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Old 20-02-2011, 07:53   #1
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House / Starting Batteries

Im just wondering how the charging of these is seperated from engine alternator and shore power charger and how the starter battery is isolated form the house ones do they use diodes?
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Old 20-02-2011, 08:54   #2
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Steve,

There are tons of posts on this very subject on this Board and on SailNet.

There are different approaches to separating the two banks. Many boats are wired with a 1-2-Both-Off switch, with the house bank attached to one position and the start battery to the other. I don't like this approach, but lots of boats do it this way.

Separation can be done by using isolators (diodes...the old way), ACR's (automatic charging relays), battery combiners, and voltage following devices like the EchoCharge or DuoCharge. Some folks use the manual method and just switch to "Both".

The preferred method these days is to attach all charging devices (alternators, battery chargers, generators, solar panels, wind generators, etc.) to the HOUSE battery bank, and to maintain the starting battery automatically using a voltage follower device like the Xantrex EchoCharge or the Balmar DuoCharge.

How you wire it all up is important, and there are basically two camps on this: (1) the KISS camp which believes in using the house batteries to start your engine routinely, and keeping the other battery as a "reserve/backup" battery; and (2) the camp which believes in a total separation via battery switches: one for the house bank and one for the start battery. I'm a firm believer in the second way, since it completely isolates the starting circuit from the house circuit, and avoids the possibility of damaging spikes and other voltage transients caused by engine starting from getting into your sensitive onboard electronics.

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Old 20-02-2011, 09:21   #3
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OK in my boat the starter battery is permanently unlinked from the house batteries so im thinking that there must be a diodes or something from the alternator to the house batteries and starting battery otherwise theyd be linked at the alternator?
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Old 20-02-2011, 09:24   #4
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You need to do some investigating!!

Also, more details in your query would have been helpful.

Hint: with the motor running, measure the voltage on your house batteries. If they're over about 13VDC, then there must be a link of some sort, probably via an isolator (diodes).

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Old 20-02-2011, 09:37   #5
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thanks, there are two isolator switches, port/starboard bank, but they just connect the 2 service batteries to the house system, ie both off no lights, one or other on, then internal lights, the main starter battery appears permanently dis connected from the house system, so i assume their is some split from the alternator output maybe 2 diodes one going to the house batteries and one to the starting battery, the shore power charger has separate outputs so they wont link through that, interestingly it says on the isolators switches do no disconnect when engine runnig, so it must cut them off from the alternator as well at the switches. Im not sure if the alternator has smart charging or not, im just trying to work it out for the addition of solar, im thinking maybe splitting the output from the solar panel ,putting in two regulators one to the service bank and starting battery.
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Old 20-02-2011, 09:46   #6
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OK, thanks. The additional info is helpful, and it underscores my earlier point: you really need to do some investigating!

You need to trace the existing wiring, draw a diagram, and be sure you've got it right before you change anything.

Also, "isolator switches"...what is that? Are they just plain battery switches? On-Off? Can you find an isolator bank in the charging circuit somewhere? Normally, these are about the size of a brick and have several studs extending out the top. They are meant to distribute a single charging source to two or three batteries. They are not favored at the moment, due to their voltage drop thru the diodes and their unreliability.

Once you understand what you've actually got, you can begin to plan for changes, including the additional charging sources.

Again, there is no need to have multiple charging paths. Run all charging sources to the HOUSE battery bank, and run that bank as ONE...not separate banks. Then, use an EchoCharge or DuoCharge to maintain the start battery.

You want to wind up with a system which does not require switching to charge one bank or another. It should be automatic.

The battery switch or switches (depending on how you choose to set up the main DC wiring) should just be disconnects...to switch a battery bank on or off.

Bill
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Old 20-02-2011, 09:51   #7
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, im just trying to work it out for the addition of solar, im thinking maybe splitting the output from the solar panel ,putting in two regulators one to the service bank and starting battery.
I think that this is a mistake. It's not difficult to keep a starting battery charged, and there's no reason the alternator can't handle this task alone. Wire the solar to the house bank, and let the engine start battery take care of itself.
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Old 20-02-2011, 14:44   #8
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its more for laying up over winter, up here we have to winterise for 6 months of the year im 55degrees north, and i dont like to leave the charger on shore power for so long unattended, so the engine start battery is getting no charge for 6 months of the year.. not so good.
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Old 20-02-2011, 14:59   #9
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its more for laying up over winter, up here we have to winterise for 6 months of the year im 55degrees north, and i dont like to leave the charger on shore power for so long unattended, so the engine start battery is getting no charge for 6 months of the year.. not so good.
No, it's not good at all. A great way to kill your battery capacity!

Steven...may I gently suggest that you step back a bit. Read the above posts again.

IF you connect all your charging sources -- alternator, battery charger, solar, wind, generator, or whatever -- to your house battery bank; and

IF you bridge the house battery bank to the start battery with an EchoCharge or a DuoCharge;

THEN you won't have to worry about the start battery. These little devices steal a bit of current from the house bank whenever it's charging and automatically divert it to the start battery. No intervention on your part is required. Start batteries require very little charging to keep topped off.

There is NO NEED to split the charging current from your solar panels, or your battery charger, or your alternator, or your onboard generator, or your wind generator.....just connect all these to the house battery bank, using appropriate fuses and regulator/controllers, of course.

This arrangement is best for your batteries and is very easy to set up.

Bill
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Old 20-02-2011, 15:29   #10
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Thanks, for the advice, being a miserable scotsman, im trying to keep costs low, i can get cheap charge controllers on ebay for ten uk pounds, bear in mind its more trickle charge to stop self discharge over time, solar up here is not so great, we checked a 30w panel and it was giving 0.11 amps in daylight, full daylight in our winter. i can get a 30w panel for 60 uk pounds about 90 us dollars 2 cahrge controllers for 20 uk pounds 30 us dollars and split the solar output, strangely enough my boat has a 240 ah agm start battery and 2x 85a gel house batteries. someone must have been paranoid about starting their engine
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Old 20-02-2011, 15:30   #11
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No, it's not good at all. A great way to kill your battery capacity!

Steven...may I gently suggest that you step back a bit. Read the above posts again.

IF you connect all your charging sources -- alternator, battery charger, solar, wind, generator, or whatever -- to your house battery bank; and

IF you bridge the house battery bank to the start battery with an EchoCharge or a DuoCharge;

THEN you won't have to worry about the start battery. These little devices steal a bit of current from the house bank whenever it's charging and automatically divert it to the start battery. No intervention on your part is required. Start batteries require very little charging to keep topped off.

There is NO NEED to split the charging current from your solar panels, or your battery charger, or your alternator, or your onboard generator, or your wind generator.....just connect all these to the house battery bank, using appropriate fuses and regulator/controllers, of course.

This arrangement is best for your batteries and is very easy to set up.

Bill

Ditto: This simple solution is what we have done also, although we used a Blue Sea, "battery combiner". (All charge sources go only to the house batteries). It is easy, reliable, and has worked well for 15 years.

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Old 20-02-2011, 15:38   #12
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but are they expensive? i just dont see the point of using an expensive item to trickle charge batteries, just to keep em topped up? bear in mind starter is agm and house are gel, so they will require different top voltages? well i think they will?
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Old 20-02-2011, 15:44   #13
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Thanks, for the advice, being a miserable scotsman, im trying to keep costs low, i can get cheap charge controllers on ebay for ten uk pounds, bear in mind its more trickle charge to stop self discharge over time, solar up here is not so great, we checked a 30w panel and it was giving 0.11 amps in daylight, full daylight in our winter. i can get a 30w panel for 60 uk pounds about 90 us dollars 2 cahrge controllers for 20 uk pounds 30 us dollars and split the solar output, strangely enough my boat has a 240 ah agm start battery and 2x 85a gel house batteries. someone must have been paranoid about starting their engine
Good grief, our Sealine 240 had a 60Ah start battery (Volvo 275 V8) and the house was a 75Ah cheapy, courtesy of the previous owner.

Since your only dealing with 3 batteries, stick the solar on the engine start and take the gel batteries home with you.

Checked the boat today, 45w solar panel was giving 0.3 amps this afternoon in the Solent

Were did you see 30w panels for £60, that seems a good price for the UK. Our semi flexible 45w is £550.

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Old 20-02-2011, 15:49   #14
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In fact I would be tempted to hoik that AGM off the boat if you are going to sell and keep it for the yacht. The Sealine will start quite happily with a cheapy power max flooded lead acid battery.

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Old 20-02-2011, 16:15   #15
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My battery combiner was not particularly expensive... Yes, the house bank, in my case, is a wet 340ah and partly discharged. Where as the tiny little 98% full engine battery could potentially be overcharged by my engine alternator, which is my only "dumb" charge source. To prevent this, I have a switch in the combiner's neg sense wire.

After about 30 minutes of engine run time, IF the line v to the house bank has reached 13v, which it should, a little yellow LED tells me that the house bank and engine batteries are combined. Since the engine battery was only down by the amount it took to crank the engine, this (30 min charge) is plenty, and I shut off the switch, thereby UN-combining the banks. The engine battery is now full and alone.

With the dockside charger, I leave the combiner on, as the dockside charger isn't charging the batteries, they are on float, at a constant adjustable v. (like 13.4)... If the different float v worried me, I would combine the batteries for 30 min once a week to top up the engine battery. (I just leave it on, dockside.)

At anchor, we use solar 100% of the time. I have the combiner switched off usually, (so it can't combine), and every few days, toward the end of the day, I flip the switch for 30 minutes. (This brings my 2% self discharged engine battery, back to 100% full ).

Since my wet batteries use a similar float v, all I am doing is academic anyway. I could probably leave the combiner engaged all the time. In fact I have forgotten and left it on for months, without the smaller battery getting damaged from overcharge.

In your case if the house bank is Gel, then all of your charge sources would be set for that v. I haven't compared lately, but I believe that this would be the same or lower v than the AGM engine battery would like. since the engine battery is about full, ALWAYS, and is mostly being "floated" by the overflow from your house bank charge, an "ever so slight" under v to the engine battery, should not hurt a thing. It might be resting at 98% charged, rather than 100%?

Do your homework on the numbers... but I don't see a problem.
Mark
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