Potential Regulator Improvements - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 63 Old 02-21-2016, 12:01 AM Thread Starter
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Post Potential Regulator Improvements

Ever since I learned that V-Stroms use a shunt regulator, which is commonly understood to be an inefficient regulation scheme, I have wondered how bad it really is. Having recently measured the alternator characteristics, I have been able to figure out how bad it is. I thought those results, and the reasons for them, would probably be of interest to some of the technically curious forum members. More interesting, perhaps to a larger group, is how much better the power generation system could work if some engineering know-how was applied to the problem rather than leaving it to Suzuki's cheap-trumps-all-else design philosophy.

I have modeled the 3-phase alternator using the following data, all taken from measurements and observations:
frequency: 3 * engine_RPM / 60 Hertz
peak voltage, open circuit, phase-to-phase: 60 * (engine_RPM/5000) Volts
resistance, phase to Y center: 100 milliOhms
This next datum is a commonly accepted value:
power available to 13VDC bus via bridge rectifier @ 5000 RPM: 380 Watts
The following datum is derived from the above, adjusted to yield available power when the shunt regulator is barely at the non-shunting condition:
inductance, phase to Y center: 1.2 milliHenry

For simplicity, and because I lack better data, I model the alternator's output voltage as sinusoidal. There is nothing in the design of its magetic structure or its windings which tends to generate a sinusoid, but since the winding inductance has such a dominant effect upon currents and would tend to filter out harmonics anyway, the sinusoidal approximation contributes only minor error to the summary results; the error is certainly small compared to the performance gains available with a modified power handling design.

I created a SPICE circuit simulation of the alternator, bridge, and DC bus using the above known/derived data and set the per-phase inductance to get the stated available bus power.

Running the sim at 2500, 5000, and 10,000 RPM, I see that the available power is remarkably insensitive to engine speed. Likewise for copper heating loss (and rectifier loss). At the lower speed and below, the output does fall off a little, consistent with what those using heated gear report in this forum.

The response to shunt regulation is quite interesting. Shunting half (or all) of the available current to ground barely changes stator heating. Based on what I can see from the simulation, and deduce from electronic principles now that I understand how the system actually works, stator heating is hardly affected by adding more power-consuming loads or eliminating some or all of them (when using the stock, shunt regulator). Torque on the rotor is affected by bus load current, as the phase of winding current aligns more or less with generated voltage. (At normal running RPM, the torque reverses 6 times per rotor rotation at each pole, although the sum of pole torques is much more level and always against rotation.)

Surprisingly, at the winding resistance I have, there is a nearly constant, 180 Watt loss in the stator windings -- relatively unchanged by either RPM or load current at normal running speeds. Because this is so high, I am going to make a 4-wire measurement of hot stator resistance to get a more accurate value. This value has almost no effect on available power because the voltage drop due to resistance is quite small compared to the effect of inductive reactance.

The reason power generation is so consistent across RPM and load change is that the stator winding inductive reactance and induced voltage are quite proportional to each other. As the engine speeds up, the frequency of the generated voltage goes up along with the induced voltage. Since the dominant impediment to current flow is the winding inductance, and since inductors impede current flow in proportion to frequency, available current remains nearly constant.

Once I established how a stock system performs, I began the investigation which motivated this work. I wanted to know what could be accomplished with a proper power converter -- one which can efficiently produce a different voltage and current at its output than what is consumed at its input. The result was astonishing to me, at first. (A rethink in light of what I learned from the simulation cured my astonishment.) It is possible, at 5000 RPM, with a relatively simple, buck topology, switching power converter, to get twice the output power (760 Watts) at about 3/5 the stator heating in comparison to the stock regulator (or the Shindengen series regulator.) Or, to get the "rated" output power, stator heating can be reduced to less than 1/6 what the stock design (or installed series regulator) suffers.

I have yet to work out what the improvement would be at delivered power levels below 380 Watts when the series regulator is installed. It acts somewhat like a switching step-down regulator, so its effect on stator heating for bikes with only stock loads is likely good enough to eliminate stator stress as a concern. But the series regulator cannot increase available power over what the stock setup can deliver, and it cannot reduce peak stator stress for bikes with 380 Watts of load.

The reason a power converter can so improve performance is that, at engine speeds used for normal riding, (not lugging), it can take power at a higher voltage and lower current in comparison to the conventional regulator(s). For any engine speed, there is a rectifier output voltage at which the product of that voltage and the available current (which goes down with increased voltage) reaches a maximum. That maximum occurs at about half of the average rectified, zero current voltage. The stock regulation scheme only operates at that maximum at about 2200 RPM. At all higher speeds, it operates past the optimum, on the high current side of the curve.

After this investigation, I believe it would be possible to build a replacement regulator which would make bikes with heated gear and added lighting work well electrically, with significantly reduced stator stress and significantly fewer problems with batteries being drained. (I think the regulator should have a "heated gear" outlet, which would be temporarily powered down when engine speed remains too low for too long to keep the battery up and heat the gear. This would happen after a few minutes at idle or lugging speed.)

I have well begun detailed electronic design of the power-converting regulator. Comments, questions and suggestions are welcome. I plan to build at least one, with an etched circuit board and commercially common parts. After that, (once it is a proven design), I'll see about offering kits or built and tested regulators, likely through an established, after-market vendor.
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Last edited by Trepidator; 02-21-2016 at 12:29 AM. Reason: Common grammar is better.
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post #2 of 63 Old 02-21-2016, 07:45 AM
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Looks pretty interesting..if its ok with you I'm going to share this with a friend of mine who lectures in physics at the Sorbonne..

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post #3 of 63 Old 02-21-2016, 08:46 AM
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post #4 of 63 Old 02-21-2016, 08:54 AM
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post #5 of 63 Old 02-21-2016, 12:03 PM Thread Starter
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Responding to
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Originally Posted by CollingsBob View Post
Looks pretty interesting..if its ok with you I'm going to share this with a friend of mine who lectures in physics at the Sorbonne..
and
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Originally Posted by NyMeTsFaN912 View Post
English please
and
Quote:
Originally Posted by mcrag View Post
I feel so inadequate.
I thought the circuit theory of the V-Strom's magneto and regulator would be interesting to those who have some familiarity with basic electronic principles, which should be regarded as some physics simplified and reduced to practical use. Nothing here would confound somebody who passed the first circuits class in an electrical engineering program or took a high school electronics course.

My conclusions, that there is much more power available from the magneto and that it can be taken with less stress upon the stator, should be interesting to those who use heated gear and grips or contemplate doing so. I explained why to show there is good reason to believe those conclusions and to subject them to critique by those able to do so. It's more than wishful thinking.

I don't know how to put the circuit theory into common English in a forum post of reasonable length. Anybody who wants to explore the concepts could peruse material such as Impedance Matching and AC Circuits.

Taking as given that electrical power flow is the product of voltage and current, the difficulty with the V-Strom power source can be seen as a mismatch between a high-voltage/not-so-high-current generator and a low-voltage/want-higher-current DC bus. The bus needs power in a form which can only be inefficiently supplied by the generator without somehow transforming voltage and current. None of the regulators I have found address that mismatch. (They drop voltage and leave current essentially unchanged.) Power converters do it ubiquitously, most of which convert AC line voltage to the much lower DC voltages needed by electronic systems. I think it is time to apply that common technology to V-Stroms and other bikes which provide less electrical power than some people need. (Making Suzuki's sorry stator design last longer is a bonus.)
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post #6 of 63 Old 02-21-2016, 01:05 PM
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I'm not so sure a power converter will help those pushing the limits with heated gear. Converting excess voltage to make more amps yet take it easy on the stator is great, but a full set of heated gear like the grips, gloves, jacket liner, pants liner and boot soles don't leave any excess voltage to convert once the heat controller gets much past half power. TANSTAAFL. You can get more I by using less E, but maximum P is maximum P.

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post #7 of 63 Old 02-21-2016, 01:59 PM Thread Starter
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Originally Posted by greywolf View Post
I'm not so sure a power converter will help those pushing the limits with heated gear. Converting excess voltage to make more amps yet take it easy on the stator is great, but a full set of heated gear like the grips, gloves, jacket liner, pants liner and boot soles don't leave any excess voltage to convert once the heat controller gets much past half power. TANSTAAFL. You can get more I by using less E, but maximum P is maximum P.
But the present system rarely operates at the magneto's maximum P. At all operating RPMs above the low end of the engine's usable torque curve, the regulators now sold are operating on the higher current side of the power versus rectifier output voltage curve. If you plot stator output power versus rectifier output voltage for any given RPM, it is a parabola, reaching zero power at either maximum voltage (and open circuit, zero current) or maximum current and zero voltage (such as the shunt nearly forces). About halfway in between, the voltage*current product (or power) is maximized, and that maximum is at a higher voltage than the DC bus (or the bus plus rectifier drops) whenever the engine runs at speeds commonly used when not stopped (or badly lugging.)

At 5000 RPM, that maximum occurs at about 40 Volts, and over twice as much power is available compared to what can be taken at 13 VDC from the bridge. If it would help, I could publish some math and plots showing this. (I hesitate to go that far in this forum. However, I am willing to share the simulation. It runs on a simulator available at no cost running on Windows.)

It's not a free lunch. An 800W power converter will require parts costing more money to get the performance left on the table by Suzuki's insistence on using the cheapest solution. They may well have made the best choice for fair weather riders on stock bikes. But I think many riders would be happy to get a few hundred more Watts from a (maybe) $130 regulator replacement. For me, just going easier on my DL-650A's 3rd stator is enough to motivate this project.
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post #8 of 63 Old 02-21-2016, 02:19 PM
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Let's just say I'll believe it when I see it.

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post #9 of 63 Old 02-22-2016, 12:19 AM
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More Power, Less Stator (damage)

This makes sense and seems doable with modern electronics. Correct me if I am wrong but your plan is to design a smart regulator that is impedance matched to the output of the magneto. Since the impedance of the magneto varies with RPM the regulator would probably need that as input. The magneto naturally tends to operate at high V and low I thus you can reduce the current losses in the stator while at the same time extracting more power (moving to the peak of the curve) compared to the current system which is impedance mismatched, operating off-peak plus a dumb shunt (regulating output to 12V).
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post #10 of 63 Old 02-22-2016, 01:05 AM Thread Starter
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Post yes, impedance matching

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Originally Posted by dmfdmf View Post
This makes sense and seems doable with modern electronics. Correct me if I am wrong but your plan is to design a smart regulator that is impedance matched to the output of the magneto. Since the impedance of the magneto varies with RPM the regulator would probably need that as input. The magneto naturally tends to operate at high V and low I thus you can reduce the current losses in the stator while at the same time extracting more power (moving to the peak of the curve) compared to the current system which is impedance mismatched, operating off-peak plus a dumb shunt (regulating output to 12V).
I think you've got the gist of the idea, for the case where maximum power is to be extracted. When less than maximum available power (at the existing RPM) is needed, the smart power converter will work off the maximum, toward the higher voltage/lower current end. This minimizes stator heating.

It is very useful to view this as you suggest, as an impedance matching problem. The magneto, for any RPM, defines a relationship between bridge output voltage and current, and the (-) slope of that curve (which is nearly a line) acts like an output impedance. The maximum power transfer will be (approximately) where the load presented by the converter takes a ratio of voltage and current matching that output impedance. (When the converter is operating at constant, controlled output power, its incremental input impedance become negative. When near maximum available magneto power, that incremental impedance has almost the same magnitude as the magneto output impedance, creating an interesting stability issue. That is partly why an intelligent controller is necessary.)

It is true that the converter needs to respond to RPM. I considered measuring it (via stator output frequency), but decided a technique used with solar panels is simpler. (See How Maximum Power Point Tracking works.) The idea is that the controller, which is able to control power flow of the converter and monitor output voltage and current (and hence power), alters demand to keep the input voltage near where maximum power is delivered. That's for when less power is available than what the converter is designed to handle. At the converter's power limit, the controller will simply demand what can be done without jeopardizing the circuitry, which will be temperature dependent. This way, the system will adapt to the particular impedance and generated voltage when running at its magneto-defined maximum and will automatically operate on the higher voltage/lower current end of the power versus voltage curve when running below that maximum (when the battery is charged and the loads demand less than maximum converter power, or when the converter is at its power limit.)
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