can a low volt solar panel be boosted to charge a 12v battery!

[bantamcattle]

brain frying a bit on the internet, so i'll throw my idea out to some humans.....<br /><br />i love used stuff and thus its provided this quandary. my audi mechanic friend has a solar panel from an audi roof that was used to power small fans. he says that it is 9v and 30watts. we connected my cheap multimeter to it and it seemed to read near 10v while in strong sun. i'd like to use it to charge my 12v batteries but am struggling to understand if this will work and if so, how.<br /><br />it seems that things like this exist <a href="http://www.ebay.com/itm/Solar-Wind-...pt=LH_DefaultDomain_0&amp;hash=item3a750ae24a">link</a> and i think it does what i need but i also wonder if a smart MPPT charge controller would do this aswell.<br /><br />would it be possible to find a second one of these 9v panels and connect them to double the voltage?<br /><br />any ideas would be appreciated, thankyou.

 

[Mortisha]

I would like to know this answer as well and what is the best solar panels needed to charge up 2 batteries the best? Great question Bandtam Thanks

 

[offroad]

look for VOLTAGE BOOSTER which can convert higher current (AMPERAGE) to a way to charge an item when you have low voltage.

Not sure if you can find a practical solution though.

 

[IGBT]

If you measured 10V on your multimeter with no load (nothing connected to the solar panel), then you will not be able to charge a 12V battery (it probably would be more likely to drain the battery especially if you did not have a blocking diode to prevent this).<br /><br />You could connect two of these panels in series, which would produce 20V open circuit (no load).&nbsp; If they really are 30 watts, then this would be a 60 watt setup which would be too much to directly connect to a battery without some form of overcharge protection.&nbsp; If it were more like, say 10 watts, then you could just connect it to the battery without any sort of charge controller, because the battery could easily handle the trickle charge of 10 watts for 8 hours of sun a day without overcharging (talking regular lead acid car battery here).<br /><br />Other than getting another panel and wiring in series, you could buy or build a simple boost converter.&nbsp; I have built some for a few dollars that will boost low input voltages like 6V into something like 15V for charging batteries.&nbsp; You can do it with a single IC plus a few passives for cheap.<br /><br />Something like these cheap little "One Hung Low" devices out of china:<br /><br /><a href="http://www.ebay.com/itm/LM2577-Boos...pt=LH_DefaultDomain_0&amp;hash=item3f1a5150e3">http://www.ebay.com/itm/LM2577-Boos...pt=LH_DefaultDomain_0&amp;hash=item3f1a5150e3</a>

 

[bantamcattle]

If you measured 10V on your multimeter with no load (nothing connected to the solar panel), then you will not be able to charge a 12V battery (it probably would be more likely to drain the battery especially if you did not have a blocking diode to prevent this).<br /><br />You could connect two of these panels in series, which would produce 20V open circuit (no load).&nbsp; If they really are 30 watts, then this would be a 60 watt setup which would be too much to directly connect to a battery without some form of overcharge protection.&nbsp; If it were more like, say 10 watts, then you could just connect it to the battery without any sort of charge controller, because the battery could easily handle the trickle charge of 10 watts for 8 hours of sun a day without overcharging (talking regular lead acid car battery here).<br /><br />Other than getting another panel and wiring in series, you could buy or build a simple boost converter.&nbsp; I have built some for a few dollars that will boost low input voltages like 6V into something like 15V for charging batteries.&nbsp; You can do it with a single IC plus a few passives for cheap.<br /><br />Something like these cheap little "One Hung Low" devices out of china:<br /><br /><a href="http://www.ebay.com/itm/LM2577-Boos...pt=LH_DefaultDomain_0&amp;hash=item3f1a5150e3">http://www.ebay.com/itm/LM2577-Boos...pt=LH_DefaultDomain_0&amp;hash=item3f1a5150e3</a>

<br /><br />thankyou, this is much help. to know that i hav options with the panel is what i need to know to go forward.

 

[SoulRaven]

They make converters to do this, but why...??? you will spend money on a converter that gives you less amps out... This idea works on paper but in reality it would take days to recharge a 12V battery... you may get lucky to get 2.5 amps/hour in the most optimal sun...<br /><br />Well all you have to do is do a goggle search "convert 9V to 12V" and there ya go to about 500 products to spend your money on...

 

[bantamcattle]

They make converters to do this, but why...??? you will spend money on a converter that gives you less amps out... This idea works on paper but in reality it would take days to recharge a 12V battery... you may get lucky to get 2.5 amps/hour in the most optimal sun...<br /><br />Well all you have to do is do a goggle search "convert 9V to 12V" and there ya go to about 500 products to spend your money on...

<br /><br />i'm not too knowledgeable on the dynamics of the setup and thats one reason i turned to the forum. i'll do some more reading but right off i don't know enough to understand the amp situation you mention. i've mostly looked at my watts used and thus trying to replace those with wattage from a solar panel. i gather from what yer saying that charging a 12v battery with a 9v panel even after boosting the voltage would create an inefficient setup (meaning less efficient than using a more traditional setup of a higher voltage solar panel to charge my 12v batteries)?

 

[SoulRaven]

Yes what your wanting to do is super inefficient and actually sinking any money into it would be, well ya know...

 

[offroad]

the only alternative I can think of is:<br /><br />1)&nbsp; Use the existing solar cells as they are.<br /><br />2)&nbsp; Charge D cell batteries.&nbsp; Which still will take long, but you can get some good rechargeable technology in D cell batteries<br /><br />3)&nbsp; Put them in a 12V container.&nbsp; You can find them.&nbsp; I got a camp fan for 12v that takes a bank of 8 D cells.<br /><br />This will take a long time.&nbsp; And it is likley inefficient.&nbsp; <br /><br />Think more about what you need that 12V for.<br /><br />

 

[IGBT]

Guys, it is not *that* inefficient.&nbsp; From an electrical standpoint, boosting 9V to 14V to charge a battery can be around 80% to 90% efficient with one of these boost converter circuits.&nbsp; So from a 30 watt panel you could get 24 or as much as 27 watts into your battery.<br /><br />But from a cost standpoint, it might be inefficient to buy a converter for the low voltage panel vs using that money to buy a better, higher wattage panel of sufficient voltage.<br /><br />

 

[bantamcattle]

what i figured on doing was using this 9v 30w solar panel with a MPPT charge controller connected to my 2 12v batteries while i wait to find a 2nd one of these 9v panels. once i can find a second one i think i can connect the 2 (in series i believe) to get them to produce at 18v. if i can use a 5$ voltage booster to get me by until a second panel shows up then this seems like a decent option even if i'm running a bit lower efficiency.<br /><br />i guess the big question is, will it run in the 80% efficient range or will it run in the 20% efficient range?

 

[IGBT]

80% range.... unless it was designed by a 3 year old.<br /><br />Edit:&nbsp; The thing that I don't understand, especially about that ebay link I posted for the $4.99 boost converter, is that the chip they use on it costs more than $4.99 by itself.<br /><br />How do the chinese manage to make an entire board, sell it with free shipping, for less than we can buy a single chip on that board?&nbsp; I guess either they use counterfeit chips or something.<br /><br />Here is the chip at Digikey: <a href="http://www.digikey.com/product-detail/en/LM2577S-ADJ/NOPB/LM2577S-ADJ-ND/363661">http://www.digikey.com/product-detail/en/LM2577S-ADJ/NOPB/LM2577S-ADJ-ND/363661</a><br /><br />And here is the data sheet on it: <a href="http://www.ti.com/lit/ds/symlink/lm1577.pdf">http://www.ti.com/lit/ds/symlink/lm1577.pdf</a>