Constant Voltage Transformer Capacitor Question

Discussion in 'The Projects Forum' started by PGB1, Jan 22, 2013.

  1. PGB1

    Thread Starter Member

    Jan 15, 2013
    58
    3
    Hi All!
    I hope this question is in the correct part of the forum. I think it qualifies as a project?

    I was given a Sola Constant Voltage Transformer years ago. It is their Model 23-13-060 CVS-1. The input voltage is 95-130 60Hz & the output is (was) 118 vac. The unit is rated 0.5 amp

    My trouble is that now the output is 127.4 volts with an input of 120.6 as measured with a RMS multimeter.

    My guess is, since the secondary voltage is high, the capacitor(s) is the source of the problem. I was expecting to find two capacitors, but there's only one.

    I removed the capacitor from the device & found 0.2mf as the reading. If I ground the shell, as it was when installed, the reading remains the same.

    The only identification on the capacitor contains:
    Sprague Clorinol Capacitor
    1.75-660ac
    9945 P48843 6826
    It is oval shaped cylinder, similar to a motor run capacitor.
    I don't know if this matters, but it measures 3-1/8 tall and the oval is 2-1/8 x 1-9/16

    So, I have the voltage range, but not the capacitance.

    Here's What I Tried-
    A) Searching this forum. I managed to sidetrack myself for a few hours & have loads of educational fun.

    B) Emmerson-Sola for information on capacitor size. They replied that they did not keep any data for that unit when they acquired Sola. Nor did some Sola sales outlets.

    C) I also contacted Vishay-Sprague. They also indicated they did not keep any Sprague Chorinol information when Vishay bought Sprague.

    D) Next attempt was to internet search any combination of numbers from the capacitor, as well as the word(s). No luck

    E) Finally, I searched the patent numbers from the Sola unit. No luck- Drawings were available, but not capacitor details.

    Do any of you have experience with this or a similar unit & suggestions for capacitor sizing?

    I appreciate your help!
    Paul
     
  2. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    I believe the unit is working properly. Try putting a load (60 VA) on the output and adjust the input voltage with a variac. The output should remain steady with input voltage swings of 95-130 VAC.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  3. PGB1

    Thread Starter Member

    Jan 15, 2013
    58
    3
    Hi Duane
    Thanks for taking the time to reply.
    I tested the unit with 2 different pure resistance loads & two different variable voltage supplies. The results were almost identical with each source & load. There was no steady 118 volt output. But, are my results within the 'normal & expected' range?

    How Tested:
    I used 46 & 58va loads (The closest I could get to 60va).
    The power sources were:
    A Variac brand 'variac' rated 2kva. Non isolation type (normal one winding).
    I repeated with an older GE Power Stat which is rated (estimated) 600va. It is an isolation type variable transformer.
    The results were identical within 1/100th of a volt for each source.

    For fun, I started at zero volts & moved up to 140. All measurements were with RMS meters. From publications I found today, RMS testing is apparently important for measuring CVTs.

    Results:
    Between the unit's specified 95 and 130 vac input, my results varied from 126.8 output (at 95v input) to 123.9 output (at 130v input). The progression was not very linear.

    I've attached a jpeg of a spreadsheet & chart I made of the Input vs Output. It also includes a Difference Of Output Versus 118 Volts


    Do you think the output range I'm getting (between the 95 & 130 specification) is within a normal & OK range? I'm not sure how precisly these are supposed to control the voltage. It is an old style, no harmonic control, no circuitry other than a capacitor.

    Thanks for helping,
    Paul
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    Sounds like the Sola CVT is working fine.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    You are getting a 2.3% change in output voltage for a 36.8% change in input voltage, which is pretty good considering the only control components are a transformer core and a capacitor. As MrChips stated, sounds like its working fine.
     
  6. PGB1

    Thread Starter Member

    Jan 15, 2013
    58
    3
    Thank you all very much for the input & advice. I appreciate the time you took to read & evaluate my question. This is a great learning place!

    I was concerned because the output was no where near the 118 vac promised on the rating plate. As Crutschow mentioned, it is simply a core and a capacitor. What was I expecting? Perfection?

    For others reading this, who may own the same device & need a capacitor, the capacitance is to be 1.75mfd. (Assuming this is the OEM capacitor)

    I must have been in "duh?" mode. I remember using Sprague Clorinol start & run capacitors years ago. They were marked with a single voltage rating (not a range), preceded by the capacitance. Here, 1.75-660 means 1.75mf & 660 maximum voltage. They often had a bumblebee resistor, too. Wish I saved those.

    If you have one that needs replacing, please hazardous waste it. I was once tasked with replacing many HV primary capacitors from that same era on due to pcb content. I suppose these low voltage ones have it too.

    Thanks again for the answers. I'm glad this device is working properly. I plan to donate it to someone I know who will use it & appreciate having it.
    Paul
    PS: Now on to study the physics behind it...
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    Data General Nova 2/10 minicomputers were designed with constant voltage transformers that delivered 5VDC without the need for electronic regulation.
    During brownouts you could see the room lights dim but the computers kept on merrily running.
     
  8. PGB1

    Thread Starter Member

    Jan 15, 2013
    58
    3
    I found a copy of the manual for the Nova 2. Their explanation of how the CVT power supply works is amazingly well detailed and explained.

    It'll become a good addition to my reference library.

    Thanks for mentioning it!
    Paul
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    I'm glad you found this. So did I - saved it for posterity.
    I spend many years programming/repairing/working with DG Nova computers.
     
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