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ext222 03-05-2011 05:45 PM

Electrical requirements
Electrical requirements

I realize that there have been many threads and articles about this subject, and have tried to familiarize myself with all of them before asking for advice so that I can ask well formed questions. I ask your forgiveness in advance if I have completely misunderstood something. Also, since each part of the system is interdependent on the others, I apologize if I seem to skip back and forth from battery bank size to alternators to solar, etc. It makes sense in my mind. :)

In October of this year, 5 of us, two adult couples and a three year old boy, plan to set out in a Beneteau 50. We plan to cruise the Caribbean, living aboard and attempting to be as energy independent as possible. As a stock former charter boat, the Beneteau 50 is configured:

Hitatchi 80a alternator
6-55 amp batteries in the house bank
1-55 amp starting battery
Engine driven refrigeration, no DC or AC refrigeration
No Genset
Standard lighting, no LEDs.
Basic instruments + GPS.
No radar.
Hot water heated by the engine.
No microwave

We intend to add several fans, switch the salon lighting and anchor lights to LED, and add a watermaker and if possible(I know, shame on us) a microwave and a RV/Marine washer/dryer. Our logic on the watermaker is that with 5 of us including a little boy (Do you KNOW how dirty little boys are?) on board, we will use a fair amount of water and would prefer not to have to put in to marinas and buy it. Additionally, the adults are all scuba divers and we want to be comfortable using our fresh water to rinse our gear after diving. The logic on the washing machine is that the wife wants it, which was good enough for me until I started doing the math. Seriously, the ability to wash a few clothes on board might allow us to carry less clothing (and did I mention how dirty little boys are?). Obviously we would need an inverter to add these AC appliances.

All that brings me to my first questions.

My math on the watermaker is 17amps/hour DC to produce 6 gallons of water means that 24 gallons of water would require 68ah to produce. (accepting that there is then some loss to backflush the system.) Am I missing anything on that? That seems reasonable to me for the convenience it provides.

The washing machine (Westland WD2100XC) draws 1300watts/120V at peak, and a cycle last 73 minutes. That seems to indicate that from an inverter I should expect it to use 1300/12=108a/h, or 131ah per cycle, plus maybe 15 percent loss from the inverter, so about 151ah/cycle. That seems to be more than is practical, even with a large house bank. Thoughts?

Without the washing machine, I still come to a daily consumption of about 260ah with 8 hours of daylight sailing or 200ah at anchor all day.

With no DC refrigeration, we assume we will need to run the diesel an hour in the morning and an hour at night to get the cold plates nice and frosty. With no other way to heat water, that will also give us hot water for showering, etc. As much as the engine driven refrigeration lugs down the engine, I am assuming it provides enough load for the diesel to keep from running into glazing issues.

Clearly we will have to enlarge that battery bank and supplement our power needs with solar/wind. How much solar and wind power we will need to get in balance will depend greatly on how much of the charge we can expect to use from the daily diesel run.

Conventional wisdom seems to call for a battery bank of 3 to 4 times the expected daily usage. If we went with a 800amp house bank, using wet cell batteries, can I truly expect the bank to accept close to 80amps from my 80amp alternator for each of the two hours a day I plan to run it, assuming with the proper regulator? Going with the "25 percent of the battery bank for wets" figure, as I understand it, a 800 amp bank will accept 200amps during the initial charging phase, so my only issues are how many amps the alternator produces at the 1500 rpm I need to run the refrigeration and the energy production loss as it heats up, and then topping off. Does that indicate I could get a high output alternator to take advantage of the larger size of the battery bank, and then just use solar or wind for topping off?

Is it possible to have too large of a battery bank?

Thanks in advance for your thoughts.

Faster 03-05-2011 06:25 PM

There are true experts here that will hopefully weigh in on most of your questions..

But I seriously doubt that running your engine/fridge for one hour per day will cut it in the tropics. I think having an engine-dependant fridge would be the first thing I'd change.. also 330 AH is not a large bank, esp given your intention to run a washing machine via an inverter. Don't forget you really only have access to about half of that before recharging is advised.

ext222 03-05-2011 06:33 PM


Sorry if that wasn't clear. The 330 amp bank is just what is in the boat that will need replacement. I was wondering if upgrading to an 800 amp bank was sufficient.

The plan was to run the engine driven fridge an hour in the morning and an hour in the evening. Do you think that is still insufficient? That has been fine for a week at time in the past with a Seafrost system, but we didn't have anything in there that needed to last over a week, either.

btrayfors 03-05-2011 08:22 PM

Running the engine two hours per day to make hot water, cool the frig, and charge the house batteries might do it, with just a bit of supplement from, e.g., solar panels. It would be nice if the alternator were larger, but it isn' is what it is! Assume there's an external regulator....if not, you're not likely to get anywhere near 80A out of the alternator for 2 hours per day.

Before you get too fancy, I'd install the larger house battery bank (yes, 800AH should be sufficient) and give it a go for awhile. A good battery monitor, like the Victron, would be helpful to provide good data on your power usage.

Look at ways to reduce your power consumption, e.g., replacing incandescent lights with LEDs.

Re: solar, you might think about two 135-watt solar panels, run in series (to give 34VDC) and a good MPPT controller. In the Caribbean, this would provide a lot of charging current throughout the day, and is virtually maintenance-free. Wind generators require maintenance, can be noisy, and can be a PITA, IMHO.

On a Bendy-toy 50, you guys should have a ball!


mitiempo 03-06-2011 12:20 AM

6-55 ah batteries in the house bank currently? Those are small batteries commonly seen on scooters. A group 24 battery is usually around 75 ah and they are pretty small. But they will be changed as you state.

The washer is the big hit. I think your numbers are a bit low. I would figure on a factor of 10 for the inverter - in other words 1000 watts takes about 100 amps @ 12 volts. That translates to about 162 ah per load.

1 hour twice a day with your existing alternator is 160 AH - almost enough for a load of clothes. If the alt outputs 14 volts plus you probably don't need a separate regulator. The battery bank will accept whatever it can put out up to about 80% soc. At 2 hours a day you won't get to 80% charge with the engine alone.

How many watts of solar panels are you planning for?

I think unless the solar can supply a great deal of the AH you need you will be running the engine more than 2 hours a day.

Now without the washer.....

It sounds like a great trip though.

Minnewaska 03-06-2011 05:29 AM

With all those toys, you really need a genset, even a small one just to run the W/D. I would think the Bene50 has a locker for it. Much more fuel efficient than running the diesel. I also agree that 12v refrigeration is a very good idea. Why burn 2 hrs of fuel every day if you are at anchor and you have wind/solar? On a long cruise, you will find yourself wanting max fuel when offshore, for emergencies and not wanting to waste it just to chill the fridge.

Here is some W/D advice. They don't hold much. If you really stuff them full, they won't wash something that is very dirty either. They are great for getting salt and sweat soaked clothing clean again. I have an unvented Spectra and it uses a huge amount of water and power to dry (yes, it uses water to dry, I can explain if anyone likes). I would plan to only wash and hang dry. I wouldn't even burn fuel from the genset to bother. Therefore, my final advice, try to buy quick drying clothes. Cotton is out.

Omatako 03-06-2011 11:36 PM

Yep, I'm not an afficionado but from my own alternators, I have an 80amp on the Yanmar, internally regulated, I know that once it is running hot it doesn't put out 80amps, more like 65.

So if you're consuming 260a/hrs in 24 hours, you're looking more lik 4 hours a day charging and that's a problem.

While I agree with the sentiments expressed about the desirability of a genset (I'm busy building one for my boat), I think the solution for you in addition to the battery upgrade is a better alternator. Something like a Leece Neville 180amp unit (my second alt is one of those).

Just as an aside, why do you believe you'll use more power daylight sailing than on anchor? I would have pitched it the other way around. One generally uses more energy when you're parked off.

Ilenart 03-07-2011 06:30 AM

I would also look at your engine manual and see what it saids about running the engine at low RPM's. I just installed a new Yanmar and the manual is very specific about not running the engine at low RPM's, otherwise you reduce the life of the engine.

On my 45ft ketch I use to own I brought a 2kw petrol generator that ran for about 10 hours on a single tank of juice. Very quiet and was happy to run for a couple of hours a day no problem.


haffiman37 03-07-2011 08:56 AM

I would have added a gen set or at least a Honda 2KW (2000) to run when using washing machine etc.
No batteries likes running 1/2 charged, gel or non-gel and you will probably never manage to get a 800 bank fully loaded without replacing the bimini top with solar panels!
As for watermaker in the Caribbean, I would not recommend unless you load up with spare filters, the water may not be as 'clean' as it looks! You may buy a lot of water for the cost of both buying and running it.
Your 80 Amp generator will probably not give much more than 50 effective charge.
I managed with 3 x 70 (lead-acid) in the house bank from Norway to Malaysia, 14 months accross Atlantic and Pacific. Ran the engine 3 hrs a day at 1000rpm, std generator.
That powered electric fridge (box), autopilot, instruments and whatever lights, pumps needed. Had a Honda 10IE as 'back-up that I hardly used.
2 adults and my 4 year old son. Used the water tanks for 'general consumption', bought all drinking water.
It is better to learn to live within the limits than trying to expand the limits beyond reason!

ext222 03-07-2011 11:14 AM

All good thoughts. Please don't think that by not responding to your questions, I am dismissing them. Rather I am going back and rethinking and working through each suggestion, learning as I go. Often, when I think I have an well formed response, I find on final reading that I failed to understand something, and I go back and try to educate myself more.

I tend to spreadsheet everything so that I can easily see how different variables affect totals. As I consider each of the suggestions and try to work out the numbers on each of them, I of course develop additional questions. Any additional help is appreciated as I try to formulate answers and better questions.

First, as several people have suggested a genset, I am confounded when I try to find a way to use all of the available energy from the generator to charge the batteries. It seems that a 5KW generator should be able to power a 417 amp charger (I recognize that is ridiculously large, just showing the math), but the largest charger I find is 150 amps. I realize that the rate at which the batteries accept charge is a limiting factor as well, but is there any way to more fully utilize the power being generated by the generator so as to run it as little as possible? As I look at my growing spreadsheet, the disparity between the 5000W produced per third of a gallon of diesel used by the genset and the 150a actually making it into my batteries just really stands out as an inefficiency as I compare options.

Second, can anyone advise current Gasoline and Diesel prices in the Caribbean?

Finally, does anyone have specific knowledge of a H/O alternator that is a direct replacement for the stock alternator on a Yanmar 4JH3-HTE? I have as yet been unable to confirm that anything larger than a 110 amp is a direct bolt-on and doesn't require double pulleys or the like.

Thanks again for the continued responses. My thinking has come a long way in the last few days.

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