Arduino Uno power problem

I have a Arduino Uno and it is running two servos with a PIR. The problem I am having is it runs fine from the PC but when using a 9v power supply 1000ma the servos go crazy, has anybody seen this or can explain to me what is going on? is 9v to much with 1000ma?

It could be that it is not enough, but without a link to the servo spec it is hard to say. It could also be a grounding problem are the supplies ground, arduino grouns and motor's ground wires all connected?

Normally a 9 volt battery will not provide enough capacity for running a servo. Test the battery with a volt meter, while the servo is running. What voltage do you get?

Thing is - is the servo rated to operate at 9V?

I thought these things were designed for 4 to 6V.

I agree, many servos are rated about 5 volts, but you have to check the specs. (bet you got a bargain price on that one).

But, did you check the voltage with a meter as I ask?

EDIT: So why did you ask

is 9v to much with 1000ma?

(And I am assuming you ment to type 1000mah.)

Mmm, I presume that when he refers to a 9V power supply, he means a plug pack ("wall wart").

Now if that is the older heavy transformer type, as opposed to a switchmode, and he is under-loading it, we will be talking of 12V or more.

That sounds like you have not got a proper ground when powering it externally. Using the USB it looks like you are getting an accidental ground that it covering up the error. The other thing to do is to check that you are getting 9V DC from that adaptor. You could be getting AC or more than 9V.

Hi, where are you getting the power for the servos? If its off the arduino board then that may be your problem.

and gets really hot

I presume you mean the arduino board, if you are getting servo supply from the arduino board this will explain it. The arduino inbuilt regulator is having problems regulating from a 9 Volt supply, instead of 5 Volt supply from the USB plug, with the servos added as extra load. You will need to fit a separate 5 Volt regulator just to supply the servos from the 9 Volt supply. The arduino inbuilt regulator is not meant to provide current for things like servos. Tom

I've had a similar problem that's been vexing me for days. Running an ethernet shield on the Uno or on the Mega would work fine as long as the PC was connected via USB. But when relying only on the wall wart power adaptor (rated at 10vDC and 500ma) the program would run for a while then fail.

I finally checked the wall wart for [u]AC[/u] power and it read about 3 volts (DC measured 9v). So the DC wasn't all that smooth. I soldered in (parallel) a 1000mf electrolytic capacitor and now the DC measures 12v and the dang thing works like a charm. (The AC still shows 2v so maybe I could have used a bigger cap.) The bottom line is all those wall warts we save just in case aren't all created equal. And just because it says it's DC, doesn't mean it's good enough.

I'm posting this since I couldn't find this information in any searches and someone else might have the same problem.

I finally checked the wall wart for AC power and it read about 3 volts (DC measured 9v).

While you soloution was correct that test method is not. Reading a meter with an AC range on a DC voltage does not tell you anything about the ripple on the voltage.

Hi, fluke DMM does...

Tom.... :)

Tells you that its there, have checked against CRO, AC voltage measured is RMS of AC component. (Qualifier, must be true RMS meter, most digital ones are these days.) (CRO Cathode Ray Oscilloscope, google it..)

fluke DMM does.

It might but by no means is it something that you can expect all DVMs to do.