Wiring / Double battery charge

[drsmooth]

Hello

Perhaps someone could offer advice on the following.

We have just purchased a 2007 T@B (June 2007). Been out on short 2-3 day excursions six times. We really enjoy being able to camp without camp site electrical connections if we choose. I have found that a fully charged battery lasts from 1.5 to 2 full days. We have a Norcold 12 volt fridge (no LP option), we run 2 cabin lights about 3 hours each night and the DVD/radio for about 1-2 hrs each night. This pretty well drains the battery.

Has anyone instructions for a novice (me) to wire and charge simultaneously two batteries connected in parallel to double our battery usage to 3-4 days? I take it this should work?? Is there some electrical thing I am not thinking about? I can build a holder to stack two. Also, any thoughts on using a small solar panel to recharge or sustain battery charge.

We are not interested in using a gas generator to accomplish this as it sort of distracts from the quiet footprint that we are trying to leave when we are enjoying the environment.

Thanks in advance for any thoughts you have on this matter. Feel free to email me directly at [email protected]


Cheers from the North,
Scott Seyler

[Micro469]

I notice from you email addy that you are in Canada....Probably Ontario....Whereabouts you from???

[Ken A Hood]

The North eh? Where about's? Im north of TO

As for the batteries, I haven't got a clue, but here's a good link to some info.

http://bart.ccis.com/home/mnemeth/12volt/12volt.htm

[Dale M.]

Basically you have it right already.... If both batteries are fairly new or in same "state" or age, just connect the two in parallel and charge as a single battery.

Batteries will only take as much "charge" as they need (chemically)... So with a "standard" charger over charging is not a issue...It will just probably take twice a long to bring them back to full charge ( float voltage)

If you have any real fears you can put a fuse in one side (positive or negative) between batteries so if one battery goes really bad and tries to draw extreme current from other battery fuse will fail.... Fuse only has to have capacity a little more than maximum current draw of all your DC accessories and fridge combined...

Here is more battery information....

http://www.batteryfaq.org/

You may want to consider LED lighting to reduce current draw (some) and if you want to increase "days of use", consider getting higher amp hour batteries (yes even if you parallel them)...

Solar panels are not generally high out put , but they can boost charge to point you may get a extra day or so before system dropped below usable voltage level...

Dale

[Mike C.]

drsmooth,

I am by no means an expert, but I think that if your batteries are the same type, the same age, same amp-hours and discharge rate, you might be ok. The problem is when you use mismatched batteries, the weaker battery, with maybe a bad cell, would draw more current than the other, think boiling acid and kaboom! Battery isolators, which are used when batteries are hooked in parallel, are basically diodes or a circuit board which keeps the current going in one direction only. Might invest in one if you really want to do this.

JMHO.

[Dale M.]

drsmooth,

I am by no means an expert, but I think that if your batteries are the same type, the same age, same amp-hours and discharge rate, you might be ok. The problem is when you use mismatched batteries, the weaker battery, with maybe a bad cell, would draw more current than the other, think boiling acid and kaboom! Battery isolators, which are used when batteries are hooked in parallel, are basically diodes or a circuit board which keeps the current going in one direction only. Might invest in one if you really want to do this.

JMHO.

Ummm.... Are you going to isolate them during charge cycle or use cycle.... With out some really fancy electronics you can not have it both ways with out some sort of "switching" circuit....

You could also separate the two batteries and use a sort of "A/B" battery selector switch so you only charge/discharge one battery at a time, but if you are not real diligent on battery use, one battery tends to get used (charged/discharged) more ...

I really think straight parallel wiring and with something as simple as fuses you are going to be pretty safe..

Dale

[madjack]

...personally, I would vote for Dale's advice...also...you might want to consider replacing the original battery when you get the new one, since a weaker battery(the old one) will pull the stonger battery down to its weakened state...in other words, for best usage, the batteries should be matched as close as is possible..........
madjack

[drsmooth]

Thank you. I think I will go with the idea posted by Dale. Also thanks for the links. Reading now.

DrSmooth (Scott) resides on Georgian Bay just outside of Owen Sound. Well, back to the wiring.

Cheers!

[Alphacarina]

You can parallel two similar batteries while you are charging them, but you need to separate them when they are being used - Boating supply stores sell battery switches which do this. They are marked "1", "2" and "Both"

Alternatively (and much simpler) is to simply go to a single, larger battery bank and eliminate all the confusion

The 'best bang for the buck' if you're looking for deep cycle wet cell batteries is to buy 2 of the 6 volt Golf Cart batteries and combine them (permanently) in series, so you have 12 volts. They are HEAVY, but the pack way more energy than any other standard size and thay last about twice as long too

A typical Group 24 battery (what you probably have now) is rated at about 75 amp hours. You can buy a slightly larger Group 27 battery and get about 100 amp hours or a Group 30 battery which has about 125 amp hours . . . . or two of the Golf Cart batteries which will give you about 220 amp hours - All of those are from a single 12 volt bank, which requires no switching or piddling with to charge or discharge . . . . The 'K.I.S.S. principle at it's best

In short, a pair of Golf Cart batteries would give you triple the capacity you now have

Don

[Dale M.]

You can parallel two similar batteries while you are charging them, but you need to separate them when they are being used -

Don

Can you quote a source for this information?

Batteries have been coupled parallel for years and the only time you need to separate them is if there is a NEED to have a fully charged battery available ( in standby) if "other" battery is flat ... i.e. to start motor of boat or car or...

No need to separate batteries if the are just supplying voltage to run appliances.. Draining each individual battery is going to give you about same amount of time as with batteries coupled together in parallel...

Dale

[asianflava]

You can parallel two similar batteries while you are charging them, but you need to separate them when they are being used - Boating supply stores sell battery switches which do this. They are marked "1", "2" and "Both"

I'm not shure since I don't own a boat, but I think those switches are to isolate your starting battery from your accessory battery. You can be out running your trolling motor, live well pumps, radio all day. When it comes time to head back you can't start your engine because the battery is too weak to start it. Isolating the start battery will prevent this. Now, if you left it on "both" and the batteries are too weak, then you are SOL.

[Alphacarina]

Batteries have been coupled parallel for years and the only time you need to separate them is if there is a NEED to have a fully charged battery available ( in standby) if "other" battery is flat ... i.e. to start motor of boat or car

Yes, there are many examples of permanently paralleled batteries around, but they don't live as long as they would if they weren't in parallel, nor do they supply as much power coupled together as they would if they were used separately. Diesel trucks sometimes have dual batteries in parallel (to give higher starting current) but they aren't usually powering much load when the truck isn't running

Almost any boat with two large battery banks will have a switch which allows them to be separated during discharge cycles and then combined so they can be charged from a single source - Usually the engine's alertnator. Frequently, neither of the 'house banks' are used to start the engine(s) - A third battery is devoted to that

Even if you take two indentical, brand new batteries and put them in parallel, they are never electrically exactly the same - One battery will always have a slightly different internal resistance than it's 'twin' and the net result is that once you take away the charging source and put them under load, they begin discharging each other with the weaker of the two sucking power from the stronger of the two - Which one is weak and strong may vary back and forth as the specific gravity of the cells changes through the discharge process

The net result is that while you should get say 100 AH from each battery (and you would if you used them separately) when they are combined, you get less than 200 AH and the lifespan of both batteries is significantly less than it would be if they were used separately. The older the two batteries get, the less similar they are (electrically) and the greater the loss and the faster they wear each other out

You're right - You CAN do it and it's frequently done and if you don't mind replacing them more often then there's probably no other significant drawback . . . . but it's still something which should be avoided if you can and the easy way to avoid paralleling batteries is just to use a single battery of sufficient AH capacity

In this instance, use of a pair of 6 volt Golf Cart batteries can give 220 AH of current for 4 or 5 years before they need replacement, while using a pair of 12 volt 100AH batteries in a permanant parallel configuration will be lucky to last 3 years

Don