Battery Junction - Olight
Page 1 of 2 12 LastLast
Results 1 to 30 of 45

Thread: Charging a car battery via a solar panel

  1. #1

    Default Charging a car battery via a solar panel

    Hi everyone.I want to keep a car battery at my camping site. I will use it at most once a week and will tap at most 30 to 40 amps out of it.What is the minimum size solar panel that will put back this amount of power into the car battery over a period of 6 days?What controller will be needed?

  2. #2
    Flashaholic* jasonck08's Avatar
    Join Date
    Sep 2007
    Location
    Redding, CA
    Posts
    1,494

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by lightseeker2009 View Post
    Hi everyone.I want to keep a car battery at my camping site. I will use it at most once a week and will tap at most 30 to 40 amps out of it.What is the minimum size solar panel that will put back this amount of power into the car battery over a period of 6 days?What controller will be needed?
    First off, car batteries are NOT designed to be deep discharged. You will want a deep cycle marine battery if you want to pull 30-40Ah out of it. Car batteries are designed to be charged almost constantly, and very shallow partial cycles.

    By 30-40 amps, I assume you mean amp hours?

    If so, 30-40 * 12 = 360-480Whrs.

    8hrs of sunlight * 6 days = 48hrs of sunlight

    360/48 = 7.5W and 480/48 = 10W.

    So assuming 100% Charge efficiency 7.5-10W would be enough. But you should probably go with 15-20W.

    Some 12v solar panels can charge lead acid batteries directly, or you could get a charge controller (don't know specific model #'s).

  3. #3

    Default Re: Charging a car battery via a solar panel

    No offense to jasonck08, but with the exception of car batteries not liking to be discharge very much, which is true, most of the rest of the post is not accurate.

    It is a common misnomer that hours of sunlight = hours of solar energy. That would only be true under perfect conditions and with perfect tracking of the solar panel with the sun. Realistically you will not have perfectly clear skies and you are likely going to have a stationary panel. Hopefully you will not have any shade. If you do, that changes everything!

    40 amp hours on a 12V battery with some charging losses (higher losses at the top of the capacity and need to overcharge a bit), so count on needing about 530 - 550 watt hours or at least 45 amp hours.

    You are in California so I assume camping close. You are inland, so fairly clear skies, but lets be cautious and say 4 peak sun hours/day. You may have a great week, clear skies, and no shade and get 8/day, but then again you may not so be cautious.

    You are likely going to have a PWM controller so at best extracting about 70% of what will come out of the panel.

    I would say at least a 30 watt panel. If you can get bigger, you are more likely to have your battery near peak capacity which lead acid batteries like.

    In terms of a controller, get a Morningstar Sunsaver10 or other high quality unit. There are dirt cheap ones out there, but do you really want to use a $20 controller with a $100-$200 battery?


    Semiman

  4. #4
    Flashaholic* TinderBox (UK)'s Avatar
    Join Date
    Jan 2006
    Location
    south shields, england, united kingdom
    Posts
    1,901

    Default Re: Charging a car battery via a solar panel

    I only have a 14watt panel, but the guide says you should use an 7amp battery, so for a 60amp battery, get a 120watt solar panel minimum.

    John.
    Intellicharge i4 - LaCrosse BC-900 - MaHa C9000 - Charge Manager 2010 - Vanson Speedy Box - Accumanger 10 and 20 -Thunder AC6
    Solar - GoalZero Nomad 7 + Guide10 - Powerfilm USB+AA Solar Charger

  5. #5
    Flashaholic* jasonck08's Avatar
    Join Date
    Sep 2007
    Location
    Redding, CA
    Posts
    1,494

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by SemiMan View Post
    No offense to jasonck08, but with the exception of car batteries not liking to be discharge very much, which is true, most of the rest of the post is not accurate.

    It is a common misnomer that hours of sunlight = hours of solar energy. That would only be true under perfect conditions and with perfect tracking of the solar panel with the sun. Realistically you will not have perfectly clear skies and you are likely going to have a stationary panel. Hopefully you will not have any shade. If you do, that changes everything!

    40 amp hours on a 12V battery with some charging losses (higher losses at the top of the capacity and need to overcharge a bit), so count on needing about 530 - 550 watt hours or at least 45 amp hours.

    You are in California so I assume camping close. You are inland, so fairly clear skies, but lets be cautious and say 4 peak sun hours/day. You may have a great week, clear skies, and no shade and get 8/day, but then again you may not so be cautious.

    You are likely going to have a PWM controller so at best extracting about 70% of what will come out of the panel.

    I would say at least a 30 watt panel. If you can get bigger, you are more likely to have your battery near peak capacity which lead acid batteries like.

    In terms of a controller, get a Morningstar Sunsaver10 or other high quality unit. There are dirt cheap ones out there, but do you really want to use a $20 controller with a $100-$200 battery?


    Semiman
    Uhhh... Thanks for the condescending response. The information I provided is accurate, yet you suggest disregarding everything. I did not say that hours of sunlight = hours of energy. Days during the summer are 14+ hours long in some places... ~8 peak hours is fairly common on a long summer day in some locations... http://www.pveducation.org It obviously depends on the environment. Where I live we get the 2nd most sunlight out of any city in the US.

    Also I see you mentioned he is in California, but I don't see any information in his post for that. Where did you get that information from? Or are you confused, and saw my location, instead of his?

    Quote Originally Posted by TinderBox (UK) View Post
    I only have a 14watt panel, but the guide says you should use an 7amp battery, so for a 60amp battery, get a 120watt solar panel minimum.

    John.
    I think that would be probably if you plan on using a lot of the batteries capacity every day. It sounds like the OP just needs a small panel to trickle charge the battery over the course of 6 days.
    Last edited by jasonck08; 06-06-2013 at 11:46 PM.

  6. #6

    Default Re: Charging a car battery via a solar panel

    I want a panel that can charge the battery in 6 days

  7. #7

    Default Re: Charging a car battery via a solar panel

    I have used solar extensively over the years. And the one thing that I have learned is that you always get the biggest panel that you can afford and physically accommodate (within reason). Spend money on a good controller.

    If you have the budget you can go for foldable panels, they really pack down small. I would recommend a 60 W foldable. Here are the specs for something like that.
    •Operating Voltage: 15.4
    •Wattage: 60
    •Current: 3.6 amps
    •Width (mm): 1207 unfolded; 336 folded
    •Length (mm): 1308 unfolded; 178 folded
    •Width (in): 47.5 unfolded; 13.25 folded
    •Length (in): 51.5 unfolded 7 folded
    •Weight (kg): 1.45 kg
    •Weight (lb): 3.19 lbs

  8. #8
    Flashaholic* AnAppleSnail's Avatar
    Join Date
    Aug 2009
    Location
    South Hill, VA
    Posts
    4,069

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by Knight_Light View Post
    (Folded panel)
    •Weight (kg): 1.45 kg
    •Weight (lb): 3.19 lbs
    Urgh. I was just wondering why there is no folded and unfolded weight. Not enough coffee in the world...

    Hours of sun in a campsite are usually much less than on a house rooftop. Most solar guides tend to assume that you are able to place the solar panels away from or above trees. I know that in dappled shade, my solar yard lights have about 1/10th the runtime of the ones in full sun. I do not know how things are in California, but a forested area in the mountains may have 12 (Peaktop) or 6 (Valley bottom) hours of sun in summer. This will be further cut by shade and imperfect panel aiming.

    For what it's worth, a bigger solar panel (That you can afford, and that won't be stolen) will almost always make you happier than a smaller one. And if a $200 solar panel will make you 10x happier than a $100, maybe it's worth that jump. However, plan on a coulombic efficiency (Energy in vs. Energy Stored) of about 1.6 on the lead-acid battery. If your charge controller is 85% efficient, then:

    "I want (40amp*hours x 12v)=500W*h per week."
    "I need to put (500W*h * 1.6) = 800W*h in per week, or 120W*h per day."
    "I need to gather (120/0.85) = 150 W*h per day for my charge controller."
    "For my region I need to de-rate the solar panel's output by (x)."
    "My good, strong sunlight there is (2, 4, 6, 8, 10) hours per day when I'll use this. That gives me the rate the panel should gather energy."
    My biggest light-hog is my camera.

  9. #9

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by AnAppleSnail View Post
    Urgh. I was just wondering why there is no folded and unfolded weight. Not enough coffee in the world....
    The folded weight is in kilograms and the unfolded weight is in pounds.

  10. #10
    Flashaholic* ChrisGarrett's Avatar
    Join Date
    Feb 2012
    Location
    Miami, Florida
    Posts
    2,050

    Default Re: Charging a car battery via a solar panel



    60w of goodness and I'm in Miami, so I get a lot of solar hours down here and I agree that most people assume too many S.H. when they're thinking things through. Unless you want to babysit your rig and I'm in a condo, bigger will be better because it will be faster, IMO. Together, those two 30w with hardware weigh in at ~2kg/11#, but moving up to the 40w panels, things start adding up, when dealing with rigids.

    You can find the milspec, foldable 62w PowerFilms, but they're over $800 the last time I checked this past August. Rigids are heavier, but more durable, have longer warranties and those pictured above are mono-crystaline, so a bit more efficient than the polys and CIG/Thin Films portables.

    Also, as semiman mentions, you have controller and charger inefficiencies, so you can never assume 100%. I don't think that my Morningstar SS-10L has a 30% loss, but I can see the controller and any of my battery chargers getting close to that number. Figure on 75% useful output when calculating this stuff and you should be close to reality.

    Doing a SLA/AGM, you only have to deal with say...half of that number, becuase that Morningstar SS-10L IS a battery charger, but there's still going to be less than the full pie going in.

    Also, the smaller controllers have certain limits to how big a battery they can charge and I don't think that they're meant to charge up a totally dead car-type battery, if I remember the manual correctly, so keep that thought in mind when putting something together.

    Anyhow, it was a fun project to do and I think something like my rig, or a nice size foldable panel, are necessities where I live and I'll be waiting during this hurricane season, but I'll be ready!

    Chris
    Convoy: S2, M1, M2, Fenix: P1D, PD32, HL30, ET: D25C Ti, SF: 6P, ZL: SC-600, Klarus: P2A, Jetbeam: BA-20, Icon: Rogue 1, L3: L10, Xeno: E03, ShiningBeam: I-Mini, Olight: i3s, SWM: D40A, M11R, V11R, Maglite: 6Ds, MMs, Solitaires, LaCrosse BC-700, Maha C-9000, XTAR VP2, MP1S, WP2 II, NiteCore i4, v2.

  11. #11

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by ChrisGarrett View Post
    60w of goodness and I'm in Miami, so I get a lot of solar hours down here and I agree that most people assume too many S.H. when they're thinking things through. Unless you want to babysit your rig and I'm in a condo, bigger will be better because it will be faster, IMO. Together, those two 30w with hardware weigh in at ~2kg/11#, but moving up to the 40w panels, things start adding up, when dealing with rigids.
    Let me start by saying that you have a sweet set up.

    Quote Originally Posted by ChrisGarrett View Post
    You can find the milspec, foldable 62w PowerFilms, but they're over $800 the last time I checked this past August. Rigids are heavier, but more durable, have longer warranties and those pictured above are mono-crystaline, so a bit more efficient than the polys and CIG/Thin Films portables.
    I agree with your more efficient comment but I don’t really agree with durability. In my opinion the PowerFilms foldable will be a lot more durable if you are constantly moving your set up around. I have seen rigid panels get damaged in transportation. Now if you go to the PowerFilms rollable then you are totally dealing with an almost indestructible product when comparing to rigid mono-crystaline panels.

    Quote Originally Posted by ChrisGarrett View Post
    Also, the smaller controllers have certain limits to how big a battery they can charge and I don't think that they're meant to charge up a totally dead car-type battery, if I remember the manual correctly, so keep that thought in mind when putting something together.
    Smaller charge controllers won’t be able to handle large current but as long as you stay within their specifications they will theoretically be able to charge any capacity 12V battery. Plus don’t forget that Pb doesn’t require a lot of current to charge. Now they may miss termination on a car battery but you can always follow the progress with a meter.

  12. #12
    Flashaholic* ChrisGarrett's Avatar
    Join Date
    Feb 2012
    Location
    Miami, Florida
    Posts
    2,050

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by Knight_Light View Post

    I agree with your more efficient comment but I don’t really agree with durability. In my opinion the PowerFilms foldable will be a lot more durable if you are constantly moving your set up around. I have seen rigid panels get damaged in transportation. Now if you go to the PowerFilms rollable then you are totally dealing with an almost indestructible product when comparing to rigid mono-crystaline panels.
    I did extensive research on the rollable/foldable solar chargers last August: Brunton, Global Solar Sunique, Goal Zero and Powerfilm. All had either 3 year, or 2 year warranties, in the case of Brunton (IIRC).

    The reason for this is that the thin wiring between the cells are not all that durable over the constant folding/rolling cycling that they encounter and they break sooner, rather than later.

    Rigid panels have glass and glass breaks, but their warranties are usually 10 yrs at 90% rated output and 25 years at 80%.

    Since I only have those two rigid panels, I can't comment on the longevity of the portables, but the warranties aren't all that long, if you look into them and that's done for valid reasons, I"d assume?

    Chris
    Convoy: S2, M1, M2, Fenix: P1D, PD32, HL30, ET: D25C Ti, SF: 6P, ZL: SC-600, Klarus: P2A, Jetbeam: BA-20, Icon: Rogue 1, L3: L10, Xeno: E03, ShiningBeam: I-Mini, Olight: i3s, SWM: D40A, M11R, V11R, Maglite: 6Ds, MMs, Solitaires, LaCrosse BC-700, Maha C-9000, XTAR VP2, MP1S, WP2 II, NiteCore i4, v2.

  13. #13
    Enlightened
    Join Date
    May 2013
    Location
    Southern California
    Posts
    95

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by lightseeker2009 View Post
    Hi everyone.I want to keep a car battery at my camping site.
    Unless you are rich and are willing to trash an SLI (starter, lights, ignition) battery very fast with those deep discharges, then you'll need at least a hybrid dual-purpose marine battery. You don't mention if you are actually intending to start a car with it when you are done. Are you?

    I will use it at most once a week and will tap at most 30 to 40 amps out of it.
    That means that you'll have to have at least DOUBLE that in overall capacity, (50% SOC after discharge - any further damages the battery, and some gear will not run well under 12v when you have reached that 50% SOC). Get the 20-hour discharge rate. If all you have is the "RC" rating, then multiply that by .6 to get in the ballpark at 80ah or more.

    What is the minimum size solar panel that will put back this amount of power into the car battery over a period of 6 days?
    Bad idea using maintenance charge levels of current to actually charge, especially longer than a period of 2 days max. All the time that you are below a full charge, the battery will be sulfating almost as much as it is getting recharged. In addition, a deep discharge really means that you need at a minimum C/12 to about C/8 to *really* charge, and not just put a superficial surface charge on the battery with a dinky little panel or maintainer.

    As for recharging fast enough to avoid sulfation (the natural process that all LA batteries do when not fully charged), plan on no more than 2 days to get it done from a 50% SOC. Otherwise you'll be "walking down" the capacity faster than you know it by not providing a decent charge level. (stratification, along with sulfation plays a part here also if we're still talking a wet-cell, and not something like a sealed AGM.

    How FAST are you trying to pull that 30-40 amps? A minute - an hour, a few days? Also what is actually your load and how are you powering it? Are you running nothing but 12v gear, or are you using inverters (msw or psw?) and are those loads inductive motors that might trip your inverters no matter what?

    Realistically, we also don't know your location which will help determine your solar-insolation hours. These are different from just visible daylight hours. A simple example is that solar insolation means that the sun is strong enough to actually do some good and get the rated output from your panels - typically between the hours of 10a to 2pm - but this varies depending on your location.

    Search for "solar insolation chart". Some governmental charts may be hard to read, whereas some solar vendors have easier to read charts where you look up your city, and can find the high summer, low winter, and average hours. If you want to give yourself some headroom, use the low winter values.

    Let's assume you have 4 hours of solar insolation in the summer. With a 2-day maximum, that means 8 hours available for charging. To replenish 40ah, at first one might think they would need an 80watt 12vdc nominal panel that puts out about 4.5a at best. BUT, chargng is not totally efficient, so lets add 15% to that. Somewhere between a 100 to 120 watt panel with a 10a Morningstar pwm controller on an 80ah approx hybrid marine battery would be my first starting point assuming that much solar insolation is actually available for a 2 day charge.
    Last edited by IonicBond; 06-08-2013 at 01:37 AM. Reason: solar insolation chart

  14. #14

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by ChrisGarrett View Post
    I did extensive research on the rollable/foldable solar chargers last August: Brunton, Global Solar Sunique, Goal Zero and Powerfilm. All had either 3 year, or 2 year warranties, in the case of Brunton (IIRC).

    The reason for this is that the thin wiring between the cells are not all that durable over the constant folding/rolling cycling that they encounter and they break sooner, rather than later.

    Rigid panels have glass and glass breaks, but their warranties are usually 10 yrs at 90% rated output and 25 years at 80%.

    Since I only have those two rigid panels, I can't comment on the longevity of the portables, but the warranties aren't all that long, if you look into them and that's done for valid reasons, I"d assume?

    Chris
    Chris not only am I familiar with the companies that you listed but I have actually used products from most of them. These foldable panels are not as flimsy as you may think. And with a little bit of tinkering you can make them a lot stronger. Now if you are talking about the rollable PowerFilm those are encased in some sort of material (almost like a laminate/epoxy)and are very rugged. I’ve seen numerous holes punched right through them and they still work.

    And you are comparing apples and oranges. Without a doubt if you have a stationary nonremovable set up, the rigid panels are the way to go. But if you have a mobile solution then they are not as durable as you think. And I guarantee you if you broke the panels by stepping on them dropping them or whatever that 20 year warranty would not cover it.

  15. #15
    Flashaholic* ChrisGarrett's Avatar
    Join Date
    Feb 2012
    Location
    Miami, Florida
    Posts
    2,050

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by Knight_Light View Post
    Chris not only am I familiar with the companies that you listed but I have actually used products from most of them. These foldable panels are not as flimsy as you may think. And with a little bit of tinkering you can make them a lot stronger. Now if you are talking about the rollable PowerFilm those are encased in some sort of material (almost like a laminate/epoxy)and are very rugged. I’ve seen numerous holes punched right through them and they still work.

    And you are comparing apples and oranges. Without a doubt if you have a stationary nonremovable set up, the rigid panels are the way to go. But if you have a mobile solution then they are not as durable as you think. And I guarantee you if you broke the panels by stepping on them dropping them or whatever that 20 year warranty would not cover it.
    I specifically mentioned that the warranties on all four brands are three years or less. That tells me something, doesn't it? Sure, people can mod things left and right and improve on them, no doubt, but the foldable panels don't have the warranty that the rigids have, if both are used normally and as intended.

    Nobody's expecting me to get warranty service on my rigids if I drop one of them on my way down the stairs.

    Those warranties are kind of short and the companies are doing that for a reason, don't you think?

    Whether the foldables end up working well past those three (or two) years, I can't say, as I went with the rigid setup, but those warranties were part of the reason I didn't pull the trigger on a PF 30w panel...it was just too short for me at that price.

    Now, to be fair to myself, I wouldn't be folding and unfolding it all that much, so those wires wouldn't get abused, as they would if I were out in the field using the panel everyday.

    Chris
    Convoy: S2, M1, M2, Fenix: P1D, PD32, HL30, ET: D25C Ti, SF: 6P, ZL: SC-600, Klarus: P2A, Jetbeam: BA-20, Icon: Rogue 1, L3: L10, Xeno: E03, ShiningBeam: I-Mini, Olight: i3s, SWM: D40A, M11R, V11R, Maglite: 6Ds, MMs, Solitaires, LaCrosse BC-700, Maha C-9000, XTAR VP2, MP1S, WP2 II, NiteCore i4, v2.

  16. #16

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by ChrisGarrett View Post
    I specifically mentioned that the warranties on all four brands are three years or less. That tells me something, doesn't it? Sure, people can mod things left and right and improve on them, no doubt, but the foldable panels don't have the warranty that the rigids have, if both are used normally and as intended.
    The key phrase here is “used normally and as intended”, but the rigid panels have a different use and intention then the foldable panels. So you are comparing apples and oranges.

    Quote Originally Posted by ChrisGarrett View Post
    Nobody's expecting me to get warranty service on my rigids if I drop one of them on my way down the stairs.
    So then you have to ask yourself a question. If you use them under the intended conditions that the foldable and rollup panels would be utilized how long would they last?

    Quote Originally Posted by ChrisGarrett View Post
    Those warranties are kind of short and the companies are doing that for a reason, don't you think?
    Because their intended purpose is a harsher environment therefore their lifetime will probably be shorter. Again apples and oranges

  17. #17

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by AnAppleSnail View Post
    Urgh. I was just wondering why there is no folded and unfolded weight. Not enough coffee in the world...

    Hours of sun in a campsite are usually much less than on a house rooftop. Most solar guides tend to assume that you are able to place the solar panels away from or above trees. I know that in dappled shade, my solar yard lights have about 1/10th the runtime of the ones in full sun. I do not know how things are in California, but a forested area in the mountains may have 12 (Peaktop) or 6 (Valley bottom) hours of sun in summer. This will be further cut by shade and imperfect panel aiming.

    For what it's worth, a bigger solar panel (That you can afford, and that won't be stolen) will almost always make you happier than a smaller one. And if a $200 solar panel will make you 10x happier than a $100, maybe it's worth that jump. However, plan on a coulombic efficiency (Energy in vs. Energy Stored) of about 1.6 on the lead-acid battery. If your charge controller is 85% efficient, then:

    "I want (40amp*hours x 12v)=500W*h per week."
    "I need to put (500W*h * 1.6) = 800W*h in per week, or 120W*h per day."
    "I need to gather (120/0.85) = 150 W*h per day for my charge controller."
    "For my region I need to de-rate the solar panel's output by (x)."
    "My good, strong sunlight there is (2, 4, 6, 8, 10) hours per day when I'll use this. That gives me the rate the panel should gather energy."

    Actually with a good AGM battery, coulombic efficiency is much closer to 110%, worse if it is much colder. At the upper 10-15% of the capacity, that drops into the 130-140 range, but over the capacity of the battery, closer to 110. A good deep cycle regular flooded in the 120% range, and same for a GEL battery.

  18. #18

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by ChrisGarrett View Post


    60w of goodness and I'm in Miami, so I get a lot of solar hours down here and I agree that most people assume too many S.H. when they're thinking things through. Unless you want to babysit your rig and I'm in a condo, bigger will be better because it will be faster, IMO. Together, those two 30w with hardware weigh in at ~2kg/11#, but moving up to the 40w panels, things start adding up, when dealing with rigids.

    You can find the milspec, foldable 62w PowerFilms, but they're over $800 the last time I checked this past August. Rigids are heavier, but more durable, have longer warranties and those pictured above are mono-crystaline, so a bit more efficient than the polys and CIG/Thin Films portables.

    Also, as semiman mentions, you have controller and charger inefficiencies, so you can never assume 100%. I don't think that my Morningstar SS-10L has a 30% loss, but I can see the controller and any of my battery chargers getting close to that number. Figure on 75% useful output when calculating this stuff and you should be close to reality.

    Doing a SLA/AGM, you only have to deal with say...half of that number, becuase that Morningstar SS-10L IS a battery charger, but there's still going to be less than the full pie going in.

    Also, the smaller controllers have certain limits to how big a battery they can charge and I don't think that they're meant to charge up a totally dead car-type battery, if I remember the manual correctly, so keep that thought in mind when putting something together.

    Anyhow, it was a fun project to do and I think something like my rig, or a nice size foldable panel, are necessities where I live and I'll be waiting during this hurricane season, but I'll be ready!

    Chris

    30% loss that I mentioned is due to the fact of voltage mismatch between the solar panel and the battery, a problem with all PWM controllers. Unavoidable without going with a MPPT controller.

  19. #19

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by jasonck08 View Post
    Uhhh... Thanks for the condescending response. The information I provided is accurate, yet you suggest disregarding everything. I did not say that hours of sunlight = hours of energy. Days during the summer are 14+ hours long in some places... ~8 peak hours is fairly common on a long summer day in some locations... http://www.pveducation.org It obviously depends on the environment. Where I live we get the 2nd most sunlight out of any city in the US.

    Also I see you mentioned he is in California, but I don't see any information in his post for that. Where did you get that information from? Or are you confused, and saw my location, instead of his?



    I think that would be probably if you plan on using a lot of the batteries capacity every day. It sounds like the OP just needs a small panel to trickle charge the battery over the course of 6 days.


    Sorry, but your response was not accurate, even for your location when one consider that not every day or week is perfect.

    You can point me to PVEducation.org but I have years of doing this including resource modelling in must work situations not to mention having designed a high performance MPPT controller and putting up my systems in many locations.

    If he went with your suggestion, the OP would have ended up with an undercharge and likely damaged battery.

  20. #20

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by IonicBond View Post
    That means that you'll have to have at least DOUBLE that in overall capacity, (50% SOC after discharge - any further damages the battery, and some gear will not run well under 12v when you have reached that 50% SOC).

    As for recharging fast enough to avoid sulfation (the natural process that all LA batteries do when not fully charged), plan on no more than 2 days to get it done from a 50% SOC. Otherwise you'll be "walking down" the capacity faster than you know it by not providing a decent charge level. (stratification, along with sulfation plays a part here also if we're still talking a wet-cell, and not something like a sealed AGM.

    That 50% figure is mainly a rule of thumb for best usage. Batteries will start sulfating at 75% of charge, but they do rapidly sulfate the more discharged they get. Saying it needs to be charged in no more than 2 days at 50% is not accurate. Sure you don't want to leave it for weeks or months at 50%, but a few extra days is not going to make an appreciable difference in capacity to a reasonable quality battery.

    You don't really need a charger that is going to charge at C/8 or C/10 either though that can be more ideal. You will still get reasonable battery life with a lower charge current.

    What really does matter is termination, hence the suggestion for a good quality charger. Many cheap chargers terminate at too low a voltage and they terminate as soon as a certain voltage is reached, and don't hold the voltage at that point long enough to truly fully charge the battery and prevent sulfation and reverse some of the short term effects. You can get the Sunsaver to terminate at a higher voltage and even for AGM batteries I would highly recommend it.

    I don't know what you mean by a "superficial" charge. To some degree, a charge is a charge, though high charge rates introduce beneficial stress. Again, what is often most important is a termination at a truly fully charged state working to remove the initial effects of sulfation. Keep in mind the last part of the charge of a lead acid battery is typically at quite small charge levels, i.e. <C/50 or even <C/100 rates.

    I have systems running >5 years with daily cycling (10-20%) and going down below 50% state of charge and often unable to get anything much past C/20 (or worse) due to weather conditions on a fairly regular basis. However, when they fully charge, they "fully charge", with a proper termination voltage and current profile.


    That said, to the OP, solar panels are cheap now, batteries are not. The advice to buy the biggest panel practical makes a lot of sense.



    Semiman

  21. #21
    Flashaholic* ChrisGarrett's Avatar
    Join Date
    Feb 2012
    Location
    Miami, Florida
    Posts
    2,050

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by SemiMan View Post
    30% loss that I mentioned is due to the fact of voltage mismatch between the solar panel and the battery, a problem with all PWM controllers. Unavoidable without going with a MPPT controller.
    Actually, I just did a little research and I found out that with smaller arrays such as my 60 watter, a MPPT controller might actually be less efficient than a good PWM controller, due to the increased computer processing power and other transitor dohickeys found in many MPPT controllers! They take more power to operate, is the theory and that is power that's not going into the battery (batteries).

    I do see the 17.5v>14.5 volt issue that you mention, but as one link pointed out, that's 14.5/17.5 = .83, so in that case, it's 17%, whereas MPPTs are upwards of 92-95% with larger arrays.

    Anyhow, thanks for your posts, as I enjoy reading and learning about this stuff.

    Chris
    Convoy: S2, M1, M2, Fenix: P1D, PD32, HL30, ET: D25C Ti, SF: 6P, ZL: SC-600, Klarus: P2A, Jetbeam: BA-20, Icon: Rogue 1, L3: L10, Xeno: E03, ShiningBeam: I-Mini, Olight: i3s, SWM: D40A, M11R, V11R, Maglite: 6Ds, MMs, Solitaires, LaCrosse BC-700, Maha C-9000, XTAR VP2, MP1S, WP2 II, NiteCore i4, v2.

  22. #22
    Flashaholic* Sub_Umbra's Avatar
    Join Date
    Mar 2004
    Location
    la bonne vie en Amérique
    Posts
    4,756

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by ChrisGarrett View Post
    ...Also, as semiman mentions, you have controller and charger inefficiencies, so you can never assume 100%. I don't think that my Morningstar SS-10L has a 30% loss, but I can see the controller and any of my battery chargers getting close to that number. Figure on 75% useful output when calculating this stuff and you should be close to reality.

    Doing a SLA/AGM, you only have to deal with say...half of that number, becuase that Morningstar SS-10L IS a battery charger, but there's still going to be less than the full pie going in....
    I love the Morningstar SS-10L but if you locate it more than 24" from your battery and don't use the largest cables that may be used with that unit you are hosing yourself and your battery.

    This isn't Rocket Surgery.

  23. #23
    Flashaholic* ChrisGarrett's Avatar
    Join Date
    Feb 2012
    Location
    Miami, Florida
    Posts
    2,050

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by Sub_Umbra View Post
    I love the Morningstar SS-10L but if you locate it more than 24" from your battery and don't use the largest cables that may be used with that unit you are hosing yourself and your battery.

    This isn't Rocket Surgery.
    How does 12ga Vampire Wire CCC (continuous cast 'four nines' copper) audio grade wire, grab ya?

    I'm only pushing at best, 3.5A through it from the panels, so I'm not too worried and I'm pretty much under 24", as well.

    I think that you're exagerating a bit, but I understand some of the issues with having wiring that is too long.

    Rock on bro.

    Chris
    Convoy: S2, M1, M2, Fenix: P1D, PD32, HL30, ET: D25C Ti, SF: 6P, ZL: SC-600, Klarus: P2A, Jetbeam: BA-20, Icon: Rogue 1, L3: L10, Xeno: E03, ShiningBeam: I-Mini, Olight: i3s, SWM: D40A, M11R, V11R, Maglite: 6Ds, MMs, Solitaires, LaCrosse BC-700, Maha C-9000, XTAR VP2, MP1S, WP2 II, NiteCore i4, v2.

  24. #24

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by ChrisGarrett View Post
    Actually, I just did a little research and I found out that with smaller arrays such as my 60 watter, a MPPT controller might actually be less efficient than a good PWM controller, due to the increased computer processing power and other transitor dohickeys found in many MPPT controllers! They take more power to operate, is the theory and that is power that's not going into the battery (batteries).

    I do see the 17.5v>14.5 volt issue that you mention, but as one link pointed out, that's 14.5/17.5 = .83, so in that case, it's 17%, whereas MPPTs are upwards of 92-95% with larger arrays.

    Anyhow, thanks for your posts, as I enjoy reading and learning about this stuff.

    Chris
    Yes that would depend on the MPPT controller. Some of the "worst" ones do not even turn on until you hit a few watts, 5 on one I measured. This is not big controller either, but 15-20amp versions. Some will behave like PWM, or at least shunt controllers at low power levels so you may get a PWM like controller from say 0-5 watts, and then an MPPT controller above 5 watts. In terms of quiescent losses, most are not too bad, 0.5 watt or so overhead. With a 60 watt array, you probably would see some advantage in practical applications, under 20watts, not likely at all.

    14.5V would generally represent a battery that is >=90% charged. At 50% SOC and charging, especially with a large battery and smaller panel, it would not be unreasonable to see a 17.5/12.5 differential or 28.5% loss. Of course, under full sun, the panel would get hot and its voltage drop. Then again, at 14.5 when the charge is tapering off, the "potential" voltage on the panel for the required charge current would be higher.


    Semiman

  25. #25
    Flashaholic* Rexlion's Avatar
    Join Date
    May 2009
    Location
    Tulsa
    Posts
    630

    Default Re: Charging a car battery via a solar panel

    With solar panel prices being so (relatively speaking) low nowadays, it doesn't make sense to go "minimum" wattage. I'd say get at least 40W, but 60W or 80W would be better. I recently bought a 75W panel from SolarBlvd for under $100, and a Morningstar PWM controller for about $25. Pretty affordable!
    ___________________________________
    ==A 3D photography nut, turned flashaholic==

  26. #26

    Default Re: Charging a car battery via a solar panel

    Thanks for all the advice and responces.
    I was asked what and how much at what time.
    I only want to run a few lights. Ampdraw will be 7-8 amps at most. 5 hours max usage at a time, one night per weekend.

    A generator might be a better, and cheaper option but they make so much noise. So much so that you will not sleep as good as you should. So it can only be used during the day. But I also thought about getting a fast charger in the 30 amp or so range. Then I can charge the battery in one or two hours with the generator in daylight hours.
    Will such a fast charge on a weekly basis be bad for the battery? How fast can you charge a deep cycle battery and a normal car battery without shortening their lifespan?

  27. #27
    Administrator Norm's Avatar
    Join Date
    Jun 2006
    Location
    Australia
    Posts
    9,235

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by lightseeker2009 View Post
    A generator might be a better, and cheaper option but they make so much noise.
    A better and cheaper option may be charging batteries at home to take with you.

    Norm

  28. #28

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by lightseeker2009 View Post
    Will such a fast charge on a weekly basis be bad for the battery? How fast can you charge a deep cycle battery and a normal car battery without shortening their lifespan?
    PB does not like to be charged fast. It depends on the discharge state of the battery but most smart car battery chargers will typically take 14 hours to do the job once it’s been discharged to a level where it will not start a car. As others have mentioned you might want to switch to a different format then a car battery.

  29. #29

    Default Re: Charging a car battery via a solar panel

    Quote Originally Posted by lightseeker2009 View Post
    Thanks for all the advice and responces.
    I was asked what and how much at what time.
    I only want to run a few lights. Ampdraw will be 7-8 amps at most. 5 hours max usage at a time, one night per weekend.

    A generator might be a better, and cheaper option but they make so much noise. So much so that you will not sleep as good as you should. So it can only be used during the day. But I also thought about getting a fast charger in the 30 amp or so range. Then I can charge the battery in one or two hours with the generator in daylight hours.
    Will such a fast charge on a weekly basis be bad for the battery? How fast can you charge a deep cycle battery and a normal car battery without shortening their lifespan?

    Good deep cycle batteries (especially AGM) with a good charger do not mind at all being fast charged. They even like it ... can potentially lead to less sulfation.

    I am not sure what types of lights you are using, but if you are not using LED lights, that may be the easiest upgrade. 7-8amps at 12volts -- 80-100 watts = 6000+ lumens of warm white light is quite a bit for a campsite! You may be able to cut that 7-8 amps down to a couple of amps.

    I have a 50 watt panel and a 50AH battery that gets used for camping. That charges cell phones, runs an IPAD, powers the lights at night, runs a portable DVD player and that is with daily use. If there are several bad days of weather, battery may get a top-up in the vehicle on one of the "sanity" day trips.

    Semiman

  30. #30
    Flashaholic* Poppy's Avatar
    Join Date
    Dec 2012
    Location
    Northern New Jersey
    Posts
    2,143

    Default Re: Charging a car battery via a solar panel

    I found that a ceiling bounced xml emitter @ about 100 lumins, lights my kitchen fairly comfortably.
    I believe that pretty much any 18650 XML light that is regulated to put out 200 lumins will do so for 5-7 hours depending upon the battery.

    A handful of flashlights, and batteries may be all that you need, and you won't have to be concerned that your nice solar unit doesn't evolve to grow a set of legs during your week's absence.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •