New power supply :)

Discussion in 'General Electronics Chat' started by tom66, Jan 18, 2011.

  1. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Here's my new power supply, £45 second hand. It's a 0-35V 0-3A (105W) linear power supply with CV/CC automatic switch-over. It's got short circuit protection too, and I've tested it.

    I have some 22 ohm power resistors (25W) and I loaded it down. Ripple is incredibly low, below about 2mVp-p, even when under 3A load at 35V (only briefly as this would be 105W into 50W total maximum.) I don't really want to exceed 1A as my wire is specified to that only.

    It weighs a ton. Manufactured by Takasago in Japan. Apparently it was sold cheaply because apparently the wrong name was printed on it (GM035-3) when it should be TM035-3. It seems like it was a simple typo as T and G are very close on a QWERTY keyboard.

    One thing is, when I put it on top or below my scope, it made the CRT display ripple a lot (it's a digital scope with a CRT display), probably due to the large input transformer creating a large magnetic field, although it didn't adversely affect measurement as the input section of the scope is well shielded. So I put it on the other side of my bench to prevent this being a problem.

    I might want to open it up and see how the caps are doing. I'm not sure how old it is. On the side I can see three massive power transistors for the regulation on a large heatsink, as well as the transformer, and some control electronics, but not much else.

    Next up - probably a spectrum analyser for EMI testing.
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I picked up a couple of Lambdas off craigslist last year, I think they're 0-30V @ 10A with adjustable current limiting as well. Came from a guy that had a repair shop, passed on and his daughter inherited them. She didn't know what she had so I got them for $10 each. Always pays to browse through those ads, also gave her $20 for a Sencore monitor tester in perfect shape but I really wish she had some of the other equipment left once I found the ad. I'd kill for the video analyzer and horizontal analyzer they put out but no big deal, the monitor tester has the inductance analyzer built in.

    Here's what I'm hoping to find in time:
    http://audiovideo-parts.com/Scripts/prodView.asp?idproduct=4155 or
    http://www.bcs.tv/store/model_detail.cfm?id=793698
    http://www.broadcaststore.com/store/model_detail.cfm?id=793706

    Of course I'd love to have my old B&K 747 tube tester back as well as the B&K 460(?) CRT tester.
     
    Last edited: Jan 18, 2011
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    Way lower on capacity the one I am making. And my one does not weight as much.

    I can get 30V @ 10Amps.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Nice score on the supply, tom66. I understand that stuff like that is really expen$ive over there.

    That's a great "score" you made, marshallf3.

    I have an old mil-spec Lambda supply that was rated for 0v-32v @2.3A that I "hot-rodded" up to 50v out. Replaced the standard Vadj trim pot with a 20k Ohm 10-turn Bourns "knobpot" that I also picked up for a couple bucks as surplus; there's no volts/amp meters on it, but the pot reads within 250mV of the output voltage up & down the scale, which is OK by me. I always double-check it with a DMM anyway.
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Yea, mine have 10 turn pots but also the meters. (although they're small)

    Wish I could have found her right when she started putting stuff up for sale, might have hit a bonanza. She has a huge box of new boxed tubes she sold to somebody for $10 as well as a lot of other things she had not a clue what were.
     
  6. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Stuff isn't that expensive. There's a store nearby which has a room filled to the top with scopes, power supplies, logic analysers... pretty cool. I bought my scope from there too. It's mostly old education, or business or military stuff, so it's pretty good; usually calibrated and serviced within the last 5 years too.

    I am also in need of a low current (~200mA) 60V supply. I have an idea about using a flash discharge circuit and stopping it at 60V somehow. As it is only to test if it can withstand a 60V automotive spike.

    Does anyone think I should open it up and think about replacing the caps? I think the caps are probably only for transients. It probably is just well regulated such that it does not need caps except for fast load changes. There's a big input filter cap for the ~40-50V output from the transformer, but I think that will be okay.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Replacing caps in old equipment is usually a good idea.

    As far as the 60v supply, you might just use a 555 timer and an inductor like shown on Ronald Dekker's page:
    http:www.dos4ever.com
    See his "Flyback Converters for Dummies"
     
  8. tom66

    Thread Starter Senior Member

    May 9, 2009
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    The thing is, I don't know how old it is. Tagasako still show a picture of a very similar power supply on their website. So I think they still make it. I have a serial number, but no date of manufacture.

    Good idea on the switcher; it's also fairly easy to build a low current supply around a cheap quad comparator like an LM339 and a small MOSFET+inductor+schottky diode.
     
  9. tom66

    Thread Starter Senior Member

    May 9, 2009
    2,613
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    What do you mean?
     
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