How many Amps are needed to operate a "12 volt car antenna" automatic coop door?

[joshremlin]

Right im slowly giving in and going to put mains power to the coop buti fort id try the idea out a wired the ariel up to 2 plugs one being 12v dc 1amp output and one 12v dc 0.8 amp and it only popped out a mm or 2 and stopped like a toy with a flat battery is it because the plugs had low amps ?

 

[hoosiercheetah]

More or less. Don't do that again. Here's why.

When you hook a motor up to power, there are two things going on at the same time - volts and amps. (There's actually a lot more to it, but that's all we need to worry about).

The volts will determine how fast the motor operates. More volts = faster motor. The car antenna is designed to run at 12V, obviously. Running it higher or lower won't hurt it, as long as you're within the motor's operating range. In this case, just guessing, +/- 5V would probably be fine, but it will change the motor speed a little bit.

The amp draw of the motor depends on the load. The more load on the motor (heavier coop door), the more amps it will draw. The antenna motor is designed to have a very light load, just an antenna going up. Having it raise a coop door is going to cause it to draw more amps. This is fine, as long as we don't draw too much.

There are three main factors limiting how much amperage we can safely draw. One is the motor itself. If you draw too many amps, you could overheat the motor and possibly melt its internal wiring. The second is the power supply (p/s). If the motor is attempting to draw more amps than the p/s is capable of delivering, you could burn out the p/s. In an extreme case it could catch fire. The third is the wiring. If you draw more amps than the wiring is rated for, you could overheat it, melting the insulation or the wire itself, possibly shorting the circuit to ground. In a dusty coop environment, this could be catastrophic.

Fortunately, it's easy to protect the system from overheating and burning up your chickens - and this is the thing that I have not seen in anyone's design - with a fuse. A fuse is designed to overheat and stop the electricity before the wiring can overheat. Having an appropriately rated fuse is critical. When these antenna are installed in the car, there is a fuse in the circuit. However, we can not simply use the same rating fuse ( I think they are usually 10 or 15 amp) because we are not using the same wiring and we have a heavier load. Our fuse has to be rated for our application, and that's where a little bit of engineering has to happen.

We have to know how many amps our motor is going to draw when lifting our door. The wiring has to be rated to carry more than that many amps. Then we need a fuse that will blow at a lower amperage than the wire's maximum, but a greater amperage than the motor will draw in normal operation. And also, the power supply has to be rated to deliver the amp draw that the motor needs to operate the door.

It sounds to me like so far, everyone who has built one of these has gotten lucky (or did the engineering and just didn't write it all out) but personally, I wouldn't just repeat someone else's build and expect the same results and safe operation, unless I was sure that every detail was identical, and I knew that they had worked through the design to be sure that all of the parts were rated for the job. If any previous builders want to chime in on that, feel free - I'm not attacking anyone's previous work, I'm just asking a fair question in order to ensure everyone's safety in the future.

The good news is, even if it sounds complicated, designing a system like this to be safe is pretty easy. You just have to operate the motor under it's load, measure the amp draw, and make sure everything else can handle it. Leave enough gap between the motor's draw and the wire's rating to put a fuse rated between the two of them, and you're all set.

I will be happy to do the engineering for anyone who wants me to. Send me a PM so I can walk you through the process. You'll have to get the antenna first. Once you have that, there are several ways to proceed - you can send me the antenna for testing and I can send you back a complete design, or you can do your own testing and design, and I'll be happy to answer questions and guide you through it via PM.

joshremlin, it's been a while since your last post, did you get it worked out? I think the reason you only had a mm or two of movement is you were over-amping the power supply, and it shut down via an internal protection. But that's just a guess.

 

[jamiewayz]

I'm going to make an automatic door opener on a timer for my chicken coop with a car antenna. I found many places on BYC and Youtube that detail how to build one. Unfortunately there are conflicting answers as to how what type of power supply (amount of amps) it would take to power the antenna.

I've read 12 volt & 5 amps (and these supplies are near to impossible to find at a reasonable price) and I also read the wii game power adapters that are 12 volt 3.7 amps will work.

I want to go with as inexpensive as possible to get the job done.

So who out here has either made a car antenna door and how many amps is yours, or who knows how many amps a car antenna would take to work?

Here are the plans that I'm going to use :
https://www.backyardchickens.com/a/automatic-pop-hole-opener

Thank you very much for your help!!!

I would think a power supply out of a old computer installed in a water tight container woulf give u 12 volts at 5 amps and a number of other options the black leads are grounds and i think yellow is 12 volts but u should put a meter on and check it