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Old 01-27-2009, 01:33 AM   #301 (permalink)
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At 60v it gets that low? Dang those 6v batteries. Well, they also last a long time. If you want to test out a controller too, it's going to look pretty funny at 144v. You'd be riding dirty... It could ruin your reputation, though. I just visited punishmentcar.com. That is awesome!

By the way, I am going to order a copper heat spreader. A big dang brick! Copper has almost 2 times the thermal conductivity of copper! So, heat will be sucked away from the mosfets 2 times better! Aluminum is better at releasing the heat to the air, so the copper will be attached to Ben's heat sink, which will efficiently vent the heat from the heat spreader.

On the EVTech list people were paying around with the idea of water cooling. It didn't sound that hard, and it wouldn't be very expensive! You drill a big hole all the way through the copper, and run water through it with a small pump. That could allow for 1000 amp currents I bet! Those mosfets would be kept chilled! There's like nothing in the world with a higher specific heat than water!

I don't really know anything about radiators, or how this would all work, like where the water reservoir would go, etc... It would be a fun feature that could be added later, if people get really greedy for more power.

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Old 01-27-2009, 12:26 PM   #302 (permalink)
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K.I.S.S.

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Old 01-27-2009, 04:32 PM   #303 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
At 60v it gets that low? Dang those 6v batteries.
WHoops, no. My bad - that was +4 floodies, not +2.
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Old 01-27-2009, 05:37 PM   #304 (permalink)
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K.I.S.S. is my life's motto! Don't worry! The first 144v version will do nothing but get a car on the freeway! I think the copper with the heat sink will help cool things quite a bit better than aluminum.
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Old 01-27-2009, 07:37 PM   #305 (permalink)
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I added a couple pictures for etching of the copper PCB to the old post. It can be found here:

The Old Post, with new stuff!
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Old 01-28-2009, 12:25 AM   #306 (permalink)
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Quote:
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Copper has almost 2 times the thermal conductivity of copper!
Wow, I didn't know that capital letters made that much of a difference...
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Old 01-28-2009, 01:17 AM   #307 (permalink)
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hahahahaha! Oops. 2 times that of Aluminum. haha!
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Old 01-28-2009, 07:55 AM   #308 (permalink)
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Now that I got the laughs out, something serious. Have you thought about a heat pipe cooler? The kind that gets fitted to motherboards to cool the CPU, I mean. Are they too small for this application? Can you use multiple sinks to achieve the desired effect?


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Old 01-28-2009, 02:16 PM   #309 (permalink)
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The annoying thing is, you want the mosfets and diodes as close as possible to each other, and if you are using 10 or 12 of each of them, it eats up about 8 inches of a big heat spreader, where the mosfets and diodes are on opposite sides of the heat spreader. Most CPU coolers are too small, and I don't know about stacking them side by side. I think it would be easier to add water cooling to the heat spreader. I think the process is really easy, but we aren't aiming for 144v 1000 amps on the first try. Maybe 144v 500amp is plenty for now.

I've looked at doing synchronous rectification instead of using freewheel diodes. There are several ways of doing it. Basically, diodes waste a lot of heat. Here's a for instance. Let's say it's 500 amps, 100% duty through 10 diodes. You get waste heat of:

500 amp*1 volt = 500 Watt.

If you are sneaky, and use Synchronous Rectification instead, optimistically, the waste heat will be:

0.009Ohm/10*500amp*500amp = 225 Watt.
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Old 01-28-2009, 02:24 PM   #310 (permalink)
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I wouldn't want to touch a 100 watt light bulb with my bare hand, let alone 5 of them.

225 instead of 500 watts sounds a lot better!

We really don't have to worry about going real high on the amps right now. By going with a higher voltage, you drop the battery amps by plenty, which keeps them happy.

My current controller is a 400 amp (peak) Curtis controller at 72 volts. Moving the same car at the same speed with 144v is only 200 amps.

In truth, a 144V 500 amp controller would give the same power as a 72V 1000 amp controller, only without roasting the batteries so much! (and needing as heavy cabling)

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