StromTrooper banner

1 - 20 of 63 Posts

·
Registered
Joined
·
788 Posts
Discussion Starter #1 (Edited)
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.
 

·
Ex- moderator
Joined
·
1,131 Posts
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..
 

·
Registered
Joined
·
788 Posts
Discussion Starter #5
towards Engish

Responding to
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
English please
and
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.)
 

·
FORUM GODFATHER.....R.I.P. PAT
Joined
·
38,049 Posts
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.
 

·
Registered
Joined
·
788 Posts
Discussion Starter #7
Yes, no free lunch

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.
 

·
FORUM GODFATHER.....R.I.P. PAT
Joined
·
38,049 Posts
Let's just say I'll believe it when I see it.
 

·
Registered
Joined
·
809 Posts
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).
 

·
Registered
Joined
·
788 Posts
Discussion Starter #10
yes, impedance matching

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.)
 

·
Registered
Joined
·
788 Posts
Discussion Starter #11
Missourians!

Let's just say I'll believe it when I see it.
That will be awhile from now. I'm sure enough of this that I plan to partially productize for the first article. (A producible design with a printed circuit board and cost-effective component choices)
 

·
Registered
Joined
·
193 Posts
Big words hurt jacketslacker's head.....

I never pretend to understand electronics other than following instructions (preferably with pictures) but it sounds like you're gearing up for some serious experiments there. Have fun and share results when you get them.
 

·
Registered
Joined
·
809 Posts
I'm sold on your idea

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.
I see. So those series R/R's that don't shunt load but disconnect load are, in effect, doing the same thing. Since these magnetos cannot actually turn off the P output (for a given RPM) it is going to manifest as either V or I. By disconnecting the load the series R/R's push operation, on average, toward the higher voltage/lower current end reducing power loss in the stator wires. That these series R/R's don't make stator failure worse tells me that the failure mode is predominantly due to heat not the high V breaking down the insulation. This is consistent with almost all the pictures I have seen where the fried stator is typically burned near the top (from about 11am to 2pm on a clock) while the bottom coils are better cooled in oil. So you have convinced me that a smart regulator could spare the coils.

As far as getting more power (the real benefit of this project in my view), I am beginning to think that the impedance mismatch is a major source of power loss and coil damage. My understanding of basic circuits is a bit hazy but if I recall correctly, when two systems are mismatched the transmitted power bounces back into the transmitting system. This is a double whammy in that you are not extracting power efficiently (high losses) and the power is being dumped into the stator coils, thus causing failures. I don't think you can get twice the power but certainly a 10-25% boost in power (ballpark numbers that I pulled out of thin air) seems feasible. Great idea if you can make it work for reasonable cost.

BTW, in thinking about your project I have thought of a simple way to protect my stator (while waiting for your Smart Regulator) without replacing the stock R/R. Since this is a heat problem I am going to get a piece of finned cooling tube and connect the generator nut port to the TDC viewing port. Because of the spinning rotor there is probably a natural delta-pressure between those two ports and so crankcase air will natural circulate through the tube and dump the excess heat. Easy mod.
 

·
FORUM GODFATHER.....R.I.P. PAT
Joined
·
38,049 Posts
My thinking has changed to the cause of the burnouts being on top is that is the place where the wires from each winding come together. The heat developed in the windings gets combined. The only oil that gets on the stator when running is splashed there.
 

·
Registered
Joined
·
788 Posts
Discussion Starter #15
naivety => failure

My thinking has changed to the cause of the burnouts being on top is that is the place where the wires from each winding come together. The heat developed in the windings gets combined. The only oil that gets on the stator when running is splashed there.
The first failed stator pulled from my 2013 DL-650A had a winding shorted to the pole lamination at the inside of the coil where the magnet wire was just wrapped around the corner of the stack. That was bad enough, as a moronic design choice. But not bad enough for whoever controls the production of the stators. The resin with which sensible motor and generator manufacturers impregnate windings was present in token amounts, and had not really reached the inside layer of the pole windings, where it might have prevented the chafing that created that short (at 12.5 months after I bought the bike). Looking at it, I had to wonder: What made anybody think this would work for long?

Regarding heat combining from windings where they join: I don't think so. Where they join is outside of the pole windings, and there is better heat flow from the copper (or solder) there than out from the middle layers around the poles. Furthermore, heat is not going to diffuse along the length of the wires. It is being generated pretty much uniformly along each wire's length; there will be no temperature gradient to drive heat toward the Y splice.
 

·
Registered
Joined
·
788 Posts
Discussion Starter #16
electronic miscellania

I see. So those series R/R's that don't shunt load but disconnect load are, in effect, doing the same thing. Since these magnetos cannot actually turn off the P output (for a given RPM) it is going to manifest as either V or I. By disconnecting the load the series R/R's push operation, on average, toward the higher voltage/lower current end reducing power loss in the stator wires.
Both types of regulator suffer from the same problem at maximum output power (as limited by the magneto and little else). Each one passes every bit of charge going to the load also through the stator windings. And at full output, where the series regulator is conducting throughout the cycle on each phase, its performance is no better at the output and slightly worse with respect to its own heating. (It uses SCRs, which have higher voltage drop than appropriately chosen rectifier diodes.)
That these series R/R's don't make stator failure worse tells me that the failure mode is predominantly due to heat not the high V breaking down the insulation. This is consistent with almost all the pictures I have seen where the fried stator is typically burned near the top (from about 11am to 2pm on a clock) while the bottom coils are better cooled in oil. So you have convinced me that a smart regulator could spare the coils.
The cheapest magnet wire, ("single" insulated, with one layer of enamel), is good for a minimum of 3 times the peak voltage it could ever see in the V-Strom stator. (At least it is good for it when first built, before the chafing begins due to amateurish construction.)

So, yes, heating must be the culprit, (at least when chafing is not).
As far as getting more power (the real benefit of this project in my view), I am beginning to think that the impedance mismatch is a major source of power loss and coil damage. My understanding of basic circuits is a bit hazy but if I recall correctly, when two systems are mismatched the transmitted power bounces back into the transmitting system. This is a double whammy in that you are not extracting power efficiently (high losses) and the power is being dumped into the stator coils, thus causing failures.
That's almost right. However, when you say "the power is being dumped into stator coils", you overstate the problem. Stator current in a stock bike is most of 90 degrees out of phase (lagging) the induced voltage. Current is relatively constant over the ordinary riding engine speed range (and it drops at idle). I will soon publish some numbers which tend to illustrate this.
I don't think you can get twice the power but certainly a 10-25% boost in power (ballpark numbers that I pulled out of thin air) seems feasible. Great idea if you can make it work for reasonable cost.
I can get over twice the bridge output power at 5000 RPM, using a power converter with less parts cost than an 800W computer power supply would have if you bought the parts. I think it is reasonable to expect to sell such a device for no more than $150. I say this having now selected all of the power handling semiconductors and the buck inductors.
BTW, in thinking about your project I have thought of a simple way to protect my stator (while waiting for your Smart Regulator) without replacing the stock R/R. Since this is a heat problem I am going to get a piece of finned cooling tube and connect the generator nut port to the TDC viewing port. Because of the spinning rotor there is probably a natural delta-pressure between those two ports and so crankcase air will natural circulate through the tube and dump the excess heat. Easy mod.
I do not see how this is going to affect the nearly oil filled space where the stator and rotor reside. Can you expand that a bit?
 

·
Registered
Joined
·
788 Posts
Discussion Starter #17
some representative figures

What follows will be of marginal interest to folks without some familiarity with electronics.

I've spent a few hours building, (checking) and running a SPICE model of the magneto and bridge rectifier. This is to aid understanding of how the shunt regulated system performs and to see what performance gains are possible with a load which optimizes current and voltage at the bridge output to get power from it at various levels.

Here are some results from the simulation which I will be using to drive the design of the bridge and power converter for a replacement regulator.:
===============
Bridge output power and loss terms at various bridge DC voltages

@ 1250 RPM (50 RPM below idle spec):
160W at 13V, 25W Cu loss, Id = 4.1 mean, 6.5 rms

@1875 RPM:
258W at 21V, 26W Cu loss, Id = 4.1 mean 6.6 rms

@ 2500 RPM:
443W at 23V, 62W Cu loss, Id = 6.4 mean, 10.2 rms (maximum)
406W at 27V, 26W Cu loss, Id = 5 mean, 8 rms
261W at 32V, 12W Cu loss, Id = 2.7 mean, 4.5 rms

@3750 RPM
709W at 35V, 68W Cu loss, Id = 6.8 mean, 10.7 rms (maximum)
413W at 49V, 13W Cu loss, Id = 2.8 mean, 4.6 rms
259W at 53V, 4.4W Cu loss, Id = 1.6 mean, 2.7 rms

@ 5000 RPM:
974W at 46V, 74W Cu loss, Id = 7.1 mean, 11.1 rms (maximum)
404W at 70V, 6.1W Cu loss, Id = 1.9 mean, 3.2 rms
260W at 73.5V, 2.4W Cu loss
(Next is for shunt regulator or series at full conduction angle.)
408W at 14V, 140W Cu loss, Id = 9.7 mean, 15.3 rms

Performance just gets better at higher RPM. However, building
a power converter to handle over 900W is challenging enough,
as no-load voltage approaches 200V (at 10,000 RPM).
===============
In the above lines, "at #V" refers to the bus voltage which would be power converted when above 14V and is equivalent to present regulator scenarios when at or below 14V.

"Cu loss" is just mean squared winding current times an estimated 100 milliOhm resistance. (This will later be refined, with little effect on the other numbers. Relative winding losses will not be affected.)

"Id = ..." shows stress seen by each of the bridge rectifiers. It is worth noting that the shunt and series regulators dissipate (up to) about 60W due to these terms. The series regulator will do so at full output power and the shunt regulator will do so at most engine speeds, whatever the load.

The power convert will likely run at 93-94 percent efficiency, so delivered output from the new regulator will be 6-7 percent lower than the figures shown at maximum (or at stated bridge voltage).

The parameters going into the simulation do not yet represent the range of values that will occur across build instances. They are derived from measurements, the service manual, and other sources that are good enough that the basic result is not going to change except for the precise value of maximum power versus RPM and losses.
 

·
Registered
Joined
·
809 Posts
I do not see how this is going to affect the nearly oil filled space where the stator and rotor reside. Can you expand that a bit?
Take something like this (but not so long and not this shape and probably aluminum to avoid galvanic effects);



...and attach that between the two ports on the generator cover (with appropriate connectors, adapter, seals & etc). I don't think there is high pressure behind the case during operation and it probably only fills with oil on shutdown. There is mostly swirling air ladened with oil once the motor is running. The centrifugal effects of the spinning rotor will drive air/oil from the TDC port through the pipe which will be cooled by the fins and returned to the case at the crankshaft-nut access port thus lowering the coil temps. So its a simple heat sink for the generator.

I'm going to have to think about your other comments...
 

·
FORUM GODFATHER.....R.I.P. PAT
Joined
·
38,049 Posts
The up and down action of the pistons will created enough pressure difference in the crankcase to pump oil six feet high out of the oil filler cap. DAMHIKT.
 

·
Registered
Joined
·
10 Posts
The reason the power dissipated in the stator does not change much
a) with engine speed - because it reaches saturation at a fairly low engine rpm; this is purposely designed this way, so that there is good power made at relatively low engine rpm. Most systems will be able to provide all the 'normal' system load current it idle, or very close to it; as the rpm is slightly increased, the stator will produce more current and that current is shunted by the Regulator to maintain the output voltage at its regulation set-point; as the rpm is further increased, the flux-density reaches a saturation point and regardless of further increased speed, the current will also be limited at this point.
b) with load - the reason it does not change with 'load' (i.e loads connected/removed on the regulated side of the R/R) is because of the shunt regulator - in order to remain in voltage regulation, whenever you remove load (say for example you turn off the headlights), then in order to maintain the regulated output voltage, that current (that would otherwise have gone to the lights) simply gets shunted instead through the parallel path of the regulator; & conversely when you add load, it reduces the shunt current when the system load is increased.
The current in the stator is essentially ALWAYS at the max it can generate and that current either flows through the load or the shunt. By fundamentals, any amount of current removed from the load MUST be diverted instead through the shunt by the same amount, in order to maintain the same output voltage.
That is why there is no change to the dissipated power in the stator, and hence generated heat, when you change the system load OR the RPM. Stator is running flat-out regardless of those speed or system load changes. Of course the power dissipated by the Regulator WILL increase as the system load is decreased, therefor IT will become hotter; the same applies to the Regulator heat dissipation as the rpm increases - except this is a fairly small rpm range as, again, it reaches saturation at fairly low engine speed anyway.

Series Regulators are a much better option to lower the power generated by the stator (and resultant generated heat), whereby the stator will only deliver the current demanded by the load.
 
1 - 20 of 63 Posts
Top