19v to 12v using LM7812

Hi

im building a mind control car set. which has a voltage of 19v, i have built the whole circuit off a breadboard, with two arduinos and two motor controllers (works perfectly). the issue i am having is converting the circuit to a breadboard version, using the 19v to power the motor drivers and the two arduino chips. i have created a circuit. to drop 19v to 12v using the LM7812 and then drop that to 5V it works great, however it gets really hot. When i connect the motor drivers to the 19v input from the breadboard it works for a bit but then the power cuts off. im assuming it is my voltage conversion causing the issue, if not im stumped. i have a LM7812 with two capacitors 100uf 63v, i followed this

im guessing this is kind of the wrong thing, if anyone knows the best way in which i can convert the voltage, or a schematic that can do it, that would be great.

oh yeah the power input is 19v 0.5A

thank you

Which regulator is getting hot, the 12v or 5v one, or both ?

You say "Arduino chips" do you mean an Arduino board or litererally a mega328 chip ?

Do you know what current is being taken by the Arduino chips.

Regulators can get warm and often need a heatsink or be clamped to a metal case, but just running 2 small boards would be unlikely to make them get noticabley hot.

A circuit diagram of what you have might help..

Hi,
You will probably need heatsinks on the regulators.
How much current are they supplying?

Tom.... :slight_smile:

It's not totally clear if you need the 12V or not, anyway, if 500mA at 5V are enough for you , you can use this :
http://it.farnell.com/recom-power/r-78e5-0-0-5/convertitore-da-dc-a-dc-5v-2-5w/dp/2078564 , direct from 19V, no heatsink needed.

Ciao, Ale.

When i connect the motor drivers to the 19v input from the breadboard it works for a bit but then the power cuts off. im assuming it is my voltage conversion causing the issue, if not im stumped. i have a LM7812 with two capacitors 100uf 63v, i followed this

No offense but this is a no-brainer. Since you’re probably inexperienced you wouldn’t be expected to know but when an LMXXXX regulator works for 5 to 30 seconds (hot) then shuts off, it is going into thermal shutdown mode because it has overheated. It is designed to turn itself off when the user abuses it by loading it too much without a heatsink. Your bad. Put a good heatsink on it.

TomGeorge:
Hi,
You will probably need heatsinks on the regulators.
How much current are they supplying?

Tom.... :slight_smile:

hi tom i guess it does require a heat sink, i tried connecting a multi meter to the circuit. however when i touch the multi meter to circuit to read the amps it just turned everything off, also i tried to connect an led with a resistor and got the same effect. everything just powered off.

vj01:
hi tom i guess it does require a heat sink, i tried connecting a multi meter to the circuit. however when i touch the multi meter to circuit to read the amps it just turned everything off, also i tried to connect an led with a resistor and got the same effect. everything just powered off.

You must be doing something very wrong if you canot measure with a multimeter or use a led like that.

You have not made it clear if anything other than the 5v regulator is running off the 12v regulator or which one is getting hot ?

Please provide a circiut diagram , only something simple, even freehand, so we can see where things are going wrong and help you get it right.

The statement "however when i touch the multi meter to circuit to read the amps it just turned everything off" tells me (if it was correct) you are trying to put the meter in current mode ACROSS the supply which will indeed shut it down because you are shorting the output. To measure current, the meter needs to be in series with the regulator not across it. You put a multimeter (in voltage mode) across the circuit to see what the voltage is and in series with the circuit (in current mode) to measure the current.

hi tom i guess it does require a heat sink, i tried connecting a multi meter to the circuit. however when i touch the multi meter to circuit to read the amps it just turned everything off, also i tried to connect an led with a resistor and got the same effect. everything just powered off.

Explain , step by step EXACTLY how you went about measuring current. Include a photo of the meter in the position you set it for . Include a hand drawn schematic (on a blank sheet of printer paper) of what you did with the meter when you attempted to measure the current.

The statement "however when i touch the multi meter to circuit to read the amps it just turned everything off" tells me (if it was correct) you are trying to put the meter in current mode ACROSS the supply which will indeed shut it down because you are shorting the output. To measure current, the meter needs to be in series with the regulator not across it. You put a multimeter (in voltage mode) across the circuit to see what the voltage is and in series with the circuit (in current mode) to measure the current.

Thanks, you sort of blew any chance we had of finding that out without telling him first that he shouldn't do it. I was hoping to confirm that from his response but it's too late now.
Since the cat is out of the bag I should mention he might have blown the fuse unless it was a 10A fuse and his circuit cannot source that much. (sounds like that might be the case)

Why would it matter ? Because I know from past experience that if you tell a newbie he shouldn't do something sometimes they won't admit that they did it ...out of guilt I would guess. This effects the troubleshooting process because now you can no longer explain the symptoms that were reported because they won't be repeated again. You could infer, however, that if they are not repeated , then they must have been exactly what you told them not to do. It doesn't matter any more. Let's wait to see we can get a correct current measurement. That remains to be seen.

raschemmel:
Explain , step by step EXACTLY how you went about measuring current. Include a photo of the meter in the position you set it for . Include a hand drawn schematic (on a blank sheet of printer paper) of what you did with the meter when you attempted to measure the current.

Thanks, you sort of blew any chance we had of finding that out without telling him first that he shouldn't do it. I was hoping to confirm that from his response but it's too late now.
Since the cat is out of the bag I should mention he might have blown the fuse unless it was a 10A fuse and his circuit cannot source that much. (sounds like that might be the case)

If I had been posting BEFORE I had my morning coffee I might have missed that - oh well, sorry about the escaped feline :slight_smile:

This process is similar to interrogating a suspect in a murder. You have to be indirect to get to the truth.
Sometimes the embarrassment of admitting they did something stupid will prevent a newbie from confessing to the crime... if you know what I mean. If they talk themselves into a corner and you can prove they did it they usually confess because they know you've got them by the short hairs....

Yep - get them to tell you what is really going on instead of what they think you want to hear. My usual is to work on some detail that just will not work as expected, so I talk to one of my cronies and halfway through the explanation, it is "oh ... NOW I see what I was doing wrong" - at which point we both laugh because they have been there too :slight_smile:

We’re waiting for a schematic ( hand drawn on a blank sheet of printer paper) of your circuit.
The most you can get out of the 12V regulator with a heatsink is 780 mA.
You do realize that if the load draws more than the 19V supply can deliver that it will just simply shutdown. By now that should be obvious. You have not posted a link for the motors OR the motor driver. How are we supposed to help you with virtually nothing to go on ?