Been waiting patiently for anyone to answer at least partially my question above, but no takers so far (page 157).
Maybe it's not a question that deserves attention.
Maybe my idea is wrong and it's all an imagination.
Would still appreciate some input though.
Regards
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YouTube
Yesterday I wanted to show my son how to build a stupendously simple amp from scrap parts I had laying around. What better inspiration then this thread and the MOFO amp?!
It is based on an IRFP7430 (nice triody curves) coupled via an bifilar winded aircore transformer to the loudspeaker. This way I don´t have to worry about him coupling a large output capacitor the wrong way (wrong polarity) and destroying the speaker.
4 parts, a powersupply a piece of aluminum plate and some wire...
Match them and use some source resistors to force current sharing.
I tend to prefer low voltage high transconductance devices so I believe several of them paralleled should sound really good. Only one way to know for sure...
Yesterday I wanted to show my son how to build a stupendously simple amp from scrap parts I had laying around. What better inspiration then this thread and the MOFO amp?!
It is based on an IRFP7430 (nice triody curves) coupled via an bifilar winded aircore transformer to the loudspeaker. This way I don´t have to worry about him coupling a large output capacitor the wrong way (wrong polarity) and destroying the speaker.
4 parts, a powersupply a piece of aluminum plate and some wire...
Match them and use some source resistors to force current sharing.
I tend to prefer low voltage high transconductance devices so I believe several of them paralleled should sound really good. Only one way to know for sure...
Thank you Ciclomanen, will try with 2.
Might need a very low DCR choke to offset the source resistors.
More likely I'll be aiming for 1 ohm DCR, otherwise it becomes prohibitively big and expensive.
The big Hammond might work well here.
Being a frugal guy I'll first try to find a suitable MOT.
Snowmobile heads is not a total joke. Bob Pease suggested VW Bug heads for heatsinking hot transistors at low cost. A scrap head is nearly worthless to the engine owner because it won't hold fire, yet has big fins and a flat surface.
Research suggests that many recent snowmobiles are water-cooled, a shame. But air-cooled heads lurk on old sleds, also nearly all lawnmowers, and there are still air-cooled motorcycles.
Research suggests that many recent snowmobiles are water-cooled, a shame. But air-cooled heads lurk on old sleds, also nearly all lawnmowers, and there are still air-cooled motorcycles.
Sorry for OT.
About snowmobile, or, well any other engine head, it is not easily doable.
Not going too deep in subject, we are talking (of course of air cooled engines), and we can put out of equation 4 stroke (less than ideal shape, space taken by valve train, cams, different sensors) and especially 4 stroke that were planned to work within "enclosure" (car, snowmobile..) due to fact they (I have yet to see exception) are planned to work with some kind of force air cooling, which we are trying to avoid).
As for air cooled (2 strokes), majority of those are small displacement, and (again) to a degree relay on forced air circulation, not to mention that generally - they are small.
You would generally (if you must) have a greater success with cylinder of air cooled engine than head, with some machine work in creating flat surface for mounting power mosfet (or anything). Cylinder, (by nature) with "funnel" design could have some success, but I did not tried it.
I do see them in specific (steampunk, industrial, you name it) designs, but not in A class design intended for long time use.
And, I have not even scratched problem of material used for automotive parts, which have significantly different requests than stationary home amplifier heat sink (just to name resistance to extreme temperatures, resistance to fuels, acids, oils, mechanical stress, which are none relevant to electronics use).
And at least, "as shame" about water/air cooling, I do agree with you, but water cooled engines in automotive application are just - better. They offer thermally much more stable engine than air cooled is, which is again important because of, well, everything (power, reliability, consumption, wear, noise, exhaust emissions..). Downside is complication of design, but benefits by far are higher than negative sides of water cooled design.
Again, sorry for OT, just my opinion when I was thinking about this (and I am much closer to automotive sector than electronics, although inseparable these days).
T.
> to a degree relay on forced air circulation, not to mention that generally - they are small.
They are "huge" compared to electronic systems.
I have a couple heads for 5HP cylinders. 5HP is 3,700 Watts. An engine's cooling load is comparable to its output power (remember 30%-35% efficiency) so there was 3,700W coming off the engine when it ran. In this design say half off the cylinder and half off the head. 1,800 Watts.
As you say, these engines are LOUDLY fan-blown. Enough to improve heat transfer 10X. So now 180 Watts fan-free.
The engine will run to 400 deg F or 200C. We can not run half that hot. Say 1/3rd or 1/4. 60 to 45 Watts safe dissipation.
About what a MoFo throws off.
We don't care what exotic alloy was used in the engine, our stresses, temperatures, and chemicals will be easy to take.
They are "huge" compared to electronic systems.
I have a couple heads for 5HP cylinders. 5HP is 3,700 Watts. An engine's cooling load is comparable to its output power (remember 30%-35% efficiency) so there was 3,700W coming off the engine when it ran. In this design say half off the cylinder and half off the head. 1,800 Watts.
As you say, these engines are LOUDLY fan-blown. Enough to improve heat transfer 10X. So now 180 Watts fan-free.
The engine will run to 400 deg F or 200C. We can not run half that hot. Say 1/3rd or 1/4. 60 to 45 Watts safe dissipation.
About what a MoFo throws off.
We don't care what exotic alloy was used in the engine, our stresses, temperatures, and chemicals will be easy to take.
I think you got it wrong. I would like to make it with pictures and data, but, that would be far OT.
Engine cooling load is not comparable to its output power, and especially not in the way that you wrote it.
Please, picture your self an (motorcycle) engine and try to imagine biggest single part (surface). It would be exhaust. As you know, engine working temperature is around 90-ish deg C, not 200 (I think every car these days has temperature gauge). BUT exhaust temperature is (lets make it safe) 600-700 deg C. I guess you see the direction where this is going. You know (rough comparison) when you car "boils up" usually follows some damage to engine (cracked block, head...), and we are talking of boiling temperature, so 100 deg C.
Head nor cylinder do not have thermal capacity not even close number you are mentioning, due to simple fact that the are cooled (also, not to forget forced air circulation) by intake, and you are presuming that there is only heat generated inside cylinder block, which is not true.
Imagine several thousand of rpm (so let's make it safe 100 times a second) sucking fresh ("cold") air cooling internals, it is like having nice fan blowing air in cylinder at rate of displacement x rpm/2 (for two stroke), and that part is very very important for cooling of engine. Easy way to check it, as we all did, put your palm near exhaust pipe, whatever comes out, it for sure came in - just much colder.
Even more, engines are designed NOT to go above those temperatures due to simple fact that fuel evaporates on higher temperatures, which is, first of all dangerous (self ignition), and not economical (big concern to engineer is to supply engine with big quantity of fresh COLD air, because of engine power (stoichiometric ratio ratio and cooling) . There are engines designed to make benefits of very high internal temperatures and pressures (diesel) but this is not of our concern.
Now, as you wrote above, to split/put 1800W to engine head (it is not real number as explained above) in piece of metal that size and weight it would glow like light bulb in very short time (I guess good comparison is electric water heater, they usually come rated at 2kW connected to, say, Chipamp heat sink, which is roughly size of 5HP engine head. Not even submerged in 80L ow water wouldn't stop it from boiling in short time).
And as for being huge compared to electronic systems, well, matter of opinion. Every heat sink that I can easily put in my palm (and engine head hat we are talking about, scooter, lawnmower is in that category) I consider small. Attached photo is from any 50cc air cooled scooter or lawnmower engine, compared to spark plug. I am sure there are variations of this type of head with slightly bigger fins, but as being rarer, an mostly having fins in "cross section" pattern, shouldn't be any more suitable fort electronic cooling than one we are talking about.
As last, about exotic alloy used in engine, well, usually it is cheapest **** manufacturer can find, with two of our priorities (looks and thermal dissipation, in order depending who do you ask) not high on the list for automotive purpose.
Again, very sorry for OT, i hope I wont be sent for cooling for some time..
Engine cooling load is not comparable to its output power, and especially not in the way that you wrote it.
Please, picture your self an (motorcycle) engine and try to imagine biggest single part (surface). It would be exhaust. As you know, engine working temperature is around 90-ish deg C, not 200 (I think every car these days has temperature gauge). BUT exhaust temperature is (lets make it safe) 600-700 deg C. I guess you see the direction where this is going. You know (rough comparison) when you car "boils up" usually follows some damage to engine (cracked block, head...), and we are talking of boiling temperature, so 100 deg C.
Head nor cylinder do not have thermal capacity not even close number you are mentioning, due to simple fact that the are cooled (also, not to forget forced air circulation) by intake, and you are presuming that there is only heat generated inside cylinder block, which is not true.
Imagine several thousand of rpm (so let's make it safe 100 times a second) sucking fresh ("cold") air cooling internals, it is like having nice fan blowing air in cylinder at rate of displacement x rpm/2 (for two stroke), and that part is very very important for cooling of engine. Easy way to check it, as we all did, put your palm near exhaust pipe, whatever comes out, it for sure came in - just much colder.
Even more, engines are designed NOT to go above those temperatures due to simple fact that fuel evaporates on higher temperatures, which is, first of all dangerous (self ignition), and not economical (big concern to engineer is to supply engine with big quantity of fresh COLD air, because of engine power (stoichiometric ratio ratio and cooling) . There are engines designed to make benefits of very high internal temperatures and pressures (diesel) but this is not of our concern.
Now, as you wrote above, to split/put 1800W to engine head (it is not real number as explained above) in piece of metal that size and weight it would glow like light bulb in very short time (I guess good comparison is electric water heater, they usually come rated at 2kW connected to, say, Chipamp heat sink, which is roughly size of 5HP engine head. Not even submerged in 80L ow water wouldn't stop it from boiling in short time).
And as for being huge compared to electronic systems, well, matter of opinion. Every heat sink that I can easily put in my palm (and engine head hat we are talking about, scooter, lawnmower is in that category) I consider small. Attached photo is from any 50cc air cooled scooter or lawnmower engine, compared to spark plug. I am sure there are variations of this type of head with slightly bigger fins, but as being rarer, an mostly having fins in "cross section" pattern, shouldn't be any more suitable fort electronic cooling than one we are talking about.
As last, about exotic alloy used in engine, well, usually it is cheapest **** manufacturer can find, with two of our priorities (looks and thermal dissipation, in order depending who do you ask) not high on the list for automotive purpose.
Again, very sorry for OT, i hope I wont be sent for cooling for some time..
Attachments
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Agree: if that is the biggest fin-head in your scrap, it can't be more than a mini-MoFo. I have a 650cc with two heads, stereo!
"..about 50-75% of total power is emitted as heat without being turned into useful work, i.e. turning the crankshaft. Approximately half of this rejected heat is carried away by the exhaust gases, and half passes through the cylinder walls or cylinder head into the engine cooling system..." Engine efficiency - Wikipedia
Sadly the one citation does not split exhaust from surface cooling; the other cite is offline.
When I was a boy, it was 30+% to exhaust, 30+% to jacket/fins, and 30+% to "mechanical output" including self-friction and pumping losses. Cooling load comparable (larger than) shaft HP.
"..about 50-75% of total power is emitted as heat without being turned into useful work, i.e. turning the crankshaft. Approximately half of this rejected heat is carried away by the exhaust gases, and half passes through the cylinder walls or cylinder head into the engine cooling system..." Engine efficiency - Wikipedia
Sadly the one citation does not split exhaust from surface cooling; the other cite is offline.
When I was a boy, it was 30+% to exhaust, 30+% to jacket/fins, and 30+% to "mechanical output" including self-friction and pumping losses. Cooling load comparable (larger than) shaft HP.
Pass DIY Addict
Joined 2000
Paid Member
My cost for stereo build:
Sinks: $6 flea market find
Black paint for sinks: $6
Wooden Base: $15 flea market find
Transformers: $50 on ebay including delivery
Boards: $20 in DIYA store
RCA Input/Speaker output terminals: $12.50 at Apex Jr
Power Brick: $25 from fellow DIYA member including shipping
PCB components: ~$30 including shipping
Misc mounting hardware ~$5-10
My grand total: ~ $170 for two channels (on the cheap)
New sinks (instead of used): + ~$100
Individual power supplies: + ~$50-70
Metal chasses (monoblocks): + ~$50-70
"Proper" chokes: + ~$50+
Sinks: $6 flea market find
Black paint for sinks: $6
Wooden Base: $15 flea market find
Transformers: $50 on ebay including delivery
Boards: $20 in DIYA store
RCA Input/Speaker output terminals: $12.50 at Apex Jr
Power Brick: $25 from fellow DIYA member including shipping
PCB components: ~$30 including shipping
Misc mounting hardware ~$5-10
My grand total: ~ $170 for two channels (on the cheap)
New sinks (instead of used): + ~$100
Individual power supplies: + ~$50-70
Metal chasses (monoblocks): + ~$50-70
"Proper" chokes: + ~$50+
