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Author Topic: 24V PSU + 7809/7812?  (Read 695 times)
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outside Seattle
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If I need to use a 24V, 2.2A PSU (typical laptop charger) because I need higher voltage for a stepper motor, do I need to add anything else other than a 7809 or 7812 to power the Arduino?

E.g. do I need any additional parts, capacitors or just out of the 7809/7812 and into the Vin pin?

Thanks.
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Draw us a diagram of the  way you think the project would be wired up.
This will give us an idea of what you are trying to do and we can then supply some help.
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Spain
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These regulators 78xx have a very low performance and remove a lot of heat.

24 volts it is a bit high voltage for the regulator of the arduino.

If you want to use  24v to power the arduino, the best solution is a step down dc-dc converter, for a 1.5 $


Link: http://www.ebay.es/itm/LM2596-Step-Down-Adjustable-DC-DC-Power-Supply-Module-New-/330646303458?pt=LH_DefaultDomain_0&hash=item4cfc0e32e2

Output Voltage: 1.5-35V (adjustable)
Output current: rated current 2A (3A with sink)
Conversion efficiency:Up to 92%

Regards
« Last Edit: February 13, 2013, 02:04:16 am by Heke » Logged

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outside Seattle
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Attached is a diagram of what I want to try to do...
- 24V Wall Wart
- Connected to 7812 voltage regulator
- 24V fed straight into an Easy Driver board (I'm actually using a Big Easy Driver, but couldn't find a fritzing part)
- Output of the 7812 to Vin on Arduino
- GND of PSU, 7812, Easy Driver and Arduino all connected
- Additional Arduino pins for step & dir
- Easy Driver connections to bipolar stepper motor (not shown)

For simplicity sake will this approach work?

Heke -- I didn't know about DC-DC converters. If the above approach won't work I'll get one of those.

Thanks.

* Uno-BED-78xx.pdf (776.2 KB - downloaded 16 times.)
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Land of Oz
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If you simply want to trial this, your setup will work fine. Just put some 0.1uF decoupling on the regulator outputs.
For a long term effect, go with Heke's suggestion.
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outside Seattle
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I had never heard of DC/DC converters before Heke's post, but now I see lots of options including these: http://www.adafruit.com/products/1065

Adafruit only carries the 5V and 3.3V versions of the above, but it seems like I would want the 9V version (TSR 1-2490 http://www.adafruit.com/datasheets/tsr1.pdf) if I am going to connect it to Vin, right?

And I'm curious, other than heat and inefficiency, what is wrong with the 78xx regulators for this type of application? I see that they are terrible with large voltage differences between input and output, but are there other reasons not to use them?

Thanks again.
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If you know the approximate current draw, you can put a power resistor in series with the regulator input lead to handle some of the power dissipation.
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