Dual Battery YJ

L.W. ("ßill") Hughes III did pass the time by typing:

Good ref site:

of pictures and explanations of the different setup methodsand why you would choose one over the other. Sistering batteries (jumping pos-pos, neg-neg) is not a good idea unless the batteries are identical, and even then it's still not a good idea.

My intention with this is to have that little extra boost for starting in cold weather. Where I live it can get down to -40C during the winter and I work 12 hour shifts and many times after a shift I will find that the breaker has tripped on the plug-ins at work.

After a bit more Google groups searching tonight I found an old post here and a simple circuit using an isolator..... this looks like it might be the ticket for what I had in mind. This isn't a necessity really but hell I have a spare battery that is identical to one I have in my Jeep and both have been bought in the last 6 months and to be quite frank I'm looking for a new project to keep me busy. :)

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My interpretation of that isolator article and diagram ... it allows both batteries to charge alright, but one battery is used for say starting, and the other battery is used for other things ... e.g. a winch ... and ... current will not flow through the isolator from one battery to the other to assist with starting. My understanding, you want the two batteries to operate in parallel for extra starting capability. If that's the case, why not just connect both batteries in parallel as others have suggested, and that's that.

OT: and the isolator looks to be solid state probably having a back to back diode setup with a diode drop (say minimum 0.7 V) to each battery effectively reducing the charging voltage at both batterys ... unless you've got remote sensing anon anon anon. Geez ... anyone remember that question on the final ... design a power supply ... using I think it was a 723 regulator?

You just need a knife blade switch to turn the second battery's output into a parallel starter feed when needed for a boost.

Charging two batteries in parallel isn't really good for long term use. One always can take more than the other so one can get cooked dry literally over time.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Bowgus wrote:

With isolators you need to adjust the regulator for higher voltage output to overcome the resistance drop of the isolators..... otherwise you will never get the batteries to full charge and ultimately the batteries can quickly fail. Isolators are pretty old/obsolete technology. Combiners (solenoid 'gang' systems) are a modern day replacement for isolators and have no voltage drop to overcome; you can do the same thing with a set of simple solenoids to control the charging and then monitor with an accurate/calibrated volt meter - much cheaper.

Best is to put both batteries > Ditto, Plus even with isolators they want the batteries to be near

Suggest that you go to the

website and lookup isolators, combiners, equalizing, paralleling, etc.

Isolaters are quite obsolete technology. Running batteries in parallel involves charging, etc. risks (when batteries are not equalized).

also go the

website for the same info as above.

The SIMPLE (cheapest) approach is to put in one BIG MOTHER of a battery (AGM type if you can afford it) Also consider a battery that has more 'deep cycle' capability (heavier plates).

Thanks guys .... It seems this is a lot more involved than I originally thought it might be. I don't want to do a half assed job so I might pass on this and place the battery in a warm place and maybe swap it into my vehicle on occassion to keep it charged.

BTW..... Opinions please>

I just had my 87 YJ painted and I like the plain look (see my page) with no decals or pinstriping on it, the wife says I should jazz it up a bit. What do you folks think?

My page:

Agreed ... but :-) ... in the boating world for example, battery banks of identical (same type, age, manufacturer) batteries are connected and charged in parallel for weight distribution purposes, for increased amp-hours purposes, for hot backup purposes ... so I figure if Jeepster does have two identical batteries kicking around and could use the extra amp-hours, then there would seem to be low risk running them in parallel.

I used to run a fleet of electric powered boats and I used to charge two of them in parallel to save buying more chargers until I started noticing far too many batteries were boiling hard while the one next to it was just bubbling.

All the batteries were bought at the same time, but they weren't all discharged the same so I figured the results were exaggerated but none the less there was a radical difference in the charging rates between these 'identical' batteries. These were deep cell marine batteries too. They are much more forgiving when overcharging or over discharging.

Hey you could be fine doing it that way, but on regular batteries I would figure their life would be lower because of the above.

Or at least use batteries that you can open up to top up with distilled water if one charges faster than the other.

When or if I go dual batteries, I will isolate them and have the knife switch for boosting while running my winch and lights off the secondary battery.

Mike

Bowgus wrote:

Actually :-) ... sealed batteries are the best bet ... that way they can't be messed with and made different by say topping one up and not the other ... okokok ... later buddy :-)