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RE: Resistor dissipation Question

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Triode_Kingdom

A

In Reply to: RE: Resistor dissipation Question posted by timp on September 15, 2012 at 20:26:39

The RH series needs a substantial heatsink. I would also be careful using those for high voltage unless you're sure of the rating. If you'd rather use a standard wirewound power resistor in place of the RH, the link below is a good place to look. Check part no. W250WL8103 (250 ohm, 60W) near the bottom of the page. There are several others on the page that also look promising.

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Buy Chinese. Bury freedom.

Surplus Sales of Nebraska - WW Resistors 200 Ohm to 250 Ohm (Open in New Window)

Follow Ups:

RE: Resistor dissipation Question - timp 21:01:47 09/15/12 (7)
TK

Thank you for the reply. I have a 13w wirewound in my hand. Do you think it is safe to use that for 8 watt dissipation?

Thanks again for the information.
- RE: Resistor dissipation Question - tube wrangler 07:42:15 09/16/12 (0)
  No-- there are many reasons, but just use a 25 watt-- as a minimum.
  
  As TK indicated, keep voltage across it way below the rating.
  
  ---Dennis---
- RE: Resistor dissipation Question - Triode_Kingdom 21:59:49 09/15/12 (2)
  I do think the 13W will be safe, but maybe on the edge for longevity. I try to derate 50%, sometimes more in tube gear. See my other reply below also...
  
  --------------------------
  Buy Chinese. Bury freedom.
  - RE: Resistor dissipation Question - timp 22:13:35 09/15/12 (1)
    Sounds like I will be mounting this sucker to the chassis. Or should just add a diode? I got whole bunch of diodes in my hands as well.
    
    Thanks again.
    - RE: Resistor dissipation Question - mikeyb 10:24:38 09/26/12 (0)
      Add a diode? You would need more that one to drop 45 volts.
      45/.7 = 64 diodes! Sort of impractical.
      
      Edits: 09/26/12
- RE: Resistor dissipation Question - timp 21:08:21 09/15/12 (2)
  Gees!
  
  You guys are absolutely right! To ensure 50w rating i need to have a heat sink size of 12" � 12" � 0.125" thick aluminum panel (294 sq. in. surface area). I need to add a kitchen sink into my psu!
  
  That's crazy!
  - RE: Resistor dissipation Question - drlowmu 21:27:45 09/15/12 (1)
    Relax,
    As far as what T_K mentioned on voltage rating, well, you are only dropping 45 VDC across the resistor, so its not a concern.
    I would use the 50 Watt resistor bolted to your existing chassis, because you do NOT need to dissipate 50 Watts, only 8.1 Watts continuous.
    Also, you can use the chassis to keep your Chipotle Burrito warm. Yumm.
    Another alternative, use two 500 Ohm 13 Watt power resistors in parallel, to become 250 Ohms at 26 Watts rated. I sonically prefer Mills MRA-12s, twelve watters, but if in series to the Output tubes, I always prefer near zero or minimum resistances !!.
    Jeff Medwin
    
    Edits: 09/15/12 09/15/12 09/15/12
    - Not exactly ... - Triode_Kingdom 21:43:45 09/15/12 (0)
      "you are only dropping 45 VDC across the resistor, so its not a concern."
      
      Except that the OP said the resistor has more than 400V on it. Looks like it's safe though; the datasheet says the RH050 has a 2,000 Vrms dielectric strength. Given that it's only dissipating 8W, your idea of bolting it to the chassis seems like a good solution.
      
      --------------------------
      Buy Chinese. Bury freedom.

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