Powering the nano with 18650 batteries

Other Hardware General Electronics
1

Bear with me, I'm not what you would call very bright when it comes to the electrical part of all this.

I just made a 3D-printed design for a gizmo based on an LCD, a keypad and a Nano. Also, the design is made around 2 TR18650 batteries in series, producing 7.4 V which I connect to the Vin (pin 30) of the Nano.

And then it fries. The voltage regulator starts bubbling and smoking.

For the life of me I cant figure out what I'm doing wrong. I measured the voltage, and it's 7.9V. Ok, a little high, but nothing the voltage regulator shouldn't handle. So I tried hooking it up to an UNO I had lying around, and it fried that too.

Please help?

2

Are you hooking it up backwards or something? Double check the polarity.

That ought to be perfectly fine.

3

I guess that's it. I must have done it twice. I am not a smart man.
Sorry for taking up your vaaluable time. If only I could scrap my own thread.

4

You shouldn't draw more than ~100-150mA from the Nano's 5volt pin at that input voltage.
Don't know what the backlight of that LCD uses...

If you have connected things right, and you draw more than that, you could use a 1N4004 diode between +battery and V-in. That reduces battery voltage with 0.7volt. Still enough for the regulator, and it won't get as hot.

The Nano's could still work on USB supply, because that doesn't use the regulator.
Leo..

5

Wawa:
a 1N4004 diode between +battery and V-in.

Well it's a little late for that now, isn't it?

(note - yes, I know that's not how you meant it)

6

Mixe:
So I tried hooking it up to an UNO I had lying around, and it fried that too.

Hmmm, you must do something wrong then.
Post pictures.
Leo..

7

Wawa:
You shouldn't draw more than ~100-150mA from the Nano's 5volt pin at that input voltage.
Don't know what the backlight of that LCD uses...

I have a 4x20 serial LCD that uses 250 mA at max brightness. It was enough to make an unheatsinked TO-220 regulator toasty enough to smell like hot electronics.

8

250mA seems an awful lot for your backlight- I regularly use 16x2 lcds and the backlight only takes 20mA at 5v.

It's pretty bright.....

regards

Allan

9

allanhurst:
250mA seems an awful lot for your backlight- I regularly use 16x2 lcds and the backlight only takes 20mA at 5v.

It's pretty bright.....

regards

Allan

I've attached it for your review. 229 mA.

NHD-0420D3Z-FL-GBW-V3-29857.pdf (576 KB)

10

How did you wire the batteries to the Nano, exactly?
My Nano runs on 2 18650's just fine.
Did yours fry with nothing else plugged in or is it possible you wired other stuff wrong and shorted the Nano and are just blaming the battery?

11

And did you have to solder the headers onto the Nano yourself? Maybe your soldering is horrific and causing shorts.

12

Jiggy-Ninja:
I've attached it for your review. 229 mA.

It does say that. That is over a watt -- does that thing double as a desk lamp too ???? :slight_smile: