Batteries and the fridge

[Stu Jackson]

This is an old thread that I picked up on last week in reviewing some other issues that have come up on the board about electrical systems and "running the fridge" all the time.  Steve is right, there have been technological changes in the electrical boat system industry since this thread first came up.

Chris, I'm glad you're happy with your system and that it works for you.  It appears that you understand how things work.  It is a great idea to have a battery monitor and should be the first thing folks install – even though many of us (me!!!) have left it for last!  Please, for new folks, learn from our mistakes and install a battery monitor FIRST.

I have previously provided my comments on this board on the dual circuit switch (http://c34.org/bbs/index.php/topic,4623.15.html) and believe it is a completely incorrect way to operate a system because all it does is connect a BAD bank with a good one.  A simple 1-2-B switch would be much better because you can isolate the two banks and also have EITHER bank serve any load you choose.  

Turing a switch shouldn't be that hard an issue to deal with.  What I have never been able to understand is the dual circuit guy's mantra about simplicity of switching.  They say it's easier.  That's just plain nonsense!  The dc switch has three positions:  off on combine.  The 1-2-B switch has four positions: 1, 2, B and off.  Wow, how much more challenging can you get!  And combine should be a position that is never used because combining a bad bank with a good one is just plain wrong for both your batteries and the continuity of operation of your boat.  

What the dc crowd is missing completely is that the 1-2-B arrangement allows for limited house loads to be run from the reserve bank if/when the house bank fails.  This is the maximum flexibility you can get out of your electrical system.  The dc switch does NOT permit this flexibility.

With our 1-2-B switch, I put in on 1 and leave it there (how simple, just like the dc "on" position), using the reserve bank as just that, not a "start" bank.  My Link 2000 tells me the condition of the reserve bank.  Even without a two bank Link, a simple multimeter would suffice to check.  Charge it occasionally and use it sometimes just to be sure, that's all that's needed.  I helped design a system recently where the owner insisted on using the start bank all the time with good reason: starting the engine sometimes wipes out electronics.  But we included a way to crossover, just in case, by being able to use the "start" bank for house loads, limited by the skipper's use of the panel switches. Your boat, your choice.

Your two batteries in the house bank indicate to me that even though it appears that you've done your energy budget, a much larger house bank would allow you to operate your microwave (within reason) without having to depend on a generator.  While you don't mention the size of your two batteries in the house bank, they could be the 4Ds.  If not, your two batteries in your house bank would then most likely be Group 31s and you'd have maybe at the most 130 AH in each battery for a bank of only 260 AH, or 130 usable.  The fridge load is 60 AH plus other loads, for the usual 100 AH daily load, making your house bank only good for one day before needing to recharge.  A larger house bank, even with only one more 130 AH battery, would go a long way to extending your time without recharging.  Alternatively, you could well have selected the generator to provide the hot water, which is a very good thing to have.   The choices are usually between the Honda Eu 1000 and 2000 units, the former doing only battery recharging while the 2000 can heat the hot water.

Of course, Steve's real world application of solar appears to be the least intrusive method of providing power.

The alternator as a source of charging banks is recognized as an inefficient method of charging, especially for the last 15 to 10% of the charge when the battery acceptance kicks in.  You may be interested in this topic on alternators and charging, as well as the Small Engine Mode link within that topic.  http://c34.org/bbs/index.php/topic,5137.0.html

You're right, isn't it great to have a system that works!  Thanks for describing what you have and how it works for you.  

[C Martinson]

Stu:

I have to disagree with your opinion (which is sound when only considering the wiring diagram) on the blue sea switch and ACR....I agree that connecting the starting battery to the run down house bank isn't smart or a good idea.  Even without a generator to charge the batteries (in a normal or run down condition) - should my house bank be run down or dead....I wouldn't want to run the house load off of my starting battery.  It isn't made for that and wouldn't last too long....what I would do is start the engine with my in tact starting battery  (protected by the switch to be isolated from the dead bank) to run the engine and recharge  the house bank from the alternator if I was on a trip without my generator.....just another idea.

To add my 4 cents now - the reason I opted for the generator in lieu of a 3rd house battery was mostly the added weight and the versatility of the generator....while the generator is probably a little heavier it provides more versatility - I have the 2000 for the hot water heater and the microwave for the admiral.  I also used to carry an emergency jump start battery but don't need to now when I have the generator.



Chris

[Stu Jackson]

Chris, I understand.  I have heard that point of view before.  

But I am NOT saying run ALL your house loads off the start (reserve) bank.

What I am saying is it is much better to have the ability to run whatever house loads YOU CHOOSE off your reserve bank.  Turn your fridge off, run your VHF and GPS.

Connecting a dead bank to a good one is nonsense.  Pure and simple.  That's why I so vehemently disagree with the dual circuit switch concept.  It sets people up so completely for when something fails that everything is bound to fail once they flip that switch to combine the two banks.  The small amount of energy left in the reserve bank floods into the dead house bank and you have NOTHING.  Good thing you have a generator.

I am open to anyone explaining why this switch concept has any merits whatsoever.  I've asked before, and am still waiting to hear.

And if your house bank is really really dead, then running the engine ain't gonna bring it back to life.  Even you said it's inefficient to run the alternator to charge batteries.

And running a generator when you're running an engine doesn't make sense to me either.

Having the reserve bank being able to power LIMITED house loads provides a backup, backup, backup.  I have a 60 ah reserve bank that''s always fully charged.  If my house bank completely fries, I still have over 30 ah left to 50% discharge and I'd be willing to drain the entire bank to get home - it's only a car battery for goodness sake - $60.  If I turn my fridge off, it still stays cold for say four or so hours.  My electronics are all battery powered, but using Ron's examples, lets say your full blown electronics array takes from 2 to 5 amps, you still have 30 divided by 5 or six hours of completely powered up sailing.  If at night, judicious use of power could allow you to run your nav lights all night long, and if you have LEDs, then you're fine for a full night.  Not too bad for a situation with a completely dead house bank: the boat can still operate.  The dual circuit switch simply does not permit this operational scenario.

And that's without the engine running.

If your ACR dies, you're out.  If my combiner dies, I switch the 1-2-B switch to B.

But you have your system and it works for you.  I have mine.  And many have something in between. And some we haven't heard of yet!

What we have here on this forum is a way to share ideas and different points of view.  I tend to rant a lot about electrical systems, because I've spent a lot of time with them.  And I share those with reasons and diagrams and explanations.  

I certainly do have my opinions, many of which have proven to have different and, perhaps, better solutions.  I just don't think the dual circuit switch is one of 'em.