1-2-both switches used to be popular in Europe
as a cheap
option (i'e' lots of builder
fitted them). They have the drawbacks mentioned above but have also been know to cause fires. When you turn it to both you cause a dead short across the batteries, it is never good for them but if one is charges and the other is flat you dump the load from the charged on. That can mean several hundred amps and the wiring
catches fire. The correct process is to charge each battery
separately always shutting the engine
off before switching (otherwise you can blow the alternator
diodes) and only switch to both when all batteries are fully charged. So are you really always going to do this?
VCR's are a simple solution that works well but carry a spare as they do fail. They are also expensive but potentially save other costs.
Diode blocks are cheap
and reliable. Although they can fail never heard of one overheating
so they seam very safe. The issue of voltage drop puts people off as the alternator
needs to run at higher than 'standard voltage'. For me this seems to be a non-issue because NO machine sensed alternator will effectively recharge a battery
, they are designed to float charge a full one. Also very few basic installations have as little as 0.7v drop in the wiring
. To make an effective system you need a battery sensed 3 step controller which then makes the diode drop insignificant, alternators happily run at 15-16v.
There are now two other options. Batt - batt chargers and true "0" drop distribution blocks which are effectively solid state VCR's. Both of these are expensive and have advantages in emergency
vehicles but I don't see them as useful on a boat.
So my advice would be; If you only occasionally charge from the alternator and are mostly plugged into the dock
look at VCR's as a cost friendly simple option. If you are regularly away from the dock
and using alternator charging
fit a 3 step battery sensed controller and choose from VCR's or diodes. Avoid 1-2-Both switches on anything bigger than a day-sailor.