Diesel generator excite /upgrade issues

[quabillion]

Ok, first post, hello to all. Now to the issue at hand. I have a Leroy Somer gen head mod#176427 / 90 and the mfg. label indicates "ACC excite" in the avr model number location. The generator does work right now but, A) i cannot figure out how it does work and B) i want to upgrade to an automatic voltage regulator. As it stands when the motor is started with no load on the generator the voltage is 126 at 61.023HZ. As more load is applied to the gen the voltage will drop in a quite linear fashon. At full load, voltage has dropped to 102 volts and 60.016HZ. This voltage swing has become quite unacceptable and I have been trying to upgrade from the capacitor based excitation to an AVR in order to get the stable voltage I want. I have done much searching and cannot find a wire diagram/theory of operation for this type of capacitor based excitation. What was found in the terminal box is 4 wires coming from the main windings, (these wires i am quite clear about their operation) and 2 more wires leading to a 70uf 500volt capacitor. No diodes, resistors, or anything else appears to be in the make up the excitation circuit, Just cap and winding, thats it. Also there are no slip rings on this generator. What i tried to do was remove the capacitor and connect these field to an sx460 avr, i also connected the avr to the output terminals, so 4 wires to the avr. First test, motor started, gen output at 3.6vac. Reverse the field connections and retry, same result. Disconnect avr and field flash the auxiliary winding with 20vdc and a 20 watt/3 ohm resistor for 5 seconds. This did improve the residual voltage up to 4.6vac from 3.2vac pre-flash. However this is still not enough for the avr to "bootstrap" the excitation circuit. I have also tried putting the capacitor in series and in parallel with the avr with no change in results. I just dunno I guess. With the aux windings connected back to just the capacitor the generator runs just like it always has with the predictable voltage drop.

All of this equipment is for my own standalone system, primary power source is solar PV, and the 6kva diesel gen is for backup and for additional overall system capacity. It does the trick as it stands but i sure would love to have that stable voltage..!

 

[itsmoked]

Have you looked in at the rotor? Does it have a small aux winding on it? To avoid slip rings they often put a 'reversed' generator on the same shaft as the main rotor. Then they put the diodes on the shaft and anything else they need. The result is they control the field to this aux generator to control what's spinning's output to the main rotor.

Can you tell if this is the case?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Add a little more capacity and the voltage will rise more or less linearly. live with the voltage drop as others have done. OR, try to jury rig a circuit to add a little capacity as the load increases.
The SX460 AVR puts out DC for an exciter. The capacitor excited generators are excited by AC. Kind of apples and bicycles. They don't inter chasnger well.
An SX460 may cost almost as much as that generator end. You get what you pay for. If you want more you will have to pay more. (For the generator end).
Some acquaintances ran an isolated sport fishing camp for years using those little capacitor excited gensets. Most people who use them are not as demanding as you are, quabillion. The sets are often not loaded fully and many users are not aware of the voltage drop issues. I am surprised to see Leroy Summer in this field. I have had good luck with their conventional sets.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[quabillion]

itsmoked; yes i can see 2 diodes mounted on the rotor and there is also windings on the rotor that the diodes are connected to. nothing else visible.


waross; When you say "add a little more capacity" are you meaning more capacitor capacity? If so i belive that i can rectify this issue with the remains of a previous attempt at voltage control. I have installed a current sensing relay on the output line and have it set to trigger at 20amps, this was used to energize a throttle kick up actuator. this did keep the voltage more acceptable but the HZ would go too high and my inverter would start to complain, so i just un-hooked it all but did not remove the components. could i say set the current sensing relay to add another capacitor to the one already in use, thereby bringing the voltage up when >20amp loads are encountered, and lowering it when the loads are <20amp. is this a feaseable jurry rig approach?

thank you both for your speedy and insightful responses

 

[waross]

I would certainly try that. You may also want to try tweaking the throttle kicker. It may be possible to adjust it to give less kick. yes, capacitor capacity. The voltage of these sets is controlled be the amount of capacitors connected.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[quabillion]

Update waross;
I installed a 3.5uf 450volt capacitor (metal case) onto the gen head, next to the OEM cap, wired it to be put into parallel when the load is >20amps, via the current sensing relay. i also found that the govner(sp?) is setup to maintain very tight rpm range, so even at full load my rotor rpm is a solid 1800. In my setup now, messin with the throttle just really affects the HZ, so no more throttle adjustments. Works like a charm. Perhaps one day i will expand on this to produce a 5 step system that would trigger a new capacitence level and thus new voltage output on 10amp "steps". 50amps is the full load rating, so 5 10amp steps. With my new setup I now have 2 voltage drop graphs, but the future 5 step system i feel will be supreme, and allowing for tighter voltage control.

Thank you for the help and getting me on the right path to my goal.

PS. I wasnt aware that i was being very demanding on the set, it is an "industry grade" machine, not a more typical "contractor grade" machine. The engine is 9.7kw and with a 6kw gen head i thought i was still in the green.

Anyway, thanks for skoolin me

 

[waross]

Hey friend, I got a little schooling too. That is the first time that I have heard of one of those machines being used in such a demanding application. I didn't think that type of generator would cut it in a demanding application, but you've shown me different. Thanks.

Bill
--------------------
"Why not the best?"
Jimmy Carter