Can anyone recommend a USB current limit circuit for solar panel

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netprince
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Can anyone recommend a USB current limit circuit for solar panel

I have been testing the foldable type usb solar panels lately (see the usb-power section), and I have noticed that several of my power banks try to draw too much current from the panel, causing the panel to crash (voltage drops too low, and power falls off quickly)

https://en.wikipedia.org/wiki/Maximum_power_point_tracking#MPPT_Implemen...

I would love create a 5v USB MPPT type circuit that monitors for this power drop-off, and automatically limits current draw before the panel crashes.  I think this could be quite similar to current limiting in an LED driver, with some different software. 

Does anyone have any suggestions?  Would be pretty neat to re-program a flashlight driver to do this.  I need one that can run at 5v and produces a variable constant current output.

Edited by: netprince on 11/26/2016 - 13:33
will34
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This step down converter is supposedly MPPT and has minimum input voltage of 5V

https://world.taobao.com/item/520823884686.htm?fromSite=main&spm=a312a.7...

bulrush
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What is a “variable constant current output”? Do you want the current to be variable or constant?

StandardBattery
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Panels are passive devices, voltage sag caused by insufficient available power is not a crash, even if it has active components in a regulator or controller. The Power banks use what they need, the best you can do is ensure the USB plug is coded to indicate it is a low power USB port, which may not work since the Power Bank will assume a minimum power capability which still might be above what you can deliver. Get a powerbank that is designed to be driven by solar, get a charge controller that cut off the output to the power bank cleanly at the right point, and possibly route the low power to a storage bank that can use it and feed it back when needed. There is not a general circuit that will work for all loads unless you have a battery bank to fill in when the panel can’t deliver. Just get a solar capable charger, it will harness what it can (which will not be everything). Or add more panels in parallel so you have more power in typical use conditions.

hank
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Quote:
Get a powerbank that is designed to be driven by solar, get a charge controller that cut off the output to the power bank cleanly at the right point

Specific recommendations would be most welcome. I need these for a proper earthquake kit.

Ronin42
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hank, et al.

In my opnion solar panels are “properly” used to charge external batteries (power banks).

for a 5v power bank so far I like the innogie 13400mah it has 4 LG 3350mah cells.

or a different solution is to use a 12v panel to charge a power bank like the ravpower 32000mah. So far its the only power bank capable of running (not only charging but actual running) of my 60w laptop.

It is voltage selectible plus usb outputs.

.04 cents worth

(“It’s good that most people can’t remember their previous lives. Otherwise
things would be a lot more complicated than they already are.”
Ajaan Lee Dhammadharo)

Jerommel
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Of course the panel Voltage crashes.
But it’s about the charging current.
Just hook the panel to the cell only with a series diode (which is probably built in) and a (overcharge) protection PCB if the current doesn’t reach more than advised for the cell.
Otherwise you can use some AMC7135 to limit the current.
(edit) you might want to protect those 7135 with a zener diode, when there is no load on the panel the Voltage will get too high and smoke them.