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Old 08-21-2016, 08:04 AM   #11
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Great! I plan on purchasing two more 6 V batteries for my eventual solar array. Since my Trojan T105 batteries are brand-new, can I wait to purchase two more or should I get them right away to make sure that all four are compatible?

I want to thank all of you who responded for your thoughtful and insightful responses to my questions.


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Old 08-21-2016, 08:33 AM   #12
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Originally Posted by boondocking View Post
There is an urban myth about WFCO converters not going into Bulk mode (14.4v) and not going out of Absorb mode (13.6v). I think this is what those presenters must believe, so they shouldn't be lecturing about RV converters.
Trojan specs call for Bulk at 14.8v, Absorb at 13.6v and Float at 13.2v. Standard RV converters (WFCO, Progessive Dynamics) etc have a Bulk mode of 14.4v, Absorb mode of 13.6v and Float of 13.2v which will not hurt 2 Trojan 6v batteries in series.
You do have a three stage converter with the above specs.
Unfortunately, the urban myth has some facts behind it. Quantifying the problem isn't going to happen to really know.

It took me some dedicated testing of my batteries and RV to determine that the installed WFCO (2014 8735P) was never going to drop to trickle mode at 13.2V. My particular WFCO simply did not meet its own spec.

As for going into bulk mode, WFCO restricts bulk mode to a battery sensed at below 12V. I could never verify that my installed WFCO would ever go into bulk mode - the 40 amp fuse popped when I actually had low batteries.

The reality is that there is a steady stream of complaints similar to mine (WFCO converters don't meet their own specs). Given the huge installed base of WFCO converters, I don't know if the failure rate is abnormal or not.

I do know that those who replace the WFCO converter with a Progressive Dynamics converter are much happier with their new converter. I have verified that my PD replacement goes into boost, absorb, and trickle modes when appropriate - according to PD specs.

As for the OP's question, any 3 stage converter meeting its specs will charge any size battery bank. How fast is the only difference. In the end, a battery cannot be charged faster than 20% of its capacity per hour, and that's only if it was quite low to begin with. Fully charging a 50% charged battery at maximum rates takes at least 5 hours no matter how big the charger.

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Old 08-21-2016, 08:45 AM   #13
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Originally Posted by Jim Coolyard View Post
Great! I plan on purchasing two more 6 V batteries for my eventual solar array. Since my Trojan T105 batteries are brand-new, can I wait to purchase two more or should I get them right away to make sure that all four are compatible?

I want to thank all of you who responded for your thoughtful and insightful responses to my questions.
Parallel battery banks have to be as equal as possible to avoid the parallel banks cross-feeding each other instead of the load in an attempt to equalize voltages.

If you buy all 4 batteries now, you want to use them equally.

If you do wait to buy the second pair of batteries, I would pair one new with one older in each bank, thereby keeping the 2 banks as equal as possible.

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Old 08-21-2016, 08:46 AM   #14
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In reality an RV 12V battery is really 6 2V cells in a singe case. Two 6V batteries in series is essentially 6 2V cells in series in two cases. Same thing.
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Old 08-21-2016, 09:11 AM   #15
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I have been to this seminar the last two years and Drew has stated both years that the Weco converter is not to be used for 2 6V batteries. I disagree with him but I have a PI converter so I can not talk as an expert or whatever. But I think that two 6V batteries and the same as a 12v battery. I do know that for very heavy discharge rates the 2 6V batteries provide much better performance than a single 12V battery. Bottom line I think Drew is wrong or this point, but does provide much good basic information.
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Old 08-21-2016, 10:25 AM   #16
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If you plan on using 4 you might as well do it now and keep the batteries as matched as possible so one bank does not cycle out before the other pair (you will have less capacity than you think if you do.

Make sure you wire the banks so the current flow through the batteries is "Ohmically" equal. See graphic.

I would also use the largest diameter and shortest (but equal) length cables you can find to connect the two 6 volt batteries together to reduce "interbattery" resistance. See attached article on why.
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File Type: pdf How to correctly interconnect multiple batteries to form one larger bank.pdf (106.1 KB, 41 views)
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Old 08-21-2016, 10:36 AM   #17
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Quote:
Originally Posted by clr View Post
I have been to this seminar the last two years and Drew has stated both years that the Weco converter is not to be used for 2 6V batteries. I disagree with him but I have a PI converter so I can not talk as an expert or whatever. But I think that two 6V batteries and the same as a 12v battery. I do know that for very heavy discharge rates the 2 6V batteries provide much better performance than a single 12V battery. Bottom line I think Drew is wrong or this point, but does provide much good basic information.
Charging or discharging is a question of voltage and capacity. 2 12 volt batteries or two 6 volt batteries of equal total capacity (AH) will require identical charge profiles. I don't understand his point.

12 volt 100AH + 12 volt 100AH = 12 volts at 200AH Parallel

6 volt 200AH + 6 volt 200AH = 12 volts at 200AH series
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Old 08-21-2016, 12:44 PM   #18
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Quote:
Originally Posted by clr View Post
I have been to this seminar the last two years and Drew has stated both years that the Weco converter is not to be used for 2 6V batteries. I disagree with him but I have a PI converter so I can not talk as an expert or whatever. But I think that two 6V batteries and the same as a 12v battery. I do know that for very heavy discharge rates the 2 6V batteries provide much better performance than a single 12V battery. Bottom line I think Drew is wrong or this point, but does provide much good basic information.
Kind of like "Handy Bob". He has some good info, but also some mis-information that people will tend to believe.
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Old 08-21-2016, 04:59 PM   #19
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zap

Herk7769, thanks for all the great info. For those of us not quite as literate as you in the ways of electrons, could you please post the proper order in which to hook up batteries to minimize the chance of a spark? I know for my two 12v batteries I hook up the positive first, then the ground. But for the 2 6volt batteries in your diagram, I am not sure. Thanks!
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Old 08-21-2016, 05:09 PM   #20
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Originally Posted by pt1655 View Post
Herk7769, thanks for all the great info. For those of us not quite as literate as you in the ways of electrons, could you please post the proper order in which to hook up batteries to minimize the chance of a spark? I know for my two 12v batteries I hook up the positive first, then the ground. But for the 2 6volt batteries in your diagram, I am not sure. Thanks!
As long as the final ground wire to the frame is hooked up last, all the others don't matter at all.
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