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1  Using Arduino / General Electronics / Re: Powering an Arduino on: August 04, 2011, 12:42:08 pm
I think what I'm going to try is a 100ohm 10watt resistor between the diode and the caps. I think this will act as a choke. If I graph it out in SPICE, I see the resulting voltage stays between 22.5 and 24.9 voltages - mostly between 24 and 25.

- Mark.

EDIT: Or a 10 ohm may be even better.
2  Using Arduino / General Electronics / Re: Powering an Arduino on: August 04, 2011, 12:19:49 pm
Can we see the diagram annotated with measured (not theoretical) voltages and currents into and out of the regulator.

I'd have to start from scratch to get that. Also, I think it important to *know* what I'm actually measuring.

A "half-wave" rectifier is one and only one diode.

And I stated only one.

- Mark.
3  Using Arduino / General Electronics / Re: Powering an Arduino on: August 04, 2011, 11:19:17 am
Quote
V peak is just north of 39v.
What does that mean? Is that something you calculated?
Is that something you actually measured?  Where?  Under what conditions?  (Loaded?  Unloaded?)

Ok, from what I understand, multimeters measure AC in RMS. V peak is RMS * 1.4, which in this case is around 39.2v. I'm measuring the input AC current at 28v (RMS).

Quote
Even after a rectifier diode, the peak DC voltage will be 39v as well.
Is that what you actually measured, or is that a theoretical assumption?
By "a rectifier diode" do you mean just a single half-wave rectifier?

I'm using a rectifier diode - which is a half-wave rectifier. Rectifiers are nothing more than 1 or more diodes put together.

I think we can assume the same peak voltage after the diode, minus some small percentage drop for the diode itself, as the AC peak.

The peak DC voltage will have little to do with the actual value of the capacitor if you are talking about an un-loaded circuit.

We would be much better off with an actual schematic drawing of the circuit with notations for what the voltages and currents are at various critical points.  A simple annotated schematic (even hand-drawn) is worth at least 10 paragraphs of prose.

I already included one.

No, it does not sound sane that you are getting 39VDC from 13VAC.  Especially if you are using a half-wave rectifier and a simple capacitor-input filter.

Agreed, except I'm dealing with 28v AC, not 13v AC. The 13v (pulsed-DC) is what I measured coming from the diode with no other components.

- Mark.
4  Using Arduino / General Electronics / Re: Powering an Arduino on: August 04, 2011, 10:04:14 am
Ok, I think I may have figured out what's going on. The voltage on the cap makes no difference (as others have stated). The input is 28v AC RMS. V peak is just north of 39v. Even after a rectifier diode, the peak DC voltage will be 39v as well. The fact that I'm using a large 2200uf cap probably means I'm increasing the average DC voltage closer to 39v (peak) from the average coming directly from the diode of ~13v.

Does this sound sane?

- Mark.
5  Using Arduino / General Electronics / Re: Powering an Arduino on: August 04, 2011, 09:33:41 am
Quote
37.7v. I'm drawing 0.18a, so not a whole lot
Yes if it is dropping 37V down to 5V that's 37 - 5 = 32V and with a current of 0.18A it gives you 5.76 Watts to get rid of. No wonder it is shutting down.

I'm using a 12v regulator.

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I'm really thinking I need a 16v 2200uf cap instead of a 35v.
A larger cap won't help here. If you have a 35V cap and you have 37.7V across it then that is probably about to blow as well.

I already have a 2200uf cap, but it's rated at 35v.

- Mark.
6  Using Arduino / General Electronics / Re: Powering an Arduino on: August 04, 2011, 08:27:01 am
I measured the input voltage to the regulator under load this morning and it's 37.7v. I'm drawing 0.18a, so not a whole lot. Also, the regulator shuts itself down in seconds. No, I don't have a heat-sink on it, but I'm guessing it would be too hot even if I did.

I'm really thinking I need a 16v 2200uf cap instead of a 35v.

- Mark.
7  Using Arduino / General Electronics / Re: Powering an Arduino on: August 03, 2011, 07:28:12 pm
Thanks, I'll read up some more. It's a cheap meter, so I have to assume rms, but I could be wrong. The caps releasing max voltage under no load makes sense to me.

I wouldn't worry about it except that the regulator got quite hot under load. I didn't want to risk burning anything, so I immediately disconnected the load. I'll test under load tomorrow.

- Mark.
8  Using Arduino / General Electronics / Re: Powering an Arduino on: August 03, 2011, 06:38:58 pm
I'm measuring just under 13v after D1, disconnected from everything else, and 38v connected. There's something else to consider here I suppose. The multimeter I'm using probably is measturing rms and not peak. The cap is smoothing out voltage so rms will get nearer peak. However, the input voltage to D1 is only 28v AC. I'm really at a loss as to where the extra voltage is coming from. I suppose the multimeter could be measuring rms on the AC side as well and maybe it's peaking closer to 40v.

I need to put this in a breadboard and test further.

- Mark.
9  Using Arduino / General Electronics / Re: Powering an Arduino on: August 03, 2011, 05:26:22 pm
Question, given the above schematic and a 2200uf 35v cap, could I be using too large a cap? I'm assuming the cap will discharge at 35v no matter the input voltage?

- Mark.
10  Using Arduino / General Electronics / Re: Powering an Arduino on: August 02, 2011, 07:46:20 pm
Ok, this is probably not very representative, but I'm not yet familiar with circuit design.

Basically, a rectifier diode feeds two caps, a 2200uf and a .01uf, wired in parallel from the diode to ground. Also connected to diode output is the voltage regulator input and it's output is connected to two more caps, a 47uf and another 0.1uf in parallel wired to ground.

- Mark.

EDIT: I'm guessing I connected something wrong. I'll review my soldering. With only a diode connected, I get a little less than half the AC voltage - which is what I would expect.

EDIT 2: Updated schematic.
11  Using Arduino / General Electronics / Re: Powering an Arduino on: August 02, 2011, 06:44:36 pm
Many thanks for all your suggestions. I created a circuit as described here. however, the voltage feeding the regulator is a bit over 38v. Can someone help a newbie and give me a hint as to what I need to lower that voltage (preferably without a transformer - I'm running out of room)?

Thanks, Mark.
12  Using Arduino / General Electronics / Re: Powering an Arduino on: August 02, 2011, 11:41:02 am
Ok, am I thinking correctly that I could simply get away with a single diode and a large (like 2200mf) cap to replace the rectifier thus reducing the voltage to the regulator? I should then add a small cap to the output of the regulator or do you think the voltage will be smoothed enough at that point?

Thanks, Mark.
13  Using Arduino / General Electronics / Re: Powering an Arduino on: August 02, 2011, 10:07:34 am
I used no capacitors in the build.

- Mark.
14  Using Arduino / General Electronics / Powering an Arduino on: August 02, 2011, 09:43:34 am
I have an Arduino Uno SMD and I recently added an ethernet shield from DFRobot:

http://www.dfrobot.com/index.php?route=product/product&filter_name=ethernet&product_id=52

For the past month or so, before I added the ethernet shield, I was running the Arduino from a 28v AC source using a this rectifier:

http://www.radioshack.com/product/index.jsp?productId=2062581

and this voltage regulator:

http://www.radioshack.com/product/index.jsp?productId=2062600

I tested the voltage going to the VIN pin at ~11.8v DC. All worked wellm until I added the ethernet shield. The combination worked fine for a time (maybe 2 hours) until I noticed the Arduino getting noticeably hot around its voltage regulator. The Arduino is now toast, but I think the ethernet shield is still fine (it responds to a ping still).

Would anyone know what I could have done wrong here to cause this? The ethernet shield has the VIN pin marked as "9V". I'm a little confused by this as I thought the VIN pin could take a range of voltage.

- Mark.
15  Using Arduino / Sensors / Re: Two wire hall effect gear sensor on: July 28, 2011, 12:04:51 pm
Great stuff, thanks! I'll try the latter one suggested. I'm attempting to sense the rotation of a carousel within a jukebox.

- Mark.
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