Powering the calculator from the USB port

[HPMike]

I understand that if I connect the DM42 to my PC via the USB port that it will get power from the USB connection and will automatically switch to a higher clock speed. So, can I safely connect the cable to my iPhone charger, or will this damage my calculator ?

[rprosperi]

I understand that if I connect the DM42 to my PC via the USB port that it will get power from the USB connection and will automatically switch to a higher clock speed. So, can I safely connect the cable to my iPhone charger, or will this damage my calculator ?

No matter what the "official" reply is, why would you do want to do this, and feasibly hurt the DM42? How many really long calculations do you do that needs that much speed?

If you need that much raw calculating power, I'd connect it to a PC/Mac using your USB cable.

[HPMike]

My PC is turned off most of the time and I mostly use my iPad for web surfing and whatnot. In fact, I’m writing this reply on my iPad right now and my PC is far away from where I’m sitting. As to speed, I do have some calculation intensive programs that can run for hours on a slower machine.

[rprosperi]

My PC is turned off most of the time and I mostly use my iPad for web surfing and whatnot. In fact, I’m writing this reply on my iPad right now and my PC is far away from where I’m sitting. As to speed, I do have some calculation intensive programs that can run for hours on a slower machine.

I guess I can at least see why you asked, under those circumstances. I also have to admit that it did take me a few attempts to understand the phrase "PC is turned off most of the time...".

The DM42 is MUCH faster than a 42S, but not sure if it could turn hours into seconds at any speed. And if the calculations are that extensive, are you really waiting to see an answer? I'm not ridiculing here, I'm just curious about how other folks use calculators. Finally, I would have guessed that needing to do math that intensive would make you want to turn the PC back on...

[Walter]

I understand that if I connect the DM42 to my PC via the USB port that it will get power from the USB connection and will automatically switch to a higher clock speed. So, can I safely connect the cable to my iPhone charger, or will this damage my calculator ?

Disclaimer: the following is strictly at your own risk.

If you're interested, take a voltmeter and measure the open circuit output of your charger.
If you've no idea what that is, keep off and stop.
Else if you find it exceeds 5V, keep off and stop.
Else I'd regard it being an applicable power source.

Warning: I'm no electrical engineer, I'm a physicist.

[HPMike]

The output from my iPhone charger is 5 vdc 1 A, which is the same as the USB charger for my HP Prime. However, those chargers are meant to recharge the batteries inside the devices as well as power them, whereas it will only power the DM42, so I’m not sure that matters. I’m also not an electrical/electronics engineer, which is why I wanted to ask this question rather than risk damage even though it seems like it should work.

[Walter]

The output from my iPhone charger is 5 vdc 1 A, which is the same as the USB charger for my HP Prime.

Is this printed anywhere or did you measure? Please follow the steps given above.

[HPMike]

Yes, it is printed on the chargers and yes, I do know what open circuit voltage means. FWIW, I just measured the output from the iPhone charger and it is 5.09 vdc.

[grsbanks]

5.09V seems within tolerance to me. The tolerance is 10%, so that's 4.5V to 5.5V.

Also, a common misconception about the output amperage is that the charger will supply that come what may. It won't. It means that the charger can supply up to 1A if that is what's demanded. It does not mean that the charger will force 1A through the circuit.

[Walter]

Following good ol'elementary electrical rules, voltage output of such a source will decrease when current increases. Thus, no problem with this particular power source.