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Electromagnet AC/DC Conversion - Help


Knuckles
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Hello.

 

I've used Dingham Electromagnets before on an old DC P4 layout.  The instructions say they can't be used with AC although this isn't strictly true as I was using the 16V AC output on the Gaugemaster Combi to good effect and just checked them on a old Hornby controller with its 15V AC supply and they work perfectly.

 

However, they DON'T work with the AC supply from my new layout with DCC track power, so fair enough.

 

Question is...how do I get them to work?   Instructions mention rectification so I'm assuming a bridge rectifier; if so any idea what type?  

 

Added a pic.

 

Any help appreciated. 20200719_181748.jpg.d566f255c90770388f63814ffa395bfe.jpg

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20 hours ago, Knuckles said:

However, they DON'T work with the AC supply from my new layout with DCC track power, so fair enough.

 

Question is...how do I get them to work?   Instructions mention rectification so I'm assuming a bridge rectifier; if so any idea what type?  

 

If you mean directly off the DCC track bus then be aware that it's very different AC (frequency and waveform) from what you were using before. It's not surprising it doesn't work. You should never connect anything like this directly to the DCC bus.

 

What current does the magnet take when energised?

 

I would not recommend powering any potentially high current devices like this even from a rectified DCC bus. If you booster is not conservatively rated for your layout then operating the magnet could affect the running of trains, due to the extra current required. You would be far better off to buy a cheap "wall wart" style power supply suitably rated for the magnet.

 

That note about rectification is potentially very misleading. Rectifying normal 16V AC would give you nearer 22V DC, not 12V! What exactly do they mean by "nominal" 12V? You would also need a regulator if the magnet really is rated for only 12V.

 

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Hello, I'm unsure what they mean hence this thread. :D

 

I think the coils use about 1 amp, it's fine for what I'm running and how much and you only use the electromagnets for about a single second.

 

I'd agree the waveform is different on DCC AC than DC AC as it no doubt is how the signals are transmitted.

 

I'm trying to avoid using the DC controller and a separate circuit though.  Don't really want to waste another plug socket you see!

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I don't want to use DCC to control the electromagnets though.  Just the track power if possible.

 

Planning to just wire the non latching push to make switches on the board edge in line with where they need to be uncoupled.

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I  understand the desire to keep wiring to a minimum, but the flip side is having everything on one supply can make fault finding difficult and as @Crossland says could affect the running of the trains.  A separate accessory bus with its own transformer, wall wart etc, has to be a better solution.  The time spent installing it may well save hours fault finding in future. Like separating track power and points so you can actually re set the points when something shorts the track out.

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I hear you.

 

Got a wee update though.  Tried a 9v battery and it worked!   It pulled the dropper pretty quick, so thinking I'll install them with a battery to each board.  Saves board join wiring and the plug.

 

If more power is needed can make a bank of different ones to achieve extra juice and if/when they run out pretty cheap to replace.  

 

Electromagnets are only used for about 1 second at a time so in theory should last ages.

 

Thinking will do this unless a better idea comes along.

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12 hours ago, Knuckles said:

I hear you.

 

Got a wee update though.  Tried a 9v battery and it worked!   It pulled the dropper pretty quick, so thinking I'll install them with a battery to each board.  Saves board join wiring and the plug.

 

If more power is needed can make a bank of different ones to achieve extra juice and if/when they run out pretty cheap to replace.  

 

Electromagnets are only used for about 1 second at a time so in theory should last ages.

 

Thinking will do this unless a better idea comes along.

 

You could make up custom batteries using rechargeable AA cells in battery holders. Rechargeables have a lower internal resistance and so can supply more current without the voltage drooping as much (just don't leave the magnet energised for too long) and an AA based pack will last a lot longer than a PP9. USe Eneloop or equivalent, rather than NiCads to avoid self discharge.

 

 

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Thanks for the tip.  Will look into it.

 

Usually I use the controllers' 15-16v AC supply and the 9V battery seems fine but I can see combined AAs being better to increase voltage if needing a bit more power to flip the coupling properly.

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Andrew's point is that a block of six AA's in a cheap battery holder will give nominal 9v and will have substantially more "oompfff" than a single PP3 9v battery, both current delivered and energy stored (so last longer between charges).   AA's are also usually cheaper.   

 

The "Eneloop" types are rechargeable, but hold their charge for months, if not years, unlike earlier rechargeable battery chemistry which would often decay away in storage.  

 

 

- Nigel

 

 

 

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