Power Supply

Everything about 41C 41CV and 41CX Hardware

Power Supply

Postby Poly-tour » Wed Jun 30, 2021 3:18 pm

Hallo!

I have a question.
I built a power supply without batteries.
Therefore I downloaded the 3D-file for the Batterie pack and fixed 2 contacts and a USB-A link into it.
The energy comes from a usual Mobile charger (5V).
I tried several chargers (0,2A; 0,5A; 1A; 2A), even a cheap solar power bank! For normal use 0,2A are enough, even the card reader worked fine! But when I try to use the wand, even 2A are to less! Although the wand was detected in Cat 2, it does not read!
As soon as I insert the serial battery pack the wand worked fine and read the lines.
Is there anyone who can explain why the wand doesn't work with my self made powersupply? How high must (may) the Ampere be for the wand? I don't want to grill the motherboard with a too high stream! Is there a sensor in the wand or in the 41 that distinguish between my powersupply an the battery pack?

Thanks for help!
Andreas
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Re: Power Supply

Postby Garth » Wed Jun 30, 2021 7:30 pm

I had to design something in my work a few years ago to charge 3 lithium batteries in series from USB, and balance the cells. What I found was that the common, thin USB cables and their delicate little connectors together had a lot of resistance. I initially had a 5V microcontroller running the show; but when I allowed 500mA of USB current, the 5V came down to about 3V, and the microcontroller would go into brown-out reset. I changed the way the microcontroller was powered; but I also had to limit the USB input current to 250mA. I don't know how much current the bar-code reader takes; but my own 41 turns on the low-battery annunciator when the batteries get down to 1.2V each, meaning 4.8V for the four. You wouldn't have to draw much current to pull the USB's 5V down to 4.8V through the common, thin USB cords and little connectors. (This also means I can't use NiCd batteries.)
Garth
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Re: Power Supply

Postby Poly-tour » Fri Jul 02, 2021 2:50 pm

Hallo Garth!

Thank you for your response!
A few weeks ago I saw in TV exactly the same you told.
They spoke about the relation between thin cables and the resistance.
I'll try it with thicker cables, may be it's better then.
The low-battery annunciator doesn't turn on by using my power supply.

Doesn't matter, the most important thing is the calculator works without NiCd batteries.

Sincerely
Andreas
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Re: Power Supply

Postby Garth » Fri Jul 02, 2021 8:34 pm

Poly-tour wrote:They spoke about the relation between thin cables and the resistance.
I'll try it with thicker cables, may be it's better then.

The tiny connectors might be an issue too. I did not attempt to see how much of the problem was from the thin cables and how much from the micro USB connector.
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Re: Power Supply

Postby Poly-tour » Sat Jul 03, 2021 5:55 am

Hallo Garth!

I add some pictures of my power supply solution.
May be it's more clearly the way my solution looks like.
Attachments
IMG_20210626_115239.jpg
IMG_20210626_122747.jpg
IMG_20210626_115148.jpg
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