By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
That’s a great question and it is certainly JAM-session-worthy, so here goes.
The short answer is no, you cannot simply parallel your 12-volt battery with the new 6-volt batteries (in series). You can only parallel batteries that are exactly the same brand and chemistry, including age. Otherwise it will result in unbalanced charging as well as shortened battery life. However, you can do a temporary parallel interconnect as a quickie jumper to start a generator or whatever. But that shouldn’t last more than a minute or two. Or you could do a Batt-1/Batt-2 selector that keeps these two battery banks separated at all times, but lets you switch in one or the other to your RV’s 12-volt system.
Here’s the diagram you sent me, which is actually pretty good except for the second disconnect switch. Note that the Blue Sea battery selector switch you’re showing allows you to connect your RV’s electrical system to Batt-1 or Batt-2, plus a third option of !+2 for both batteries. But as you guessed, you only want to use the Batt-1 position or the Batt-2 position. Leaving it in 1+2 Mode with the 12-volt and 6-volt batteries connected together in parallel for more than a few minutes would likely cause battery life problems since they’ll try to equalize the charges between them. And you really don’t need the second disconnect switch since that function is included in the Blue Sea switch.
However, you won’t be able to charge all three batteries at the same time even if the switch was left in “Both” mode. My suggestion is to only use the Batt-1 or Batt-2 positions and never run the two sets of batteries in parallel (Both), but go ahead and charge them separately by simply selecting one or the other battery selection for a few hours.
Note that I’ve looked around and can’t find a battery selector switch without the parallel (Both) battery function. So if you do use this switch, be careful not to use the 1+2 selection for longer than a few minutes at most. And if anyone reading this knows of a Batt-1/Batt-2 switch that doesn’t have a Both (parallel) selection, please let me know in the comments below.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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