I have a limited electrical knowledge and have a few questions.

I have an Allpowers Foldable Solar panel, which has two USB outputs, and one 18 volt output. I understand that, in full sun at 18V, the panel would be producing 4.44 amps.

I was considering purchasing a 20000mah 'jump start' battery and want to be able to recharge it with my solar panel. I believe this is a lithium battery, although they don't specifically say on their site: https://www.suaoki.com/u10.html

The charging input for this battery specifies the charging input as 15V, 1A. The customer support folks for the battery felt that my solar panel would damage the unit if I tried to charge directly from my panel.

My questions are:

1) Is the problem the excessive voltage in full sun, or, would the problem be the excessive amps, or both?

2) If the problem would be the voltage, would using a buck converter to lower the voltage (to 15V) make it safe to charge through the 15V, 1A charging plug on the battery?

3) Is the excessive amperage a problem, or would the battery draw only the 1 amp that it needs?

4) While I have seen a number of inexpensive converters that would limit the output voltage from the solar panel, I have not found one that would convert 18V, 4.44A to 15V, 1A. Does this type of voltage and amperage limiting converter exist, or is is simply that the extra amps don't matter in this case?

Thanks for any information you can provide on this.

  • \$\begingroup\$ re point 4 are you talking about simple voltage convertors or solar charge controllers? this is one link out of many : photonicuniverse.com/en/how-to-choose/solar-charge-controller \$\endgroup\$
    – Solar Mike
    Commented Jun 28, 2017 at 6:20
  • \$\begingroup\$ Solar Mike on point 4, not just a charge controller (I have similar one). More like DC-DC power supply, where input can be 18V, 4.44A, and then output can be varied to the devices input specification, such as 15V, 1A. I know there are AC power supplies where you can 'dial' the exact voltage and amperage. I guess I need to better understand the first three questions. If it is just getting correct voltage, and the higher amperage doesn't matter, then maybe just a buck converter might work. Just trying to make sure I wouldn't burn up the jump-start battery. Thanks. \$\endgroup\$
    – Larry McD
    Commented Jun 28, 2017 at 6:55
  • \$\begingroup\$ The main problem is that you (a) want to violate the specifications you have and (b) you don't have enough information to understand what might happen. How about buy an adjustable buck SMPS from fleaBay or Amadong, and set the output to 15v? The current will sort itself out. \$\endgroup\$
    – Neil_UK
    Commented Jun 28, 2017 at 7:37
  • \$\begingroup\$ 20000mah? Yeah right. \$\endgroup\$ Commented Jun 28, 2017 at 7:39
  • \$\begingroup\$ Thank you for your responses. I don't want to violate the specs of the battery unit. It also has 2 USB outputs for charging phones, tablets. I'm just trying to understand about the excess current and want to be able to charge this when I'm off the grid. Your answer does help. Thanks. Bruce, that's just what the specs say. I don't have one yet. Your skepticism is probably justified... \$\endgroup\$
    – Larry McD
    Commented Jun 28, 2017 at 8:08

1 Answer 1


1) Voltage. As long as the voltage is within spec, the jump starter will draw as much current as it wants, not more. If the voltage goes over spec, all bets are off.

2) In principle, yes.

3) Not a problem, will only draw what it needs (as long as voltage is ok).

4) Superfluous amps don't matter. They're simply not used.

  • \$\begingroup\$ Thank you Dampmaskin. Your answers helped clear it up for me. I am ordering an 8A buck converterthat will let me set the voltage to 15V. Thank you for the information! \$\endgroup\$
    – Larry McD
    Commented Jun 28, 2017 at 8:12

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