Is mismatching a desk calculator and wall transformer a problem?

I’ve been unpacking some things that have been in storage and have found a little Canon Palm Printer Calculator that I haven’t used in a while. It can run on four AA batteries or on a DC adapter. The batteries are dead and I don’t have new ones right now so I’ve tried to find an AC/DC adapter for it. I haven’t found the Canon adapter (if I ever had one) but I did find some others. Two of them had connectors which were too small but one fits fine. The adapter which fits has an output of 12VDC and 500mA. The back of the calculator specifies 6VDC and 2.4 watts.

Note that the calculator can optionally print to a paper tape but that’s turned off. I’m sure the adapter has plenty of power especially if not printing. I’m not sure how milli-amps and watts relate off hand (I know it’s a simple formula) but I know the calculater will draw the power it needs. I’m wondering if the 12 volts being double what is called for is a problem.

Since this isn’t an expensive lap top or similar, I briefly tried the “no guts, no glory” approach and tried using the mismatched adapter. The calculator seemed to work as it should (didn’t try the print to paper option). What is the impact of the higher voltage? My guess is either very early overall failure or else a much reduced life for the LCD display. I’m sure some of you have have something more definitive than a guess.

The calculator may have a voltage regulator that will overheat and fail eventually.

Somebody did that with a scale here at work. It worked for a while, but eventually the plug part in the scale burnt out and now we can’t use an adapter with it at all, just batteries.

12V will most likely kill the calculator immediately. The 6V requirement matches what 4 1.5V batteries in series supply, so there is probably no voltage regulation between the power input and the electronics.

Once when I put too much voltage in my label printer, it would partially melt the ink tape and it would stick to the label (the ink tape works like a typewriter ribbon). I don’t think your calculator is thermal, so this probably won’t happen to you.

Was it accompanied with funny smells?

No, actually there were no other symptoms. But it was just a little over voltage, not 200% like here. I only knew because it was spitting out the ink tape.

A voltage that’s too low might not work, but it probably won’t hurt it. A voltage that’s just a little too high will probably work, but might have some odd behavior, and will almost certainly wear out the device quicker than it should. A voltage that’s twice what it’s supposed to be will almost certainly destroy the device immediately.

First up, I am slack jawed in amazement. The whole calculator has an RRP of only $15 or $20 (depending on model.) The AC adaptor seems to be a $6 option, so you probably never had one. We are well into the “how the hell can they sell it so so little money” territory. The time to ask about killing it with the wrong power is worth more than a new calculator.

But as a more general principle. Semiconductor systems like this typically have a hard maximum voltage rating. Operation of the component above this leads to quick, and sometimes instantaneous failure. Double the nominal voltage is usually swiftly fatal. If not immediate, the circuits will be stressed enough that lifetime will be very significantly shortened.
So, there is some possibility the calculator has a regulator that is managing to drop the internal voltage to within limits. For $15 I am somewhat amazed that it would, but stranger things happen. It may be that the 6v supply is only needed for the printer, and the processor is regulated down to something lower, and this is why you get away with it. This will still probably stress the regulator as it will be trying to dissipate very much more energy than it would ordinarily need to. That said, a CMOS processor with an LCD display draws almost negligible current, so it may be OK. Curiously the LCD display is probably pretty resilient to overvoltage, at least within wider limits.

As an example of how sad things get, I have been looking inside a couple of very expensive Lexicon Home Theatre processors. Despite the serious price, and vaunted high end engineering, the systems have no protection for overvoltage. The power supply they used also has no failure protection. And the power supply is permanently on. Eventually a 2 cent capacitor dies in the power supply, and (due to a strange quirk of the PS design) results in the 5v power rail being connected directly to the 15v rail. Thousands of dollars of equipment is instantaneously destroyed and is not economically repairable.

I have a related, possibly off-topic question.

Why didn’t the designers make different connectors to prevent this confusion? I can’t plug a 110V lamp into a 220V outlet, nor can I plug a USB cable into a headphone jack. So why do so many of these adapters use the same connectors?

Generally-speaking, lower voltage electronic devices won’t kill you if you plug a 12vdc transformer into a 6vdc printer so there is less safety regulations and it’s cheaper to use standard size plugs and receptacles.

A 6vdc device wasn’t designed for 12vdc. The device will over heat and it will lead to early failure.

You can check with a Radio Shack-type outlet to see if they have a comparable adapter or check online.

Thanks all. I think I’ll spring for some new batteries. :wink: Interesting story about the Lexicon, I remember that brand from the old days.

Found this on Lexicon in Wikipedia:

I got some new batteries and am happy to report that the calculator works and seems just fine despite my ill-advised experiment. The printer works as well.

My daughter killed her cellphone that way.

$15 for a printing calculator? I can’t even get a good scientific calculator for that little. The last time I looked at printing calculators, they were around $50.

I’ve had it for quite a long time and didn’t recall paying much for it. It’s the Canon model P1-DH V and you can still get it at an office store for $17-18. Can’t beat the price.