Starr - Tec Hogger

[jerryl]

  Need info on a Starr-Tec Hogger.    Locos run great in one direction, Barely move in the other direction when the direction switch is thrown.
   Probably in the powerpack & not the controller. Do you know what is used to change direction?   The switch on the hand contriller is only connected to the powerpack with a phone cable & couldn't carry the necessary amperage to power a large Scale Train so there must be some kind of relay or electrical circuit  to reverse the polarity inside the box.   Thanks

[Jim Banner]

I am not familiar with the inside of the Star-Tech Hogger but I am familiar with electronics.  There are a number of ways that they could be reversing the polarity to the track.  A relay is one of them.  I have designed and built a number of power packs with tethered walkaround controls and using a relay has been a feature of most of them.  As you have pointed out, it allows the use of light weight cable between the hand held throttle and the base unit.  It also puts the heat in the base unit, not in your hand.  On occasion, I have custom built these units with two direction switches, one for mainline reversing and the other for reversing return loops.  One thing they all had in common is that you could hear the relays throw.  And the bigger the scale, the heavier the relay and the easier to hear it throw.  So - first test - see if your Star-Tech Hogger has a relay by listening for it when you throw the direction switch.

If you do not hear a relay throw, then your Star-Tech Hogger probably does not have one.  If that case, it might use a single power supply (internally) and an "H-bridge" output or it might use two power supplies (internally) and a half bridge output.  The difference is this:  The H-bridge (also called a full bridge) uses four power transistors, one from power supply positive to rail #1, one from rail #1 to ground, one from power supply positive to rail #2 and one from rail #2 to ground.  When running a train forward, the transistor from supply plus to rail #1 controls how positive rail #1 is compared to power supply ground while the transistor from rail #2 to ground is turned on, connecting rail #2 to ground.  The other two transistors are turned off.  For reverse, the other pair of transistors is used.  The transistor from supply plus to rail #2 controls how positive rail #2 is while the transistor from rail #1 to ground connects rail #1 to ground.  A fault in any one of the four power transistors or in any of the small transistors controlling them could cause your problem.

A cheaper way to attain the same results is to use a half bridge which requires only two transistors.  It does require a second power supply which produces a negative voltage compared to ground, but that requires only two more diodes (cheaper than the two transistors not needed.)  One rail is always connected to ground.  The other rail can be set increasingly positive via the transistor from it to the positive connection of the positive power supply or it can be set increasingly negative via the other transistor, the one from that rail to negative connection of the negative supply.  This is a natural for common rail wiring but unfortunately, also suffers from the usual high voltage problem of common rail wiring when multiple supplies are used.  A fault in one of the power transistors or a failure in one of the power supply diodes can cause the problem you describe.

Power transistors usually fault because of (over) heating and the fault mode is usually catastrophic failure, either to open or shorted.  They do not normally partially fail.  So the running at low speed in one direction is likely not a transistor fault, but it could be.

Rectifier diodes also tend to fail catastrophically.  In a half bridge type circuit, failure of one diode in one power supply can mean full speed in one direction, much slower speed in the other direction.  That is because one power supply is rectifying both half cycles to give full output while the other power supply is rectifying only every second half cycle to give only half the output.

There is one more possibility and that would be that your locomotive runs well going forward but poorly in reverse.  But when you put it on the track the other way around, it still runs well going forward and poorly in reverse.  This would indicate that the problem is not in the power pack at all but rather something wrong with the locomotive itself.  If this is the case, let us know which locomotive you have so we can suggest alternate solutions.

I won't say that is the long and short of it.  More like the long and longer.  But it should give you a pretty good idea about what is going on in there.

Jim

[jerryl]

  Thanks so much for the informative reply.   I did test it with different locomotives with the same result.  I did take a basic RCA electronics course years ago, but this is probably over my head.  How would I identify which type of circuit I have? Don't really have anyone I know of that could help. Do you think you could identify the circuit if I sent some pictures to you & could tell me what components could be at fault? ( don't really know how to post pictures, but could email them to you) Thanks Again,   Jerry

[Jim Banner]

Jerry, I could take an educated guess on the type of circuit from a photo but troubleshooting from a photo is not usually possible.  If you would like to send some photos, click on my name just above my photo and that will take you to my email address.

Jim

[jerryl]

  I was just told today that the Starr-Tec uses a relay to change polarity, that may be easier to fix than a transistor system. I will open it & send pictures.   Jerry