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Author Topic: Solar Panel energy to DC  (Read 940 times)
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Azerbaijan
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Hi,

I have DC to DC converter:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=221030281255&ssPageName=ADME:X:RTQ:US:1123#ht_3903wt_1210

And 6v solar panel. I want to have stabile voltage from solar panel so bought this DC-DC module. This module converts 0.9v-5v to 5v. I have tested it with various voltage batteries and output is 5.22-5.75 and this is good. The problem is when i connect solar panel it is not outputs any little voltage and LED light is not lights. I know that solar panel have AC output and that is why i have connected 4 diods to create diod bridge for to get DC output but after this DC-DC module also not worked smiley-sad I want to know how i can make it work, what is the problem in Solar power. Also solar panel output is also 3-4v in low light places.
Let me know please how to conect solar panel and this DC-DC module.

Thanks,
Turkel.
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I don't think you connected the grounds, Dave.
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Quote
I know that solar panel have AC output
They do?
The PV panels themselves will be DC, so where does the AC come from ? (assuming you don't have eccentric AC sunlight in your locality)
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As AWOL says, the solar panels I use are D.C. I am not aware of any A.C. solar panels. They require an inverter to generate A.C. for household stuff.

The solar panels I use require a single diode (or some other circuitry) to prevent draining the battery when there is no light. My solar charger takes care of that for me.

They are not an "on or off" type device. The current and voltage decrease with a decrease in sunlight.
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nr Bundaberg, Australia
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Quote
6v solar panel.
Quote
module converts 0.9v-5v to 5v
Quote
output is 5.22-5.75
Something's not adding up, especially as the open-circuit voltage of that panel is probably way over 6v.

Quote
and this is good
Not for the Arduino it isn't, 5.75 is getting pretty close to the 6v max and way above the recommended.

______
Rob

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Rob Gray aka the GRAYnomad www.robgray.com

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A few points about solar panels:

- They are unlike a battery in that they give out a highly variable voltage, dependent on how much current you try to take from them
- Open-circuit (ie no current, nothing connected except a voltmeter) they'll show a voltage much higher than the nominal 6 volts shown on them
- When under load, the voltage drops considerably
- The "6 volts" printed on the label will only be accurate when you are taking a specified current from them (and assumes they are flooded with light). You should be able to work out the most efficient current by dividing the power rating of the panel in Watts (should be printed on it somewhere) by 6 volts.

To use solar panels, you usually need to have something to store the power and act as a buffer - either a battery or a big capacitor - it's unusual and difficult to run a circuit straight from the panel. Rather than figuring how to convert the solar power straight into 5v, look at powering your circuit from a rechargeable battery or a big capacitor, then look into solar charger circuits to keep the battery / cap charged from the panel.

h
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Solar panels behave like current sources in parallel with diodes (because that's exactly what they are!).  You probably need to stiffen up the voltage regulation to the input of the DC-DC converter with a largish (try 100uF to 2000uF) capacitor across the solar panel - the converter is needing a voltage source to work from (and it takes current in bursts so the capacitor can provide the high peak currents).

Without a capacitor a solar panel's voltage will drop dramatically if you ask for too much current (even for a few microseconds)
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Wow I am impressed at the technical knowledge about PV panels. In the northern hemisphere they are pointed south for fixed installations... This is what I did for nearlyy 20 years and the idea's about Big or Super Capacitors is right on line... Use that panel to charge 2 2V2 4 AH gates cells. The Gates cells are SLA technology and they were an excellent choice for a project that generated 12V @ .2A to charge a 4700 uF cap to activate a latching solenoid for irrigation control. If you are measuring AC then you are in your room or it's night and the panel is seeing street lights... As it was pointed out so accurately they (PV panels) only generate DC and again in the Northern hemisphere in southern cal... they are at peak for 6 - 8 hours a day depending on the season... So a battery is the best choice and SLA or Sealed Lead Acid batteries are the best for utilizing solar technology on a small scale... Those big Nickle Cadmium batteries are best for large scale installations or at least they were 5 years ago... I've been retired for 4 years and my last year was strictly soil measurement stuff. But as usual I digress. 4 Amps taken at .5AH is 8 hours of constant use. IMO

Doc
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Azerbaijan
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Thank you very much guys, till now i am trying to do what you are posted and finally did it smiley
First i have tried this with Capicator and it is not worked but then i have replaces capacitor with 3.7v lipo batterty:
http://www.ebay.com/itm/10x-3-7V-150mAH-RC-LiPo-Battery-Syma-S107-S108-S026-Venus-331-Avatar-Z008-/270935961879?pt=Radio_Control_Parts_Accessories&hash=item3f150ab117#ht_1221wt_976

So the scheme is the plus side of changeable voltage from solar panel comes to zener diod and from diod goes to 3.7 battery and minus side connected directly. Then for usage the another zener diod connected to batter by plus side (vice versa than other diod) and minus of battery side directly to whatever i will power up. So output from battery with diod is the voltage which i use and can increase voltage by the board which i have posted above.

So for now this works perfectly smiley but i don`t know what is happens inside battery. Can battery overcharged ? Because of this scheme can battery life reduced, then what i can do prevent this ?

Turkel.
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nr Bundaberg, Australia
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I see a problem, the panel output is not regulated.

I don't know about Lipos but normal batteries (wet cell, AGM etc) do not like having high voltage applied to them, for example a 12v battery should be charged up to about 15v (bulk charge), left there for a while (absorption) then dropped back to about 13.5 (float). If Lipos are similar then the max voltage applied should be about 5v and then not for a long time.

IIRC the charging regime is even more critical with Lipos than my wet cell example above.

Also I don't see why you need the second diode (the one to the load).

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Rob
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Lipo batteries must not be overcharged otherwise they will be destroyed.
4.2 volts is the maximum voltage that the battery can be charged too, then you need to stop the charging process.
It would be easier to use 3 AA size nimh batteries as these can tolerate overcharging as long as the charging rate
is C/20 or less.
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LiPo batteries must not be overcharged, otherwise they will be destroyed, and destroy whatever is near them in the resulting fire (and possibly stuff that is farther if the fire spreads).  Fortunately, most LiPo batteries have built in circuitry to prevent/slow overcharging.

On the flip side, using a Arduino to monitor battery charging sounds like a really nice application, and you could customize to take the ambient light into account, the battery's charge state, and possibly expected demand.

Overcharging isn't great for NiMH cells either, they vent hydrogen gas and lose capacity.  But they don't catch fire like the LiPo ones.

Further, if you're worried about overcharging, one solution is to run more cells in parallel.  So if you have 4 NiMH cells in series (for about 5V), then you can put another 4 in parallel with those, increase your storage capacity, decrease the overcharging risk, and spread any overcharging damage out over more cells, so each cell is less affected (it's not linear, so each is damaged significantly less than if fewer cells took more overcharge.)  Unless you have one honking big solar panel, a 12 battery array (3 groups in parallel of 4 cell batteries) should be able to take whatever you throw at it.  (Remember that a single "battery" is technically a cell, and when you put one or more together, as in a 9V, you make a battery.)  And you won't have the same voltage levels with more cells in parallel, but a lot more current capacity before the voltage drops too much.  Best way to calculate this all is to do the math, remembering that you charge at about 1.4 C (or 1.4 times the current in = the current out.)  So if you need to fill an empty 1400 mAH hour cell, you need to put in 1960 mA for an hour, or 980 mA for two hours, etc., and that lower charge levels are better in general.  I'd try to stay under 500 mA/hr if you can, so put in enough cells in parallel so that your peak current to the cells, divided by the number of groups of cells in parallel, is under 500 mA.  And if you have too many cell groups in parallel, the problem is akin to having too big a gas tank in a car.  Extra weight and space, but that's really the only downside.

On the regulation, I thought that the power input to the Arduino boards (at least the newer ones) is regulated, so you can put in 6v and it will be regulated down to 5V.  If not, just get a 7805 and a couple of small caps (or a LM317 and the right resistors, but that's more trouble for 5.0 V.)

Good luck with the project, it must be hard to get parts out there in central Asia.

Regards,
Martin
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Martin Melhus
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