Mixing different volatage batteries

[Padlin]

Have 2 new 6v Interstate batteries, if I have enough room for just 1 more, would this work for 12v? if so, where would you connect the load.

[mlts22]

x2 on battery bank switch. There is getting a job done, and getting a job done right. The battery bank switch is the right way to do it.

Only thing I might add is an inline catastrophic fuse or circuit breaker on the lines so if a dead short does happen, you are out a fuse, not your wiring or your entire rig.

[wolfe10]

http://www.perko.com/catalog/category/battery_switches/

[64thunderbolt]

Sloop Smitten wrote:
Here is how I wired mine with a selectable switch. That way you can run them all at once or isolate as desired.

Looks like something I might try. What kind of switch is that? Bad thing about 6's is if one goes you are out of 12v power all together.

[Sloop_Smitten]

Here is how I wired mine with a selectable switch. That way you can run them all at once or isolate as desired.

[MEXICOWANDERER]

Mess with your jumper cables. It doesn't get any easier than that...

[Padlin]

So it'll work okay, provided it's wired correctly, as smkettner states/shows.

"Optimum" charging configuration sounds like it'd be done as separate banks.

Don't know that I want to mess with the switch so I'll have to think this one over. Maybe wait till after my next trip and see how I make out boondocking with just the 6's.

Appreciate the help.

[2oldman]

Older discussions here:
(Don't worry, 8 year old information is still valid)

Add 12v to 2 6v 2006
12 and 2 6v 2010

[time2roll]

Padlin wrote:


Or this

Connect the load to the left hand 6v+ for better results.

NOTHING should connect to the 6v series jumper between the 6v batteries.

I would actually connect the load to the 6v pair and let the 12v tag along.

[64thunderbolt]

BB_TX wrote:

sch911 wrote:
This way would be better:

Much much better unless you want to destroy your batteries.

Correct

[DrewE]

Padlin wrote:


Or this

This will not work properly. You're only giving the load 6V. It is only very marginally better than your first drawing, which had the batteries shorted out. This one probably wouldn't blow up, or start a fire right away, but it won't work and could well destroy a battery or your converter/charger over time

The 12V battery is, broadly speaking, equivalent to two 6V batteries in series. The 12V battery has six cells in series internally; the 6V batteries each have three cells in series. The main difficulties alluded to by other posters are due to significant differences in cell structure between the two batteries.

Based on the pictures you're posting, I would suggest that you have someone else (with a decent knowledge of things electrical/electronic) check out your actual wiring before you connect things up. It's easy enough to cross yourself up when you're quite clear on what needs to be done, and having only a fuzzy understanding of things doesn't make it any easier.

[MEXICOWANDERER]

Temporarily connected is OK. But for whatever reason the temptation to "leave them connected" becomes quite strong. I would use jumper cables not permenant lugs and cables. The recipe for each class of battery is different, voltage wise.

I remember being lazy 30 years ago and playing Layback Lenny with a mixed bank of gel and calcium/calcium batteries. Swift kick in the butt time. I lost 5 Sonnenschein gel batteries over thar one. Woowee that shivered my timbers.

[BFL13]

Roy, while camping for a few days it doesn't matter if one gets to 89% while the other gets to 91%. It will all get sorted out at home later on, when you do each up to baseline SG separately.

Where this all goes sideways is when the RVer has to park his rig in storage because he is not allowed to park it at home. Now all sorts of "work-arounds" have to be deployed.

[RoyB]

I have never had good luck mixing two 6VDC batteries in series with one 12VDC battery.

I have found it is best to be sure the batteries you're connecting have the same voltage and capacity rating. Otherwise, you may end up with charging problems, and shortened battery life.



I have on occasion connected these two battery groups together using my BLUE SEA 4-position battery switches still maintaining 12VDC but when it comes to charging them I would never combine these two groups. I would charge them as independent groups.

The differences of the two type of batteries would not charge the same when paralleled together with a single charger source...

The same less battery performance is probably screwed up as well when drawing current from the two groups in parallel but that is more livable.

When charging you want both group to get to their 90% or 100% charge state before using them again...

I'm probably splitting hairs here but have been following this procedure for a few years now and getting long battery life...

All of this is only based on observed approximate charge states of each of the batteries.

Roy Ken

[wa8yxm]

B1+ to B2+ as shown
B2- to B3 + (not as shown)
B1- to B3 - (not as shown)

Or you can think of it like this

The 12 volt battery is represented by

-{Battery}+ 12 volts

The Six volters like this

-{Bat}t{ery}+ 12 volts

That is two half batteries in series

The combined
-{Battery}+
{Bat}t{ery} 12 volts