Another Newb with questions!

System Posts: 2,511 admin
Hello All!

I've been reading posts and trying to figure this out for a few days now, but just don't think I'm getting it. So here is what I would like to do. This project is for a camping solar power primarily for Burning Man.

We want to run a small AC fan and some small lighting at night. I realize I should try to get everything DC, but that will have to wait till next year. Anyway, I calculated the power consumption to be about 10AH per day including inverter draw.

Equipment list:
55AH optima blue top marine deep cycle
30watt 1.7amp solar panel
7amp charge controller
600watt inverter (a little much, but we may use this at home as well)

For where we are goign to use this setup (Black Rock desert, NV) we will be getting around 5.5-6 charging hours, so that should give us 9.35-10.5ah per day. I may be a little short with the solar panel. What do you all think?

Thanks in advance!


  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Re: Another Newb with questions!

    If 10 AH and full sun with your current system... You will probably just fine...

    1.7A*5.5 hours * 80% battery eff. = 6.6 amp*hours

    You will be loosing about 3.4 amp*hours per day...

    Discharge your battery to 50%--

    55AH * 50% = 27.5 amp*hours

    27.5/3.5=7.85 days of use with solar + battery

    Now, realistically, for longer battery life, you should recharge the battery with a gas generator on the morning of day 4... Keeping a battery below 75% capacity will cause the sulfates to harden--and that will quickly reduce the capacity of your battery.

    The other thing, is go with a cheap, true deep cycle battery... Don't spend the money on a very expensive (for the capacity) RV/Marine Starting battery...

    Check the low power efficiency of your inverter... Many are ~8 watt or so in idle power... In your case, that would be:

    8 watt/12 volts = 0.66 amps basically, about 2/3'rds of your power usage (assuming 10 hours per day/night of power usage at 10 AH = 1 amp average load).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Another Newb with questions!

    You didn't state your lighting situation. That will be more power drawn.

    You can save money - skip the charge controller for this year, it will do nothing for you.

    Check out a computer store for a 12VDC case cooler fan, many styles are out there.
    Also, computer stores have Cold Cathode case lights, but I don't know if they are 5V or 12V.
    And hop on over to the Alternative Energy Zone Village before you depart for the burn.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • System2
    System2 Posts: 6,290 admin
    Re: Another Newb with questions!

    Thanks for the reply, Bill!

    You are very correct on the inverter. It is exactly 8watt=.66amp no load draw and was calced into the total daily draw.

    Question about battery charging through the truck alternator. I'm assuming that you just hook it up like you are charging a regular car battery, but how long does one leave it going for? This is a 55AH AGM deep cycle. I don't want to over-charge it, but I've read that you can't take readings with a tester while charging and will need to let the battery sit with no load for up to 3 hours to get a good reading after charging like this.

    Thanks again!
  • System2
    System2 Posts: 6,290 admin
    Re: Another Newb with questions!

    Mike, I calced the lighting draw (EL wire) in the daily AH load, so it is included.

    Without the controller would I just hook the panel right on the battery and just take readings every now and again? Or is there little chance of overcharge with this setup?

    Thanks Guys!
  • FreeBrrd
    FreeBrrd Solar Expert Posts: 116 ✭✭✭✭
    Re: Another Newb with questions!

    I just bought case fans & cathode light for my 'camper'. Best cfl / amp and best price I found at I got the Scythe "800rpm" because that was the best cfl / power in my range. It's not a bunch of air flow. I got the 12 white cold cathode lights - They're pretty cool. Like micro flourescents. You can just stick them on. I'm probably going to use velcro so I can move them. I'm not in the camper yet so haven't tried living with them, but they seemed pretty bright when I plugged them into my computer to test. & only $5.?? for a pair. Even with a little switch. I bought some y cables to make extension cables out of. I couldn't find just connectors to plut the fan connectors in to.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Re: Another Newb with questions!

    The minimum charging current where would need a charge controller--probably around 5% of battery capacity... or 2.7 amps or so...

    And since you are "deficit charging" anyway--you know that the battery is not going to be overcharged.

    Bring along a 1/2 gallon of distilled water and just watch for "boiling" (more then just light bubbling... That will indicate that you are beginning to overcharge the battery. You can also get a cheap hydrometer too..

    But for a week of use--probably about 5 more things you don't need to bring with out.

    I would try and get a much smaller inverter... A true sine wave would b great--but you can find small 100 watt or less inverters for a few tens of dollars now (Costco is selling a small inverter+usb charger right now). Almost has to use less than 8 amp (but as one president used to say--"Trust but verify"). :cool:

    My daughters have a coach that does "art" (actually very good art) and this will be the first year he has missed Burning Man for awhile (fatherly obligations). Very mixed feelings. It sounds like a very interesting place to be (also fatherly obligations). ;)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Another Newb with questions!

    i was going to go with addressing you by initials and decided that's a bad idea, but i feel that you may need a bit more pv power as you are borderline between production and use. high heat will lower output watts a bit and few pvs will consistantly get their stc ratings especially for 5-6 hrs a day. then there are system losses that occur and those ocassional clouds too so you better err on the safe side and go to 45w or better stc. even the charge rate for a 1.7a pv into a 55ah battery is borderline at a 3.1% charge rate.
  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    Re: Another Newb with questions!
    GeminiWB wrote: »
    Question about battery charging through the truck alternator.

    Not a good idea. A vehicle alternator is not a continuous duty alternator, and thus is not designed for bringing up a deeply discharged battery. I've burned up more than one alternator in my past, before finding this out. Gets to be a vicious cycle too. Had a battery go bad, and by the time I discovered it and replaced it the diodes in the alternator had burned out. Replaced the alternator first chance I had, which was when the battery was too deeply discharged. By the time the battery was charged again, the alternator fried again. Didn't get the issue fixed until I replaced the alternator and battery together. Now, I replace the alternator and battery as a package, I don't replace one without replacing the other at the same time. Since then, I've also learned why Auto Zone is not a good place to buy parts from, and now spend the dough for factory replacement parts when it's an electrical need. Well, actually for alternators there's a shop near me that rebuilds alternators in-house which I use as they can build an alternator to make more juice.

    If this is just a 3-5 day event, with the low draw you are looking at you might just pick up 3-4 used batteries, charge them up at home, then use them directly. After the event is over, recharge them and sell them back to the used battery store. Then, start putting back the scratch needed to do a correct solar panel setup with DC appliances for next year.
  • System2
    System2 Posts: 6,290 admin
    Re: Another Newb with questions!

    Thank you all for your input! Very useful et all.

    I just found out that one of my camp-mate will be bring a generator that will be capable of charging deep cycles, so I will be able to hook up on the 3-4 day and bring the battery back up to full, then continue to use the panel to keep it above 50% for the rest of the week.

    I think next year I will try to get all DC stuff and ditch the inverter or at least only one for charging small batteries (camera, laptop). And get a 60watt or better panel so not to have to use a generator.

    Thank you all again for your input!

    Wes B.