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Author Topic: Charging system theory  (Read 5018 times)
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msi1259
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05/09/07 1408 Hours
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« on: 08/31/09 2016 Hours »
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Charging systems seem to be a common topic, so I thought I would put down what I know of permanent magnet alternators in the hope it may help someone. Feel free to make any corrections or clarifications.

Permanent Magnet Alternators:

Electricity is generated in a conductor when a magnetic field passes through the conductor (Faraday's Law) . The amount of power generated increases:
- with an increase in the strength of the magnetic field
- with an increase in the speed of the magnetic field (flux) passing through the wire
- with an increase in the number of turns of wire the magnetic flux is cutting.

The VStrom charging system is comprised of three parts: magnets (flywheel/rotor), wire coils (stator), and  a regulator/rectifier.

The Magnets:
The magnetic field could be increased with stronger magnets, or by a reduction in the air gap between the magnets and the coils. This flux is concentrated by putting a ferrous material inside the coil of wire. The magnets are placed in the flywheel with alternate poles facing the coils, so the coils are subjected to alternating (North -> South -> North...) poles as the flywheel spins.


The Stator:

The number of turns of wire have to fit in the available space, so an increase in wire size (diameter) will decrease the number of turns. Less turns will reduce voltage at near idle speeds, while conversely, more turns will produce too much voltage at higher speeds that will have to be absorbed by the stator and regulator. Thicker insulation on the wire adds to it's diameter, and generally thin / better insulation is more expensive. The wire is subjected to engine vibration as well as vibration from the rotating magnetic fields.

As the metal core the coil is wound on is also an electrical conductor , some current is generated inside the metal – these currents are called “eddy currents” (similar to eddy (swirling) currents in a river). These currents cause heat, so the stator cores are made  of laminated plates that are insulated from each other to reduce these parasitic losses. As the laminated plates switch magnetic polarity as the magnets pass, the laminations tend to heat from the constant reversal, as well as lag the change slightly ( hysteresis). Above a certain speed, the laminations cannot switch magnetic polarity fast enough (saturation), and available power output will start to drop.  (see http://www.protolam.com/page3.html for the complexity of lamination choices). Thinner laminations and/or better metals both reduce core losses, but increase cost. Picture of a stator showing fine stacked laminations on the pole pieces:



As the copper wire has some direct current resistance, (0.2 to 0.5 ohms between B1,B2,B3 on attached diagram), heat will also be generated in the windings from the current flowing through it.  Some alternators are loose wound (the wire coils are not potted in epoxy), so engine oil can get to each wire too help cool it  – but vibration and corrosion become more of an issue. (used oil can become corrosive). Wire wound into a coil shape also has a resistance to alternating current (inductance), that increases it's losses with increasing frequency (RPM)

A graph of stator power output  vs RPM should show a fairly smooth rise to the maximum output (5000 rpm on the VStrom), and then flatten or even reduce slightly with increasing RPM. The increased power output due to the higher speed of the magnetic flux cutting the wire is offset by the increased magnetic core and copper losses at higher RPMs. Output graph shows less voltage at low rpm on the ElectroSport stator, but more at higher RPM – likely done with less windings of larger diameter and better core material to reduce the higher RPM losses (?) - (from ElectroSport site) “is built with the highest grade lamination materials and the copper windings are triple insulated for maximum reliability.”



The Regulator / Rectifier:

The alternator (stator / flywheel) puts out AC (Alternating Current) that alternates from positive to negative. The rectifier steers the positive going pulses to the Red battery lead, and the negative going pulses to the Black battery lead (sort of like one way valves for water). The diode symbol is an arrowhead with a vertical line - the direction of the arrow is the direction current will flow from positive to negative. When current is flowing through a diode, it will drop ~0.6 volts across it, in the reverse direction no current should flow. At 30 amps out, each diode is dropping 18 watts (30 amps x 0.6 volts) peak.



The regulator portion is an integrated circuit (IC) that senses the output voltage, and should it go high - the IC turns on a SCR (silicon controlled rectifier). The SCR is a diode that doesn't conduct until the third terminal (the gate) is pulsed by the IC. The SCR then shorts the stator winding (i.e. B1 to B2 through the SCR and diode 5), converting the excess power to heat in the stator and rectifier/regulator.

The alternator system creates a lot of heat  - each 25 amps generated requires ~1 horsepower (HP) to spin it. (1 HP equals 746 watts).  Permanent magnet alternators are generally only 50->60% efficient, (Efficiency = Output / Input ) with the losses converted to heat in the stator and.or at the regulator/rectifier. Regardless of the load, because the regulator shorts the stator on over-voltages, the alternator runs at peak output at all times.

 
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greywolf
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01/31/06 0643 Hours
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DL650AL2
Evanston IL USA
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« REPLY #1 on: 10/01/10 1451 Hours »
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A MOSFET regulator or a series regulator is probably a better choice than the stock SCR type. http://www.triumphrat.net/speed-triple-forum/104504-charging-system-diagnostics-rectifier-regulator-upgrade.html
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Pat
Nicknames I use to lessen typing - Vee=2002 - 2012 DL1000s, Veek=2014+DL1000As, Wee=2004-2011 DL650s, Glee=2012+DL650As
DEcosse
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08/21/13 1934 Hours
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SV650S; Speed-Tona
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« REPLY #2 on: 08/23/13 0102 Hours »
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Quote from: greywolf


I am the author of that  Grin
I have updated information on Series Regulators in that thread and also have included here -
http://www.vstrom.info/Smf/index.php/topic,20426.0.html

If stators are failing, then the sure choice is a Series Regulator vs a MOSFET Shunt unit.
If you are going to change the R/R and the stator is still functional, the Series units will give insurance against future stator failure.
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greywolf
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01/31/06 0643 Hours
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DL650AL2
Evanston IL USA
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« REPLY #3 on: 08/23/13 0109 Hours »
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A series type is definitely easiest on the stator. It needs to be in the air stream though and is bigger.
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Pat
Nicknames I use to lessen typing - Vee=2002 - 2012 DL1000s, Veek=2014+DL1000As, Wee=2004-2011 DL650s, Glee=2012+DL650As
DEcosse
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08/21/13 1934 Hours
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« REPLY #4 on: 10/08/14 1708 Hours »
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A graph of stator power output  vs RPM should show a fairly smooth rise to the maximum output (5000 rpm on the VStrom), and then flatten or even reduce slightly with increasing RPM. The increased power output due to the higher speed of the magnetic flux cutting the wire is offset by the increased magnetic core and copper losses at higher RPMs. Output graph shows less voltage at low rpm on the ElectroSport stator, but more at higher RPM – likely done with less windings of larger diameter and better core material to reduce the higher RPM losses (?) - (from ElectroSport site) “is built with the highest grade lamination materials and the copper windings are triple insulated for maximum reliability.”





One of the local guys installed an ElectroSport stator and indeed it exhibits the low output as shown in the graph - at ~ 2000 rpm it produced enough current to bring the output voltage up to the regulation point (where the regulator actually begins to work to limit the voltage).
I suggested he measure the stator and compare to his original:
He found the outer diameter to be slightly smaller - 4.175" vs 4.225".
The smaller diameter means that effectively the field strength of the rotor is lower

So I would speculate the Electrosport possibly
1. has more turns, and this is what produces higher power
2. is slightly smaller diameter to limit that higher rpm power but at the cost of reducing the low rpm power.

Quote from: msi1259
Electricity is generated in a conductor when a magnetic field passes through the conductor (Faraday's Law) . The amount of power generated increases:
- with an increase in the strength of the magnetic field
- with an increase in the speed of the magnetic field (flux) passing through the wire
- with an increase in the number of turns of wire the magnetic flux is cutting.


i.e. the first factor is negative, second factor is neutral, third is a positive.

The flux saturates, just like the OEM, but because of the higher number of turns, it produces more power further up the rpm level.
(or the turns could be similar, with gains in the core to help reached a higher saturation point with higher rpm, even with the lower field strength)
Again, all speculative, I don't have the bike to be able to make actual relative measurements (other than the diameter of the stator which the owner measured)
« Last Edit: 10/08/14 1711 Hours by DEcosse » Logged
richw
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03/11/10 2115 Hours
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Baltic, Conn. USA
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« REPLY #5 on: 10/08/14 1923 Hours »
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Greywolf

so its a year with your Series RR

What is a report ?
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greywolf
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01/31/06 0643 Hours
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DL650AL2
Evanston IL USA
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« REPLY #6 on: 10/08/14 2135 Hours »
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Greywolf

so its a year with your Series RR

What is a report ?
Not one problem. A number of others have similar experiences. The was one charging system problem reported but the specifics were not clear and it didn't seem to be a problem with the R/R.
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Pat
Nicknames I use to lessen typing - Vee=2002 - 2012 DL1000s, Veek=2014+DL1000As, Wee=2004-2011 DL650s, Glee=2012+DL650As
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