solar panel DC current

[ravaka]

I have ordered 4 solar panels that each put out 2.5V at 50mA
I am trying to figure out how to wire them so that I can achieve 5V at 200mA for a small project. If I run them all in series, I get 10V at 200mA right? If I run them in parallel, I get 2.5V at 200mA?

Can I wire 2 of them in series and the other 2 in series, and then run both arrangements in parallel to achieve 5V at 200mA? Or, should I just connect all 4 in series and then use a regulator to reduce voltage from 10V to 5V. Lastly, would a regulator reduce the voltage and amperage? I need to keep the 200mA.

Sorry if any of that doesn't make sense, I only have basic DC skills

Thanks

 

[Analog]

you can only get 5V at 100mA for 4 of them. Two of each in series, then parallel the lot of them.

 

[ravaka]

I have already hooked up 2 panels in series (am waiting on an order for 2 more) and achieved just under 5V. Wouldn't 4 of them in series get me 10V? What is a way to double/quadruple amperage?

 

[rjvh]

What is a way to double/quadruple amperage?

Put the cells parrallel

Robert-Jan

 

[audioguru]

You can get the rated output only at noon on the equator of earth with the solar panels facing the sun. At any other time or location the output is much less.

You get 10V at 50mA if four are in series. If you use a 5V linear regulator then you will have 5V at 50mA. The regulator will waste 250mW.

You get 5V at 100mA if two are in series and are in parallel with another two in series.

you get 2.5V at 200mA when four are in parallel.

You cannot get 5V at 200mA.

 

[ravaka]

thanks audioguru, that makes sense
i am thinking of trying two solar panels, each rated at 4.8V at 100mA. If I run them in parallel, I should get 4.8V at 200mA right?
the battery i am charging with them is a Lithium Ion 3.7V. the standard wall-charger for the battery puts out around 600-800mA. I am hoping my 200mA panels will charge it too, just much slower...

 

[audioguru]

the battery i am charging with them is a Lithium Ion 3.7V.

A lithium battery catches on fire if it is not charged properly. Battery charger ICs:
1) Limit the charging current.
2) Test the voltage and if it is less than 3 1V then a low current is used until the voltage is higher.
3) Limits the voltage accurately to 4.2V.
4) Times the charging and measures the current drop when the battery is fully charged.
5) Turns off the charging when the battery is fully charged.

 

[Willbe]

thanks audioguru, that makes sense
i am thinking of trying two solar panels, each rated at 4.8V at 100mA. If I run them in parallel, I should get 4.8V at 200mA right?
the battery i am charging with them is a Lithium Ion 3.7V. the standard wall-charger for the battery puts out around 600-800mA. I am hoping my 200mA panels will charge it too, just much slower...

Constant current charging at the C/20 or C/100 rate should be safe, but check it. For a 500 mAh battery the C/100 rate is 5 mA.
Charging at the C rate of 500 mA shortens the life of the battery [and they do it all the time].
There is some rate below which you will not get any charging.
BTW, you probably need to charge for X hours to get 2/3 of X hours of service from the battery.

 

[ravaka]

audioguru,
what kind of integrated circuit should I use? would one off of a car charger work? i have a car charger for the device too and could disassemble it. or, can I buy or order one?

Willbe,
what exactly are mAh? i am still learning about some of these things...
let's say my battery is an 800mAh battery, could I charge it with a current of 200mA?

If one of you guys would be willing to sign a confidentiality agreement, I could share my invention with you and get your technical expertise. I think that's what I really need. Contact me privately, my email addy is mss239@gmail.com

 

[audioguru]

audioguru,
what kind of integrated circuit should I use? would one off of a car charger work? i have a car charger for the device too and could disassemble it.

You have a small "3.7V" lithium battery, not a huge 12V lead-acid car battery. They are completely different and their chargers are completely different. Most semiconductor manufacturers (Maxim-IC etc) have a battery charger IC for lithium. It does what is required to stop the battery from catching on fire since lithium is a very active element.

what exactly are mAh? i am still learning about some of these things...
let's say my battery is an 800mAh battery, could I charge it with a current of 200mA?

mAh is milli-Amp-hours. It is how many milli-amps a battery can provide in one hour, but sometimes it is spec'd at less current for 10 or 20 hours for less loss.
Your 800mAh battery might be able to be charged at 1C (800mA) or it might catch on fire. It would probably be safe to charge it at 0.25C (200mA) if the voltage is limited to 4.20V.

 

[ravaka]

A lithium battery catches on fire if it is not charged properly. Battery charger ICs:
1) Limit the charging current.
2) Test the voltage and if it is less than 3 1V then a low current is used until the voltage is higher.
3) Limits the voltage accurately to 4.2V.
4) Times the charging and measures the current drop when the battery is fully charged.
5) Turns off the charging when the battery is fully charged.

Can you give me a link to an IC that I can buy that does all this? I tried browsing through Maxim's site and got a little overwhelmed. Thx again audioguru!

 

[Willbe]

what exactly are mAh?

https://en.wikipedia.org/wiki/Amp_hours

BTW, a watt is a measure of power equal to 1 joule/second, and watt-hours are a measure of energy. It's easy to confuse them. Power is the rate of expending energy.

 

[Externet]

Ravaka - an alternative:
If the correct use of a specialized charger IC is too complex (or hard to obtain) for a beginner, you can connect your solar panels in series-parallel to yield 5V and feed the Li-ion cell with a 1N5335B zener diode in parallel to the cell only while charging, and disconnect the zener while not.
The zener will waste a little power and not allow the voltage to go over the maximum allowed at full sunlight, and will not do much at average sunlight.
There is no absolute need to push to the limits a Li-ion cell for it to hold a decent under 100% amount of charge.
An easier possible source to find the specialized IC to charge a Li-ion cell is inside a defunct laptop Li-ion battery pack.
Miguel

 

[ravaka]

The zener will waste a little power

I'm trying to steer away from any components that will cut down amperage. Does a zener diode regulate just voltage? Or voltage and amperage?

I read more about lithium ion batteries on wikipedia and now understand the need for a constant voltage in order to charge properly. Since sunlight is sporadic in intensity, a diode or IC would probably be necessary.

 

[audioguru]

The charger IC has its max voltage set very accurately to 4.2V and includes a diode to prevent the battery from discharging into the solar panel at night.
A 1N5335 is a 3.9V zener with a minimum voltage (-5%) of only 3.7V. A lithium battery would barely charge. add a diode and the voltage is much too low.

 

[Willbe]

the need for a constant voltage in order to charge properly.

With solar cells having a high internal resistance you might get a constant voltage, more or less, across the battery. At low currents the battery may act as its own Zener.

Nowadays chargers are directed at charging in a big hurry from a voltage source. From existing charge protocols you can reverse-engineer what the battery must be acting like at these charging rates, but I think these protocols are for the fastest possible charge with minimal shortening of battery service life. And the manu. is not particularly motivated to preserve battery life.
Your app. kinda' goes in the opposite direction, so I think a lot of constraints can be relaxed.

If you can e-mail an application engineer at a battery manufacturer, he/she might be willing to help you. Try to get an idealized equivalent circuit, a piece-wise linear math model, for a cell at a low/medium charge rate. We already know what-all precautions are necessary at a high charge rate.

 

[ravaka]

Thanks Willbe, I will try to track down a lithium battery producer...
A question about mAh...
If my battery is rated at 800mAh, and my solar array puts out 100mAh, would it take 8 hours to fully charge the battery??
I agree with you on the diode/IC debate. The IC in a home or car charger is regulating a large current that, without it, could possibly cause leaking/exploding lithium batteries. Whereas, with regard to voltage and amperage, my solar array is already in the ballpark of what the lithium battery needs to charge.
Am I on the right track?
BTW, I have a 4.8V 100mA solar panel hooked up to a device with a lithium battery right now. It doesn't seem to be charging very fast, if at all, thus my amperage may not be high enough. What do you think?

 

[audioguru]

A lithium battery cell must have its charging voltage limited to 4.2V or it might catch on fire. Battery charger ICs make the voltage limit within 1% of 4.2V.

The Ah rating of a battery is its discharge spec. Its charging is not 100% so more charging current is needed than its discharge current by the load. maybe 120% to 140% more charging is needed.

Why not look at the detailed datasheet for the solar cells and for the lithium battery?

 

[Willbe]

If my battery is rated at 800mAh, and my solar array puts out 100mAh, would it take 8 hours to fully charge the battery??
BTW, I have a 4.8V 100mA solar panel hooked up to a device with a lithium battery right now. It doesn't seem to be charging very fast, if at all, thus my amperage may not be high enough. What do you think?

At 100 mA, I'm thinking 1.6 (+/- a wide tolerance) x 8 hrs = ~13 hrs to charge and 8 hrs to discharge.
Battery manufacturers don't seem to be too up front with this efficiency issue.

If you ever get the thing fully charged, you could measure its capacity by discharging it according to the manu's protocol down to some cutoff voltage. Which brings up the +/- tolerance of the 800 mAh value at which you declare that a battery "passes."

 

[Ubergeek63]

https://en.wikipedia.org/wiki/Maximum_power_point_tracker

for the fastest charge from solar you need to be concerned with both ends. a 1AHr lithium can be charged at 1A but need close watching and a solar panel's characteristics vary wildly with ambient conditions also needing close watching.