The topic of tortoise hum problem has been discussed in the past but I have a very specific question about the AH-362 MRC Tortoise Switch Power Supply which I do not think was available when the hum issue was discussed.
I am using the AH-362 MRC Tortoise Switch Power Supply to control several Tortoises using a simple SPDT switch. The MRC has three wires, common, +12VDC, and -12VDC. The common is conntected to one Tortoise motor lead and the other two outputs to the SPDT switch which feeds the second motor lead. The Tortoises have a hum when switched either way. Is this due to the power supply and if so, how could I solve the problem? What am I missing?
Potential downside of using that type of power supply with SPDT instead of a standard DC supply and a DPDT toggle - it's only half wave rectified to there is plenty of leftover AC hum.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
wouldn't adding 1000uF caps help?
greg - Philadelphia & Reading / Reading
gregc wouldn't adding 1000uF caps help?
RR_Mel I guess that would depend how much ripple was there, a large cap could increase the voltage if there is a lot of ripple. I’d try a 500 watching the DC voltage for increase. If it doesn’t raise the voltage more than a volt a 1K or pair wound really put a dent in the hum. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
I can't speak for the power supply in question, but my whole layout is full of home made center tap DC power supplies.
+12 volts to neutral, -12 volts to neutral, 24 volts phase to phase for my control relays.
But to built them I put a full wave bridge on each of two transformers then connect the positive and negative together. No hum, on my switch machines or my 24 volt relays.
A 500uF cap on each bridge output will smooth it out more.
Sheldon
That's the difference between full wave rectification and half wave. I don;t have one to take apart, but I would make a pretty heavy bet that MRC did not use two power supplies common'd together - rather a simple center tap transformer with a single diode on each of the legs installed opposite each other so one is + relative to the center tap and the other is -.
Adding filtering may work, but check the resulting output voltage - adding a significant filter capacitor raises the voltage to the AC peak so if it's already near 12V without the filter caps, adding them can easily push it over 15V. This might not be a problem if you have LEDs in series with the motors as position indicators, a pair of bicolor LEDs in series will drop the voltage back under 12.
rrinker That's the difference between full wave rectification and half wave. I don;t have one to take apart, but I would make a pretty heavy bet that MRC did not use two power supplies common'd together - rather a simple center tap transformer with a single diode on each of the legs installed opposite each other so one is + relative to the center tap and the other is -. Adding filtering may work, but check the resulting output voltage - adding a significant filter capacitor raises the voltage to the AC peak so if it's already near 12V without the filter caps, adding them can easily push it over 15V. This might not be a problem if you have LEDs in series with the motors as position indicators, a pair of bicolor LEDs in series will drop the voltage back under 12. --Randy
Yes, I suspect you are right about that power supply.
I went back and looked at the Tortoise spec sheet and saw that it said filtering was not necessary. At stall, they draw about 15mA thus creating a hum if ripple is present. My conclusion is that if you can stand the hum, you probably will not hurt the Tortoise machines especially when using a center tap MRC AC to DC converter.