Are you using the same Bachmann decoder? No overvoltage issues for me, I'm a hair under 24 volts, like 23.7.
Also you even quoted me, it happens with brief power interruptions (over switches), nothing to do with overvoltage, which if true would happen anywhere on the layout.
What is your actual track voltage (read with a true RMS meter or equivalent)
By the way, there's a simpler way to do a voltage dropper, it's been on my web site for a long time. (clearly you use one full wave bridge and vary the number of diodes "in the centre" for the drop required.
Also 1N4001 diodes are only 1 amp, that is not a good idea, should be at least 3 amps or more depending on the loco.
Greg
Hello Greg,
Thankyou for your comments,
I hadn't seen your web site prior to this reply so have had a read, quite a lot of information within, Thankyou
Let me start by saying that I bought four of these module (I know expensive) soon after they were released so they have been running without this problem for about three years now.
Let me explain why I believe the problem is related to track voltage, and for your information my track voltage is 22.9V with a true RMS meter.
When I initially installed the four units, including lighting, all four locos were test run on my indoor test track and performed faultlessly, the problem only manifested itself on the outdoor track where the symptoms you describe were experience at some points and also bizarrely on one section of very dirty track. This occurred with all four locos.
Back on the test track, and I couldn't replicate the problem. The only difference was my indoor test track was on a different DCC system, one that is only intended to drive up to O Gauge, which as you are probably aware has a track voltage around 18V.
To evaluate this I used the indoor system (lower voltage) power pack on the outdoor LGB system and low and behold all four locomotives ran faultlessly over the whole layout, (about a 60 meter run).
To work out what was going on I coupled one of the sound modules to my Scope and started poking around, the results were interesting, you yourself have said the boards are not particularly good and this is certainly the case when it comes to back emf control (or snubbing), when running on 22V with intermittent contact I picked up power spikes in the motor control circuits hitting 29V, and this is when the problems occurred.
The instruction manual makes reference to not exceeding 28V in analogue mode so to me was another clue.
The installation of the diode string has brought the spikes down to just above 26V and all is OK.
As I say since modification, I have had no further issues in three years.
I was aware of the way of using a Bridge Rectifier with a diode string but as I often have piles of single diodes around I used them.
I would agree about using 3 Amp diodes in general but bearing in mind the Bachmann Thomas Locos only draw about 700mA when loaded and by using the back to back string they are only on a 50% duty cycle they don't even warm up after hours of running.
Subsequent to the above I was talking to a UK DigiTraxx supplier and installer, and he acknowledge that it was a know problem an the diodes is the solution but one the don't talk about officially.
I believe the NMRA standard for a Gauge 1 DCC control is it should be capable of receiving up to 40V, I know the ESU units do.
I see you are still looking at a stay alive connection for these modules, I have found that a stay-alive coupled across the obvious power points will happily keep the lights running and the sound working but no traction current. I have let this one rest at the moment but may start investigating further during this unprecedented lockdown we are experiencing.
Anyway I trust you find the above helpful
Andrew
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