Variable DC input inverter ?

Thread Starter

Externet

Joined Nov 29, 2005
2,240
Hi.
Do you know if such animal exists in the market ? Variable 10VDC to 40VDC input to 120VAC 60Hz , 250 to 400 W output ? Or any trick re-purposing / modifying equipment ? -No batteries involved-
 

MrAl

Joined Jun 17, 2014
11,687
Hi.
Do you know if such animal exists in the market ? Variable 10VDC to 40VDC input to 120VAC 60Hz , 250 to 400 W output ? Or any trick re-purposing / modifying equipment ? -No batteries involved-
Hi,

There are plenty of converters on the market that take a low voltage DC input (like 12vdc) and convert to 120vac 60Hz. The input range you have there though sounds a little wide. I think the normal range is 11 volts to 15 volts or something like that.
To go double that range (up to say 30v) would require the control circuit to be able to cut back more to provide a different pulse width. Of course component ratings would have to increase also to handle the increase in voltage.
The upside is that at 30 volts the input current would only be about half of what it would be at 15 volts.
There may be 11vdc to 24vdc units available I've never needed that though, so I never checked that out, but I know they make products for a 24vdc input also.

In theory you can have any pulse width, which allows a wide range of input voltages, but in practice other things come into play like frequency and rise time and dead time and stuff like that. A work around would be to use a buck circuit on the front end, albeit with a significant loss of efficiency.
 

MisterBill2

Joined Jan 23, 2018
19,370
The application sounds like a Boost mode Supply with a variable duty cycle. That would get you to 120 volts DC, and then a PWM inverter to produce a sine wave, or some approximate version. That circuit would be similar to the very high efficiency engine driven packages that use a variable alternator and smart engine speed control to produce fairly clean AC power.
The military uses a similar package for some equipment that accepts a wide range of input voltages. Not sure if any of it is surplus yet, but it might be.
 

Ian0

Joined Aug 7, 2020
10,236
Of the two usual types of inverter:
  • H-bridge driving a line-frequency transformer using the leakage inductance as a filter, or
  • Boost converter creating a 325V bus (for 230V AC out), followed by a H-bridge to create the AC.
If designed for a 24V input (i.e. 20V to 30V) then the current would be double at 10V input, so the converter would have to be designed for double its rated power. That would make it more expensive, and it would be catering for a fairly limited market.
Some of the more primitive (cheaper) boost-converter types have a fixed ratio boost converter, and regulate the RMS voltage by varying the output duty cycle, so that circuit woudn't be usable.
 

MisterBill2

Joined Jan 23, 2018
19,370
A boost converter taking 10 volts up to even 120 will not be very efficient.
A just plain?? transformer/PWM inverter delivering some higher voltage to convert to 120 AC will be the way to go.
 
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