larry@tapa.uucp (Larry Pajakowski) (12/12/89)
In refurbishing my old Lionell train transformer I replaced a copper oxide rectifier of about 1in. diameter with a silicon diode. In the original circuit a compensation winding of 5 volts was switched in series with the copper oxide diode to keep the output from sagging too much. I'm trying to get some idea of the series resistance of the copper oxide diode so I can put a resistor in series with the silicon diode. I suspect the resistance is about 1 - 2 ohms. Anybody have any experience. How about old Gamewell alarm power supplies? Larry Pajakowski
stimac@strider.uucp (Michael Stimac) (12/13/89)
In article <1989Dec12.022128.3128@tapa.uucp> larry@tapa.uucp (Larry Pajakowski) writes: >In refurbishing my old Lionel train transformer I replaced a copper oxide >rectifier of about 1in. diameter with a silicon diode. In the original >circuit a compensation winding of 5 volts was switched in series with the >copper oxide diode to keep the output from sagging too much. I'm trying (typically, this rectifier is part of the circuit to blow the whistle on older Lionel trains, which were activated via a DC-sensitive relay) Are you getting unsatisfactory results changing only the diode, without the extra resistor? (ie, does the train speed up when you sound the whistle?) Since the transformers were not well-regulated, the output would drop when the whistle motor kicked in (nearly doubling the load); I think the extra five volts is to compensate for this poor regulation more than for the resistance of the copper oxide diode. >to get some idea of the series resistance of the copper oxide diode so I >can put a resistor in series with the silicon diode. I suspect the >resistance is about 1 - 2 ohms. > >Larry Pajakowski Michael Stimac (TCA 72-4800) ....sun!oliveb!tymix!stimac
grr@cbmvax.commodore.com (George Robbins) (12/13/89)
In article <3103@tymix.UUCP> stimac@tymnet.com (Michael Stimac) writes: > In article <1989Dec12.022128.3128@tapa.uucp> larry@tapa.uucp (Larry Pajakowski) writes: > >In refurbishing my old Lionel train transformer I replaced a copper oxide > >rectifier of about 1in. diameter with a silicon diode. In the original > >circuit a compensation winding of 5 volts was switched in series with the > >copper oxide diode to keep the output from sagging too much. I'm trying > > Are you getting unsatisfactory results changing only the diode, > without the extra resistor? (ie, does the train speed up when you > sound the whistle?) Since the transformers were not well-regulated, > the output would drop when the whistle motor kicked in (nearly > doubling the load); I think the extra five volts is to compensate > for this poor regulation more than for the resistance of the > copper oxide diode. Gee, I seem to recall the sped up a but when you did the whistle anyway - added to the excitement and all. Is the rectifier a simple half-wave job? If so the winding would probably be to compensate for the lower RMS voltage of the half-wave rectifed current. Is is really copper-oxide and not selenium? Shouldn't be too hard to dig up some voltage drop stuff for selenium recitifers/stacks... -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@uunet.uu.net Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
brian@ucsd.Edu (Brian Kantor) (12/13/89)
Probably the simplest way to simulate the voltage drop of the old copper-oxide rectifier is to series several silicon diodes. That way you'll have a relatively constant voltage drop despite a varying load, which a resistor would not give you. - Brian
ISW@cup.portal.com (Isaac S Wingfield) (12/15/89)
Brian Kantor writes: >Probably the simplest way to simulate the voltage drop of the old >copper-oxide rectifier is to series several silicon diodes. That >way you'll have a relatively constant voltage drop despite a varying >load, which a resistor would not give you. > - Brian I'm not sure that is a good simulation; my vintage 1951 Simpson VOM uses a copper oxide bridge on the AC ranges - so did all VOM's for many years. Working from memory, I believe CuO rectifiers have: Low forward conduction drop (necessary for good VOM performance) High series resistance (not a problem in VOM's) Poor high frequency response - cutoff around 100 kHz, I think Low reverse blocking voltage I'd try just one Si diode, and add a series resistor if necessary. I believe CuO devices were used in "Varistors" also; low FCD would be desirable here. Happy holidays Isaac isw@cup.portal.com