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How to regulate the voltage from USB solar panel ? Answered

Hello,
I got some USB solar panels.
They output 3.5W at 6V each.
I think the usb wire is directly wired to the panel without regulator and without diode like it should be.

I would like to use them to power a usb power bank.

My problem is that I measure output voltage from 3,5 to 6V.
When there is a cloud, voltage is not enough and when there is full sun I get a little too much.
(Is it fine to charge at 6V instead of 5V through USB ?)

I would like to know if there is a simple way to regulate the voltage to 5V and to let the current fluctuate with the sun instead of the potential.

Ideally I would like to keep usb connectors (to avoid soldering, wiring and modify the circuit easily) but any idea is welcome.

Thank you :)







9 Replies

user
iceng (author)2014-09-15

3.5w @ 6v is ==> o.58A max

The best LDO regulator won't function on a mere 1 volt difference and that is at full sun.

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user
iceng (author)iceng2014-09-15

BTW .... I don't think there is an inverse diode there because it would preclude using several units in series to attain a higher voltage without a 2v loss.

Adding units in parallel needs the low forward drop of a schottky diode which will subtract o.4V leaving 5.6V and that ca be shunt regulated by a 5.1 volt Zener diode.

You can improve on the voltage lost by the schottky diodes by using this wonderful circuit ( second pic ) and drop only o.04 volts, allowing the solar collector to work in less light then before !!

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user
MathiasLeroy (author)iceng2014-09-16

Hello,

- I got confirmation that there is a diode bewteen the solar panel and the USB cable.

- When I said 6V, I meant measured at the USB output.

- This circuit looks way overcomplicated. And I would like to keep usb / minimal soldering.

Thanks for your help

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user
iceng (author)MathiasLeroy2014-09-16

Sorry can't help when changing iformation confuses

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user
MathiasLeroy (author)iceng2014-09-16

I totally agree :) Thank you for your help anyway !

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user
MathiasLeroy (author)iceng2014-09-15

I can branch several in parrallel to increase current, this should not be a problem.

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user

I was planning to put 2 or 3 in parallel to get between 1 and 2A.

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user
mpilchfamily (author)2014-09-14

Under a load the total output will be under 6V. Chances are there is a protection diode built into the panel already.

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user

Exact, I just asked the manufacturer.

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