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120w, 12v, panel direct connect to 5v usb attempts

J

Juanitto

New Member
Joined
Mar 2, 2024
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14
Location
Andalucia
Hi,

I'm a newbie and I want to direct connect a 120w, 5a solar panel to 5v. 3a usb to charge the devices during daytime.

First attemp was with a 12-24v controller but it get "fried" in the end (don't know why, because I supposed that the 2 usb outputs are also regulators, but seems not):

...and after get "fried" shows like this (the files in the attachement)

The second attempt was to buy these regulators: Youmile 10 piezas DC-DC Buck Converter 6-24V 12V/24V a 5V 3A Módulo de cargador USB Regulador de voltaje reductor Módulo de fuente de alimentación con cable rojo y negro de 24 AWG https://amzn.eu/d/hBSmuCM in order to split the cables from the panel and to connect, say, 4 of them (5vx3ax4=60w, the panel has max 120w), but when I tested one directly on the panel cables it get "fried"! Don't know why because the panel is 12v, 120w, so max 10A! The strange thing is that it works with a usb car charger (lighter plug) in direct connect but why doesn't also work with the regulators which I bought?!? What kind of regulators (better with usb) would you recommend to make a setup with 5-6 usb outputs direct connected to the panel? Guess it is possible since a car charger can do it!

Thanx
 
PV->SCC->Batt->12v to 5v DC Converter (12/24 to 5v 3A USB)
I have one on my 12v system, works fine with a battery in the set up.
 
littleharbor2 said:
If I am understanding you correctly, you do not have a battery connected. The very first thing you have to do with a solar controller is connect a battery. Some controllers will" fried" if you connect solar first without a battery.
Click to expand...
I want to use without battery! The panel is big enough for 5-6usb outputs (I guess), as it works with lighter usb car charger for sure there are some proper dc-dc buck regulators: do you know some? So, without controller&battery, like the foldable one for e.g.
 
I have successfully used a victron 75/15 without a battery. The manual talks about doing this, it does warn that power may be unreliable.

I tried 25w panel to 60 w buck just to see, it will power usb plug fine in full sun anything less than full sun will allow the buck to reduce voltsge to 0.

The Victron with no battery keeps the load output at float voltage setting. As far as I can tell, using a 75/10 is the simplest way to go for your intended use.

I have a $12 10A Renogy pwm which gives a reliable 5V 2A output, but it requires a battery to be attached.
 
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I also successfully put a usb automotive plug directly on the leads of one 25w panel, It does work as it is rated for 24v. This setup didn't seem to charge fast but it was a short test.
 
Another benefit a Victron unit is that if you buy the proper model you can see watts consumed through the load terminal of the scc. This is a great way to test usb cords for intermittent opens or just checking charge speed, or battery capacity of 5v devices.
 
Juanitto said:
My panel (max 120w, 12v): ECO-WORTHY 120W Panel Solar 12V Monocristalino Placa Solar Aplicable para RV, Autocaravana, Barco, Cobertizo, Caravana, Casa, Sistema de Panel Solar Fuera de la Red https://amzn.eu/d/7eRfa6O
Click to expand...
I can't figure out the Spanish. What is the Voc of the panel?

If this is the panel you have, then you need a power converter that can go up to 25-30v with a working voltage of 20v. It is a "12v" panel because it is designed for charging 12v batteries (which need 14v or so to charge). The 20v gives enough headroom to step down to charging voltage.


The USB power converter you linked to has a maximum voltage of 24v. It could be that the 24.5v Voc of the panel fried the converter. try putting a resistor between the panel and the USB power Converter to reduce the voltage it sees. Any small resistor should work. You don't need to reduce the voltage by much. Make sure the resistor doesn't get hot.
 
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DIYrich said:
I can't figure out the Spanish. What is the Voc of the panel?

If this is the panel you have, then you need a power converter that can go up to 25-30v with a working voltage of 20v. It is a "12v" panel because it is designed for charging 12v batteries (which need 14v or so to charge). The 20v gives enough headroom to step down to charging voltage.


The USB power converter you linked to has a maximum voltage of 24v. It could be that the 24.5v Voc of the panel fried the converter. try putting a resistor between the panel and the USB power Converter to reduce the voltage it sees. Any small resistor should work. You don't need to reduce the voltage by much. Make sure the resistor doesn't get hot.
Click to expand...
Wow! I knew that the solar panel delivers not stable or constant electricity, but to label it "12v" while it has more than double it's miskeading for a newbie like me. Thanx for the tip with resistor, I'll try it since I stll have 8 regulators already bought, but can you send me an amazon link with an exemple of such a resistor?
 
Try this: get eight 2.7v zener diode, or one 21-23.5v zener diode. Wire the 8 in series to block 21.6v. Anything above that will bleed to ground. That might be an easier way to protect the power converters. You want a voltage above operating voltage, but below the 24v max of the power converter.
 
DIYrich said:
Try this: get eight 2.7v zener diode, or one 21-23.5v zener diode. Wire the 8 in series to block 21.6v. Anything above that will bleed to ground. That might be an easier way to protect the power converters. You want a voltage above operating voltage, but below the 24v max of the power converter.
Click to expand...
Hi again, sorry my dumbness but I'm not sure I get it well! You reffer at something like in the attached sketch? If so, can you help me please with further infos? Where to buy such a diode and what characteristics should have in order to harvest the entire capacity of the panel without "bottlenecks"? The diode voltage should be max 24, but what about the current? Maybe min 20A should have, ....and what resistence ohm should have? Thanx
 

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Juanitto said:
Hi again, sorry my dumbness but I'm not sure I get it well! You reffer at something like in the attached sketch? If so, can you help me please with further infos? Where to buy such a diode and what characteristics should have in order to harvest the entire capacity of the panel without "bottlenecks"? The diode voltage should be max 24, but what about the current? Maybe min 20A should have, ....and what resistence ohm should have? Thanx
Click to expand...

Electronics store. Also available from Amazon in the USA, don't know if Amazon in Spain does. Search for "zener diode". Maybe some online stores will popup.
 
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