Advice for various DC-DC stepdown/up

[duffbeer911]

Hi,
I'm in design phase of a small solar project and looking for some advice powering various DC devices. Rather than having an inverter and going DC-AC-DC I'm thinking of just keeping everything DC. Only thing is I have a few different devices of varying voltage ... 5v, 9v, 12v, 24v. My batteries will be a 12v bank. Is there some kind of predesigned DC-DC bank or junction box of sorts? or should I look at making my own? Or, am I completely on the wrong track and this is not a good idea?

thanks in advance!

[Sunking]

5v, 9v, 12v, 24v. My batteries will be a 12v bank. Is there some kind of predesigned DC-DC bank or junction box of sorts? or should I look at making my own? Or, am I completely on the wrong track and this is not a good idea?

Not well thought out. To start there is no device on the market I know that can take 12 volts input and convert to all the voltages you have listed. It is possible to do it, but takes a fairly complex switch mode converter. A simpler approach is to use a 24 volt input, but you are stuck with the same problem of no known device to convert to all the voltages you have listed although much easier to convert down vs both down and up.

But here is the big challenge or I should say problem. Although a simple series voltage regulator only needs about 3 electronic components to build or about $10 bucks worth of parts is very inefficient. To convert down to 12 volts is 50% efficient meaning for every 2 watts input you only get 1 watt out and the other is burned off as heat. That is the good news. As you convert 24 down to 5 volts efficiency drops to 20% or 5 watts in and 1 watt out with a red hot converter making a space heater. Again a Switch Mode converter is better than 90% efficient but I seriously doubt you could design or build one unless you are an EE wiht Switch Mode Converter design experience

Now you know why most folks just use an inverter and the device AC charger. Makes things simple and somewhat efficient.

[duffbeer911]

Thanks for that very helpful reply. Wow, I did realise there would be loss and some heat but am surprised to find out it would be more lossy than using an inverter. But to me this is good news.... much easier to just buy an inverter and save the hassle.

Thanks

[Mike90250]

You can search Digikey and Newark (electronic component stores) and find individual DC-DD converters, in the voltage and wattage (amps) range you need, with about 90% efficiency. Adding all the extra parts needed for each converter, and you are looking at >$100 for each voltage needed. But it would be efficient. And time consuming to lay out a circuit board for each one, and build it up.

[bcroe]

Dc-dc

These days lots of small size switchers are on Eb*y starting around $3. Build
your system for the main load voltage, and use the above for other voltages.
Most have a common negative input - output wire. I have built a lot of
switchers, but don't bother any more for this small stuff. Bruce Roe