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Topic: Issue with 7809 1.5A Linear Voltage Regulator  (Read 637 times) previous topic - next topic

eboudreau26

Hello,

I've been using a voltage regulator (which has a heat sink) to try and convert a 12V power supply into 9V to power a few motors. I need a little over 1A of current. However, the current seems to be maxing out at about 0.6A when I use the voltage regulator. The motors with the same circuiting work fine when I use a 9V supply with a max of about 1.2A and don't use the voltage regulator. 

Does anyone know what the issue could be here? This is my first time using a voltage regulator.

Thanks

wolframore

please post schematics. Is the regulator getting hot?
Bad Boys Rate Our Young Girls But Violet Goes willingly - Get Some Now :) - ELI the ICE man

DVDdoug

The 1.5A rating doesn't tell the whole story...  The heat/power dissipation usually limits the amount of current you can get.  

The good news is that the 79xx regulators are thermally protected so they don't permanently burn-up and die when they get too hot.   They just shut-down, or partially shut-down.  

It's easy to calculate power dissipation - You're dropping 3V across the regulator at 1.2 Amps, so that's 3V x 1.2A = 3.6 Watts.

What's NOT always easy is calculating the thermal characteristics of the heatsink.   You may need a bigger heatsink, or heatsink grease, or a fan (or cooler environment for your heatsink), etc.

Or, one (not very elegant) solution is a separate voltage regulator for each motor.

The best solution is usually a switching (aka "switchmode") regulator.    Switching regulators are more complicated so it usually best to buy a complete regulator board, but they are nearly 100% efficient so they don't have the same heat problems.      

The efficiency also means that you can get 1.2A out of the regulator with less  than 1.2A in (when the voltage is stepped-down).

FantomT

Voltage regulator short-current protected, limiting output is not gonna to work well with a motor, as it''s need x10 times current at start-up - known as stall current.

eboudreau26

Thanks for the replies, and yes, the voltage regulator is getting very hot. I'll look into getting a bigger heatsink and/or putting it in a cool environment, and if that doesn't give me the required current output then I'll look into a switching regulator.

I'm also extremely new to this; I'm a mechanical engineering student working on one of my first real Arduino projects. So, the less complicated the better :P.

eboudreau26

What do you guys think about me buying a 9V output 2.5A buck converter? Again, the extent of my knowledge on these things is basically just a few articles and youtube videos. Does it connect it in a similar way, and I'd just simply connect the supply 12V and the ground to the input and ground of my buck converter, and the output and ground would connect to the rest of my circuit, giving me 9 volts and hopefully enough current to run the motors? 

MarkT

Hello,

I've been using a voltage regulator (which has a heat sink) to try and convert a 12V power supply into 9V to power a few motors. I need a little over 1A of current. However, the current seems to be maxing out at about 0.6A when I use the voltage regulator. The motors with the same circuiting work fine when I use a 9V supply with a max of about 1.2A and don't use the voltage regulator. 

Does anyone know what the issue could be here? This is my first time using a voltage regulator.

Thanks
Much better to feed 12V directly to the motors, and use PWM to set the speed, these days we use switching
to regulator power to loads like motors, not the series resistance of a regulator - much less waste
power and heat.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

DrAzzy

Switching regulator to generate the necessary 9v is an appropriate solution.
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TomGeorge

#8
Feb 24, 2019, 07:31 am Last Edit: Feb 24, 2019, 07:32 am by TomGeorge
Hi,
Can you post a picture of your project please, so we can see your component layout?
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Have you got the bypassing capacitors that the spec sheet recommends on the 7809?

What is the 12V supply?

When you have this problem, what is the voltage from the 12V supply?

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

elvon_blunden

#9
Feb 24, 2019, 08:05 am Last Edit: Feb 24, 2019, 08:06 am by elvon_blunden
Have you got the bypassing capacitors that the spec sheet recommends on the 7809?
Please indulge me with a question slightly OT.... if the 78xx spec sheets recommend certain caps, why don't they just build them in? (Implication of not doing so is that there are cases where no / different caps are better?)


Smajdalf

Please indulge me with a question slightly OT.... if the 78xx spec sheets recommend certain caps, why don't they just build them in? (Implication of not doing so is that there are cases where no / different caps are better?)
I think there are two reasons:
1) Different application may need different caps.
2) Integrating a cap large enough is more expensive than adding an external one. (I think this is more important here.)
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

TomGeorge

Please indulge me with a question slightly OT.... if the 78xx spec sheets recommend certain caps, why don't they just build them in? (Implication of not doing so is that there are cases where no / different caps are better?)
It would be difficult to do at a substrate level, and yes values may have to be tailored for different conditions.
Without at least this minimum you can get the regulator oscillating or in, I suspect this case, poor regulation to changes in load current.
Tom.... :)
PS. A valid and not an OT question.. :)
Everything runs on smoke, let the smoke out, it stops running....

elvon_blunden


eboudreau26

Ok, this is a fritzing schematic I made a while back, but it should give you all a good idea of what I'm trying to do. I have MG996R Servo motors and 12V stepper motors. So the voltage and current specifications for the steppers and servos aren't the same, but I tested it with a laboratory DC power supply and I can get all of the motors to run at a good speed when I'm giving them 9V and about 1.2 A max. Basically I'm trying to find the cheapest and easiest way to run all of these motors at a decent speed, since I'm very low on time, knowledge, and (especially) funds.

TomGeorge

#14
Feb 25, 2019, 09:23 pm Last Edit: Feb 25, 2019, 09:25 pm by TomGeorge
Hi,
OPs fritzy;

For a start you are going to need more than 2A to drive that lot, what do you expect the current to be when they are driving a load?

Can you post links to specs on the three steppers and to the stepper driver modules you are using?
If your layout is exactly like that, then I'm surprised that it is performing at all, the protoboards are not rated for much current, especially three steppers.

If you are supplying the 5V from the servo end, then try supplying  it from the UNO end.
All the servo and stepper current will be causing a volt-drop in the wiring that will possibly be putting noise on the supply that eventually gets to the UNO, causing it to reset.

Try putting 100uF or 1000uF capacitors on the supply rails as well as 0.1uF caps.

Currently you have everything daisy chained together power supply wise.
Really each servo and stepper and UNO should have its own power wires going back to a central pair of connections.

What are you measuring the current with and do you measure the 5V voltage when you project exhibits these problems?

I hope when you connect 9V to the motors to test, you disconnect the feed to the 5V pin of the UNO?

Can you post a picture of your project so we can see your component layout.

When you used the LM7809, did you put the recommended capacitors around it?

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

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