I'm hoping you smart folks can help me. I'm puzzled by what I thought would be a simple DC battery to DC adapter swap.
The device I'm trying to mod is a a microchip activated pet door (SureFlap Microchip Pet Door on Amazon for about $150).
It normally takes 4x Alkaline AA batteries. The manual does NOT recommend using rechargeable batteries because they may trigger a battery replacement warning due to their lower voltage.
I thought, I could take a 6V 3A adapter (actual 6.3V on DMM) and splice on some alligator clips, clip them onto the battery springs and not have to worry about my cats being locked in/out due to a dead battery. I was WRONG.
This mod resulted in a powered device, but no longer would the door trigger to my pet's microchips. Switching back to the batteries eliminates the issue completely. therefore, I know the device is not broken.
I have confirmed power is being provided to the device, by taking my DMM probe to the springs on the device, and by pushing the "Learn" button on the device, which puts the door into the learn mode (unlocks the latch mechanism to allow a pet to pass through and register, it's supposed to re-latch to confirm a learned chip).
Issues while on DC adapter power:
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Putting the door into "Learn Mode" initiates the unlock mechanism for the pet to pass through, but does not complete the learn process (re-locking) no matter how many times I try. It just hangs perpetually unlocked in this mode until it is canceled. Again, going back on battery only mode I can learn a chip easily.
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The device has a memory function so microchips do not need to be re-learned after a battery swap. However, previously learned chips no longer trigger the door to open. I can no longer get the door to trigger for my cats. Again, going back on battery only mode I can learn a chip easily.
I thought initially I had an under-powered adapter, as I had a 6V 1A (6.0V on DMM) lying around. I bought a 3A adapter mentioned above and the problem persists. I am absolutely puzzled.
Is there something I am missing about the characteristic differences of DC batteries and power supplies? I've had success in the past doing the exact same mod with toy motors and the like, but I'm wondering if the issues is due to the device being a more complex electrical device.
4x Alkaline batteries are 6.3V on my DMM, so I don't think over-voltage is an issue. Also, my 6V 1A power supply is dead on 6V.
Best Answer
So I pulled the cover off one of these a couple of months ago with the same plan in mind, this is our second door, and the batteries only last 3-4 months.
The system seems to run the batteries both in parallel and in series.
The 6v of batteries in series seem to run the electronics and the 3v in parallel seem to run the rfid loop, so supplying just 6v DC gives the appearance that it all works, but failed to ever pick up tags.
I still want to hard wire the SureFlap. Plan is to make a pair of 3.3v supplied with different earths.