Parallel charging question

Options
Wxboy
Wxboy Solar Expert Posts: 70 ✭✭✭✭
in Solar Beginners Corner #1
Currently I have a small system that I'm looking to grow with time. It's easy to add a panel here and there but it's not so easy to add a battery as I have money so I'm thinking about increasing my battery size in the near future and I have a question about parallel charging. I've read that 2 batteries in parallel is fine, 3 is ok, but anything over that is asking for trouble. I've been kicking around many different scenarios but I keep coming back to the Sears DieHard Platinum AGM batteries because they are easy to get and they have a 3 year full replacement warranty which I like. But 3 of them at 100 amp hours is not really enough power to satisfy me and I was wondering if the following scenario would help with charging. I have a marine battery switch so I was thinking about have two 100 amp hour batteries set up in 2 banks. Then if I set the switch to all I would be charging and using both battery banks. I'm not sure if this would help with consistent charging current flow vs. having a line of 4 batteries paralleled together. Probably not but I figured I would ask.

A few side notes...
1. If I hook up 4 batteries I'll be a little light on the solar power end of things(380 total watts or about 6% charging rate) but sometimes you just don't have the money to upgrade everything at once so I want to go a little overboard with batteries and then add solar as money allows.

2. My system is not set up based on loads, I just use as much power as I can based on what's available from the sun and batteries so I'm not building a system based on needs, it's just based on growing it with time and using it to whatever it's potential is at the time. The DieHards have no charging current limit so I can add as many panels as I want to a given battery bank.

3. I would prefer to buy Concorde Sun Xtender batteries because you can buy bigger batteries or 6 volt batteries but I haven't found any locally that I can pick up and I am not going to pay hundreds of dollars in freight. Deka was an option I was considering based on local supply and price but their agm's are rated at 500 cycles based on 50% DOD and that is worse than the DieHard(Odyssey) agm's.

4. And finally I use agm batteries because I don't want to get involved with a ventilation system.
· Share on Twitter

Comments

  • Himins
    Himins Solar Expert Posts: 54 ✭✭✭✭
    #2
    Options
    Re: Parallel charging question

    Well I have found this page usefull. Not sure why you were led to believe this parallel battery wireing issue, would love to read what your found...but study every word on this page, perhaps it will help you reframe your question.
    http://www.smartgauge.co.uk/batt_con.html
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Options
    Re: Parallel charging question
    Wxboy wrote: »
    Currently I have a small system that I'm looking to grow with time. It's easy to add a panel here and there but it's not so easy to add a battery as I have money so I'm thinking about increasing my battery size in the near future and I have a question about parallel charging. I've read that 2 batteries in parallel is fine, 3 is ok, but anything over that is asking for trouble. I've been kicking around many different scenarios but I keep coming back to the Sears DieHard Platinum AGM batteries because they are easy to get and they have a 3 year full replacement warranty which I like. But 3 of them at 100 amp hours is not really enough power to satisfy me and I was wondering if the following scenario would help with charging. I have a marine battery switch so I was thinking about have two 100 amp hour batteries set up in 2 banks. Then if I set the switch to all I would be charging and using both battery banks. I'm not sure if this would help with consistent charging current flow vs. having a line of 4 batteries paralleled together. Probably not but I figured I would ask.

    Switching between one bank and another can offer some advantage, providing you remember to do it. Using the switch just to connect the two banks is a waste of money; you can connect multiple batteries with bus bars (common connection points) as per method #3 on the Smart Gauge diagrams Himins linked to.
    A few side notes...
    1. If I hook up 4 batteries I'll be a little light on the solar power end of things(380 total watts or about 6% charging rate) but sometimes you just don't have the money to upgrade everything at once so I want to go a little overboard with batteries and then add solar as money allows.

    12 Volt system using a PWM controller will only provide as much current as the panels can supply (Imp * the number of panels). That is what determines maximum charge rate. I'll hazard a guess at 20 Amps from your 380 Watt array. That's 20% on one 100 Amp hour 12 Volt battery, 10% for two, 6.6% for three, 5% for four. Providing you don't use any loads while charging this would still work with four batteries.
    2. My system is not set up based on loads, I just use as much power as I can based on what's available from the sun and batteries so I'm not building a system based on needs, it's just based on growing it with time and using it to whatever it's potential is at the time. The DieHards have no charging current limit so I can add as many panels as I want to a given battery bank.

    All batteries have a charging current limit, eventually. :D You're no place near it for these AGM's. I'm a bit concerned about these being actual deep cycle batteries, though; I doubt they are.
    3. I would prefer to buy Concorde Sun Xtender batteries because you can buy bigger batteries or 6 volt batteries but I haven't found any locally that I can pick up and I am not going to pay hundreds of dollars in freight. Deka was an option I was considering based on local supply and price but their agm's are rated at 500 cycles based on 50% DOD and that is worse than the DieHard(Odyssey) agm's.

    4. And finally I use agm batteries because I don't want to get involved with a ventilation system.

    Ventilation of flooded cells is not the big concern some people make it out to be. Unless these are stored in some tight location there will generally be enough air exchange to make the build-up of hydrogen gas a non-issue.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #4
    Options
    Re: Parallel charging question

    Himins, thanks for the link.

    Cariboocoot, I don't know what makes batteries true deep cycle batteries but the DieHard Platinum AGM's seem to be the best balance of cost and availability that I've come across so far again mostly because there are no shipping charges . They are rated very similar to other brands of AGM's for cycle life other than the Concorde Sun Xtenders which seem to be the best but they have a high price to go along with the reputation. The DieHards which are said to be re-branded Odyssey's are rated at about 700 cycles to 50% DOD and 1800 cycles at 25% DOD. Trojan AGM's have slightly better ratings but I would have to pay shipping which negates any extended life. Plus the DieHards have that nice 3 year full replacement warranty.

    I agree with you on the hydrogen gassing especially since my batteries are in a basement with leaky windows but I prefer to play it safe in this area.

    Ok, back to the wiring. So if I use a battery bus bar I am ok hooking up 4 or more batteries in parallel as long as the wires to each battery are the same length?

    Anything special I need to look at for bus bars(I've never used one before)? Would this one work...? http://www.solar-electric.com/tbb.html

    Regarding wiring I currently use #6 AWG from the controller to the batteries. I assume I can also use the same size wire to go from the buss bars to the battery terminals? Total length of wires from the controller to the buss bars and then to the batteries would be approx. 4-6 feet.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Options
    Re: Parallel charging question

    If they give you that info on the batteries (20 hour Amp hour rate, life cycles) then they probably are deep cycles.

    You can connect four or more batteries in parallel via bus bar. It is not perfect, but it is better than any other method of paralleling them. The problem is the batteries themselves will have variations in resistance which will increase over time. Thus the more parallel connections the greater the problem with current sharing regardless of the connection method and wire lengths. You can minimize the problem, but you can't make it go away.

    Those Outback bars will take three 0 AWG wires. This may not be enough for four batteries, and the 0 AWG may be too light for your application. 6 AWG is probably sufficient for the charge controller, but are you running an inverter? It's pretty easy to be drawing over 150 Amps with an inverter and that needs larger wire than 6 AWG. That's not saying they won't work, just that you have to be sure you can connect the wires you need.

    Some people make their own out of copper bar stock. Basically all you really need is a bolt you can fasten all the necessary wires to and keep away from shorting against anything.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #6
    Options
    Re: Parallel charging question

    I hadn't considered the inverter hookups but I use 2 AWG so I guess that means all wires from the bar to the batteries would have to be 2 awg. I'm not loving that. The only copper I have lying around here are some old copper pipes that were taken out of service.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Options
    Re: Parallel charging question

    Looking at your sig you have a 2kW inverter. On 12 Volts that's 167 Amps at peak Watts & nominal Voltage. Most of the time you won't be at that level, but the Voltage drop through 6 feet of 2 AWG at that current can be pretty high - in the 3% neighbourhood which is more than you'd want.

    I can't really advise on building your own bus bars because there's so many things that could be misinterpreted. I can say it's better to err on the side of caution and make wiring/connections heavier than you might need.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #8
    Options
    Re: Parallel charging question

    I do plan to upgrade to heavier gauge wires for the inverter as the system gets larger. So far I haven't really been able to draw much more than 300 watts for any length of time so the 2 awg has been fine but as I expand the system I want to go with 2/0. The inverter wires are currently 4 feet long so I don't see very much drop. Hopefully I can upgrade the batteries, wiring, and maybe even add a panel this winter.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #9
    Options
    Re: Parallel charging question

    I've still been thinking about this and how I can hook up 4 batteries in the least expensive manner possible and I have a few question.

    I understand the concept of busbars but I can't seem to find any that can accept 6 large wires(2 awg min or up to 2/0 max would be ideal) and is rated for high amperage. Anyone know of any products being sold that don't cost a ridiculous amount of money?

    Now back to my original thought of the battery switch since I have an idea that if there are busbars out there that do what I want I have a feeling they are going to cost way more than I want them to. I already have the battery switch so it would be nice if I could make that work. I would hook up 2 batteries in parallel to the battery 1 connection on the switch and 2 batteries in parallel to the battery 2 connection each using equal length positive cables and then I would set the switch to ALL so both banks are connected. Now the negative cable is where is gets a little more confusing for me. In my previous setup which was not meant to be charged together I had a negative cable from one bank connected to the charge controller and a negative cable connecting the two battery banks(neg-neg). This worked for charging one bank at a time but I'm thinking if I have the switch set to ALL that the current sharing won't be even between the 2 banks so I'm looking for feedback on that. If that is the case then I'm thinking I could have the negative cable come out of the charge controller into a small busbar(2 terminals) and then equal length negative cables could then go to each battery bank or side or whatever you want to call it since it would always be used in the all position forming one big bank. Thoughts, comments?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #10
    Options
    Re: Parallel charging question

    I am not sure I understand your question... Instead of being generic--Exactly what is it you are trying to do (battery voltage/AH, number of batteries, bus voltage, maximum operating current charging/discharging, etc.).


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #11
    Options
    Re: Parallel charging question

    BB, I want to upgrade my current 136 amp hour battery bank to 400ah. I have picked out four 100 amp hour 12v batteries and I am looking for the cheapest way to connect them that will allow good current sharing between the batteries in my 12 volt system. The existing batteries will be kept on standby since they still work but I'm not looking to fit them into the equation right now. I have a marine battery switch so if I can use that to keep cost down then I will.

    I also plan to add one more 255 watt panel so I'll have 2 panels connected to the Classic 150 and one 125 watt panel connected to a pwm controller. And now that I mention that controller that further complicates the hookups which I hadn't considered until now. I don't really have to use the pwm controller since I bought that setup for camping but I've been using it as extra power recently.

    Busbars may be the best option but not if they are going to be very expensive.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Options
    Re: Parallel charging question

    The Poor Man's Bus Bar is called a bolt. You just have to keep it mounted/isolated so that nothing can accidentally come in contact with it. The trick is to keep all parallel wiring equal length over-all. The shorter these parallel wires are the better; you don't want to run feet of wire from the batteries to the inverter and use it as the common connection point. The negatives can be/should be connected at all times; no need for two switches.
    · Share on Twitter
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #13
    Options
    Re: Parallel charging question

    You could even use the switch as the "bolt" if you don't plan on fusing them, 4 12 volt batteries all parrallel is not something we recomend...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Options
    Re: Parallel charging question
    Photowhit wrote: »
    You could even use the switch as the "bolt" if you don't plan on fusing them, 4 12 volt batteries all parrallel is not something we recomend...

    Reasons for which can be found here: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    As well as in many other threads in the forum; it is a common issue.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #15
    Options
    Re: Parallel charging question

    Just an update on this thread...for Christmas I received a couple of bus bars so I finally hooked up the four 12 volt deep cycle agm batteries in parallel. I'm using 2 awg pre-made wire connectors to connect the batteries to the bus bars. I am however seeing differences in current sharing between batteries. The difference in current sharing does vary a bit but it is higher than I would expect. Anything I can do to try to minimize the differences in current sharing? I have swapped around wires but that didn't seem to do anything. It certainly seems that it's a difference in internal resistance in the batteries but being that they are all new it seems strange. Two of them have an Oct. 12 manuf. date and the other two are Dec. '12. Only one of the batteries isn't really holding it's own. That just happens to be the last battery that I hooked into the system so it has a couple of less charge cycles in it since I was doing some experimenting first with two batteries and then three and then all four. It is one of the Dec. 12 batteries. My only idea for now is to disconnect that one battery and put it through a few charge cycles by itself. Or will this problem maybe smooth out on it's own after a few more cycles of the bank? The batteries have not been taken down more than 25% DOD yet and only to that level a handful of times.

    Here are two examples of the current sharing at different loads...

    Bat 1 12.9 amps
    Bat 2 12.0
    Bat 3 12.2
    Bat 4 10.3

    Bat 1 22.0 amps
    Bat 2 20.4
    Bat 3 20.0
    Bat 4 17.5

    And lastly I know this is not the ideal setup but it's where I'm at in this stage of my system. Years down the road I hope to have a 48 volt inverter and battery bank with less parallel batteries.
    · Share on Twitter
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #16
    Options
    Re: Parallel charging question

    Thats about how it works with Paralleled batteries, The first Battery always takes the most abuse ( Charging & Discharging ). The SOC of each will balance out and they'll feed back into it. It's best to number the batteries and shuffle them around once a year when you do cable maintenance. At least thats how I do it for longest life.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #17
    Options
    Re: Parallel charging question

    Blackcherry04, I agree with you if I had the batteries wired directly together but with the bus bars there really is no first and last batteries, right?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #18
    Options
    Re: Parallel charging question

    If you wired something like Marc's post #12 ... Then there is no last battery.

    The "issue" of current balance can be the result of poor/bad electrical connections, battery differences (condition, temperature, etc.)--Or just natural.

    The amount of current difference for your is not huge (2x between high and low current--I would be very concerned). If you cannot find any differences between batteries and wiring--Just live with it.

    And, although battery position should not matter--Some folks have seen it does matter (to their systems) and will swap batteries around once a year to even out everything (like BC4 suggested).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • H2SO4_guy
    H2SO4_guy Solar Expert Posts: 213 ✭✭✭
    #19
    Options
    Re: Parallel charging question

    What bus bars did you end up with? I have the Midnite versions, but would like some with more capability for more and larger wire. Did you consider a pair of L-16 batteries when you were thinking of batteries? You can get around 400 AH in one string.

    Skip
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #20
    Options
    Re: Parallel charging question

    you can try to single out the weakest battery and give it a good long absorb charge to see if it helps it, but if you move the battery around in the pecking order and it still shows low current in and out that there's not much you can do about it. maybe ask the manufacturer if they suspect a problem that is under warranty as this one battery could slightly drag down the others in performance in time.
    · Share on Twitter
  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #21
    Options
    Re: Parallel charging question
    H2SO4_guy wrote: »
    What bus bars did you end up with? I have the Midnite versions, but would like some with more capability for more and larger wire. Did you consider a pair of L-16 batteries when you were thinking of batteries? You can get around 400 AH in one string.

    Skip

    H2SO4_guy, I'm using Blue Sea powerbar/busbars. I'm actually using two types right now since I received them as gifts. One is a 4 post powerbar and the other is a 2 post powerbar. Eventually I'll upgrade the 2 post to another 4 post. See links below to the manufacturer's site.

    http://bluesea.com/category/82/35/products/2104

    http://bluesea.com/category/82/35/productline/overview/399

    As for the batteries I kind of went with what I had to right now but in the future I plan to go with larger higher capacity batteries and probably lower voltage individual batteries to get a better balanced bank. For now I'm just growing the system and going with the best balance of cost and convenience. It will cost me more in the long run but I'm ok with it.
    · Share on Twitter
  • H2SO4_guy
    H2SO4_guy Solar Expert Posts: 213 ✭✭✭
    #22
    Options
    Re: Parallel charging question

    Thanks for the link. Interesting idea with the ability to stack ring terminals to get the desired amount of cabling. I have put a 5/16" stainless steel bolt through the Midnite bus bars and it works just fine, but always seem to need more on the bus!

    Skip
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
    · Share on Twitter

Categories