Guys, need some help on heatsink.
Tried to search the suitable heatsinks or aluminum panels which can work as heatsink, but couldn't find any.
Want to know which are alternative materials which I can use as heatsinks for the LM3886?
There are some options mentioned on first page of this thread to create a heatsink using different shape aluminum panels. I can arrange such aluminum sections but my doubt is on attaching them together. How to attach them with each other? Using screws? Or using any metal glue? Will the glue not work against the heat absorption? Or do I need to put some thermal adhesive in between and then put the glue?
Tried to search the suitable heatsinks or aluminum panels which can work as heatsink, but couldn't find any.
Want to know which are alternative materials which I can use as heatsinks for the LM3886?
There are some options mentioned on first page of this thread to create a heatsink using different shape aluminum panels. I can arrange such aluminum sections but my doubt is on attaching them together. How to attach them with each other? Using screws? Or using any metal glue? Will the glue not work against the heat absorption? Or do I need to put some thermal adhesive in between and then put the glue?
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Use Pentium 4 processor heatsink with fan and connect to 12 v supply for the fan to operate. you can buy it from local market and they can be available at 150 starting price per unit.. Chinese model with fan will be more than sufficient. If you have access to old computer store / vendor they can provide you for free.Use necessary insulation and apply good quality compund. The cabinet also can be one of old computer desktop case which you can repaint according to your need or buy new slim cases available in market. Enjoy and share pics....
Datasheet doesn't have mention about heatsink size. But the one readymade LM3886 board came with 4" X 2.5" heatsink which has around 1.75" longer fins.
I sisn't do any calculation neither I understand these calculations and language but I am looking for a 10"-12" longer heatsink with height of around 5". Not sure about fins but considering atleast 1" longer fins
Does the break between two heatsinks matter that much? My plan is put two channels on one heatsink. It will reduce my efforts towards building the cabinet.
I wouldn't prefer a noisy fan. There are already lot of fans, one in the computer, one in the projector and I don't want another one in the AMP.
I talked with my computer vendor friend and he told me that Pentium PIII heatsinks have square shape and I think those can be used without the fans also. Won't that heatsink be effective enough without fan?
I also inquired about the heatsinks used in the inverters, will get confirmation about availability on Monday but not sure if those are suitable or not.
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nope, not without the fan if You are going to listen to them loud.
but...
there is a quite decent approach,
http://www.tme.eu/hu/Document/b93ab9ed2763db46467df39bc87c7c2a/67F050-Airpax.pdf
that is what You need, and a simple computer fan.
now comes the part to make it silent, use a voltage regulator or series diodes or whatever You prefer, drop the voltage to around 10 volts for the fan(s).
This device has to be secured to the heatsink close to the IC. With good thermal contact.
I think the one that switches ON at 70c and switches off at 50c will do the trick for You.
If You do not push the amp hard, the fans will not turn on.
If You do push the amp(s) hard, then most probably You won't hear the fan at all.
allso, when the heatsink temp. drops to the 50c, the fans will stop.
I think it is quite nice, right?
but...
there is a quite decent approach,
http://www.tme.eu/hu/Document/b93ab9ed2763db46467df39bc87c7c2a/67F050-Airpax.pdf
that is what You need, and a simple computer fan.
now comes the part to make it silent, use a voltage regulator or series diodes or whatever You prefer, drop the voltage to around 10 volts for the fan(s).
This device has to be secured to the heatsink close to the IC. With good thermal contact.
I think the one that switches ON at 70c and switches off at 50c will do the trick for You.
If You do not push the amp hard, the fans will not turn on.
If You do push the amp(s) hard, then most probably You won't hear the fan at all.
allso, when the heatsink temp. drops to the 50c, the fans will stop.
I think it is quite nice, right?
Yeah, but there isn't anything about the size relevancy. Something is written in some technical language which is beyond my understanding right now, maybe I could understand sometimes later after reading a lot on that.
Thanks for the idea Arty, thats really cool and worth to try out. Really appreciated it.
But my problem is I am new in the DIYs and never been into electricals in the past. My first target is to bring the current setup in running stage. Once it starts playing, I can gradually start experimenting with these stuffs which I wold love to do later on for the sake of new learnings. But rght now I want simplest and easiest routes to follow.
Handling the power has been a biggest troubling thing for me so far during this project and I don't want to fall again in the mess-up of bringing down the power for the fans.
do you know your supply voltage?
Do you know your speaker impedance?
If you don't know both, you CANNOT start your build.
Speaker Impedance : 4 ohms
Supply volts : +/-32v after rectification from a shared transformer/PSU to 5 X LM3886 (I may use another lower volt transformer if I find the volts too high after playing the amp for a while)
look back at the plots on page 14.
Find Vcc for 68V on the graph.
Go up from there and cross over the 8ohm dotted plot. Stop when you reach the 6ohm dashed plot. You can't go higher the graph tells you that +-34Vdc (=68V) can only go down to a 6ohms speaker.
Reduce the supply voltage to 60V (+-30Vdc).
Go up until you reach 4ohms.
Now go left to find the 45W for Pd
Keep going left until you reach the group of numbers 1.6, 1.2, 1.0
These are the heatsink size for the ambient temperature (Ta) around your heatsink.
An external heatsink in India might have Ta from 30ºC to 45ºC. Take the 40ºC value of 1.2
That is shown in the second line of the title as "Max Heatsink Thermal Resistance (ºC/W)"
1.2C/W is the heatsink that National recommend for a 3886 running on +-30Vdc when powering a 4ohms speaker and the chip is kept Tc=96ºC
That is far too hot. Tj will be approaching 125ºC
Use double that size. i.e. 0.6C/W.
For two chips use 0.3C/W
That is far too big for a reasonable amplifier, i.e. +-30Vdc in India with Ta~40ºC and 4ohms speakers, does not result in a reasonable amplifier heatsink.
You need to learn how to read the datasheet !
When you come back and confirm you understand this far, I will show you how to work out a reasonable heatsink for a stereo 3886 amplifier.
Find Vcc for 68V on the graph.
Go up from there and cross over the 8ohm dotted plot. Stop when you reach the 6ohm dashed plot. You can't go higher the graph tells you that +-34Vdc (=68V) can only go down to a 6ohms speaker.
Reduce the supply voltage to 60V (+-30Vdc).
Go up until you reach 4ohms.
Now go left to find the 45W for Pd
Keep going left until you reach the group of numbers 1.6, 1.2, 1.0
These are the heatsink size for the ambient temperature (Ta) around your heatsink.
An external heatsink in India might have Ta from 30ºC to 45ºC. Take the 40ºC value of 1.2
That is shown in the second line of the title as "Max Heatsink Thermal Resistance (ºC/W)"
1.2C/W is the heatsink that National recommend for a 3886 running on +-30Vdc when powering a 4ohms speaker and the chip is kept Tc=96ºC
That is far too hot. Tj will be approaching 125ºC
Use double that size. i.e. 0.6C/W.
For two chips use 0.3C/W
That is far too big for a reasonable amplifier, i.e. +-30Vdc in India with Ta~40ºC and 4ohms speakers, does not result in a reasonable amplifier heatsink.
You need to learn how to read the datasheet !
When you come back and confirm you understand this far, I will show you how to work out a reasonable heatsink for a stereo 3886 amplifier.
Thanks a lot for taking pain to write down the explanation Andrew, it was indeed very helpful. I read all that data earleir as well and got little bit of thing in mind and your explanation made it more easier to understand after reading the datasheet again.
Now I could reach till the C/W thing. But how do I calculate the size of the heatsink? After reading on heatsinks, I could understand that its the active surface area which matters so I can't use a big aluminum block, there should be longer fins to keep the size of the amp reasonable. How to calculate how much total surface area I need.
Usual heatsinks used in the amplifiers have more gap between the fins compared to the computer processor heatsinks. Does the thickens of the material and the wider/narrower gap between fins also play the role or we can use the computer heatsinks?
Finally how effective the custom made heatsink will be considering there will be lot of joints?
Now I could reach till the C/W thing. But how do I calculate the size of the heatsink? After reading on heatsinks, I could understand that its the active surface area which matters so I can't use a big aluminum block, there should be longer fins to keep the size of the amp reasonable. How to calculate how much total surface area I need.
Usual heatsinks used in the amplifiers have more gap between the fins compared to the computer processor heatsinks. Does the thickens of the material and the wider/narrower gap between fins also play the role or we can use the computer heatsinks?
Finally how effective the custom made heatsink will be considering there will be lot of joints?
Yeah, it is. Any issue with this PCB?This is same Elektor type PCB,If I am not wrong .
yes, the gap between the fins do play a role. as do the thicknes of the fins and baseplate. Close gap and thin fins are designed for active cooling (fan).
passive cooling demands more space between the fins so that the air between them stays cooler. the thicknes of the baseplate determines how far in diameter around the active device the heat will effectively spread.
a custom made heatsink with a lot of joints will not be very effective. every joint is a weakspot. in this case hotspot, where there will be trapped hot air that will affect the performance.
Unfortunately I don't have access to any manufacturer,
I would have to pick heatsinks form scraps without any specs, thats why I asked what size/area do I need. These might be old computer heatsinks or most probably aluminum heatsinks used in power inverters.Looks like I will have to go for a fan-cooled heatsink in worst case.
After digging a lot on internet, could find one source:
Buy HeatSinks for amplifier at low prices in India, online.
They have one heatsink with dimensions of 196/100/33mm with Rth 0.6 K/W rating. Can I use this heatsink to cool down two LM3886 chips? I know Andrew is feeling like kicking me from behind
while I am talking about this but is that gonna become really that risky or I can try out this first and can add more heatsinks later if I face any issue?
Also, do I need to put a thick aluminum or copper spacer between the chip and the heatsink?
Buy HeatSinks for amplifier at low prices in India, online.
They have one heatsink with dimensions of 196/100/33mm with Rth 0.6 K/W rating. Can I use this heatsink to cool down two LM3886 chips? I know Andrew is feeling like kicking me from behind
while I am talking about this but is that gonna become really that risky or I can try out this first and can add more heatsinks later if I face any issue?Also, do I need to put a thick aluminum or copper spacer between the chip and the heatsink?
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