Inverter design

[Badwolf]

Morning,

Not retro-computing, but definitely 'proper' electronics & I'd like some input.

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I've an electric motor scooter. Not the fold-up kids toy style things that are a menace to pavements everywhere, but a Vespa-type thing. Anyway it runs on Li-ion batteries of a nominal 60V (therefore up to 76ish when charged).

I don't use it as much as I used to and storing batteries flat or fully charged isn't optimal.

I figured I might as well build a little circuit up to let me discharge the charged batteries to a good-to-store level, measuring the power output and input so I can estimate their charge level & quantify their capacity after what's now five years of pretty poor storage.

So far, that's just dumping their energy (slowly) through an old incandesent bulb meant for mains voltage.

Why don't I use that power for something useful instead?

TLDR: I'm thinking about building a 230V inverter for a 60-80V DC input.

The inversion itself seems simple enough logically. Power MOSFETs in an H-bridge configuration. But of course, that's a square wave and one at ~70V.

I'd need a roughly 3:1 up-transformer with decent current handling capabilities (let's say I'm aiming at up to kilowatt output) and they don't seem to trivial to find.

Could I wind my own using mains core? Dunno.

What can/should I do about the square wave?

Just idle musing at the moment, but anyone got any great ideas or experience in the matter? :)

BW

[exxos]

Most cheap UPSUs have square wave output which is generally not good. This is why you pay big money for ones with proper sinewave output. Of course you are going to need some fancy electronics to get the timing right to basically emulate a sinewave. Sounds like a big headache to me :(

It probably would just be easier to use a generic off-the-shelf inverter with a high voltage input as possible. I would assume there should be some 24V ones out there. Then have a switch mode to step your 60V down to 24V.

Though by the time you have done all these power conversions then you probably burned up a lot of your wattage anyway.

[Badwolf]

My lad has a 12V inverter and I have a DC-DC converter that I think can do 80->12V, but yeah, I was trying to avoid a nasty intermediate voltage.

That said, it might be worth trying as a starting point to see how warm things get.

This is interesting, though:- https://www.instructables.com/DIY-Pure- ... -Inverter/

His design is 12V, but it uses a module available cheaply enough on ebay for the sine wave bit:- https://content.instructables.com/FOB/O ... XP6I91.pdf

Still doesn't help out with the 70->230V transformer, though.

BW

[Badwolf]

I'm still quite tempted to do this. I think I'll wind my own transformer too. Probably will be terrible, but I quite like the idea of actually controlling the whole shebang from a Pi Zero or Pico or something to have joule (/kWh) counting and support charge & drain modes.

But I spent 15 minutes in the shed yesterday and got shouted at for not looking after the baby enough, so I've decided to buy a dirt cheap (£25!) inverter off AliExpress. Only 300W continuous, but might be worth taking apart if nothing else!

https://www.aliexpress.com/item/1005003468530891.html

BW

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