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I've noticed the cells are all put in parallel in these devices and it lead me to asking myself what kind of inverter could they be using? Like isn't it a bit inefficient to convert from such a low voltage all the way up there to 120VAC?

Please elaborate and let's discuss, as I am building something similar and I want to know how the 3.7V inverter works

BELSmith
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    "*Please elaborate and let's discuss ...*" Sorry, SE sites are not discussion sites. Ask a specific, focused question that can be answered. The second part of that sentence is fine but it should really be backed up with your research findings. Other information that might be useful in composing an answer would be the specifications and link to a datasheet for the OmniCharge. In particular what current, voltage tolerance and THD you hope for. – Transistor May 08 '21 at 11:03
  • Please read the answer I picked... – BELSmith May 08 '21 at 11:59

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I briefly read the specs on one of the Omnicharge devices. It tells me it will supply 100W of 120/240VAC. That translates to an input of around 30A @ 3.7V. That is not too unreasonable if they choose their mosfets carefully. If we were talking about 500W, then the losses would start to mount up and you'd generally want to go to a higher DC input voltage.

What we're talking about here is I2R losses - going to higher input voltage means less current thus less loss due to resistance of the wiring, battery internal resistance, mosfet on resistance etc.

Realistically, the whole proposition is a bit dodgy. 100W of AC isn't going to power much apart from your phone charger, your laptop charger and your cordless toothbrush. Running a phone/laptop charger via AC is really stacking up the losses. Maybe there's another use case I haven't considered?

Kartman
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  • I'd say Moniters and TVs would be the best use case, for me that is.. – BELSmith May 08 '21 at 11:58
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    Ok, that might get you 5 hours or so of runtime. – Kartman May 08 '21 at 12:05
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    As to how they actually implement the electronics, my guess is a push-pull converter as opposed to a boost or flyback converter to keep the transformer small and efficient to get the 160/320V dc rail then a h-bridge to generate the AC waveform. – Kartman May 08 '21 at 17:17