Ghetto Solar Float Charger

Discussion in 'The Projects Forum' started by luvv, Jul 10, 2012.

  1. luvv

    Thread Starter Member

    May 26, 2011
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    Hello AAC,

    Due to recent wind storms knocking out power,I have come to the realization a fully charged battery is a good thing to have on hand.

    Primarily to run a small fan,because I have discovered I can't sleep w/o the sound of one.

    The idea I have is a solar float charger for a 12v 2.6 Ah SLA all integrated w/ a small PC muffin fan.

    Then all I need do when bed time rolls around is go outside,grab the unit,flip a switch and enjoy 4-5 of sleep.

    So doing a little digging in the closet and attic a I came up w/ a few parts I'm hoping to make work.

    They are:
    A P.O.S HF Amorphous solar panel rated @ 1.5W 120ma max out.
    http://images.harborfreight.com/manuals/44000-44999/44768.pdf

    A Johnlite brand SLA bat. rated @12v.2.6 Ah (from a old spot light)

    Did a little testing on the panel and " control circuit," first off the best I could get from the panel on this overcast day was 64 ma@23v.

    Knowing I would have to do away w/ the cigar lighter plug,I cracked it open to see what was in there.

    Not much,couple diodes, couple resistors and a super secret Chinese COB...
    Well from what I gather, you need a blocking diode and some sort of overcharge protection for this kind of application.

    The 1n5819 is obviously the blocking diode, and the tiny C4V3 zener must be the over charge protection.

    Well if that is true what could the COB be..well I think its a oscillator.

    According to the pdf the little red led will flash when its charging...that has to be a lie.
    Testing the circuit w/ my psu,it starts flashing around 2v. input...gimmicky..

    There is however a few things I don't understand,the zener is in parallel w/ a 47k 1/8w resistor,what is the point of that?

    Secondly, there is a 5k 1/4w in series w/ battery negative out,to limit returning current to the cell?

    Wouldn't any unused current be equal to the output current of the cell?

    Anyhow,I'm sure I'll have more ignorant questions as the project gets rolling..

    Thanks

    ~luvv~
     
  2. wayneh

    Expert

    Sep 9, 2010
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    There must be a problem with your schematic, as R1 is grounded at both ends.

    But anyway, why do you care what's on the board? It's specifically made to do what you want - to charge a 12V lead battery. I think it would be fine for your application, although you won't get enough out of it to run the fan overnight. I haven't done the watt-hours math, that's just a hunch. The controller probably stops charging the battery based on a voltage setpoint, and you might be able to verify that.
     
  3. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Yea the R1 is in series w/ the boards negative output,I wondered myself why it was even used.
    My guess is it's used as some sort of dummy load when the battery is fully charged bet eh,w/e.
    The the question that perplexed me the most was the R2 in parallel w/ the zener..
    Not experienced w/ zeners,just kinda looked funny to me.

    So far as why I wanted to know the specifics of the boards function,well that is two fold, #1. that board is not part of my plan,it's going bye bye.

    And #2. perhaps most importantly,my curiosity is never ending and must be satisfied.

    How do you figure it wouldn't work?
    Panel outputs 60ma on overcast day,my fan is 40ma @ max.

    The panel would charge a minimum of 6 hrs a day, I sleep a average of 4.5.

    Beyond all that,this is float charger,the battery will be fully charged on day one.
    My goal is just to be able to reach for a battery powered fan and know it will run.
    No digging for D cells,no cannibalizing my pc ups,and most importantly,not fighting angry mobs for batteries at the store.

    Anyhow,I've already started putting the interface for the fan,wall wart charger and panel together in my head.

    I'll raid my bins and see what I can come up w/,and up some more pics and another wacky schematic.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Well first of all I didn't figure, I just guessed from the size of the panel and the fact that moving air requires more power than mere electronics. Your panel may be bigger than I understood. Are you saying it actually puts 60mA into the battery on an overcast day? That's better than I thought.

    40mA at 12v for 5 hours is a total of 2.4 watt-hours.

    The battery charging, discharging process is maybe 50% efficient at best. Best efficiency for a ni-cad is when the charging occurs at 50% charge, which of course it cannot stay at. Efficiency drops as full charge is approached.

    So, rough estimate, you'll need to collect about 5 watt-hours to make up for the battery losses. Your panel is rated at 1.5W, so even 5 hours of charging at 1W should give you enough to run your fan. Could be dicey on an overcast winter day but otherwise it looks good.

    I think you've got a good chance of at least getting to sleep. Just not sure the fan will always be running when you get up. ;)

    Oh, and FWIW, your charging might be simple. All those solar lights you see just rely on the fact that a ni-cad can tolerate a continuous overcharge trickle up to 0.1C. If your battery bank is big enough, all you need is your panel and a blocking diode to prevent reverse current when it goes dark. If the battery can't stand the full current of the panel when already fully charged, then you need a controller to dump excess current. You mentioned D cells. Most of the rechargeable D cells are just AA cells in a larger package, for which they charge more. Buyer beware.
     
    Last edited: Jul 13, 2012
    luvv likes this.
  5. luvv

    Thread Starter Member

    May 26, 2011
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    Uh Oh, well umm I just tested short circuit current @60ma,is that not the same thing as into the battery?

    Well w/ any luck,the fan will only be needed for 5hrs a day, 2-3 times a year, should be plenty of recovery time even if I decided not to mains charge the battery.
    Worst case I'll buy a lil 5w panel on ebay for 20$ and be done w/ it.

    At the moment,I'm trying to figure out a suitable interface between the panel,fan,battery and mains charge adapter.

    One part I'm having issue w/ is a one button,one led voltage test function.

    What I don't want is a comparator circuit as my space on the board will be extremely limited.

    So looking around I found this http://www.reuk.co.uk/Make-a-Simple-Battery-Status-Monitor.htm


    Add a DPDT switch to disconnect the panel during test and it's what I'm looking for,one problem tho,I don't own a 8.6v zener...

    Only have a 10v 1N4740,now like I said before,I don't fully understand zeners but I know current is relative to it's breakdown rating.

    Is there any way to make it work? or must visit the dreaded radio shack...

    Here is what I have so far, a ghetto schematic and pile of pieces..

    D1/D2 are the Shottkey diode CTB34,two in one package, no idea what I pulled it from but it had a slightly lower voltage drop then some of the others I had.

    D3 is a 1N5400 3A,included because that is what the batteries original charge board used, tho the wall wart only outputs 350ma.


    Let me know whatcha think so far.
     
    Last edited: Jul 13, 2012
  6. wayneh

    Expert

    Sep 9, 2010
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    No, that's the absolute maximum current across a zero voltage drop. Once you put a fully charged battery at, say, 14.5V in the circuit, the current will be MUCH less. But I think you'll do fine to get started with what you have and add more if/when you determine it's not enough.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    So in your diagram, the panel is "M"? If it is, you need a blocking diode to prevent reverse current. One of your Schottky diodes would be great. Or are jumpers 1 & 4 for the PV panel and the wall wart? That IS how you could OR them together.

    As I understand it, the green LED will be lit until the battery hits 10V? That's really lower than you should take a 12V battery, if you care about how long it lasts. Better than 8.6V, but too low. Maybe the shack has a 12V zener.
     
  8. luvv

    Thread Starter Member

    May 26, 2011
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    The "M" is the fan motor, the panel itself isn't shown, the panel input will come in @ J1 and pass through the shottkey,through the dpdt nc switch and to the battery.

    They don't show a schematic on the REUK page but, I imagine it's suppose to be like this.
    If the battery voltage is above 12.6 the led is lit, as the zener is breakdown mode allowing current to flow to the led.

    Now here is the part I have a hard time understanding,the zener's voltage drop and breakdown rating are both related to amount of current applied to them.
    And that is how they come up w/ the 8.6v zener and the 127ohm resistor to light a led.
    What I wondered is there a way to manipulate the V/I prior to the zener making a 10v.zener a proper substitute?
     
  9. wayneh

    Expert

    Sep 9, 2010
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    Oh duh, the fan. And oh duh, the LED voltage drop. The zener and the LED drops combine to define the on/off voltage. You could consider using a red LED with your 10V zener, since the red LED will have a lower forward drop than a green.
     
    luvv likes this.
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    As Wayneh said the charging current into the battery will be less than the short circuit current.

    With a 12v solar panel and 12v battery the charging current is usually around 70-80% of the short circuit current, so expect about 45mA charge current.

    On your 2.6Ah battery the self discharge is likely about 10mA so even with no circuit at all attached the battery will discharge at about 10mA for 24 hours a day and charge at 45mA for maybe 4 hours a day on average, IF you get lots of sun. That's not great.
     
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  11. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Ok, enough of the HF panel,I'll step it up a bit,ordered this one http://www.ebay.com/itm/5W-MONOCRYS...=596461901890751147&pid=100015&prg=1006&rk=1&

    If it won't do it, idk..I'll give up and buy a generator....

    Suppose I'll have to buy or build a charge controller for it now?

    I'll have to beef up the interface circuit a little bit also,but eh w/e..

    Maybe I can use the HF panel to make a over kill solar garden light lol..
     
  12. wayneh

    Expert

    Sep 9, 2010
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    That'll probably come in handy for other uses as well. Charging cellphones, camping lanterns, etc.

    Now you can get a bigger fan. ;)
     
  13. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    A 5W panel will put maybe 4.5W at 12v or 375mA into your battery in full sun condition, with a 2600mAh battery that is 1/7th of the rating so it's a bit too much current to run without a controller IF there is no current used. You might get away with it but with reduced battery life.

    But IF your fan is always run for X hours a day it might be fine with no controller. :)
     
  14. luvv

    Thread Starter Member

    May 26, 2011
    186
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    Yea, a lot of variables to contend with,like full sun..tons of hills and trees where I'm at..
    Figured at best maybe 6-7 hrs of full sunlight, 2 out of 7 days of perfectly clear skies.
    Time in use,maybe worst case 4 days a year@4-5 hrs per day..

    All that has made me come to one of two conclusions,buy a bigger battery,lawn and garden or perhaps a nice refurbed auto battery.

    Or build some sort of fail safe, of which I see two acceptable options.
    Limit max current to around 250ma via lm317 or a zener current shunt.

    Both of current limiting options prove to be a bit of a challenge for me considering I have never used either in such a fashion.

    So I have a few questions regarding both,first the lm317..
    Does the 317 drop a couple volts in the same manner it does when used as a voltage regulator?
    If so,that plus the shottkey drop would put the sweet spot from 16.8 max down to around 13.8
    I know it could also also prove to limit the charging cycles by dropping it's voltage in non ideal conditions.
    That could be a good or bad thing depending on the charge condition of the battery..

    And now zener shunting,I've seen schematics where the the zener dumps in to dummy loads both resistive and inductive,have also seen them set up w/ a transistor to short the panel.
    From what I understand the most basic zener shunts leak current all the
    time.
    Which could be a bad thing if for say, we get 2 weeks of rainy,cloudy days..
    Any way to form a near perfect shunt with the least amount of board real estate?

    Any how here is the updated schematic using the 317, I haven't assigned any values yet but its the same parts from the previous.

    D1&D2 are both combined into one package CTB-34 and panel input is on J1 .
    J2 is the barrel jack for the wall adapter, etc etc.
     
  15. wayneh

    Expert

    Sep 9, 2010
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    You might find this circuit useful. Look at the zener, transistor arrangement on the right hand side. The zener sets the voltage (5V in that circuit, for a 4.5V SLA) at which the transistor begins to open to dump excess PV current. I think the "off" current thru the zener is negligible.
     
  16. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Thanks,
    I had seen that post while searching threads here but hadn't noticed the use of the zener in the circuit.

    Still pretty up in the air on what is the most reliable/appropriate method,suppose it will come down to some bread boarding.

    But then can't do much more then wonder until the panel makes it's way here..
    Then I will know for sure what the panel is capable of on any given day and will build accordingly.
     
  17. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If you will be using a LM317 then you can just set it up as a voltage regulator, at about 13.6v or 13.8v and rely on the panel 375mA max as the current limiting.

    A 2600mAh AGM battery is small and will have quite a bit of internal resistance so a fixed voltage charger will work good enough as a complete solar charging system.

    It's not going to be a high performance charging system and give you full battery capacity but as self maintaining system it will make sure the battery is safe and at least has a reasonable charge in it.
     
  18. luvv

    Thread Starter Member

    May 26, 2011
    186
    31

    Well, a few things have changed since yesterday,one,I accidentally won a bid on a identical panel,so now I have 2.
    And two,I hooked up the SLA to its original charger and after 8 hrs it wont go over 11.8v,so I guess it's dead or dieing.
    I'll give it a try on my smart charger later, but given the 15$ price of Chinese 5Ah,I'll probably just upgrade.

    So what do you think of 750ma Max. into a 5Ah?
     
  19. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Hmm, that sounds like it has a shorted cell, 11.8 * 6/5 = 14.1v. When you disconnect the charger, within a few minutes does the voltage drop from 11.8 to about 10.8 or so? If so i'm pretty sure its bad and one cell is shorted. That's a common enough fault, those AGM batteries only last a couple years at best, and if they experience long times left discharged they can die in a few months.

    I think if you buy a new 5Ah battery it is well worth the cost of a LM317 and 2 resistors (or a resistor and trimpot) to make a voltage regulator, so it can never overcharge.

    As far as 750mA in full sun and a 5Ah battery that sounds like an ok combination if you don't have any big loads draining it.
     
  20. luvv

    Thread Starter Member

    May 26, 2011
    186
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    Well I am still waiting for cells and a new battery, but that has given me plenty of time to consider ways to go w/ the project.

    Have decided to scrap the idea of tracking the sun, 2x 0.8kg each is just to heavy to mess w/ w/o alot of effort.

    Secondly,I found what is to be my battery box,a military ammo can, nice and rugged.

    Will be able to fit 2 more 5Ah bats. in it w/ a little over head room for control circuit aaand...

    Well, I don't know yet, have been considering what on board device could be a useful addition to the project.

    Strongly considering things like a regulated 5v usb out for charging phones and such,or perhaps a compact weather radio or CB.

    If you guys got any good under 50$ ideas,I would love to hear them.

    And now on to another regulator question or two..

    Been wondering,would there be much advantage to replacing the LM317 w/ a switch mode regulator.

    My real concern(unfounded at the moment) is the lm's v drop +the shottkey diode drop would have my underpowered panels falling below 13.8v a lot.

    Add to that, no longer tracking the sun will pretty severely limit the panels full exposure time.

    Now here is the the big question, would buck booster like this one

    http://www.ebay.com/itm/LM2577-3A-D...464?pt=LH_DefaultDomain_0&hash=item231e192020

    help to maintain a charging voltage even when the panel isn't at it's prime?

    I know these things have a current trade off, but lets say the panel falls to 11v out and only 200ma, down from it's stated max of 16.8@ 750ma.

    Wouldn't the booster be able to still float the batteries @ 13.8 and say 50 ma ?

    Do booster regulators work also to limit voltage/ current when the vin is greater then the set output?

    I don't know jack bout them,just spitballing, let me know watcha think.
     
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