I'm building a layout for my 4 year old son. This will be his own personal layout because he's a little rough with Dad's locos. So I decided to get him started with his own trains. I bought a Thomas starter set, and sante-fe flyer starter set. Both sets came with those little square throttles. It's cheaper than buying the pieces individually.Well I measured the A/C output one day and the 16VAC output was measuring 28VAC!So I thought, "Maybe the supply isn't well regulated and needs a load to settle down to 16VAC." So I put the Sante Fe flyer on the track and turned on the throttle full blast. I then put my voltage probes across the rails...26VDC! YIKES.This happened not once, but twice with two separate power supplies. (Each starter set came with it's own power supply)
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
DigitalGriffinWell I measured the A/C output one day and the 16VAC output was measuring 28VAC!
DigitalGriffinSo I thought, "Maybe the supply isn't well regulated and needs a load to settle down to 16VAC." So I put the Sante Fe flyer on the track and turned on the throttle full blast. I then put my voltage probes across the rails...26VDC! YIKES.
Is that a typo? You should be only reading VDC from a Bachmann powerpack. There should be no AC on the track.
It wasn't a typo. I measured the wall wart/power supply which is rated for 16vac
I then measured the output from the throttle which is just a fancy rheostat and bridge rectifier...No correction circuitry what so ever.
No filter on those old power packs and you will see AC also.
At one time, some power packs used some AC off the secondary to simulate pulse power. Many years ago I built a few hand held power packs to do that.
A capacitor filter on the full wave bridge will smooth out those peaks but the voltage can still be higher without, say a small load load.
Power pack specs are when the pack is delivering the required current to the load.
I remember seing AC readings many years ago but I knew the packs had no filtering.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
One of those same cheap-o power packs came with the large scale Thomas set from Lionel I got my oldest when he was 3 (scary, 23 years ago - still have the train, too). It almost set my apartment on fire - forgot to unplug it and a few hours later the bottom was black sludge which wouldn;t come off the carpet no matter what, more than jsut melted plastic from the bottom of the case.
But hey, I have like 4 or 5 of them that came in a box o' junk I bought, if you want a few more. I don't find these things even worthy of powering accessories. Poor speed control, prone to literally melt down, and WAY overvoltage, even with a load. ANd we wonder why people buy train sets then give up teh hobby after a few months - between the horrible track comming apart constantly and the poor fit when it does stay together, leading to kinks and derailments, plus the power packs burning out, or buring out the motor in the loco, little wonder a newcomer doesn;t stick with it.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
A filter cap will just make things worse, if it's already putting out 26VDC unfiltered. Adding the proper cap adds a charge pump so you will get peak instead of RMS - over 36 VDC!
rrinker A filter cap will just make things worse, if it's already putting out 26VDC unfiltered. Adding the proper cap adds a charge pump so you will get peak instead of RMS - over 36 VDC! --Randy
And that is why I would never do it.
Those chepo power packs always worked fine but I do remember reading a fix for those old black power packs in the MRH forum.
The control was not a rheostat that I have ever seen.
All the Bachmann power pack is, is a printed circuit board with on large transformer, a couple resistors, and this wheel with contacts. As the wheel turns, the contacts complete the circuit through a different set of printed tabs, hence the Bachmann transformer really is an incremental variable DC power pack and not a continuous variable DC power pack.
I wonder if this is what he has?
richg1998 All the Bachmann power pack is, is a printed circuit board with on large transformer, a couple resistors, and this wheel with contacts. As the wheel turns, the contacts complete the circuit through a different set of printed tabs, hence the Bachmann transformer really is an incremental variable DC power pack and not a continuous variable DC power pack. I wonder if this is what he has? Rich
Well for a pot to work there has to be a current device in the circuit like a simple 1 transistor throttle, a rheostat can directly control the current BUT has the problem of matchign the resistence to the motor current draw, thus with an old HO rheostat pack you have no control over N scale or modern low current HO models, they just take off at full speed when you crak the throttle because they don't draw enough current to caus enough of a voltage drop through the rheostat. Wiring it up like a pot can work but is hugely inefficient. Using a bunch of pc contactcts to switch different resistences in the line is chea. Real cheap. There were some that were actually variable transformers like AC Lionel transformers, but the problem with that back in the day was the selenium rectifiers then in common use don;t like to see variable voltage. A friend of mine has a set of rather monsterous variable transformers with rectifiers driving his layout - unlike many other types of throttles you get max power even at the slowest speed. He's mostly a Tyco/AHM collector and with his power supplies even those rather poor quality old motors run nice.