250 ma load and 3A supply - is it okay?


MilwRoader_Steve

MilwRoader_Steve

Well-Known Member
I know, a stupid question:

Walthers New turntables. They give a range of power supplies in either VAC or VDC. That, I'm okay with. They want 250ma, I assume that is a max?

So, Can I power this from a 18VDC common supply that is rated for 3+ amps? I'm also putting in some Kadee electromagnet decouplers, and they need 18 VDC and 3A. I doubt I would run both the TT and the decoupler at the same time, but what if I did? Can I connect both loads to a power supply that is rated for 18 VDC and 3.33 A?

So bottom line question is this (and I think I know he answer, but would appreciate hearing it in plain-speak from someone more knowledgeable): If a load only draws 250ma, can I hook it to a source that provides significantly more than that?
 
Short answer is yes you can hook a smaller load to a higher output source. If you think about it you do it all the time. Can you hook a 1500 watt hair dryer to the same outlet you plug a 100 watt lamp into? Watts are computed by multiplying voltage X amps, so if you know any 2 you can compute the other.
On the first question, your output of 3.33 amps is higher than your max need of 3.250 amps. So you should be fine.
 
Thanks. I mentioned it was a ... ... ... elementary question. I have an old laptop PS rated for 18 VDC and 3.33A that I plan to use for a 18 VDC bus.

Probably scary how much wiring I have done over the years with my limited skills and knowledge, so your affirmation is much appreciated. There will be more Qs <grin> ------Steve
 
Not so fast!! What does the TT say the maximum voltage should be for the power supply? It matters. As you raise voltage, you also raise the motor's obligation to use available wattage/amperage. Yes, it may not NEED to use more than about 0.4 amps, but if your power supply exceeds the maximum rated voltage, you will find that you can overdrive the motor in the TT and burn it out. Say something like a foam rubber 'bush' falls into the pit and jams up the works. The motor tries to work the bridge past the jam, and it does this by increasing its amperage draw. Increased amperage = more heat = burned out motor or other electrical components that are in series.
 
if its rated for 12VDC and you operate at 18VDC it will also run faster , which is usually undesirable in TT . Walwarts are cheap 12V 1amp is <$10, you can also get a LM317 adjustable linear regulator board for usually <$3.


Switch mode power supplies (laptop or usually non class 2 walwart) are usually well regulated so they will current limit out and the voltage will sag if overloaded.They limit the VA / watt output so the supply doesn't overheat and start a fire. If it does overheat it should do a thermal shutdown.

You may have to protect the supply from the uncoupler with diode , the flyback from the coil could kill the supply, and any other silicon thats on that supply.
 
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I love when folks talk electronics. I have no real clue except I know to stay away from the house wiring.

TomO
 
Here is the specs:

2860 specs.jpg
 
I would use a separate supply for turntable to be safe . The flyback off the electromagnetic uncouplers could kill the the controls on the TT. In any case I would put diodes across the uncoupler coils.

Without diodes the flyback off the uncoupler coils could easily reach into the thousands of volts.
 
It says not to use track power throttle, if I ever get one of these, would one of my extra throttles do the job if used independently here ?
 
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