MEP 002a sx460 AVR conversion 7.5 amp breaker trippping.

[herbertv2]

Ok i have my Mep rewired for a sx460 AVR, now it keeps poping the 7.5 amp breaker on the front of the machine and shutting down. I removed P60A from the A1 relay. That stoped poping the breaker, but the engine will only keep running when held in the start position, and then the generator will only put out 0.8 to 1.1 volts AC. When reconnected the volts jump to about 30 just as the breaker pops.

I read about there needs to be a 50 ohm resistor wired into the field wiring to prevent the breaker from tripping, where should i wire the resistor in? or is there another solution?

 

[rustystud]

I had the same problem with mine after converting it. Right now I'm redoing my whole conversion. There is a feedback problem from "A1" the starting relay. The stator needs 12 volt to excite it so I'm going to use one battery to supply this and eliminate the whole "A1" relay. Mine would work and work great, but there where times when the breaker would pop-off and there you would be with no power. Totally unacceptable in an emergency generator !

 

[herbertv2]

I had the same problem with mine after converting it. Right now I'm redoing my whole conversion. There is a feedback problem from "A1" the starting relay. The stator needs 12 volt to excite it so I'm going to use one battery to supply this and eliminate the whole "A1" relay. Mine would work and work great, but there where times when the breaker would pop-off and there you would be with no power. Totally unacceptable in an emergency generator !

I was following your conversion.

Though if I under stand right A1 also controls the two shut down features protecting the engine from overheating and low oil? I was thinking possibly adding a 24v to 12v step down transformer, and a spdt relay and or diode to isolate the flash circuit from the a4. though it seems the a4 needs power from the field circuit to function when I remove the field wire from the relay the engine wont keep running., I need to take a better look at the wiring diagram and draw what I'm thinking down on paper to make sure it will work.

 

[Triple Jim]

If you're trying to get from 24VDC to 12VDC, look for a DC to DC converter with the right current capability and input and output voltages for your application. There are very inexpensive ones available these days from various electronics suppliers and auction sites.

 

[rustystud]

I was following your conversion.

Though if I under stand right A1 also controls the two shut down features protecting the engine from overheating and low oil? I was thinking possibly adding a 24v to 12v step down transformer, and a spdt relay and or diode to isolate the flash circuit from the a4. though it seems the a4 needs power from the field circuit to function when I remove the field wire from the relay the engine wont keep running., I need to take a better look at the wiring diagram and draw what I'm thinking down on paper to make sure it will work.

I had already considered all that. There are just too many functions that the A1 relay controls. So I plan to add a relay that will take the control currant from the engine sensors to shut-off the fuel control solenoid. If I could just figure out where this feedback problem is I could eliminate it, but so far it has eluded me !

 

[rustystud]

If you're trying to get from 24VDC to 12VDC, look for a DC to DC converter with the right current capability and input and output voltages for your application. There are very inexpensive ones available these days from various electronics suppliers and auction sites.

At this point I will just take a feed line off one of the batteries to power a simple relay that will feed the regulator until the crank switch is off.

 

[Triple Jim]

I'm sure that'll work fine, RS. I posted about the DC-DC converter for Herbert, when he said he was thinking of using a transformer to step down 24VDC.

 

[herbertv2]

After looking at the wiring diagrams, I think I'm going to rewire it like you, add a relay to control the fuel control solenoid, to retain the engine protection. and Use a push button with a diode to control the Flash circuit and to isolate the field wiring from the 24V to 12V converter. Not sure if the diode would be absolutely necessary, but I like it being there to prevent any feed back from the field wiring going into the 12v converter, when flashing the field.

The feed back almost has to be coming from the sx460, what confuses me is disconnecting the field from A4 should only disable the flash feature, but it also seems to stop the engine from running too. So I'm not sure if I have two issues now or if it's all related to the feedback to a4

 

[rustystud]

After looking at the wiring diagrams, I think I'm going to rewire it like you, add a relay to control the fuel control solenoid, to retain the engine protection. and Use a push button with a diode to control the Flash circuit and to isolate the field wiring from the 24V to 12V converter. Not sure if the diode would be absolutely necessary, but I like it being there to prevent any feed back from the field wiring going into the 12v converter, when flashing the field.

The feed back almost has to be coming from the sx460, what confuses me is disconnecting the field from A4 should only disable the flash feature, but it also seems to stop the engine from running too. So I'm not sure if I have two issues now or if it's all related to the feedback to a4

I'm sure it's the feedback. I like your idea of using the diode too.

 

[herbertv2]

well the feed back problem is clearly the sx460 It don't seem to like having a flash circuit wired in with it almost acts like a dead short in the field wiring when you try to flash the field. I'm going to sry using a relay that will isolate the sx460 from the field wiring while flashing, and when the flash button is release it should switch it back to it will report on how that works.

 

[Isaac-1]

Do you have polarity of F1 and F2 wired correctly? (I think the common SX-460 uses the X and XX nomenclature)

 

[herbertv2]

well I just destroyed the sx460... or perhaps it was faulty to begin with not sure but it just toasted one of the transistors mounted to the heat sync. I powered up the flash circuit it started to make power then POP! just as I was releasing the flash button, when the voltage went over 100 volts, and back down to nothing, also discovered the 5 amp breaker I installed in the line going up to pin 7 on the AVR did not trip like it should have , I put 5 amp circuit breakers on both legs going to pin 7 and 8. I had the 5 amp breaker tested and it would seem it is a mislabeled breaker it trips at 40 amps...

 

[herbertv2]

yeah I tried wiring the field both ways, f1 is x and f2 is xx right? that how I initially had it wired up them figured perhaps I was wrong and tried the other way. If I disconnect the field from the sx460 and give the field 12 volts the genset makes 140 volts on each leg.

 

[Triple Jim]

What does your present flashing circuit look like? Is it as original, with 24v being applied through a 56 ohm resistor?

 

[herbertv2]

No the Flash is now 12v reduced with a 24v to 12v via a 10 amp converter that gets it's power directly from the 7.5 amp breaker, connected to a SPDT relay controlled by a push button to isolate the field from the SX460 when flashing, when connected directly to the SX460 field wiring via the push button it kept overloading the converter and tripping it's internal overload breaker so I added the relay.

After the sx460 failed, I removed it, and hooked the flash circuit up by itself to make sure the flash field wasn't to much draw on the 12v converter and eliminate any chance of a short or errors in the flash wiring, and the generator immediately jumped right up to 140 volts like it should when flashing. I have a new sx460 ordered now.

I double checked the volatages from the batteries I'm getting 24.3 volts, and the output from the converter is 12.1V

 

[rustystud]

No the Flash is now 12v reduced with a 24v to 12v via a 10 amp converter that gets it's power directly from the 7.5 amp breaker, connected to a SPDT relay controlled by a push button to isolate the field from the SX460 when flashing, when connected directly to the SX460 field wiring via the push button it kept overloading the converter and tripping it's internal overload breaker so I added the relay.

After the sx460 failed, I removed it, and hooked the flash circuit up by itself to make sure the flash field wasn't to much draw on the 12v converter and eliminate any chance of a short or errors in the flash wiring, and the generator immediately jumped right up to 140 volts like it should when flashing. I have a new sx460 ordered now.

I double checked the volatages from the batteries I'm getting 24.3 volts, and the output from the converter is 12.1V

I haven't worked on my generator project for several months now (trying to get the deuce ready) . I'm beginning to wonder how the SX460 handles the flashing circuit. Does it ground the signal ? If it does that would explain the overvoltage I kept having. I have also fried over three SX460 modules now. This is getting expensive. I should have just left it with the circuit breaker bypassed. It actually worked then.

 

[Triple Jim]

I wonder if the regulator doesn't like being suddenly disconnected by the relay contacts when it's trying to supply current to the exciter field. Flight Systems said their regulator shoudn't need to have the field flashed, since residual magnetism is enough to get things started. Maybe this isn't the case, but that's what they said. If it really still needs to be flashed, how about flashing with a small current, limited by a resistor like the original system did, and don't disconnect the regulator, instead of suddenly opening the regulator's output with a relay and supplying high current 12v directly to the exciter field?

 

[herbertv2]

Leaving the fields directly connected to the sx460 and supplying a flash current creates an overload on the flash circuit. The the sx460 don't seem to get enough power from the resdidual magnetism usually only around 1.5- 3 volts. Something else I noticed was that the one 5 amp breaker that was working correctly that I have on the lines from L1 and L3 that feed pin 8 and 7 on the avr, if I used an unfused connection directly from a battery to attempt to flash the field, would trip I did that when I thought the 12v converter wasn't supplying the required power to flash the field I did that as a temporary test.

 

[rustystud]

I was unable to get any power from my MEP-002A without flashing the field. The generator doesn't hold any magnetism that I can see. At this point I just might try and use two large capacitors and use them to control the field. A lot of cheap generators use that system. You just need to get the correct amount of capacitance needed to hold 120 volts. My small 16hp Beiggs@Stratton 10KW used two 56uF caps. I'm really tired of buying new SX460 boards !

 

[Triple Jim]

Leaving the fields directly connected to the sx460 and supplying a flash current creates an overload on the flash circuit.

That's why I suggested limiting the flash current with a resistor like the original circuit did. I get the impression you're connecting 12VDC directly to the exciter field, but maybe I'm wrong. I have no idea how much current is needed to get the generator working, but with a 24v supply, the 56 ohm resistor the original system used will limit the current to less than 1/2 amp even if the field is shorted.