I am about to replace a burned out snap relay switch machine with a tortoise. The relays have been powered by a 16 volt DC power source. (That worked the relays very well until I was working on something, did not have my hearing aids on, and leaned on the momentary contact switch for several minutes… Duh!) I am replacing the burned out unit with a tortoise and want to still use the 16 volt DC power source as it is a seperate bus going around the layout for DC powered units. My question is this: How much resistance should I add in series with the torti to bring the voltage in line for operation? I believe that the torti has about 600 ohms resistance and can take about 20Ma. My guess is that I should add somewhere between 600 and 1000 ohms to get the best operation?
I’m thinking smaller - you only have to drop 4 volts at 20ma. Now I’m trying to dredge up some stuff I haven’t used in 20 years… it’s not the same as a simpel voltage drop. Maybe around a 420 ohm resistor, if the internal resistance is 600 ohms.
Or just put some 1N4001 type diodes in series - 7 of them will give a 4.2 volt drop with no heat issues. And since they can pass 1 amp - you could gradually switch over a dozen turnouts to tortoises and power them all from the same dropping diodes.
Thanks Randy! I’ll try the1N4001 Diodes where I have several Torti close to each other. For this location, I think I will try the resistor. Worst I could do would be to burn up an expensive Switch Machine… [;)] I have been running two Torti in series with no problem off the 16 volt power source. It has enough kick that both work smoothly and at the same time. That’s why I was thinking 600 ohms in series with the pack.
That would work for up to 3 Tortoises, with a typical 1 watt Zener. The other option is a +12v regulator, with an appropriate heat sink you can get up to 1 amp at 12 volts out of the typical 7812.
Replying to this thread has made me glad I took an old computer power supply and converted it to run my stuff. From one little unit I have plenty of 5v and 12v power to run electronics and power my Tortoises.
Care to elaborate? I would assume the zenner would have to placed before DPDT toggle in order to work? Can you supply a scematic for me?
How you did the conversion might make an interesting tutorial for the forum and might be something I would want to try as I add to the layout (it will be growing into another room in the basement). I’m looking for the simplest solution for this. I am using the Aristo-crap transformer because I have too much invested in it to have it sit on the shelf, and it has the power to handle everything I want to install needing DC at the same time. It is rated at 16 volts, 5 amps (although a meter placed across the leads reads 20 volts). Am I correct that a resistor placed in series would effectively limit the tortis current draw from the transformer to within the max. that can be handled by the torti?
With 16v at 5 amps, you could set up 5 voltage regulators and make 5 seperate 12v at 1 amp each circuits. If you don’t make a habit out of shorting the outpts, no extra fuses are even required - the 7812 regualtors will shut themselves down if overloaded, but doing that constantly isn’t good for them.
You can;t run them at full power without a proper heat sink and some thermal compound. And various ones will vary from manufacturer to manufacturer. I’m sure there is SOME difference between the 39 cent ones and the 1.29 ones (and Radio Shack just repackaged 39 cent ones and sells them for 2.99 - so avoid those!).