parallel batteries

[davechezz]

Hi all been reading throu a few post about batteries, as um new to all this and trying to learn as much as possible.. Why should you not string batteries in parallel if it increases amp hours and what about wiring in series/parallel.. I have 6 12v batteries wired series and then parallel. How is it bad for batteries?

Dave

[jflorey2]

Hi all been reading throu a few post about batteries, as um new to all this and trying to learn as much as possible.. Why should you not string batteries in parallel if it increases amp hours and what about wiring in series/parallel..

Because lead acid batteries balance themselves by overcharging and dissipating the excess energy by breaking water down into hydrogen. This eventually requires water replacement, but in the meantime it means that if you have a long series string of batteries and you charge them with the appropriate voltage, then the "highest" cells will reach 100% charge and gas a bit while the lower cells slowly reach full charge.

If they are in parallel strings that often doesn't happen (unless the strings are perfectly balanced, which is unusual.) What happens instead is that string A, being newer/better, takes most of the charge current and balances itself. String B, being slightly older/inferior, takes less current. That means the weakest cells in string B never reach full charge. During discharge they reach very low voltages, and this is bad for lead acid batteries. So that cell in string B degrades. During the next charge cycle, string B takes even less current, and the cell gets damaged more. And so on and so on.

If you start with completely balanced cells you can often get 2 strings to work OK; sometimes even 3 strings. I maintained a heavily used 4 string system for about 4 years but it was a royal PITA; we had to replace batteries about every 12-18 months and keeping them watered was annoying since once they got unbalanced they didn't take water equally. And the frustrating part was that it was generally one or two cells that went bad per string, but there's no way to replace just one or two cells without unbalancing the system even more than it was.

About the only way parallel batteries work is if you can float them for a very long time; if you float them for long enough all strings will eventually equalize in voltage. (Which is why UPS systems can get away with parallel batteries.)

[Sunking]

Hi all been reading throu a few post about batteries, as um new to all this and trying to learn as much as possible.. Why should you not string batteries in parallel if it increases amp hours and what about wiring in series/parallel.. I have 6 12v batteries wired series and then parallel. How is it bad for batteries?

Dave

Try reading the Stickies.

Have you read this one yet? If you had you would have already known. In your application use Conventional or Diagonal shown in External Link provide.

[davechezz]

Yep read both, i think i have my batteries connected in the cross diagonal method not 100% as dont have all + and - in a line i have mine all opposing each other also says inthe smartguage method to have your charge point and take off point on same is this correct as in previous post i was told that my inverter was picking up the charge voltage and shutting down because battery hadnt had time to absorb voltage?? Bit confused

dave

[Sunking]

Yep read both, i think i have my batteries connected in the cross diagonal method not 100% as dont have all + and - in a line i have mine all opposing each other also says inthe smartguage method to have your charge point and take off point on same is this correct as in previous post i was told that my inverter was picking up the charge voltage and shutting down because battery hadnt had time to absorb voltage?? Bit confused

dave

I bet you are confused, I am after reading that. What I can tell you with certainty this part is Horse Feathers.

[QUOTE]i was told that my inverter was picking up the charge voltage and shutting down because battery hadnt had time to absorb voltage??[?QUOTE]

Cables can have something to do with Inverters tripping off-line, but that has nothing to do with the Absorb aka Saturation charge.Most Inverters, even cheap ones have a Low Voltage Disconnect inside them. As the name implies it disconnects the Inverter from the battery if the voltage gets to low. To save the battery from complete destruction. It is a common problem that comes from ignorance on the relationship of Power, Current, Voltage, and Resistance relationships. Result is you get too large of an Inverter, use too small of wire, over unnecessary distances. Result is Voltage Sag that comes from both Battery and all wiring between the Inverter.

So if you are having issues with your Inverter tripping off-line is going to be a compatibility issue.

[pop3y3]

I’ve been planning an off-grid system based off of the Tin Hat Ranch diagram in the linked pdf.

http://tinhatranch.com/wp-content/uploads/2015/05/THR-400-W-Solar-System-SchematicR1.pdf

I only want enough power to run low watt things like a laptop, some LED lights, charge an IPod, and maybe be able to brew a pot of coffee or two, and possibly run a small chest freezer.

So far I only have the 4 100 watt panels I’ll run in series and an MPPT 4215 TracerBN that can take up to 150v in and support either a 12 or 24v battery bank. My next purchase will be the batteries and inverter and I’d planned to follow his guidance but I’ve just recently stumbled upon this forum and now I’m second guessing Tin Hat’s battery setup (and his 1000w inverter, too).

He has 4 6v 235AH GC2’s wired in series/parallel to get a 12v 470AH bank. Would it make more sense from a battery longevity standpoint for me to just run them all in series for 24v at 235AH and bear the added expense of the 24v inverter?

Also, you mention in the parallel sticky that folks are stuck in a 12v box. Is there a reason for that? Does the prevalence of 12v devices like mobile ham rigs, etc, lead people in that direction? If I don’t plan to use anything that’s native 12v then maybe 24v with less amp hours makes more sense for me?

[pop3y3]

I'm not sure what I'm doing wrong - I wrote a post once and when the browser crashed and I lost everything I was about to say I rewrote it in Word and tried to copy/paste here but now it looks like my post is gone? I don't want to do the same thing again for fear I'll be double posting. Should I try text only vs a word doc?

Edit: I see this post, so I'll try to paste my text only post next. Sorry for the confusion! -

Paste: I’ve been planning an off-grid system based off of the Tin Hat Ranch diagram in the linked pdf.
http://tinhatranch.com/wp-content/up...chematicR1.pdf

I only want enough power to run low watt things like a laptop, some LED lights, charge an IPod, and maybe be able to brew a pot of coffee or two, and run a small chest freezer.

So far I only have the 4 100 watt panels I’ll run in series and an MPPT 4215 TracerBN that can take up to 150v in and support either a 12 or 24v battery bank. My next purchase will be the batteries and inverter and I’d planned to follow his guidance but I’ve just recently stumbled upon this forum and now I’m second guessing Tin Hat’s battery setup (and his 1000w inverter, too).

He has 4 6v 235AH GC2’s wired in series/parallel to get a 12v 470AH bank. Would it make more sense from a battery longevity standpoint for me to just run them all in series for 24v at 235AH vs his parallel setup and bear the added expense of the 24v inverter?

Also, you mention in the parallel sticky that folks are stuck in a 12v box. Is there a reason for that? Does the prevalence of 12v devices like mobile ham rigs, etc, lead people in that direction? If I don’t plan to use anything that’s native 12v then maybe 24v with less amp hours makes more sense for me?

[inetdog]

Should I try text only vs a word doc?

It depends on the Word doc format. If you try to paste a heavily formatted document in either MS Word proprietary, HTML or XML tagged format, chances are the Forum software will either ignore the formatting or get very confused.
You can use the Preview button next to the Post Reply button to see how it will look.

[pop3y3]

Well, heck, now I see both my original post and the second attempt. Newbie mistake, sorry.

[inetdog]

Also, you mention in the parallel sticky that folks are stuck in a 12v box. Is there a reason for that? Does the prevalence of 12v devices like mobile ham rigs, etc, lead people in that direction? If I don’t plan to use anything that’s native 12v then maybe 24v with less amp hours makes more sense for me?

The causes of the 12V box that ties you to a 12V system include:

Needing to match an existing 12V system, like in a RV,
Wanting to supply DC equipment meant for 12V,
Just not thinking that there are inverters, etc. for other than 12V based on what they see in the stores or featured online.

The other 12V box is the notion that you have to build up your 12, 24 or 48V system out of 12V batteries because that is all you see at the auto supply store.
Often it makes more sense, for example, to build your 24V system as one string of high amp hour capacity 6, 4 or even 2V batteries instead of trying to put multiple pairs of 12V batteries in parallel. This happens most with high capacity battery banks, but it could affect your planned 24V system too.
There is a limit to the number of AH you can get in one 12V battery and still be able to afford it and lift it. You can easily get twice the AH in a six volt battery of the same size, and so on.
(What is roughly the same for the same size battery of the same chemistry is the watt-hours, the product of volts and AH.)
(You should be able to deduce most or all of this from the sticky threads.)

[pop3y3]

Makes sense. What are your thoughts on how Tin Hat Ranch wired his 4 6v batteries? Would I be prematurely killing batteries by running any portion of it in parallel or are there so few in a string that any off balance effect would be negligible?

[Mike90250]

Since you have 4, 6V batteries. I'd work toward a 24V system.

The freezer and coffee pot are the tough items. 400W of PV is not likely going to be enough to power it for 10 months of the year, You might get enough sun for 2 months to keep things going, but you may find you need 600-800w of PV to keep the batteries happy,

It generally takes a 1Kw inverter to have enough surge capacity to start the compressor motor in the cooling unit. And most small fridge/freezers have thin enough insulation, the consume as much power as full size units !! Check the energy specs for yours, or use a kill-a-watt meter and measure it for a week.

[pop3y3]

Ok, thank you for the confirmation. The more I read here the more I lean that way. I've seen THR's series/parallel schematic elsewhere in this forum and the parallel balance issue on that setup hasn't yet been called out so I'm guessing, without seeing any math or anecdotal evidence to the contrary, that it's a non-issue for such a small setup and the 4 batteries being effectively connected diagonally.

Even so, it seems I can't go wrong starting out setting it up as 24V series only since many 24v devices allow you to drop back to 12v if needed (minding potential wire AWG issues) but stuff that is marketed to the 12v crowd doesn't allow for 24v.

Case in point, after reading this forum I actually just canceled an amazon order for the Stanley (not GCPro) 12v 25a charger because it wouldn't do 24v in favor of the GCPro version of the same thing that runs 6-48v that I found on EBay from their PepBoys storefront for 103.53. 20 bucks cheaper than Amazon and 100 bucks cheaper than pepboys offers from it's own (not ebay) website.

Thanks, again! Love this forum...so much great info.

[pop3y3]

Using CamelCamelCamel browser extension on Amazon to watch for good deals. Two months of waiting and then the price dropped on this 24v Pure Sine inverter. Don't know if this is the place to post things like this but in case someone wants a good deal on a cheap inverter. Lets just hope it's just inexpensive and not "cheap".

https://www.amazon.com/dp/B01DNAW1EQ/ref=nav_timeline_asin?_encoding=UTF8&psc=1