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Old 08-30-2011, 09:45 PM   #21
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Second, our camper came with about a 400AH battery, so the most economical thing for us would be to get a second one of the same size--is that what you did?
Giant "Gulp" here. How did a 12 million dollar battery get into your camper? I thought only the Cassini probe had that?

You sure that was not 400 CCA?
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Old 08-30-2011, 10:38 PM   #22
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Just a combination of good luck and a bad memory, I'd say... The battery (Interstate brand) says 405 CCA on the label. I find as I near 70 that remembering to distinguish betwixt cold cranking amps and amp hours slips a bit.
If I had a battery that would put out 400 amps I'd get a lot more use out of my inverter! Do they have 400AH batteries in the C130s, BTW?
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Old 08-30-2011, 11:14 PM   #23
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Just a combination of good luck and a bad memory, I'd say... The battery (Interstate brand) says 405 CCA on the label. I find as I near 70 that remembering to distinguish betwixt cold cranking amps and amp hours slips a bit.
If I had a battery that would put out 400 amps I'd get a lot more use out of my inverter! Do they have 400AH batteries in the C130s, BTW?
The really large battery in the C-130 has about 200AH if I remember correctly.

You have an HD24-DP (or dual purpose battery - starting and deep cycle compromise marine battery).
Interstate Batteries

Since it is a dual purpose battery its capacity is stated in Reserve Capacity at 25 amp load - 100 minutes. Not Amp Hours

Typically, DP batteries in the 24 class have Amp Hours in the 40-75 AH range at 20 amps. The discharge graph is not linear and they only posted data at 15 amps (3.2 hours) and 25 amps (1.7 hours). So say for the sake of argument it is 2 hours at 20 amps (to make the math easy). That would make your battery a 40AH battery.

I attached a graph and some articles that explain why marine DP batteries are OK for campers that use shore power 90% of the time and backup brakes. For any kind of boondocking you should really look at 1 or more dedicated deep cycle ONLY batteries with AH in the 150-225 EACH range.

Similar to the interstate SRM-4D (160AH or so) or a pair of matched U2200 6 volt batteries in series (232AH). In series you remember the AH stays the same and the voltage is doubled.

Certainly not worth buying two of. IMHO
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Old 08-30-2011, 11:30 PM   #24
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To answer your other questions:

are your batteries parallel connected, or do you use just one at a time while charging the other?

You should manage 12VDC batteries in a matched "cell" of two 12VDC batteries. They should be connected as ONE battery cell (meaning the camper's + terminal goes to the + of one battery and the negative (ground) wire goes to the negative post on the other battery, The two positive terminals are tied together and the two negatives are tied together.

6 volt DC batteries are in matched series cells of 12 volts.

The reason for this is to equalize the resistance path through the batteries when charging and discharging. Otherwise one battery will become "stronger" than the other and the weaker one will carry all the load using it up faster than the other. You of course won't know which one and will change out your stack early for no reason.

The very top graphic shows a multi cell "stack" of 6 volt batteries.
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Old 08-31-2011, 08:24 AM   #25
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I am once again indebted to you for the information and advice. Whatever expertise I may still possess at my age is certainly not in battery technology! In fact I'm not sure what it IS in, except relaxing and doing crosswords.

I did know mine was a compromise battery; what I hadn't known was how to crosswalk between CCA and AH ratings. And I'd reached the same conclusion you have, that a dual battery system with true deep cycle batteries was beyond my needs, given the cost.

It does seem there might be a marginal benefit, though, to putting a second group 24 compromise battery alongside the original, bumping up my off-grid time somewhat.

I assume that's what D-mo did, though I couldn't see from the photo whether the second battery was wired in or whether he kept it as an isolated reserve (thus my questions). Back in my sailing days many cruising sailors with dual batteries would use an a/b switch to isolate one battery so they could start their Onans at need.

It appears I've hijacked my own thread here, for which I humbly apologize to the moderators... D-mo, if you're still there, tell me more.
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Old 08-31-2011, 08:44 AM   #26
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Okee Dokee

I thought you would enjoy that pic ... anywhoo i have a couple of answers to your questions. The small battery that came with the camper was given away to a friend. I replaced it with two deep cycle group 27 12 volters, purchased at the same time. Both have a reserve of 100 ah a piece, so there is lots of buffer there.
The reason I went with a dual 12 volt system is two fold. 1. for ease of purchase and replacement and 2. if one of the battries happens to tank during along trip .. i would not be left without battery power, which would happen if one of the golf cart 6 volters crashed. I know that its a long shot .. but hey thats just me.. always thinking ahead.
The battries are wired properly in parrallel, and are charged together either by the converter or my solar. The little grey box just holds some fusing that was hanging around that made the job unsightly. If the two batteries where of different age and or size, i would not put them in parrallel, and just switch when one become depleated.
Basically its as simple as that. No switching, no fooling around with chargers, they just sit there and charge up on whatever is thrown at them.
I have no inverter in the trailer as i find that throwing that device into the mix, just complicates things. I carry a separate battery pack inverter system that i use for my CPAP. It is also charged via solar when not on electrical sites. I installed a 12 volt receptical between the stereo and the floor light switch, which teathers in the powerpack for charging when i am recharging the group 27s.

cheers d-mo
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Old 08-31-2011, 12:36 PM   #27
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OK! That takes care of the questions I have for now. I had thought that since the battery is only a few months old I could just get another one like it, but you've made me think that--after going through all the trouble of making a new bracket and wiring it up--I should buy two new ones instead. I'll look at the Group 27 prices this winter. For now, though, we're gearing up to leave Sept. 5th for 18 days in Michigan's Upper Peninsula, where you can't go ten miles without seeing something beautiful. The number of awesome vistas and campgrounds to got with them in the U.P. is amazing. We'll see how we do on power saving. 25 years of motorcycle and tent camping has made us pretty independent of the grid so far.
My inverter, BTW, was an impulse buy. I saw it for $100 on Craigslist. It actually works! Whether I'll have a practical use for it (other than sucking batteries flat in moments) remains to be seen.
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Old 09-03-2011, 09:09 PM   #28
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Ok, the vidoe's up on YouTube. Search for "Screen door and other ideas for a-frame camper".
Watched your video...great ideas. Where did you find the thumb latches that replaced the keyed latches on the outdoor storage doors?
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Old 09-03-2011, 09:35 PM   #29
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We got ours at a local RV dealer with a good parts department. Before finding them there, I had found several places on the Web that have them. I don't have them bookmarked, though, so can't send links. You could google either RV thumb latch or baggage door latch and probably find what you need. Good luck!

Later edit: here's a link, if I can successfully paste it in-- http://www.rvadenver.com/entry_door_hardware_&_acc_.htm. Go quite a ways down the page that comes up.
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Old 09-04-2011, 01:12 PM   #30
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We got ours at a local RV dealer with a good parts department. Before finding them there, I had found several places on the Web that have them. I don't have them bookmarked, though, so can't send links. You could google either RV thumb latch or baggage door latch and probably find what you need. Good luck!

Later edit: here's a link, if I can successfully paste it in-- RV Door Locks, handles and baggage locks. Go quite a ways down the page that comes up.
I am going to order a set of latches, do you remember what size the cylinder is?

Thanks!!!
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