This is my first question and I'm a total beginner at this, so, please be kind :D

I have a kitchen scale that eats up 2AA batteries every 2-3 days, so I thought to power it via a USB wall charger (for mobile phone) and a phone usb cable soldering the red and black cables to the scale.

Since the scale takes 2AA batteries I suppose it expects 3 volt, but correct me if I'm wrong, the wall charger + usb cable will give 5.

Could this work just like this?


First off there is definitely something wrong with the kitchen scale if it is truly using up the batteries every few days. No reputable manufacturer would release a product that worked like that. Whatever the problem is I would question whether the unit is even accurate anymore. So in the long run you should really consider simply replacing the unit with one that does not consume batteries like this.

Now about your battery eliminator idea. DO NOT DO THIS AS YOU HAVE PROPOSED. The unit was clearly designed to operate at approximately 3V. You should not attach a 5V supply to it. Now since we have already established that the unit is already broken in some way if you increase the voltage from 3V to 5V the current draw from the source will most likely be even more than the batteries are getting loaded with. This could lead to further damage in the scale or overload the charger unit. And if the charger is some very cheap import they often die in dangerous ways if they are overloaded.

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    \$\begingroup\$ +1. It shouldn't even drain the batteries in three days if you keep it on 24/7. Mine has an auto-off so I don't know how long it would last, but I can't imagine a tiny slow microcontroller and an LCD would drain in three days. \$\endgroup\$ – pipe Apr 23 '16 at 16:46
  • \$\begingroup\$ Thanks for your explanation. I guessed there was something wrong with the scale but couldn't have it replaced so I thought about this solution, cause, apart from the battery drain problem, the scale it's perfectly accurate! Anyway I will avoid this as you suggest. Anyway, do you know a solution? Should I find a 3v wall charger? \$\endgroup\$ – RingK Apr 23 '16 at 16:47
  • \$\begingroup\$ @RingK A second hand store may have a 3 V charger. Anything else will be more expensive than getting a new scale, unless this is an epic scale. There are ICs that converts 5V to 3V but shipping and handling for a single chip will probably cost 10 euros or so, if you can't find it locally. \$\endgroup\$ – pipe Apr 23 '16 at 16:50

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