I have a KW transformer that up until recently had been working quite well. However, now the internal circuit breaker throws upon trying to draw a load through it. I’ve pulled it off the layout, and on my bench have:
opened the case, replaced a few very old frayed and corroded wires
replaced the power cord
I buttoned everything backup and retested the transformed on my workbench by hooking up my multimeter to the right side A & U lugs. I get a consistent 0.2-20 volt reading depending upon the throttle position. However, as soon as I attempt to put any load on it the internal breaker throws and the warning light comes on. This makes me think the perhaps something has gone bad with the breaker - before I go off and start to blindly replace parts, are there specific troubleshooting steps I can take to narrow down the problem?
Looks like the contact roller for the left side of the transformer needs to be replaced as well - is this something a reasonably savvy DIYer can undertake?
Alright, I found the “search” function for the forum and found many others who had indicated problems with the circuit breaker staying open was a common KW problem. I also saw where some suggested replacing the breaker with an automotive style 10 AMP breaker. So before went off to the auto parts store I grabbed an extra 10A fuse and bypassed the breaker with it. I did a quick test, and it appears to deliver current to locomotives now. So my remaining question - did I bypass the breaker properly (and forgive the butchered soldering job, old and new solder don’t seem to mix real well)?
It does seem like the breaker is the problem. What are you using for a load? Try watching the voltage between A and C as you connect the load. Does it immediately drop to zero, or is there voltage there until the circuit breaker trips?
Actually, the rivets I buy you can just crush the end and keep them in. I also solder them on that end to make a better contact. The ZW is much easier, you don’t have to disassemble things to replace the rollers, just take the top off.
The problem is very likely that the circuit breaker is shot. They wear out from tripping again and again over the years, and finally get to where they won’t carry even enough current to operate a train.
Older KWs have a screw on the CB to adjust the current capacity. I forget which way is higher and which is lower, but if yours has the screw, you can play around with it until it will carry a reasonable load. If it’s a later one without the adjusting screw, you’ll have to replace it.
I don’t recommend fuses as the fuse will blow when the train derails. An automatic resetting automotive breaker will work better and will not require so many bad words[:)]
Thank you all for the feedback. I soldered in a 10A automotive auto-resetting thermal breaker. It seems to work, but is a bit slow to act - takes about 10-15 seconds to trip. Any thoughts on going to a smaller 5-7A breaker - would this trip more quickly?
The original breaker did have a screw, and I thought that backing it in or out might do just what you said. Unfortunately, I’d already pulled the breaker out and replaced with an automotive breakr before I read your post. Thanks for the tip though!
The breaker is modeling the heat buildup in your transformer and wiring. It’s supposed to trip when that becomes excessive, that is, not instantaneously. If you’re using 16 AWG wire or heavier, you’re good to go.
