How do I convert 16v AC to 12v DC?

[AndyID]

As Ruston only wants to power DG electromagnets, I'm thinking the simplest solution might be a rectifier of some sort and a suitably sized power resistor.

 

However, we'd need to know a couple of things:

 

1) What is the output current rating of the transformer?

 

2) Is the output of the transformer "centre-tapped" or does it only have two possible connections to the secondary winding?

 

3) How "smooth" does the supply to the electromagnet have to be? In other words, will it work properly on full-wave rectified DC without a smoothing capacitor? 

 

EDIT:

Another question: Will the electromagnet work on AC? Perhaps all that's needed is a resistor.

Edited May 16, 2017 by AndyID

[kevinlms]

As Ruston only wants to power DG electromagnets, I'm thinking the simplest solution might be a rectifier of some sort and a suitably sized power resistor.

 

However, we'd need to know a couple of things:

 

1) What is the output current rating of the transformer?

 

2) Is the output of the transformer "centre-tapped" or does it only have two possible connections to the secondary winding?

 

3) How "smooth" does the supply to the electromagnet have to be? In other words, will it work properly on full-wave rectified DC without a smoothing capacitor? 

 

EDIT:

Another question: Will the electromagnet work on AC? Perhaps all that's needed is a resistor.

Electrical Supply – The Dingham electromagnets should be operated on a nominal 12V DC supply (usually obtained by rectification of 16V AC). Switching MUST be via a non-locking push-to-make switch (e.g. All Components Code SMT6 or Maplin Code FH59P) or a non-locking biased-to-off toggle switch (e.g. All Components SPB1 series or Maplin Code FH03D). The electromagnets will NOT operate on AC.

 

From

 

http://www.dingham.co.uk/em_inst.htm

 

 

I would advise that the CORRECT power supply be used for the job. Perhaps other brands are different, but I doubt it. The coils could have a higher resistance, so a lower Amp power supply could be used, but the principle remains the same.

 

 

Edit to add.

 

I believe post 11, had the correct and simplest answer.

Edited May 17, 2017 by kevinlms

[AndyID]

Electrical Supply – The Dingham electromagnets should be operated on a nominal 12V DC supply (usually obtained by rectification of 16V AC). Switching MUST be via a non-locking push-to-make switch (e.g. All Components Code SMT6 or Maplin Code FH59P) or a non-locking biased-to-off toggle switch (e.g. All Components SPB1 series or Maplin Code FH03D). The electromagnets will NOT operate on AC.

 

From

 

http://www.dingham.co.uk/em_inst.htm

 

 

I would advise that the CORRECT power supply be used for the job. Perhaps other brands are different, but I doubt it. The coils could have a higher resistance, so a lower Amp power supply could be used, but the principle remains the same.

 

 

Edit to add.

 

I believe post 11, had the correct and simplest answer.

 

I imagine the solution offered in post 11 would work, but it doesn't exactly meet Ruston's requirements. He would like to use a transformer he already has.

 

So no AC then, but it seems that rectified AC should work if Ruston's existing transformer can deliver enough current.

Edited May 17, 2017 by AndyID

[kevinlms]

I imagine the solution offered in post 11 would work, but it doesn't exactly meet Ruston's requirements. He would like to use a transformer he already has.

 

So no AC then, but it seems that rectified AC should work if Ruston's existing transformer can deliver enough current.

 

Thst isn't Ruston's conclusion on his last post on page 2 (sorry the mobile version of RMweb doesn't have post numbers). If his existing transformer doesn't have the grunt required, then another solution is required - hence my recommendation of post 11.

 

Edited for typo.

Edited May 17, 2017 by kevinlms

[AndyID]

Thst isn't Ruston's conclusion on his last post on page 2 (sorry the monile version of RMweb doesn't have post numbers). If his existing transformer doesn't have the grunt required, then another solution is required - hence my recommendation of post 11.

 

We don't know if his transformer can handle the current or not. That's why I asked the question. The problem he had was that the regulator he bought can only deliver one amp but the electromagnet needs 1.5 amps.

[kevinlms]

We don't know if his transformer can handle the current or not. That's why I asked the question. The problem he had was that the regulator he bought can only deliver one amp but the electromagnet needs 1.5 amps.

Ruston's original post says this.

 

"I would like to be able to run the uncouplers using the same 16v AC transformer as the loco controller and points use, so is there a gadget available that can convert 16v AC to 12v DC?"

 

Whether it has enough capacity seems most unlikely. Regardless, I wouldn't recommend it. Definitely a no, no, if Ruston uses a common return.

 

Others have also commented on the unsuitability, of using a device that takes a large amount of current. Almost certainly, such a spike would affect train running, if the same supply was used.

 

Edit to add.

 

Unfortunately, 'something for nothing' is the way this thread has been become. If the criteria is to use one power supply for everything, that's what DCC can do, but it relies on sophisticated electronics and protection to do so. However, that is nowhere near the wanted solution, Ruston asked about.

Edited May 17, 2017 by kevinlms

[Porcy Mane]

Cheap and cheerful.

 

http://www.gaugemaster.com/item_details.asp?code=GM40&style=main&strType=&Mcode=Gaugemaster+GM40

 

Gaugemaster-gm40.pdf

 

I know folk that have been using these to rectify 16v AC to 12v dc for decades. Usually for  12v accessories but also E-magnets. You just have to ensure that the 16volt AC supply can supply 1.5 amps max.

 

Gaugemaster use a similar AC/DC adapter plate with their 16 volt AC WM1 wall wart and how many thousands of those are powering train sets and their associated accessories around the UK.

Usual disclaimer.

 

Similar  cheap as chips converters can be had from Ebay but it looks like their maximum current capacity is 1 amp.

 

http://www.ebay.co.uk/itm/AC-DC-Converter-6-12V-to-12V-Full-bridge-Rectifier-Filter-Power-Supply-Module-DT/182013000391?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D43783%26meid%3D41d565090fc24d3c828e97aee437fbd7%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D172283119483

 

I've successfully used the positive side (LM317) of this board to power DC accessories and self wound electro-magnets. It can work with 1.5 amps.

 

http://www.ebay.co.uk/itm/262483263496?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

P

Edited May 17, 2017 by Porcy Mane

[meil]

That will not give you DC it will give you full wave rectified DC.

[AndyID]

That will not give you DC it will give you full wave rectified DC.

According to the info posted by Kevin the electromagnet will operate on full-wave rectified DC.

[Porcy Mane]

According to the info posted by Kevin the electromagnet will operate on full-wave rectified DC.

 

Exactly. It successfully operates the magnets. Most of the sources I linked to above also have smoothing caps. Nothing to get hung up about.

[meil]

According to the info posted by Kevin the electromagnet will operate on full-wave rectified DC.

That wasn't my point. You made an incorrect statement. I'm not concerned whether it operates the electro magnet or not.

[Baby Deltic]

 

I had a similar problem when I was building the control panel for Sumatra Road. The centre transformer in the panel is a 24V transformer which actually gave out 28VAC and 37VDC when rectrified which was a pain in the backside because regulation by voltage divider and 78XX series regulator would have created a lot of heat and limited the current to 1-2A. Luckily, being a service engineer I was able to raid a stockpile of obsolete kit and get hold of a 24VDC switched mode supply. The circuit board from this was removed and bolted in my control panel using the 2N3055 transistor mounts to secure it via the transistor to the base plate. Being switched mode, there is little to no heat given off by the 2N3055 and there is enough grunt to power multiple SEEP point motors simultaneously with or without a CDU. I obviously use a CDU to avoid the risk of a point motor catching fire if a switch malfunctions and stays closed.

[ejstubbs]

That wasn't my point. You made an incorrect statement. I'm not concerned whether it operates the electro magnet or not.

 

 

Sorry, couldn't resist 

[kevinlms]

That wasn't my point. You made an incorrect statement. I'm not concerned whether it operates the electro magnet or not.

Huh. but that is the purpose of this thread, started by Ruston - to operate his uncouplers, preferably by the same power supply used for other things. However as he has discovered, it seems that its not practical to do so, as his 'converter', doesn't give enough power. The ucouplers require 1.5 Amp, but it only supplies 1 Amp.

[AndyID]

That wasn't my point. You made an incorrect statement. I'm not concerned whether it operates the electro magnet or not.

Humble apologies, but what was incorrect about it?

[Ruston]

Thanks to everyone who has contributed to this but, to be honest, I have been blinded by science a lot of the time, not to mention being given conflicting information,

 

One piece of conflicting information that is that I am being told by some people that the electromagnets will work on AC and that they won't, by others.

 

FACT: They do work on AC because I have now tried them for myself. They work just as well as on the large 12vDC battery that I was using.

 

But I suppose that being 4 volts more than they were designed for means I could possibly damage them, So here's another question that I expect won't have a straightforward answer (Anything involving electrictity never seems to be straightforward!).

 

Can I put a resistor in line in the 16v AC circuit to bring it down to 12v? If so, how many ohms resistance do I need to do this?

[AndyID]

Thanks to everyone who has contributed to this but, to be honest, I have been blinded by science a lot of the time, not to mention being given conflicting information,

 

One piece of conflicting information that is that I am being told by some people that the electromagnets will work on AC and that they won't, by others.

 

FACT: They do work on AC because I have now tried them for myself. They work just as well as on the large 12vDC battery that I was using.

 

But I suppose that being 4 volts more than they were designed for means I could possibly damage them, So here's another question that I expect won't have a straightforward answer (Anything involving electrictity never seems to be straightforward!).

 

Can I put a resistor in line in the 16v AC circuit to bring it down to 12v? If so, how many ohms resistance do I need to do this?

 

Hi Ruston,

 

You are correct. There is no straightforward answer

 

It depends on the inductance of the electromagnet and I don't think we know what that is. It's quite possible that the inductance is great enough to limit the current on 16V AC so that the power dissipated in the electromagnet is about the same as it is on 12V DC in which case you don't need a resistor at all.

 

I'd suggest you do a little experiment. Operate the electromagnet magnet a few times on DC and see how hot it gets. Let it cool down then do the same test with AC. If there is no noticeable difference in the temperature you are good to go.

 

We know the electromagnet has a resistance of around 8 ohms (12 divided by 1.5) so if you think you need to reduce the voltage with a resistor I'd suggest you try 2.2 ohms. You could get two of them and put them in series to make 4.4 ohms or 1.1 ohms if you connect them in parallel. They should be at least 5 watt resistors.

 

Hope this helps!

 

Andy

[Junctionmad]

Most electromagnets will work on AC and DC , however the magnetic field reverse on AC and overall strength of the electromagnet will be lower in AC then DC.  Some electromagnets are would so the they have to be used on DC , typically ferrite based etc 

[Ron Solly]

Unless the existing power supply used by Ruston has independent secondary windings - one for train control of DC  & a second for AC for accessories such as lights, no way would I use the nominal 16Vac Output for circuits requiring  over 1 amp whilst running locos as the sudden heavy load can make the loco stutter.