TREAD help

[ucbEE]

I am thinking of building a TREAD for my Millet Hybrid. From Tangent's website, it seems pretty advantageous to use a AC-DC wall-wart as the power source. Can anyone recommend me a cheap wall-wart that with the specs for the job? Also, what's a good enclosure for the TREAD?

 

[n_maher]

Tangent's site has two good (and cheap) AC-DC wall warts listed in the parts section. I chose the MT7171 (DigiKey part #, about $10) which should work just fine for a Millett, both voltage and current specs are just fine. Depending on what you've got for an enclosure the TREAD could fit right in there - see my recent PIMETA thread - if not it wouldn't take much to house. Fully populated I think it's about an inch tall, 2 inches long and 1" deep. I'll double check those measurements for you tomorrow. But it'd probably be a waste to put it in a separate enclosure, it really shouldn't the source of any noise as far as I can tell.

HTH,

Nate

 

[Megaptera]

Basically just look for an AC adaptor that can provide enough current and the proper voltage, and has a plug that's the right size for whatever jack you've got, and you're set. If you're like me at all you probably have a huge stash of wallwarts in all random voltages, and you might find something usable there even. But the voltage and current ratings are the important things: you'll need to know those before you can pick out an adaptor to use.

And as n_maher says, the TREAD board is tiny and probably won't interfere with other circuitry. Generally you want to put PSUs in seperate enclosures because transformers can induce hum, but with a wallwart you're doing that anyway.

 

[ucbEE]

Thanks for the replies guys. I am putting the TREAD in a seperate enclosure solely for convenience's sake. I currently have an Elpac 24v which I though about using with the TREAD but I was under the impression that the resulting voltage wouldn't be high enough. Won't it drop to something like 22v? If that is sufficient, I should just be able to run the TREAD off of the Elpac right?

edit: Does anyone know if one of these will fit in the smallest hammond case?

 

[rreynol]

Quote:

Originally Posted by ucbEE Thanks for the replies guys. I am putting the TREAD in a seperate enclosure solely for convenience's sake. I currently have an Elpac 24v which I though about using with the TREAD but I was under the impression that the resulting voltage wouldn't be high enough. Won't it drop to something like 22v? If that is sufficient, I should just be able to run the TREAD off of the Elpac right? edit: Does anyone know if one of these will fit in the smallest hammond case?

I don't think that it will easily fit. I'd be concerned with the height of the large cap on the tread board as well as the height of the heatsink. With a little bit of ingenuity, I'm sure you could fit it nicely into one of the smaller hammonds.

 

[n_maher]

Quote:

Originally Posted by ucbEE Won't it drop to something like 22v? If that is sufficient, I should just be able to run the TREAD off of the Elpac right?

Or sell the Elpac, and buy the crappy wallwart I mentioned above, which as I've got configured puts out 24V at the TREAD's output. Total cost would be almost nothing and you'd have a much nicer PS. Or run the Elpac through the TREAD and see how much it drops, which should be much.
Quote:

Originally Posted by ucbEE edit: Does anyone know if one of these will fit in the smallest hammond case?

I don't think so, even flopped on it's side. Plus, I have a special hatred for the smallest hammond so I hardly ever think about using it

. And if it were me, I'd try to avoid having multiple enclosures, unless you want to be able to move the PS between amps.

N

 

[Jam_Master_J]

My TREAD is 24V in and 21.25V out.

 

[n_maher]

Quote:

Originally Posted by Jam_Master_J My TREAD is 24V in and 21.25V out.

Have you tried adjusting the trim pot? Or did you jumper it?

 

[rreynol]

What I'm curious about (and maybe someone else can chime in on) is this situation. If you are using a AC/DC wall wart rated for some current output @ 24VDC and the regulator is going to have a voltage drop associated with it, how is it that the regulated output can be adjusted up to 24V? I would think that the maximum regulated voltage would be somewhere around the DC input - the drop across the regulator (also minus any other voltage drops). I havent measured the regulated output of a loaded tread board. Is this the case? Is the maximum regulated voltage output under load less than 24V even if unloaded, you can adjust the trimpot to 24V out? If it is, then that would make sense to me.

 

[Megaptera]

What happens is that if you see an unregulated wallwart rated for 24VDC, that's the rating under load. If you just measure straight from the plug, unloaded, it's going to be a couple volts higher -- that's where the regulator's voltage drop comes off of, in a sense.

 

[Jam_Master_J]

Quote:

Originally Posted by n_maher Have you tried adjusting the trim pot? Or did you jumper it?

Yep, and it seems to have absolutely no effect. I've never getten a measurement more then 3 mV off from the average no matter the setting.

 

[n_maher]

Quote:

Originally Posted by Jam_Master_J Yep, and it seems to have absolutely no effect. I've never getten a measurement more then 3 mV off from the average no matter the setting.

Something's not right then. Mine did nothing for an entire section of adjustment and then all of a sudden it started to change. Did you run it from stop to stop? Most trim pots like this will emit a small click when they are at the end of their range. I'd suggest turning it one way all the way to the click and then running it through the full range while checking the out put voltage. Maybe you already have, in which case I stand by my statement that something is not right.

N

 

[Jam_Master_J]

Oh ok, I haven't tried that much turning. I gave it basically a full rotation on both sides of the starting point and nothing changed it. If this isn't working what should I be testing I wonder?

 

[n_maher]

Quote:

Originally Posted by Jam_Master_J Oh ok, I haven't tried that much turning. I gave it basically a full rotation on both sides of the starting point and nothing changed it.

If you used the standard value from Tangent's parts list or got the kit you've got a 25 turn trim pot!

I'd say mine did nothing for the first 10 turns and then started to adjust.

HTH,

Nate

 

[Jam_Master_J]

25 turns

?! Well that's actually kind of a relief. I'll give it a try tomorrow (my TREAD is at work).