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  #1  
Old 10-07-2013, 08:54 PM
Acrophil Acrophil is offline
 
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Location: GA
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Default Alternator field fault




I am getting a field fault on the alternator occasionally. The wire has been checked from end to end. The alternator has been bench checked twice. I can reset it on the VPX and it never recurs on the same flight. Airpower 60 amp. Output is normal when the field is not shorted.

It was doing this before the panel upgrade and VPX.

Any ideas?
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  #2  
Old 10-07-2013, 10:12 PM
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vlittle vlittle is offline
 
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It's virtually impossible to diagnose electrical problems on internet forums, but I'll try.

Does your alternator have an overvoltage crowbar built in? If so, it may be tripping and shorting the field circuit.

You said you have an Airpower alternator, but is this actual brand or just the distributor?
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  #3  
Old 10-08-2013, 06:34 AM
Acrophil Acrophil is offline
 
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Default Alternator fault

Whoops
AL12-EI60/B PlanePower alternator.

Yes I know it is nearly impossible to do over internet. I can't do it and I am standing here looking at it!

Just want to perform obvious checks before sending back to PlanePower for a real bench check.
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  #4  
Old 10-08-2013, 07:31 AM
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Walt Walt is offline
 
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What do you have the field current set at? The PP alternator will draw a full 5A (and maybe a little more) when asked.
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  #5  
Old 10-08-2013, 07:48 AM
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vlittle vlittle is offline
 
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Check this post: http://www.vansairforce.com/communit...&referrerid=61
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  #6  
Old 10-08-2013, 09:38 AM
Acrophil Acrophil is offline
 
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Default Field fault

Walt
Field amps are usually around 4.5 . I don't know that it is adjustable.

Vern
Very interesting thread. My fault generally occurs during run up. I reset and field is usually around 4.5 and output is 14.5 volts. I have not tested for over voltage protection. Thanks for info

Phil
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  #7  
Old 10-08-2013, 10:32 AM
rvsxer rvsxer is offline
 
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Phil,

How is your field switch wired? I just finished a project here at SteinAir and Marc at Vertical Power told me to use the dedicated alternator field C/B in the VP, and to make sure to tie it to a switch input (not "always on"). The field switch on your panel then only provides a ground to close that VP switch. If you do it this way a field trip will annunciate "overvoltage" instead of "short circuit". It also insures full functionality of the VP with respect to the charging system. This may not solve the tripping problem but since your VP shows "short circuit" after a trip it's probably not wired the way Marc recommends.
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  #8  
Old 10-08-2013, 03:07 PM
Acrophil Acrophil is offline
 
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Default Little knowledge

Thanks Mike. A little knowledge is dangerous snd I didn't
even have that much! Will check and fix it.

Phil
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  #9  
Old 10-08-2013, 08:14 PM
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Bill.Peyton Bill.Peyton is offline
 
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Since this was happening pre VPX I would suggest that the over voltage crowbar is kicking in to soon and tripping the over current protection in the VPX. Sounds like the alternator is bad. The PP alternators have a built in over voltage crowbar. The crowbar shorts the field to ground when an over voltage condition exists. Thus tripping the field breaker.
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  #10  
Old 10-08-2013, 10:03 PM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by Bill.Peyton View Post
Since this was happening pre VPX I would suggest that the over voltage crowbar is kicking in to soon and tripping the over current protection in the VPX. Sounds like the alternator is bad. The PP alternators have a built in over voltage crowbar. The crowbar shorts the field to ground when an over voltage condition exists. Thus tripping the field breaker.
It's critical to make sure every connection in the field circuit is solid. Turn on the master, measure the voltage at the master bus then measure the voltage at the input to the field connector on the alternator. This is a bit tricky... you'll need to push the voltmeter probe into the back of the connector to intercept the terminal.

You should have less than 0.25 volt difference. Any more and you need to start looking for problems.

If this measures OK, then start looking into the alternator. It's possible to remove the alternator and build a bench tester like I did, but it's probably easier to remove the brush/regulator/ovp assembly and test it on the bench.

You'll need a current limited variable voltage power supply. Set the current limit to 1 amp and vary the voltage upwards starting at 12V. The OVP trip point should be around 17V. My failed OVP tripped at 13.8V.

This takes some electrical skills, so find the guy on the field named 'Sparky' and ask for help.
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