NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Basic Electronics » Too much power?

December 03, 2009
by Farmerjoecoledge
Farmerjoecoledge's Avatar

I've accidently gave my board 19.2vdc. Initially I thought it was 12vdc but my mulimeter reads 19.2. There's quite a diffrence there, but it fried the cpu and programmer. So how much of that overload (for about a min) got through to the crystal or for that matter the other way to the usb? The capacitor? I don't have replacements for these but would a fried crystal interfere with programming? I'm thinkin it would can someone send me one, i can't find one locally and the shipping is a killer.

December 03, 2009
by hevans
(NerdKits Staff)

hevans's Avatar


You are very likely using a wall adapter that will have a certain voltage at a certain current. Many times the voltages of these adapters under no load is higher than when they are under load. However, any amount of voltage too far above 5V can potentially damage your devices. You should be very careful when dealing with power supplies and higher voltages (that is the reason we opt to start beginners off using 9V batteries that are much less likely to damage components).

Given a high voltage any of your components may have been damaged, but can't just assume that something did or did not get damaged. There are always ways to start narrowing down what might have been damaged so you can have a better idea of what to replace. Based on your other posts in this forum, and the email conversation we have had with you, it is clear that the development environment on your computer is not completely right. After we are able to get your computer compiling the code, recognizing your new cable, and at least attempting to communicate with the chip, then we can start seeing what sorts of errors you get and proceed to find out what parts you damaged.


December 05, 2009
by Capt
Capt's Avatar

Hei, I did something similar, i bypassed the voltage regulator and gave the hole board 18ish volts. I'd only fired the MCU and the programer. It's now working fine whith a new programmer and A MCU.

December 05, 2009
by Farmerjoecoledge
Farmerjoecoledge's Avatar

Eye Capt,

Good to know i'm not the only one. I'm still hopeing that's all I fried. I got a software/compiler problem right now. So it doesn't want to fix itself by uninstall/reinstall now i'm at a loss. I'm jealous, I should have been up and running a month ago.


December 06, 2009
by n3ueaEMTP
n3ueaEMTP's Avatar

Hey guys,

I can sympathize with both of you. I've gone through two MCUs due to VCC being greater than 5V. I was looking over the "store" section of the site & came across a NerdKits USB to Serial TTL Cable. It replaces the circuit board programmer & the serial to USB converter that came with my kit (this might be useless to you if you already have the part but I'm guessing you don't or sending too many volts might not be a problem). This new NerdKits USB to Serial TTL Cable uses USB power to power your entire NerdKit. No more need for a 9V battery or 7805 regulator. I picked one up with the intent of using it on a finished project by adding a connector to the end. Turns out I'm going to need another one already because I don't want to go back to the "old way." I'm hoping it will also prevent me from frying any more MCUs as well.

Chris B. n3ueaEMTP

December 07, 2009
by mrobbins
(NerdKits Staff)

mrobbins's Avatar

Hi n3ueaEMTP,

If the most expensive part you've ever fried is a < $10 MCU, then you're either a robot who never makes mistakes, or you're not trying hard enough. :-)


December 07, 2009
by FWSquatch
FWSquatch's Avatar

I hear ya, Chris. The new USB cable is a big improvement.

December 07, 2009
by hevans
(NerdKits Staff)

hevans's Avatar

Hi everybody,

I would like to throw in a word of caution here. Although the new cable is able to provide you with a nice 5V supply, in some ways you need to be more careful with this power, not less. With a 9V battery the power source and your NerdKit was completely isolated and the worst you could do was drain a $1 battery or damage a few components.

With the new cable it is easy to forget that the power is live as long as the cable is plugged in, and now that your computers power supply is providing the power it is potentially exposed to any mishaps.

That is not to say that you should be afraid to experiment with your NerdKit. Your computer generally does a pretty good job of shutting down the USB port when there is too much current, but please be as careful, if not more careful, when using the new cable.


December 08, 2009
by Capt
Capt's Avatar

hevans, Mine laptop shutsdown imediantly when 5+ meets Miss ground.

The most expensive part i've fried was a $4500 electrical engien :D

January 25, 2010
by sepeters
sepeters's Avatar

Guys, no reason to endanger your PC or any other components... The spec for USB is 5V, MAX 500mA, just run your USB power wire through a 500mA fuse. Here's a link for the right part from amazon.


January 26, 2010
by carlhako
carlhako's Avatar

Hi Ive also deep fried an mcu mine happen to be the one supplied by nerdkits :(. I accidently put 12v straight into the power rails instead of through the regulator realized straight after i put the wires in when no leds came on the led array kit. Power was on for maybe 5-10 seconds, chip was fairly warm and would no longer run. Weird thing is i could reflash the boot loader using a isp programmer, but then when trying to upload a new program it would fail straight away. Nothing else was affected other than the chip. Ive now got a old mobile charger puts out 5.2v with no load its rated 1amp.

+1 for the fuses ive got a 400ma, i broke the positive soldered the wires straight to the fuse then wrapped in tape. already saved me a dead short once.

February 21, 2010
by VictorsNerdery
VictorsNerdery's Avatar

Does anyone know what kind of power is needed to burn out the lcd? Also would 9V of power for a couple minutes kill the MCU?

February 22, 2010
by Farmerjoecoledge
Farmerjoecoledge's Avatar

Hi VictorsNerdery, Welcome to my good old post.

Let me guess, Your lcd is burnt but you didn't give it alot of power, not enough by your way of thinking. The lcd that comes with the kit is powered by the boards 5v power, so my guess (again) is anything over say 20volts will burn it out.

And 9v for 2min, in my experience anything over 5v for any lenght of time would be enough to make debugging hell. These things are super fusy, the regulated 5v isn't really the best either, but it works.

I don't mean to pick but, try to explain more.


February 23, 2010
by BobaMosfet
BobaMosfet's Avatar


Anything over what it is rated for can damage it, because that pulls too much current through it. We're not talking minutes or seconds, either. We're talking microseconds in most cases.

The spec sheet will tell you exactly what the max is for both.


Post a Reply

Please log in to post a reply.

Did you know that you can make a huge, multi-panel LED display? Learn more...