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Old 08-02-2008, 13:33   #1
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Battery Isolator - or isolating switches

Soon I have to wrap my head around the boat electrics, and that is starting from scratch as we ripped it all out, not a wire is left.

I was wondering if battery isolaters are a good thing to use in the design inlieu or in conjunction with the big selector switches ???

Will be designing a 12V system, with 2 to 3 batteries and all the usual electronics and goodies in a cruising vessel.

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Mick
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Old 08-02-2008, 14:06   #2
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Isolators are used to separate the starting battery from the house battery. It allows the charger to charge both yet allows you to run the house gear from only the house battery and make sure you can still start the engine. It's a one way valve to use a plumbing analogy.

The old diode isolators do the job but with about a 1/2 volt drop in voltage. There are alternative approaches that use electronic switches to eliminate the voltage drop at a higher cost.

If you had a typical set up with two large group 4 batteries (400 amp hours) and a starting battery. I would have three switches an On/Off for the starter battery normally on and On/Off combiner to join the house to the starter battery in case you lost the starting battery normally off and a 1/2/both/off for the two house batteries normally Both. This lat switch allows one to be switched out should one battery fail. There are other approaches but this is a setup for maximum flexibility.

An isolator has nothing to do with the switches. You need to address isolation some way.

We have a few threads on electrical plans here and it is just a great idea to go through these. The details of some of the parts are covered in other posts. We also have quite a few other experts on the subject as well.

You need to design the whole wiring system at one time. Charging and batteries as well as DC and AC distribution. You'll need to consider 12 volt regulation and includes issues with your alternator. If you expect to use any wind or solar power you'll need that power regulated and integrated.
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Old 08-02-2008, 14:41   #3
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Mick,

Forget isolators. Old school, and not needed. Paul mentioned one of their limitations...voltage drop.

Consider yourself lucky: no wires left in place. This is an ideal way to start. Now, you can do it right.

What's right? Experts may have slightly different takes on it, but these days "right" is often defined as these 5 elements:

1. a starting battery, dedicated to the engine starting chore only and, as Paul says, with it's own robust ON/OFF switch.

2. a house bank of adequate size, built up by paralleling 12V batteries (or 12v battery banks made up of 2V or 6V units). The size will depend upon your needs. The type of battery will depend on your desires, your wallet, and available space. These house batteries should also have a robust ON/OFF switch (my preference) or, optionally, a robust ONE/TWO/BOTH switch so you can switch them to the starting circuit if needed. Personally, I prefer just the ON/OFF switch, and a short piece of wire or jumper cable kept handy in the VERY UNLIKELY event that your starting battery goes dead.

3. adequate charging devices: alternator and smart regulator; wind generator; solar panels; mains-powered battery charger; onboard generator; etc. All charging sources should be connected to the HOUSE BATTERIES, i.e., they should be used primarily to charge the house batteries.

4. an EchoCharge device, or a "battery combiner" which is used to charge the starting battery. I much prefer the EchoCharge...a $100 solution which is trouble-free and which will keep your starting battery topped off.

5. a means of measuring battery voltage or, if you prefer, of monitoring battery usage. I prefer just a digital voltmeter. Many others prefer a device like the Link monitor system which keeps track of amps in and amps out, and gives some indication of battery state-of-charge.

Remember that a starting battery is called upon to provide a great deal of current...sometimes upwards of 250 amps....to start the engine, but for a VERY SHORT TIME. Do the math. A 250-amp draw for even 30 seconds (and if your engine takes longer than this its got real trouble) is only a tiny draw in amp-hours....only about 2AH. It doesn't take long to replenish this tiny draw in your starting battery.

What DOES take time is to replenish the 100-200 AH lost from your house batteries each day (on a typical 40-50 footer). So, you wanna optimize the way in which these house batteries are replenished. They should never be drawn below about 50% charge (12.2V resting voltage), and they should be recharged as quickly and as fully as possible when cruising, remembering that undercharging is the main killer of batteries.

To recap: (1) a starting battery with its own ON/OFF switch; (2) an adequately sized house battery bank with its own ON/OFF switch; (3) all charging sources connected to the house batteries; (4) an EchoCharge device to keep the starter battery topped off; and (5) a means of battery monitoring.

Needless to say, all connections should be clean and tight, and all wiring should be of adequate size. The ABYC electrical code provides good guidance on wiring practice (particularly, the E-11 "AC and DC Electrical Systems on Boats").

That summarizes the current "best practice".

Final note: battery switches are not created equal. IMHO, you're better off investing in a very robust battery swich, rather than the flimsy ones at the low end of the market.

Hope this helps a bit,

Bill
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Old 08-02-2008, 16:24   #4
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Hi ribony...dont forget the isolator (combiners) NOT the old diode type !! Virtualy no loss. I use a 1/2/both/off rotary swtch with a "hellroaring" brand solid state combiner isolator Hellroaring Battery Isolator/Combiner BIC-75300. This charges the engine battery first from both aleternator and solar panel then house battery. The isolator from the states $170 aus, the rotary swich from whitworths.Whitworths Marine: 12v Battery Switch 4 Position Very simple and you can still disconect everything if you want to, or use your house battery to help start the engine. Wire your bilge pump(s) direct to the engine battery with its own fuse and manual/auto/off switch..
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Old 09-02-2008, 13:51   #5
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Wow, excellent ideas there (printed). Glad we asked that Q before trying to design the layout.

Now I better head off to do some research on the electronic battery combiners.


Thanks

Mick
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Old 09-02-2008, 14:46   #6
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Look for Knottyboys electrical plans for his proposed new trawler. The plans evolved over some time and the plans as well as the discussion will walk you through the process he went through. There is a great deal of really top notch electrical discussions already here.
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Old 13-02-2008, 13:42   #7
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Tried searching for knottyboys / knottyboy but could not get a result ?
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Old 13-02-2008, 13:50   #8
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You want Rick at knottybuoyz
http://www.cruisersforum.com/forums/members/knottybuoyz-1704.html

Rick’s Gallery:
http://www.cruisersforum.com/gallery/browseimages.php?do=member&imageuser=1704

BYW: Rick’s wife Lori < Knottygirlz > just had a heart attack (her prognosis is very good).
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Old 13-02-2008, 21:11   #9
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I am scrapping my isolator and installing and echo charger. You h)ve to remember with an isolator there is a voltage drop across it so its tough to get a full charge which is the problem I have with my system right now. The zantrex echo charger is dead simple to wire in and I think conceptually my whole arrangement is much simpler (just a battery switch, house batteries, starter battery and the echo charger except now you don't have to worry about how your starter battery is charged).

see Xantrex Technology Inc. - echo~charge - Product Information

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Old 22-02-2008, 15:17   #10
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How different is an echo charger than a combiner - automatic chargin relay?
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Old 22-02-2008, 15:39   #11
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Good question.

I believe the differences to be as follows:

1. a battery combiner is a device which, when it senses a sufficiently high charging voltage, combines the battery banks -- i.e., uses a relay to switch them together. It is a high-current device.

2. an echo charge device also senses a sufficiently high charging voltage, but uses a controlled, relatively low-current to charge the second battery or battery bank.

I have had a Xantrex EchoCharge device for several years now, using it to keep the starting battery charged. It senses a charging voltage (over about 12.8VDC) on the house batteries, and then puts up to 15A as needed into the starting battery to keep it topped off. It does not overcharge the starting battery, is totally automatic, and thus far has been perfect.

I believe it is one of the best ways to go to keep a starting battery charged, while using all onboard charging sources (alternator, wind, solar, generator, AC battery charger, etc.) to keep the HOUSE batteries charged.

Bill
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