Help with Breakers b/c Panels, CC, and Batteries

Hello all. I need help in determining what types of breakers to use between our panels, charge controller, and batteries.

We have a hunting camp that we installed 6 110W 24V Shell panels back in 2004, using a Xantrex C40 CC. A family friend/solar hobbiest did the installation. We are currently adding 4 more 305W Astronergy panels, and have a new Xantrex C60 charge controller.

In looking at the old system, between the panels and the old C40 CC, and between the C40 CC and the batteries, they installed just two 20A 120VAC braekers - GE THQL style like this: LINK.

I would think these woudln't work being AC, but they have been working fne for years, with no trip issues that I am aware of.

Can I just get two 60A breakers of the same style since these have worked, or is there a better (DC-only) style that I should get.

I have a Square D 2-space load center that takes the breakers that have the spade-style connector similar to this:
LINK

Thoughts? Thanks in advance for your help.

Greg

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Breakers b/c Panels, CC, and Batteries

    Welcome to the forum.

    It's a good thing faults in DC systems are rare because you are quite correct: those breakers aren't rated for DC and wouldn't work properly. A 110 Watt 24 Volt (are you sure? Unusual but not impossible) panel would produce a mere ~3 Amps. All six such panels in parallel probably wouldn't trip one of those breakers.

    So let's start straightening out the wiring now. How are the existing panels wired? I would assume all in parallel on the C40 for a 24 Volt system. And it should be a 24 Volt system or else even more power is being wasted as the C40 is a PWM controller and can't down-convert higher Voltage into extra current.

    The new Astronergy panels @ 305 Watts are likely 'GT style' meaning they will not have sufficient Vmp to charge a 24 Volt system. If you can please give us the specs on both types of panel: Vmp, Imp, Voc, and Isc. In all likelihood you will need an MPPT type controller for the new panels.

    You will probably also be needing proper combiners and breakers for DC as in the products offered by MidNite Solar: http://www.solar-electric.com/elenanddcdi.html
  • au1999au1999 Registered Users Posts: 4
    Re: Help with Breakers b/c Panels, CC, and Batteries

    Thanks for the quick reply. I don't have the information in front of me for the old panels, but I'm pretty sure they are the Shell SM110-24. They are wired in parallel to the C40. Our system is a 24V system. We have 12 Trojan T-605 6V batteries, 4 in series, 3 rows in parallel.

    The new panels are Astronergy CHSM 6612P 305-watt. I have them connected parallel via a Midnite Solar MNPV4-MC4 Array Combiner, which has 4 individual 15A fuses built in.

    The specs on the Astronergy panels are Vmpp = 35.77V, Impp = 8.53A, Voc = 45.29V, and Isc - 8.95A. I did measure 39+V at the where the breakers should be from these panels on a very cloudy day.

    I spoke a good bit to the folks at Wholesale Solar where I ordered them, and Xantrex/Schnider and these are the components they recommended, so I hope I wasn't mislead.

    Thanks for your help in this.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Breakers b/c Panels, CC, and Batteries
    au1999 wrote: »
    Thanks for the quick reply. I don't have the information in front of me for the old panels, but I'm pretty sure they are the Shell SM110-24. They are wired in parallel to the C40. Our system is a 24V system. We have 12 Trojan T-605 6V batteries, 4 in series, 3 rows in parallel.

    There's two problems right there: 1). three parallel battery strings; 2). the T-605 is 210 Amp hours, so you have 630 Amp hours trying to be charged from ~18 Amps of current (3 Amps from each of 6 panels). Unless there is some other charge source regularly used, those batteries are toast. That's enough panel to keep them up (with no loads) but not enough to properly charge them.

    I'll suggest you re-evaluate your loads and thus battery capacity requirement. It sounds like this is one of those "lots of batteries and a few panels" systems of old which followed the incorrect assumption that they would charge over time.
    The new panels are Astronergy CHSM 6612P 305-watt. I have them connected parallel via a Midnite Solar MNPV4-MC4 Array Combiner, which has 4 individual 15A fuses built in.

    The specs on the Astronergy panels are Vmpp = 35.77V, Impp = 8.53A, Voc = 45.29V, and Isc - 8.95A. I did measure 39+V at the where the breakers should be from these panels on a very cloudy day.

    Well that is good in that Vmp around 35 is what is needed for a 24 Volt system. Four 305 Watt panels is 1220 Watts and would probably be better served by an MPPT controller anyway (34 Amps max current on a PWM, about 39 on MPPT). It could also facilitate wiring (two parallel strings of two panels in series) for higher Voltage/lower current to the controller to reduce losses and wire size. Something worth thinking about anyway.

    I spoke a good bit to the folks at Wholesale Solar where I ordered them, and Xantrex/Schnider and these are the components they recommended, so I hope I wasn't mislead.

    Obviously you're investing some significant money here, so you might as well get the system right up to snuff. :D
  • au1999au1999 Registered Users Posts: 4
    Re: Help with Breakers b/c Panels, CC, and Batteries

    Yes, we have a portable generator that we've been supplementing with, but that's why we are hooking up the four 305W panels to the battery bank. Should be an extra 51A, right (hence us getting the C60 charge controller)?

    Since we already have the C60 bought and mounted and everything wired except for the breakers, are we OK where we are at this point? The MPPT makes sense, but we don't want to have to purchase extra equipment if we don't have to. Again this is a hunting cabin, not and every day dwelling.

    If so, then my original questions is what would you recommend for breakers b/n the panels & CC and the CC & batteries? For both the 110W and 305W panel arrays?

    Back to your original problem with the 3 parallel strings, I assume it's best to only have 2 parallel strings and larger capacity batteries? What's the downfall of the 3 strings?

    Thanks!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Breakers b/c Panels, CC, and Batteries
    au1999 wrote: »
    Yes, we have a portable generator that we've been supplementing with, but that's why we are hooking up the four 305W panels to the battery bank. Should be an extra 51A, right (hence us getting the C60 charge controller)?

    No. The total current will be Imp * number of panels or 8.53 * 4 = 34.12 Amps maximum with a PWM type controller. You could expect slightly more with an MPPT controller (about 39 Amps). Even with 34 added to the existing 18 that's 52 Amps total, or a maximum 7.8% charge rate on 660 Amp hours of battery. Much better, but a tad shy of the 10% (without loads) rate that we'd like to see.
    Since we already have the C60 bought and mounted and everything wired except for the breakers, are we OK where we are at this point? The MPPT makes sense, but we don't want to have to purchase extra equipment if we don't have to. Again this is a hunting cabin, not and every day dwelling.

    If so, then my original questions is what would you recommend for breakers b/n the panels & CC and the CC & batteries? For both the 110W and 305W panel arrays?

    Go with the MidNite combiners & breakers if you can. Best stuff you can get for this. Example: http://www.solar-electric.com/misomnsoarco4.html You can get them with fuses or breakers. Be specific what you are trying to do when you order so that you get the right number of and current rating breakers/fuses. You'd need two combiner boxes because you have two separate arrays & charge controllers.

    BTW it's possible you could have put all the panels on one controller if the old panels had similar Vmp to the new ones. As it is you probably don't want to parallel up ten panels. You still could, perhaps, if the wire run from array to controller were short enough that the wiring for 60 Amps wouldn't be a problem price-wise (6 AWG probably).

    The output from the charge controllers to the batteries is easier to deal with: simply use the maximum wire size for the controller and install appropriate fuses/breakers. There are several ways of doing this including Blue Sea terminal post fuses, MidNite e-panel or disconnect boxes, stand-alone fuse holders, etc. Just stay away from the automotive stuff as it has been found to be somewhat exaggerated in specifications.
    Back to your original problem with the 3 parallel strings, I assume it's best to only have 2 parallel strings and larger capacity batteries? What's the downfall of the 3 strings?

    Thanks!

    The parallel battery strings issue is one of sharing current evenly through multiple strings. The more strings, the greater the likelihood of problems. Lower Voltage also increases the potential for failings. Two in parallel is easy to do without any fancy equipment. Three or more becomes difficult. Take a look at the Smart Gauge diagrams here: http://www.smartgauge.co.uk/batt_con.html Method #1 is what most people get caught up with; laddering. Method #2 works best with just two strings. Method #3 is what we recommend for three or more strings. Method #4 is too confusing for most people to get right. The basic principal is to keep the wiring lengths and thus resistance equal on all the parallel current paths so that the batteries get equal charging and discharging.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Help with Breakers b/c Panels, CC, and Batteries

    too bad you have the Homeline breaker box, if it was a SqD QO series it is good for 24V DC use as are the QO breakers...
     
    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
  • au1999au1999 Registered Users Posts: 4
    Re: Help with Breakers b/c Panels, CC, and Batteries
    westbranch wrote: »
    too bad you have the Homeline breaker box, if it was a SqD QO series it is good for 24V DC use as are the QO breakers...



    So If I get two of this type of QO breaker (LINK) then I can hook one leg up between the PV panels & the CC, and one leg between the CC & the batteries? The spec sheet only shows 120/240VAC, but I see where the QO family sheet shows 48VDC as well.

    I assume I'd use this type of box (LINK). This is a 70A, so I'd assume I'd need at least a 100A using 2 50A breakers?

    Thanks!
    Greg
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Help with Breakers b/c Panels, CC, and Batteries
    au1999 wrote: »
    So If I get two of this type of QO breaker (LINK) then I can hook one leg up between the PV panels & the CC, and one leg between the CC & the batteries? The spec sheet only shows 120/240VAC, but I see where the QO family sheet shows 48VDC as well.

    I assume I'd use this type of box (LINK). This is a 70A, so I'd assume I'd need at least a 100A using 2 50A breakers?

    Thanks!
    Greg

    Something of a problem putting the breaker for input to the charge controller and output from the charge controller in the same 'standard' plug-in box: the breakers will have a common connection to the box's bus bar when they don't want a common connection at all.

    In other words this SquareD system is meant to have the breaker distribute power from the bus bar through two breakers to separate circuits. The charge controller has no such common point between input and output.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Help with Breakers b/c Panels, CC, and Batteries

    What I was referring to was, you can use a QO box as a combiner box, so all the + wires go to a breaker and to out to the CC comes off the buss bar, on needed for each array as they go to separate CC's (at this point). It looks like you will need boxes with 4 and 6 CB's if you parallel the PV's.
     
    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
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