Can hot resistors ignite polyfil - diyAudio
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Old 25th April 2011, 05:35 AM   #1
sunil is offline sunil  India
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Default Can hot resistors ignite polyfil

Hi,

I'm building a version of 'Rabbitz' crossover detailed here.

I'm building a second pair with this design.

There is polyfil on the rear baffle & sides which I'm certain will touch components of the x-over. Is this a problem ? Are the resistors likely to ignite the filling material ? Also, are there ways to prevent it ?

Any help will be most appreciated, thanks.

Cheers.
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Old 25th April 2011, 05:46 AM   #2
sunil is offline sunil  India
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There's a answer in this thread, which says it can even set the cabinet on fire.

Can this happen to any design and how can I prevent this. Thanks.
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Old 25th April 2011, 06:02 AM   #3
andy2 is offline andy2  United States
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I am not sure if the resistor will set fire but I do have some residual glue of my 3.3ohm resistor on the tweeter xover and if I play really load on some recordings, I could see smoke from the glue material.
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Old 25th April 2011, 09:27 AM   #4
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Most fibre fill materials should be fire resistant as they are designed to be used in furniture, and as such, in most countries have to conform to quite strict standards. Take an offcut outside, and try setting fire to it with a match. It will probably just smoulder, then go out as soon as the flame is removed. If not, allow lots of clearance, or buy some different material.
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Old 25th April 2011, 10:33 AM   #5
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I'd've thought that, if the resistors are getting hot enough for that, you should get some aluminium clad ones, or add a small heatsink.

Have you actually tried the crossover? How long can you hold your finger on the resistor before it hurts?
Some resistors get hot, but the first crossover would be putting most of the power through the woofer, so I'd really doubt the resistor will get hot at all.

Chris
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Old 25th April 2011, 11:16 AM   #6
DavidL is offline DavidL  United States
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Simply use larger wattage resistors. You can parallel several resistors of higher ohm value to obtain the value needed. Also mount the resistors so that they have air flow on all sides of them. If the resistors are getting too hot then the design is frankly bogus.
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Old 26th April 2011, 05:43 AM   #7
sunil is offline sunil  India
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Thanks for the ideas and thoughts. I asked the question to be reasonably safe while attempting this. I've decided to go with:

* higher powered resistors
* use velcro to hold the polyfil securely in place so theres very little chance it it coming in contact with the x-over

Once its complete, I'll post pictures if it will help other diy'ers.

Also, looking at the 2 circuit diagrams can somebody please help me understand what kind of power will be taken up by the resistors. My drivers are standard Vifa P13's with Vifa XT25-04. Thanks.
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Old 26th April 2011, 08:35 AM   #8
rabbitz is offline rabbitz  Australia
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Quote:
Originally Posted by sunil View Post
I'm building a version of 'Rabbitz' crossover detailed here.
Built heaps with this type of crossover and the resistor never gets warm. I use a 10W ceramic or MOX for that location.

If you lose sleep over it, add a little cage over the crossover.

BTW, the crossover is for the P13/D27TG and will not work with a XT25TG tweeter.
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Old 26th April 2011, 09:48 AM   #9
AndrewT is offline AndrewT  Scotland
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I would expect most artificial fibre "wools" to be combustible.

Glassfibre and rockwool are not combustible. But the glue/s used to make them into wool blankets will be combustible. I would expect the glue to be just a tiny w/w proportion of the total blanket weight.
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Old 26th April 2011, 09:58 AM   #10
sunil is offline sunil  India
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Thanks for the support. The series x/o is going to a P13/D27 design. I'm doing a second P13/XT using 'Sheldon Stokes - quadesl.com' x/o and mixed the two up in the post.

Its reassuring to know your experience with the resistor.
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