For the non-computer automotive alternator mechanical relay system, the field is switched on until the system voltage reached an upper limit, about 14 volts in the cold, perhaps 13,.6 volts in the warm, at which point the field current is switched off until the voltage drops a small amount, when it then switches back on. There is no set frequency, but rather a dancing between limits.

 

For the non-computer automotive alternator mechanical relay system, the field is switched on until the system voltage reached an upper limit, about 14 volts in the cold, perhaps 13,.6 volts in the warm, at which point the field current is switched off until the voltage drops a small amount, when it then switches back on. There is no set frequency, but rather a dancing between limits.

Dear Friend

I understand that the rotor field current should be turned on and off based on threshold voltage values. However, my original question was about handling the initial rotor excitation current at startup.

Earlier, you mentioned that at startup, the rotor should be energized in a mechanical unload state by applying a low current first. Based on this, I suggested the following approach:

Gradually increasing the excitation current to prevent the stator from generating full power immediately. For example:

• Start with a 10% PWM duty cycle,
• Increase to 30% after 2 seconds,
• Increase to 60% after 4 seconds,
• Reach 100% after 10 seconds.

Is this approach correct? What would be the best method to handle the startup current of the rotor efficiently?

Thanks again for your insights and guidance.

 

Somebody may have said that, I do not think that I said it. Possible, but if I did, ir was in error. I do occasionally make errors.

 

I'm a bit confused about the best way to handle the rotor's startup current. What would be the most effective approach? I’d really appreciate any guidance from you all.

 

Since we really don't know anything about your Generator, other than it has a Diesel-Engine,
one solution might be using a Tachometer to ramp the Voltage up vs the Generator's RPM.

What's wrong with the original, factory-installed-Regulator ?

What specifically gives You the idea that the "Start-up-Current"
must have special considerations given to it ?

What bad thing(s) will happen when the "Start-up-Current" is not "handled-correctly" ?

Why do You feel that a "Micro-Controller" needs to be employed to control the Current ?

What's wrong with simply delaying the Output-connection until the Voltage is stable ?

What are the Voltage and Current Output-Ratings of your Generator ?

Where are all of the manufacturer's recommendations ?
( Please attach all relevant PDF-Files, and at the very least, some clear Name-Plate-Photographs ).

After these questions are adequately discussed,
and some general guide-lines are established from the manufacturer,
then the method for controlling the Winding-Current can begin to be discussed.
.
.
.

 

Consider that the rotor in most alternators is a single coil electromagnet. And then know that the most common operating mode is the field being switched on and off to hold the sensed voltage someplace in the system within a set of limits. Also consider that really it makes the most sense to let the engine get up to the intended speed before starting to operate the alternator, which is the main load in a "generator" system like I think the TS is describing. I know that in my backup AC power system I always let the engine speed stabilize before engaging the loads. Probably that is applicable to a diesel generator system as well.

 

There is no point to using PWM , except at extremely low frequencies with an alternator exciter circuit. The inductance of the exciter coil is in the henries range, meaning the time constant is very slow. Thats why a simple on/off control just works. Its easy to run into loop stability problems with anything more sophisticated.

 

There is no point to using PWM , except at extremely low frequencies with an alternator exciter circuit. The inductance of the exciter coil is in the henries range, meaning the time constant is very slow. Thats why a simple on/off control just works. Its easy to run into loop stability problems with anything more sophisticated.

Kaindub makes an excellent point. The possible exception being if very tight regulation of the alternator output voltage is required. But there is a response time issue because of the exciter inductance, as "K" points out. For extremely tight regulation it is likely to require an additional regulation scheme after the alternator output. That is often provided by the "INVERTER alternators, which are actually, most often, a separate inverter following a DC output alternator. Much more complex, but much better regulation.