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Alternator charging intermittently

RVFan671

Well Known Member
Need your help/ideas on what to prioritize to root cause my issue; alternator itself, voltage regulator, or wiring?

So I pulled my tail off of my RV4 to add doublers that were necessary on horizontal and vert stab. Plane hasn't flown since mid or early February. I had to crawl around in the tailcone which I figured could have knocked some wires loose but nothing found. I also added a bracket between alternator and an empty starter bolt. Otherwise I didn't touch the charging system while I was down for maintenance.

I planned to test fly last Friday but when I fired it up and went through checks, I was showing a draw and 11.5 volts or so, not 14.5 to 14.7 like usual so I pulled the cowl to test field and battery connection on alternator and any loose wires in tailcone. Everything tested fine but I noticed the ground wire coming off the shielded field wire and the alternator ground (both at alternator end) looked like they could have a break in the wire due to prior owner performing a weak splice. Well I decided I'd run the plane at least to see if it was charging and low and behold it was. I didn't fly it but ground ran it for 5 to 10 minutes charging the whole time even after flipping off my alternator switch and master and flipping back on.

I cut ground and power (for field only) back and spliced on new wires and better protected them. I plugged it all in and fired it up last night and no charge! Ran same test procedure of field and 12v at alternator back to battery. Now this time I wasn't confident I was getting power to the positive field wire. I would see 12v but then id move around and seemed to read 0 then move more and get 12v. Not sure if my multimeter probes weren't getting into the plug or if I had a wiring issue. So decided to chase the field wire back. Went to voltage regulator and it seemed to have 12v when my master was switched on. Tested my alternator switch because it also seemed like it could be a culprit but it tested fine. Go back out to field wire at the alternator and it tested fine.

Fired up and the thing is charging again (like after my testing on Friday). Flipped alternator and master and did numerous restarts and it was showing 14.5v on one EFIS and 14.3 on the other (not sure why they differed and I didn't notice if they differed before or not).

So should I be pulling the denso 14184 alternator that has fewer than 30 hours on it? Or should I be checking voltage regulator and wiring to see if there is a break somewhere else? How do I test voltage regulator and wiring for this intermittent issue?
 
I had similar issue

I also have a -4 with a Denso alternator. A few years ago, I got intermittent cut-out of the alternator dropping to 12 volts then bouncing back to 14.5ish. In troubleshooting, I found the female side of the Denso plug assy had a broken spade receptacle cracked in half at the crimp. The other one for the warning light was also cracked, but not all the way. I did away with the receptacle, crimped on new terminations and made sure the wiring was really well secured to prevent vibration from causing the situation again. I also applied some silicon potting for extra measure. Those spades will crack in a minute when subject to vibration.
 
I had the exact same problem on a 7 we used to own. I spent weeks checking everything and finding several "could be" which I repaired. Each time it would charge and I'd think it was fixed but it wasn't. In desperation, Rather than just checking volts and continuity, I decided to take EVERY connection loose and physically inspecting each one. I started at the B lead connection to the alternator. It looked fine and I then twisted it to look at the other side and the connector came off in my hand! The plane had flown 400 hours without a problem but apparently the crimp just was slightly loose and it had been arcing inside the connector and burning the wire so it was gradually getting looser and looser. Lesson learned, twist, pull and tug on every wire.

Next, a friend with an 8 had identical indications. Myself and another A&P worked on it many times trying to isolate the issue including taking the alternator to a shop and having them run test it. After many additional hours of checking wires, grounds, voltage regulator, etc., the other A&P decided to just take the alternator apart. Danged if he didn't find one of the brush springs broken! It would work ok sometimes but then the brush would break contact and his voltage would drop to battery volts.

Hope this helps.
 
These are both very helpful. I fired my plane up last night and went for my test flight finally and alternator was charging the whole time. I haven't pulled the B lead off so I'm going to do that and probably crimp a new end on it too. The field crimps were new installed due to my initial troubleshooting already. I'll be keeping an eye on it too.

Any others, feel free to share your experiences. It is helping me learn and decide what might need further investigation on my part.
 
My bud found the CB wire connection wasn’t tight on mine while under the panel looking at something else.
 
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