So I'm trying to build a mobile solar charger for camping, mainly for cellphone and some 18650s for my electric cigarette. I'm using:

Should Draw max 36W for 2 Fast charging devices, I can't find a datasheet...



I can not find a Datasheet for the life of me but it says it is rated for up to 50W



Specifications Nominal power Pmax 50 W Voltage at rated power Vpmax 18 volts Open-circuit voltage Voc 21.60 volts Short circuit current Isc 3.05 amps Maximum Power Current 2,78 Amps Ipmax Cell efficiency 18.25% Temperature range -40 ° C / + 85 ° C Tolerance + / -5 % Flexible Solar Cells Monocrystalline Dimensions: 680 x 550 x 2 mm Weight 1.4 kg

As a tech stack, I just connected everything together. I'm coming from a comp sci background so my experience is a bit limited.

At first it looks good, I adjust voltage to 12 V, and my panel delivers between 17-19 V to my converter in midday sun. If I plug in a single slow charging device into USB, converter shows about 0.3 A output at 12 V, like 3.something watts. As soon as I plug in a second device, output voltage drops to 0, nothing charges anymore. The same thing happens when I plug in my phone and the charger tries to quick charge, wtf am I doing wrong?

I need to be able to pull like 12 W (1 A at 12 V) at least for my 18650 charger, or at least charge my phone at 18 W, I never thought I would be able to use the full 50 W, I was hoping for half that, but 3 W? Not even worth taking it really.

  • 2
    \$\begingroup\$ You seem to have linked to Amazon ad pages instead of datasheets which would give proper technical specifications. See what-to-check-for-when-buying-an-electronic-component-or-module for some comments on the importance of this. \$\endgroup\$
    – Transistor
    Jun 19 at 11:34
  • \$\begingroup\$ Place PV panel in full sun. Connecr ammeter on 10A range directly across panel output (this will not harm panel). You should get around 3A. (Panel is rated at 18V, 3.05A.). IF you do not get this then panel is faulty. || Operate converter from a charged 12V car battery. Full converter output should be possible. || See how the two tests work together. || You MAY benefit from a large capacitor on panel output (1000 uF?) but should not be needed. \$\endgroup\$
    – Russell McMahon
    Jun 19 at 12:02
  • \$\begingroup\$ I dont own a car (or car battery for that matter) but I have some Power supplies in the 12-19V range that I would be willing to sacrifice for testing this. Trying to borrow a voltmeter as we speak, will update with results. But from your Advice I recon my setup should work in theory, if everything worked correctly? \$\endgroup\$
    – ceejay
    Jun 19 at 12:13
  • \$\begingroup\$ Panel SHOULD be very ample for task. Owning even a cheap digital multimeter with a 10A range is a very good idea if you do anything at all electrical. (They start from about $US10 equaivalent in NZ). The setup SHOULD work. \$\endgroup\$
    – Russell McMahon
    Jun 19 at 12:23
  • 1
    \$\begingroup\$ The PV is a current source which needs a a much larger low ESR storage cap or battery to drive the voltage converters low impedance input \$\endgroup\$ Jun 19 at 13:47
  1. Would recommend getting a solar-specific converter. That panel can deliver 3A, but that's at 0V (short circuit). The converter may be drawing too much current, seeing the voltage collapse, going into low voltage shutdown for a few ms, etc. A large capacitor across the panel may help but the ideal is a converter with either MPPT or an input current limit or input voltage regulation.

  2. I know the idea of solar power when camping is very appealing, but if you're hiking I would first check how many charges you could get off a power bank with the same weight as your solar panel setup ;)

  • \$\begingroup\$ The panel is rated at ~3A at 18 V. [[ Imp = 2.78A, Vmp = 18V]] \$\endgroup\$
    – Russell McMahon
    Jun 19 at 13:31
  • \$\begingroup\$ No it's not. 3A is the short circuit current. And who knows what the inrush current is when the dc converter tries to charge its capacitors. \$\endgroup\$
    – DamienD
    Jun 19 at 13:34
  • \$\begingroup\$ it says it's rated for 2.5A at 18V ~ 50W I bought a MPPT Charge Controller now. I thought about what you said, but this is actually for a long bicycle trip, almost 3 weeks, and it's also intended to charge 2x 18650 Batteries per day for Electronic cigarette, lights, musik box, and so on. Also the idea was to have a 12V Car Socket to plug in a cooling box for trips to the lake and stuff... \$\endgroup\$
    – ceejay
    Jun 19 at 21:36
  • \$\begingroup\$ @DanielD. Imp = 2.78A \$\endgroup\$
    – Russell McMahon
    Jun 20 at 4:30

Without looking at the specs of the products (as I have to go through many pages for each: please post data sheets). I would guess that the solar panel is not delivering enough amps (current) despite what its maximum is. You either need stronger sunlight on the panel (lenses and mirrors could provide more solar energy), or connect more panels in parallel.

Another possibility is to slowly charge a battery over few hours from the panel and then discharge over short time for larger amps.

edit: maybe also step down to 5v as this is enough for usb and will prevent your phone from trying to charge at 9v (if it uses that standard of quick charge). 5v is the standard for usb. I do not know if it is acceptable to send 12v down usb as I am not too familiar with this.

  • \$\begingroup\$ Im stepping down to 12V because the charger takes 12V/24V. the Charger itself handles the conversion to 5V itself. Panel should give ~2.5amps at 18V, im testing in full sun, and I'm not expecting magic here, but come on, getting 3W from 50W Rated Panel??? Lenses and Mirrors are not feasable for me just like more panels since i would like to fit the whole panel on the back of my bycicle for a trekking tour \$\endgroup\$
    – ceejay
    Jun 19 at 12:01
  • \$\begingroup\$ It's actually in the specs of your panel: it will give you 50W if you draw 2.78A in full sun, but this will collapse to 0W if you increase that current just a bit to 3.05A. Non-linear behavior like this will confuse a converter that's not specifically designed for solar power -- even if the actual load is way less than 50W. \$\endgroup\$
    – DamienD
    Jun 19 at 13:11
  • \$\begingroup\$ try bypassing the 12v converter and supply 5v directly from the initial converter into a usb cable. the 12v converter will expect a largely constant supply. I'd also recommend using a capacitor to even the load. \$\endgroup\$
    – MrOtto
    Jun 20 at 13:14

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