Overheating voltage regulator B

The iS engines have a 600W stator (3 phase generator) mounted to the end of the crankshaft.  The stator itself is split into 2 parts, 200 W for the primary functions like 1 injector set and 1 spark plug set, the fuel pumps, and a few other things.  There is not much electrical load, it looks after the main parts that keep the engine running.  The big part of the stator, some 400 W, also handles 1 injector set and 1 set of spark plugs with that it has a massive amount of energy to charge all the battery, run all your electrical needs with a lot to spare.  (approximately 30 amps worth) Here is where it gets interesting.  The A regulator, the one that the 200 W is connected to, is well balanced and the regulator has no issue to handle this power.  The B side however runs into some huge issues as it carries the big loads and when you do not consume them it has to do something with that energy.  We need to note that these are what are called shunt regulators, which means all the energy that is not used must flow into the ground.  If we have too much energy flowing, if it has little to no cooling air on the wires and the ground plate that the regulator mounts on...well things can get toasty, they fry, the burn, they can fail.  Sling and Vans have it right, if you have a very light load on the system you have to address the heat of current flow to the ground, this is where the optional heat sink can really help you.  

You can check out how these work in some other publications.  Check the net, this is a common issue in motorcycles with the same type of electrical systems.  In some aircraft the fuse boxes are tucked away with almost zero air flow, the results are not happy ones in that you may have failures due to the lack of cooling of the regulators. The A, don’t worry about it.  The B one, yup, that one can fail if you do not address the energy flow.

Cheers

just a note that I should have made clear.  The fuse box is what shuffels the power.  It is the computor that runs the injectors and sparks, it splits this up so one side only handles 1 set of each for reducndnecy.  The power from the stator split is due to the fact that the A side computor and related bits it controls draw a lot less thant the B side (the 400 watt side) All the battery charging, and draws you put on the aircraft, will be from  that path.  

Cheers

The 915iS has the same regulator but now that there's a new 24 volt option, how will that affect overheating since it is 800W? Is the new Rotax 915iS C24 also using the shunt regulators?

Edit to answer my own question: The C24 only uses a shunt regulator to supply 12V to the ECU and engine components but the airframe bus is fed 24V via the DC-DC converter which is most likely a switching regulator, because the voltage is too high.

Rotax Wizard wrote:

The iS engines have a 600W stator (3 phase generator) mounted to the end of the crankshaft.  The stator itself is split into 2 parts, 200 W for the primary functions like 1 injector set and 1 spark plug set, the fuel pumps, and a few other things.  There is not much electrical load, it looks after the main parts that keep the engine running.  The big part of the stator, some 400 W, also handles 1 injector set and 1 set of spark plugs with that it has a massive amount of energy to charge all the battery, run all your electrical needs with a lot to spare.  (approximately 30 amps worth) Here is where it gets interesting.  The A regulator, the one that the 200 W is connected to, is well balanced and the regulator has no issue to handle this power.  The B side however runs into some huge issues as it carries the big loads and when you do not consume them it has to do something with that energy.  We need to note that these are what are called shunt regulators, which means all the energy that is not used must flow into the ground.  If we have too much energy flowing, if it has little to no cooling air on the wires and the ground plate that the regulator mounts on...well things can get toasty, they fry, the burn, they can fail.  Sling and Vans have it right, if you have a very light load on the system you have to address the heat of current flow to the ground, this is where the optional heat sink can really help you.  

You can check out how these work in some other publications.  Check the net, this is a common issue in motorcycles with the same type of electrical systems.  In some aircraft the fuse boxes are tucked away with almost zero air flow, the results are not happy ones in that you may have failures due to the lack of cooling of the regulators. The A, don’t worry about it.  The B one, yup, that one can fail if you do not address the energy flow.

Cheers

I've been doing some more research to try to understand this and after reading https://www.apriliaforum.com/forums/showthread.php?240785-Facts-about-shunt-based-regulators I have learned that the waste of power is caused by high-resistance SCRs being used instead of low-resistance MOSFETs and not because current is being "wasted" being shunted to ground. The excess energy isn't actually being dumped to ground and shorting a PM alternator isn't like shorting a DC generator. A completely shorted PM alternator actually has no magnetic drag! So an ideal shunt regulator is exactly as efficient as an ideal series regulator. The heat generation is a factor of how much current flows through SCRs (with series regulators, high-load means high current through SCRs, with shunt regulators, high-load means low current through SCRs).

In other words, a shunt regulator does not use the stator windings as a resistive "dump load" like I thought.

So please ignore my previous misleading claims based on this common myth.

On my sling 2 912iS the connector out to stator wires look overheated. I took the plug apart and it looks overheated inside the connector to the stator. From the SI 915i-006 the connector change out is optional but from the observations/inspection it looks like it should be mandatory. Could not find anything except this Si 915i-006. Is there any other info on the connector besides this Si ? Any others have observed hot plugs?