Using Green Pre PSU as FETboy PSU? (and why you shouldn't do it)

[fucanay]

[quote author="Ptownkid"]The other route is to what matta said and use one secondary and center tap of a higher voltage xfmr.[/quote]

I think this is the best idea for this. The regulator just gets way too damned hot. 14-16 volts is a lot to regulate down. I would definitely prefer to be only doing half of that or even a bit less. I'm having a serious problem with the fact that these transformers spit out so much more voltage than they are labeled. It kind of makes using the secondaries in series impossible without a huge heatsink. Bah.

Matt

 

[kato]

I had to drop in and find out why a thread titled "Using Green Pre PSU as FETboy PSU?" is now 5 pages long.

This is a good learning thread and will be great help to future labbers trapped in PSU hell. I was glad to find the LM317 calculator exists. I admire that you worked out a solution with the parts you had on hand rather than buying extra stuff to make it easier. I would award a "true DIY spirit award" to you, if there was such a thing.

Where did you get the Fetboy PSU schematic?

I'm gathering you created it from PeterC's original and just chopped out the parts you didn't use. I'm thinking it would be perfect for Neve builds since they don't require a bipolar supply. And also future fetboys which are now on my radar. If you're reasonably sure the schematic is error-free, I'll try to build one from your schematic.

Thanks for documenting your work. It's the first +24v & +48v PSU I've seen around here (i.e without the -24v.)[/i]

 

[fucanay]

The only issue I think I'm having, is that the Regs still get too hot. I could take the easy way out and just throw a big old heatsink on it, but I would rather figure out how to drop the voltage after the bridge and before the regulator. So far, I'm not having much luck figuring that out other than I need to put in a series resistor, but I'm not entirely sure how that is supposed to work. I'm not sure what value to use and I only had a 470R and 100K in a 2 Watt. Is there such thing as a 2 Watt trimmer? That would be cool to have in here so it wouldn't matter if the transformers If anyone want to help me figure this out, we could have a pretty damned good PSU here.

And somebody really needs to make boards like this for the Neves and the Fetboys or anything else that needs +24 and +48. Maybe I should do it. I'll need to learn how to design boards first though.

Matt

 

[3nity]

You know i'm working on my Fetboys with a Spectrasonics in the same 2U rack and i planned to use the same technique as yours Matt.

My transformer is a 12V-0V-12V but i'm not sure anymore.

Thank you.

 

[kato]

[quote author="fucanay"]The only issue I think I'm having, is that the Regs still get too hot. I could take the easy way out and just . . .[/quote]

The best solution for the long term longevity of the unit is to start with the right transformer, give those poor regulators a break.

You could use voltage dropping resistors but they'd be dissipating a lot of heat and wasting a lot of power.

 

[fucanay]

[quote author="kato"][quote author="fucanay"]The only issue I think I'm having, is that the Regs still get too hot. I could take the easy way out and just . . .[/quote]

The best solution for the long term longevity of the unit is to start with the right transformer, give those poor regulators a break.

You could use voltage dropping resistors but they'd be dissipating a lot of heat and wasting a lot of power.[/quote]

I don't know how much more right I can get. I mean, it's a 12-0-12 wired in series to get 24, but it's actually putting out 28.7, so it pushes it up just a bit too much.

 

[kato]

[quote author="fucanay"]
I don't know how much more right I can get. I mean, it's a 12-0-12 wired in series to get 24, but it's actually putting out 28.7, so it pushes it up just a bit too much.[/quote]

I understand. A 12-0-12v would seem to be correct.
But earlier on this page you say "14-16 volts is a lot to regulate down." And I would agree. 28 down to 24 should be fine - but 40 down to 24 seems like a lot.

You can make do with voltage dropping resistors or just a big ass heatsink with no problems I'm sure. But for future builds, it's worth considering post-rectification voltage. The right transformer may actually be 18v or 20v, rather than 24v.

Also worth noting: the toroids I've bought from Amveco and Antek skew high. They sometimes measure a full 3v higher than their stated rating.

 

[studiosteve]

Matt. You’ve persevered and won the PSU battle. Congratulations. I’m thankful that it wasn’t me. Thanks to everyone else for the heavy lifting while I was elsewhere.

I’ve just read the top of the first post on this thread and seen your solution. And I’ve gone to JLMs site and looked at his wares. So I can say yes, that certainly is a way to go. And I guess the best way to go.

But........, then you go on in the post and say that you did finally get the Green PSU card to work

Well my problem is that I’ve already gone and purchased the Green PSU card & components. I’ve had everything on a back burner for about a year now (including a Fet-Boy Kit), and now I’m ready to start (I have a ruptured disk and time on my hands).

So does the middle part of your post that says that you CAN get a Green PSU to do the job still stand? And is that the final solution for the Green PSU choice?

Thanks again for everyone’s hard work.
Steve