solar panel and voltage increase help please

Thetruthking

Hi I have 2 solar panels connected in series and they produce about 7.2v to 7.6v, (alone about 3.6v each!) they are rated 20w each, I also have a 50amp solar charge controller, battery, dc to ac invertor..

my question is how can I increase the voltage that the panels are producing from the 7-7.6v to 13-14v so I can connect it to the solar controller to charge the battery? I do not want to have to change the panels as they are good ones that seam to make a lot of power! for example a 50w car headlight bulb,, they light it up fairly strong when connected to the soler panels alone! I just need to find a cheap enough way to increase the output voltage to 14 or so to connect to the controller to charge the battery!

thanks in advance for any help

freddyuk

Buy more panels. You will not increase the voltage from a panel any way you try it. You need 16-18volts off the panels to charge a 12 volt battery.
Frankly you need to rethink your plan. You are getting maybe 2.5 amps from your panels to charge a battery of ?? You will not be able to push the amps into the battery without higher voltage. You need 30 or 50 watt panel or buy another 20w. Sell your 50amp controller (your panels are only 2.5 amps) and buy a smaller one to help the budget.

Thetruthking

the panels produece 14 amps at the moment going by my amp meter, their large panels, about 1m squared,
I don't actually understand the amps and watts etc, I get the voltage and I kno I need at least 14 to charge the battery,
I just looking to know where I can get a step up invertor to take it up to that level!
Im guessing amps is the push behind the voltage? and watts is how much it uses am I right? is their any way to simply work this out?
I post the details on the back of the panel to see what they are rated!

Thetruthking

these panels came in a kit of 10 but I only have 2 so I get one fifth of what is detailed below

ok the info on the back is

BYD Company 10panel kit

Rated max voltage (pmax) 230w
Tolerence +/- 3%
Voltage at pmax 30.00
Current at Pmax 7.67A
Open Circuit voltage (voc) 36.00V
Short circuit current (isc) 8.59A
Max system voltage 1000 vDC
Class A Module

as I only have 2 I get about 1/5 of this info above! I currently at the moment have 7v but I need 14 to charge a battery! I pressure im getting a high wattage from them but I don't know how to work this out
watt vs amp vs voltage I don't get it!
for examply if my battery is 100Ah how long will a 100W bulb last on it or how many amps does it use

freddyuk

Thetruthking wrote: »

the panels produece 14 amps at the moment going by my amp meter, their large panels, about 1m squared,
I don't actually understand the amps and watts etc, I get the voltage and I kno I need at least 14 to charge the battery,
I just looking to know where I can get a step up invertor to take it up to that level!
Im guessing amps is the push behind the voltage? and watts is how much it uses am I right? is their any way to simply work this out?
I post the details on the back of the panel to see what they are rated!

You have 2 x panels at 23 watts each. So the most "power" you can get is 46 watts. The "power" you need to do any thing is watts. Watts = volts * amps. So each panel gives you 3 volts (vmp) and the maximum amps = 7.67 so 3 * 7.67 = 23.01(watts). The panels will never give maximum power and these may be -3% as they are imperfect. (+/- 3%). You have 2 panels connected in parallel so same volts but 2 x amps so 7.67 * 6 = 46 watts.(2 x one panel).
To get more volts you need to connect in series when volts will be 3 x 2 = 6 volts and amps will stay the same = 7.67 so 6 * 7.67= 46 watts. Exactly the same power! Still not enough volts to charge a 12 volt battery.

An inverter converts the DC power to AC power and losses occur. It will convert the DC power into AC power with losses of about 20%. It will not "step up" the power it will actually use some power you have produced to convert to AC.
A 100 watt light bulb uses 100watts and in 1 hour it will use 100 watt hours. To convert that to "battery power" divide by 12 (volts) = 8.33 (amp hours) so the battery at 100 amp hours will run the bulb for 8.33 hours. In fact it will not because again losses occur but in a nutshell that explains it in rudimentary terms.
Never run a battery flat as it will be damaged.

Capt'n Midnight

There are two types of power supply - ones that step down "buck", these are the most common and most efficient, the ones that step up "boost" less common and not as efficient. ( Buck-boost is really two power supplies in series and with the losses of both so not used as much, of curse you can also get constant current supplies but not so good for solar. )



If you are feeling brave and aren't too worried about things catching fire or the wheels falling off
http://www.buyincoins.com/s/boost.html :P

freddyuk

So going back to the original post how are you proposing to get more voltage from 2 x 20w modules to adequately charge a 12 volt battery?
I am fascinated.......and always willing to learn.

Capt'n Midnight

Capt'n Midnight wrote: »

If you are feeling brave and aren't too worried about things catching fire or the wheels falling off
http://www.buyincoins.com/s/boost.html :P

I've one of those, it's an LTC1871 boost converter. I've tested it at about 92% efficiency unless it's dropping out (input variation of 9v under output) in which case it's about 50% and under-voltage. Capt'n's right it's only for the brave, the trimpot's junk and comes off the worm drive. I replaced the first one with the wrong pot (out of stock) and blew a mosfet, replaced the mosfet then blew that. Ordered another one, trimpot failed again so I cut it open and adjusted it from the wiper...working fine now.
You could spend a bit more and get a higher quality one. You need to get the generator at least 0.3v higher than a 12v lead acid battery terminal voltage to get it to accept charge and with a charge termination of 14.4v (SLA) or 14.7v (FLA) you'd need about 18v-22v open circuit.
A 46watt panel is borderline trickle-charge territory, either you have a small battery or demand or I'd recommend going higher. You'll lose (rough figures) 20% power to charge reluctance, 5% to wiring and charge control and 10% to the boost converter, as well as a environmental losses (low sun etc) then a further 20% loss to your inverter on discharge.

There's also the possibility of rewiring the cells to give you a higher voltage with less current, depending on their layout (and if they're individual cells not the amorphous type). Bittova pain to do though and you'd need to reseal them.

Thetruthking

Thetruthking wrote: »

I don't actually understand the amps and watts etc

Ohm's Law Illustrated

Capt'n Midnight

Sir Liamalot wrote: »

I've one of those, it's an LTC1871 boost converter. I've tested it at about 92% efficiency unless it's dropping out (input variation of 9v under output) in which case it's about 50% and under-voltage.

AFAIK lot of the efficiency loss is down to the voltage drop across the diode. Some designs use mosfets instead but that only works for lower currents.

Anyway the big problem is that the internal resistance of a solar panel changes according to the amount of light. Lots of light and it's a low resistance , very little light and it's higher. This extra resistance in series affects the optimum voltage / current at which to extract power and you meed a tracking power controller to match it.

Sticking on a voltage doubler would bypass the optimisation of the MPPC ( maximum power point controller ) so you might as well ignore it and go straight to the battery from the doubler. (maybe an MPCC could change the load on the doubler - but they are also non linear so maybe)


Alternatively you could put the solar panels directly on the 3 cells of the battery (via a diode) and have a timer so half the time you charge one half of the battery. The switching could even be mechanical


If the voltage from the panels had got up towards 11.8V then you'd simply buy an inverter / laptop charger designed to be used on a car cigarette lighter.


BTW is the 7.2 / 7.6 v the ratings or what you've measured with no load ?

The cost of a decent MPPT controller would buy an awful lot of solar modules. For under 600watt solar I'd stick with a PWM charger.
How do you recommend wiring to three cells of the battery? 6 inch nails popping outtov cells 3 and 4? It's not recommended for many reasons. Cell imbalance would be a big one, especially if you load the battery while charging.
You could use two 6v batteries and series link them when you load them breaking the charger I suppose.

You'd hardly need a charge controller at all if it's not reaching 14v under load, just a diode...but then in some cases with small systems when you look at the power loss due to voltage drop across a diode it's more frugal to not have one. That said though it wouldn't make a good charger either.

You could get three boost controllers and have one step up to 10v feeding the next up to 16v to avoid the drop out, then one spare because they're cheap crap that break. Or just a decent boost regulator.

All in all though I think just trade for a more suitable module and be done with it.

Capt'n Midnight

Thetruthking wrote: »

I do not want to have to change the panels as they are good ones that seam to make a lot of power! for example a 50w car headlight bulb,, they light it up fairly strong when connected to the soler panels alone!

have you measured the output ? , because car headlights don't light up at 7V

Thetruthking

Thetruthking wrote: »

the panels produece 14 amps at the moment going by my amp meter, their large panels, about 1m squared,

Are you sure they're only 1/5 of the rating? 1m² is a huge 23W panel .

Can you post a datasheet, label photo or link for your modules?
I think you might have modules for a 24v system. When you tested them was it midday with an unobstructed perpendicular view of the sun on a bright day?

Capt'n Midnight

Sir Liamalot wrote: »

How do you recommend wiring to three cells of the battery? 6 inch nails popping outtov cells 3 and 4? It's not recommended for many reasons. Cell imbalance would be a big one, especially if you load the battery while charging.

The context is it has to be cheaper than buying another pair of panels and "If you are feeling brave and aren't too worried about things catching fire or the wheels falling off "

so maybe Homer Simpson's nodding bird ?

6 inch nails into a battery , that's crazy talk , the acid would dissolve them :rolleyes:


Again getting the right batteries might cost more than extra panels.


you can get voltage doublers based on capacitors in parallel and then in series fairly efficient - but not off the shelf

Capt'n Midnight

Capt'n Midnight wrote: »

6 inch nails into a battery , that's crazy talk , the acid would dissolve them :rolleyes:

First time I tried it I used 6 inch zinc galvanised screws :eek::eek: :pac:

Thetruthking

Thetruthking wrote: »

BYD Company 10panel kit

Rated max voltage (pmax) 230w
Tolerence +/- 3%
Voltage at pmax 30.00
Current at Pmax 7.67A
Open Circuit voltage (voc) 36.00V
Short circuit current (isc) 8.59A
Max system voltage 1000 vDC
Class A Module

Your spec. doesn't match any of these but I think it's the ballpark.
Those are the ratings per module more than likely.
That makes me wonder if your meter is auto-ranging or manual and perhaps you misread the decimal? Two of those panels open circuit in series would make 72VDC and 460W.

What's the charge controller? If this is the case they're optimised for a 24v bank if wired parallel but a good charge controller set to 12v bank should be able to handle the voltage and buck it as required, check the manual just to be sure.

Capt'n Midnight wrote: »

If the voltage from the panels had got up towards 11.8V then you'd simply buy an inverter / laptop charger designed to be used on a car cigarette lighter.

They're nasty little blighters, fires waiting to happen even when they're fused. A dedicated cig. lighter socket in a vehicle is 15A, usually the cheapo extensions you buy are 5A-7A. A typical cheapo inverter model can be 300w = 25A @ 12v. Even if you don't exceed the socket rating the extension might go without warning. Not to mention it's a spring loaded high current plug that will arc if given the chance. Best place for an inverter is hard-wired on overspec-ed cable with aftermarket external protection (usually they don't have a DC-side fuse).

I don't think it's a good idea to go direct from panel to inverter if that's what you are suggesting, a low load condition will likely over-voltage without the battery to buffer.

Capt'n Midnight wrote: »

you can get voltage doublers based on capacitors in parallel and then in series fairly efficient - but not off the shelf

Interesting...might have need of one of those do-fer's myself.

Capt'n Midnight

Capt'n Midnight wrote: »

...you can get voltage doublers based on capacitors in parallel and then in series fairly efficient

Am I missing something here? How would this circuit work for a low impedance high load power application? The capacitors will be constantly draining.

There's some load demonstration at the end. Final 10 mins not relevant..skip away.

Thetruthking

Capt'n Midnight wrote: »

have you measured the output ? , because car headlights don't light up at 7V

yep its 7.62 v right now and I put a H7 car bulb onto it and lights up good :-)

Thetruthking

freddyuk wrote: »

So going back to the original post how are you proposing to get more voltage from 2 x 20w modules to adequately charge a 12 volt battery?
I am fascinated.......and always willing to learn.

I feel the same way! wasn't online for a few days but will read all the comments now and see if I can do anything!

Try a midday reading and get back to us. 7.62 volts sounds about right for this time of day.

Capt'n Midnight

Sir Liamalot wrote: »

Am I missing something here? How would this circuit work for a low impedance high load power application? The capacitors will be constantly draining.

the trick is to switch them very fast so they don't drain much

Ah ok. I'll give it a bash on a single phase alternator I have that's underwhelming me at the moment. I'll let you know if it works...I'm sure I can russle up them gubbins from scrap.

Capt'n Midnight

Capt'n Midnight wrote: »

...switch them very fast...

Well using the AC wave at ~30Hz is just making the situation worse. I might get a micro and use PWM switching from the farside of the bridge and some downstream relay driving but that could take a while. Possibly easier and more fruitful just make a better alternator.

freddyuk

Sir Liamalot wrote: »

Your spec. doesn't match any of these but I think it's the ballpark.
Those are the ratings per module more than likely.
That makes me wonder if your meter is auto-ranging or manual and perhaps you misread the decimal? Two of those panels open circuit in series would make 72VDC and 460W.

What's the charge controller? If this is the case they're optimised for a 24v bank if wired parallel but a good charge controller set to 12v bank should be able to handle the voltage and buck it as required, check the manual just to be sure.

I think you are missing the point here. It is a "10 panel kit" thus the OP has 2 x of the total of 10 ie. 2 x 23wp.

Vis: " Hi I have 2 solar panels connected in series and they produce about 7.2v to 7.6v, (alone about 3.6v each!) they are rated 20w each,"

AND "these panels came in a kit of 10 but I only have 2 so I get one fifth of what is detailed below

ok the info on the back is

BYD Company 10panel kit

Rated max voltage (pmax) 230w
Tolerence +/- 3%
Voltage at pmax 30.00
Current at Pmax 7.67A
Open Circuit voltage (voc) 36.00V
Short circuit current (isc) 8.59A
Max system voltage 1000 vDC
Class A Module


You are going off into the land of electrical wizardry which the OP probably does not understand - I certainly don't and it does not really address the question. But hats off for knowing all that stuff.:)

Bottom line is he has 2 x 23 watt solar panels and needs more than that to charge 12 volt batteries.

I'd be happy to be corrected but something here doesn't add up.
A typical 22v 30watt panel is 0.25m², a 100W panel is 0.5m², 150W is 1m² and 230W is 1.5m².
BYD as far as I can find don't produce anything under 130W.
Doesn't that mean the tolerance is +/- 0.3% too...no way.