Battery Charging with 6 volt batteries

[thebigitalian]

We have a new travel trailer that came with two 6 volt batteries instead of 12 volt.  What is the proper way to hook up the battery charger to the 6 volt batteries which are wired in serial?

Thanks for your help.

Cris and Catherine

 

[Steve CDN]

When batteries are wired in series, battery #1 negative is connected to positive of battery #2.  Therefore if you place a volt meter on positive of battery #1 and negative of battery #2 the voltage is 12VDC.  Your 12 volt charger would be conncted to positive of battery #1 and negative of battery #2, the same poles where your reading would be 12VDC.

Series connection adds the voltage of each battery to the other.

 

[Karl]

Steve and Cris,
Let me clarify a little bit if I may: You won't find one battery marked #1 and the other #2. What you will find is two batteries connected by a large jumper cable; one of them will have it's plus (+) terminal going to the minus (-) terminal of the other battery. You can ignore this cable and the two battery posts this cable is connected to. However, each of the batteries will have another terminal and a cable attached to it. These are the terminals you want to connect your battery charger to; plus (+) from the charger to plus (+) on the battery, and negative (-) on the charger to negative (-) one the other battery. Even if you could find a 6-Volt charger these days, resist the temptation to charge each one individually. Batteries charged in series (as they are in connected in your coach) will only charge to the capacity of the weakest battery, thus ovoiding an imbalance between them. If you have 'flooded cell' batteries, i.e. those that have removeable caps, charge them as per above and then check and record the specific gravity of each cell in each battery with a hydrometer (available at Fleet Farm, Home Depot, Wal-Mart, etc.). These readings should be very close to each other. If not (one cell in the battery is quite different from the others), It's time to replace it. You may also want to have a service station do a 'high amperage load test' to determine the batterys' health. I believe this is the only way you can test AGM or sealed batteries, but someone else may have comments on that. Hope this helps.

 

[Lou Schneider]

When you connect two 6 volt batteries in series to get 12 volts, you've made a single 12 volt battery out of them.? ?Treat the pair as if they were a single 12 volt battery.

If you want to use an external charger, connect it's leads to the posts where the trailer wires connect.? Ignore the posts that simply connect one battery to the other.

 

[Steve CDN]

Lou,

Your explanation is the clearest and most concise way to describe series connections of batteries I have heard.  Thanks for posting that!

 

[Ron]

When you connect two 6 volt batteries in series to get 12 volts, you've made a single 12 volt battery out of them.? ?Treat the pair as if they were a single 12 volt battery.
If you want to use an external charger, connect it's leads to the posts where the trailer wires connect.? Ignore the posts that simply connect one battery to the other.

Excellent discription Lou.  Very clear and understandable.

 

[Karl]

Steve,

Geez, what did you expect? I did a stint as a tech writer and we got paid by the word ;D

 

[Steve CDN]

Karl,

We appreciate having your expertise available to our Forum members.  Thanks

 

[knightrider163]

what if you have 4 - 6 volt batt making 2 12 volt batt how would you charge them i have the in 6-6 =12  6-6 =12  12-12 =12

 

[Lou Schneider]

Welcome to the RV Forum!

You have two pairs of 6 volt batteries, like I said above (13 years ago!) each pair makes a single 12 volt battery.  So you have two 12 volt batteries in parallel.

All of your batteries should be the same make and age for the best results.  Old and new batteries don't play well togther.

Stagger connect each pair so you have so you have the (+) wires from the charger and load on one set of batteries and the (-) wires on the other set.  This equalizes the wire lengths and number of connections so the two sets will charge and discharge equally.

If you connect both (+) and (-) to the same battery pair, then jumper over to the other pair, the first pair will charge and discharge more deeply than the other, i.e. it will do the majority of the work and wear out sooner.

Here's a quick sketch that shows how to connect the batteries:

 

[John From Detroit]

IT does not matter if you have a single 12 volt battery
Two six volts in series making one 12 volt battery
Two 12 volt in parallel making one big 12 volt
oer 4 six volt wired in two pairs making 12 volt the pairs in parallel making `12 volt
Or a collection of 12 volt batteries of different types (some six volt pairs some 12 volt)

You have ONE 12 Volt battery,, You charge all the above the exact same way.

The only difference is how FAST you can charge them.

Xantrex suggests, WIth most battery types (LIFELINE AGM and GEL batteries are the exception in the world of lead acid) a maximum charge rate no more than 30% of the C/20 amp hour rating..

Lifeline that's the minimum,, Gel it's 20 or 25% (Forget wich)

Since you don't have those. Don't worry about it.

But you charge them just as you would a single 12 volt. only either more amps or more hours.

2 pair at 220 amp hours is 440 amp hours, times 0.3 is `112 amps max charge rate.

NOTE: Slower charge rates tend to make 'em last longer (Overall life) up to a point.. I went from 220 amp hours to over 500 by adding more batteries.. I went from watering new batteries every mother's day to just shy (like a month) of 4 years before they needed water.. Original lasted 9 years, I expect these to hit 10 no problem.  You see I did NOT upgrade the converter.

 

[knightrider163]

) thank you guys for clearing this up for me