Speedster Redux and the Dynomometer Puzzle: Speedster Redux's Surprising Dynamometer Results

In this week's episode, we take the Speedster Redux, with it's 57 CALB 180AH cells, brand new Netgain Warp9 improved motor, and Soliton1 controller to task. We do this by putting it on a dynamometer and actually measuring both power IN to the system from the batteries and power OUT of the system on the rollers. We found this exercise illuminating and suspect you will as well.

The bottom line is that we can put about 111kw or 145 HP into the system and we seem to get about 125 HP out the other end.

This would appear to compare very well with the 76 HP we had reported on previous dynamometer tests. And we really should compare Apples to Apples. But we didnt'

And here's why. Our earlier tests have been primarily of interest to me to learn how much current, and how much voltage, comprising how much power, was REQUIRED to go a certain speed and RPM on the road. As such, we would load the dynamometer with the approximate weight of the vehicle, and then go to speeds in ten mile increments in each gear.

At that point, we measured RPM, HP out, Torquie out, and voltage and current IN. Of course, we're lookihg for power consumption at these various speeds and RPMs with an eye on our battery capacity and potential range. We all know that you get MORE miles at 35mph in town than you do at 80 mph on the freeway. Those dynamometer tests, lacking a wind/airpressure component, were illuminating.

This time, we're really interested in something else entirely. We face the daunting task of the Winston Battery Elescalade project. This is gonig to require us to move about 8200 lbs of stuff down the road. We have a couple of strategies to do that.

First, we're going to go to a larger diameter motor AND we are going to use TWO of them. Why does motor diameter matter? It is not precisely that it is capable of more current or voltage. It's not capable of more voltage and the differences in current capacity are nominal.

The power of an electric motor is applied at the air gap. This is a very small gap between the armature, or rotor, and the stator - the field windings. At that point, two magnetic fields collide and being of opposite polarity, they exhibit an irrestably repulsive force.

But we take the output of the motor at the shaft, which is in the dead center of the motor. The amount of "torque" we get is then to a very persuasive degree a function of how much leverage we have between the point of most intense magnetic flux interaction, ie the air gap, and the center of the shaft. The SAME force caused by the SAME voltage and current, will appear as a much higher torque value if it has a longer arm. And for this reason, the 11 inch motor is more powerful than the 9 inch motor, and similarly a 13 inch motor would be more powerful yet.

At the same time, the longer the arm, the faster the surface of the rotor must travel for any given RPM. And so the higher the centrifugal forces that seek to tear the motor asunder and turn your drive train into a claymore mine. Primarily, with DC series motors this is a function of the ability to hold the commutator together. We observer a nominal limit of 6500 rpm, while AC motors, which do not have this commutator, are often rated to 9000 or even 11000 rpm. They don't really make any power at those lofty RPMs at all, but they don't explode either.

So while the 13 inch motor is impressive in torque, we start to get into some RPM limitations that are not to our advantage.

In the case of the Elescalade, we went to a PAIR of 11 inch motors, instead of a single 13 inch motor.

THIS allowed us to do a couple of things. For one, by using TWO controllers, one for each motor, we can DOUBLE the amount of power our controllers can handle. In this case, we selected the Soliton1 for a couple of reasons. It has an "idle" feature that is quite well thought out and let's us use an automatic transmission. And it purports to handle 300kw - 1000 amps at 300v.

The 11 inch motor is pretty much limited to 192v. Traditionally, Netgain motors have been limited to 170v to prevent arcing of the commutator. Helwig insists that their new Redtop brushes are arcless at up to 192v. And so that is what Redux, really a dress rehearsal in many ways for Elescalade, is powered with.

The Soliton 1 won't of course do 300 kw at 192v. But with two of them delivering 1000 amps and assuming we sag to 150v applied while producing 2000 amps out of our 400Ah cells, we would have a 300kw drive train. 150 x 1000 x 2 = 300,000.

We are also plowing some new (for us of course) ground with the automatic transmission. We then become interested in the concept of efficiency. Efficiency is for these purposes a comparison of the amount of power IN to the drive train compared to the amount that shows up at the wheels. If we put 100 HP of electrical power IN to our drive train and get 85HP to show up on the dynomometer, we would be 85% efficient. There are GOING to be some loses in an automatic transmission. If we could chart our efficiencies using the Soliton, a 9 inch Netgain and a manual transmission, we could expect the efficiencies of the 11 inch and Soliton to be quite similar on an automatic transmission. And so the difference in efficiency between the Elescalade and the Redux would be MOSTLY isolated to the use of hte automatic transmission. That difference would be intensely interesting to me.

The best laid plans of mice and men go aft aglay....

So on THIS series of dynamometer tests, we are interested in something quite different. First we load the dynomometer to 5500 lbs. Then instead of going to specific speeds, we simply tromp the pedal to the metal. Between the increased rate, and the constant acceleration, limited in rate only by what the drive train will do, we can get maximum power at various speeds and rpms. Not how much is REQUIRED to maintain that speed and rpm, because we are not maintaining it, in fact we are accelerating THROUGH it.

This poses some problems in capturing current and voltage. That we attacked with a video camera. We can go to any point on this acceleration curve on the dynamometer data and retrieve torque, horsepower, and RPM for any given mph speed. We pick the usual 10/20/30/40/50/60/70/80/90/100.

Then with a video of the meters on the car, we can go back and get voltage and current off the meters for the resulting RPM values.

THAT gives us our voltage, current, kw power, and indeed HP IN to the drive train. By comparing HP in to HP out, we get efficiency.

Here was the problem. We did this FULL RPM range acceleration in ALL FOUR gears. The most current we ever measured was 755 amperes at 3900 rpm in fourth gear.

IF this holds true on the Elescalade, we're looking at a total power input of not 300kw, but more like 225kw. And I'm trying to move 8200 lbs with a drive train slightly more powerful than the Tesla Roadster.

Oh, it will drive fine. But it won't do any 7 second 0-60 or impress anyone. Nothing to apologize for, but 12 seconds more like.

I did confer with EVnetics about the shortfall and we haven't come up with much yet. Mr. Jenkins insists that they MOTOR CURRENT 1000AMPS inside the controller is what they are talking about when they claim 1000 amps and that this is an industry standard widely observed with ALL DC controllers and some magic magic explanation about the difference between motor amps and current amps that I'm not smart enough to make out. With the pedal floored and the car accelerating uphill, they should all be the same.

I posed this question to Otmar of Cafe Electric regarding the Zilla 1K. His replay was no, at full power it does 1200 amps motor current for the 1000 amps battery current but that this difference disappears when the ripple goes away at 100%. So no industry "standard" that I can tell.

We also have measured in all cases MORE current than spec on our AC controllers, the Curtis, the TIMS600 and the Rinehart Motion Systems.

There remains Seb's argument that we are not really loading the motor. I don't know how much more we can load the motor. It is doing all it can under constant acceleration and at 5500 lbs. If it could do more, we should accelerate faster - that's all. His contention is that if we bring the motor to a stall we'll see the 1000 amps.

No thanks. No stalled motor with maximum current. I am starting to understand their absolutely mystifying score of 7:0 vs the Netgain Motors. They've melted 7 motors without killing a Soliton. Impressive, but I don't want to blow up my motor. I want it to make 1000 amps at 150v while driving the car.

We do cover the Soliton settings in this video. We publish the data. Make me smart. Make me go. Make me more power. I'll be your buddy. I don't know how to make it go harder than this. If it would do more, it should accelerate faster - not demand to be stalled.

Ergo our 9.00 second mile. We're really putting about 125 HP down on the road. If we could do 1000 amps, that figure would be more like 165HP and we probably would be down around 7 seconds, if not 6.

I view it as an open question and a mystery at this point. I still love the Soliton1, but can't make it do those power levels we were hoping for. If you can, chime in.

BTW, as several of our viewers have noted, apparently Otmar and Cafe Electric have come to terms with a production facility and the Zilla will be back in production - of all people, Manzanita Micro. I'm not very popular with them either. Rumor has it ANOTHER fire with the Rudman Regulator - all very secret of course so I can't mention it.

Jack Rickard