Does anyone know of any 1ohm, 2-5Watt resistors that aren't inductive (ie. not wire wound in any way)? I need some for my snubber and the only ones I can find at that resistance and power level that aren't wirewound are some PulsEater A series resistors from Ohmite...and they cost $12 a pop! THat's even more than the mica caps! (but I've switched to cheaper polypropylene caps since).

I need 7 per motor controller so that increases the cost by 30%! For the snubbers! Both the most numerous major part and the most 2nd expensive (second only to the DC-DC converter!) It's ridiculous!

 

Have you tried the DigiKey search? 5W, 10 Ohm, ceramic
for less than $3.00 each. This is just one example. There are others quite a bit cheaper, depending on volume. John

http://media.digikey.com/PDF/Data%20...RA%20Audio.pdf

 

I already came by those. THey're actually wirewound. It's wire wound on an alumina ceramic core. It also says it meets or exceeds some mil specs for wirewound resistors. I took another run at DIgikey and the only other ones I can find are Metal Oxide resistors...except in the datasheet it says they are trimmed with a spiral cut which won't do as far as inductiveness goes.

 

Hi Dknguyen,

Do a search for thick film resistors, Vishay produces some.
The one's that I use are not from Vishay.

http://www.nikkohm.com/nikkohmpdfs/T...oteRNP002e.pdf

http://www.alldatasheet.com/view.jsp?Searchword=RNP20S

http://www.nikkohm.com/products.htm



on1aag.

 

Phoenix makes some 3W metal films you can get at Digikey.

ETA: Actually I'm not sure you can get them in 1 ohm.

ETA: Yes they do, part number PPC1.0ECT-ND

 

Sorry for the misleading link. The datasheet called them non-inductive because they were wound in the Aryton-Perry manner so the windings oppose and presumably cancel inductive reactance. That mil spec seems to be a temperature spec that several of the other so-called non-inductive resistors also meet. John

 

THanks. I've been mainly looking at ceramic/carbon resistors. It seems thick film types are what I need (for some reason I thought thick film was only in SMD, maybe that's thin film?)

I'm probably going to go with TA resistors from Ohmite. Since I know for sure they aren't trimmed with spiral cuts like the axial resistors. THose $14 resistors sure take a huge over load for a long time though.

Yeah I'm trying to avoid them all together since surely, non-inductive wirewounds, can't beat resistors that have less inductance to begin with.

EDIT:
Are film capacitors able to handle the surge requirements though? THey are definately much cheaper.

MORE EDIT: I might go with the OY bulk ceramic resistors instead. The lowest value is 3.3R but they only come in up to 2W which is somewhat cutting it close- no biggy though since I guess I will just parallel 3 or 4 of them and that will also deal with the power problem. They cost about $1 each but $4<<$14, especially when x6.

 

Caddock makes non-inductive resistors. I think Digikey, among others, carries them.

__________________
stevez

 

Stevez is very correct . They are wire wound at that wattage but are non-inductive (specifically ask for Non-inductive wire wound resistors).
They are specially wound by doubling the wire and wind as double with proper spacing. The ends may come to one side - but are terminated suitably.

__________________
Regards,
Sarma.

 

I've read that even non-inductive wirewound resistors are too inductive for snubber applications. There are even recommendations against using metal-oxide and carbon compositions trimmed with spiral cuts). It's even gone so far as you might need an active probe to accurately measure the snubbing waveform since the probe capacitance can load the circuit too much. THere was one article that just plain said often the inductance of the resistor is too high, period.

I also read the only time wirewounds are used for snubbing is when the power levels are too high, and when they are they should be damped against with a mini-snubber just for the resistor to keep the inductance from ringing. I think bulk ceramic resistors are replacing that though since they have less inductance and also don't have catastrophic failure.

The rise times in my circuit are 50ns (calculated), so I assume the snubbing waveforms will be in excess (maybe far in excess) of 20Mhz. I'm pretty sure any wirewound resistor fails at that frequency. It seems that a lot of non-inductive wirewound resistors are meant for audio applications since they have low noise, but those are only in the low kHz range.

 

Perhaps you meant "non-inductive" when you typed "non-conductive"

the Non-inductive are supplied to educational institutions for test and experiments.
If some one is selling normal wire-wound as non-inductive we can't help but we can catch them and ask for replacements.

You are correct that carbon film resistors are behaving inductive.
There used to be other type"carbon composition" type. These are generally non-inductive and used in RF circuits and perhaps you may get them in the wattages you need -- Costly though!!!

If you can get hold of insulated Nichrome or Manganin wire, perhaps you can make N.I resistors yourself. you have a to take required length and wind half in clockwise and balance in anti-clockwise on a refurbished w.w resistor body. In fact you may take a 2 ohm wire wound resistor and carefully clean the paint and start opening from the center and re assemble in the fashion described above.

how ever you are to clamp the two cut ends at the centre using a connector or rivet and ensure it is perfect joint.

__________________
Regards,
Sarma.

 

Oops, yeah. Non-conductive resistors are quite cheap.