3.3V on a 3V device?

On 3/8/2010 3:20 PM David Nebenzahl spake thus:

Scratch that business about using diodes. Dunno what I was thinking there (or not thinking) ...

--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

carefully check (with noload and full load) the voltage of the wart. You might be lucky and use it, as long as it stays between ~2.7 and ~3.4 volts, but most warts surprise you in a rather unwanted way, and you better stay away from them....

Parallel diodes don't reduce the voltage drop significantly.

There are diodes that have a much lower voltage drop so one of those might be acceptable.

If it's a switchmode adapter - light as a feather - then it's probably regulated at the nameplate voltage which I assume to be 3.3 V from the subject line. But if you know or can measure the current and its reasonably constant, the resistor will work.

--
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ 
 Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ 
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm 
        | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line.  Or, you can contact me via the Feedback Form in the FAQs.

If you're using a regulator, there shouldn't be a problem. And you can always stick a silicon power diode in series with the /regulated/ output to drop the voltage 0.6V or so.

Does the 3 volt number come from the fact that the camera runs on two AA batteries? If it will work with the Li AA 1.7 volt cells, then you should be ok up to 3.4 volts at least.

Tom

On 3/8/2010 4:51 PM tm spake thus:

The instructions with camera (a Fuji Finepix A205 that I got for $1) specify either alkaline (LR6) or rechargable NH-10 AA cells; since this camera is, what, about 6 years old? I don't think it was made to use LI cells. So it's probably expecting about exactly 3 volts. (The external power jack is marked 3V at 2.5W.)

So do you think 3.3 volts is going to bother it?

To the previous confused respondents to this query, I don't have a wall wart. I was looking at buying a 3-volt one (not 3.3 volts; that's the voltage regulator I have), but I didn't because, well, I only paid $1 for the camera (it works) and I'm a cheap SOB.

--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

How many rechargeable cells does it take? Two? Then it should work properly on two NiMH cells.

Why don't you just use high-capacity rechargeable cells -- which you doubtless already own -- to power it? Are you going to be trailing a power cord?

---- The Lady from Philadelphia

Well, if it will run off of two nicads, that is only 2.4 volts nominal. So, it shouldn't hurt to put one 1N4001 in series with the 3.3 volt supply and drop it down to about 2.6 volts. That would be the same as two charged nicads at 1.3 volts each.

Tom

The fact that the camera uses two cells doesn't mean that it requires a 3V external supply. My old DC215 which uses 4 cells won't work off a

6V battery plugged into the power socket -- the external PSU is 7.5V. There is presumably an internal regulator.

Conversely, some cameras do _not_ have any internal regulation and expect a stabilised supply. But as Sjouke says, cheap wallwarts may not be stabilised and the voltage can rise alarmingly on low loads. People trying to avoid buying the manufacturer's expensive PSU have been known to destroy their cameras.

Is the required voltage (and polarity) given on the camera, probably near the socket? Or tell us the model and someone may know (rec.photo.digital may be a better place to ask).

You may be able to get the correct PSU secondhand on eBay from someone with a dead camera (as long as they didn't kill it as above :-).

Chris

On 3/8/2010 9:21 PM snipped-for-privacy@proemail.co.uk spake thus:

Yes, I thought I'd already written that in this thread, possibly more than once: it takes 3 volts (and says it uses 2.5 watts), and has the polarity marked. So I figure a 1 amp power supply would be about right.

I'm tending to believe that 3.3 volts will be just fine, but maybe I'll wait for more confirmation (or not).

Oh, and I don't intend to use the camera tethered to a power cord: I'd like to use the external power supply to transfer pictures to my computer, to save the batteries.

--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

...

Two alkaline AA cells will provide around 3.2V when new. I'm positive it will work just fine on 3.3V.

Nope.

--
Real life:   Thomas Törnblom             Email:  Thomas.Tornblom@Hax.SE
Snail mail:  Banvallsvägen 14            Phone:    +46 18 444 33 21
             S - 754 40 Uppsala, Sweden  Cellular: +46 70 261 1372

On 3/8/2010 11:17 PM Thomas Tornblom spake thus:

Thank you. I think that increases my confidence level to somewhere around 97.3%.

--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

Most electronic stuff powered by poorly regulated wall warts will survive a 10% +- tolerance. I've been using a 3.3 volt charger on my

2003 Gateway camera for a couple years now with no problems other than the age of the LioN batteries now suffering reduced charge capacity.

There's nothing wrong with the diode route to drop the voltage by a (reasonably) constant amount, but just use a Schottky type, which will have a forward voltage drop of around 0.3 to 0.4v - or just about what you're looking for ...

Arfa

On 3/10/2010 9:48 AM Arfa Daily spake thus:

Can they handle the current (~ 1A)?

In any case, I'm reasonably sure that I can run the camera on the 3.3 volts without fear of damage.

--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

Of course they can. All switchmode power supplies, including those that provide many amps of output, use such diodes as their secondary-side rectifiers ...

Arfa

On Mon, 08 Mar 2010 15:20:07 -0800, David Nebenzahl put finger to keyboard and composed:

Unless the 3.3V regulator is a fixed type, it may be possible to bring it down to 3.0V by changing a feedback resistor. Can we see a photo of the PCB?

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.

On 3/10/2010 7:45 PM Franc Zabkar spake thus:

It's just a TO-220 regulator, for chrissakes. An NTE something something ... don't have it here at the moment, but it's just a fixed 3.3V regulator. So no, not possible to rejigger it w/a resistor.

I'm just going to use it as-is. I don't think 10% overvoltage will hurt the cam.

--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

One assumes that a 3.3V regulator is a fixed regulator (or otherwise the OP would not be having a problem).

Fixed regulators' outputs can be changed, too, but only raised. This is usually done by inserting a Zener diode in the ground-reference line. (CMIIW.)