[tomb]

Agreed. You have nothing "loaded" without the PPA.

 

[tourtelot]

I was thinking about what would constitute dummy load but I didn't come up with anything I thought might be appropriate.

D,

 

[grenert]

100 ohm 10W 5% Wirewound Resistor (2-Pack) - RadioShack.com

 

[tourtelot]

Thanks. I'll pick some up this morning and re-measure the TREAD.

D.

 

[tourtelot]

Wowzer! The TREAD didn't seem very happy with the wire-wound resistor. The output voltage seemed pretty unstable, the unloaded value of the 18VAC supply did not change and the resistor got smokin' hot; way too hot to touch. Of course, the regulator warmed up as well but it never got really hot.

D.

 

[grenert]

So we're all on the same page here:
What is the value of the resistor you used?
Where did you connect it?
Where did you measure voltage, and what was it?

I would expect the resistor to get a little hot; imagine a 6W light bulb.

 

[tourtelot]

When I ASSUME I make an ass of me. So here's what I did.

It is a 100ohm 10W wire-wound from RS. I connected it across the output to simulate a load. I measure the "loaded" VAC at the input to the TREAD and the DC voltage on TP 2 and 3 (the output).

What did I do wrong?

Thanks.

D.

 

[tangent]

P=V^2/R, V=18, R=100, so you made that resistor dissipate over 3 W, which is certainly plenty of warmth. That's well under the resistor's rating, so I wouldn't be worried about burning it up, though in my own dummy loads I put heat sinks on such resistors just to prevent burns to the more delicate nearby humans.

Another application of Ohm's Law is I=V/R, so this resistor caused it to put out 180 mA, well over what you actually need to run the PPA. That makes it a good test.

As for your measurement report, it's a little unclear. What you should be measuring is DC and AC from TP1 to TP3, and DC and AC from TP2 to TP3. This gives four values:

- unregulated DC
- pre-regulator ripple
- regulated DC
- post-regulator ripple

Post the measured values, under load, not subjective impressions, please.

 

[tourtelot]

TP1-TP3
DC 24.6
AC 0.70

TP2-TP3
DC 22.3
AC 0.18

 

[tangent]

I'm going to assume those are all in volts; that is, you measured 0.18 Vac after, not 0.18 mV after. If that's right, one of two things are happening:

- your meter is really low quality, so that this low measurement is below its ability to make useful discernments; or

- the regulator really is putting out a good fraction of a volt of ripple, in which case it's not working right

Can you post hi-res pictures of the build? And, what meter are you using?

 

[tourtelot]

Yes, volts. The meter is a "Fluke 89 IV True RMS Multimeter."

Let me see. "Hi-rez" photos that will go 19.5mb? Those are going to be tough to see.

I am going to put this down for a bit; I may or may not pick it back up again. My interest level is waning quickly, but a sincere thanks for all the help that you have offered.

D.

 

[tourtelot]

Hi Tangent-

I rechecked the values and placement of the components and they all look good. The only difference I see is that the VSET is a 700ohm trimmer. Probably okay.

Just so I am on the same page, I have a 100ohm 10W wire-wound across the output of the supply.

Here's the weird thing. I only get less than one VDC adjustment across the output TP2 to TP3 on the complete VSET range (20+ turns). What could cause this? Does it have anything to do with the "high" amount of AC on the output?

D.

 

[tourtelot]

Double post. Sorry.

 

[tourtelot]

So perhaps I had the 100ohm load resister wired in correctly. I just for fun ran the TREAD with the output wired as follows: VDC+ out through the 100ohm resister and into the plus side of a DVM. The - side of the DVM to the VDC- (ground). Got full control with the VSET and measured the following voltages:

TP3 to TP2
.12mV AC
23VDC

TP3 to TP1
68mV AC
27VDC

Better?

D.

 

[Lifthanger]

in voltage measuring mode your multimeter has a very high resistance.
what you did is put a much higher valued resistor behind the 100 ohm. Which means current will be very low which makes this a bad way to test your tread. effectively its unloaded this way.

remember: measure voltage in parallel and current in series. that way the multimeter wont affect what your measuring.

edit: i have no idea about the tread, but these are basics for multimeter use.

voltage measuring mode: high resistance
current : low resistance. this is why you should never measure current without a load in the circuit. it'll be shorted and kill the fuse or the whole multimeter.