Managing variable voltage of solar panel PV to charge battery

So I bought 2 of these panels and connected them in parallel. I checked their open circuit voltage and it comes to about 7V in full sunlight.

The cheap battery chargers take 4.5-5.5V and the panel outputs from 4 to 7V.

How can I stabilize the voltage to be 5V from range of 4-7V? Also what is a good homemade way to measure maximum current that the panels are capable of?

pangu:
So I bought 2 of these panels and connected them in parallel. I checked their open circuit voltage and it comes to about 7V in full sunlight.

The cheap battery chargers take 4.5-5.5V and the panel outputs from 4 to 7V.

How can I stabilize the voltage to be 5V from range of 4-7V? Also what is a good homemade way to measure maximum current that the panels are capable of?

Maximum current is with a short circuit. put your VOM in current measurement position to measure AMPS and see what you get.

Your 7V measurement is "open circuit" voltage. You will not have open circuit with your battery charger. Measure the resistance of the input to your charger and put a resistor close to that value across the output of your solar panels and then measure the voltage.

Paul

Simple shunt limiter, voltage greater than 5.1 is "wasted" in the 10 Ohm R (about 0.4W in this case).
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Hi,
I know that you already bought does solar panels but sometime there it is a better solutions. What about one of the attached link. It will give you a battery backup when there it is not sun and it is water proof. Also it will put out USB 5 volts output. Just a recommendation. Maybe it is too late.
http://www.ebay.com/itm/Waterproof-300000mAh-Portable-Solar-Charger-Dual-USB-Battery-Power-Bank-F-Phone-/162346499410?var=&hash=item25cc9afd52:m:mmboHnfeBlxpJeeehFODbmQ

There is no way that the battery linked in reply #3 stores 300 Ampere-hours of charge!

Avoid any seller who makes such nonsensical claims.

That may even exceed the amount of energy available in the equivalent volume of gasoline.

FYI, the folks at Tesla apparently call roughly that amount of energy a "brick".

...nonsensical claims...

Much stronger words come to my mind. Your restraint is appreciated. :slight_smile:

tauro0221:
Hi,
I know that you already bought does solar panels but sometime there it is a better solutions. What about one of the attached link. It will give you a battery backup when there it is not sun and it is water proof. Also it will put out USB 5 volts output. Just a recommendation. Maybe it is too late.
http://www.ebay.com/itm/Waterproof-300000mAh-Portable-Solar-Charger-Dual-USB-Battery-Power-Bank-F-Phone-/162346499410?var=&hash=item25cc9afd52:m:mmboHnfeBlxpJeeehFODbmQ

I like doing dyi and learning how things work.

Paul_KD7HB:
Maximum current is with a short circuit. put your VOM in current measurement position to measure AMPS and see what you get.

Your 7V measurement is "open circuit" voltage. You will not have open circuit with your battery charger. Measure the resistance of the input to your charger and put a resistor close to that value across the output of your solar panels and then measure the voltage.

Paul

So making voltage divider? The post under yours is also adding zener. I'd like to understand how it would work.

I have not yet bought battery charger. I'm thinking about buying pre made battery bank, it will be less hassle and it already got battery and charging circuit.

Perhaps they mean microamps but used the m instead of the µ in translation :smiley: That would be a more realistic 300mAh

No, its called fraud.

The photo shows 20,000mAh on the back of the unit which is also probably nonsense, but
not quite so stupidly out.

If you go to the *fine print, you will see this
"*Manufacturer's Nominal Capacity: 300000mAh; Actual capacity: ~18000-20000mAh."

Which equates to --You might get 10,000mAh...maybe.

I like this selling point as well
"Meet an emergency: When you go outside or power cuts, you also can use your mobile phone with solar energy."

I want one of THOSE solar panels. Actually, 100 of them might just power my house.

ok, after getting some time to do more research I've checked the specs of the chargers ICs and the common one is TP4056 which has –0.3 – 8V rating, if It would be greater than 8V, I think that I'd use DC-DC step down converter

MarkT:
No, its called fraud.

The photo shows 20,000mAh on the back of the unit which is also probably nonsense, but
not quite so stupidly out.

Power bank capacities are already a bit of a scam since it based on the nominal capacity of the battery cells inside, not the amount of charge it can deliver to another battery. The "charging ability" needs to be derated by maybe 50% to cover the conversion loss.

This isn't just an online problem though. I bought a "10,000 mAh" battery bank from Microcenter. When I cracked it open, the LiPo had 8000 mAh stamped on it. A small lie, but still a lie.

For some reason, battery sellers on Amazon and ebay are horribly and blatantly fraudulent to a much larger degree than I've seen with other electronics products on there. I don't understand why.

Jiggy-Ninja:
For some reason, battery sellers on Amazon and ebay are horribly and blatantly fraudulent to a much larger degree than I've seen with other electronics products on there. I don't understand why.

Not just battery sellers.
I just received a bunch of 6watt downlights from China.
Cracked one open, and found 3watt worth of smd LEDs inside.
The 'transformer' that came with it delivered 265mA with a Vf of 9.75volt to the LEDs.
That works out to 9.75*0.265= 2.58watt.
More than a 50% lie.
Stupid tactics, because if I had known they were <=3watt I would have ordered the (more expensive) larger ones.
Leo..

Because they know that 99.95% of the general public has no concept of "mAh", they just look for the biggest number for the lowest price.
Like the 6 HP air compressors that ran on 120VAC that the "home improvement" stores used to sell, the only data on the motor was "120 volts", the 6 HP came from the 35 Amps the 1 HP motor drew when starting.