I've got a Kadee #309 electromagnetic uncoupler. The directions say to use a 16 volt, 3 amp power supply. This is a hefty supply, but I found one at All Electronics. After I ordered it, I noticed a reader comment that the supply needs a "load resistor" to work properly.
I connected things up, and when I energized the magnet, nothing much happened. The voltage on the supply dropped to zero. When I released the button, it returned to 16 volts after a few seconds. So, I'm assuming that the coil is drawing too much power and the supply is shutting down until I release the button.
I'm a physicist, but the closest I get to double E is my shoe size. How big a load resistor should I use? Would it go in parallel with the coil, or in series? I plan to try a 10 ohm load first, because I have one around, but can anyone tell me what I should do?
It takes an iron man to play with a toy iron horse.
What's the model of power supply?
Springfield PA
HamltnblueWhat's the model of power supply?
It's this one:
http://www.allelectronics.com/make-a-store/item/PS-4002/POWER-SUPPLY-5V/12A-16V/3A-5V/0.8A-15V/0.8A/1.html
All Electronics doesn't have a spec sheet for that power supply, but at the top of the column containing it there is a notation "Must be tested under load."
This normally means that the power supply won't turn on until it has a sufficient load.
Unfortunately, there's no way of knowing what load is required unless you can find a spec sheet for it and know which output requires the load. My guess is that it would be the -5VDC output.
EDIT: Google to the Rescue. By typing EOS VLT100-4002, the search turned up all kinds of information about this power supply, including data about the required load --
http://www.e-datacom.com/pdf/ec/EOS%20VLT-100.pdf
The 3 amp load of the uncoupler exceeds the minimum load on the suitable voltage, so that shouldn't be a problem. Is the coil actually getting energized? See if a piece of metal is attracted to it while energized. They aren't made to be left on continuously though. The power supply isn't shutting down, is it? ANd you are using the proper output conenctions, those supplies have multiple voltages and 5V won't budge the uncoupler. Even the 12V might be a little weak. The only other option I see is 24V.
Personally I think that electomagnet is the most useless thing Kadee ever made. It need far too much power - there have been a couple of articles in MR and other mags about modifying them to be more efficient. That thing dates back to when anyone with a decent size layout had a 20 amp tranformer to power everything because the average HO loco drew 1.5 amps.
Edit: I see the model with 16V outout. If it shows 16V and drops to zero when you activate the electromagnet, you're overloading it. Minimum load on the 16V output is 0.1A, 100ma. Too little load is definitely NOT your problem.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks. I'll give it a try with a few different resistor in different configurations. With no load at all, my meter reads about 16 volts, so at least I know it's working.
Oddly, I have another one of these. I run it with a measley 12 volt, 1 amp supply, and it operates just fine. I tried this one on that supply. It would energize, but it wouldn't generate enough of a field to pull over a coupler.
If you read the comments on the link above one of the people note that you have to put a 3 amp load on the 5v output for the others to activate. I'm sure you can get a better supply than that.
The #309 works just fine for me. A GREAT item; although building your own would not be terribly difficult, it does take a little time and effort - easily avoided by the purchase of said item.
I use a home-brew power supply made from a Rat-Shack 3-amp transformer, a heavy-duty Rat-Shack bridge rectifier, and a hefty filter capacitor (also Rat Shack). Works great. No 'load resistor' needed.
Even a physicist should be able to do that.
One caution: as others mentioned, leaving the coil energized for more than a few seconds can develop excess heat, with possibly disastrous consequences.
jrc (MSEE, MSphysics; FTL drive engineer)
Measure the coil resistance of this new one that doesn't work and the old one that does. Bet the new one has a short int he coil somewhere. Like I said, if you're getting 16V out of the power supply with no load, it doesn't need a resistor to create a minimum load, the amp or so that the Kadee coil is supposed to draw is over the minimum load listed on the spec sheet.
I think the uncoupler itself is fine. I swapped out that supply for a 12-volt, 4-amp supply externally fused at 3 amps. When I hit the button, the voltage dropped a bit, and the magnet energized. However, it wasn't enough of a magnetic field to open the couplers. So, I'll have to look around for a heftier supply, one that doesn't have the "load" quirk.