5 amp field circuit tripping

I think I've read most of the archives relating to this, and it seems there has been quite a few with this problem, with no single problem being the source of it.

I’ve had a continual intermittent problem with my 5 amp field breaker tripping on me. Don’t know if it was related, but some 50 hours or so ago, I was starting to get low amp warnings, and my amps were oscillating from 1-3 amps, and then climbing back up to 9-11 or so. It did this about a handful of occasions, but eventually the problem went away. Some 30 hours or so ago, I had my first 5 amp field trip on me. It did this twice, but hadn’t came back until about the last couple of hours. Now it’s gotten fairly bad. Three start-ups in a row, it tripped on me each time after start-up. Two other times, it waited until about 20 minutes into flight before tripping on me again.

B&C first suggested I try replacing my circuit breaker. I did, and that’s when I went 20 minutes before it tripped again. My alternator is a 1998 I think; it’s the L-40 (40 amp) alternator and at the time I was told they only used one wire going into two prongs. It was suggested I take that wire and run a jumper from it to plug into both prongs. I did that as well. Again, I went another 20 minutes before my 5 amp field tripped on me again.

Bill has been great to work with through all of this, and he’s still confident it isn’t the alternator or voltage regulator and that both will easily go to TBO. My whole set up only has 536 hours. I'm not the builder, but for the first 70 hours or so didn't experience this problem. My volts generally show about 14.2 when I’ve been monitoring it. Amps seem to be doing quite well too, with no more oscillating. I turn on and off electrical devices such as landing light, night lights, electric fuel pump, and nothing causes it to trip. The 5 amp field trip just does so at any time. I’ve tracked down the wires from the alternator to the circuit breaker, and can’t find any breaks are bare wire showing anywhere. The terminals and screws show to be secure.

Do you think a good electrical guy on cars, might be able to pinpoint my problem? I’m basically a parts changer, so anyone that can at least read and understand what the ohmmeter is telling them, is better off than me. And if it isn’t the alternator or voltage regulator, nor the circuit breaker or wire going to it, what else is left that you suggest I try?

Just a shot here...
but have you checked the grounds? Poor grounding can be a source of many different problems.

There'll be some experts to chime in to help before long.

I agree with checking all connections, especially the ground on the regulator itself (pin 7). A poor ground will make the regulator think its seeing an overvoltage conditon and will trip the 5 amp field breaker.

+1 for Walt's comments.

Check the terminal crimps as well at every connection including from the main buss, to the CB and through the charging circuit. Changing the CB as suggested would be worthwhile.

You could also measure the field current (multimeter in series) to determine if you are near the trip point (5 amps). If you are not and the CB is working properly you are most likely seeing over voltage trips. As Walt has suggested the most probable cause would be bad connections including to ground.

Good luck -

Every terminal crimp has been checked, including ground. Pin 7 is only about three inches of wire going to the ground. Terminals look secure and is clean, no sign of corrosion. I could still be missing something, so will go back through all of the othere wires again. As I mentioned in the OP, I?ve already replaced the CB on the 5 amp field amp.

Looking through the archives, other posters have said this was the potential problem or was it: alternator, voltage regulator, CB, wiring terminals, battery, master switch, shorts, ground, and I think Walt mentions going to a 7.5 CB field amp, and I think slightly thicker wire (Walt, correct me if I?m wrong) in one post for a fix on one system. Another with an older 60 amp BC had to have another slight altercation done to it, but it doesn?t appear to apply to my 40 amp, and I checked with Bill on that.

I'm not very good at operating a multimeter, so will get some help with it. I?ve got a car guy that is expert on electrical systems in these parts, and I?m going to try see if I can get him to take a look. I?ll keep you guys apprised; maybe it?ll help out somebody else provided he locates the problem.

14 year old technology

Don't eliminate the alternator. The internal diodes and their associated mounting could have an intermittent short or simply a leak under load. Given the difficulty in troubleshooting an intermittent problem and the alternator age (1998) have you considered getting some help and just converting to an internally regulated alternator? The hrs troubleshooting this one may justify the expense and you will have a simpler system to maintain down the line.

Another possibility is that the Voltage Regulator sense line is getting spikes.

Where does your sense line physically connect to?

If you can completely isolate your airframe wiring and it still trips, you know it is in the alternator or regulator. "Completely" is hard to do, especially with a remote regulator. This fixture I built will not help you but something similar might. It is a simple set up that attaches via aligator clip to the B lead then through a fuse to pos. 1 and 2 on internally regulated alternators. [/IMG]

You can then test fly and watch your volt meter or amp meter and determine if the fuse has blown.

I have had the SAME problem TWICE.

Your field contacts on the alternator are loose.

Replace the field contacts (all of them) at the alternator and the connector if you cannot remove / replace the contacts.

A loose field contact will cause the alternator to go on and off. When it comes on, there is a voltage spike that trips the Over Voltage Protection and that pops the breaker.

I spent over 2-months troubleshooting the problem you describe on my airplane a year ago. I went through everything including buying a milli-ohm meter to measure ground wires.

To test your field contacts, unplug the field connector. Find a faston tap and slide it in the contacts in the connector. They will all slide in and out easy. IF the contacts in the connector are good, the male test contact will be hard to push in and you will need pliers to pull it out.

Sounds like Gary may have the answer, at any rate it will be something just like that. You only have a few wires so someone could make you replacement wire assemblies to swap out if you prefer. A cool head is necessary to solve these problems.

I did have a similar problem myself but in my case it was a bad fast on (or 'quick-connect' if you prefer) terminal - it had lost its gripping strength and was loose on the regulator terminal - not the B&C regulator btw. The OV circuit is the B&C product. This intermittent connection was tripping the CB exactly like you have experienced.

Brushes

At 536 hours, you may need to clean or replace the alternator brushes if you haven't already tried that.

jdeas said:

Don't eliminate the alternator. The internal diodes and their associated mounting could have an intermittent short or simply a leak under load. Given the difficulty in troubleshooting an intermittent problem and the alternator age (1998) have you considered getting some help and just converting to an internally regulated alternator? The hrs troubleshooting this one may justify the expense and you will have a simpler system to maintain down the line.

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I’ll keep that in mind, JD. I haven’t ruled anything out on fixing the problem; I believe this is a $500.00 alternator, and the voltage regulator is another few hundred, so I might have to consider something else entirely, but hope it doesn't come down to that. And Paul, I'll keep those brushes in mind too, if we narrow it down to the alternator.

az_gila said:

Another possibility is that the Voltage Regulator sense line is getting spikes.

Where does your sense line physically connect to?

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Gil, I’ll pass this on to whatever electrical guy I find because I'm not sure what to do with this.

JonJay, I like the looks of that, and might be building something similar. It’ll depend on what other stuff I can maybe find out, but that that might be helpful.

RV6_flyer said:

To test your field contacts, unplug the field connector. Find a faston tap and slide it in the contacts in the connector. They will all slide in and out easy. IF the contacts in the connector are good, the male test contact will be hard to push in and you will need pliers to pull it out.

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Gary, after I tripped again, I pulled my cowling off, and looked at the terminal plugs. Those that went on the male prongs itself were tight; not easy to get on and off although I could use my fingers; didn’t need any pliers. I just put two new female terminal plugs on it before my last test that Bill sent me. I think I'll go look at this again though.

I’m going to print all of this thread out. All of you have given me plenty to think about and look over, and I’ll give this to whatever electrical guy I’m ever able to locate to come out. I appreciate all of your help very much, you guys always come through. I’ll let you know whatever the problem was if and when we get it fixed. I’ve gone about as far as I can go with it, and I’m going to need somebody with a heck of a lot more smarts than me, that is for sure.

I'm not far away if you need me.

I had the exact same thing. On a trip to Oshkosh I was tripping the breaker continuously. I talked to Bill at his booth he said it was the plug in the back of the alternator. I didn't want to believe him but replaced it when I got home. Nothing has tripped since I've replaced the plug. do that and you should have your problem solved.

Hey John, I'll be out at the airport on Saturday and can bring my Fluke digital multimeter and would be happy to have a look and see if I can spot anything.

Thanks Walt, for now, I'll see if I can get someone locally. One of these days, I'm going to make it to Roanoke.

strahler13 said:

I had the exact same thing. On a trip to Oshkosh I was tripping the breaker continuously. I talked to Bill at his booth he said it was the plug in the back of the alternator. I didn't want to believe him but replaced it when I got home. Nothing has tripped since I've replaced the plug. do that and you should have your problem solved.

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You talking about the plastic plug that the two wires go into? Mine has a plastic plug inside the alternator. Bill gave me two terminal female clips along with a plastic plug. I thought at first that was the plastic plug that went into the alternator which I figured I didn?t need this one too. This evening I realized the plastic plug Bill sent me actually connects and clips on the outside of it very nicely. So now, I put my two terminal clips inside that and plug it in to the two metal prongs. My first field test was without the plastic plug, and as I had mentioned, I went 20 minutes before it tripped on me. I?ll try it again tomorrow with that to see if it made a difference. Thanks.

Neal@F14 said:

Hey John, I'll be out at the airport on Saturday and can bring my Fluke digital multimeter and would be happy to have a look and see if I can spot anything.

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Neil, you do that for me, and I?ll make it right with ya. Not going to let you do this for free. I know with your regular job and with everybody else needing your help at the Valley, it doesn?t leave you much free time for anything else. I?ll be there Saturday, that is for sure. Thanks a bunch.

Neal came out and checked connections. All seem fine there. Had Barry at ATEX bench test my alternator. That checked out fine. He said he didn?t test voltage regulators. Did two brief flights, and no trips, but 17 minutes into the third flight it tripped again.

I?ve got the white rocker switches that were probably purchased around ?98 and one is used for my alternator, and think I will replace that next, then go from there. Neal suggested trying that. Does anyone know if Van?s still sells those? If not, I might need to locate another source or pick up a used one.

You may want to try swapping out the battery, a faulty battery may be allowing a voltage spike to trip the OV sensor.

Breakers

Are there to protect the wiring - have you looked for burned/toasted wires in the circuit? Some times we search too far away from the cause when trouble shooting electrical problems. YMMV. Hope that you find the problem soon. Good hunting!

E. D. Eliot said:

Are there to protect the wiring - have you looked for burned/toasted wires in the circuit?

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Yes, spent quite a bit of time on that.

Walt, if problem is still not solved after I replace the alternator switch and voltage regulator, I?ll probably go there next. Since both of those are cheaper than the battery replacement, that?s the only reason I?m trying those first. Not sure if Van?s still sells my rocker switch though, or at least just that switch alone without having to buy the entire bank. I?m still searching in the catalog. At least in cranking power, the B&C battery has been great, and was purchased sometime in 2011. I?d hate to replace it, only to have to let one go to waste if that wasn?t the problem. This has been a problem on and off for some six months or so and eventually at the rate I?m going, I?ll have an entirely new electrical system installed on my 6.

Right now I have the B&C voltage regulator. Neal recommended one out of a 1975 Ford LTD that I should pick up for a small fraction of the cost of the VR that I now have. I looked at this thread which has quite a few happy with that particular VR.

Just an update. I replaced my $230 VR with a $25.00 1975 Ford VR that Sam Buchanan recommends to everybody, and at least thus far after 20 hours have not had my field circuit breaker pop since that time.

O-Reilly's gave me three choices with one only about $16.00 and a limited 90 warranty, I think. Another one was about $20.00 and a one year warranty. Then the $25.00 one with a lifetime warranty. I splurged, and told them to give me the last one.

I think the overvoltage protection in the B&C VR is what trips the field breaker. The automotive VR won't have this so that may be why your breaker isn't tripping. Add one of those neat little "Nuckolls" style overvoltage protectors to your system. The cost will still be minimal.

It seems it was set too sensitive or had another problem with it. I did all the other recommendations Bill suggested at B&C, but the problem didn?t go away.

What?s a Nuckolls over voltage type protector? I?ve googled it, and haven?t come up with a single hit.

I think he's talking about Nuckolls "crowbar". When voltage goes up and hits the setting on the crowbar it throws a short across the breaker and takes the alternator offline.

I had an A&P with me in the right seat on a maintenance test flight once after some electrical work in the 172, we were talking about taking the alternator online/offline while in flight and the heartburn that causes with the regulator trying to "catch up" and frequently causing a voltage spike that will trigger the OV crowbar and trip the field breaker. What he told me makes sense, though I haven't had occasion to try it since that flight - he said before re-engaging the field breaker (in flight), pull the engine to idle and slow to near stall speed (to get engine rpm down to idle or close to it), then close the field breaker again. The regulator will still be calling for near-maximum field current to the alternator to correct the low-voltage condition, but at reduced RPM the alternator output cannot go high enough to trip the OV circuit before the regulator can recover and dial the field current down. The first 1/10 of a second when you close the field breaker is where all the action happens, it's that transient surge that causes the problem.

Again - not my wisdom - YMMV.

Thanks, guys, I got some hits on the Nuckoll?s crowbar. Some arguing for it, and some against it. gmcjetpilot wrote a critique of using one with Nuckoll responding rather lengthy to the each of his objections.

http://www.aeroelectric.com/articles/The_Truth_about_Crowbar_OV_Protection.pdf

I'll have to study this a bit more to decide if it is for me.

Did you get your rocker switch? I may have one if you are still looking. I bought 20 a few months ago, but don't know if they are the same as what you are looking for...

pa38112 said:

Did you get your rocker switch? I may have one if you are still looking. I bought 20 a few months ago, but don't know if they are the same as what you are looking for...

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No, I didn't. I'd like to buy one or two as a back-up as well. I've got some outside projects going on, but sometime next week, I'll send you a pic of mine, and let's see if they match up.

Thanks....