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Old Jan 12, 2013, 12:26 PM
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Definitely connect them in parallel. Like lipolys, Pb batteries do not need to be matched with respect to capacity, age, internal resistance, usage history, etc. in order to be successfully used in parallel. Since they're in parallel, by definition they're at the same voltage and overdischarge of the lower capacity battery is impossible without also overdischarging the larger capacity battery.

Connecting two Pb or LiXX batteries of the same nominal voltage simply makes a larger capacity single battery and can be charged and discharged without separating the parallel connection with no issue.

Mark
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Old Jan 12, 2013, 12:34 PM
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Originally Posted by wjs View Post
Parallel will give you capacity of both at 12v. Series will give capacity of one, but at 24v. Unless you really need it, I will stay with 12v. The best way would be to charge both seperately when they need charging. You could overcharge one if you try to charge in parallel. As long as they stay ~close, you should not have too much issue running one down too much as long as both same capicity. Leave input cutoff V a bit higher on lipo charger to account for error and not drain one too much.
I'd much rather parallel connect them for various reasons. What I'll probably do is pick up one new battery and try it with the battery I already have and if it doesn't work out I can always get another identical new battery. I may even wire in a couple of shunts so I can monitor individual amp draws.


Mike
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Old Jan 12, 2013, 02:24 PM
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There is a difference between can and should.


http://www.windsun.com/Batteries/Battery_FAQ.htm#Mini Factoids


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In situations where multiple batteries are connected in series, parallel or series/parallel, replacement batteries should be the same size, type and manufacturer (if possible). Age and usage level should be the same as the companion batteries. Do not put a new battery in a pack which is more than 6 months old or has more than 75 cycles. Either replace with all new or use a good used battery. For long life batteries, such as the Surrette and Crown, you can have up to a one year age difference.
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Old Jan 12, 2013, 02:29 PM
wjs
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Originally Posted by MikeCr View Post
I'd much rather parallel connect them for various reasons. What I'll probably do is pick up one new battery and try it with the battery I already have and if it doesn't work out I can always get another identical new battery. I may even wire in a couple of shunts so I can monitor individual amp draws.
Mike
Cool. Let me know how that works out. I am doing same. I bought this Switching gate, so I can power field charger either from AC or DC and it switches automagically (AC being first selected when available). I did not know you could charge 2 Pb batters in parallel without any issue. If that works, then I just need to add another 12v also and both with charge when connected to AC.

http://www.powerwerx.com/batteries-c...switching.html
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Old Jan 12, 2013, 04:24 PM
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Pb and LiXX in parallel:

http://www.rcgroups.com/forums/showthread.php?t=932319

I have two deep cycles that have different age, size, and cycles and they have been connected in parallel and serviced by a single Battery Tender charger for many many years. Nothing but perfect success so far.

Mark
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Old Jan 12, 2013, 05:13 PM
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Originally Posted by everydayflyer View Post
There is a difference between can and should.


http://www.windsun.com/Batteries/Battery_FAQ.htm#Mini Factoids


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In situations where multiple batteries are connected in series, parallel or series/parallel, replacement batteries should be the same size, type and manufacturer (if possible). Age and usage level should be the same as the companion batteries. Do not put a new battery in a pack which is more than 6 months old or has more than 75 cycles. Either replace with all new or use a good used battery. For long life batteries, such as the Surrette and Crown, you can have up to a one year age difference.
So which is it? This information contradicts what I just read. Do the batteries have to be the same or not?
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Old Jan 12, 2013, 05:25 PM
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If connected in series, it's very wise that batteries be matched. If connected in parallel, it's absolutely not necessary.

The Windsun information simply errs on the side of caution as series vs. parallel connections are not clear to all.

Mark
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Old Jan 12, 2013, 05:55 PM
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THere are variables one such example. In July of 2005 I placed two new 125Ah flooded cell deep cycles in parallel and used them as my field power source. I used them 4 to 7 days a week 9 months of the year. I never discharged them deepr than 50% and most times closer to 20 to 25%. After six years one was dropping fast and was pulling dowth of them down. I disconnected the bad one and the other one lasted another few months. Chances are fairly good that if I had caught the one going bad the good one would have lasted much longer.

The same thing has happened many times with LiPoly cell connected in parallel. IN years past a 3S 2200 was most likely 6 cells of 1100 capacity connected as groups of 2ea. in parallel then connected in series. One cell would go bad and that its matching (paralleled) cell with it.

FYI there are still LIPolys being sold today that infact have 2 or 3 cells paralleled and used as a single cell in 3S or larger LiPolys and yes sometimes one of these cells fail befor the onther ones. As I posted in post #78

There is a difference between can and should.

Charles
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Old Jan 12, 2013, 06:28 PM
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I don't know, all this makes my head hurt. Maybe I should just say to heck with it and buy a generator like I originally planned.


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Old Jan 12, 2013, 06:38 PM
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There is a difference between can and should.
By this same argument folks should not be using or charging lipolys in parallel, yet countless are doing so with zero issue. Perhaps a warning of impending doom should be communicated to these folks as well?
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Old Jan 12, 2013, 11:20 PM
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I don't know, all this makes my head hurt. Maybe I should just say to heck with it and buy a generator like I originally planned.


Mike
I got a Honda EU2000i and never looked back. Not sure why I'm even following this thread.
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Old Jan 13, 2013, 06:15 AM
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I got a Honda EU2000i and never looked back. Not sure why I'm even following this thread.
That's a great little generator. I used one in my previous job for field work. Just wish I could afford one.



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Old Jan 13, 2013, 08:13 AM
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By this same argument folks should not be using or charging lipolys in parallel, yet countless are doing so with zero issue. Perhaps a warning of impending doom should be communicated to these folks as well?
Here is a bit of my simple logic. A 12V Pb is six cells in series , non that I have seen have taps available for cell monitoring / balancing , most these days do not even have removeable caps and even flooded cells ones which do have caps are mostly used by people that do not own a hydrometer.

On the other hand a six cell LIPoly would most likely have balancing leads and be charged on a balancing charger. How many electric flyers connect two six cell LIPoys in parallel and do non balanced charges , fly them and never check indivual cells , leave them connected in parallel for years and hundreds of cycles I have no idea.

I do know that many who use deep cycles in parallel; for trooling motors tend to just charge them and use them until they start to perform poorly. I have seen and read about many such setups which fail in two years or less . Many smart boaters replace their deep cycles every year or two. I feel that most electric flyers would feel that this is to short of a service period.


Charles
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Old Jan 13, 2013, 08:24 AM
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I've gotten 6-7 yrs out of a gell cell but they ain't cheap.
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Old Jan 13, 2013, 08:36 AM
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I have a AGM which is 12 yeras old which still performs it function fine. It is a starting battery for a 7Kw generator.

I have a 50Ah 12V spirial cells AGM which is 8 years old and still delivers just over 1/2 of its' original capacity.

My two 125Ah flooded cells lasted 6 years under heavy useage .

Two 125Ah (250Ah total) flooded cells $125 , one 50Ah sealed AGM $220.

Charles
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