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Old 10-23-2008, 02:03 PM   #15
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Decades ago I was told by several people that one way to even out the charge being fed to each battery in a parallel bank was to connect the positive and negative cables to opposite ends of the bank - so if the positive cable is connected to the positive terminal of battery #1 then the negative cable should go to the negative terminal of battery #3. I have to idea if this is actually valid or not...
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Old 10-23-2008, 05:10 PM   #16
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by SargeW:
All the batteries are connected with 00 gauge welding cable. I checked all 3 batteries (same brand, bought at the same time) with a cheap hydrometer. At least 2 of the cells in one of the batteries are weak. No dead ones yet........ </div></BLOCKQUOTE>Yeah, but that's all it will take to screw up the balance. They have to be a matched set throughout their entire life or you're going to have issues with some over charging, and others never reaching full charge.

Alan: I have heard the same thing, and would agree IF you are pulling or charging at a monstrous rate in either direction. I'll have to go look at a sheet I kept of cable size vs. current vs. length, but I'll bet a Taco that you could pull at least 500A through that short #00 jumper before seeing a significant drop, and most of that will probably be at the lug crimp.

I have also seen some interesting criss-cross cabling of 6V banks (3 if I remember) that, in normal situations is complete overkill. But in this case the guy can, and does run his A/C off the battery bank. THAT'S a load!

(Later that same night) I just looked at the wire calculator on the mentioned page. A 500A draw through 12" of #00 has a .08V drop. I could live with that..
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Old 10-26-2008, 04:20 PM   #17
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Well, I made it through four days of dry camping with the existing batteries. I would usually run the generator 2 hours in the morning and two hours at night just before the quiet hours. I noted that the batteries would take a big initial load, 14+ volts, then the charger would step it down. It is a 3 stage charger. My biggest concern was that after an initial charge, the panel would show 13.2 volts right after shutting down the generator.

When I left it sit with little parasitic draw, the charge would show 12.7 or so with no significant draw being put on them. I switched the refridgerator to LP, and unplugged as many of the smaller loads as I could. A couple of nights we watched a few hours of TV via Direct satelite, or one night a 2 hour DVD movie.

That would bring the batterys down to about 12.2 or 12.3 volts. They would generally hover there over night (pretty cold nights btw, 30 to 40 degrees). I wouldn't run the heater at night, and just piled on the blankets. In the mornings I would run the LP heater on battery until generator hours started at 0800.

I was pretty conservative on the batteries most of the time, just using a few reading lights or such. So now I think that the batteries are weak (at least a few of the cells) but not fatal yet. What is your impression guys?
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Old 10-26-2008, 09:43 PM   #18
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SargeW,

Your batteries registering 13.2V when charging is secured is a normal, also the voltage decreasing to 12.7V under no load is expected, it takes a little time for the battery bank voltage to bleed off the charging voltage. 12.7V is what you should read on a battery that is 100% charged with no load. The 12.2V - 12.3V reading indicates your batteries are 50% to 75% charged. With as little load you had on them I would say that those couple of weak cells you discovered are probably affecting the overall capacity/performance of your battery bank. You probably have some self discharging going on because the other cells are trying to charge those weaker cells. Under normal circumstances you should be able to run your normal hotel loads (water, lights, TV, refer and etc.), including a furnace set around 60 degrees, overnite and have your battery voltage read around 12.2V in the morning. I do it all the time with 4 six volt batteries.

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Old 10-27-2008, 05:20 AM   #19
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That is where I would like to be. Unfortunately mine are dropping quick to the 12.2 - 12.3 range with a minor load. I am looking in 6V replacements, but am running into a space issue. Still working on that one.
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Old 10-27-2008, 12:53 PM   #20
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Smartgauge has some good explanations on this topic - see Interconnecting multiple batteries.
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Old 10-28-2008, 05:58 PM   #21
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I remember seeing a similar write-up when I was at GTE a lifetime ago, but they really have hard loads on their batteries. I looked at hard charge cycles awhile back when swapping in the 6v DC'c and didn't see anywhere close to the variances described here (but I also wired it as example #2). I also kept the tray out long enough to see if one was hotter than the other and never noticed any significant differences. But it also seems that since the battery temp sensor (at least on mine from the factory) is bolted to the rear battery, that the charger would taper off per temp readings from the rear battery, and that seems to be the one people are having trouble with.

PS- What's a 35mm AWG equivalent?
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Old 10-28-2008, 10:21 PM   #22
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">What's a 35mm AWG equivalent? </div></BLOCKQUOTE>

2 AWG
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Old 10-29-2008, 07:24 AM   #23
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Now see, that explanation makes a lot of sense to me. I don't think I would need to go to the example given in the number 3 diagram, but it makes good sense to me to employ the second method.

But one big question, in our setup the battery bank has a set of cables extending off of each end of the bank. I presume that one end is the charger input, and the other is the output to the coach. Would that have to change in some way to acomplish the second senario of battery balancing??

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Old 11-03-2008, 07:03 AM   #24
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I've been following this thread and reviewing the recommended battery connection url. This weekend I opened my battery compartment (3 12v deep cycle marine) and found that there appears to be some merit to this 'balancing' arrangement.

I found the battery closest to the engine to be connected to the load on both the + and - terminals. It was also heavily 'corroded' on the + cable connection. The other batteries, connected in parallel, looked fine.

I cleaned all the batteries, checked water level (didn't need to add any), reinstalled them (put the previously corroded battery in the middle) then hooked up according to the diagram. The + cable from the coach went to the first + terminal...the negative from the coach went to the last - terminal. For the inverter/charger connections, I reversed the positions. The + cable went to the last battery and the - cable went to the first battery.

Turned on the battery switch and no explosion. Turned on AC from the power pedastal and no explosion. Charger operated correctly and batteries did not boil or fume.

So now we monitor and check. But it all seems to make sense.

I used the cable connections as an indication of where they came from. I could see the + cable for the coach disappear under the frame. The - cable for the coach I could see connect directly to the chassis frame. The + cable for the inverter/charger I followed through a floor opening up to the I/C. Same for the - cable.

Hope this works. One of my chief complaints about all this battery power was a lack of battery power. My battery bank would not last more than 5 or 6 hours just running lights and exhaust fans.

I also purchased a battery minder desulphator. I've been using this for awhile. Hopefully this will work better.

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Old 11-03-2008, 09:57 AM   #25
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That great Jim! I haven't switched my cable set up yet because I still want to change out my 12V with 6V batteries. I am just having some issues figuring it out because my tray is a about 2" shorter than some of the other posters.

That and I have a bro-in-law that works for Napa. Their battery supplier is Excide. He can get me quite a good deal on the Excides, good enough for me to give them a try. I just have to decide which ones to go with.

Keep us up to date on how your new hook up works out. When I checked my batteries with a hydrometer I found at least one weak cell in each battery. One had 3 weak cells. Weak was one ball of the hydrometer sinking to the bottom of the tube.

I took one of the weaker batteries to an auto parts store and they put a load tester on it. Their reply was Since the needle stayed in the green part of the scale the battery was still good. Yet I was having the same results as you.

I think a change is in my future.....

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Old 11-03-2008, 10:50 AM   #26
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Another idea I'm toying with Marty, is the use of 1 battery vice 2 or more. My tray is big enough for a 4D or 8D 12v battery. However, the cost might be prohibitive.

Second idea is just going with 2 6v. Even though there is room for 3 12v, 2 6v would handle my electrical needs if they stay healthier longer than the 3 12v. I think the durabilty of the 6v plays into the longevity of the electrical bank.

So my thinking is: my 3 115amp-hour batteries (345 total) are not as durable as 2 6v 260 amp-hour (which stay at 260 total). I think the 6v can handle the load shedding better, longer, and take recharging better due to their better construction. (note: amp-hours is the 20hour rate)

So if this doesn't work well, then I'm contemplating a 'change' as well.
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Old 11-03-2008, 02:29 PM   #27
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That was my thinking too Jim. Two beefy 6V as opposed to the 3 12V which I have now. I had 2 6V in the 5ver that I had before I bought the MH. They were bullet proof, and I could drain them hard while boondocking and hit them with the generator for a few hours and they were ready for another night. If I cant figure out how to get 4 6V in the tray, I would go with 2 6V. Much tougher batteries.
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Old 11-03-2008, 07:17 PM   #28
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You can get 12v deep cycles that are as durable as 6v golf cart batteries, but they are pricey. Trojan makes top quality 12v deep cycles, but the sales volume is low (mostly large boats) and dealers have no incentive to discount them. The Trojan SCS200 is a Group 27, 12v deep cycle with a 115 AH rating. he SCS150 is a Group 24 rated for 100 AH. There are also AGM versions available (I use 4 Trojan Group 31 AGMs @ 110 AH each).

But the 6v golf cart deep cycles deliver the most amps for the dollar if you can find them at a discount.
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