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Old 07-21-2013, 12:08 PM   #1 (permalink)
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EV Motor Cooling Question

I posed this question in my build thread but will ask here too (to cheat and maybe get more views/answers?).

I cannot justify buying a new, bigger motor. So I will install forced cooling. I am thinking of using a marine bilge blower like this: Bilge Blower Buy 1 Get The Second 1 Free 12VDC 3" Opening | eBay
It is 12V, 3A, 90 CFM. EVSource has a similar one that puts out 105 CFM but for a lot more money. But I can't decide how I will switch this fan on/off. Two options I am throwing around are:

1. Epoxy a 165F (or so) thermal switch to a brush. The cooling fan will turn on once the brush reaches 165F and turn off if it drops to 15F below that.

2. Switch the fan on/off with my [currently unused] pot box idle microswitch. The fan will turn on as soon as the accelerator is depressed. This is a much simpler solution, and the one I am leaning towards.

Which is the better option??

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Old 07-21-2013, 05:29 PM   #2 (permalink)
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Quote:
Originally Posted by mechman600 View Post
I cannot justify buying a new, bigger motor. So I will install forced cooling. I am thinking of using a marine bilge blower like this: Bilge Blower Buy 1 Get The Second 1 Free 12VDC 3" Opening | eBay
It is 12V, 3A, 90 CFM. EVSource has a similar one that puts out 105 CFM but for a lot more money. But I can't decide how I will switch this fan on/off. Two options I am throwing around are:

1. Epoxy a 165F (or so) thermal switch to a brush. The cooling fan will turn on once the brush reaches 165F and turn off if it drops to 15F below that.

2. Switch the fan on/off with my [currently unused] pot box idle microswitch. The fan will turn on as soon as the accelerator is depressed. This is a much simpler solution, and the one I am leaning towards
36 Watts is an awful lot just to move 90 CFM. Any 120mm PC cooling fan will put out more CFM at 1/10 the power and half the cost. You would have to construct the method of ducting.

What about external ducts that draw air in while moving and direct it over the motor?

#2 switch solution sounds ideal, since simple often means better. With a more efficient cooling fan, it wouldn't matter if it runs a little more than it needs to.
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Last edited by redpoint5; 07-21-2013 at 05:35 PM..
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Old 07-21-2013, 05:43 PM   #3 (permalink)
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That blower will produce a much higher pressure then a computer fan, it looks like a good choice and a reasonable price.
I'd do both switching options, that way the fan is on whenever the motor is to keep it cool and the fan will stay on if the motor is hot and it should then stay on even if you park the car.
I'm not sure how you plan to attach a thermoswitch to the brush, my motor brushes are to small to do that and the brushes need to be able to move freely.
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Old 07-21-2013, 09:15 PM   #4 (permalink)
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Much better to put a temperature sensor in the windings. I've done motor durability testing, and we drilled a small hole into the steel stator (from the outside), then embedded a thermocouple. The temperature sensor should be as far into the steel as you can get. Ideally, it should be within 1/16" of the copper winding. In practice, within 1/4" should be good enough.

Google electrical insulation temperature rating to find the maximum allowable temperature.

And yes, you need a blower with enough pressure to push air through the motor. Computer fans are worthless for this. It needs to be a centrifugal blower. Try to take the inlet air from a high pressure area such as the bottom center of your front grille.
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Old 07-22-2013, 10:27 PM   #5 (permalink)
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I was gonna say the same thing about computer fans being worthless for pushing air through tight spaces. Centrifugal fans are what the EVers out there seem to use.

Ryland - didn't you attach a thermistor to a brush on one of your EVs to measure motor temp?

I am not as concerned about stator temp as I am with comm temp. That's why I thought the brush thing might work because it's probably the closest thing to comm temp.

I appreciate all your input.
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Old 07-23-2013, 12:00 AM   #6 (permalink)
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Ryland - didn't you attach a thermistor to a brush on one of your EVs to measure motor temp?
Yes, I put a 1/16" thermocouple in the brush with JB weld, it's just a sensor and not a switch, to switch I'd need a $40+ controller, altho I think an Arduino could do the task as well, I just don't know how to program it yet for that.
Thermocouple is what I think what I used, a friend of mine bought boxes of them for a collage research project and gave me the ones that did not get burned up so I have a few, Message me if you are interested in one or two.

JLD7100 (DC 12V) PID Temperature Controller is the temperature controller that I'd like to buy, but other things are higher up on my budget.
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Old 07-23-2013, 01:14 AM   #7 (permalink)
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Quote:
Originally Posted by JRMichler View Post
Try to take the inlet air from a high pressure area such as the bottom center of your front grille.
Trust me...at the speeds this thing travels, there is absolutely nothing high pressure about the bottom center of my front grille!
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Old 07-23-2013, 07:52 AM   #8 (permalink)
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You can also stack blowers to get higher pressure if needed, useful if the opening for cooling the motor doesn't seem big enough, just add another blower inline and it will boost the pressure so the cooling air can squeeze past the coils.
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Old 07-24-2013, 01:14 PM   #9 (permalink)
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Quote:
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Trust me...at the speeds this thing travels, there is absolutely nothing high pressure about the bottom center of my front grille!
Velocity pressure at 25 MPH is 0.3 inches w.c. That's comparable to the pressure of an automotive heater blower.

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