adding to coach battery capacity

[brianokeefe]

Hello All

I have a 1990 Warrior on the 1 ton Toy chassis. I do not have a working generator and even if the old Tecumseh I do have ran (died 8 months ago) I wouldn't want to use it as it's smoke blowing rattletrap compared to new models out there. I also don't want to haul a portable and the fuel for it at that would be on the rack at the rear.
So I'd like to beef up the coach battery capacity. The current battery is less than a year old and rated at 100 ah. I have a 4K W inverter it's hooked to and it will run a piece of med equipment I need for about 6 hours. I'd like 8-10 hrs. I thought of getting a small, sealed AGM battery that I could put inside the coach and connect it to the inverter too so that all 3 components would be wired together and the batteries would charge when driving. The smaller battery that I'v found is 35 AH. There seems to be a question among the people I've asked as to whether the smaller battery would just diminish the overall AH when I operated the coach from batteries only. So I thought that I could just connect the smaller battery to the inverter where the larger battery already is connected and everything would be happy and I'd get longer juice production.
Can anyone give me an answer on this? Many,many thanks

[ron_dittmer]

brianokeefe wrote:
After the advice here and checking with battery stores it's obvious that any 12V set up would be no improvement and probably worse. I will explore the 6V solution and using sealed batteries can have one in the coach. I just need to find a good supplier as they are not available here in my town. My current coach battery is a 10" depth so that's the max I can go.

My 6V batteries are sealed AGMs, purchased from Sam's Club. I selected them because of the difficulty in monitoring fluid levels for my particular situation. My battery compartment originally had a slide-out tray for the lower profile 12Vs. I needed more height for 6Vs so the slide-out tray had to be replaced with a steel plate to gain enough height to get them to fit.

Shown here are the 6V AGMs installed.


Here were my original 12V batteries in the slide out tray. Removing the tray gained around 2" in height which made it work. The tray wouldn't hold two 6V batteries anyway. I would have had to buy a different tray.


AGMs require a higher output from the charger. Fortunately my whole-house RV inverter has a setting for AGM batteries. The instructions in the owners manual had me move a jumper on the side of it. My carry-along charger also has a setting for AGMs.

I understand AGM batteries can be placed on their side. That might help them fit where you need them. AGMs at Sam's Club were twice the price of their lead acid 6V batteries.

[brianokeefe]

After the advice here and checking with battery stores it's obvious that any 12V set up would be no improvement and probably worse. I will explore the 6V solution and using sealed batteries can have one in the coach. I just need to find a good supplier as they are not available here in my town. My current coach battery is a 10" depth so that's the max I can go.

[pianotuna]

Hi LOG,

The 3 12 volt jars need to be wired in a balanced manner.

LOG wrote:
What would be a solution on my coach? I have three 12 volt batteries in parallel. Two 6 volt batteries would be less amp hours than the three 12 volt batteries. And, there is not enough room in the battery compartment for four 6 volt batteries.

[brianokeefe]

Or I could get a 12V 50 AH lithium for $700!!!! Not going to happen.

[ron_dittmer]

brianokeefe wrote:
I can try and find 6V batteries of the size that will fit in my limited compartment space. It just fits the current 12V deep cycle one. I could get 2 larger (dimension) in which one fits into the battery compartment and one I could put in the closet and connect them in parallel. If I did that by connecting both to the inverter, thus they'd only charge or do nothing than run the 12V coach system, if the inverter isn't on. Is that a solution? Sort of loath to replace the inverter because 1) it was expensive and 2) it will run a toaster, coffee maker and even a toaster oven.

Two 12V batteries in parallel, each in a differnet compartment with a gap between them is a very bad scenario. Two 12V batteries must be butted against each other with minimal length cabling between them. Even then it's not ideal as previously explained. You will do so much better separating two 6V batteries hooked up in series.

[brianokeefe]

I can try and find 6V batteries of the size that will fit in my limited compartment space. It just fits the current 12V deep cycle one. I could get 2 larger (dimension) in which one fits into the battery compartment and one I could put in the closet and connect them in parallel. If I did that by connecting both to the inverter, thus they'd only charge or do nothing than run the 12V coach system, if the inverter isn't on. Is that a solution? Sort of loath to replace the inverter because 1) it was expensive and 2) it will run a toaster, coffee maker and even a toaster oven.

[LOG]

What would be a solution on my coach? I have three 12 volt batteries in parallel. Two 6 volt batteries would be less amp hours than the three 12 volt batteries. And, there is not enough room in the battery compartment for four 6 volt batteries.

[Matt_Colie]

Brian,

If you really want your Ppap to run all night, you need to:
Find a machine that is as low a power demand as possible. They are out there.
Replace your current house bank with a pair if GC2s (6V golf cart batteries) in series.
If still needed, install a smaller and more efficient inverter because the parasitic load of the 4kW inverter is going to be higher than a more reasonably sized unit.

Avoid putting lead/acid batteries in parallel. If you must, have a box of baking soda to clean up when they go off.

Matt

[pauldub]

Do you know the power consumption of your medical device. That's the first thing you need to know in order to figure out how much battery capacity is needed to run it for 6 hours.

[Travelin2]

It's just like kids and dogs.....you put a good one in with a bad one and the good one always becomes bad, the bad one never becomes good. Batteries work on the same principal.

[ron_dittmer]

garyemunson wrote:
Adding to Ron's informative post, even when the charger is off, the mischief continues. The stronger battery will attempt to charge the weaker one until it is dragged down to the weaker one's level.The extra discharging cycles will quickly degrade the good battery to equal the older one.

Ah yes!

[garyemunson]

Adding to Ron's informative post, even when the charger is off, the mischief continues. The stronger battery will attempt to charge the weaker one until it is dragged down to the weaker one's level.The extra discharging cycles will quickly degrade the good battery to equal the older one.

[ron_dittmer]

Don is right, don't mix batteries because your efficiency will be greatly diminished.

What I did with my rig might be of interest to you. My rig originally came equipped with a pair of 12V house batteries hooked up in parallel. After going thru two sets of 12V batteries, each set operated inefficiently after year #2, I replaced them with a pair of 6V batteries hooked up in series which operates so much better. I bought mine at Sam's club at an affordable price. Keep in mind that 6V batteries are bigger so your compartment needs to accommodate them.

The trouble with 12V batteries in parallel is that one battery always drains faster than the other which then their combined voltage gets quickly diminished. Then the charger tends to over-charge the good one trying to wake up the weak one. That is why acid boil-overs are common with pairs of 12V batteries. The problem perpetuates when the weak battery won't take a full charge. Then everything goes into self-destruct mode with the charger constantly trying to charge up what can't be done.

Two 6V batteries in series is wired like everything else that works on battery power, from flashlights to most every hand-held electronic device. Batteries in series drain in unison which utilizes their stored power much better. And in the case with 6V lead acid batteries in series, you get a much better recovery charge because they charge in unison.

[pianotuna]

It won't diminish capacity but it would be far better to get two new batteries that are identical, than to mix a smaller newer battery with a much older one.