I want to power a "suitcase boombox" amp using 4 Li-Ion 18650's. To charge these batteries I'm thinking TP4056, because they're small cheap and have nice charging features.

From what I have read so far that even at first glance having multiple TP4056's with their own DC-DC isolation seems weird, it's alledgedly not a bad way to mitigate some of the battery balancing downsides.

Two questions:

  1. Are there any pitfalls of this approach? Apart from DC-DC isolation (see next question)?

As discussed on the internet and here on EE, to charge the batteries using multiple TP4056's, one needs isolation. Commonly mentioned is the isolated 0505S DC-DC converter. Big downside is that it's only rated for 1W. To get most out of the charging process you'd want more like 5W.

I'm not finding any cheap/small/simple DC-DC buck converters, but I do see some AC/DC 220VAC>5VDC converters that claim to have isolation, such as this one: https://www.aliexpress.com/item/AC-DC-5V-700mA-3-5W-Power-Supply-Buck-Converter-Step-Down-Module-for-Arduino/32451069599.html (or will this burn down the house?)

  1. Do these AC-DC converters provide the required isolation (or how to tell?)

1 Answer 1


From the pictures of the circuit board that looks like it has "functional isolation", but the parts on the underside seem a little close together for me to say that it could have "safety isolation" too. Also that greem film capacitor looks like the wrong type for its location.

So, the batteeries probably won't explode, but it might electrocute you.

  • \$\begingroup\$ Thx for your feedback. Could you elaborate a bit on the "wrong type for its location"? -- I'm thinking to just get a few to see what happens, it's not like they're expensive ;-) \$\endgroup\$
    – svenema
    Feb 2, 2018 at 11:08
  • \$\begingroup\$ beside the transformer is usually a "Y" capacitor (look up "Y capacitor"), and the one they have there doesn't really look like one. \$\endgroup\$ Feb 3, 2018 at 10:33
  • \$\begingroup\$ in the photo I can't clearly see where the copper is and is not, nor can I read the markings on the parts, what you're getting the the best guess of someone on the internet you have never met. \$\endgroup\$ Feb 3, 2018 at 10:39
  • \$\begingroup\$ Ah, yes, I know about them, ok thanks. Has been helpful, stranger ;-). \$\endgroup\$
    – svenema
    Feb 3, 2018 at 13:10

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