Can oil cool a small amplifier chip without heatsink?

MrAl

Joined Jun 17, 2014
11,389
Linear is obsolete though buddy. What you are saying will work though. I was messing around with class AB amplifiers 20-years ago. So loud that the bloke over the road wanted to murder me! I tried some LMxxx linear ICs in water. They stayed cool enough.
Hi,

Linear vs switcher is STILL a cost vs application decision, not a random guess just because a switcher is more efficient in most cases.

In theory a switcher should be able to beat a linear, but there are other considerations which often weigh in favor of the linear. You'll hear many stories like this.

Also, this isnt just an opinion, it is a fact and can be easily proved. Proved by the fact that many high power power supplies are made with BOTH switcher AND linear, and for good reasons. The front end is switcher for better efficiency, and the back end is linear for better ripple and regulation. If a switcher always beat a linear there would be no need for the linear back end.
 

alfacliff

Joined Dec 13, 2013
2,458
in the old days, you could get a lot more power from a 6l6 supspending it in oil. these days solid state stuff wont really take too kindly to over voltage or current. the internal connections are sized for certain power levels, and would be more expensive to make thicker or wider to handle more current why not just go for a higher rated amp chip?
and a small heatsink in oil works better than no heatsink, just the chip in oil. even better is a tab silversoldered onto a copper tube with water flowing through it. just mount the chip to the tab. flowing water or oil is much better than static non moving sealed in air.
 

MrAl

Joined Jun 17, 2014
11,389
Hi,

A plastic container is not as good as metal because the plastic acts like an insulator. If there is plenty of open surface area that will help to a certain extent.

When the area is enclosed in insulators the problem becomes mostly one about the specific heat capacity of the substance being heated. A high value means it takes longer to heat up to a certain temperature, while a low value means it heats up fast.
This will determine how long the unit can run until the oil heats up and the chip burns out. Hopefully it does not start a fire.

If you could get a hold of one of those CPU water coolers you could modify it to be used with your chip. They have a circulation pump and radiator and fan to dissipate the heat. That would be a pretty nice setup.
 

Johann

Joined Nov 27, 2006
190
I don't want to look for a new heatsink, instead I want to remove the old one and put the whole thing in a small bowl of oil. My question is, will a chip about 2.5x the size of a to-220 transistor case dissipating maybe 10 watts or so of heat or so be able to transfer that heat into the oil without a heatsink? Since I only use it for short runs I won't have to worry about all of the oil overheating, and if I start using it more I can always point a fan at the surface.
Time is on your side if it is only going to be used for short runs.
 

inwo

Joined Nov 7, 2013
2,419
Trying to think of an advantage to using a 6inx6inx2in open container of oil over a similar sized metal anything.:confused:

No, nothing.................
 

alfacliff

Joined Dec 13, 2013
2,458
no heatsinks? the last 200 or so pc supplies I fixed had heatsinks and at least one fan in each one. maybe you are jmistaken about what a heatsink is, or how mch it weighs? some I supplies I have worked on use copper heat spreaders and have built in liquid cooling passages to help spread the heat for the heatsink to disapate.
 

alfacliff

Joined Dec 13, 2013
2,458
one advantage of a linear supply over a switcher is thagt they have more storeage in their filter caps. line dips and brownouts dont affect them as much. some old supplies I have will even hold the load up several seconds after you turn them off.
 

MrAl

Joined Jun 17, 2014
11,389
Hi,


That is an interesting point yes.


Just for reference, if the 6x6x2 inch container held water instead of oil, it would take about 10 hours to heat the water up to boiling temperature (100 deg C) with only 10 watts of heat. That's partly because of the specific heat capacity of water so for oil it would be slightly different. You can compare the heat capacities of both substances to compare.

So distilled water would give you maybe 7 or 8 hours of use even with negligible container to air heat loss.
 

Thread Starter

rudyauction8

Joined Jan 27, 2012
250
Trying to think of an advantage to using a 6inx6inx2in open container of oil over a similar sized metal anything.:confused:

No, nothing.................
Well I have a dozen laying around. Why would I fork out $10 plus for a container for a $10 amp when I have perfectly fine containers laying around. Like others have said, it'll take much much longer to heat the oil -even completely insulated- than I ever intend to have it running. And yes, I happen to have the oil laying around. That's what gave me the idea.


Side note, does anyone know if motor oil is conductive? I have gallons of it still sealed in my garage.
 

inwo

Joined Nov 7, 2013
2,419
Well I have a dozen laying around. Why would I fork out $10 plus for a container for a $10 amp when I have perfectly fine containers laying around. Like others have said, it'll take much much longer to heat the oil -even completely insulated- than I ever intend to have it running. And yes, I happen to have the oil laying around. That's what gave me the idea.


Side note, does anyone know if motor oil is conductive? I have gallons of it still sealed in my garage.
Sorry,:p
I didn't mean a metal oil container.

Meant to suggest similar size and mass metal scrap without oil.
 

MrAl

Joined Jun 17, 2014
11,389
Well I have a dozen laying around. Why would I fork out $10 plus for a container for a $10 amp when I have perfectly fine containers laying around. Like others have said, it'll take much much longer to heat the oil -even completely insulated- than I ever intend to have it running. And yes, I happen to have the oil laying around. That's what gave me the idea.


Side note, does anyone know if motor oil is conductive? I have gallons of it still sealed in my garage.

Hi again,

Oil used to be used as an insulator and maybe still is used in oil filled caps. But it probably depends on the oil used. Thus, you'd have to test it. Compare the oil ohm readings with a given sample volume and shape size to a similar container of tap water or distilled water. See what is different. You can also use a low voltage to test and measure the current then compare currents.

I also found a reference for specific heat capacity of vegetable oil. It's about half that of water, so the previous calculation i did in this thread with water can be halved. That means your container would heat up to 100 degrees C in about 5 hours, assuming there was no heat loss. Since there is at least some heat loss, it should take longer than 5 hours.
 

Thread Starter

rudyauction8

Joined Jan 27, 2012
250
I finally got around to giving this a try, I put the original amp and 2 others in the oil: a 2.1 amp with 3 tda2030a chips and a single channel amp with 2 bridged tda2030a chips, and after 4 hours at full volume the oil is warm to the touch, no more than 100 degrees F. Before the oil the 2 tda2030a based amps would overheat and go into thermal shutdown in just minutes at full volume. So I'd say this is a complete success, and I intend to use oil now whenever I have a small circuit that overheats and doesn't need to be moved around.
 

Johann

Joined Nov 27, 2006
190
I don't know, but I'd guess there would be slight conductivity (depending on type/brand) due to additives.
I have once tested a mono grade engine oil with a high voltage tester used to test transformer oils. The oil container with the oil sample contains two ball-shaped electrodes which are separated by a calibrated gap between them. A slowly rising AC voltage is then fed to them until it breaks through where after the machine trips, but the voltage reading remains on the HV voltmeter for recording purposes. Anyway, the mineral engine oil tested to 40 kV before the trip occurred! So I guess it will be O.K. for low voltage DC, provided it is not unfriendly towards the insulating materials used in your project, something I did not investigate.
 

MrAl

Joined Jun 17, 2014
11,389
Hi,

I think he said he already had those and didnt want to buy anything else, so we were looking at ways to cool this without spending any more money.
 
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