Reader Question: Why don't electric motors short out in the rain?
Tesla Roadster motor
One of our readers dropped us a note the other day with a very valid question about electric motors:
I'm a big fan of Autoblog Green. My wife and I both plan on buying 100% electric cars as soon as we can. My wife asked me why don't the electric motors short out in the rain or when they get wet. I said "I don't know" I'll see if I can find out. Can you shed any light on the subject?
Well, yes, I can. Unlike consumer electronics devices, cars and trucks have to be designed to work in a much wider range of environments from -40F to 120F and in sand, rain, snow and anything else imaginable. In order for cars to work reliably, electronics and electrical components have to be specifically designed to seal out the elements. Connectors and housings have seals to keep out water and other stuff that doesn't belong. Of course many and rubber and plastic parts often dry out and crack. To avoid this, special materials have been developed and these parts have to go through extensive durability testing to insure that they can last the life of the car. Testing occurs both in the lab and on the road in all conditions. This is just part of why it takes so long to develop and validate new cars. Trust us, all EV drivers are thankful it happens, even if the wait for new electric cars is so long.
Reader Comments (Page 1 of 1)
Whopper 2:02PM (3/24/2008)
And in spite of engineering's best efforts field failures still happen which results in recalls. One has to wonder what will happen if en EV happens to run into weather like Missouri has been experiencing. Or if you have an accident. Hear that noise in the background? That is a trial attorney rubbing his hands in anticipation.
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brn 3:02PM (3/24/2008)
That's great. Now can you touch on the "-40F to 120F" part? From what I understand, the batteries won't cut it in those conditions.
I guess that makes EV's "fair weather" cars. :)
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Sam Abuelsamid 3:22PM (3/24/2008)
The -40F to 120F is the standard temperature range that all major manufacturers use when engineering vehicles. All the major systems have to work within that band. Having said that, there are tolerances when mass producing and occasionally parts will fail. Sometimes more often than they should, but for the most part, most vehicles are pretty reliable.
As for EVs and hybrids, based on my experiences with three different hybrids in the past couple of months, batteries remain a pretty dubious proposition at temperatures of about 15 and below. For the foreseeable future, EVs probably will remain largely fairweather vehicles.
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Sayyad 5:14PM (3/24/2008)
Well, not exactly. It just depends where the EV is made; our local conversion shop up here in the frigid north (I swear, 12 foot snowbanks this year, and it's not even a record) specializes in winterized EV conversions. They even had the government test a couple, with impressive results:
http://www.revconsultants.com/REVcold.htm
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Chris M 5:23PM (3/24/2008)
It is possible to make a motor totally waterproof, just consider all the deep well submersible pumps in operation. On my parents farm is a electric submersible water pump that has been working reliably for over 30 years!
If you need more proof, just consider the Rinspeed Squba concept recently demonstrated. All electric, and about as waterproof as you could get in a car.
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KarenRei 5:25PM (3/24/2008)
My impression was that it's mainly NiMH and lead-acid that have temperature problems. A123 batteries, for example, are rated from -30C to 70C (-22F to 158F). And they have so much power density, I don't think that them running a bit weak power-wise would be a problem. So long as they don't lose energy density with temperature, which I don't think any li-ions do, I don't see a problem unless you live in Alaska (in which case, just install an electric starter heater; even if they're running at only 10% power, that's still a ton of heat you could dissipate).
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murray 6:21PM (3/24/2008)
There are a few points I'd like to add.
To create a short circuit, you need to provide a path of lower resistance than the path current is already traveling. In the case of many electric circuits, water won't do that, because the resistance of the circuit is already low. A simple battery-motor circuit is an example of this (though I realize EVs are not simple). Furthermore, you would need to submerse the car, or part of it, to even have a chance of creating a short.
And finally, while some components of EVs (and regular cars) may be susceptible to water, electric motors aren't particularly. In fact you can take an electric motor, connect it to a battery, and completely submerse it in water, and it will simply continue to run. At least this is the case with basic DC motors.
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KEVIN 7:33PM (3/24/2008)
Pretty cool to know lol
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stevefazek 7:53PM (3/24/2008)
Lithium and Nickel batteries dont have problems with extreme cold as much as lead acid. Both cant give out as many amps when they are cold but also remember as the start to drain amps all batteries do generate some heat and they generate heat when they are charging. SO the car makers have to engineer a well insulated battery compartment for future EVs. I am sure they will sell cold weather packages for them as well such as a battery bank heater instead of a block heater.
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brn 10:20PM (3/24/2008)
Thanks for the comments. After reading them, I did a little googling. While they're working on improvements, it seems that temperature is still a very serious issue with batteries.
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Student 1:48AM (3/26/2008)
First I'd like to introduce myself as a student at an engineering school currently developing a hybrid powertrain/electric drive (think diesel-electric trains) Mini Formula for the SAE Formula Hybrid competition this May.
Murray; good points. If the impedance of a motor were that of water, it simply wouldn't run. Obviously due to extenuating circumstances, don't dunk a teenie DC servo into a cup and expect proof, however.
The greatest complications (the one's which add 1,000's of man-hours) to designing a hybrid drivetrain are these difficulties precisely. In fact, when all is said and done, oftentimes solving one issue will solve another. To cite a recent example of my own: The successful completion of a circuit which re-routs massive regenerative braking energy ended up being a great battery surge protector. The thing likely saved 13 standard car batt's.
In essence, expect that we engineers have all your bases covered. The only problems I can expect are manufacturing faults or poor materials choice (but doesn't that seem to be the problem with all cars today? hmmm...).
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