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Listening to the Voices on the Wind

posted Jun 27, 2011, 5:12 AM by Christopher Hubbell
I encountered an interesting thread this morning on SailboatOwners.com which illustrates a point I've experienced many times.  If you go an Internet forum to ask a question, and you have no background on the topic, be prepared to sort through a spectrum of authoritatve answers.

The thread I'm referring to asks the following question:

10, 20, OR 30 Amp Charger? What Do You Recommend?
According to the customer serviice guy at Xantrex it appears the TrueCharge 10A Multi Stage charger I have on board has a broken fan and needs to be replaced. Whenever it's turned on it gets so hot I can't place my hand on it. When speaking to him I explained that I mostly use my boat for day sails once a week and while in the slip I leave the battery charger on until I return a week later. My house bank is now 440 AH powered by four golf cart batteries wired in series. When I am away from the slip I almost always stay on the hook for whatever period of time I'm away. He told me that replacing the 10A charger with another 10A charger was not a problem. Based on the time I leave the boat in the slip between sails the 10A charger would recharge my batteries just at a slower rate than the higher rated chargers. According to what I understood him to say the only advantage of the higher rated chargers was they would charge my bank at a faster rate. If I had the time the 10A charger would be fine for my use.

If I need to go to a bigger charger I will but from what the customer service guy told me why not just stay with the smaller less expensive model? There's a lot of people on this forum that know a lot more about batteries and chargers than me so I'm looking for and suggestions or comments.



Answers were all over the place, and all stated in a manner I would consider authoritative.  In fact, this really comes down to understanding electronics and batteries, and the answer is a pretty simple one.  If the Patron Saint of Internet sailing had not chipped in, this poor soul would have been convinced that he needed a 40A charger.  Fortunately, MaineSail responded with his usual clear advice.

"A good quality 10A charger should have zero issues charging a 450Ah bank dockside..
"

That's not to say that a larger charger is a bad idea.  As stated in the thread, some bigger ones have equalization features, or other features which make them more desirable.  However, those features are outside of the laws of physics which cover lead acid batteries and charge acceptance rates. (OK, an equalized battery does make a difference...).

I have a 10A ProMariner charger aboard Ravat which was installed yesterday.  When I bought it on eBay, the price couldn't be beat.  It will easily charge my banks in the usual overnight it's allotted and it cost 1/3 what a new 20-40A charger would have.

The point of this article is that you really need to learn a lot of things about a wide variety of topics to understand your boat and truly design its systems in a way that you can understand and troubleshoot them.  You may not care about anything but sailing, and that's fine in itself.  But remember that over the life of your boat you will have many choices to make.  If you depend on other's advice at each decision and never learn the foundations you are doing little more than rolling the dice.

Seven days to launch target, and I'm beginning to feel quite a bit of stress...  Much to do yet.


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