1955 Porsche 550 Spyder on the Dyno - Comparing Curtis 1238-7501 and 7601 Controllers - 650 Amp Upgrade

This week we return to Slingblade's Dynamometer for another test. I'm a little weary of test graphs this week as I've been making a number of them. But this is probably more interesting to you.

High Performance Electric Vehicle Systems http://www.hpevs.com has kind of cracked the AC drive market with the only system we're aware of for less than $5000. They produce a sturdy little 50kw motor with a face mount matching the popular Netgain Warp 9 which it makes it very easy to install with available adapter plates.

They don't do the controller at all. They use a Curtis model 1238 3-phase AC controller. Curtis controllers are widely dismissed by the cognoscenti in EV land in favor of more exotic offerings such as our just reviewed EVnetics Soliton1 and the Cafe Electric Zilla.

But if we use EVALBUM's 3218 conversions as a representative sample, we find over 50 different controllers in use but 27% of ALL listings are Curtis powered - 878 vehicles. Since probably a third of the vehicles are bicycles, motor cycles, and lawn mowers, this is probably more like 50% of the market. Number two would be Alltrax at 276 and the long time darling of EVland, the Cafe Electric is a distant third with 155 installations. Our recent find, the Soliton1 has 22 vehicles listed.

Curtis makes controllers for industrial electric vehicles, floor washers, fork lifts, etc. We've talked to them and they profess to be oblivious to the Electric Car end of the world and claim to want nothing to do with it. But their products are migrating in that direction with brake light signals, regenerative braking (on a fork lift?) and more.

HPEVS has done an outstanding job of integrating the Curtis with their AC line of motors. The 50 kw AC-50 is the most powerful and most popular of these. And they've quickly gained a foothold. We used the HPEVS system in Speedster Duh to considerable effect and Duane Ball used it on his Spyder 550 as well.

Just this past month, Curtis began shipments of a new model 1238-7601 controller which is a bit of an upgrade from the 1238-7501 we had been using. The 7501 was nominally a 96 volt controller with a current limit of 550 amperes. We routinely run this controller at 120v and understand that it can withstand voltages up to 130 before shutting down to protect itself.

The new 7601 ups the current limitation by a full 100 amps, to 650 amps total. If you could put 120v in at 650 amps, that would render 78 kw. If we are low enough to get it to start, we actually sag to a little over 100 volts at those current levels and ergo, perhaps 65-70kw are truly available. That's potentially 94 eHP input to the motor.

ALL the other AC systems available that we are aware of START at about $5000 or $6000 for the controller and perhaps the same or slightly less for the motor - typically with a 30kw motor rating and 100-125kw on the controller. To get to 150-200kw in the Tesla/AC Propulsion range, you are in the $15,000-$35,000 range buying a really untested undeveloped one off prototype dream of some crackpot and it just makes no economic sense in an electric vehicle.

The advantages of AC are widely touted as regenerative braking, efficiency, and durability.

We have tested regenerative braking on both HPEVS and the MES-DEA products and were heroically underwhelmed. The oft cited 10% or 15% gains are simply nonsense - entirely myth based on observations of output and input. Real world tests of routes in the same car with it ON or OFF provide results of 5-7% AT BEST and this is very much a function of the driver and terrain. I actually generally get negative numbers when I'm driving.

As we see in this set of tests, the efficiency theory seems to be blown as well. If you take the motor and controller as a unit, they appear no more efficient than our series-DC and chopper PWM controllers - indeed the numbers would indicate LESS efficiency.

As to durability, it again makes sense. But we have no data. There are no brushes to change. Certainly.

But a funny thing happens in AC induction land. ALmost all the high end systems from Siemens and MES-DEA and UQM etc seem to be high voltage, comparatively low current devices. You rarely see anything beyond 300 or 350 amps through the windings of these motors. Instead, voltages are normally used to achieve higher powers- usually STARTING at 300v and going as high as 1000v in some systems.

This poses some problems for an electric car. To get such high voltages, you wind up with an extremely large number of cells. Our Mini Cooper has 112 cells in series, each of 100Ah. Further, all the peripheral equipment has to work at that 375 volts as well, our air conditioning compressor, our DC-DC converter, our water heater, and the list goes on.

HPEVS has carved out a niche as the ONLY sub $5000 AC system out there and it does it at LOW voltages and HIGH currents. Very unusual and a characteristic of their motor. If they can get a controller to do 650 amps and a BIT higher voltage, say 200v, we could in fact see 130kw.

Rumors exist noting that Curtis is CONSIDERING (not really working on) a 144 v model of this controller. That would be very useful.

In the interim, this 96v 650amp model tests out very well as you'll see in the accompanying graphs. We did a full 650 amps and upped our HP on the rollers to 74 from about 63 just by doing the controller swap.

As you can see, the -7501 model offers improvements of 15 to 25% depending on what you're looking at but torque jumps as much as 25%. If nothing else, this considerably widens the size of vehicle this system would work on - probably very effective at up to 3000 lbs. It's relatively low price under $5000 (we don't actually have pricing yet on the new model), relatively easy connection and configuration, make this drive system a contender for most electric car conversions we've seen. You will not get the torque or horsepower of an 11 inch series DC out of this package, but it is very sturdy and offers the advantages of AC if drivability is your thing instead of racing. It would still be under a little strain in our 3500 lb mini cooper. But at 3000 lb and below, with a transmission for leverage, this is a good package that got better.

Enjoy

Jack Rickard