A11 rebuild

[shanekarl]

While Peter was out at the farm this weekend he suggested we open up my A11 and check it out and see if it needed to be rebuilt. To be fair my generator was producing power fine at this point so this was preventative maintenance to ensure it does not fail when I need it; it turned out to be a great precaution!

After checking the capacitor we found it was reading 20.69uF and did indeed need to be replaced - it had a good life being that was made the 37th week of 1977. In addition to the reading of the capacitor we found discoloration on the transformer and the the H1, H2 and X2 posts on the transformer had become cold soldered and the wires just pulled off them. The good news is the transformer tested good.

I had ordered a new cheap but equal spec capacitor last week from Zero just incase we needed it : https://www.zoro.com/dayton-run-capacitor-20-mfd-440v-oval-2mdz2/i/G2015623/#specifications

While working on the A11 Peter also put a fuse between the capacitor and transformer so that if the capacitor ever does fail it wont cause the transformer to burn out. After the rebuild the capacitor tested 20.04uF.

Peter resoldered all the connections on the transformer and we reinstalled the a11. Before firing up the generator we also tested my excite coil and it read 2.95ohms (very good condition). We fired the generator up and it worked perfectly.

 

[peapvp]

I am going to put my 25 cents in here as well.

First, I would like to thank Shane for his hospitality!

Over the years we have had multiple SS members with their A11 failing. It was with this knowledge that I had advised Shane to purchase a C2 Capacitor from Zoro before my arrival.

Mouser still sells the original C2 from Cornell Dubilier, but at over US$ 400 per piece now. They have 4 in stock. So Zoro is the more cost effective solution.

This was the first time that I was able to get involved before a bad C2 burns up Transformer T2.

As I had expected, C2 dries out over a period of decades. During this drying out period, C2, which is directly connected to T2 with two of the 4 leads, becomes a short, not in in terms of actual resistance, but impedance (resistance with AC Voltage)

This lowered impedance starts to heat up T2, which in turn first starts to loose its solder connections from the heat. The actual wires are attached to a little plate with a single wire hook which is soldered to T2. Because this little wire on each plate is rounded forming a hook, the connection doesn't come off T2 but starts to make poor contact. The repeated heating of T2 de-solders these little wires with the junction actually becoming a cold solder joint. Because of the hook form they stay "connected". A very very light wiggling will reveal the condition. In Shane's case, I was able to pull out H2 and X2 without de-soldering.
The solder connection was that bad.

In Shane's case we were able to save T2 for the moment, but we will see on how far the clear insulation coating of the copper wires of the windings of the transformer have broken down. My estimate is, looking at the excitation process when starting, that T2 should have quite some time left.

We caught this fairly early here in this case.

I would recommend to any owner of a 004A, 005A, 006A(slightly different A11) to inspect A11 very thoroughly while your system is still working and take preventive measure.

The A11 in Shane's case are fixed to the Genset with 6 Bolts which required a 5/16 Spline Socket with two 6" extensions. We soaked all 6 Bolts in WD-40 for 30 minutes prior to loosening these bolts.

I have new T2 replacements available on my website, in the case you need one.

We took care of all these items this weekend first and we will install our Auto Start Kit and ATS on my next visit to Shane.

Peter

 

[Triple Jim]

After checking the capacitor we found it was reading 20.69uF and did indeed need to be replaced

I have a feeling that I'm missing something. If it's a 20 uF capacitor, measuring 20.69 seems to be well within spec, at less than 4% high.

 

[peapvp]

I have a feeling that I'm missing something. If it's a 20 uF capacitor, measuring 20.69 seems to be well within spec, at less than 4% high.

I figured, one member would point this out.

The uF reading is done with a DMM. In this case a Radio Shack DMM I had for over 15 years now. The measurement range goes up to 100uF.
The capacitor is from 1977, week 37 - 45 years old. The Genset was reset in 2000 by ANG in Oregon, then painted for Iraq / Afghanistan after 9.11

Electrolytic Capacitors contain a liquid called electrolyte. Unfortunately, Electrolytic Capacitors loose their sealing ability in heat.
The two screw terminals have a cermic isolator which has a rubber gasket. Those two gaskets will not last forever.

This Genset was in storage for a very long time. The DMM performs a capacitance test. What we are concerned here is actually an impedance test.
The rule of thumb with the DMM is as follows:

Since this DMM does not do an actual impedance test at 50Hz or 60Hz, but a capacitance test at several KHz, the displayed result of 20.69uF has to be de-rated for 50Hz or 60Hz,

Then, the impedance, ESR and capacitance will be far below 10uF and closer to 0 to 5 Ohms in Impedance, posing a "short" on the transformer.

The actual Impedance test has to be done at the operating frequency of the capacitor in question and I have this test Equipment (HP) here in my Lab.

The case wold be different if this would be a DC Electrolytic Capacitor, but this is a AC Capacitor (Motor Start) in an AC Circuit.

Further more, with all due respect, Electrolytic Capacitors in DC circuits would need to be reformed after this many years of idling around if they were still fully sealed and what do think of how long a passive part is going to last?

The life expectancy and de rating information is listed in the manufactures datasheet:

Data Sheet

I wrote this up in another thread in 2019 on how a capacitor has to be de rated for life expectancy when not operated:
Link to thread from 2019

I hope this clarifies it!

Peter