MEP 002a sx460 AVR conversion 7.5 amp breaker trippping.

[herbertv2]

That's my plan I am going to try the 56 ohm resistor will a 5 watt resistor be enough?

Would feeding direct 12v power to the exciter field cause the field to overload the 5 amp breakers from L1 & L3 going to pin 7 and pin 8 on the AVR?

Also is it right that I have the avr picking up signal from L3 and L1?

I know the wiring for getting 220V is correct because when I fed power to the exciter directly bypassing the AVR all together I was getting 140 volts at both L1 and L3

 

[Triple Jim]

I really need to see a wiring diagram of what you have before I start recommending components or giving advice about why the 5A breaker tripped.

When the generator is running properly, there should be 240VAC between L1 and L3, and 120VAC between each one and L0. As I remember, that regulator can be configured to run at 120V or 240V.

 

[herbertv2]

There is how I currently have it wired, i'm thinking the reason it blew the sx460 was due to the one breaker not tripping till it hit 40 amps and it should have tripped at 5, but that brings the question why it was tripping the 5 amp breakers. I apologize for my chicken scratch I hope it it legible. my output box is wired the same as Rusty Studs. The a1 engine start relay is gone, I replaced it with a spdt relay that is contorled by the overheat and oil pressure safety switches.

 

[Triple Jim]

One problem I see is that the Flight Systems SX460 manual shows terminal XX to be the negative field terminal.

The only way I see that one or both breakers could trip is if the SX460 already failed.

From the Manual:

"To flash the field, the generator must be stopped and the field leads disconnected. Momentarily connect the field leads to a 12 volt battery for 3-5 seconds, observing polarity (positive to F+, negative to F-). Repeat a few times. CAUTION: Do not come in contact with the field circuit because a high-voltage “kickback” will occur each time the circuit is interrupted."

I think it's likely that the kickback mentioned caused the failure, since both leads to the SX460 were not disconnected during the entire flashing process. Getting current flowing in the exciter field and then switching the SX460 back in the circuit a few milliseconds later with the relay could have exposed the regulator to a several hundred volt spike.

Is this a real Flight Systems regulator? If so, I'd talk to a technical guy at the company and ask how you can flash the field without damaging the regulator. According to the manual, you shouldn't have to flash the field every time you start the generator. If you really do, and want to keep doing it with a pushbutton, I think you at least need to use a big schottky diode across the field terminals to absorb the kickback so the regulator doesn't see it.

The "kickback" happens when you get a current flowing in a coil and then suddenly open the circuit, causing a high voltage spike. It's what makes a spark coil work in a breaker points ignition system.

The Flight Systems SX460 manual is here: https://www.flightsystems.com/pdf/model-460-manual.pdf

 

[herbertv2]

No I have the cheaper Chinese version. Kinda glad I did now, was sorta hoping to get it running with the Chinese version and if I had issues with them failing I'd buy the more expensive Flight Systems unit.

Hmm so does XX = F2 and X = F1? If that is true That is how I wired it up trying to running it with out flashing the field and got nothing.

 

[Triple Jim]

The generator's schematic shows F2 as the positive field connection. The SX460 manual shows "X" as positive. This appears to be saying that X should be connected to F2.

I don't claim to know much about the SX460, and I have no idea if all the clones are accurate copies. Also, I've never seen any of these in person.

 

[herbertv2]

I wonder if energizing the exciter field backwards and when the relay would switch things back to the AVR could cook the AVR too.

the only reason I redid the engine control and the exciter controls in the first place was due to the backfeed issue on the A1 relay and triping the 7.5 amp breaker.

 

[herbertv2]

Still nothing, I flashed the field as per the instructions. by disconnecting the field from the sx460 flashed the field with the generator shutdown, hooked it back up started it not generating power. I have a 56 ohm resistor wired in now on the flash circuit, debating now to wire the relay back in while making sure the polarity matches up, but I'm concerned now if that will fry the sx460 again.

 

[herbertv2]

The residual magnetism seems to only create about 1.2 volts, so I excited the field with the generator running but with the sx460 disconnected to save from frying it, the generator output is 251 volts, with the resistor wired in exciting with 24 volts, exciting with 12v the output was 248 volts. It seem the generator is still good but not holding enough residual magnetism to start the sx460

 

[Triple Jim]

...debating now to wire the relay back in while making sure the polarity matches up, but I'm concerned now if that will fry the sx460 again.

If you try it again, use a Schottky diode across the field terminals to prevent the spike when it gets disconnected from your flashing circuit as I suggested above. It's obvious which way to connect it, since the wrong way will cause a short circuit. A reasonable diode might be something like a SB360 (link to Mouser page) I can't guarantee it will prevent a problem, but it's the usual way to deal with spikes like this.

 

[herbertv2]

http://www.smc-diodes.com/products/data/15SQ045 N1007 REV.B.pdf will that work just asking because I have 2 of them, and a bunch of 1n4007

 

[Triple Jim]

Yes, it's a bit healthier than the SB360 too. The standard silicon diodes aren't as fast as a Schottky for clipping spikes.

 

[herbertv2]

I tried f1 on the anode side and f2 on the cathode side and tried it, it would make about 30 volts power, and trips both 5 amp breakers on l1 and l3 that go to pin 8 and 7 on the sx460.

 

[herbertv2]

risking the sx460 I tried it without the diode again, it only trips the breaker from l1 the starts to generate power wildly got it shut down just as the voltage went over 200 on l1, last time I think what made the sx460 fail was the bad breaker that hit t he sx460 with over 40 amps on l1

 

[herbertv2]

Do you think changing it over so it monitors 120v instead of 220v change anything?

 

[Triple Jim]

I tried f1 on the anode side and f2 on the cathode side and tried it, it would make about 30 volts power, and trips both 5 amp breakers on l1 and l3 that go to pin 8 and 7 on the sx460.

As I said before, if a breaker trips, the regulator has already failed. There's no way it should draw that much current if it's working right.

Do you think changing it over so it monitors 120v instead of 220v change anything

I doubt it, but that's a question for the manufacturer.

 

[herbertv2]

same result I'm thinking what ever nuked cvt1 is taking out the sx460 as well. it just blows my mind if you apply power directly to the exciter field it makes lots of power, but you install the sx460 the avr dies... found out the 56 ohm resistor limits the voltage from 12 down to about 5.5 volts under load exlplaining why with the resistor it was generating around 45 volts on l1, straight 12v increased the output to 145 volts on l1

 

[Triple Jim]

In your system, the regulator is connected directly to the exciter field, and is powered from the output lugs of the generator, right? If so, other than your flashing circuit, there's nothing else connected that could cause the failure of your regulator.

 

[herbertv2]

could it just be that the genset is wore out? that it don't create enough power from it's residual magnetism to start with out being excited? ANd the process of exciting it is what is doing the avr in?

the genset is painted tan and have read somewhere that the tan ones were overseas ran in the desert, which shortens the genset life? its has 1204 hours on it. and at least 200 to 400 of that I know was at 100% capacity running block heaters and oil pan warmers in the dead of winter.

Tired of throwing money at this generator, hoped an actual flight systems sx460regulator would have been the fix but seem even it failed.

 

[Triple Jim]

What you said does not sound likely. As I said, I believe that sending flashing current through the exciter field, then cutting it off while switching it to the regulator with the relay is a problem. Are you sure you've disconnected all the other wiring from the field circuit, so that it's exactly as in the diagram on page 3 of this thread?