Rectifier regulator theory

[Stromper]

Does anyone really know as opposed to speculation etc.

The permanent magnet / stator alternator in a bike makes near 80Volts AC.

This is delivered to the Regulator rectifier.

I think the AC wave is chopped at the 13 Volt about and heads to the bike

The rectifying is straight forward.

So what if anything happens to the remaining part of the wave from 14 to 80 Volts peak.

I won't waste time with the various theories I've heard

[2v2Ducati]

The regulator/rectifier gives it off as heat. Ein=Eout

[DuncanMoto]

Burned off in the form of heat. +1

[gadget]

It would be easier to explain face to face since this kind of question is usually accompanied by a crapload of diagrams on cocktail napkins but I'll give it a shot.

The 80 VAC is 40 volts above 0 and 40 volts below. It looks like a clean sine wave.

A rectumfryer converts this to DC by reversing the negative portion of the AC waveform to a positive.
Now you have a VERY noisy 40VDC.
It actually looks like a bunch of hills smashed together on a o-scope.

At this point the regulator clamps the voltage down to 13VDC and converts the rest of the noisy voltage into heat.
It only has to convert from 13 to 40 volts since it has been rectified from AC to DC.

This is why most regulators have heatsinks or a metal plate with a hole through it so that it can be bolted to a heatsink.


btw
The reason why the "extra" voltage is discarded:

The frequency of the raw AC voltage that the alternator is producing is not stable.
It increases and decreases as the RPM of the engine increases and decreases.
This means that in order to produce a clean 13 VDC the alternator must produce a lot more AC voltage and the regulator must be much more robust to deal with this widely variable voltage.

[nhbubba]

Don't they usually incorporate some capacitance to make up for the valleys from Vo to 0V as well. Been a long while since I've built a regulator.

[Stromper]

OK

My question distilled down relates actually to the stator

It would seem that you could produce a mechanically superior stator if the coils were basically potted with a nice high temperature compound.

However if extra heat is dissipated in the stator coils themselves than encapsulating them in epoxy would greatly increase their temperature and perhaps melt or decompose the electrical insulation.

2nd question

Does the R/R care (?) what the 12V load on the bike is. Meaning if you add lots of lights etc and use more wattage is there less heat sluffed off elsewhere ? If this is so would a large resistor between the R/R and ground help visa Vee the stator temperature? Some think the extra energy used by the bike reduces the amount of heat at the generator components.

[gadget]

OK

My question distilled down relates actually to the stator

It would seem that you could produce a mechanically superior stator if the coils were basically potted with a nice high temperature compound.

However if extra heat is dissipated in the stator coils themselves than encapsulating them in epoxy would greatly increase their temperature and perhaps melt or decompose the electrical insulation.

I do not know nearly as much about the mechanics of alternators and generators as I do about electronic theory.
but...

The "extra" heat that we have been talking about is generated by the regulator side of the RR as it deals with providing a consistant 13VDC with adequate amperage for the circuit.

The alternator does produce some heat. I know that car alternators are designed to allow air flow through them as a form of cooling. I imagine that motorcycle alternators would have more contact with metal to provide a heatsink.

I have seen coils completely immersed in resin compound. I do not think it provides any advantage except to increase durability. Most wire on stators and rotors are varnished. If you nick the varnish, the wires will short and the alternator will fail. I imagine this allows a more compact winding and reduced weight.

2nd question

Does the R/R care (?) what the 12V load on the bike is. Meaning if you add lots of lights etc and use more wattage is there less heat sluffed off elsewhere ? If this is so would a large resistor between the R/R and ground help visa Vee the stator temperature? Some think the extra energy used by the bike reduces the amount of heat at the generator components.

Yes, the R/R "cares". The more lights etc that you put on, the lower the resistance (they are added in parallel). The lower the resistance the more current flows through the regulator.

If you continue to add devices to the circuit, you will get to a point where the resistance of the circuit is reduced so far that the regulator burns out. This is because the regulator is not designed to be robust enough to deal with such a high volume of current. A good analogy would be over-reving an engine until it fails. The regulator will work harder and harder to maintain adequate current until the heat generated literally burns the semiconductor material up.

[gadget]

Don't they usually incorporate some capacitance to make up for the valleys from Vo to 0V as well. Been a long while since I've built a regulator.

yes, regulator circuits do incorporate capacitance.
here is an excellent example of a variable regulated power supply.
http://www.eleccircuit.com/l146lm327...ator-0-40v-1a/

[Stromper]

The idea about extra equipment was the theory the more power used by the devices meant less power needed to be dissipated.

I also saw some description that the heat given off by the R/R was due to the internal resistance and voltage drop of .6Volts through the scr and not as a result of deliberate energy dissipation. The superiority of the MOSFET R/R being the lowered internal resistance of the MOSFET device compared to the SCR. agree or disagree?

[gadget]

The idea about extra equipment was the theory the more power used by the devices meant less power needed to be dissipated.

I also saw some description that the heat given off by the R/R was due to the internal resistance and voltage drop of .6Volts through the scr and not as a result of deliberate energy dissipation. The superiority of the MOSFET R/R being the lowered internal resistance of the MOSFET device compared to the SCR. agree or disagree?

agree...to a point, it sounds a little bit oversimplified.
Electrical circuits are not 100% efficient (even superconductors are not perfectly efficient). That loss in efficiency is normally exhibited by a conversion of electrical energy into thermal energy. So it must be taken into account when designing the circuit at the outset.

The problem with designing a motorcycle electrical system is that you want it to be as efficient as possible but you also want it to be capable of adding additional devices. For example, I add all sorts of gadgets onto my bikes. My BMW was so sensitive to this that unless I trickle charged it every night, the ABS system would disable during the initial start up.
Triumphs (my latest) are also nortoriously sensitive to this as well.

[RandyO]

Some think the extra energy used by the bike reduces the amount of heat at the generator components.

the RR on my son's old VFR is right under the seat, it gets hot, when you turn the heated grips on, the RR cools down

[oVTo]

the RR on my son's old VFR is right under the seat, it gets hot, when you turn the heated grips on, the RR cools down

So he has a choice between a heated seat or heated grips? Sucks this time of year.

[Stromper]

Well the understanding I have is that its the EXTRA power that is shunted to ground by the scr's. The SCR have internal resistance so the power going through them heats them up.

My loin cloth and spear are getting itchy

[ZX-12R]

Here are some more details on motorcyle rectifier/regulators.

A typical motorcycle charging system has a 3 phase stator with a permanent magnet rotor. It generates 3 phase AC power at voltages ranging from 40-90VAC when measured phase to phase. Because of the permanent magnets, for any given RPM it will always generate constant electrical power regardless of the load attached to it.

Since nothing on a motorcycle runs on AC, the electricity from the stator is fed through a set of rectifying diodes which creates a DC voltage that has a small amount of ripple in it. The voltage into and out of the rectifier looks something like this:



The voltage of the resultant DC waveform is high enough where it would damage your battery and all the electronics which make your motorcycle run. This is where the regulator comes in. In motorcycles, they tend to be a simple zener regulator with a heavy duty pass transistor. The regulator limits the maximum value of the DC voltage to the battery and the rest of the bike. Any excess power that isn't used is shunted to ground. Heat in the R/R is mostly a result of excess power flowing through the regulator to ground. The more current that flows, the hotter it gets.

It seems counterintuitive at first but the regulator does get cooler when you attach a larger electrical load to it. Since the stator outputs a fixed amount of power at any given RPM, any power that isn't consumed by your electronics is shunted to ground which is where most of the heat is generated. If you increase the load on your system, more power is consumed from the charging system and less has to be shunted to ground which keeps the regulator cooler.

If you attach too much load to the charging system it will reach a point where the voltage from the stator drops so much that the regulator stops shunting voltage to ground and the battery picks up the slack for any extra power needed above what the charging system can provide. When you get to this state, your battery will begin to discharge since there isn't enough power available from the charging system to keep it topped off. In extreme overload cases, excessive current can flow in the stator which can cause it to overheat and fail.

[NobodySpecific]

Since nothing on a motorcycle runs on AC

Great explanation I just want to point out that this is just a general rule, as my XT has an AC headlight, but 12V DC for the rest of the electronics (signals, tail/brake light, gauges). That actually makes it nice for attaching heated gear to it, as the heated gear won't dim the headlight.

[ZX-12R]

Don't they usually incorporate some capacitance to make up for the valleys from Vo to 0V as well. Been a long while since I've built a regulator.

The battery in your bike is a giant capacitor that filters out any period of time where the regulators output voltage is less than the battery's.

[ZX-12R]

Great explanation I just want to point out that this is just a general rule, as my XT has an AC headlight, but 12V DC for the rest of the electronics...

I was describing a modern charging system on a motorcycle. Your XT350 doesn't have the same 3 phase charging system that modern motorcycles have. It has a stator with 2 lighting coils and 1 pulser coil. The pulser coil is used to time the engine. One of the lighting coils is used to feed your headlight which will vary in brightness depending on engine speed. The other is rectified and used to charge the battery in a similar way as explained above.

[Degsy]

When they break they smell god awful. Like a burning kitten.

[Stromper]

OK OK getting close....

To clarify in my own mind
Say (without wiring problems) you put a big shunting resistor on the 12V side of everything. Almost all the power would go outside and not through the SCR's as the drop would basically turn the rectified higher voltage and sink it to less than 12V?

In the stator winding itself what condition would cause more heating in them?

Does my possible (Loin cloth) inductance in them ever actually reduce the current running through them?

Can you imagine some backfeed that would cause a high voltage spike so much that it arcs through and fries the insulation? If this is true would a MOV spike protector maybe increase a systems longevity ?

We await your wisdom

[ZX-12R]

Say (without wiring problems) you put a big shunting resistor on the 12V side of everything. Almost all the power would go outside and not through the SCR's as the drop would basically turn the rectified higher voltage and sink it to less than 12V?

I'm not exactly sure what you are asking here but if the shunting resistor has a low enough value which would cause it to consume all available power from the generator then there would be virtually no current being shunted to ground directly from the regulator.

In the stator winding itself what condition would cause more heating in them?

As your load approaches and exceeds the power available from the generator, the voltage at it's output starts to drop and current increases. With the increase in current comes an increase in heat due to the resistive nature of the stator windings. Increasing heat also increases resistance which can compound the problem.

Does my possible (Loin cloth) inductance in them ever actually reduce the current running through them?

The inductance of the stator shouldn't change by any appreciable amount since the wire is wound around a stationary core with fixed properties. The coils themselves are not allowed to change their relative positions or increase their number of turns so there is really no mechanism for the inductance to change.

Can you imagine some backfeed that would cause a high voltage spike so much that it arcs through and fries the insulation? If this is true would a MOV spike protector maybe increase a systems longevity?

Are you talking about the high voltage side or the regulated side? While I've never run across a scenario like you are asking about, the most likely way I could see it happening would be related to a failure in the ignition system where the high voltage of the coils is back fed into the low voltage electrical system. It takes a very powerful arc to erode wire insulation and the average power found in the coils is not very large. It would be more likely that a spike would fry electronics in an ECU or related system. In either case properly installed MOVs would increase the likelyhood of the electrical system surviving such a spike.

[NobodySpecific]

I was describing a modern charging system on a motorcycle. Your XT350 doesn't have the same 3 phase charging system that modern motorcycles have. It has a stator with 2 lighting coils and 1 pulser coil. The pulser coil is used to time the engine. One of the lighting coils is used to feed your headlight which will vary in brightness depending on engine speed. The other is rectified and used to charge the battery in a similar way as explained above.

I was just trying to clarify the "nothing on a motorcycle runs on AC" statement, that's all

I'm a EE, I do have some idea of what's happening

[yesterdayze]

One part that seems to be missing from all of this that might make it a little more simple is frequency:

Gadget and zx-12r's already explained the phases and such so I will try to not repeat too much.

The stator is generally 3 phase as mentioned. This makes it more efficient, puts less strain on the rectifier and generally gives you more consistent ripple free output.

The big thing to remember though is that what comes out is DC voltage with a LOT of ripple. The battery acts as a big old capacitor to help smooth that out. Push the output higher than what the battery can output and you will start seeing that ripple again with the baseline being the highest voltage the battery can output.

In household AC the frequency is fixed around 60hz (60 cycles a second). Not so with the stator on your motorcycle. The faster you go the faster the frequency. With AC output one of the things commonly done to control brightness of lights, speed of DC motors etc is to do what is called PWM or pulse width modulation. You basically output a signal that goes from 0 volts to your peak voltage but vary how long it is on each time. Typically you then slap a capacitor on the other end to smooth it out and voila. Varying the frequency varies the voltage while keeping the current the same. This allows very accurate adjustment of the voltage without lowering the amount of current you can supply. The heavier the load, the more current is needed while the voltage stays the same.

In your stator you have basically the same effect after the rectifier and before the regulator. The rectifier redirects all negative voltage to one output and all positive to a different output. When you look at how a rectifier diagram looks it actually makes perfect sense:





Notice the arrows... Positive can only enter the bottom of the arrow and exit it in the direction it points. Negative cannot. Likewise negative can only enter the line side and go the other way. So obviously the end result is that positive will only ever come out one side and negative out the other. If you took that and put it straight to your battery you would be charging your battery with anywhere between 13 and 40 volts or so depending on how fast you are going. At 13 volts you would be fine as the ripple would be handled by the battery. At about 15 volts you would have minor ripple. Depending on the tolerance of your CDI and such by the time you started getting over 15 volts you would be burning things out and needless to say your battery would start to boil.

Good regulators can take excess voltage and convert it to extra current to feed power hungry things. The faster you go, the higher the frequency, the higher the frequency the closer together those wave forms appear and the end result is less of a dip between each phase resulting in higher voltage observer. The regulator uses PWM to chop the voltage it is getting to regulate the voltage without lossing current. As mentioned, when it has to chop it off it will get hotter as it is taking the brunt of that power and bleeding it off as heat by way of resistance to ground. So like zx12r mentioned, if the regulator is poorly designed too little load can overheat it just as fast as trying to get it to supply too much.

Stromper, it is possible, and really common, to have one side of a rectifier die. When this happens it can short the voltage coming out of that leg of the stator. This will definitely cause the windings, wire leading to the rectifier and such to overheat. Because most are 3 phase though the other legs will continue to supply enough and be rectified such that your bike will still run. Perhaps just as well from all appearances in fact. It ends up looking like the stator is at fault but every time you replace it you just burn it out again because it is really a faulty rectifier.

As for a big resistor outside the SCR. Current always flows to the path of least resistance. SCR's resistance varies slightly by heat and all that, but depending on how high the resistance of that resistor is odds are good the voltage would still just go through the SCR. Now don't misunderstand what I am saying, voltage will still hit the resistor, but think of it like water pipes. Put in a big pipe and flow water into a pool with it. Now stick a little pipe into the side going to the same pool. You'll still get water through the little pipe, but it won't stop the big pipe unless you make the little pipe that much bigger or block (open circuit) the pipe. Rough analogy, anyone that know electronics understands the pitfalls of the analogy but it is a good way to get an idea. That is also where you get the heat.... take the pipe analogy... smaller pipe with the same flow equals more pressure. Same voltage, lower resistance to ground equals more electrical 'pressure/current' which equates to more heat. V/R = I. Higher current through something means more heat unless that something is made for it.

High freguency rather than high voltage is more apt to burn through insulation. Usually a motorcycle won't do that short of a preexisting short.

An MOV is basically a variable resistor. I think it is Metal Oxide Varistor but someone can correct me if I am remembering incorrectly. Been a long time since I got my degree... now it is just a hobby and I don't have to know what just how haha....

In a nutshell an MOV sits parrallel to the voltage coming in and has such high resistance that for all intents and purposes it acts as an open component... BUT get a high enough voltage spike and it breaks down that resistance and more or less shorts out... that is the resistance drops rapidly causing the voltage surge to be clamped down to ground preventing it (hopefully) from harming other components.

[RandyO]

I do not know nearly as much about the mechanics of alternators and generators

[snip]

I know that car alternators are designed to allow air flow through them as a form of cooling. I imagine that motorcycle alternators would have more contact with metal to provide a heatsink.

ferget about car alaternators and big beemer & goldwing alternators, they are field strength regulated. they have no permenent magnets and only produce the electricity that is demanded

complete different design & concept than what Rich is askin about

[Kurlon]

I'm trying to remember who, but someone is making a R/R that disconnects stator feeds based on load. No load, no stators hooked up, no excess current to shunt to ground. Batt voltage dips, bring online one phase, need more bring a second online, etc. Mainly marketed towards racers as a way to get back some of the HP drag caused by a traditional charging system while still keeping operating voltage up on bikes with moderate runtime draw, aka EFI bikes spinning big revs.

[TheIglu]

When they break they smell god awful. Like a burning kitten.

It's the fur that stinks, shaved kitten smells pretty good.