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Old 07-28-2009, 10:58 PM   #1
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On my little sail boat I have two batteries, house and starter. The set up has three switches, one for each battery and a link switch.

My question is, if I just use the house battery and it runs down a bit what will happen? With the link switch and the main battery turned on will the main drain into the house?

Should I not use the link and only use the main (starter) battery if the house battery is down. Think I need all the power I can get to turn the 18hp over.

I run a little trickle charging solar panel to the main battery, which so far is working very well.

Thanks in advance for any help with this.
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Old 07-28-2009, 11:14 PM   #2
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IMHO ... keep the 2 batteries seperate while you are running lights & gadgets ... as soon as the house battery indicates it is running low (my laptop is usually the first to bleat) start your engine using the (isolated & fully charged) cranking battery ... once the engine is running switch the connecting switch so that both batteries get charged ... when charging is complete isolate the two batteries again ...
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Old 07-28-2009, 11:39 PM   #3
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Not knowing the amperage of your batteries makes it a little difficult to add more than what Tadpole advises.

The general rule is that the STARTER battery should have sufficient amperage stored to start the engine on its own.

If the engine can only start by utilizing the power of both batteries then either

the engine battery requires additional charging or a new battery of sufficient amperage is needed.

A voltage reading of between 13.2v and 13.8v on an engine battery (in good condition) should turn an engine over sufficiently fast so that it will fire-up within 10 seconds.
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Old 07-29-2009, 12:35 AM   #4
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Thanks tadpole, always is so simple when one knows how.

I've been starting with both and not had the confidence to try different.

Dont know what the battery amps. are. But should take a look shouldn't I, it could be handy, it will say on the battery I'm thinking.

My total battery knowledge is that one must make sure they dont dry out and not to over fill them, thats if they not sealed, which mine arent. Also to keep them charged.

Not sure that my votage readings are as high as 13.2 > 13.8 will take a look at that as well.

This is a big learning curve.

Thanks guys.

Fran
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Old 07-29-2009, 02:14 AM   #5
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Hello Fran,

Understand that you have never used ONLY the engine battery to start the engine?

Could I suggest that you do just that, Use only the Start battery.

During the process of starting an engine ( let's assume that your's is an 18Hp Universal diesel) a lot of amperes are drawn from the battery, Once the engine has started it should be run until the amps have been restored by the engine's alternator.

By using both batteries, one never knows if the Engine battery alone is up to the job.

The danger is that one will forget to disconnect the link between the engine and house battery and both could be run down to a level where the engine cannot be started.

Here is a useful site on testing Lead acid Batteries etc.... CLICK HERE

Richard
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Old 07-29-2009, 07:28 AM   #6
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Thanks Richard, interesting. I now know much more. Seems to me next time I replace the batteries it will not be with same sort I now have. Will let you know how I get on in the next day or to in regards to how she starts and the readings I get.

Thank you so much

Fran
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Old 07-29-2009, 09:12 AM   #7
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Fran,

Just noticed that your boat is an H28 - What a lovely boat, I remember many years ago sailing one in the Bay of Islands with the owner Jim O'Brien who had a house in Opua overlooking the bay.

I don't if was a ketch like this one (Jim's was a Herreshoff design - but built in NZ)

H28.jpg

Richard
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Old 07-29-2009, 12:09 PM   #8
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13.2 Volts is a good float voltage while a battery is being charged. 13.8-14.2 is a good bulk charge voltage. A fully charged battery at rest (removed form charger for several hours) will read no higher than 12.8 12.6-12.8 are good at rest voltage reading. If the battery will not easily start your engine at this voltage, either the battery is sulfated and needs to be equalized (controlled overchaging) or is undersized. It could also be at the end of it's service life especially if it has been heavily discharged.

If the battery reaches it's peak charge voltage in a very short time after being discharged, that is an indication that it is not accepting much charge. Try equalizing. If that doesn't improve that battery's performance, replace it.
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Old 07-29-2009, 02:45 PM   #9
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More knowledgeable members than I have posted suggestions, but I'm not sure that the most elementary information regarding batteries has been discussed.

As husband Peter told me, there are two kinds of 12V batteries. *Starting batteries, which put out short bursts of power in order to start an engine. *Deep-cycle batteries which are designed to be discharged deeply and are not expected to put out short bursts of significant power. *This is covered with much better terms and explanations in such books as The 12-Volt Bible for Boats and Nigel Calder's*Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems.

Before spending a lot of money on such a book, check this website for a start on learning more about your boat's battery system. *Battery Tutorial*
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Old 07-29-2009, 02:56 PM   #10
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Also see the Cruising Wiki's page on Care and Maintenace of Batteries.
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Old 07-29-2009, 09:20 PM   #11
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Thanks so much everyone for the advise. I've been doing much reading and am now much better informed.

My girl is a sloop, and yes 100's of H28's built in NZ. They are fine little yachts, lots of fun. I think most are a little longer than the original design of 28' and like mine a sloop, which is 29' 6".
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Old 07-31-2009, 01:21 AM   #12
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I'm going to add a few notes -- my 2.2c worth (inc GST).

Nigel Calder's book is an excellent resource, and no offence to Nigel because he's trying to cover a broad area in one volume and trying to keep it under a million pages, but he misses a few small details (which you can get from reading between the lines in his book anyway).

Engine/starter batteries and Deep cycle batteries are entirely different beasties as has been pointed out.

Do not use your house batteries, even cojoined to your engine battery, to start your engine. Deep cycle batteries handle a deeper discharge than cranking batteries, but they do not handle being discharged *quickly*. You will damage the batteries and reduce their long term life if you try to discharge them quickly (which is what a 600A or more starting current will do). Your high-cranking, low cycle, engine starter battery is designed to do that -- throw out a lot of current very quickly for the purpose of starting the engine. Once you've got the engine started then you can co join the batteries.

A modern solution to that is to have a voltage sensitive relay (VSR) instead of a battery switch. This joins the batteries when the voltage on the charging side is above 12.8V -- a healthy charging current, and breaks the join when it is not. So you can safely start the engine with just the starter battery and once the alternator has kicked in then the VSR will activate and you'll be charging both battery banks.

Do not rely on a high output alternator to charge your house batteries. Nigel Calder talks about having a second alternator to provide a 90A or 120A or even higher charge current (200A alternators I have seen in service on even smallish boats) to quickly charge deeply discharged deep cycle batteries, but what comes out slowly must also be replaced slowly. If you have, for example, 200Ah of deep cycle house batteries then you probably don't want a charging current much higher than about 40A or so. Better still is to use (when you have it available) a smart multi stage AC battery charger.

Furthermore, as Nigel points out, it is damaging to the engine to drive a large high HP diesel engine at low RPM for extended periods just to charge the batteries. Diesel donks are designed to work, and work hard. Running your main engine at 1200RPM or so for 2 hours every day to charge your house batteries won't help your engine any more than it will help your batteries. If you don't have access to shore power then you are better to have an on board AC generator and run the output of that into your battery charger and then into your batteries.
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Old 07-31-2009, 07:55 AM   #13
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Quote:
Originally Posted by delatbabel View Post
I'm going to add a few notes -- my 2.2c worth (inc GST).
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Old 08-01-2009, 11:35 PM   #14
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Finding all of your batteries are discharged to a point where the engine will not start is a bummer.

I have found that the best arrangement is to have a separate alternator to charge the dedicated starting battery of more than ample capacity(to allow for aging). Do not have a battery switch to connect to the house battery system.

If, in the remote case, the starting battery will not start the engine, use jumper cables in this emergency situation.

If you have a battery switch between starting and house systems it is too easy to forget that you left it on.

Been there. Done that.

Boating is fun!

Gary
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