The alternator was replaced due to field post burning off on 60 Amp system. Then load meter dance began. Replaced master/ign switch and both 40A main and 5A field breakers. With every switch off all breakers open, the load indicator never drops below 20. When the landing light is turned on, (13VDC 100Watt) the load jumps to 35. I believe this is due to bad voltage regulator (upgraded electronic model). We are installing a new LED type lamp tomorrow. Q: should the load meter be much less than 20 (range of 0-40) with all loads out but fuel pump? Also, mechanic used a non shielded wire cable on the current lamp. We are replacing with shielded. Could lack of shielding cause load/amp jump?
1967 Piper PA-28-140. Load meter high (20A) with all loads off.
- Thread starter SoupDog
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Sounds like you have a shotgun A&P. Shoot parts at a problem until you hit it. Expensive for the pilot; a money-maker for the A&P.
What caused the field post to burn off on the previous alternator? Was that issue addressed?
What sort of troubleshooting has been done? Any? Has yout A&P gotten out his trusty multimeter and checked the entire charging system?
I bet it's something simple.
Check the connector on the field wire. Occasionally, the conductor strands inside the sheath (insulation) will work harden and break one at a time from vibration. I suggest cutting off the existing connector and crimping on a new one.
There is an extensive section on alternators and troubleshooting the charging system in your maintenance manual.
These may help:
What caused the field post to burn off on the previous alternator? Was that issue addressed?
What sort of troubleshooting has been done? Any? Has yout A&P gotten out his trusty multimeter and checked the entire charging system?
I bet it's something simple.
Check the connector on the field wire. Occasionally, the conductor strands inside the sheath (insulation) will work harden and break one at a time from vibration. I suggest cutting off the existing connector and crimping on a new one.
There is an extensive section on alternators and troubleshooting the charging system in your maintenance manual.
These may help:
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Without any systematic troubleshooting results, can't offer any input. However, I would first determine the cause of the field post failure before attempting any else.
You have non-pullable breakers. So you always have some stuff on when the master is on. Turn coordonator, engine instruments, and so on. There's enough stuff that isn't on the avionics master.
The battery will draw some power as well to recharge. What is the voltage with the alternator on? Too high and your battery will pull some amps, cooking itself in the process.
Are you sure your pitot heat switch is working properly, if you have a heated pitot tube? That will account for a good chunk of your 20A.
Troubleshoot smarter, don't throw parts at it. Measure voltage, measure current with a good amp clamp, tally things up.
The battery will draw some power as well to recharge. What is the voltage with the alternator on? Too high and your battery will pull some amps, cooking itself in the process.
Are you sure your pitot heat switch is working properly, if you have a heated pitot tube? That will account for a good chunk of your 20A.
Troubleshoot smarter, don't throw parts at it. Measure voltage, measure current with a good amp clamp, tally things up.
Dan Thomas
Touchdown! Greaser!
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What is a 40 amp breaker and loadmeter doing in a 60 amp system? I can see overloaded wiring here. Replacing master and ignition switches is just money into the toilet. Neither of those carry charging currents.
Loadmeters use a shunt across which a milliammeter measures a tiny voltage drop. When the shunt's connections get old or oxidized or corroded, the resistance increases and the loadmeter will read falsely high.
At the typical 14V operating voltage, a 100 watt lamp will draw 7 amps. A jump from 20 to 35 implies, again, a bad loadmeter shunt.
Your mechanic needs some remedial training. Shielding will not affect amperage in a DC system.
A sulfated battery can run the charging amperage way up. The sulfate peels off the plates and falls to the bottom of the cells, shorting the plates and reducing the battery's internal resistance, driving up the amperage.
The burned-off field terminal could have been caused by a loose and arcing wire terminal. And that is caused by poor inspection practices.
The OP needs someone that knows what he is doing, even if he costs more. The cost of shotgunning the parts at this airplane will cost way more.
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