Simple but confusing question about large electromagnetic lock

[Troon_Patrol]

TL;DR I have a commercial grade 1500LB 12/24 DC electromagnet. It has no COM/NO/NC only power supplied/denied. It holds beautifully strong when powered. It's operating power is 12/24VDC controlled by jumpers, it is currently set to 12VDC. The power running to the unit is simple low voltage copper wire approximately 15 feet if that makes difference. Voltage at the unit is roughly 13.5 VDC not miles away from 12VDC.

When power is cut to the magnet, emphasis on CUT, 0 volts it still holds with a large amount of force maybe 100-200lbs or so, this is not acceptable this magnet needs to simply release as it's designed. I have two separate units I have tried both produce the same results. As a redneck engineer I'm running out ideas here. The relay I installed cuts all power to this thing and it's still holding very strong, I've tested this 3 different ways including just disconnecting the entire controller and power and obviously checking with a volt meter. bridging the power supplied to the magnet seems to have no effect on reducing it's residual hold. Time seems to be a factor, I give it 3 seconds of power and cut and it releases just as it should I leave it engaged for hours and it holds for dear life without any source of power.

Whats the solution? Do I shim the surfaces with something that reduces hold?

Picture of very similar unit for reference. Once again the units I am working with have only 2 wires for power only. The unit pictured appears to have extra wires a closed sensor alerting the controller unit when/open closed.

 

[bar soap]

Heat the magnet up really hot with a blowtorch and the unwanted magnetism should go away. If that doesn't work beat it with a hammer and that might make the residual magnetism go away. After that it should only work with power supplied

 

[Dagoth AMOGUS]

Look for a terminal you can hack to override the door controls

 

[Grim_Autismo]

Do you have a voltmeter? If it's not dropping to 0, then there could be residual power, and it's fucking it up; you'll want to check it to be sure. (You say it's on 0 volts, but unless you check it, you won't know for sure, it could be power in the field). The metal plate may have also become magnetized after a long period.

Asked around, someone said that if it's supposed to unlock with a keycard or something else, and it's not being triggered, it won't unlock. Could be this is an issue for you too with those sensors, something worth checking out.

 

[Sam Losco]

There should be a little circuit board where you wire up that is there to quickly de-magnetize it when voltage drops out. Those boards go bad and the magnet will then hold charge like that for a while. One trick to help is to put a small strip of electrical tape (or something similar) on the surface. Those magnets are strong but they don't extend out far at all so simply putting some tape on it will lessen the hold strength. This applies to when you want it to hold as well, so if it's a 1200lbs hold force, the tape will lessen that some, but not enough to really matter unless you go overboard. I'm talking like a 4-6inch piece of tape is all you want.

If there is no circuit board and you're wiring straight to the magnet, then that's your problem.

What you described "Time seems to be a factor, I give it 3 seconds of power and cut and it releases just as it should I leave it engaged for hours and it holds for dear life without any source of power." is exactly what happens when the board is going bad or not present.

 

[PovertySprocket]

Tried reverse polarity or hooking a draw (car taillight bulb)?

By reverse polarity i mean sending a much lower voltage backward to counteract the direction of the residual magnetism.

 

[geckogoy]

Whats the solution?

Heat the magnet up really hot with a blowtorch and the unwanted magnetism should go away. If that doesn't work beat it with a hammer and that might make the residual magnetism go away. After that it should only work with power supplied

This guy is probably right that the components are residually magnetic

Can you report back on whether either chunk is passively magnetic and if its particularly strong? The electromagnet side even if magnetized might not have that much metal in it so may not be that strong, in which case you may just get a new chunk of steel for the non magnet side and not even have to torch anything

 

[The Connected Nose]

Make sure you're switching/cutting power on the positive wire. If there's no internal MOV, might need to add one, just make sure it's oriented properly.

I'm not an expert, but those are usually required to shunt any residual current away from the magnet so the field collapses quickly.

 

[TheOtherSideofMakeBelieve]

I have zero experience with these in particular but I have worked with chinese electronics so I'm only mostly pulling this out of my ass based on experience and what other people have said here. If it's a straight-from-china job that was exported despite being intended for the chinese market, usually those have the polarities of the wires backwards compared to American standards, black for negative/neutral and white for positive/hot. For AC stuff this tends to not matter, at least from a functionality perspective, though it might be a safety issue if something easy to touch remains hot while the device is powered off. In the case of this though, I imagine the electromagnet would function regardless of the polarity of the DC power it's getting but someone mentioned there generally being electronics inside that are supposed to function to demagnetize it once power has been killed. Those, I would imagine, are far less likely to operate if they're getting -12v rather than the +12 they expect

 

[Troon_Patrol]

Heat the magnet up really hot with a blowtorch and the unwanted magnetism should go away. If that doesn't work beat it with a hammer and that might make the residual magnetism go away. After that it should only work with power supplied

The "mating" ferrous plate has no magnetic charge. The electromagnet assembly itself is an aluminum body and has at least a 3/16" Aluminum plate separating it from the structure supporting it, it has steel ferrous screws, these are in the factory appropriate places.

Look for a terminal you can hack to override the door controls

This an entry point I want to secure, not bypass or gain entry to. The idea is to have nominally 1500LBs holding the entry point shut till I kill power and it opens. 101 ways to bypass or destroy the unit and gain entry that is not the goal here. I can honestly break into realistically anything and hotwire about %90 cars on the road that is not the goal here.

Do you have a voltmeter? If it's not dropping to 0, then there could be residual power, and it's fucking it up; you'll want to check it to be sure. (You say it's on 0 volts, but unless you check it, you won't know for sure, it could be power in the field). The metal plate may have also become magnetized after a long period.

Asked around, someone said that if it's supposed to unlock with a keycard or something else, and it's not being triggered, it won't unlock. Could be this is an issue for you too with those sensors, something worth checking out.

Yes of of course I have voltmeter and as I said I am literally cutting all power to the unit by disconnecting both pos/neg 13VDC so even if I had no volt meter I'm dead sure I am depriving this thing of all power.

These are very simple devices with small board that has two very small flat capacitors (MOV resistors) approximately the size of 1/4" in diameter. The idea I cut power to this thing and these two tiny little devices are running it for longer than literally 2 seconds makes no sense to me. There are no other components on the board , no internal battery, not COM/NO/NC wiring.

I engineered the entire system myself and it was working fine for years. A pocket sized remote triggers the controller, the controller powers the entry point open (think hospital auto door) with a powerful DC motor it also provides 12VDC to a basic automotive relay I added, this relay cuts ALL power the maglock. Its not that complex system but it does involve several components from at least 4 different manufactures.

It's supposed to go:

Remote click> maglock releases> power door opens.

Remote click power door closes, magnet meets and secures entry.

worked great for years then got maglock issues and just relied on the door motor to keep the point entry secure, there is of course a manual lock should the need arise.

This guy is probably right that the components are residually magnetic

Can you report back on whether either chunk is passively magnetic and if its particularly strong? The electromagnet side even if magnetized might not have that much metal in it so may not be that strong, in which case you may just get a new chunk of steel for the non magnet side and not even have to torch anything

Once again the mating ferrous plate is non magnetic at this time, won't even hold paperclip. When power is applied for a mere 3 seconds and then cut it separates without issue.

Make sure you're switching/cutting power on the positive wire. If there's no internal MOV, might need to add one, just make sure it's oriented properly.

I'm not an expert, but those are usually required to shunt any residual current away from the magnet so the field collapses quickly.

I had a long talk with tech support and what I thought were capacitors were actually MOV units, they are the only two components on the board, the board is literally an +/- connection two MOVs and 4 jumper pins for 12/24 VCDC settings and YES they are set for 12 VDC. Actual power at the board is running about 13VDC. Tech who seemed to know wtf he was talking about didn't have an answer for me. I am certain I have polarity correct but I might swap polarity to see if that does anything.

 

[Vecr]

I had a long talk with tech support and what I thought were capacitors were actually MOV units, they are the only two components on the board, the board is literally an +/- connection two MOVs and 4 jumper pins for 12/24 VCDC settings and YES they are set for 12 VDC. Actual power at the board is running about 13VDC. Tech who seemed to know wtf he was talking about didn't have an answer for me. I am certain I have polarity correct but I might swap polarity to see if that does anything.

Do you know what the MOVs are? If you can solder I'd buy new MOVs and build a new circuit board and see if that fixes it.

 

[Troon_Patrol]

Do you know what the MOVs are? If you can solder I'd buy new MOVs and build a new circuit board and see if that fixes it.

There are markings, I'll break out the electronic microscope tomorrow and see if I can get some specs.

Yes, I have a reworker and a very good Hakko soldering rig. I have removed and reinstalled 30-40 leg micro-controllers and reinstalled them, I absolutely hate that level of detail but, yes I am capable of simple two leg components replacement.

EDIT: I attempted to get them to just send me a controller board, they wouldn't. These units are made in china and probably 3 companies at least put their name on the exact same hardware. I might just find a another company willing to send me another board.