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Electronics => Electronics => Topic started by: blackbeard on October 04, 2009, 04:50:30 PM

Title: VR for arduino burning out.
Post by: blackbeard on October 04, 2009, 04:50:30 PM: so i've been running a 9v 500ma adaptor for my arduino since my Snooper robot needs both 5 and 9v power (one camera, 2 micro servos and a 5v transmitter for the camera) and it seems that my arduino can't take the strain. the vr gets super hot and for a moment i thought i burned it out when the short out light went on. it went away after a few minutes of cool down though. anyone know how i can make it so i don't burn my arduino out?

edit: p.s there is NO schematic since most of the bits are self contained (hobby servos, pre built a/v transmitter and camera)
Title: Re: VR for arduino burning out.
Post by: Razor Concepts on October 04, 2009, 05:19:21 PM: Have you tried it without anything connected to it?
Title: Re: VR for arduino burning out.
Post by: blackbeard on October 04, 2009, 05:22:59 PM: it doesn't get hot nearly as quickly but it does heat up
Title: Re: VR for arduino burning out.
Post by: Soeren on October 04, 2009, 10:02:07 PM: Hi,

You need a heatsink on the regulator.
Title: Re: VR for arduino burning out.
Post by: blackbeard on October 05, 2009, 11:12:08 AM: Quote from: Soeren on October 04, 2009, 10:02:07 PM
Hi,

You need a heatsink on the regulator.

hmm that could work. i'll throw on a ram sink and see how it goes :P
Title: Re: VR for arduino burning out.
Post by: Joker94 on October 06, 2009, 12:38:12 AM: A heatsink should do the trick, it did on mine.
Title: Re: VR for arduino burning out.
Post by: waltr on October 06, 2009, 08:04:02 AM: Just a little techno info on VReg heating on the common, easy to use three-terminal regulators like the LM7805 family.
A voltage regulator drops the input voltage to produce an output voltage. This voltage drop times the current draw equals the power dissipated by the VR.
So (Vin-Vout) * I = Watts of heat. This number is then used to choose a heat sink or to determine if a heat sink is not needed. In the example posted above if the circuit is drawing 500mA the VR needs to dissipate 2Watts of heat, (9v-5v)*0.5A = 2W.

If your VR is getting much hotter than expected there could be other reasons.
If you are using a Wall wart power supply check its output voltage with a DV voltage meter. Then check the ripple using an AC voltmeter (a DMM will work on 50-60Hz). Many of those cheap wall warts either have poor voltage regulation and/or poor AC filtering.
Try powering from a battery, pure DC without any ripple.

Finally, sometimes linear regulators oscillate. This is usually due to improper bypass caps on the input or output, or the leads from the regulator to the caps is too long. Check the data sheet for recommendations and add a cap very close to the regulators input or output pins.

Hope this helps
wr
Title: Re: VR for arduino burning out.
Post by: blackbeard on October 06, 2009, 09:24:47 AM: i attached a copper ram sink to it and it hasn't had any problems although the heatsink still gets fairly hot. i'm going to try reglating before the arduino and powering the camera (the big power muncher of the setup) directly to the source. thanks for the info
Title: Re: VR for arduino burning out.
Post by: Soeren on October 06, 2009, 04:24:56 PM: Hi,

Use a heatsink with a lower K/W (Kelvin/Watt i.e. "cooling capacity" i.e. larger surface area [usually made by more/longer fins]) and the temperature goes down.
And remember to use a thin layer of zinc grease in between to give good thermal contact.

If the sink is slightly warped, a bit of emery paper on a glass plate can do wonders to make it level.
Title: Re: VR for arduino burning out.
Post by: blackbeard on October 07, 2009, 08:16:15 AM: well i solved it by adding a 5v vr and just using the circuit before the vr for the camera. should prolong the life of it.