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Old 21-10-2010, 11:58   #1
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Experience with Batteries

Once apon a time I was a new boat owner, ... The boat was setup with two dual purpose starter batteries, (one for each engine), and half the lights/outlets/pumps were on one battery, half were on the other. The generator was on its own and the 30 amp charger had three taps. I used the boat often part of the year and not for months the other part. Every time I used the boat and anchored overnight the next morning was an exercise in fear as I ran around turning off all circuits in the boat, jumpered both batteries together and tried desperately to get one engine to start on the first crank, (because if it didn't the batteries wouldn't have enough juice for another go). Tha resulted in several hours running the generator, (hopefully it started) waiting for the starter batteries to charge enough to crank one engine. Running the generator all night, (located under the master cabin), was a no go. Besides it tended to do something rude like throw a belt, or a pump impellor, or blow a hose around 3AM flooding the master cabin with smoke and steaming hot water, and making a horrendous noise, (more than its usual lawnmower at full throttle sounds). When the boat was idle I either left the charger off which resulted in stone dead batteries with a few inches of water in the bilge, or leaving the charger on which resulted in stone dead dry as a bone batteries that had boiled off the electrolyte.
A complete rewire later solved most of these problems, (the PO(S) that sold me the boat must have never left the dock more than an hour or two). First I removed all wiring except the starter from the batteries. then ran both alternators to an isolator then to all batteries. Then I installed a house bank that only had house load. I removed all external charging from the generator starter battery except a jumper solenoid connected to one other for emergency starting. To keep the boat from sinking when I'm away I have two float switches one runs off of the charger which now has a switch to isolate from all batteries. the second runs off of the house bank and a sonalert. Every two weeks I drop by and turn on the charger switch to top off the batteries for an hour or so then leave the charger on the bilge switch only. The generator problems I solved with a pure sine wave inverter and 2 * 200 amp hour house batteries. The inverter has an automatic switch to transfer load to active source. Now at night I just turn off the generator, the inverter automatically switches on, (the TV doesn't even blink). In the morning the low battery alarm comes on about an hour into breakfast, I just restart the generator, when the voltage stabilizes the inverter turns off by itself, and recharges the house bank. Anybody else have simular problems or same or better solutions?
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Old 21-10-2010, 12:19   #2
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First I would get a charger that you could leave on all the time without wrecking your batteries. I have to add water about twice a year with my promariner. Next I would get a battery selector switch so you can isolate each bank. You must be running a fridge to deplete your batteries over night. I have a 2800W inverter for my 120V needs but not the expensive pure sine wave type. Most electronics do not need pure sine wave only motors. Most of my power tools I bring on board are battery operated. I have one motor perkins 4107, one 3kw generator (I never use due to stink and noise) two starter batteries, and 2 banks of 2ea 6 volt golf cart batteries at 220amp per bank.
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Old 22-10-2010, 10:18   #3
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Yes I run a fridge and courtesy lights plus anchor light. The TV usually runs several hours into the night also. A bank switch would be good, I haven't installed one yet because I haven't run into any problems, (yet), running the house batteries in parallel, (they are a matched set with same manu code/date). A switch to run off of one battry and switch to the other when low and a dual float charger would be optimum, but so far the current system is working.
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Old 22-10-2010, 10:37   #4
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I would put a fix high on your list. If one battery goes it will take the other with it, and you don't want this to happen when you really need them.
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Old 11-11-2010, 16:34   #5
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Great story, Capn_Bill. I laughed at your description of the problem. Very funny.

I know the feelings of worry about will the batteries have enough charge to start the motor. Sailing back in the dark on my first sea trial of my new (old) boat, I watched the voltage readout on the GPS dropping, dropping, dropping, very low. Since there had been battery problems, I thought I would not be able to start the motor and have to call Coastguard. However, the motor started and later I found the GPS connection was very poor so reading lower than what the battery really was.
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Old 11-11-2010, 20:32   #6
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I got as far as the part where you mentioned the isolator. Get rid of the isolator. It has an inherent 0.7 v voltage drop meaning you will never fully charge your batteries through it and that will kill any battery in short order.
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Old 12-11-2010, 07:10   #7
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The isolator is a necessary evil right now. The only alternative is to get a seperate alternator for each battery, (All 4 of them). The alternators put out a little high anyway so the drop from the isolator is ok. The charger has a seperate circuit for each battery and is connected directly, (only the two engine alternators go to the 4 batteries).
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Old 13-11-2010, 12:00   #8
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you can get rid of the diode isolator and change to a contactor isolator, when the engine is running the run switch closes the contactors and charges the batteries, then when you shut down the all open, your charger should charge each battery/bank by its self,
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Old 13-11-2010, 12:12   #9
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my start battery serves as a start battery. The circuit is hooked to a blue sea battery combiner. once the start battery is good the house batteries get charged. I can manually connect house and start but thats an emergency. some folk don't like these combiners but mine have worked the charm for 3 years now. It reverses too so the solar panels charge the house and then when the voltage is good everything gets topped up. my experience not advice
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Old 13-11-2010, 15:17   #10
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Originally Posted by Juniper View Post
you can get rid of the diode isolator and change to a contactor isolator, when the engine is running the run switch closes the contactors and charges the batteries, then when you shut down the all open, your charger should charge each battery/bank by its self,
Here in the US what you describe is generally referred to as a "battery combiner" or "voltage-sensitive relay". It is connected between battery banks (or individual batteries) and senses the voltage on each battery bank, and when one reaches 13.2 volts it closes the relay to allow the second bank to charge. The basic operating concept is that only batteries that are under charge will exceed 13.2 volts and batteries under discharge will always be under 13.2 volts, and are therefore connected when charging (above a certain charge level) and isolated (open relay) under discharge.

As Juniper noted this is a essentially a lossless circuit because it doesn't use diodes, so efficiency is superior to a combiner. The internal control circuits use only a few millivolts (insignificant). You can apply charging sources on either bank, and once the voltage gets to 13.2 it will add the second bank.

I agree with Juniper that it's a better way to go than isolators.
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Old 14-11-2010, 10:17   #11
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i chose not to use the usual perko switch as they are prone to breakage--- my ericson has a set of 3 toggle switches-- one for batt bank 1 , another for bank 2 and one for the 1000 wtt charger/invertor. works great and no problems.
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