Re-energise an Old Newage 250 KVA Generator?

"Dorman engined" or did you mean "Lyndoor^TM engined"? _{sorry couldn't help myself, its Friday afternoon}

Have you checked the output of the "separate small ac generator inside at the back end" from the output terminals of the small AC gen, through the diodes to the rotor?

Hi

It really does have a Dorman engine - proudly says all british made.

Please how do I get to check the output of the small ac generator. its output coils and diodes are on the spinning shaft.

There is a bakelite? box mounted on its field coils.

Westray,

"Please how do I get to check the output of the small ac generator"

Use a multimeter.

KJK

Please check all wiring of excitation system for loose connection. Measure voltage directly on alternator terminals using a multimeter.

For verifying if the exciting system if working properly, you must disconnect the automatic voltage regulator (all connections) and apply a 12V DC on the alternator field and check if voltage is obtained. And then you can have an idea about the problem.

Hi and thanks for the help.

The alternator terminals are in heavy case above the alternator tight under the fuel tank. Not sure how I get to them without dismantling a lot. However I could get to the other ends of the cables inside the control box.

The exciter alternator has a bakelite? box mounted on the field coils. is this the AVR? I have not tried to open it up yet, as it is not obvious how it opens. It looks like there might be 2 small trimmer screws on the cover.

On the outside of this cover is a glass fuse (intact) a resistance and some connections.

The control box instructions say "hold overide button in to start and wait for the safety circuit light to come on". It starts fine but this safety circuit light does not come on and none of the lights to indicate under or over voltage etc come on.

I am going to look inside the control box next in the hope there is a relay that is not making contact after starting up. Could the exciter circuit be disabled until the safety circuit has come on?

Hi and thank you.

That is a really clear explanation. It confirms my basic understanding of what I thought I was looking at. I think the message I got with this generator some years ago from the utility company, who had it as a standby, was that they had trouble starting it. I certainly had no problem starting the engine itself.

I now suspect they meant they had trouble getting it to generate because it was very seldom used (or even started), so would have lost its residual magnetism.

I will endeavout to follow your clear instructions.

Just two queries:

1. Am I right in assuming the AVR will be the bakelite box inside the alternator casing mounted on the stator of the exciter?

2. Can I test the diodes in circuit or will enough current flow elswhere to confuse the result?

I will report back in a few days and thanks again.

1) I think the bakelite box is the AVR since you said that there was some potentiometer to regulate the voltage and the gain. To make sure, there should be 2 wires going from it to the exciter field.

2) The diodes should be tested out of the circuit preferably. You can test the whole bridge (6 diodes) by disconnecting the 3 phases from the exciter and the 2 wires going to the main field. There will be One or two other components which are the Fly back diode and a surge protector (not all models have them but the Newage alternators will have them). If the brige shows a failure like a short somewhere, then disconnect these extra components and check again. They might be faulty and they will cause short circuit of the field current which will prevent the field current buildup. if your are not sure about the checking of this unit, get help from an competent electronic engineer to check it.

Hi The Aggrekko plant plate said it was a Newage generator, so that was what I put in the initial heading to this query however I have discovered the generator is in fact a Dale. The 3 -phase bridge rectifier on the shaft consists of two aluminium discs with the stud diodes mounted in them. It is not easy to be sure but I do not think there are other components on these plates. I disconnected the main rotor field leads from their posts on the output side and tested from one phase input to the output side with the diode test function on a DMM. I did this for both output connection posts. As hoped, I got 480 (approx) millivolts as the reading on each (with the leads reversed for the negative side) and open circuit each time with the leads the wrong way round. From this I figured the rectifier section is OK. The field windings have a resistance of about 2 ohms measured with a DMM. I flashed the field windings with 12 volts for a few seconds twice. A lot of current initially flowed judging by the spark, but the wire did not get hot so I assume this was just inrush, then limited by the magnetism produced. I then reconnected the field wires and started the engine. Still not generating but the voltage flicking up more than before. I have looked more at the exciter. You advised the there should be two wires feeding the stator. it is a multicoil unit and it looks like the separate stationary coils are wired separately back to the control gear bits on its outside. so there are not two wires in and out but several. There are two separate "control" units one each side mounted on the stationary coils. They are different. one has a fuse (intact) and a fixed resistor and the 2 possibly trimmer screws and several wires connected in a circular pattern. the other side has a strip connector with two separate sets of wires and an adjustable rehostat. I am trying to work out if the "safety circuit" (which is not lighting up) on the main control and monitoring board reacts to the generator coming up the voltage etc of if it has to initiate that process by flashing the field through the AVR. is it possible to add photos to help this discussion? Over to you for more thoughts/suggestions please.

GA from me, great info LAA!

Hi again.

I have already posted more thoughts today (attributed to "guest" as I was not logged in when I started) but here is more, corrected and updated info.

There are seven black wires that come to the "AVR" (assuming that is what it is) from the main body of the alternator. I do not know if they originate from the control panel or if some are phase wires from the main stator windings.

The AVR is in two parts, one each side of the exciter stator. There are, as you said, just two wires going into the exciter field coils, so I will be able to energise it independently. I have not yet removed the two AVR units as I need to mark up the wires first.

I have not worked out how seven wires are used unless the AVR is monitored from the control panel. Could it also have an auto flash on start up circuit in there?

I flashed the main rotor field yesterday as instructed.

I now have 25 - 30 volts across the phases at the main output of the unit. This not seen on the control panel voltmeter but is there when I put a DMM on the output connections.

I reckon this is the voltage produced by the residual magnetism I put in by flashing it. ( I had this voltage output from a 30 KVA brushed alternator (also ancient and needed flashing) before I sorted the exciting voltage section on that machine)

All this suggests that the AVR could be faulty. I would like to take it out so I can get to the exciter field wires and put DC in there as you advised.

In your post you said to mind the polarity on the DC input to the exciter field. I do not see at present how to identify which wire should be + unless I can identify the rectifier section of the AVR and hence the + output. I do not have it off the machine yet but parts of the AVR units appear to be sealed boxes so without breaking it I may not see the diodes.

It then occurred to me that it maybe does not matter which is + as the DC field coils are there to produce an AC output from the rotor and this should work either way round.

try to excite the inner core via a 12 volt battery

if you know how

generators tend to lose their magnetic field when stored for a long time

exciting the inner field via battery or A.V.R. usually does the trick

but check your terminals carefully

do not energise the wrong way

Just a conclusion to this thread.

I followed LAA_Lucke's advice. Flashed the rotor field, tested the diode bank, bypassed the AVR and tried a 12v input to the exciter field.

This worked so I was confident to replace the AVR.

A new AVR is now fitted and the machine is working just great.

So thanks for everyone's input and help.