Join Date: Aug 2006
Location: Arlington, VA
Thanked 13 Times in 11 Posts
Rep Power: 12
Halekai is correct: the Balmar DuoCharge or the Xantrex EchoCharge devices are the preferred way to go, because:
1. Their operation is totally automatic; you don't need to switch any switches.
2. They are not combiners and, as he correctly pointed out, it's not a good idea to combine batteries with markedly different charge levels.
3. Instead, they do exactly what denverDon wished: they do nothing UNTIL they sense a charging voltage on the house batteries. Then, they bleed off whatever current is required (up to 30A for the DuoCharge or up to 15A for the EchoCharge) to completely charge the starting battery.
4. Halekai is also correct in that it takes very little AH to start a diesel. If your diesel starts normally, i.e., in a few seconds, only a tiny amount of AH will be withdrawn from the battery. This requires only a very short time @ 30A or 15A....minutes really...to completely recharge the start battery.
5. These devices will not overcharge your start battery. They just sit there doing their own thing, requiring NO maintenance or other intervention on your part.
My EchoCharge has worked flawlessly for four years now (attached to a 675AH house bank and a 100AH start battery...all flooded). I've installed a number of DuoCharge's on customer's boats. All work perfectly, so far as I know.
There is NO WAY you can wire a boat so that you can match these results. NO HUMAN INTERVENTION -- switching this and switching that -- can match this.
And, while battery combiners and islolaters will work, neither is a good idea IMHO when there are better alternatives to not only work but protect and prolong the life of your very expensive batteries.