Question about 100w solar panel for small devices

Discussion in 'Off Grid Living' started by juntjoo, Sep 7, 2017.

  1. juntjoo

    juntjoo Monkey

    I'm thinking about getting a 100w solar panel from harbor freight and for now only using it to power some USB devices(i.e flashlights, phone, batteries, etc) for this Irma hurricane. I'd plan to use it later for larger projects but for now I don't want to invest in a small solar charger that I'll probably never use again.

    So for this to work do I just need an inverter to supply AC(for a device that will just switch it back to DC :p) or would it be better, or necessary to connect a large battery that can store power for when there's no sun?
  2. oil pan 4

    oil pan 4 Monkey+++

    Harbor freight is over priced crap.
    You can buy the same crap off ebay for 1/2 the price.

    The only thing that can be ran directly off a solar panel is a battend charger.
    Pretty much everything else needs a battery.
    You can not run a stand alone power inverter straight off a solar panel. The no load voltage will be so high the inverter won't turn on. If it did turn on anything that draws a load will cause the voltage to drop and the inverter to under volt fault.
    You can not connect the panel straight to the battery it will fry it. There has to be a charge controller between the battery and panel.

    If you stay along the east coast you will need it again. This isn't going to be the last hurricane.
    Cruisin Sloth likes this.
  3. juntjoo

    juntjoo Monkey

    Thanks. When you say you can run a battery charger off it, do you mean the same things as the "charge controller"?

    Okay, so from what I've been gathering, you need something to control the erratic current from the sun basically to fall into like a power reservoir, or battery, which from there you can either use it directly or convert it to AC with an inverter. Do I got it basically?

    Yeah I did notice on Amazon similar for a lot cheaper. And I've been here for over a decade and haven't lost power for more than a couple days(knock on wood). But I was talking about spending money on something I would only use in an emergency being wasteful(small solar charger) vs something I would plan on using all the time as in a larger solar power setup. But I'm not sure exactly what or when that setup will be so maybe a smaller emergency and/or camping solar charger would be a good investment. IDQK yet. Better figure it out soon...
  4. Seawolf1090

    Seawolf1090 Retired Curmudgeonly IT Monkey Founding Member

    Solar always charges a battery, never use it to directly run a device. Voltage out of the panel varies erratically, so the charge controller is needed. The HF charge controller is considered cheap and poor. A better one is a good investment.
    Last edited by a moderator: Sep 7, 2017
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  5. duane

    duane Monkey+++

    I agree on Harbor Freight being junk, but I have had just about as good luck with them as the internet. HF has a 100 w system, 3 panels, charge control, connectors, some 12 v LED's and supports for about $140 on sale or with discount coupon. Use the old 45 W set as backup for my greenhouse with a marine battery for storage and use 12 v pumps, lights, fans etc and don't convert it. It has outputs for computers, cell phones etc. Been worth having just to keep batteries charged in winter for farm equipment. Haven't bought one of 100 w units yet. Usable now and not perfect if needed is much better than optimal and not available. In my limited experience even 100 w on a site with no power and a large deep draw battery, I use about 100 amp hours, is a very useful tool. Lights to close greenhouse, fan to keep it inflated if power fails, 12 v pumps to water from tank, etc. Box it comes in is small, easily stored and carried and the 45 w one will fit in metal garbage can. Have one stored as well as a dry charge battery and the acid for it. If I get a 100 w one, will take old ones out and test them, about 5 years of storage, and probably worth the cost just to test the concept.
    Gafarmboy, Homer Simpson and juntjoo like this.
  6. oil pan 4

    oil pan 4 Monkey+++

    Solar panels do produce erratic currently the but that is not why you need a charge controller.
    A 12v panel makes up to 22 volts at no load. A 100 watt panel can easily over charge even a very large marine deep cycle battery with out a charge controller.
    Last edited: Sep 7, 2017
    ghrit likes this.
  7. Tevin

    Tevin Monkey+++

    I agree you can do better than Harbor Freight, but that wasn't your question.

    So here we go: You will need a battery no matter what. If you want to hook that up to an inverter, then go for it.

    If all you want to do is charge cellphones and other small electronics, then it would be easier and cheaper to simply wire a female 12 volt automotive lighter socket to the battery and charge your stuff from that. An inverter adds inefficiency and expense to your setup, so if you can get away without it, that's a net-plus.

    Good luck.
    juntjoo likes this.
  8. Dunerunner

    Dunerunner Brewery Monkey Moderator

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  9. Homer Simpson

    Homer Simpson Monkey++

    I have the older 45 watt H F setup, so I have some ACTUAL EXPERIENCE with an at least similar set up. I have owned it for 6 or 7 years. My set up was not to bad for the money. I'm sure There is better for the money, and I really doubt it will be shipped and delivered before the storm reaches the USA east coast.

    My older H F set up, will charge a usb device off the charge controller, but not well without a battery also connected. I suggest a battery, even if it is your riding mower or car battery. No, neither is optimal, but would work in a pinch for a few days. The fluorescent bulbs my kit came with are surprisingly bright for the 5 watt draw that each has. I hear the led bulbs in the newer kits are even brighter, not sure on the draw. The H F battery is a rip off, a mower battery is much cheaper, if you don't have one.

    Originally posted from my phone, edited for spelling.
    Last edited: Sep 8, 2017
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  10. Cruisin Sloth

    Cruisin Sloth Special & Slow

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  11. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Best 12Vdc battery for free to ask to be a governor of the controller , then take a Buck controller or a IBM control chip down to 5Vdc 0r up to 30Vdc from the Buck !!!
    Thats the way to do it within the DC ranging without a transfer of ACV .
    Dunerunner and juntjoo like this.
  12. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Last edited: Sep 8, 2017
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  13. ghrit

    ghrit Bad company Administrator Founding Member

    Power flow:
    -Sun to solar panel.
    -Solar panel to charge controller
    -Charge controller to battery. You need this because panel voltage varies with insolation. In mid day you can let magic smoke out of things and boil out the battery. Do not let out the magic smoke, it costs money. Boiled out batteries are dead, and very difficult to resurrect. In fact, don't bother trying.
    -Battery to DC loads at battery voltage. (Other than battery voltage will not be a very satisfactory. Magic smoke can ensue.) If you need other than battery DC, you'll need another gadget or two. My choice would be to accept the loss resulting from converting DC to AC then using wall wart things for the various other voltages you might want. YMMV, uv cuss.
    -Battery to inverter if you need AC. Considering that you may need AC as for charging cell phones and computers from wall wart type chargers and flashlight batteries, the inverter should be full sine wave modulation, not chopped sine such as pulse width modulation. The reason is that they are more efficient and quieter. (Cost more, too.)

    CS picks only good stuff, never fear to get what he recommends. But you are OUT OF TIME for Irma. (Unless you have a good local source.)

    I deliberately did NOT try to guess at the DC voltage you may want or need in the future. There are too many different considerations. That said, your minimum system should be 12 volts.

    Good luck.
    Last edited: Sep 8, 2017
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  14. Seawolf1090

    Seawolf1090 Retired Curmudgeonly IT Monkey Founding Member

    Also, the inverter wastes power, using energy even when hooked up but unused. Converting from DC to AC then back to DC introduces more losses.
    juntjoo and Cruisin Sloth like this.
  15. Cruisin Sloth

    Cruisin Sloth Special & Slow

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  16. juntjoo

    juntjoo Monkey

    Your guys are friggin awesome! You all just supplied me with a little book to read to get started. Thanks so much. It will definitely take some time to go over but this thread will be a great service to get me going in the beginning. Thanks
    chelloveck likes this.
  17. oil pan 4

    oil pan 4 Monkey+++

    If you find something you think you want to buy post it on here first.
    The solar market had been flooded with cheap made in China garbage in recent years.
    juntjoo likes this.
  18. juntjoo

    juntjoo Monkey

    Will do definitely
  19. DKR

    DKR Raconteur of the first stripe

    FWIW, I knew a fellow who managed a golf course in Las Vegas. It seems most golf carts run on 36 VDC. That means 6 x 6VDC batteries.

    He shared with me that usually, for their course, if a cart couldn't do 36 holes without a full recharge, they pulled the battery string for replacement.

    Now, he also pointed out that in most cases, the issue was with a single 6 VDC battery, the others in the string were otherwise still in decent shape. I tested several of the 'salvage' batteries and was able to purchase a few them for the price of the salvage lead.

    If you have a golf course in your area, it may be worth checking with the cart maintenance folks to see if this would be possible for you.
    Seawolf1090 and juntjoo like this.
  20. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    The other place to look, is if you know anybody in the Cellular Phone Maintenance industry.... They routinely replace the Backup Batteries at Cellsites and many have good life still in them...
    chelloveck and juntjoo like this.
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