dual charge controllers

I got invited today to a nearby farm where the owner has set up 38 used 50watt panels to run his place. It was installed over time and on the cheap and he wanted me to give him some ideas on modernizing it - or at least organizing it. Someone had set up his system with dual morningstar prostar 30amp charge controllers on 4 Rolls 6v 500amp hour batteries. 20 of the panels went to one controller and 18 to the other. I was watching the display and when one showed charge input of a reasonable amount the other showed 0 and vice versa. I've a high end fluke rms clamp-on and it showed the same thing. Sometime 0 on one cable and sometimes on the other. At the time the batteries were at 26.95 and the morningstar light was flashing on both indicating it hadn't reached full charge yet. He told me that it does eventually reach full charge but I didn't hang around to wait.

Getting home I looked at Morningstar and Rolls specs and it appears the float might be barely okay for the Rolls but the bulk might be too low. Of course it being a mid range controller there's not much you can do about it. I can't figure out how they can both monitor effectively the batteries nor how equalization could work.

My question is.... Does this seem reasonable or are they in conflict somehow? In which case does the battery charging process never get full benefit of the entire array - just getting portions of the array on alternating seconds. The wiring seems to have been done by someone with some electrical background with a full set of good breakers but both positives feed both controllers with an intervening switch or breaker of a type I wasn't familiar with. Now as I'm thinking back I think they were joined on the input. Both outputs went to a single positive post.

The panel wiring is a huge mess and I figured I'd propose to put in a couple of combiner boxes and a good MMPT controller anyway. Still he's got the power he needs apparently and nothing is broke. I've not yet taken the time to review all his loads but will sometime. He's poor so I'm undecided on whether to mess with his system at all. Still he says he wants to add some more heat lamps for his piglets so you can imagine!

Thanks for your thoughts,

Dan

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: dual charge controllers

    it's harder for us to say than you as we haven't even seen it. it could be in conflict or miss wired, but without more to go on we can't say. we don't even have the luxury of knowing if all of the pvs are aimed the same way.
    for an improvement would be a rewire with proper fusing and combiners, but the best improvements may be to go with mppt controllers and an even higher working pv voltage that would be downconverted to the present battery bank voltage.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: dual charge controllers

    to add to Niels comments, a few pictures would really help understand the setup...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
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    West Chilcotin, BC, Canada
  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    Re: dual charge controllers
    dellsworth wrote: »
    I was watching the display and when one showed charge input of a reasonable amount the other showed 0 and vice versa. I've a high end fluke rms clamp-on and it showed the same thing. Sometime 0 on one cable and sometimes on the other. At the time the batteries were at 26.95 and the morningstar light was flashing on both indicating it hadn't reached full charge yet. He told me that it does eventually reach full charge but I didn't hang around to wait.

    This kind of behavior is not unusual if the controllers are in parallel and are in a voltage-regulated mode -- float, for example. Say you have both controllers set for a float of 27.0v. It's impossible to get two controllers to regulate at the exact same voltage, so #1 might be trying to regulate at 27.0v and maybe #2 is at 27.01v, just as a rough example. When the battery voltage hits 27.0v, controller #1 is going to attempt to scale back its charge so that it doesn't overcharge. But controller #2 is going to keep charging because it's trying to reach 27.01v. Depending on how close the two controllers' regulation points actually are, they might fight back and forth as the battery lingers around the setpoint. You might have something else going in in terms of wiring or whatnot, but what you're describing wouldn't be all that strange.

    Marc
  • dellsworth
    dellsworth Registered Users Posts: 20
    Re: dual charge controllers

    Thanks for your responses. I do need to get some pictures. I asked the owner to send me some. We'll see if he complies and I'll share them with you. I think Marc explained closest to what is probably happening except they were probably still charging toward bulk. Still perhaps it looked like it was at bulk when one was letting in a 19amp surge and the other "saw" voltage above max. I believe this since the light was flashing and they were below what Morningstar shows as their spec (which I can't change). Still I guess what Marc says makes sense even though they hadn't gotten perhaps that close to full charge. So how fast does this happen? It seems very inefficient to me since you can't use your entire array continuously. I've never installed or even seen a dual controller system before but I guess logically with big systems there's no way out. Incidentally, they are in parallel...
    Responding to Neil. All the PV's are pointing the same way but they are used with several different manufacturers and ages. I wouldn't be surprised to find one or two not even working well. The owner just checked them with a multimeter looking at the voltage only.

    I've really enjoyed the installations I have done with combiner boxes. Still they seem to be in design conflict with mppt controllers. If I combine say 8 of the panels to a single combiner switch to get nominal 96V that's great for the mppt but rough on doing diagnostics. At the moment I've installed almost all 24V systems and simply put each pair on it's own switch. I guess you could wire combiner box to combiner box like a tree hierarchy...

    I've really got to get some pictures but the place is 2 hours from me... Thanks again for your comments. Dan
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: dual charge controllers

    If you haven't already read them, there is are a couple of strings on the board here about combining panels and the down side of mismatching panels. If I remember correctly 'Crewzer' was a major commenter on them. A 'must read' for what you have described. Not that it will affect the CCs but overall output may be lower than expected due to mismatching.
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada