07-30-2011, 01:51 PM
RobertInOntario Wrote:The transformer's serial number is 20509 and its input is 120V, AC 60Hz 125 mA,
Output 19V, AC 0-16V, DC ; total output 7VA. Model number SDK-789.
Here's one for sale on eBay -- <!-- m --><a class="postlink" href="http://cgi.ebay.com/Athearn-Model-Train-Transformer-Power-Control-SDK-789_W0QQitemZ360381879926QQcmdZViewItemQQssPageNameZRSS:B:SRCH:US:102#ht_704wt_878">http://cgi.ebay.com/Athearn-Model-Train ... _704wt_878</a><!-- m -->
Maybe I should buy an extra one!
As to the transformer, it still seems that I have to crank it up near its "maximum" point (around the 80-90 mark) to get the trains to run at a moderate speed, even my almost brand-new locos. However, on the other/older transformer, the same trains will go at a moderate speed with the throttle in the half-way or moderate position (hope this makes sense).
Thanks!
Rob
Rob
The 7VA (VA = volts times amps) rating is too wimpy for older locomotives. It translates to a maximum of slightly more than 0.5 amps at 12 volts. It certainly won't handle the load of throwing a switch machine (typically 1-2 amps) without choking eventually. The rheostat (the part that controls the speed) is probably cooking under the load of your engine and any lighted cars, and can/will eventually fail. I had an old AHM train set power pack with a similar rating that went down that road. I was able to salvage the power pack by using the AC terminals as a power supply for a transistor walk-around throttle I built. This didn't improve the output rating of the power pack, but did make a nice throttle for my better locomotives.
As I have gotten more experienced, I refuse to put up with locomotives drawing more than 0.6 amps. The mechanism needs tuning or the motor needs new magnets or replacement if the current draw is that high. An ammeter is a great tool for base-lining locomotive performance and tuning mechanisms.
In the meantime, use the Railpower power pack for your older trains. It has a much larger power rating, and MRC built them with sturdier components than the typical train set power pack.
my thoughts, your choices
Fred W