Bob, you've talked about using diodes and rheostats to lower voltage a few times but I was wondering if you can give me some recommendations.
I want to lower my UCSs from my higher voltage set up for my fixed voltage 022s. This is to operate my Log and coal loader cars more gently and still be to uncouple easily on the spurs. I would rather use a rheostat instead of diodes so I can tweak voltage.
You mentioned a sort of puny radio shack one a while back, but I'm wondering if this would b sufficient to run the three UCS I have on my layout. If not can you give me the spec I and or supplier where I can get this from?
Any help would be appreciated.
Mike s.
Mike, I mentioned the Radio Shack rheostat just to warn away from it. For trains, I would normally suggest an old Lionel rheostat. I just don't know how much of a load an operating car is; however, it is likely that it would draw substantially less current than a train, which might require a higher resistance than the Lionels have. The real problem is that the current drawn probably varies a lot among operating cars, which could make for an adjustment nightmare if you have more than one.
So I suggest that you reconsider the diode approach, which is pretty much insensitive to the load that you put on it. It doesn't have to be fixed at one voltage. If you can find a rotary switch, you can make it quite adjustable. Just use the switch to tap into a string of diode pairs. If you want to have a different adjustment on each track, you can use a single diode string with three switches.
If you are satisfied with a single adjustment or willing to have a separate diode string for each track, you can even make the adjustment with toggle switches (although I think a rotary switch is nicer).
Bob Nelson
Bob,
through some testing I believe I can get my operating cars to work well at 10 volts or so and that is enough to do uncoupling as well.
For simplicity sake, and because I have no experience with diodes, could I go the rheostat route if I'm looking at 10 volts or so? And if so, do you mean the old prewar rheostats I see on ebay. LIke the #81. There seems to some called battery rheostats that have a coil with a slider but then there are others that have a slider that seems to fit into holes along a coil and may not provide the same latitude of adjustment.
The "battery" rheostats are what I was talking about. I don't know what the others you have seen might be.
The problem with a rheostat is that the voltage drop that it produces increases with the amount of current that the operating car draws. In fact it is the product of the resistance (in ohms) and the current (in amperes). So, for example, if you set the rheostat to 5 ohms (their typical maximum resistance), the voltage drop would be 5 volts if the car draws 1 ampere, but only 2.5 volts if it draws half that much. Unless all your cars draw the same current and the rheostat has enough range to be adjusted for 10 volts at that current, you will have a problem.
The diodes are a very simple project. Get a handful of bridge-rectifier modules rated for a few amperes. Wire the + and - terminals of each one together. Then wire the modules together into a string using their other terminals (possibly marked ~). Connect one end of this string to the transformer output terminal. Connect the other terminals to the rotary switch, with the common of the rotary switch going to the uncoupling section. Make connections both to the points between the rectifier modules and to the +- terminals. You will get roughly half a volt drop from point to point along the string; so a 5-volt reduction will need about 5 rectifier modules.
thanks, Bob, When I get to this particular project i might need some more guidance but I've bookmarked the post. I appreciate the help on this one.
Mike S.
The diode idea sounds great....really gives control over individual items.
underworld
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