Input Appreciated

[mtetleton]

I’m building a prop for my children’s band performance this year. I built a box that will conceal a drop down cloth panel. I’m trying to open the door remotely to reveal the panel by it rolling down. I bought an electrimagnetic door closer and it works, but it’s powered by a 12v 23amp battery. The magnet has to be on to keep the door closed and turned off to open the magnet/door. The issue is that the small battery only last about 7 minutes pushing current to the magnet, which isn’t nearly enough time for the band to get on the field and perform before the battery goes dead, revealing the panel and ruining the show. I need an alternative that will keep the magnet closed at least an hour and be controlled by remote, so the band director can open the door and reveal whenever she wants. Any help would be greatly appreciated.

 

[For The Popcorn]

Something like this electric car lock solenoid could work for you. Pulse it with one polarity, the solenoid plunger extends. Pulse it with reverse polarity and it retracts.

 

[Diver300]

Depending on the force on the closer, you can almost certainly reduce the current in the closer and keep the door closed. If you use PWM or a buck regulator you should be able to get a lot longer from the battery.

 

[mtetleton]

I looked up the buck regulator. The magnet I bought has a 65 lb holding capacity, so if I reduce the input, are you saying it would reduce the magnet holding strength and thereby use less energy/battery? I probably only need 15-20 lbs of holding capacity. And would this go between the rf switch and the magnet?

 

[For The Popcorn]

The electric car door lock I showed about requires power only when changing states. Push a button. Power is applied and the solenoid retracts. Release the button, no more power draw.

 

[mtetleton]

Popcorn……can it still be placed behind the rf switch and be controlled remotely? At that point, the only draw on the battery constant would be the light on the rf switch, correct?

 

[For The Popcorn]

Yep. It may take a bit of engineering to make it pull some locking mechanism reliably – something like a loose-fit pin. Those guys have about a 1" throw, and I suspect 8 C or D batteries would operate it reliability. Perhaps even 8 AA batteries.

 

[Diver300]

I looked up the buck regulator. The magnet I bought has a 65 lb holding capacity, so if I reduce the input, are you saying it would reduce the magnet holding strength and thereby use less energy/battery? I probably only need 15-20 lbs of holding capacity. And would this go between the rf switch and the magnet?

Yes, it would be between the RF switch and the magnet.

As you only need about 1/3rd of the force, that should work with 1/3rd of the current, so 1/3rd of the voltage and 1/9th of the power, so it should last a lot longer.

Have you got the specifications of the magnet and the battery? Is it a lead-acid 23 Amp-hour battery? To get one of those to be discharged in 7 minutes takes a lot of current, at least 50 A, which would mean over 600 W of power. That is more than a 65 lb magnet would use.

 

[mtetleton]

The rf switch calls for a 12v 23a battery for power, which is about half the size of a AAA battery. The magnet says it takes 0.5 Amp (minimum) required power. I’m just not knowledgeable in power ratings.

 

[Diver300]

The rf switch calls for a 12v 23a battery for power, which is about half the size of a AAA battery. The magnet says it takes 0.5 Amp (minimum) required power. I’m just not knowledgeable in power ratings.

OK, I had seriously misunderstood what battery you were using.

You could use a much, much larger battery, and make it rechargeable, and it would still be small.

As far as I can see, the 12V LR23A battery is rated at 55 mAh, so I am quite surprised that it lasted as long as 7 minutes if the magnets takes at 0.5 A

I suggest that you buy a 5 V to 12 V boost converter, such as this:- https://www.ebay.co.uk/itm/175750409127
Then cut the round plug off the end and wire the red and black cores to the +ve and -ve respectively of where the LR23A was connected.

Then plug the boost converter into a rechargeable power bank. The cheapest power bank from Anker will run the magnet for several hours.

 

[mtetleton]

That totally makes sense Diver. For $7.99, I went ahead and bought the door lock solenoid as a back up plan. Both of your ideas have been such a blessing for our band kids. Thank you both for your direction and recommendations on this project. The parts will be in tomorrow, so I will let y’all know the results.

 

[mtetleton]

It works! I ordered a couple of the wrong parts but got the right parts in. I ran it all night long on a 10,000 Mah battery bank and it held. We will at most need it to hold for 1 hour. Thank you again to both of you for your input in helping me build this prop. Maybe I’ll be able to post a short video of it actually working. Thanks again. Michael