Question 1

Hello! i need to use them with input 28vdc, will this voltage damage the unit? thanks!

Accepted Answer

Anything over 20V will cause these units to shutdown. The original listing (when I bought them) said they had a range up to 24VDC input. None of them worked for me trying to use a 24VDC power supply. I have since come back to rate them and see that they have changed the description to indicate the max input voltage is 20VDC. I wasted my money on them.

Question 2

Which is positive input and which is negative?

Accepted Answer

Look closely,  the ground is attached to ground plane. The positive input is isolated from the ground plane.  It should be obvious.

Question 3

I wanted to solder four 18650 flat top batteries to this. Can i recharge those batteries with this board after they are drained from charging phone?

Accepted Answer

No, this board only works in one direction (high voltage -> 5V). 
You need a Li-Ion/LiPo charger board for recharging 18650 cells. 
E.g. https://www.amazon.com/Makerfocus-Charging-Lithium-Battery-Protection/dp/B071RG4YWM

Question 4

How do i charge samsung galaxy a7 pad with this board? i use large solar panels dc. i don't use ac. i don't need to charge battery. the opposite way.

Accepted Answer

The ac adapter’s turn ac into dc the battery in the phone is DC Just about everything that plugs in the AC converts it to DC for its internal workings televisions radios phones etc. USBs normally put out 5 V DC and 12 V DC you need to find out what your phone uses set the board to that DC voltage level and plug in your USB cable to your phone That’s basically the short and sweet for the actual hook up and all that information you’re gonna have to look on some stuff on the Internet

ASIN	B01HXU1C6U
Best Sellers Rank	#385,983 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #1,711 in Power Converters
Brand	HiLetgo
Color	Red
Customer Reviews	4.4 4.4 out of 5 stars (405)
Input Voltage	6 volts
Manufacturer	HiLetgo
Mfr Part Number	3-01-1126-B
Model Number	HiLetgo-...
Number of Items	1
Number of Outlets	1
Number of Packs	5
Output Voltage	5.1 volts_of_direct_current
Plug Type	NO
Power Source	DC power supply
Unit Count	5 Count

HiLetgo 5pcs DC-DC Buck Step Down Module 6-20V 12V/20V to 5V 3A USB Charger Module

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