCharge or a DuoCharge. This little device sits between the house batteries and the start battery. When it senses a charge on the house batteries, it bleeds off some of the charging current to top off the start battery. In implementing this strategy, you'd want to connect all onboard charging devices (alternator, battery charger, solar panels, etc.) to the house battery bank.

The logic here is that the start battery requires very little charging. Typically, to start a small to medium-sized diesel requires a lot of current for a few seconds, resulting in a usage of only about 1 amp hour from the start battery. This is replaced in minutes by the alternator and, unless you have fans or other devices connected to the start battery it thereafter requires only a small maintenance-level charge.

If you choose to rearrange your charging systems in this manner, be sure to include a properly sized fuse on the alternator output (in your case, a 50A ANL fuse located near the house batteries).

Bill
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Old 02-09-2010, 06:18   #3
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We have done as Bill suggests and used a BEP VSR. Works well.

Power Store&

However, we also have a solar panel to trickle charge during the week. Onboard the dog sits on the solar panel (because its nice and warm) which stops the solar charging which then means the VSR drops out with a click. Dog wonders what the noise was, gets up to investigate if its food and moves off the solar panel. Panel start charging so VSR kicks in and with a click connects the house and engine start battery together again. Dog gets bored and returns to lie on the solar panel...............

Wifey and me sat there listening to this iregular clicking sound every couple of minutes.

Pete
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Old 02-09-2010, 06:21   #4
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Bill is correct and gives an optimum solution. Of course marine systems get abused as does mine...

I have 3 batteries like you but they are all the same make and model (70a/h delco marine). In reality I start on both knowing that the batteries are fairly well charged from week to week. In fact both is the setting 90% of the time.

I run the engine anywhere from 5-10 minutes motoring out and getting the sails set. Then I shut down the engine and almost always stay on both. We sail all day with the radio and instruments running. At the end of the day I always get a good crank and start.

On a weekend trip I will switch to house when we get where we are going. After running the the house for 2 days the cheap cigarette plug monitor may show less than 12 volts on the house. I have then started on the start battery and switched to both planning for about a 1 hour motor or motor sail if the wind is still up.

As Bill points out this is somewhat abusive to the system but it has been working reliably for about 4 years.

In your case you have to choose what to do. I would recommend 2 things.

- Get a cheap cigarette lighter monitor at target, walmart, autozone or something so you have some idea of the state of battery
- Instead of the trickle charger - I don't like the idea of having AC power on the boat while I am gone - get a 5-10w solar battery topper.
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Old 02-09-2010, 06:55   #5
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This debate is as old as the Phonecians.

While I prefer a battery combiner or isolator or Echo Charger, the practice of using the battery switch will work just fine. 99% of boaters do it that way.

And although I agree that there are some risks of leaving your boat plugged in to shore power, there are greater risks of having your batteries run down trying to power a bilge pump which is trying to save your boat from a leak. Install a galvanic isolator and the risk of keeping plugged in mostly goes away.

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Old 02-09-2010, 07:28   #6
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thank you all very much for the advice, this is very helpful.

Bill- If I installed the EchoCharge, would I be right in assuming that when I leave the boat for a few weeks attached to my solar trickle charger that I'd set the battery switch to the House bank and I'd know that it wouldn't be pulling from one battery to give to the others (except for the bleeding from the house to the start battery)?

Ex-Calif- Am I right in assuming that you have 1 battery set aside for the starter battery and two batteries in parallel serving as your house? Also do you have a solar battery topper? And if so, what setting do you put your battery switch on when you leave your boat on the solar panels?
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Old 02-09-2010, 07:49   #7
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David,

If I had a proper shore power connection and on-board charger I would have no problem either.

I think OP is considering an automotive type trickle charger with a power cord run from shore.

I wouldn't do this on my boat for 3 weeks at a time. I wouldn't trust the shore power circuit protection or the charger for that long.
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Old 02-09-2010, 08:33   #8
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Quote:
Originally Posted by Ericsn25Chespk View Post

Ex-Calif- Am I right in assuming that you have 1 battery set aside for the starter battery and two batteries in parallel serving as your house? Also do you have a solar battery topper? And if so, what setting do you put your battery switch on when you leave your boat on the solar panels?
Correct on the battery set up.

Unfortunately, while I visit WM and Pep Boys every trip the 10w solar panel just hasn't made it to the top of the boat bucks spending plan ;-(

What I really want is two 40 watt panels on the bimini but that's such a nice to have thing for me and my boat I don't think it will ever make it.

I keep things topped up with the alternator - Sometimes I have to "choose" to motor sail to top up things but usually we are motoring for other reasons or have not used much juice. It's worked for 4 years this way.

To give you an idea of our weekend "worst case" consumption - On the hook or in a marina with no shore power.

2 fans X .4a X 10 hours = 8 amps
instruments X .5a X 12 hours = 6 amps
lights X 2 X 1.25a X 5 hours = 12 amps
radio & incidentals .5a X 10 hours = 5 amps

31 amps per day X 1.3 (efficiency factor) = 40 amps per day X 2 days = 80 amps.

The house bank is 140 amp hour. My consumption calculation is conservative because I don't think we have ever discharged the batteries that far.

After this kind of weekend I start on the start battery (70a/h) and switch to both and sail or motor sail for about an hour or more.
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Old 02-09-2010, 08:44   #9
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Ericsn25Chespk,

The EchoCharge only draws current from the house batteries when it senses they are being charged (voltage over about 12.8); otherwise it just sits there waiting. It will not overcharge the start battery, nor will it deplete the house batteries.

Operation is TOTALLY AUTOMATIC. You don't have to switch anything in order to get charging going to the proper batteries.

But you do have to wire things correctly:

1. ALL onboard charging systems (alternator, solar panels, battery charger, etc.) wired to the house battery bank, with an appropriate fuse near the battery bank (ANL or terminal fuse with an AIC rating of at least 5000 amperes);

2. Start battery on it's own ON-OFF switch. The Blue Sea Systems 6006 switch is compact and inexpensive, and more than sufficient for any current you'll encounter.

I see you're in the Chesapeake area. Give me a buzz if you have any further questions...expect to be around most of the time thru the weekend. Shoot an email to bill at wdsg dot com and I'll send you the tel number.

Bill
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