I saw Chris's post about a charger recommendation and I need one too as mine is original circa 1974.

What I am thinking though is to get a new smart charger but also a battery inverter, some sort of house battery bank to run the fridge etc. while we are out. This would include a low battery alarm to alert when the genset needed to be run. Ideally this would keep the starting batteries isolated from any house electrical use.

I have just the engine batteries and the genset battery as it stands now. When we go out I have to run the genset to keep the fridge running.

Is a system like I described worth the money invested? Do any of you guys have similar systems? I assume these old CC's came with dual voltage refrigerators vs the AC home center model I have now.  



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I haven't gotten it reinstalled but long ago I added an inverter/charger.  This was back in the day that only modified sine wave inverters were available.  It was great, no more defrosted fridge when cruising.  The small fridge in the 35 only draws about 90 watts with the light on when cooling, no load for a genny.  This also allowed use of some power loads up to the rated 1000W.  Given current technology a pure sine wave inverter charger would be my choice.  The latching with the inverter was really cool.  The clock on the microwave would not drop out whether going from inverter to shore power or genny.  Incidentally the fridge was 115VAC only.  As soon as the inverter sensed 115VAC input it went into charge mode.  This did require me to add switching for the various battery banks so the charger wasn't trying to charge banks being charged by the engines when the genny was running.  Your question about low voltage, the inverter quit ~11.2 VDC which was supposed to leave sufficient charge to start the engine(s).

Most sailboats are setup like you are talking about, but they don't have all the toys a powerboat has.  They do not have full size refrigerators, freezers, dishwashers, washers, dryers, etc.  Most of their refrigerators are DC and the house batteries are different from the starter battery.  Sailboats also only have one diesel engine and if they do have a gen set it is usually a very small one.

My house batteries where 4 6 volt deep cycle wired to an 1800 inverter/chager to run the house while under way.  They also provided the DC power to the fridge.  When plugged to shore power it charged the batteries, I never had a problem with the setup.  While under way I'd run the genset every couple hours to charge the batteries if we had been using electric.  I also had a wind generator mounted on the stern that kept the batteries charged without using the genset.

This may be big enough for your 35.


It really depends on the value you place on it. I certainly think so, but then I'm building our boat to live without charging the batteries for ~40 hours, and yes that's two fridges my kids watching TV all the lights, etc, etc. But none of that comes cheaply.

My suggestion would be to sit down and do the math on the power consumption of your fridge and how long you need it to run for. For example, if it's a 120V home version, say at 5A and you are using an invertor to power it from a 12VDC battery bank, it will draw 50A@12VDC + invertor efficiency loss, let's call it 85% efficient. So your draw from the batteries would be 59Amps (approx). Let's say you typically need it to run for 4 hours, and assume that the fridge is on 50% of the time to keep temperature.That's 118Ah (59A*4hrs*50%). Since you only want to draw your batteries down to 50% (or you will kill them quickly) you will need at least 236Ah battery bank. That sounds a lot like 2 6V golf cart batteries to me (which would be ~ 225Ah bank).

If the fridge is the only thing you want to run, this will work easily - but as you decide to run more and more, you will need more batteries. The other approach would be to buy a new 12VDC fridge that also consumes 5A and a significantly smaller battery. In the same 4 hours, the DC fridge will only use 10Ah (you could run it on the same battery bank above for 45 hours).

There is a massive difference in power consumption of home vs marine refrigerators, even if the marine fridge is 120V.


Excellent information, your boat will draw power like a sailboat.  Are you an old sailboater?

Not a sailboater, but we almost went that way with our first boat. I built our 32' powerboat to live for 30 hours on the hook. We often spend 2 or 3 days in the bays of Georgian Bay and don't want to hear the sound of an engine unless we really need to.

Our 47 will draw a bunch of power, but I'm also loading it down with batteries. :-) It currently has a 32V bank for the house with a 50A 32-12V convertor. This bank is ~250Ah @ 32V (about the same power as a 650Ah 12V bank). This will run the 12V refrigerators, the 32V vacu flushes and the water pump. I am also adding 6x 6V 240Ah batteries to create a new house bank of 720Ah @ 12V - this will run everything else - lighting, 2000W invertor (mostly for the TV, Stereo and coffee). We should be able to survive at least 41 hours on battery without starting the generator, except for using the stove/oven. When that runs out, the charger will put out 100A off the generator, so we'll jump back up to ~85% charge in around 3 hours. The batteries and invertor will be running 4/0 cable, less than 10' long.

Byron Schaeffer said:


Excellent information, your boat will draw power like a sailboat.  Are you an old sailboater?

Love the idea! We can't get away w/o the genny unless underway though. Simply too much heat/humidity around DC. We put drinks in the cooler and 4 big freezer packs in the fridge. That'll easily keep it cold for several hours during the day or even overnight, depending on how many times you open it of course.
Sorry for the delayed response, but I just saw your post. Been awhile since I had a chance to read the forum. It's not expensive to run the diesel generator. If the noise bothers you, that's usually the issue, then it's going to wind up being way simpler and cheaper to get an enclosure or sound blanket for it and call it a day vs. doing what you're talking about. With one of those installed you can barely hear it running. By the time you run two fridges, the ice maker, a tv or a light or two, your power draw on this boat is going to be more than you think. And that still won't get you enough power for a/c or heat.

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