Electrical System upgrade

[Henry Boyd]

Looking for some input on upgrading the electrical system.

The current set-up is single engine with two starting batteries, no genset.

We are on a mooring and spend most time on the hook. I would like to increase battery capacity to support an inverter for small AC loads (coffee maker, microwave etc.). A genset seems out of the question between cost, planned continued ownership, and they way we use the boat.

First my thought is to add one/two AGM batteries for house circuits, and one/two cranking for starting. Since the charger is OEM, my thought is to replace it with an inverter/charger.

So as a starting point is the plan sound, or is there a better way?

I seem to recall a new battery switch and charging relay that handles the charging of multiple battery banks. Has anyone installed, this and what is the experience?

Thanks

Henry

 

[Mr Salt]

I believe that your starting point should be how many amp hours are you going to use both as DC and as 120 voltage. Once you know that you can figure out what size battery capacity you need, but first you have to multiply consumption by 3 because only 1/3 of a battery is really usable. How often do you plan to recharge the batteries? You will need an alternator that will have sufficient capacity to recharge the batteries for the period of time that you run the engines. Sail boaters have this problem all the time. There is a book called Practical Electricity for Sail boaters that will help you with the specific calculations.

Have fun

Mr Salt
2001 540 CPMY
Caterpillar C-12s
Cape May, NJ

 

[Henry Boyd]

Mr. Salt,

You raise an interesting point about alternator charging capacity. Last summer we stayed close to home. In doing so we used the boat more, but ended up doing a lot of low RPM cruising, our mooring requires a 30 minute no wake speed (because of depth restrictions) drive to get to to the ocean. On a lot of weeknights we only took the boat down to the mouth of the river had dinner and came home. On the weekends we basically took off on Friday went about 14 NM anchored for the weekend and brought the boat home on Monday. We used the dinghy to re-supply.

Your comments make me wonder whether my idea that we had insufficient battery capacity is wrong, and in fact we just didn't run the engine enough to charge the existing batteries. The solution being perhaps a larger capacity/ more efficient alternator, or maybe a solar panel to charge the batteries during the week/weekend.

Any ideas on how to test that hypothesis?

Henry

 

[Four Suns]

Ever thought about getting one of the high-tech wind turbines that are on a lot of sailboats? Since you are on a mooring, how do you keep your batteries topped off?

 

[Mr Salt]

Henry;
The only way that it could be figured out is look at all of your electric demands and compute their amperage draw. The task is not that difficult but it is time consuming and is subject to guessing as to how long you run the appliances. Then you would need to know what the output of your alternator is. Automotive type alternators have high oputput at high rpm, so I would expect that if you are doing a lot of idling or slow speed you are not getting a lot of electricity out of yours. The book that I referred to in the first reply is called "Sailboat Electric Simplied", it is written by Don Casey and published by McGraw Hill. Electricity doesn't know the difference between a gas, diesel or sailboat so the principals set forth in the book work for any boat. The book will walk you through what you need to do.

Mr. Salt
2001 540 CPMY
Caterpillar C-12s
Cape May, NJ

 

[Henry Boyd]

Mr. Salt,

I'm not so sure that in our case it is as simple as determining amperage draw. You are correct that is the process to follow. But in our case the possibility exists that we simply did not operate the boat long enough and and high enough RPM to sufficiently charge the batteries over the course of last season. So the issue may not be battery capacity, but charging capacity. The situation is that last year we used the boat the most we ever have in terms of hours aboard. In the past battery capacity was never a problem, but we ran the engine longer, went farther afield, but because of work issues used the boat less in terms of hours aboard.

To answer Gary's question, we have never had a problem with battery charge until last year, so we just used the boat.

I will see if I can locate a copy of the book you mentioned.

If I am correct adding batteries won't solve any problems and will only exacerbate the situation. Gary has suggested a high performance wind generator as an on mooring charging solution. I'm not sure that would work as our mooring is up river and by intent is located in a secure protected area. Our little cove is the storm anchorage for all of the commercial fishermen in the area.

As for moving to a marina and having shore power, that isn't going to happen because the little cove Bella is moored in is located behind our house.

Does anyone have any idea as to the specs on the alternator that came with the 02 496? Or better yet can anyone provide insight in determining a RPM vs time curve for a given alternator capacity that could predict a minimum time period to adequately charge a specific class of battery?

Henry

 

[Sorrento 25]

If you are having problems maintaining your charge now with only DC loads and two batteries you will never stand a chance once you add a large inverter and inverter bank. Even a larger 100+ amp alternator will not help much. My 2000W inverter charger routinely draws up to 100+ amps@12VDC from shorepower for many hours after being out for only two days and one night with some substantial cruising time on plane with the alternator helping out. A generator is the only practical solution in your case.

Turbines and solar panels of sufficient capacity are big $$$ too.

 

[Mr Salt]

Henry
\
I didn't notice it the first time I replied, I see that you boat is now 6/7 years olf. Have you replaced the batteries? Another issue with batteries if they remain in a discharged state for a "long" period the plates will sulfate which renders that area of the plates in operative. Your batteries could simply be getting old because they are not being maintained at the proper charge level.

Concerning the alternator charge rate it should be on the alternator and you should be able to contact the alternator manufacturer or the engine manfacturer and see what they can tell about the output curve..

I think that you conclusion about adding batteries is a reasonable one. If you add batteries you will not sufficiently charge them either, although it will take longer to drain them down.

It sounds like the issue is two fold. First the boat is not plugged in when it is not in use and secondlyly your form of usage does not provide sufficient time to recharge the batteries

Mr Salt
2001 540 CPMY
Caterpillar C-12s
Cape May, NJ

 

[Tail Chaser 661]

I have three battery's.
One for starting, Two for Aux.

If I really drain the Aux battery's.
I may run the engine 1800rpm or more to peg the amp gauge and get a good charge going.