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Topic: Excessive current draw by strike lock (Read 3 times) previous topic - next topic

DaveO

I have just replaced a power supply.

Output is 12VDC with continuous current of 2A and peak 5A.

The 12VDC is used to power :

1. a small radio transmitter, then
2. a GSM unit, then
3. an external 3 channel remote control receiver, then
4. 12V devices, including 2 strike locks for exterior gates, then
5. voltage regulator to 8VDC for powering the Arduino, then
6. voltage regulator to 5VDC for powering relay output boards, temperature sensors, ACS712 Hall Effect Sensor board, etc

The ACS712 is connected to the 12V line, between '2' and '3' above.

Under normal conditions, the sensor registers current draw between 1.25 A and 1.35 A.

If I trigger a relay to activate the first 12V strike lock on Gate 1 ( for 2 seconds ) , current increases to 2.51 A, and then back down to the 1.3A range.  This is the 'heavy duty' lock.

If I trigger another relay ( same relay board )  to activate the 12V strike lock on Gate 2 ( also for 2 seconds ) , current increases to more than 4.7 A.

The cabling to both gates is the same type - 12 core 'house alarm' type cable.
Gate 1 is further in distance than Gate 1.
Gate 1's cable has data wires used for other items in the same cable.
Gate 2's cable is used only for the Gate lock.

The specs on the second strike lock is that it uses less than 500mA.

At this point, the system resets.

My logic is that the power supply is protecting itself and as soon as the current exceeds the rated 5A Peak, it shuts down. This causes the current to drop, and it turns itself back on again.

I am reasonably certain that the reset is not just the Arduino side, as the items mentioned in 1, 2, 3 and 4 ( before the Arduino system ) are also affected by the reset.

So in summary, Gate 1 ( heavy duty ) is drawing about 1.2A

Gate 2 draws in excess of 3.7A.

Any ideas on where my current is going ?

DaveO

#1
Apr 30, 2013, 10:06 pm Last Edit: Apr 30, 2013, 10:08 pm by DaveO Reason: 1
OK. Having done some additional searching, it would appear that a short is the most likely cause of the problem.

Would I be correct in thinking that if the 12VDC+ line ( controlled by the relay ) is somewhere damaged and touching a metal object, that this would be considered a short, even if the object being shorted to is not connected to the 12V circuit in any way ?

And that the circuit resistance would drop, current flow would increase ( just draining away as fast as it can through the short ), current draw would exceed the power supply 5A peak rating, and this would cause the reset ( which then disables the relay which disconnects the shorted wire from the 12VDC supply ) ?

CrossRoads

Sounds like an excellent discussion of what might be occurring.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

outofoptions

Have you tried measuring the resistance of each circuit?  I'm guessing your 'strike lock' has a coil?  If it binds it might draw more current.

CrossRoads

Possible also that a relay closure is unintentionally wired in parallel with coil.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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