jfalsone wrote:
Sorry to dig up an old thread but this one interested me, especially the comments made by Velera concerning the matching of capacity to intended use. I plan on 1-2 week cruising moving forward, mostly local Chesapeake Bay but also New England in the future. Currently, my house bank are two Group 31 Deka deep cycle batteries with about 200 AH capacity. I just installed a new Dometic Cold Machine and replaced almost all lights with LED. Dometic recommends 300 AH capacity. Don't know what assumptions they made but I am under capacity on paper. Current bank and starting battery are in the usual location under the quarter berth / nav seat. Original WB50 with original alternator. I have a Xantrex Link 10 battery monitor that I am just becoming familiar with. Can anyone with a similar setup and cruising requirement give me some advice? I'd say I'd be on anchor for 2-3 days tops in most cases, then using the engine to go somewhere. Wondering if I should consider a third battery for the house bank. Thanks.
Ok. I agree with the Dometic folks that you probably need about 300 Ah--because you are likely to use about half that in a 24 hour period. I have 440 in my banks of 6v golf cart batteries and it is really too much--my "smart regulator" senses when the batteries are getting close to full charge and cuts back on the alternator output and it takes forever to get a full charge on them. So I have too much capacity for what I use and it is not healthy for my system. I have no starter battery and have never needed one in 27 years of cruising.
In looking at your situation, another consideration is your ice box: the Tartan came with a relatively good ice box, but how you use it can mean a BIG difference in how long it runs and how much battery you use. Here are some tips: seal the covers with some refrigerator door seal and make sure both doors have insulation on the back (some Tartans did and some didi not). Put some drain plugs in the holes in the bottom of the box so that your cold does not run down into the bilge. I was able to cut my running time by about 20% by putting a very small computer fan (wired to the compressor fan power) in the botttom of my box to keep the air circulating so that everything in the bottom did not freeze while stuff at the top was warmer. These things will make 10 times the reduction of energy usage than installing LEDs in a Tartan 37.
You probably do not need to buy a huge new alternator. I am not sure what yours puts out (let us know but 80 amps is probably enough) and you do not tell us whether you have an external regulator. As I said in my original response--it is important, as you are doing--to think of your battery, charging systems vs usage as a system and assess it in its whole rather than looking at one thing. If you were doing only a day or two, I would think what you have is fine. But describing your usage, I think an upgrade is probably in order. You do need to have two banks so that you can isolate a bank if one develops a bad cell. Not common, but devastating if it happens at the wrong time. You do not need a starting battery if you have two banks as I have noted before. Even Nigel agrees with me these days.
Ray Durkee
T37 #373