Rather than reinvent the wheel

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Discussion Overview

The discussion revolves around the design of a 12 VDC to 24 VAC converter for a consumer product related to solar panels. Participants explore various approaches, including existing designs and components, while considering cost and efficiency factors.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using an off-the-shelf 12VDC to 120VAC inverter combined with a 120VAC-to-24VAC transformer as a potential solution, noting the availability and cost-effectiveness of these components.
  • Another participant raises concerns about the complexity and cost implications of using a transformer, especially for a consumer-grade product, emphasizing the need for cost engineering.
  • A participant calculates that 300 watts at 12V would require handling 25 amps of input current, suggesting the need for a high current step-up inductor or a high-frequency transformer.
  • One participant proposes developing a non-ground referenced output by using a buck or boost regulator followed by a pulse width modulator to achieve the desired voltage output.
  • Several participants mention the possibility of contacting manufacturers to create a custom 24VAC model based on existing designs, indicating this may be a simpler route for commercial purposes.

Areas of Agreement / Disagreement

Participants express multiple competing views on the best approach to design the converter, with no consensus reached on a single solution. There are differing opinions on the practicality and cost-effectiveness of various methods proposed.

Contextual Notes

Participants highlight limitations related to cost, component availability, and the complexity of the design process. There are also unresolved assumptions regarding the specifications and requirements of the converter.

Who May Find This Useful

Engineers and designers involved in power conversion, electronics design, and those interested in solar energy applications may find this discussion relevant.

Phrak
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I'm tasked with designing a 12 VDC (from lead storage batteries) to 24 VAC (peak to peak, sinusoidal, and unregulated) 300 Watt converter. This will be a consumer quality product--something to do with solar panels.

Rather than completely reinvent the wheel, I thought I could find something close online. I've only come up with goofy amature designs. One block might be a 12V to -12V inverter. I haven't found a low voltage efficient power converter for this yet. Is there anywhere I can go for professional quality schematics for this?
 
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I'll do a little searching, but one thing that comes to mind is to use an off-the-shelf 12VDC to 120VAC inverter (common, cheap, UL approved), and a 120VAC-to-24VAC transformer (also common, cheap, UL approved). If we don't find a good pre-existing inverter to 24VAC, then this might be a good alternative. Especially if you can come up with some use for 120VAC in the system as well...
 
berkeman said:
I'll do a little searching, but one thing that comes to mind is to use an off-the-shelf 12VDC to 120VAC inverter (common, cheap, UL approved), and a 120VAC-to-24VAC transformer (also common, cheap, UL approved). If we don't find a good pre-existing inverter to 24VAC, then this might be a good alternative. Especially if you can come up with some use for 120VAC in the system as well...

That's an idea, but this gets complicated in terms of cost. This is a consumer grade product that would probably get knocked-off in China in the thousands. My customer would be asking his costomer to gather parts made in China, then ship them back to China for reassembly, then back here to end users. On top, a 300 Watt, 60 Hz transformer is a pretty large chunk of iron. Avoiding low frequency conversion such as 60 Hz conversion is a plus if your an engineer, but the bottom line is really cost engineering. They should cost my customer's customer about 20 dollars a unit or so.

All these practical matters is not something I like to get mixed up with. My job is to know what my customer wants, not what he thinks he wants, and deliver it. In this case I need to design from basic components, up--I need to deliver some useful scribbles on paper.
 
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300 watts @ 12 v = 25 amps of max input current to handle.

That would require a high current step-up inductor or a high frequency magnetic core transformer to step-up the voltage driven by a high current oscillator (20-40 KHz).

Are you considering building a test prototype to see if it works?
 
berkeman said:
I'll do a little searching, but one thing that comes to mind is to use an off-the-shelf 12VDC to 120VAC inverter (common, cheap, UL approved), and a 120VAC-to-24VAC transformer (also common, cheap, UL approved). If we don't find a good pre-existing inverter to 24VAC, then this might be a good alternative. Especially if you can come up with some use for 120VAC in the system as well...

Berkeman has the right idea. Just go from one of these designs and modify for 24VAC output. Also have to size the components right for the power out, etc. Here are a couple of schematic links: (No warranty, real or implied. Your mileage may vary, etc.)

http://www.aaroncake.net/circuits/inverter.asp"

http://www.free-electronic-circuits.com/circuits/12-to-120-volt-inverter.html"

Haven't examined these closely, but they are certainly modified sine inverters.

Here's a link to what seems to be a pretty good design overview with references: http://www.wpi.edu/Pubs/E-project/Available/E-project-042507-092653/unrestricted/MQP_D_1_2.pdf"

One other option, and for commercial purposes, probably the best one, is to simply contact the companies who make these things and have them do a 24VAC model for you. It will be a very simple mod for them to make to an existing, proven design. Good luck!
 
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what said:
300 watts @ 12 v = 25 amps of max input current to handle.

That would require a high current step-up inductor or a high frequency magnetic core transformer to step-up the voltage driven by a high current oscillator (20-40 KHz).

Are you considering building a test prototype to see if it works?

First of all, I got the output wrong. I was just deciding that my customer was nuts and wanted a 24 V rms output rather than what he asked for. Now he tells me I misunderstood. He does want 24 VAC.


For a non-ground referenced output, I was thinking of developing 37 VDC with a buck or boost regulator, then following with a pulse width modulator to chop alternately 0 volts and 37 volts into an inductor in series with the load (at 20 to 40 KHz as you say).
 
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rolerbe said:
One other option, and for commercial purposes, probably the best one, is to simply contact the companies who make these things and have them do a 24VAC model for you. It will be a very simple mod for them to make to an existing, proven design. Good luck!

I'm a company that designs process control and power conversion electronics. I get paid to design.
 
Phrak said:
I'm a company that designs process control and power conversion electronics. I get paid to design.

:biggrin:
 

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