Author Topic: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia  (Read 1266 times)

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Offline Lorenzo_1

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Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« on: August 31, 2017, 11:13:38 pm »
Hi. I need one of these for the primary side of a LeCroy power supply. Been looking at RS Components, Radio Parts and Element-14/Farnell without success. I think the one installed is perhaps metal oxide/flameproof type - green body & matt finish.  From the size I think 2W (it's 9mm x 3mm in the body) Any suggestions?  I can find them online in US/Canada but postage is high.  Also ex China/Hong Kong with free postage but unknown quality.  Grateful tips as to what to avoid/prefer.
 

Offline Rbastler

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #1 on: September 01, 2017, 12:05:57 am »
You could use two 1.5M in parallel, say 1W each, if there is enough space.

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Offline David_AVD

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #2 on: September 01, 2017, 07:16:48 am »
How much of a hurry are you in and where are you located?

Digikey has 750K 2W ones and I could add a couple to my next order.
 

Offline xavier60

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #3 on: September 01, 2017, 08:24:28 am »
Over the years I have had trouble finding resistors that are reliable at high voltages. I take notice of a resistor's voltage rating instead of just its wattage. In recent years I have been using High Voltage Thick Film Resistors, usually Welwyn brand.
« Last Edit: September 01, 2017, 08:38:22 am by xavier60 »
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Offline Lorenzo_1

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #4 on: September 02, 2017, 09:38:04 am »
Thks for the replies.  I'm not in a great hurry as the PS is currently working fine with 2x1W 1.5M carbon composition resistors in parallel (all I could get locally) - Cairns is not an easy place to do these sorts of repairs as Jaycar's about the only supplier.  Before deciding whether to take up  David_AVD's kind offer, I could use some advice on what's recommended for primary side of this SMPS.  The dead one I removed is 9mm x 3mm and matt light green finish - sits across 340V DC rail behind bridge rectifier with primary side ground at 170VDC (schematic & photo attached).  I've taken it to be 1W and presumed it should be capable of handling at least 200V. 

I figured it might be metal oxide type - hence I was looking for those.  Would an HV thick film resistor substitute OK or should I stick closer to a like-for-like replacement?  Are there generic recommendations for appropriate composition of this type of SMPS resistor? I presume some fire/transient resistant type is recommended - does it matter if you put in something with kV volt rating if that's readily available here? 

For David_AVD - perhaps you can PM me to advise when you'd need a decision from me about adding one/some to your next order.



 

Online blueskull

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #5 on: September 02, 2017, 10:07:38 am »
I presume some fire/transient resistant type is recommended - does it matter if you put in something with kV volt rating if that's readily available here?

Most 2W MOX resistors are rated for 500V+, so any should work. But really, I don't think metal film or carbon film won't work either as long as the rated voltage is enough. After all it's just a bleeding resistor.

If you don't need capacitor self discharging, you probably can get around without this resistor at all.

Traditionally we say X caps across AC need to be transient rated due to EMI filters can be before AC fuse. Anything after fuse don't need to be transient rated (except for parts across pri-sec isolation barrier). Input MOV should clamp voltage to a safe level, and after bridge rectifier, AC input cap should also absorb transient energy.

If the DC bus sees 500V+, then the resistor is the least of your concern. Other things will pop much earlier than the resistor.
 

Offline David_AVD

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #6 on: September 02, 2017, 01:07:06 pm »
I order from Digikey or Mouser every week or two, so give me a yell when you need them.  Should be able to pop them in an envelope so only a couple of bucks all up.
 

Offline Lorenzo_1

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #7 on: September 02, 2017, 07:54:07 pm »
Thanks David. Will do. I'll PM you if that's OK.
 

Offline David_AVD

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #8 on: September 02, 2017, 09:25:03 pm »
No problem.
 

Offline David_AVD

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #9 on: September 13, 2017, 03:06:49 pm »
I have your resistors ready to send.  Just need to double check address and give you PayPal details.
 

Offline Lorenzo_1

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Re: Where to buy 750kOhm 2W metal oxide(?) resistor in Australia
« Reply #10 on: September 13, 2017, 08:04:34 pm »
Thks David.  I've PM'd you.
 


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