Another newbie needing help

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Sammy
Sammy Registered Users Posts: 5 ✭
in Solar Beginners Corner #1
Hello all -
I have an off-grid cabin in the mountains of Virginia which I bought about 1 year ago. The prior owner was using a simple 3 12-v battery bank with a 300 watt inverter to power lights, occasional TV or radio. he then used a 200 watt generator for tools and to recharge the batteries. (water heater, stove, fridge run on propane)
I have converted the 3 12-v system to a 6 battery 24 volt system and upgraded to a xantrex 24 volt prosine 1800 inverter.
I still recharge the batteries with a generator and a Samlex 24 volt battery charger.

My ultimate plan is to install a hydropower system. However, in the short term, I thought it would be nice to have a small solar panel set up so that when I arrive at the cabin for weekends, the batteries are juiced and ready to go without using the generator. Typically, in a weekend, we dont use much power, so I figured I could avoid using a generator at all except for the rare times when we can spend a longer period of time or its rainy, etc. Also, when I do get the hydro system set up, I would not leave it running while I was not there but thought that during longer absences, the solar panel could keep my batteries charged - almost like a trickle charger)

I have a grape solar 195 watt panel (GS-S-195-FAB3) and a xantrex c60 charge controller (which I will eventually use for the hydro)

My primary questions are with the safety aspects of fuses/breakers/disconnects. Since the panel puts out max of 5.38 amps , would a 10 amp fuse be sufficient? All of the fuses at the local hardware store are AC fuses of 120/240 volts - do i have to find one rated to 24 volts?
Where do I install the fuses and the disconnect? How do I pick the correct disconnect?
Also, I know that hydro requires a diversion load - my understanding is that solar does not? And does it matter if I may be gone for up to a month during winter months?

I'm heading up there next week for 7 days and was hoping to get all my materials together for installation
any help would be greatly appreciated
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  • Sammy
    Sammy Registered Users Posts: 5 ✭
    #2
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    Re: Another newbie needing help

    I forgot to mention - the inverter leads to an AC panel which is fully wired - if there were power company lines, it could be hooked right up to the panel - the cabin is fully wired like any on-grid house.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Another newbie needing help

    Welcome to the forum.

    The panel doesn't actually need any fuse on it, as there is only one.
    Your charge controller should have a fuse on its output to protect things in case it shorts and the batteries try to dump a ton of current through it. Normally this would be in accordance to its maximum rated continuous output, which is 60 Amps in this case. That puts the fuse at 80 to 100 Amps (check the manual). However, for just that panel you don't need a fuse at such a high rating as the continuous current will never be more than the Isc of the panel: <6 Amps. You could in fact use a good quality 10 Amp automotive fuse here. But don't expect it to be permanent or to work for the hydro system.

    The most important fuse you can have is the one between the batteries and the inverter. Check the inverter manual for rating. I think it's 150 or 200 Amps on that model.

    Solar does not require a dump load: the charge controller goes between the panel and the battery and will simply turn off the panel connection when the battery is full. With PV no circuit = no power. The same is not true of wind or hydro turbines which put out power all the time they are spinning; there must be some place for that power to go or they can spin out of control and self-destruct.

    When you go looking for top-quality permanent circuit protection be sure and check out the products our host has listed here: http://www.solar-electric.com/cipr1.html
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
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    Re: Another newbie needing help

    Welcome to the forum.

    My first suggestion is to define your loads, both as a function of average daly WH loading, as well as your peak loading. We often hear folks say, "we don't use a lot of power, just a bit of light, a tv, radio etc," but with further converstion, by the time they realize all the power needs it is not insignificant.

    If you can rltively accurately define your loads, that will dictate the battery bank size, and thaqt in turn will dictate the proper solar ( and genny) charge regimen. Keep in mind, thaqt loads always grow with time.

    My rule of thumb is this...take e name plate rating of the PV, divide that number in 1/2 to account for all cumulative system loses. Then take that number and multiply it by 4 to account for the average number of hours of GOOD sun you can expect, or day averged over the course of the year. You can fudge that number a bit depending on location, (but in VA I wouldn't! ). So for example, a 500 watt PV system might look like this, 500/2=250*4=1000 WH/day

    People most often over estimate thier solar capacity while at the same time under estimate thier loads. As a quick comparison, we live off grid, with 400 watts of PV, (lp fridge, stove water heat, genny for tools) and we routinely use 500-800 WH/day. Our system is pretty well balanced through out the year, and you can see the formula is just about correct.

    To answer hither questions, PV does not require a diversion load, just a controller. (your C-60 is. Lot of controller for 195 watts of panel. You need a fuse at the battery both for the load side as well as the charge side. If you only have one PV panel you don't need a series fuse. I use Square D QO breakers and boxes that are DC rated for 48 volts. A small Sq D panel can be very useful for wiring a number of different devices and schemes. I also use BlueSea fuses at the battery, and as series fuses in the battery string.

    consider our site sponsor for many of your hardware needs, like fuses, enclosures etc.

    Good luck and keep in touch,

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: Another newbie needing help

    If we knew the Amp hour capacity of the battery bank we could determine how helpful that 5 Amps from the panel would be. It is not very much current; doubtful it would be enough to do much more than maintain. 5 Amps is 5% of 100 Amp hours, which would be minimum charging on maximum battery. Any battery capacity above that and you're looking at maintaining rather than charging.
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  • Sammy
    Sammy Registered Users Posts: 5 ✭
    #6
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    Re: Another newbie needing help

    Thanks for the input -
    What about a DC disconnect? Do I need one or does a 10 amp breaker between the panel and the charge controller suffice?
    I then put a 60-80 amp breaker between the controller and the inverter?

    The inverter leads directly into the main panel so I would not need anything after the inverter, correct?
    I do have a in-line fuse already between the battery bank and the inverter.

    Do breakers need to be installed in a box?

    Ultimately, if this works out and I do get to hydro, I will use the C60 for the hydro and get a smaller controller for the panel -
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    Re: Another newbie needing help
    Sammy wrote: »
    The inverter leads directly into the main panel so I would not need anything after the inverter, correct?
    I do have a in-line fuse already between the battery bank and the inverter.

    The inverter should be connected directly to the battery and will need a breaker, I think 175Amp is suggested for a 24V 1800watt prosine, Though I have I of mine on a 125Amp. Check the manual. Sorry missed that you had a fuse between them... I slips, I fall, I pick my self back up...lol
    Sammy wrote: »
    Do breakers need to be installed in a box?

    Easiest to buy a DC disconnect box

    You can go for an E panel which would include the items needed to meet code. but your (and my) Prosine 1800 units can't meet code for residences, they either don't carry the proper UL listing or can't be installed to Code, in that all wiring AC and DC must be in conduit. I have one that carries the UL 1741, but there is no provision to install this with the DC wiring in conduit, unless you put the whole thing in a UL box.
    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.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Another newbie needing help

    With this set-up you don't really need a disconnect on the PV and/or the controller; the power is so low that if for some reason you did want to disconnect it pulling the fuse would suffice.

    The inverter should have at least an 80 Amp fuse or breaker on it. This is a spot where a disconnect may be desirable too, as you may want to completely power down the inverter when you're not there (instead of turning it off; it could still consume some power then). These are nice for that function (breaker-disconnect in one): http://www.solar-electric.com/mr60ampdccib.html

    If the output of the inverter is connected to a standard AC service panel, then all the loads would be connected through standard breakers. Most likely an 1800 Watt inverter would fault before any of the breakers would trip (15 Amps @ 120 Volts = 1800 Watts so the inverter would only be able to supply the equivalent of one fully-loaded circuit).
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  • Sammy
    Sammy Registered Users Posts: 5 ✭
    #9
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    Re: Another newbie needing help

    The batteries are rated at 105 amp hours - i have them in parallel-series to have 315 amp hours at 24 volts

    The AC output from the inverter goes to a male plug
    There is then a female plug that leads to the house AC panel

    When I am using the generator, I can plug the house directly into one of the outputs on the generator and then plug the battery charger into the other

    When I am not at the cabin, the inverter is not plugged into the house so there is no drain at all
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Another newbie needing help

    Well 315 Amp hours with 5 Amps from the panel is a mere 1.5% rate, meaning that one panel will not actually charge the batteries but it will keep them from self-discharge (providing no loads are attached) while you're away.
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  • Sammy
    Sammy Registered Users Posts: 5 ✭
    #11
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    Re: Another newbie needing help

    Did I calculate amp-hours correctly?
    If I have 3 batteries are they additive?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
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    Re: Another newbie needing help
    Sammy wrote: »
    Did I calculate amp-hours correctly?
    If I have 3 batteries are they additive?

    Batteries in parallel: Amp hours go up, Voltage stays the same.
    Batteries in serial: Amp hours stays the same, Voltage goes up.

    Basic battery equivalent power thread: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #13
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    Re: Another newbie needing help

    Are they actually "24 volt" batteries? (12 cells in one battery block).

    Usually not too many of those around. Normally 3-6 cells (6-12 volt) unless you are working with larger industrial batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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