Looks like a good test well run. 0.6A is right in the ball park.
As somebody pointed out, wheels slipping is full load and is above the load you'd normally run at. Temperature rise is the usual metric used in specifying the load rating. Total temperature counts when your defining the limits.
Try the test with the engine blocked on a piece of track.
Actually - it's a cheap switcher out of some old piece of computer equipment - capable of 8A (supposedly) 12V and 12A 5V (1.2A -12V).
The inductive "kick" was probably screwing with the regulator...
Certainly good enough for sitting on a shelf... Some day maybe it'll once again have more than 9 inches of track to run on.
best regards...
These power supplies do not play well with motors, actually. there was a thread about this a while back, and I forget the technical reasons. Should work fine as source for layout lighting, though.
Try an electrical lubricant (eg, ConductaLube, made by AeroCar). It will reduce contact resistance at the commutator, and you should see a drop of 30% or more in current draw at any given load.
The ordinary PC power supplies need a solid load on their logic power (5 or 3.3Volt) in order to stabilize the regulator. With no load on the logic power all sorts of bad things happen.
David Starr
What would e an effective "...solid losd..."?
Incandescent bulb of appropriate voltage? Resistor just disappating heat?
I'm looking to use some older PC PSes to provide power for slow motion switch machines from the 12 v. leads.
Thanks.
Yes, which is why I installed load resistors permanently across all three supplies... "bleeder current" is about 5% of rated load...
*usually* that's enough to keep it happy... obviously with a seriously inductive load - it wasn't happy and all. IIRC it came out of a large hard disk cabinet - which is why the +12V is so "beefy"...best regards...
yeah, you have the idea - some current to keep the output filters bled off so the regulating circuit can keep control. Without sufficient "load" the supply could drift slightly high - the regulator - in trying to bring it down - would come close to completely shutting down - and when a load would hit - it would take a bit for the regulator to react...
Lab quality supplies often use "active sinks" - i.e. pass elements to a minus supply to "suck down" the filters really fast when needed. Most lab supplies I'm familiar with are rated to "sink" roughly 10% of the current they are designed to supply.
Back to your question - use a resistive load that consumes enough current so that your powered device doesn't overload the supply while working - yet enough load so the supply is stable when the switched load is cycled off and on... A little trial and "tweak" can determine good enough values...
best regards...
Thank you!
I'd go for 1 amp or more on a PC supply. That's maybe 50 LEDs, or 15
6-volt incandescent lamps, or a 5 ohm resistor. The 5 ohm resister will get hot, 'cause 1 amp times 5 volts is 5 watts. I'd go for a 10 watt or larger resistor to keep the heat down.David Starr
I wouldn't put anything, especially anything conductive, on the commutator. Lubricants tent to clog up the gaps between com plates with carbon dust soaked in oil and also prevent free movement of the brushes in the brush holders. It may appear to improve things but the gain is short term.
What happens between the brush and com is as close to voodoo as any electrical thing gets. The surface of the com plate carries a film made up of brush and commutator material, and whatever is in the air... usually moisture. Solvents, smoke, gasses, oils, etc nearly always do bad things to the film.
The surface has to be CLEAN (before the film is formed) and even, and the brush pressure between 3&4 pounds/sq inch. Given the tiny size of these brushes, that's a very small force. If things are working right, there will be very little sparking and the com surface will have a uniform color, usually copper (but sometimes darker) with no streaks. Too much brush pressure wears the brushes and acts like a brake while too little will electrically erode the com and brush surface.
The product I recommend does none of these things. It just works as I describe, is all. It also cleans the commutator (as you rightly recommend doing in the part I've snipped.)
[...]
I was looking through my old MR's today and I found this in the Jan 1994 60th Aniversary Issue. They asked their readers what was the most profound change in the hobby over those 60 years. One reader reponded:
"Athearn's introduction of the HO scale diesel in
1954 (under the Globe name), in my opinion, changed the industry overnight in three ways. First, it forever legitimized the use of styrene plastic for locomotives. The detail of the engine exceeded everything else at the time, incluing metal castings. Second, its low cost but high appeal probably introduced thousands of budget-minded people to the hobby. Third, many a die-hard steam modeler probably found a sudden need for diesels on their pikes with this model! More amazing is the fact that the Athearn F7 will have been in production for 40 years in 1994 and is still a great-looking, low-cost, popular model. Happy Birthday Model Railroader and Athearn F7." L. Ivan Potoski, Henderson, NV.Have something to add? Share your thoughts — no account required.
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