# Radiators



## ruckus (Apr 15, 2009)

Hello,
It depends on the amount of heat you need to dump. You can estimate this by taking the max input power (Volts x Amps) and figuring the % efficiency loss. Better to go a little big than a little small.

So a 60kw continuous system would lose about 3% in the controller (over-estimated) and about 10-15% in the motor. Again, always overestimate the cooling needs. 5% x 60 = 3kw of cooling for the controller. 15% x 60 = 9kw of cooling for the controller. So you are looking at 12kw of cooling.

Now obviously, 60kw is a TON of continuous power. That is like a full-size van on the freeway and up hills. You can estimate your vehicle's actual continuous load using this calculator:
http://ecomodder.com/forum/tool-aero-rolling-resistance.php

Again. DO NOT SKIMP. Round everything up or add 10-20% to the final answer. If you live in a hilly area or in Arizona, you will need more cooling.

Here is a 120kw continuous BLDC bus motor which is using a normal car-sized radiator. So you will probably need something smaller than that..










Cheers


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## poprock (Apr 29, 2010)

Hi Richard; Any of the 3 cyl 1ltr Daihatsu's have a very small radiator as per pics. 500mmx400mm inc overflow tank.. Approx 4kg.


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## ruckus (Apr 15, 2009)

Exactly.

Motorcycles, four-wheelers, tranny coolers, etc.

Ebay has a million...


One decision worth considering is whether you want separate units for the controller and motor. On one hand it complicates things, on the other, do you really want your motor cooking your controller? If you use only one cooler, I would run the cool water through the controller first, then the motor. The controller should only add a small of heat compared to the motor.

You can also do a single loop with two coolers. So it would go through the controller, then a small radiator to get the temp back down, then the motor, and then the larger radiator.

I won't be surprised to start seeing 'super' coolers using air-conditioning units for high-power applications such as racing.

Cheers


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## Richard Wood (Jun 27, 2008)

Thanks Ruckus for the tip about the separate cooling systems for motor and controller.
I am hoping that those with water-cooled AC units will post some links or pics of what they are using in practice. If I go down the path of water-cooled it will help if I can put in a much smaller radiator than the existing in to both save weight and free up space.
Richard


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## Richard Wood (Jun 27, 2008)

Thanks Poprock1 for the pics, are you using one of them in an EV? I'm wondering if even those are bit overkill, but I have no basis to think that, just hoping.


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## poprock (Apr 29, 2010)

No, I'm not using it. It was removed from my current testbed, 98 Sirion using a 36v bldc with an Axe 7245.


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## Duncan (Dec 8, 2008)

Hi Richard
An easy rule of thumb
Car radiators are designed to cool an IC engine,
Modern IC engines operate in thirds
One third of the energy to the wheels
One third of the energy to the cooling
One third of the energy to the exhaust

So the cooling requirement is about the same as the horsepower

Look at a car's radiator - look at the power of the most powerful model
Then double it to allow for degradation
That is how much heat that radiator can dissipate

So the smallest IC radiator you can find will be more than enough for a monstrous EV


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## jeremyjs (Sep 22, 2010)

ruckus said:


> Exactly.
> 
> Motorcycles, four-wheelers, tranny coolers, etc.
> 
> ...


One thing I wouldn't do is split the loop with a single pump. You can get into a situation where almost all of the fluid is moving through one side or the other if one side has less resistance, either due to differences in tubing length, number and angle of bends, or differences in the flow rates of the cooled devices themselves. If you do split it, make sure you have a pump for each loop, even if you only use one radiator, or better yet don't split them at all. There's really not much point with the relatively small amount of heat the motor and controller produce and how quickly the fluid will carry it away. Just make sure you use a properly sized radiator. Just about anything capable of cooling an ICE will be massive overkill, but if it's already there, and not in the way, you might as well use it.


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## Richard Wood (Jun 27, 2008)

Ok, so coming from the other end then. If the smallest car radiator is way overkill for an EV of any size, then what would typically be the most useful to minimise weight. Is a motorcycle radiator still overkill?


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## Duncan (Dec 8, 2008)

Richard Wood said:


> Ok, so coming from the other end then. If the smallest car radiator is way overkill for an EV of any size, then what would typically be the most useful to minimise weight. Is a motorcycle radiator still overkill?


Hi Richard
You are not talking about much weight
More importantly you need to minimize the air flow through the radiator as that is draggy
On a race car you would use duct tape to reduce the flow on a cold day

You will only have ~ 5Kw to dispose of so a heater core is about the size you need

If you are making a light weight special then worry about it - if converting a car just use the radiator and reduce the size of the air intake

I am using a home made copper heat sink directly in the air flow


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## ruckus (Apr 15, 2009)

You can always hit Ebay with "transmission cooler fan"

sort by cheapest... and 'blamo'.

http://motors.shop.ebay.com/i.html?...&_osacat=6030&bkBtn=&_trksid=p4506.m270.l1313

skip the first few, then it gets pretty good...


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## Jesse67 (May 12, 2009)

I would use a heater core, considering the output of most car heaters as compared to the pitiful output of my 1800W electric heater, a standard heater core should be able to dump several kw no problem, with proper airflow of course. If you convert your heater to electric you'll also have one just sitting around.

***Just like Duncan said above if I had read more carefully....!


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