Need help finding 8ohm 50W resistors

[newb]

Im building a head switcher and need 5 8 ohm 50 watt resistors
where would I find these?

[lightningfingers]

dude, I dont think they make 50W resistors (i could be totally wrong though). I have seen 10W, 39ohm at maplin, 5 of them in parallel would get you close.......

[RDV]

Here's a 7.5 ohm @ 50watts

http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=351020&e_categoryid=359&e_pcodeid=71046

RDV

[The Tone God]

They do make resistors in that wattage but I think finding them and how much they cost will be restrictive.

My suggestion would buy a bunch of resistors and wiring them together. Say four 2ohm 20 watt resistors wired in series. Its cheaper and easier to find.

Andrew

[Paul Perry (Frostwave)]

My suggestion would buy a bunch of resistors and wiring them together. Say four 2ohm 20 watt resistors wired in series. Its cheaper and easier to find. Andrew

It might be easier to wire in parallel, because then you can have 2 parallel stacked boards & mount the resistors between them. I have seen this for making low-inductance RF loads (immersed in oil, for cooling).
I would search the surplus companies sites, there are usually some low value high watt resistors that you can convert by a combination of series/parallel.

[p1_ind]

Mouser sells a 50W 8ohm resistor

http://www.mouser.com/index.cfm?&handler=data.listcategory&D=*284hs508.0f*&terms=284-hs508.0f&Ntt=*284hs508.0f*&Dk=1&Ns=MfgrPartNumber%7c%7cSField&N=0&crc=true

I bought a 10ohm for use in a Peavey SP-3 speaker cabinet crossover.

Adam

[Paul Perry (Frostwave)]

Careful where you put it, that's a lot of heat!

[Boofhead]

The common 25W, 50W and 100W resistors are only rated at those powers when you bolt them onto a heatsink - un heatsinked the rating is quite a bit lower.

I think the tubular high power resistors don't need a heatsink - these types usually cost more.

[newb]

how would i heat sink these they are going into a rack mountable case to be made into a head switcher

[Paul Perry (Frostwave)]

I assume (but, you would be wise to check!) that the metal case of the resistor casing is insulated from the resistor itself.
If so, it is just a matter of making the back of the box from THICK aluminium & putting the flat surface in contact, maybe held there by some kind of clamp.

[Boofhead]

heat sink these they are going into a rack mountable case

Code Select Expand



If air-cooled, I suspect the heatsink would be quite large.  When you put the heatsink the a confined space with no air flow, it doesn't actually do it's job it ie. getting the heat off the component and into the surrounding air.  The solution is to use a fan, a smaller heatsink (one more fins placed in the air flow would work better).  You need to arrange the fan so it blows onto the heatsink with air from outside of the rack unit.   I believe the Marshall rack unit uses a fan.

If you use a fan then you should realizes might hear it sound of the fan.  It's possible to turn the fan off when driving at low levels- either manually (at a risk you may forget to turn it on when needed) or automatically.


[Boofhead]

my post looks funky.

Forgot to say you need ventillation to let the hot ait out - in otherwords the fan pumps in from outside across the heatsink then out side the box through the vents.

[Lonestarjohnny]

get the Dale resistor's, they come burried in a aluminum finned case.
I built my load bank out of these for testing amp's without the speaker's hooked up, I can pump signal into the amp and i've checked the dale's, they never get hot, just litely warm after testing, i got these at a electronic's salvage yard for a few buck's,
Johnny

[birt]

just a suggestion but if you have an old broken tv, check it.
those things are loaded with high watt resistors

[Boofhead]

get the Dale resistor's, they come burried in a aluminum finned case.

That's only the case, with that case you will find the power rating is somewhat less than the rated power - one quarter the rating!  The case acts as a heatsink but it's not enough for full power.  You are supposed to screw that (small) finned case down onto a larger (real) heatsink.  If you read the Dale Specs (from Vishay) it will show the full rating on a large (unfinned) panel 8"x8" or so!

[Gilles C]

My suggestion would buy a bunch of resistors and wiring them together. Say four 2ohm 20 watt resistors wired in series. Its cheaper and easier to find. Andrew

It might be easier to wire in parallel, because then you can have 2 parallel stacked boards & mount the resistors between them. I have seen this for making low-inductance RF loads (immersed in oil, for cooling).
I would search the surplus companies sites, there are usually some low value high watt resistors that you can convert by a combination of series/parallel.

You can also wire some in series with 2 pcbs.

Here are examples of resistors connected in parallel and in series with pcbs

http://www.finitesite.com/gtechblues/My_images/ResLoad.jpg

I found 8 x 1 ohms resistors cheap so I wired them in series to make a 8 ohms load.

Gilles

[bigjonny]

just a suggestion but if you have an old broken tv, check it.
those things are loaded with high watt resistors

Yes.  They also have high Voltage capacitors.

birt, good suggestion, and no offense intended... However,  as a note to all: when suggesting the opening up of a TV/monitor/amp, it's probably best to put a disclaimer that it can kill you.  You cannot assume everyone knows this in a public forum, and personally, I wouldn't want someone's harm on my conscious.  A little more effort to type each time; a lot more public awareness.  IMHO, its the polite and responsible thing to do.

Only open up one of these things if you understand the risks involved.

[birt]

just a suggestion but if you have an old broken tv, check it.
those things are loaded with high watt resistors

Yes.  They also have high Voltage capacitors.

birt, good suggestion, and no offense intended... However,  as a note to all: when suggesting the opening up of a TV/monitor/amp, it's probably best to put a disclaimer that it can kill you.  You cannot assume everyone knows this in a public forum, and personally, I wouldn't want someone's harm on my conscious.  A little more effort to type each time; a lot more public awareness.  IMHO, its the polite and responsible thing to do.

Only open up one of these things if you understand the risks involved.

you're right :oops:

i know about the risks and sometimes i'm even not carefull enough myself :oops: