YES.
FACTS.
Simple things like saying "To build this, I did this calculation which told me I needed a heat sink that kinda looked like this about this long and this wide, and I found it at this place" would mean so much to me, but it's information that is consistently missing. It's always just a picture (or not) with no explanation as to why it's that big or why that material was chosen, nothing.
In fact, pointing out the typo in the Mouser catalog was enough information to put my mind at ease that I WAS understanding the math, and was just second-guessing myself based on bad info, and could have possibly avoided posting about this in the first place.
Facts, man, just the facts.
Listen, have you built a chip amp? What chip? At what voltage? Bridged or stereo? What did you use for a heatsink? Is it commercially available or did you make it yourself? Did you try other materials or products that didn't work so well? Did you do the math or just go by trial and error?
I'm not asking you to build the darn thing for me, fer pete's sake, just looking for good solid practical information.
It seems heat sinking is some esoteric black art that involves blood initiation to get to the secret of.
Hmm... maybe that's it after all
I have been all over google, various datasheets, manufacturer specs, other people's project pages, you name it, but the one thing that has eluded me is...
FACTS.
Simple things like saying "To build this, I did this calculation which told me I needed a heat sink that kinda looked like this about this long and this wide, and I found it at this place" would mean so much to me, but it's information that is consistently missing. It's always just a picture (or not) with no explanation as to why it's that big or why that material was chosen, nothing.
In fact, pointing out the typo in the Mouser catalog was enough information to put my mind at ease that I WAS understanding the math, and was just second-guessing myself based on bad info, and could have possibly avoided posting about this in the first place.
Facts, man, just the facts.
Listen, have you built a chip amp? What chip? At what voltage? Bridged or stereo? What did you use for a heatsink? Is it commercially available or did you make it yourself? Did you try other materials or products that didn't work so well? Did you do the math or just go by trial and error?
I'm not asking you to build the darn thing for me, fer pete's sake, just looking for good solid practical information.
It seems heat sinking is some esoteric black art that involves blood initiation to get to the secret of.
Hmm... maybe that's it after all
Last edited:
I have recently built two chip amp using Peter Daniels excellent pcb's;one using LM4780's in parellel and the other the 3875's. Both use 10mm thick alluminium as heatsinks.The 4780's both on a piece 300mmx100mm and using +-35v dc supplies this runs warm reaching approx 35C.On the other hand the 3875's are mounted on two pieces 300mmx80mm [case similar to PD's integrated] and barely get warm after several hours of use with +-32v dc.Hope this is of some help.
YES.
I have been all over google, various datasheets, manufacturer specs, other people's project pages, you name it, but the one thing that has eluded me is...
FACTS.
Simple things like saying "To build this, I did this calculation which told me I needed a heat sink that kinda looked like this about this long and this wide, and I found it at this place" would mean so much to me, but it's information that is consistently missing. It's always just a picture (or not) with no explanation as to why it's that big or why that material was chosen, nothing.
In fact, pointing out the typo in the Mouser catalog was enough information to put my mind at ease that I WAS understanding the math, and was just second-guessing myself based on bad info, and could have possibly avoided posting about this in the first place.
Facts, man, just the facts.
Listen, have you built a chip amp? What chip? At what voltage? Bridged or stereo? What did you use for a heatsink? Is it commercially available or did you make it yourself? Did you try other materials or products that didn't work so well? Did you do the math or just go by trial and error?
I'm not asking you to build the darn thing for me, fer pete's sake, just looking for good solid practical information.
It seems heat sinking is some esoteric black art that involves blood initiation to get to the secret of.
Hmm... maybe that's it after all
You should take another look at post #8. I think that it contains the info that you are looking for. I build active speakers with LM3886 chipamps, and the fin area seems to be in the ballpark for what works well for me, as long as the chipamp ICs are mounted correctly to the heatsink, e.g. with a small film of thermal compound (I use the TF or insulated version).
Heatsink USA has good service and reasonable prices. They are my single source for heatsinnks.
-Charlie
From a purely practical standpoint, I save various odd pieces of suitable metal scrap to use as heatsinks. I've even taken a long narrow piece of tin or aluminum and wrapped it around a pen so my heatsink is just a loose coil of metal connected at one end, not unlike the spring steel you may find in a wind-up toy. It's worth knowing basic heatsink design requirements, but tbh more often than not I just guesstimate the "yes, that's plenty of mass and surface area" for the needed dissipation.
I've often wondered at the effectiveness of plain aluminum stock for heat sinking, as I have seen it used in many places.
Thank you for your example, let's see if we can work through this...
The only practical example I could find for calculating the thermal properties for a given volume of aluminum is here: Thermal design
So if the volume of the aluminum is:
10x30x100mm = 240,000 cu. mm = 0.24 Liters
We get 0.24 = 0.8 / (Rt^1.47)
I'll skip the complexities and ask Wolfram Alpha to handle this:
http://www.wolframalpha.com/input/?i=0.24%3D0.8%2F%28x^1.47%29
So we get a number of 2.2683C/W, which is the thermal resistance that should match or exceed the datasheet value.
My brain is now thinking more of sleep than figuring further, so I'll let this lie for the nonce, and just say that the LM3875 datasheet, page 14, has an excellent step-by-step method for Determining the Correct Heat Sink.
Check it out, good night.
Yes, very informative, and have found similar heatsinks at other online resources. Bigger than I thought I would need, but the numbers don't lie (this time
).Sage advice, that... the only problem being I don't have experience and wisdom enough yet to do that very thing for myself.
The energy put forth in this very thread has done much to change that, however...
The volume is largely immaterial.
It is the surface area that dissipates the heat.
Volume only comes into play with MASSIVE heatsinks that are trying to dissipate heat over a large area.
Think of it like a tank of water.
You are trying to get rid of a river of water constantly flowing to fill your reservoir.
The river is the heat you are trying to get rid of.
If the heatsink had holes ion it to let the water out, you can visualise how it is working.
The more holes in the largest area will let out the most water.
In a MASSIVE heatsink, you would need a huge alluminium tank in order to feed the heat to all the holes.
I can't get much more simple than that.
Last edited:
The volume is immaterial.
It is the surface area that dissipates the heat.
Volume only comes into play with MASSIVE heatsinks that are trying to dissipate heat over a large area.
Typo. Sorry.
I was referencing Marra's post about the chunk of aluminum 10x80x300mm. If I recall correctly, I mentioned that I was tired. Thanks for the correction.
Hmm, really? So I could cut and bend up some old sheet aluminum I have lying around, and it would work? Sweet.
Although I could see problems with that being dimensionally unstable (warps, etc causing surface contact voids) and so probably more prudent to use properly machined aluminum stock.
Sure, except I was having quite the trouble figuring the math for individual chipamps to arrive at that magical number. What would be EVEN COOLER is if they also provided a list of "Recommended to work with..." devices (which was kinda the point of my OP), but I'm sure that list would be prohibitively large and quickly out-of-date, so scratch that idea, I'll just do the bleeping math. *grumble*
Thanks all, i know SO much more about heatsinking than I did when I started.
Really, I mean that.
Last edited:
If volume is sufficient, surface area is what determines the heat loss to air. If you have a lot of surface area but the fins are too thin, the internal conductive resistance will be too high and much of your surface area will go to waste, lowering your effectiveness.
some commercial products DO use zigzagged sheet metal crimped to a piece of L-angle as a heatsink. It is usually quite inferior to a real aluminium extrusion.
For the chipamps you mention it will probably be adequate, however by the time you have manufactured this yourself (unless you have the tools and materials to hand for little/no cost), you can buy a sensible extrusion already.
For your reference, A 2xLM3886 amp I built uses a 160mm wide, 25mm deep, 70mm high non-anodised extrusion I got from eBay, with 25v supplies. It gets warm when driving a 4 ohm load at decent volume, but not excessively so.
For the chipamps you mention it will probably be adequate, however by the time you have manufactured this yourself (unless you have the tools and materials to hand for little/no cost), you can buy a sensible extrusion already.
For your reference, A 2xLM3886 amp I built uses a 160mm wide, 25mm deep, 70mm high non-anodised extrusion I got from eBay, with 25v supplies. It gets warm when driving a 4 ohm load at decent volume, but not excessively so.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.