Wednesday, March 19, 2008

Even more stuff about electric cars

I found a company which specializes in selling components and kits for building your own electric vehicle. I'm not so sure I want to buy anything from them though, because the first page I visited in my search for data about their motors contained information which was (perhaps intentionally?) ambiguous. Then I saw a statement which was blatantly misleading. In fact, it was either unacceptably ignorant for someone in their position, or an outright lie. So I sent them an email in an attempt to clarify matters. Here is a copy of the email:

I am considering building an EV, but I have a real problem with your stated specifications. First, you list your (model number deleted) as 22.12 ft./lbs of torque continuous at an input voltage of 156. You give the RPM as 12,000; the HP as 18.77 and KW as 14.
OK, 14 KW is 18.77 HP, but 22.12 ft/lb torque at 12,000 rpm is about 50 HP. How about supplying a real peak and continuous torque curve, complete with rpm? Also, showing current draw vs. torque output per rpm would be very helpful. This would be real data I could use to design my system.

My second problem is your statement, "...and gas engines are rated at their peak horsepower unloaded."

This is absolutely, blatantly untrue. Do you really believe this, or are you deliberately misleading people?
Just in case you are unaware, no power source outputs anything (at its power take off) until that power is used. An engine running at no load produces nothing but heat. The way gas engines are rated is running them through their rpm range against a load brake (hence the term Brake Horsepower, or bhp), which measures torque. The load applied is whatever is the maximum the engine is able to sustain. In other words, the engine is fully loaded. Torque is measured directly, and horsepower is calculated by the formula: torque in ft/lbs x rpm / 5252. The peak hp rpm is generally somewhere around double the peak torque rpm. Also usually measured is Brake Specific Fuel Consumption, which is a measure of how many grams of fuel is consumed per hp/hr or KW/hr, which are directly convertible (as you know, judging by your rating of the *bleep* as 18.77 hp or 14 KW) as 1 hp= .746 KW.
Please clear this up, so that I may make an informed choice.

Thank you;

I await their reply.

Update: June 10, 2010. Over two years later. They never replied. I think it's safe to say they never will.

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