ElectricMotorcycleForum.com
Makes And Models => Zero Motorcycles Forum | 2013+ => Topic started by: nigezero on July 31, 2014, 08:46:27 AM
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Hey all; it's clear that simple cost effective cooling solutions are key for sustaining ongoing hi power applications from what I'm reading. I'm sure heaps of people are innovating but struck me that I haven't seen a thread yet of such solutions.
So; here's a pretty logical looking possibility courtesy Gizmag; wrap it in copper mesh-claims are 500x cooling area compared to fins!
http://www.gizmag.com/silent-power-pc-passive-cooling/33145/(http://img.tapatalk.com/d/14/07/31/u2ara2av.jpg)
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I'm not sure this would work well in motor applications.
You need moving air through the fins to evict the heat.
More surface area is fine, but there's not going to be a ton of moving air through the mesh. Or that's what it looks like to me.
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More surface area is fine, but there's not going to be a ton of moving air through the mesh. Or that's what it looks like to me.
I'd agree with protomech. I know some manufacturers of air-cooled engines have REDUCED the number of fins and achieved better cooling; it's a balancing act between surface area and airflow. Better ways of increasing surface area exist such as bead blasting or anodic treatment to roughen the surface up.
Also, that copper mesh doesn't CONDUCT heat very well because the individual copper wires are very thin. A nice thick fin conducts heat away from the motor very fast, all the way to the end of the fin, so all the surface area is effective at transferring the heat into the airstream. That copper mesh would probably heat up very close to the source of heat but not transfer the heat to the rest of the mesh very well, so much of the increased surface area wouldn't be hot enough to transfer heat to the airflow.
Fins are good. Make them relatively thick to conduct heat quickly, rough them up for good surface area, space them and orient them so you get good airflow between them, anodize them a nice dark black so they radiate infrared energy away well, and you're about as good as you're going to get without going to a water jacket.
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anodize them a nice dark black so they radiate infrared energy away well,
I agree with everything said except this statement. At the frequency of the IR put out by a hot motor surface the black doesn't radiate any better than plain aluminum. At the frequency of the sun's IR, however, black is very effective, that's why solar water heater pipes are black. It has just been customary to anodize heat sinks black to the point that it would look strange to see them any other color. The most important factor in radiating the low IR is a non-shiny surface. Bead blasting works well for making the surface rough, among other methods. Just the process of anodizing usually breaks the shiny surface and helps.
My own fast cooling method wouldn't help at highway speeds but when I'm going to do a long hot dirt climb I carry a spray bottle of distilled water. The evaporation of the water sprayed on the motor, when it's approaching 250*F, brings the temp down super fast. I've thought about installing a spray bar system using an electric pump so that I don't have to stop to spray the motor. However, I wouldn't have to use it often enough to make that complication seem worthwhile. I use distilled H2O so that the evaporation doesn't leave a mineral deposit on the motor. :-[
Trikester
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Trikester, your analysis is astute and correct. Let me strengthen your point: "Black" is a color, which refers to visible light, which isn't relevant with respect to heat radiation until an object is literally starting to glow (dull red, at first, well beyond the temps we're talking about). But, black anodized aluminum DOES have a higher emissivity in the IR range than un-anodized aluminum, so it DOES radiate a bit better in the IR range. And I'm sure you're aware that the blackbody radiation curve is quite broad, so even if an object isn't visibly glowing, there can still be a fair amount of energy in the visible band. I work in the electronics industry, and they do charge more for a black-anodized heat sink, because it does perform measurably better than an un-anodized heat sink. It's not a huge improvement, a few percent, but as EV owners we understand the benefit of a few percent improvement.
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It seems to me that the first restriction I'm hitting on my bike is the ESC temperature (electronic speed control, below the saddle with the big radiator) and not the motor temp. Same for you ?
Laurent
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In industry, to increase surface area dramatically for bonding you would acid or laser-etch the metal. I'm not sure it would stay etched very long in the case of an electric motor housing being exposed to dirt, water, and air though. Maybe an electroplating process or zinc dip would protect it.
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I was a co-founder and head of engineering of a successful high power switchmode power supply company. We found that black and clear aluminum heatsinks worked equally well, as long as the aluminum was not shiny, and that it didn't pay to have them dyed black. All anodize is clear to begin with so black costs more because it is another step to dye the anodized surface which is aluminum oxide. The radiation of hot electrical surfaces is quite far below the beginning of light visible to the human eye. The sun's IR radiation is much closer to visible, and black works very well there.
It's interesting to realize that a black object exposed to the sun becomes a frequency converter. It readily absorbs the higher frequency IR radiation from the sun but because the object isn't heated to anywhere near the sun's temperature it does not re-radiate the lower frequency IR out through the black surface as well as it absorbed it. This IR frequency conversion makes black solar heaters work very well.
BTW - It is a big mistake to actually paint a heatsink black because the layer of paint acts as an insulating barrier to heat radiation. Better to rough it up and leave it natural in that case. The black dye used on an anodized surface does not degrade the heat transfer like paint does, so there is no down side to black dyed anodize, except extra cost.
Trikester
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Trikester, take a look at this data sheet of a heat sink we use in one of our products: http://media.digikey.com/pdf/Data%20Sheets/Ohmite%20PDFs/W_Series.pdf (http://media.digikey.com/pdf/Data%20Sheets/Ohmite%20PDFs/W_Series.pdf)
I'm not trying to pick a fight, I really just want to understand better. They offer two finishes for each of these heat sinks, degreased or black anodized. In all cases, their claim is that the anodized one DOES dissipate heat a little bit better than the degreased one. Do you think the anodizing process adds surface area (perhaps they acid etch to prepare the surface or something), raises the emissivity, or do you think they're just plain wrong? The degreased one that we use retails for $2.90, the anodized one goes for $2.99, so the price difference isn't much.
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My guess is that the natural color one is smoother than the black one. I didn't see if it was clear anodized or not. Just the process of clear anodizing will break the surface shine which may be just from the prep etch and/or the anodizing process itself. One definitely wants the surface to appear dull for good radiation. A shiny surface (especially a polished one) reflects the IR back into the body of the heatsink just as it shines in the visible light we see coming back to our eyes.
Given the same surface roughness we could not measure a difference between black and clear when testing our heatsinks. As you say, the radiation of a black body is broad so there might have been a difference that was less than our measuring capability. However, a body at say 200*F is a very low frequency radiation in the IR spectrum.
BTW - It was an engineer who worked for me that first brought all of this to my attention, many years ago. I had not given it much thought before that because I was so accustomed to seeing and using black aluminum heatsinks.
Trikester
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Isn't the primary mode of heat transfer forced convection in this case?
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Still think black anodized would look better than gold. Both heatsinks should be matching.
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I agree that I like the looks of black heatsinks. They have that look of doing the job they are supposed to do.
Nobody commented on my practice of spraying distilled water on my motor when it goes into heat limit on a slow, long, steep climb. Has anybody else done this with their motor? It could work with the controller also since it is also water proof. Evaporating water is a great coolant!
Trikester
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Trikester, I've thought about doing the same thing, and was glad to hear that you've performed the experiment. I (obviously) don't take my SR in the dirt, but I do ride in so cal, and it gets warm here. So far I've only triggered the high-temp alarm once, and only to the point where the light began to flash, not until it started cutting power. But I agree, evaporative cooling is VERY effective, and it does seem logical and straightforward to mount a small reservoir, a windshield-washer pump and a switch somewhere near the handlebars to provide a spritz now and then to keep the motor comfy. It seems like there'd be hardly any risk in doing so, since the motor has to be sealed well enough to ride in the rain.
I guess my only question would be, if the motor's getting warm, don't you imagine that the controller and the batteries are also working pretty hard? If you add a way to keep the motor cool, you might just move the heat stress to another part of the system. Granted, those parts of the system should be able to protect themselves too, but it's just a variable that the engineers didn't design into the system, and it might not be obvious what all of the effects might be.
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I agree that I like the looks of black heatsinks. They have that look of doing the job they are supposed to do.
Nobody commented on my practice of spraying distilled water on my motor when it goes into heat limit on a slow, long, steep climb. Has anybody else done this with their motor? It could work with the controller also since it is also water proof. Evaporating water is a great coolant!
Trikester
If the heatsinks will ever be exposed to direct sunlight while in operation , then the bare Aluminum or clear anodize sounds like a wise choice! Low-E is not an issue with sufficient convection/fan airflow...
[Worked at Raytek for 5 years in the '70s ;] 8)
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I guess my only question would be, if the motor's getting warm, don't you imagine that the controller and the batteries are also working pretty hard? If you add a way to keep the motor cool, you might just move the heat stress to another part of the system. Granted, those parts of the system should be able to protect themselves too, but it's just a variable that the engineers didn't design into the system, and it might not be obvious what all of the effects might be.
They are working hard, but all three systems (motor, controller, battery) are thermally monitored and can throttle back power as needed.
I wouldn't say it wasn't a design consideration - the motor controller, for example, has a large heatsink mounted on it for cooling - but it's certainly true that as soon as you eliminate one weak point in the system then you will expose the next (slightly stronger) weak point.
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I've found that it is my motor that is the heat problem. That is where the most power is being dissipated. I think the controller is more efficient than the motor at any given current level. It makes sense because the controller is comprised of switched MosFETs while the motor has copper windings. It is easier to reduce the "on" resistance of the MosFETs (bigger FETs) than the winding resistance of the motor.
Maybe we should insists that Zero wind the motors with pure silver wire to reduce the resistance. Oh, and we could also ask them to form the heatsinks from diamond, the best conductor of heat. Can't understand why they don't take my suggestions. ;)
Trikester
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Trikester, its very common to use water sprayers on intercoolers. The finer the spray the better and adding alcohol improves evaporation further.
If you fancy a project you could try CO2. It would give you very rapid cooling for short bursts.
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Yeah, CO2 would work well but difficult to replace in the boonies. Distilled water can be found in supermarkets and if out in the boonies, streams or springs can supply an emergency supply of water. The dissolved minerals would not pose a problem if only used once in awhile.
If I were racing (like Pikes Peak) I might consider CO2 since it is a one time, brief, deal. Although I would have to determine the stress effects of such quick cooling on the outside while the motor is still generating quite a lot of heat inside. It could cause the gap to close and magnets to drag and destroy the motor. Actually with CO2 one could consider injecting it directly into the interior of the motor so that the cooling was more evenly placed. That might work quite well! Then the exiting CO2 could be piped to the controller heatsink even if the CO2 had absorbed a lot of heat going through the motor it could still carry heat away from the controller heatsink.
I think we could come up with a lot of ways to cool the bike power components for short, high use, periods of time. My water bottle solution was something I quickly supplied myself with in the very small town of Big Pine CA (one small hardware/grocery store). BTW - I did this on my e-trike but it would work as well on my FX.
Trikester
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The copper's definitely designed for free-convection with very low flow rates. I have gigantic radiators on my PC which is water cooled with no fans to similar effect.
Yeah I'd say black is more going to absorb the solar load for any components in the sun than help significantly radiating at our component temps.
Very interesting about flowing gas through the motor housing. Anyone know if there's any grease or anything in there that would get blasted out? You could use air if you could dry and clean it and keep it weatherproof. Could be easier than going liquid cooled.
trikester, are you allowed to tell us anything about Hollywood's liquid cooled motor? Is it just a jacket that replaces the heat sink piece? As you point out having a huge thermal gradient could cause things to crash so we should keep that in mind. I've never sprayed mine as I was worried about cracking it but that's cast iron engine block thinking, probably not as likely with aluminum.
When I went to my first Supermoto trackday I rigged up two computer fans to run off the 12V power outlet and stuck them on the motor between sessions which cooled them nicely. Didn't take much flow, it just has such poor cooling from the factory that any little bit makes a big difference. Cooling enough to keep up with max power draw (>80mph or continuous hill climb) might take a stronger flow.
EV thermal and CFD are my job and I've been wanting to do something with my FX but having just had it off the road for a month upgrading the suspension I don't want to pull the motor quite yet! Anyone know how much a motor costs? If it's less than a grand I might get one to experiment with... Very interested in digging into this, it's my biggest remaining issue with the bike now that the suspension's up to snuff! (:
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IIRC it was around a grand. Check with Zero.
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Sorry I wouldn't be at liberty to say anything about HE's liquid cooled motor but maybe Harlan would be willing to tell something. I'm sure he is working on the next generation cooling method so maybe he would be willing to tell about the present generation which still had some flaws (no surprise there).
I think that the requirements for cooling on something like the PPIHC race can be quite different than requirements for a sustained high speed highway ride or a slow steep dirt climb like I have been faced with. If I was just planning on the PPIHC (which I'm not) I might just pump distilled water (non-conductive) through the motor and blow it out onto the controller heatsink, a one time, non-recirculating, short term method. Jeff made the climb in just under 12 minutes so there would have to be that much time's worth of water supply, at whatever rate it was being pumped. Probably a good idea to add a rust inhibitor to the water,also.
Battery temp is also a potential problem on something like the PPIHC race. Unfortunately it is far more difficult to cool the battery pack since it is a large enclosed mass. :'(
Trikester
BTW - Harlan, are you following this thread?
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What about oil cooling? read ˜4 posts after this one:
http://electricmotorcycleforum.com/boards/index.php?topic=4424.msg29049#msg29049
"simply filling the motor slightly less than halfway with ATF almost doubled the continuous power output. "