What is % efficiency of real world power controller ?

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HCT's picture
Last seen: 4 years 7 months ago
Joined: Wednesday, February 7, 2007 - 08:16
Points: 137
What is % efficiency of real world power controller ?

Awhile ago,someone pointed out that I forgot to include losses of the controller when calculating the efficiency % of power delivery to the motor from a battery .

My guts feeling response , without any research whatsoever was . " I hoped that efficiency was in the 92%-98% area and expected to be vary in relation to power delivery , expecting the 98% in the high power , the 92% in the low level region .

Was pleasantly informed by LinkOfHyrule

. They all seem to hover around 98% efficiency regardless of size

Very glad to hear this , however having designed in the past DC-DC converter of various type I remember that all circuit have a fixed loss which really play chaos on the efficiency of low power system .

Not knowing much about controller and having no time to research controller efficiency,would appreciate getting some numbers obtained from the many controllers used by the members of this site,even if the number come from the advertising brochure.

Very interested in the following specification , max power ( volts,amps,watts)and the efficiency at specifying level , like 20% or 50% or even optimum 100% .

Thank you for all your help .

LinkOfHyrule's picture
Last seen: 13 years 2 months ago
Joined: Wednesday, October 17, 2007 - 14:54
Points: 730
Re: What is % efficiency of real world power controller ?

I think I was a little vague with that statement. I say that most seem to be around 98% efficient because that's the typical number I see on a lot of the spec sheets.

Anyway, the efficiency of a controller is largely determined by three things, all related to the FETs: the on resistance of the FETs, the switching speed of the FETs, and the switching frequency.

Low end/low power controllers will be something like 95% efficient because of slow, high resistance FETs. Since these are only powering a few hundred watts, a 5% loss won't heat up the controller much, and the losses are forgivable. You get what you pay for.

The mid/high-range controllers will be using superior FETs for their lower resistance and the fact that they can go from totally off to totally on faster (and vice versa), reducing the amount of time they spend in a partially conductive state. These are the ones that get about 98% efficiency. Much more and they start to get very hot, since even a small percentage of a multi-kW system can generate a lot of heat.

This is the reason 4110s are so highly prized for use in controllers; they switch quickly, and they have exceptionally low on resistance, on the order of about 3mΩ. This means that they can both handle higher currents (because they generate less heat) and the controller is overall more efficient (because more power gets to the motor instead of being dissipated by the FETs).

I suspect, however, that many controller's efficiency numbers are the efficiency they get when at full throttle and not doing any current limiting. This equates to the FETs being completely saturated, eliminating the switching losses when at partial throttle.

Compared to the losses in the FETs, the other losses (capacitor leakage current/power for the logic) are negligible, being on the order of a few milliamps (I measured my controller at 10mA at standby).

Almost all of the more common controllers will be switching somewhere between 15 and 20kHz. Most I've seen (and heard, ugh) switch at 18kHz. Dunno why that frequency, but there you go.

I doubt anyone has done any real testing on the efficiency of their controllers because the losses are usually small compared to, say, the length and gauge of wiring used or efficiency of the motor, especially when you are using controllers with several high-powered FETs in parallel.

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

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