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I'm in the middle of a project and I've recently bought a 26,000mAh portable charger with 4 USB ports on which can each deliver 5V and 4.8A max. In my project, I'm using an amplifier which needs an input of 12V 2A. What can I use to get 12V at 2A from the USB ports on the portable charger?

user2943160
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Doug Hill
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  • Since just one port is able to supply the 24W you need (according to the information you presented), and they all share the same battery anyway, you might as well just use one port and a DC/DC converter. If you're willing to risk your battery pack, you may be able to simply adjust the feedback network on its internal DC/DC converter to give 12V out instead of 5. – Ben Voigt Sep 10 '16 at 15:47
  • Right ok, I had no Idea there was such a thing as a DC/DC booster converter, would it be like this one? http://www.ebay.co.uk/itm/DC-DC-Converter-USB-Step-Up-Boost-Module-DC-5V-to-12V-Power-Supply-Solar-charger-/281128296063 – Doug Hill Sep 10 '16 at 16:24
  • This sounds like a bad idea - and I'd also be suspicious of the supply not really meeting the claimed specs, especially after typical USB connectors/wiring there may well be noticeable voltage drop at such currents. – Chris Stratton Sep 10 '16 at 17:20
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    Rememper that it is likely a LiPo cell at 3.7V so you will only have 8 aH at 12V and with a 2A load you only get absolute maximum of 4 hours of use. Open it up if you can and post a picture, members here could give a more informed view of the battery and internal circuit capabilities and modification possibilities. I suggest you try and get a 12V sealed lead acid battery if you can with a suitable charger. – KalleMP Sep 10 '16 at 19:26

2 Answers2

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5V * 4.8A = 24 Watts.

12V * 2A = 24 Watts

Since no step-up regulator or boost converter can do 100% efficient, you can't do this. Even assuming 90% instead of the typical 80%, that's 24 W * 1.1 = 26.4 W / 5 V = 5.3 Amps in. Half an Amp more than you can provide.

Now if your 12V device can run at a lower voltage or a lower current or both, it's possible. Use an ammeter with the amplifier at full strength to see what the peak current drawn actually is.

Consider getting a smaller or more power efficient amplifier, or a power bank that's designed for 12V and 5V out.

Passerby
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  • Right, okay. I was originally going to order a battery which can provide enough but I was seeing if I could save some money using this. Thanks for doing the math, really helps me :D What If I use a slightly bigger booster, including the inefficiency, you could get it to do the right amount? Or can you get higher than 12v? @Passerby – Doug Hill Sep 10 '16 at 16:23
  • The boost converter isn't the problem, it's your power source, the power bank that's limited to 5V and 4.8W. Boosting to a higher voltage than 12V won't help you. – Passerby Sep 10 '16 at 18:09
  • @Passerby: According to OP, it does 4.8A **each**. That sounds incredibly suspect, but it is what we're told. – Ben Voigt Sep 10 '16 at 18:26
  • @ben I was assuming that's the max out total, based on my experiences and most common power banks. If it can do 19 amps total, that's a different story. Both the lipo cells and the switcher inside has to handle that though. – Passerby Sep 10 '16 at 18:43
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You cannot save money by buying a finished equipment that does not fit your direct power requirement, because the cost of developing of additional converter.

For your power level (12V 2A) I would consider something like a portable jump-start device used in car industry, like this one:

enter image description here

Ale..chenski
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