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Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
So, there I was, doing yet another test-run on my boost converter, charging a duo of 450v 470uf caps. Everything was going smoothly. A couple of seconds after start-up, the light comes on.... I went to check the voltage... 440v. Perfect. I check it again a few seconds later: 439. Then I hear it 'beep' on for a fraction of a second: 442.... 441... 444... eventually climbing all the way to 456 before I shut it off.
Sooo. I crank the thing all the way down, set to stop at 400V. Multimeter time. I eventually find that my 15V regulator is... acting strange. Since it provides 15v to my comparitor, it was my first suspect. So, I plop the multimeter on to find that the 15.2 or so volts turns to 15.3, 15.4,.... and continually rises at about .03 per second. I let it rise to almost 17 volts before turning it off.
Just a bad voltage regulator? I don't have any spares laying around to test... I would have to order more.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I'm assuming your boost converter is not isolated from your +15V voltage. You may be getting crosstalk between the two voltages. I would try running the +15V by itself with nothing else connected to see if it is okay. Also, monitor the input voltage to the regulator. If the input voltage is too low, it might create the same symptoms you are seeing. Make sure you have at least 2V and ideally about 2.5v or more (per the datasheet) headroom.
Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
Thanks for the advice.....
Isolated the vreg... still climbing. But I noticed something. Voltage across my batts seemed to increase as well. I'm starting to think my dmm is screwey. Hmm. Maybe since the dmm has a low battery, it's throwing off readings?
Oh, and I'm using 2 12v batteries, so the input V is about 27v, or +9.5 over min/ -8 under max input V.
Hmmm. Maybe I'll dig around tomorrow and see if I can't find another vreg.
Banned Registered Member #110
Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85
As the battery weakens on Multimeters, their voltage readings may rise. I say may because this is not a guarantee but a most likely to occure event and is Manufacturer and design dependent. Now, practically speaking, every meter I used does show a greater than error voltage when operating off weak batteries.
On to regulators. Isolate it, use dummy resistor loads at low current then high current load, try with and withouth heat sinks, use the correct input and output filter capacitors from datasheet, then make an assessment. If problem persist, can it.
P.S. If not already, do all you can withing the law to get a Digital Scope. You will thank not me but yourself on first usage.
Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
It was my $4 dmm. I replaced the battery and to my surprise, there's nothing wrong with the voltage regulator. In fact, it's working brilliantly, putting out 14.98V constant, no fluctuations.
Registered Member #79
Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
LOL!
*wipes a tear* I'm sorry. I'm just glad I'm not the only person that's happened to. If wouldn't be that yellow $4 one from HF? I did the same thing about two months ago, wasted about 20 min trying to figure out what the heck's going wrong. So I got another meter, and had the same problem. It was the batteries on both the meters.
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15V V-reg wierdness.
to get a Digital Scope. You will thank not me but yourself on first usage.
