How was this bad science ?Jean was using ac voltage from a transformer and the volts from the motorcycle alternator is also ac volts.The only difference will be the frequency of the voltage. I look forward to your test results .
More charging info
- Thread starter worntorn
- Start date
- Joined
- Feb 10, 2009
- Messages
- 2,997
But why would the alternator get hotter when the current is shunted through the regulator or Zener, than when the current is going through a halogen bulb?
When connected, the bulb gets hot because of its power. Bulb power is the product of current through the filament and voltage drop across the filament. W=IV.
60 watts = 5 amps x 12 volts.
The rest of the alternator’s (e.g.) 10 amps current output goes through the ignition and the battery and some is shunted by the reg.
When the light is off, the regulator shunts 5 amps more than it does when the light is on. That will make the reg warmer, because there is a voltage drop across its components and more current is passing through them.
I don’t see how that makes the alternator hotter. The current going through its windings is still 10 A and the voltage drop across its windings has not changed.
- Joined
- Feb 10, 2009
- Messages
- 2,997
- Joined
- Jun 25, 2004
- Messages
- 929
It gets hot because, with a shorting regulator, the two output wires of the alternator are shorted together by the regulator. It is a similar situation as locking the shaft of an electric motor and turning the power on. The current draw to power the motor spikes until something gives, typically a fuse or a breaker. If there is nothing to relieve this spike, heat is generated.
In the case of the alternator, there is nothing to relieve the current spike and the windings of the stator become a heating element.
This only happens when the alternator is grossly oversized for the steady state current requirements of the bike, and the regulator is forced to short a significant proportion of the power generated to prevent an over voltage situation in the electrical system.
With a zener, the bled off power is converted to heat at the zener, hence why a zener is always attached to a heat sink.
Hope this helps.
Last edited:
Fast Eddie
VIP MEMBER
- Joined
- Oct 4, 2013
- Messages
- 21,721
I concur.
With a shunting type regulator, excess current leads to heat build up in the regulator.
With a shorting type regulator, (Podtronics, Boyer, even Tri Spark MOSFET, etc) excess current leads to heat build up in the alternator.
With an open type regulator, (like the SH775) you get neither as the excess current is essentially switched off at source.
At least that’s my understanding from reading this:
Last edited by a moderator:
- Joined
- Feb 10, 2009
- Messages
- 2,997
I guess you’re calling shunting the DC “shunting” and shunting the AC “shorting?”
Sorry if I’m repeating things and contributing to the thread becoming crazy, but how can switching the headlight off cause an excess of current in the alternator?
Last edited by a moderator:
No, initially Jean was testing why the podtronic was showing a short circuit .
- Joined
- Feb 10, 2009
- Messages
- 2,997
I’ve got a regulator box that shunts the AC.
Ok, so at 5000 rpm with the headlight on, how many amps are passing through the stator of a 10 A permanent magnet alternator?
Then I switch the headlight off. How many amps are now passing through the stator? Is a permanent magnet alternator not a constant current generator?
Fast Eddie
VIP MEMBER
- Joined
- Oct 4, 2013
- Messages
- 21,721
As is explained in the link, a shunt type regulator works like a trad zener set up in that it dumps any excess current to earth. So, as you say, the alternator is always producing 10amp (in your case) and if the headlamp doesn’t take it, the zener does if fitted. But if you’ve a shunt type regulator instead, that dumps the heat into the housing. So, no change for the alternator, but heat build up in the regulator.
If you’ve got a short type regulator, then when you’re not using all of your 10 amps, the alternator stator input legs are dead-shorted by the control circuit, effectively closing the gate to the introduction of more incoming power. This creates a heat build up in the stator. MOSFET work the same, but switch MUCH faster.
If you’ve got an open type regulator (like a SH775) then, instead of the control circuit dead-shorting the input legs of the alternator stator, it actually opens the circuit (or disconnects the alternator stator input legs completely. This totally takes the load off the alternator stator, allowing it to run a lot cooler.
Most of the above text is lifted from the GTiller article that I linked in post #65, it really is worth a proper read.
- Joined
- Jun 25, 2004
- Messages
- 929
No, it is not constant current - both current and voltage vary with rotor speed. The rating - in either watts or amps - is usually a peak, and typically occurs at a high rotor speed, say 5000-7000 RPM.
The power that the alternator generates has to go some where, unless the circuit is opened (series style regulator).
There was a graph earlier on in this thread that showed how current generated varied with rotor speed.
In the case of turning your headlight on and off, lets say you have a 60 watt halogen bulb, draws 5 A at 12 VDC. At high revs, you have lots of excess power to run this bulb and say the other 2-3 amps of power consumers that you are running, say an excess of 2 amps or 24 watts.
Shutting the head lamp off under the same conditions, now you have 7 amps or 84 watts of excess generated power that needs to be dealt with. For the sake of simplicity, let's say that power and rotor temperature vary in a linear fashion - you now have 3.5 times the heat rise you would have with the headlight switched on. If the delta T were 25C per amp (plus the ambient inside the primary, lets say 80C from engine heat and a hot day at 30C), your stator temp at with a 7 amp consumed load would be about 130C, where as head lamp off with only a 2 amp consumed load the stator temp would be 255C. That is enough to char the potting on the stator.
Note that the delta T in this case is a contrived number to demonstrate a point. Please don't use this as an actual. But is is likely not too far off....
And this is only with a 10A (120 watt) alternator. Start adding more watts, and the issue gets a lot worse.
maylar
VIP MEMBER
- Joined
- May 13, 2007
- Messages
- 4,213
I hear that, bro. "Someday" will be a rainy weekend in my garage. I have the knowledge and test equipment to do it right. I'd post results on my web page and link to it here for discussion.
When I'm having a day without back pain, which my doc says is coming soon...
- Joined
- May 7, 2005
- Messages
- 7,204
It is in TT's example, he said 5000 rpm not 5000 to 7000 rpm.
- Joined
- Feb 10, 2009
- Messages
- 2,997
The modern regs that are on the AC short-circuit the stator coils when voltage gets high, yes, so when shorted, the 10 amp current goes through the stator coils and some transistors in the reg.
The stator heats up in proportion to the current and the voltage drop across the coils. The reg heats up in proportion to the current and the voltage drop across the reg.
Is there something wrong in the above?
If you have a Zener on the DC, it short-circuits the DC circuit, often through the frame. There’s no real “earth” involved. The Zener heats up in proportion to the current and the voltage drop across the Zener. The rectifier heats up in proportion to the current and the voltage drop across the rectifier.
The stator still heats up in proportion to the current and the voltage drop across the stator. Unless there is less current going through the stator, it won’t run any cooler than with the reg that shorts the AC.
Is there something wrong with those last two paragraphs?
I have read the linked Gtiller stuff and I don’t find it convincing.
I can see that regulation by shunt or short can become unsuitable as modern vehicle alternators become more powerful, implying big amperage requiring big electronics and big cooling systems. Shindengen say as much on their website.
The stator heats up in proportion to the current and the voltage drop across the coils. The reg heats up in proportion to the current and the voltage drop across the reg.
Is there something wrong in the above?
If you have a Zener on the DC, it short-circuits the DC circuit, often through the frame. There’s no real “earth” involved. The Zener heats up in proportion to the current and the voltage drop across the Zener. The rectifier heats up in proportion to the current and the voltage drop across the rectifier.
The stator still heats up in proportion to the current and the voltage drop across the stator. Unless there is less current going through the stator, it won’t run any cooler than with the reg that shorts the AC.
Is there something wrong with those last two paragraphs?
I have read the linked Gtiller stuff and I don’t find it convincing.
I can see that regulation by shunt or short can become unsuitable as modern vehicle alternators become more powerful, implying big amperage requiring big electronics and big cooling systems. Shindengen say as much on their website.
maylar
VIP MEMBER
- Joined
- May 13, 2007
- Messages
- 4,213
The difference is something called source impedance. Any kind of shunt regulator needs a series impedance to limit the current. A transformer has virtually none, an alternator does. That's why Jean melted wires during his test. For a proper bench test he would have to have included the equivalent inductance and series resistance to simulate an alternator correctly. Inductance acts as a current filter, and it's reactance (resistance) is a function of frequency. A 6 pole alternator produces 300 Hz at 3000 RPM, not the 50Hz from an AC main. All in all, I call it bad science.
I really need to test my system on the bike and publish the results. What I would want to measure is the DC load current vs. AC alternator current at different load and RPM conditions. My gut feel (conjecture at this point) is that the alternator current is nowhere near the "dumps 10 amps" number touted in Grant's posts.
- Joined
- Feb 10, 2009
- Messages
- 2,997
If the stator gets hotter with the lights off, then more current must be going through it. Are you saying that’s what happens?
Or is it still 10 A, but the voltage drop across the stator has got higher?
Power (producing heat) is current times voltage.
I suspect Maylar has a better handle on this than I have. There must be people who know everything about it. Where are they!
It would be simple to measure the heat in the stator after a run with the stock setup then after the same run with a Podtronics.
My bike has both fitted.
I would do this with a fully charged battery, lights off, maybe a ten Mile run then immediately measure stator temp.
Let everything cool back to room temp, make sure ambient temp is the same +-2 degrees , then run again and measure
This method might be +- 4 or 5 c, but that shouldn't matter.
If the difference is minor, then the shorting/shunting is much ado about nothing.
If the pod regulated stator is 20c or more hotter than with Zener, then I would be concerned.
Glen
- Joined
- Feb 10, 2009
- Messages
- 2,997
Sounds sensible. If the series Shindengen was a bit cheaper, you could try that too.
maylar
VIP MEMBER
- Joined
- May 13, 2007
- Messages
- 4,213
With a shunt (or shorting) regulator, all the current from the alternator becomes DC load current when the output voltage is below the regulator's control point. No excess current is shunted to ground. The stator's temperature is indeed a function of the load (watts) that it's delivering. Once the voltage reaches the regulator's "regulation" voltage (maybe 14.2 - 14.5 volts), the regulator starts shunting current to ground, which will increase the stator's temp. How much is yet to be adequately determined.
With lights on, the alternator has to supply that current as well, which would also raise temperature. But with lights on the RPM at which the regulator "regulates" is higher because the AC voltage is lower. So the question is does headlight current produce more or less heat in the alternator at low RPM. This needs to be documented IMO.
Why not use one of the latest lithium starter batteries from Air batt or EarthX, these are the next gen of batteries and they can take a hammering compared to their predecessors. And I do believe they will easily accept 14.4V, as each cell controls its own charging cycle.
