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how to prevent voltage/power drop to arduino when AC compressor kicks in

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how to prevent voltage/power drop to arduino when AC compressor kicks in

My Electrical question:

 

Background:

 

House furnace fan power supplies 120 VAC to my attic 120 VAC AC in line duct fans.  

 

I have a micro controller (Arduino) which controls two dampers in the attic to redirect the air flow to either the two bedrooms OR the hall and bathroom.

 

https://www.arduino.cc/en/main/arduinoBoardUno

 

The arduino, damper power, and optically isolated relay power come from this circuit.

 

I have put a receptical on the 120 VAC line to provide power to the system.

 

The Arduino is powered by a 9V DC 650 mA plug in power supply plugged into the receptical.

The optically isolated relays are powered by 5V DC plug in power supply plugged into the receptical.

The electric dampers are powered by a 24 VAC plug in power supply plugged into the receptical.

 

Works great.  The arduino cycles the two dampers every 30 minutes as long as there is 120 VAC coming from the furnace fan.

 

 

Problem:

 

When the AC compressor kicks in there appears to be a voltage drop resulting in the arduino rebooting.  Equivalent to powering down the arduino and then powering it backup.  I have observed this first hand when the AC compressor kicks in.  The reboot is instantaneous.

 

 

Solution:

 

Can I put a capacitor across the 9V DC leads into the arduino to mitigate the momentary voltage drop?  What kind and type of capacitor (assuming I know what I am doing) do I need.

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HELP!!!!!!!!

asked May 2 by john_armsby (120 points)

1 Answer

0 votes

An interesting and frustrating problem but relatively common.  I would first get your AC power checked; you should not have that type of power drop when the Compressor cuts in.  I am assuming your compressor is 220V.  You should also see your lights flicker and or dim with what you describe, if not you have a circuit problem that needs immediate attention.  This also indicates that the drop out is quite long allowing your 9V power supply to collapse, again assuming it is a regulated supply.

I am not sure what you are saying with a instant reboot, as I do not know what your code looks like.  If it is kicking it out it should be like a normal power on reset.  It is common when large motors start there is an inductive transient generated on the power line, it is possible that is what you are seeing.  I base this on the problems goes away when you add capacitance.

To size the capacitor I would start with 1000uF per amp on the 9 volt side.  When you have enough to fix the problem double the value, paralleling two is the best approach.  Reason someday one will fail; the other will keep it working.  The capacitor would be a cheap aluminum cap, lead orientation doesn’t matter get one that fits your design.  e sure the 9V power supply is ok and not on its death bed.

I think the most important thing is to check the wiring; it must be #12 minimum to the furnace.  I think what is really causing the problem is the furnace blower, it is on the same circuit as your controls and comes on with the compressor.
answered Jun 11 by gilshultzhome-com (17,410 points)

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