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On Board Battery Charger assistance


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Not trying to hihack this thread - but I am in the same boat as above.  My boat has an on board 2 bank charges I want to use for my trolling batteries.  I just switched from a 12v system to a 24v system (with the jumper that goes from neg to a positive).  I took one of the cables from my on board charger and was trying to connect to the coordinating + terminal and it sparked!  I quit and unplugged my jumper and hooked it up as usual to my portable charger.  I was very concerened hooking it up to a 24v system correctly.  So I am still disconnecting my trolling batteries and charging them individually but I have an on board and really want the convenience.  

I am most worried about messing up my system - everything works great now (except the on board charging situation)!  

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When connecting the charger to the batteries, connect the negative and positive leads of the charger to their respective battery.  It's very common to get a small arc when you first connect the charger.  My Pro Mariners always make a small arc when I first connect them.   As long as the same set of negative and positive charger leads are connected to the same, how the batteries are tied together makes no difference to the charger.  You can have 10 batteries connected together in series (120 volts) and still charge each battery with a 12 volt charger, without disconnecting any of them.

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Good thread, guys.

One thing I didn't see mentioned - I may have overlooked it, if so I apologize - you've got to keep the batteries topped off with water.  This is especially important if you use an onboard charger because if you let the battery water level fall it'll get hot when you charge it, causing even more water loss, making it get hotter next time and so on until you finally fry the battery.

This happened to me when I put a charger on my last boat.  It was a real pain watering the batteries, hard to see the water level, so after replacing the TM battery I installed a battery filling system.  It connects the cells in all the batteries, you fill it using a squeeze bulb.  Stops when the cells are topped off so you can't overfill it.  I use distilled water.  I recently put this system on my new boat, a Triton with 2 TM and 1 cranking battery.  I had 'em put a three bank charger on it, despite the dealer assuring me I'd "never ever" need to charge the cranking battery.

Couple of other comments:

1) If you're going to use a charger for the cranking battery its best to replace it with a deep cycle battery.  Cranking batteries aren't designed to be discharged then recharged like the trolling motor batteries.  You lose a few cold start amps but thats easy to fix - get a bigger battery.

2) All batteries have internal resistance; therefore, its normal for a fully charged battery in good condition to show a voltage drop when its loaded.  You'll see this same thing on your car if you turn the lights on when the motor's not running - turn the ignition on and look at the voltmeter; you'll see it drop to 12 volts or less.  I put a charge meter on my old boat.  I could run the TM for a minute or two, then hit the meter button - it'd show about half charged.  If I let it sit for a minute or two then read the voltmeter again it'd be right back up.

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Hopefully there's no fuel vapors in the compartment, if so you need to fix that, but you have nothing to worry about mounting the charger in there. The charger is fully sealed and once the cables are connected to the batteries you leave them connected so there's no chance of a spark. The only time it would have any chance of making an arc is when plugging and unplugging the AC. Get one of those AC connectors with a cover that mounts in the gunwall somewhere so you don't have to raise the cover to get to the charger cord and then theres nothing in there that can cause an arc.

You just don't want to get it into too tight of an area that it can't get air circulation around the charger case and make it get too hot.

i dont plan on mounting an AC cover but wouldnt it be the same if i always plugged the charger in first then plugging into the outlet in garage?  this way there is never a loaded connection made in the hatch on boat.

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Plugging the charger in first, then the cord would work just fine.

Maintaining water level and using distilled water is extremely important.

On the post above, must have been one dumb dealer and you were smart to ignore him and install a bank for the cranking battery, there have been numbers of studies done on tourament pro's and other bass boats showing the cranking battery is usually down to about 80% charge at the end of the day unless they made long run back to the ramp.  Plus the fact that it's just as important to keep the charger connected when the boat is not in use to keep the batteries at full charge.  A lot of people are too used to the old, cheap automatic charges that fries a battery if left connected and they have a hard time with leaving a good charger on all the time, but that is the best for the battery.

Deep cycle batteries do ok as cranking batteries on smaller motors but can cause you problems on the bigger, Direct Injected V-6 motors, they may not deliver the cranking amps needed.   The 200/225 Fichts are very demanding when it comes to cranking one of those.  For those, you need to run a big, dual purpose battery.  

I would question the condition of my batteries or cable connections if my battery charge indicator (BCI) was dropping that much while running the TM.  Even on max, the battery should drop very little if everything is good.  I run a Curtis, 24V digital BCI mounted at the front deck on my batteries that constanlty monitors the level of charge an it never drops when the motor is running and goes back up when not.  Once a battery gets near the end of it's life cycle or has become heavily sulphated, they will do that because they can't deliver the amp demand.

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