Please help me make my system safe

RybrenRybren Solar Expert Posts: 348
I have a recently purchased off grid cottage property that, in all likelihood, will never see the grid. The previous owner installed a small 60W solar array with a 12V marine/rv combo starting deep-cycle battery. The panels are 4 x 15W amorphous (sp?) (from Crappy Tire for my Canadian Friends; I believe that they are made by Sunforce). The battery is rated at ~600 cca and 75Ah reserve. The controller is a Sunforce 7A (I suspect that it's a really cheap shunt type) The panels are connected to a 4 to 1 pigtail that is connected to the controller which, in turn, is connected directly to the battery. The system feeds DC to two cabins for lights only. The distance to each cabin is about 50 feet (think of a triangle with the PV array and battery at the apex). I can't tell what gauge of wire is used for the run to the cabins, but if I had to guess, I'd say 10AWG. Wiring inside the cabins to the lights is standard 14/2 household wiring. (both cabins are about 12'x30')

Lighting consists of 2 x 13W 12V CFL bulbs and 2 x 4W LEDs in one cabin, and 1 x 13W CFL and 4 x 5W LEDs in the other cabin. We've only been using the cabin for 1 or 2 nights per week and some of the lights may get run for about 1 - 2 hours per night. For grins, I checked the voltage in one of the cabins at mid-day and it read 13.85V. I checked it at sunrise the next morning and it read 12.75V


I know that the system is far from ideal, but it does seem to meet my needs for now (the cottage will only be used from mid-April until mid-Nov) I do plan on doing a complete overhaul and upgrade at some point, but that will be the subject of a differnt thread.

For now, my main concern is one of safety. Neither the panels nor the battery is grounded and there are no fuses anywhere in the system. My question is: What steps should I take to ensure that the system is safe? As I am a complete newby, detailed suggestions would be greatly appreciated.

Thanks

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please help me make my system safe

    Sounds familiar. Like the systems people around here have until I convince them to throw them out and get something worthwhile. :p

    Safety!
    Four 15 Watt panels will probably struggle to put out 1 Amp each @ 12 Volts. If one shorts out the other three could feed it 3 Amps and could set it on fire. If these are the ones I think they are it's not much of a worry, but if you want to be sure you could put a 2 Amp fuse in line with each one.
    Charge controller is likely a shunt type. Let me guess; little yellow box with three LED's and two wires in, two wires out? Most it's going to produce is the panel current: 4 to 5 Amps top. You can put a 7.5 Amp fuse on its output.
    The battery is the biggest danger in the place. That can hand out all 75 Amps in a blink if something shorts the output. This is the most likely cause of problems. Looks like the loads total less than 60 Watts, which is about 5 Amps on 12 Volts. Pretty easy to handle that amount of current in terms of wiring. The Voltage drop would be more of a concern so larger than minimum wiring makes sense; hence the 14 AWG household wire. I would definitely put a fuse on the battery (+) before any wiring in or out, just in case. Stop the current at 10 Amps and there should be no trouble from accidental shorts. Fortunately you can use standard auto blade fuses for this, and it doesn't look like the demands will be so great that you run in to the "cheap fuse holder" problem.
    I would not worry about grounding anything. Essentially it is a floating DC only system, just like a car.
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Please help me make my system safe

    Install a battery post (Bluesea) fuse at the battery. You want to protect all the wire from the potential battery current. I would fuse the PV source at maybe 15 amps, and the loads at about he same. My guess is that you have a pretty good voltge drop from the battery to the loads.

    I would not be concerned about lack of grounding. You might try to ground the PV for a modicum of lighting protection.

    Bottom line, you seem to be doing fine,, more PV and more battery in the future

    When in doubt, too many fuses is worse than too few.


    https://bluesea.com/category/5/21/productline/overview/378
  • RybrenRybren Solar Expert Posts: 348
    Re: Please help me make my system safe
    Sounds familiar. Like the systems people around here have until I convince them to throw them out and get something worthwhile.
    more PV and more battery in the future

    That is my plan for the future. I'll be bugging you guys relentlessly to ensure I've got the AIM down pat.
    little yellow box with three LED's and two wires in, two wires out?

    Close, a little blue box but otherwise the same. A Canadian Tire $19 special by the looks of it.
    Install a battery post (Bluesea) fuse at the battery. You want to protect all the wire from the potential battery current. I would fuse the PV source at maybe 15 amps, and the loads at about he same.

    Would the loads and the controller connect to the same fuse? Assuming that I won't be able to source one of these locally, I guess I could use the blade type as an interim step.

    What precautions should I take (if any) when disconnecting the panels, controller, and battery to install the fuses?
    I would not worry about grounding anything.

    Good to know.
    My guess is that you have a pretty good voltge drop from the battery to the loads.

    I really expected to see a very large drop, and 12.75V first thing in the morning surprised me. Although, I must admit that the LED bulbs (MR16) sometimes flicker, which makes me think that they're not getting what they need.

    Thank you very much for the advice. I'm heading up to the cabin in the morning and will pick up some fuses and holders on they way.

    Cheers
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please help me make my system safe
    Rybren wrote: »
    Would the loads and the controller connect to the same fuse? Assuming that I won't be able to source one of these locally, I guess I could use the blade type as an interim step.

    The Blue Sky fuse Icarus mentioned may be available from a local marine supply. Otherwise it's the automotive blade type.
    What precautions should I take (if any) when disconnecting the panels, controller, and battery to install the fuses?

    Turn off the loads, cover the panels. This should drop current flow in and out of the battery to near zero where it won't be a problem.
    I really expected to see a very large drop, and 12.75V first thing in the morning surprised me. Although, I must admit that the LED bulbs (MR16) sometimes flicker, which makes me think that they're not getting what they need.

    The Voltage drop concern isn't so much from night to morning as from the battery to the load. You may ready 13.8 Volts at the battery, but by the time the power gets to the last thing in line 2 or 3 Volts can disappear in the wiring. This is a function of the system Voltage, the wire size, the wire length, and the load draw. It can be quite a problem on 12 Volt systems.
  • RybrenRybren Solar Expert Posts: 348
    Re: Please help me make my system safe

    Thanks for the continued input.

    Sorry for not being clear. The voltages that I measured in my first post were at a light fixture in one of the cabins. Of course, my measurements or meter could be off.
  • RybrenRybren Solar Expert Posts: 348
    Re: Please help me make my system safe

    Question on the BlueSea Battery Post fuse: Do you connect the loads and the controller to the same fuse block (assuming they require the same rating) or should I get two fuse blocks and connect them to the same battery post?

    Thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Please help me make my system safe
    Rybren wrote: »
    Question on the BlueSea Battery Post fuse: Do you connect the loads and the controller to the same fuse block (assuming they require the same rating) or should I get two fuse blocks and connect them to the same battery post?

    Thanks.

    Fusing is to protect a particular circuit, and the fuse rating is based on the expected current within that circuit as is the wire size.
    The Blue Sea post fuse would be like a "main fuse" in a service box; it guards against over-current from the total loads to the battery. Circuits coming from that point will have different current loads and wire sizes and should be protected individually. This includes input from the charge controller.

    Whereas the battery might need a 100 Amp fuse to handle all the current going out/in, the charge controller is only capable of about 5 Amps and if it should short a fire would start in the wiring connecting it to the battery before the 100 Amp fuse would blow.

    Given the size of your system, you could limit the battery fuse to 10 Amps and expect that to handle everything. But, if that one fuse gets overloaded by anything you lose everything else, including charging. So it is best to fuse circuits individually.
  • RybrenRybren Solar Expert Posts: 348
    Re: Please help me make my system safe

    Thanks. I think I've got it.
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