# 6.5kva genset - catalogue of errors! no power, field flashing not working



## Rion (Jul 8, 2015)

Hi all, new here... i've been having a variety of problems with a 6.5kva genset made by a french company called SDMO (not recommended!), the engine is a yanmar L100 single cylinder diesel, the alternator is Mecc Alte, brushless, non-AVR, it's supposed to give 115 or 230 VAC (switchable) at 3000rpm. 

To give it its full title, its an SDMO SD6000E auto-start diesel, and was bought in 2013 as "brand new" although its much older actually an '07 machine which has sat around for a few years, surplace stock i suppose which eventually ended up on ebay where i bought it for a "good price".

I had some issues with it from day 1 but suffice to say (for now) that i overcame them and the genset ran fine up to 2200 hours

I live off-grid and rely on the generator to recharge my batteries and/or for heavy loads, which is why it has done a fair few hours. I've been extremely careful about regular servicing and remaining vigilant for any faults, this being my 5th generator!! I generally run it in 4-5 hour sessions in the evening, almost every day in winter, less in summer. Occasionally it might be run for 8 hours on a heavy working day requiring tools, etc but never longer than that. I've never known it to become excessively hot and it has plenty of air flow around it being basically outside with a shelter to keep the rain off.

In january of this year the wiring to the stop solenoid on the engine burnt out. I have no idea what caused this, whether the solenoid is faulty in some way, although i dismantled it and re-soldered the wiring and the plunger operates normally. However, since the wiring was direct into the solenoid itself and i had to prise it apart to do the repair, i was unable to stop the solenoid leaking when i refitted it. In an attempt to be able to at least run the generator manually, i made a bypass of the solenoid. Unfortunately due to my incompetence in refitting the fuel pump i failed to engage the throttle pin with the throttle lever properly and when i started the generator the engine raced to very high revs for the length of time it took me to pull of one of the fuel lines - about 30 seconds max. During this time i observed the exhaust getting red hot and flames shooting out of it... there was also a nasty burning smell.

I have to admit i didnt actually realize the mistake i had made with the throttle and so feared much worse things, like some kind of major engine failure. Being reliant on a generator almost daily (especially in winter) i went out and bought a relatively cheap petrol generator which i have been using since... and tried to forget about the other generator for a while! The following week my van engine blew up.. but thats another story!

In the last month or so i finally found time to have a look at the diesel genset. I found an alternative stop solenoid and fitted that to the injection pump, refitted the injection pump - correctly this time. The engine starts and runs great, the stop solenoid works and the wiring isnt getting hot. However, i discovered that there is no power from the generator/alternator. This i found surprising since the unit gave power just fine before i started having the problem with the stop solenoid.

So after some reading up i began to suspect it might need "field flashing". I tried feeding DC from the battery into the exitation coil. I tried 230V AC ("for an instant" as recommended by the Mecc Alte users manual for the alternator), neither of these methods worked. Then i discovered that the capacitor had a deep cut in it from where it had been cable-tied to the frame of the alternator by the manufacturers SDMO in their infinite wisdom... leading to wear caused by vibration over time. Great - so i needed a new capacitor... ordered one, it took two weeks to arrive for some unknown reason, i've fitted it today and still no joy! Have tried both DC and AC methods of excitation previously mentioned (oh yes, i tried the drill method also which did nothing)... so now at a complete loss. The capacitor i bought is not a direct replacement although it's the correct rating and almost identical in size/shape/orientation. Worth mentioning also that when i read about the DC method of field flashing, various guides all say to observe the correct polarity of the excitation coil... there is no polarity or colour-coding on mine.. both wires are black and the capacitor, both the old one and the new one, have no markings.

i know this is a long thread but thought it best to put down the whole story in case any of it is relevant, i will update the thread shortly with some pictures and more technical info e.g readings between coils, etc - just wanted to get it started for now and invite any suggestions as to what might have gone wrong

bye for now...


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## Rion (Jul 8, 2015)

*Pics and info...*

Hello again...

just did some testing with a multimeter:

4 wires coming off the windings are colour coded Red Yellow Green and White

(all resistance measurements taken with digital multimeter set to 200 ohm range)
R/Y resistance = 00.9 ohms 
G/W resistance = 00.5-00.6 ohms

infinite resistance between all other combinations of the four wires.

with genset running, the resistance between the R/Y or G/W combinations fluctuates from 00.6 up to around 20 ohms repeatedly.

resistance between the two excitation coil wires is 01.5 - 01.6 ohms

Voltage of windings while running:
first measurement i took after starting was G/W which rose to 1.2vac (multimeter in 200v range), then went down to 0.6vac and stayed there. Then took R/Y which was 0.6-0.7 continuous, even after stopping and starting the engine did not rise to 1.2v like the G/W did on initial startup. Then tried re-testing the G/W after stopping and starting and this time it did not rise as before.

on applying 12vDC from the starter battery to the prongs of the capacitor, which are connected to the excitation winding, the voltage rose to 9vac then settled down to 8vac, for 5 seconds, then removed DC wires and voltage fell back to 0.6vac. 
Repeated process with polarity of DC reversed, same thing happened but voltage only rose to 8vac then settled to 7vac, then back to 0.6 after removing the wires. 
This test was carried out on the R/Y wires, i didnt repeat the process on the G/W wires since doing this testing requires breathing in the exhaust fumes of the machine (wearing fume mask but still eyes were watering!) - another excellent bit of design from SDMO

I then started up the other generator i have and touched the prongs of the capacitor with 230vac, there was a bright blue flash and the alternator on the SDMO generator slowed down, there was no noticable change in ac voltage coming off the SDMO, although i was mainly keeping my eye on the AC wires so as not to electrocute myself! i also tried reversing the wires and this time noticed there seemed to be sparks inside the alternator at the moment i touched the AC onto it.... wont be trying that again! i wonder if this is supposed to be done when the unit isn't running? manual for the Mec alte alternator was not specific!

Finally, have attached a pic of the old and new capacitors side by side... theyre not identical but i would have thought close enough? There's a lug on the back end of the replacement one that wasnt present on the original - i'm assuming this is for mounting purposes and not an earthing point? never heard of a capacitor needing to be earthed and the old one certainly wasnt...

So that's it really, i've done as much as i can and hit a brick wall... hopefully this info will help someone point me in the right direction


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## Rion (Jul 8, 2015)

*screenshots from mecc alte manual*

Hi all, just looking at the specs in Mecc Alte pdf manual for the alternator, resistance values are given for the stator, rotor and excitation winding.. all i can glean is that my reading for the excitation winding seems a little higher than specified... my reading: 1.5-1.6 ohms, specified value: 0.91 ohms

as for the stator/rotor values i'm having a hard time making sense of which is which?! The wiring diagram isnt helping me much either! 

mine's the S20W-95 50hz


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## Rion (Jul 8, 2015)

*further testing...*

Hello....

a bit more info today but still no joy... 

one thing i didnt check was obvious ground faults... there is no connectivity to ground on any of the windings or the excitation winding.

Have inspected the diodes... no visual signs of deterioration. resistance measurement in situ shows 5 ohms either way, however with the multimeter set to beep mode, shows current flow one way, not the other. I'm told i have to desolder the diodes to test properly but am not willing to go down that road just yet as it will involve dismantling the alternator... i will if i have to eventually though!

tried feeding 12vdc to the capacitor/excitation winding for 12 second bursts repeatedly again today just to see if a more vigorous approach would do anything. Nope.

So i'm fully out of options now. I'm told it's cheaper to replace an alternator than fix it, which seems crazy to me as the cost of new one is about 800 euros.

i'll leave this post here.... later in the year i'll probably dismantle the alternator fully, see if that yields any info.

Bye for now


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