For all you guys building nice, hot, class A amps, note that if you want the innards to run cooler than the heatsinks, you need to make ventilating holes of some sort in both the top and the bottom.
If you don't, it's just the same as if you never made the holes in the top! (Ask me how I know this!)
And I should know better. I used to be in the furnace business, and it's pretty fundamental that if air is to flow out, it must flow in (and vice versa).
The net area open to convection is the smaller of the open area in the top or the bottom.
If you don't ventilate, the air contained in the box will come up in temperature over time until it's just about equal to that of the heatsinks.
If you don't, it's just the same as if you never made the holes in the top! (Ask me how I know this!)
And I should know better. I used to be in the furnace business, and it's pretty fundamental that if air is to flow out, it must flow in (and vice versa).
The net area open to convection is the smaller of the open area in the top or the bottom.
If you don't ventilate, the air contained in the box will come up in temperature over time until it's just about equal to that of the heatsinks.
Vince,
Like this http://www.diyaudio.com/forums/showthread.php?postid=92763#post92763 do you mean?
Chris
Like this http://www.diyaudio.com/forums/showthread.php?postid=92763#post92763 do you mean?
Chris
This is also an issue with the X Aleph.
There is siginificantly more heat generated losses from the internals such as chokes/resisters, rectifiers and even the transformers who are being asked to deliver twice the current.
The losses in heat (50-100 watts)from these components have to go somewhere, and obviously the air temperature in the box will rise appreciably as a result without ventilation.
Heatsinking these items to the outside world would help, but this must them be then accounted for in the heatsink surface area.
The box must still be ventilated or the air temperature will approach that of the heat sinks.
I am sure many who are currently building their monster X Aleph will be surprised to find their box is too hot without ventilation, even with the lid off
(ie holes in the bottom)
I recently did the upgraded from the Aleph 2 to the X Aleph 100 and I propose to deal with this in revision 1 of the chassis- layout.
This will mean re arranging the position of the transformers to be each placed on the floor of the box (the coolest place), each surrounded be vent holes (at moment stacked on top each other for space reasons).
I also plan a row of vent holes along the length each side of the floor of the box (1 cm))
The rectifiers, which gernerate a lot of heat will be moved and bolted the a large channel section each side of the box for heatsinking.
The capacitor smoothing filters will be supported well above the transformers on a channel section, with the driver board mounted horizontally at the rear...it will look not unlike a Pass X Series.
I am not sure about the lid yet, there will be holes . but maybe a fan for the summer as well!!
I hope this helps illustrate some the facts about this hot topic.
Here is an image of some of the hot parts.
macka
There is siginificantly more heat generated losses from the internals such as chokes/resisters, rectifiers and even the transformers who are being asked to deliver twice the current.
The losses in heat (50-100 watts)from these components have to go somewhere, and obviously the air temperature in the box will rise appreciably as a result without ventilation.
Heatsinking these items to the outside world would help, but this must them be then accounted for in the heatsink surface area.
The box must still be ventilated or the air temperature will approach that of the heat sinks.
I am sure many who are currently building their monster X Aleph will be surprised to find their box is too hot without ventilation, even with the lid off
(ie holes in the bottom)I recently did the upgraded from the Aleph 2 to the X Aleph 100 and I propose to deal with this in revision 1 of the chassis- layout.
This will mean re arranging the position of the transformers to be each placed on the floor of the box (the coolest place), each surrounded be vent holes (at moment stacked on top each other for space reasons).
I also plan a row of vent holes along the length each side of the floor of the box (1 cm))
The rectifiers, which gernerate a lot of heat will be moved and bolted the a large channel section each side of the box for heatsinking.
The capacitor smoothing filters will be supported well above the transformers on a channel section, with the driver board mounted horizontally at the rear...it will look not unlike a Pass X Series.
I am not sure about the lid yet, there will be holes . but maybe a fan for the summer as well!!
I hope this helps illustrate some the facts about this hot topic.
Here is an image of some of the hot parts.
macka
Attachments
Flames
JH said:
"Sometimes I'm seriously thinking about the air flow holes.
If the amp is getting very hot and fresh air is supplied inside it, it might ignite a fire. Therefore, I prefer a totally closed box having laaarge size of heatsinks on its sides."
Flames won't make it past a metal mesh so use some metal window screen to cover your ventilation holes if you are worried about fire. Just an idea.
Greg
BTW What is the source of fuel for this fresh air induced combustion you anticipate? Does your Aleph run on petrol?
JH said:
"Sometimes I'm seriously thinking about the air flow holes.
If the amp is getting very hot and fresh air is supplied inside it, it might ignite a fire. Therefore, I prefer a totally closed box having laaarge size of heatsinks on its sides."
Flames won't make it past a metal mesh so use some metal window screen to cover your ventilation holes if you are worried about fire. Just an idea.
Greg
BTW What is the source of fuel for this fresh air induced combustion you anticipate? Does your Aleph run on petrol?
jh6you,
In certain industrial environmental conditions intrinsically safe operating enclosures (explosion and dust proof) are necessary.
This is for areas like grain silos, coal mines & treatment plants or other areas were the possibility of instantanious conbustion from air born dust particles is a concern.
Your average living room should be okay....unless of course you are a mad scientist (by the name of Pass..muhahahah..just joking) or you are prone to erratic Fart Attacks.
macka
In certain industrial environmental conditions intrinsically safe operating enclosures (explosion and dust proof) are necessary.
This is for areas like grain silos, coal mines & treatment plants or other areas were the possibility of instantanious conbustion from air born dust particles is a concern.
Your average living room should be okay....unless of course you are a mad scientist (by the name of Pass..muhahahah..just joking) or you are prone to erratic Fart Attacks.
macka
jh6you
I agree totally regards air in for air out.
In fact today I have been looking at RS Components Catalogue, they have some nice aluminium and stainless steel open mesh of different varieties, ranging from 30 - 68 % open space, and not too expensive, about A$90 for two sheets 500 x 500mm
At least this will make the opens legitimate and safe to prying fingers and stop other pests getting in there and creating havoc.
By the way, parts can explode, namely capacitors if their ripple current rating is exceeded.
In a search on the subject Mr Pass has suggested the ripple current rating of the caps should be at least 3 x the DC draw of the circuit. Of course this assumes a certain ambient temperature in the box, no doubt the higher the temperature, the more likely there is be trouble and low life span of the caps.
Last but not least, painting the whole outside of the box black will make the heat transfer more efficent. aka Aleph
Despite the humour, this is a critical area of the project and the cause of a lot of disappointment and expense later on if steps are not taken to correctly engineer the design.
Hence I do not leave my X Aleph 100 on for more than an hour or so in its current physical state (just about to watch Arnie the Terminator...the original...the seatbelt sign is On..Muhahahah)
macka
I agree totally regards air in for air out.
In fact today I have been looking at RS Components Catalogue, they have some nice aluminium and stainless steel open mesh of different varieties, ranging from 30 - 68 % open space, and not too expensive, about A$90 for two sheets 500 x 500mm
At least this will make the opens legitimate and safe to prying fingers and stop other pests getting in there and creating havoc.
By the way, parts can explode, namely capacitors if their ripple current rating is exceeded.
In a search on the subject Mr Pass has suggested the ripple current rating of the caps should be at least 3 x the DC draw of the circuit. Of course this assumes a certain ambient temperature in the box, no doubt the higher the temperature, the more likely there is be trouble and low life span of the caps.
Last but not least, painting the whole outside of the box black will make the heat transfer more efficent. aka Aleph
Despite the humour, this is a critical area of the project and the cause of a lot of disappointment and expense later on if steps are not taken to correctly engineer the design.
Hence I do not leave my X Aleph 100 on for more than an hour or so in its current physical state (just about to watch Arnie the Terminator...the original...the seatbelt sign is On..Muhahahah)
macka
macka said:
It's also my concern. As far as I understand the maker's specification of electrolytic capacitor life span is based mainly on the rated operating temperature. And, I remember that the life span is getting longer when the operating teperature is lower than the rated one, ie life span ~ x (T rated/T operation)^2.
Sure, I like low inner space temperature.
JH
Hi, guys...
In order:
.
Mad K:
I think you know how I know, but it went like this... Built the amp from the bottom up. Last thing was to make a top plate. Bright idea: Make ventilation openings in it! Before I even turned the thing on I said, "damn! I didn't even think of ventilation in the bottom!" Sure enough, the inside runs at the same temp as the heatsinks.
Chris Ma:
Yes, that looks great to me. Might want to think of using some perforated metal to keep anything from shorting something out there. Nice looking amps.
JH:
I think that there is no possibility of combustion there. I believe that nothing there would have an ignition temperature of less than 600C or so. Even with no ventilation, you do have air in the box. You can't prevent combustion unless you purge the thing with nitrogen or some other non-flammable gas and keep it pressurized. IMO that's not practical or necessary.
Macka:
Regarding that mesh, you might want to check with a general purpose industrial supplier to get it cheaper. Here we have McMaster Carr www.mcmaster.com that has just about anything you can dream of, and I can get it in one day at a reasonable price. Take a look and search for their 9232T211 part. It's a sheet about 1M^2 for US$35. Just one of many choices.
When(ever) I build my A-X I'm thinking of spacing the heatsinks about a cm away from the rest of the chassis to let the air flow across the back side of them. With black heatsinks, I think that the slot along each side of the chassis might be hardly noticable.
In order:
Joe (Mr. Dirt): We can talk, but really, that's pretty tough to figure definitively. Maybe you're kidding? The static pressures there are so small; certainly I don't have any way to measure such things. They're just a slight variation on the local atmospheric pressure. And of course, once you open some holes and start to get some flow, the temperature drops and the pressure drops too. Since this is engineering which depends a lot on estimates and the like, you open some inlet and outlet holes until you like what you get.
.Mad K:
I think you know how I know, but it went like this... Built the amp from the bottom up. Last thing was to make a top plate. Bright idea: Make ventilation openings in it! Before I even turned the thing on I said, "damn! I didn't even think of ventilation in the bottom!" Sure enough, the inside runs at the same temp as the heatsinks.
Chris Ma:
Yes, that looks great to me. Might want to think of using some perforated metal to keep anything from shorting something out there. Nice looking amps.
JH:
I think that there is no possibility of combustion there. I believe that nothing there would have an ignition temperature of less than 600C or so. Even with no ventilation, you do have air in the box. You can't prevent combustion unless you purge the thing with nitrogen or some other non-flammable gas and keep it pressurized. IMO that's not practical or necessary.
Macka:
Regarding that mesh, you might want to check with a general purpose industrial supplier to get it cheaper. Here we have McMaster Carr www.mcmaster.com that has just about anything you can dream of, and I can get it in one day at a reasonable price. Take a look and search for their 9232T211 part. It's a sheet about 1M^2 for US$35. Just one of many choices.
When(ever) I build my A-X I'm thinking of spacing the heatsinks about a cm away from the rest of the chassis to let the air flow across the back side of them. With black heatsinks, I think that the slot along each side of the chassis might be hardly noticable.
Vince I was being sarcastic with you but in a nice way....we design HVAC units and use very precise magnehelic guages on every unit....tyupically a convection system has very little negative pressure on the inlet. It`s when you start using an induction system then that becomes a crucial factor......as far as our electronic controls we have to provide readings for the CSA inspector because they are mostly built integral to the unit.
cheers!!The DIRT®
cheers!!The DIRT®
Thanks Kenny,
Well the best is yet to come.
I will shortly refer to equations for the thermodymanics of the enclosure, particularly if you are like me and aim to use the existing enclosure, thus the solution as Mr Pass put it is "In a word FANS".
However, its not that simple and the selection of the right Fan requires some calculation for the correct operation of the fan and the desired level of cooling with the box.
My investigations so far lead me to believe the total energy losses with the box (less the heat sinks) is in the order of 100 watts worst case scenario.
This includes the transformer losses (based on manufacturers data), and PSU11 simulations for rectifiers and the chokes under the X Aleph operating conditions.
For practical purposes, if the maximum temperature of the toroidal transformer insulation tape is 105 C and the temperature rise is 60 C under full load, then the highest allowable ambient temperature inside the box is 40c worst case scenarion.
Given that it is summer in the USA and the air temperature has been in the order of 102 F (38 C) in the Reno area recently as I understand it, then you will have a problem if the box ventilation is not designed correctly.
The technology in fans is such that devices with noise levels of 12 dba are now available from at least PAPST, and while for absolute silence no fan is best, reliability is an over riding consideration where a big bang and then dead silence in the middle of a your favourite tune is frowned upon!
macka
Well the best is yet to come.
I will shortly refer to equations for the thermodymanics of the enclosure, particularly if you are like me and aim to use the existing enclosure, thus the solution as Mr Pass put it is "In a word FANS".
However, its not that simple and the selection of the right Fan requires some calculation for the correct operation of the fan and the desired level of cooling with the box.
My investigations so far lead me to believe the total energy losses with the box (less the heat sinks) is in the order of 100 watts worst case scenario.
This includes the transformer losses (based on manufacturers data), and PSU11 simulations for rectifiers and the chokes under the X Aleph operating conditions.
For practical purposes, if the maximum temperature of the toroidal transformer insulation tape is 105 C and the temperature rise is 60 C under full load, then the highest allowable ambient temperature inside the box is 40c worst case scenarion.
Given that it is summer in the USA and the air temperature has been in the order of 102 F (38 C) in the Reno area recently as I understand it, then you will have a problem if the box ventilation is not designed correctly.
The technology in fans is such that devices with noise levels of 12 dba are now available from at least PAPST, and while for absolute silence no fan is best, reliability is an over riding consideration where a big bang and then dead silence in the middle of a your favourite tune is frowned upon!
macka
Attachments
Regards fans here is an interesting post from another thread:
Correction!! Post #46
Quote:
Originally posted by JDeV
Actually I thought everything over again, did some calculations and decided (after reconcidering your comments) to reconnect the fans, but replacing the existing "out of old PC powersupplie" 1's with the highly aclaimed (and highly )
Papst 8412NGL fans. ...BTW - these new fans are not really much an improvement on the noise issue, IMO Expected much more for $30 worth of fan.
These fans, Papst 8412NGL , ARE very silent - if you mount them correct. I made mistake to mount them inside "cages", which cause alot of "wind noise" not from fan itself but from air being sucked through holes in cage. Apologies to "Mr. Papst" - if there is somebody called that I also dropped the fan supply to just 10Volt, which made them virtually completely noiseless.
Correction!! Post #46
Quote:
Originally posted by JDeV
Actually I thought everything over again, did some calculations and decided (after reconcidering your comments) to reconnect the fans, but replacing the existing "out of old PC powersupplie" 1's with the highly aclaimed (and highly )
Papst 8412NGL fans. ...BTW - these new fans are not really much an improvement on the noise issue, IMO Expected much more for $30 worth of fan.
These fans, Papst 8412NGL , ARE very silent - if you mount them correct. I made mistake to mount them inside "cages", which cause alot of "wind noise" not from fan itself but from air being sucked through holes in cage. Apologies to "Mr. Papst" - if there is somebody called that I also dropped the fan supply to just 10Volt, which made them virtually completely noiseless.
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