Electrical System not Charging

stsavios

stsavios

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stsavios
I've got a Piper Cherokee, and for some reason, the electrical system is not charging correctly. I've replaced the battery and the alternator, but it will only charge (at a high rate) just after it is started, then the ammeter goes to "0", even when I have a load placed on it (i.e., all lights on, avionics on, etc.).

Also, not sure if it's related, but the radio emits static when at a higher RPM. Only started to do so when the charging system started acting up, so I figure it's related.

I'm wondering if it's the voltage regulator? I really don't know, and any help would be wonderful.
 
Depending on how the ammeter is wired, this might be normal... If it's showing the current flowing to the battery only, you wouldn't see a positive or negative flow when the battery is charged. You'd only see a negative flow when the battery was discharging (too much load for the alternator), and a positive flow when the battery is charging.


Put another way, your meter may not be wired to show the load on the alternator.
 
stsavios said:
I've got a Piper Cherokee, and for some reason, the electrical system is not charging correctly. I've replaced the battery and the alternator, but it will only charge (at a high rate) just after it is started, then the ammeter goes to "0", even when I have a load placed on it (i.e., all lights on, avionics on, etc.).

Also, not sure if it's related, but the radio emits static when at a higher RPM. Only started to do so when the charging system started acting up, so I figure it's related.

I'm wondering if it's the voltage regulator? I really don't know, and any help would be wonderful.
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Are you an A&P? :eek: Never ceases to amaze me that people buy certificated airplanes "cuz they are XxxxxX, but yet they do not comply with the rules for maintenance. Buy an experimental! Rant over.

Replace the voltage regulator with one from NAPA like eveyone else does. ;)

Seriously, ( I don't care if you do the work) before you start replacing perfectly good working parts have them tested first. Take them off and take them to a good automotive shop and have it tested. Preferably to a shop that rebuilds starters and alternators. Remove all safety wire or they might not touch it. Take the voltage regulator to NAPA and they can cross it over to a $20 part instead of a $200 part.
 
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TMetzinger said:
Depending on how the ammeter is wired, this might be normal...
Click to expand...

I know the battery itself isn't fully charged... and it only charges for a few seconds after start, if at all.

As for the radio, any ideas what might be going on there? I'm just a little concerned that the problem only started occuring when the charging system seemed to be acting strange.
 
Most likely worn alternator brushes or a bad connection. Once the affected stuff gets hot with current flow (because of resistance) it quits working.

Dan
 
Dan Thomas said:
Most likely worn alternator brushes or a bad connection. Once the affected stuff gets hot with current flow (because of resistance) it quits working.
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Alternator has 0.2 hours SOH ... I'm pretty sure it's not that, but I could be wrong
 
I have a 71 Cherokee. The ammeter shows alternator output. When you turn a load on, like the landing light, the ammeter should show an increase in current. Mine typically shows 5 to 10 amps after the battery has recharged after starting.

The alternator field switch (half of the red master switch) tends to develop some resistance in the switch contacts that usually leads to a cycling ammeter indication. You could eliminate the possibility of that switch causing the problem by jumpering the switch to see if it has any effect on the problem.

Check voltage. It should be about 14 volts with the engine running.

Check all connections for tightness, both in the field circuit and the output circuit.

If you've already replaced the alternator and the battery, the only other active elements in the circuit are the voltage regulator and the overvoltage protection relay.
 
Graueradler said:
If you've already replaced the alternator and the battery, the only other active elements in the circuit are the voltage regulator and the overvoltage protection relay.
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And the ampmeter. What's the bus voltage with the engine on and the alternator turned on?
 
stsavios said:
Alternator has 0.2 hours SOH ... I'm pretty sure it's not that, but I could be wrong
Click to expand...
That right there is a red flag. Was it replaced because the charging was bad, or for other reasons? Who overhauled it? We have had some alternators fail very shortly after we bought them and found that the factory had put too much grease in the rear bearing; it gets flung out and lands on the slip rings, where it gums up the carbon brushes and increases the field circuit resistance so that the charging rate drops right off. The resistance causes heat, the heat raises the resistance further.

I have a very special tool I use to troubleshoot charging systems. It's a small piece of plywood with four screws in it and four long wires attached to those screws. One wire gets grounded to the firewall. One goes to the field wire off the regulator. One goes to the alternator output and one goes to the A terminal on the regulator. With things hooked up and me in the cockpit with the engine running, I can use a meter to check voltages between the ground screw and the others. Field should be around 5-8 volts or so, depending on load. Output should be 14 or better. The A terminal should readout output voltage. If one wanted, an additional wire can be attached to the S terminal on the regulator, and it should read system voltage. That terminal turns the regulator on and is fired by the alternator side of the master and its breaker. The regulator uses A terminal current to feed the field, not the switch current.

First thing, though: Pull the F wire off the regulator and put an ohmmeter between that wire and ground (to measure the alternator's field resistance), and turn the prop some (backwards, to avoid mag impulse clicking). Make sure the mags are off anyway. The resistance (12 volt alternator) should be 3-5 ohms. I bet it's way higher on yours. It should remain steady at the ohm reading when you turn the prop. A changing resistance is a bad sign.

Dan
 
Turns out it was the Alternator field wire. Came loose while running up the engine, and would sporatically charge. System is charging great now.

I'm just wondering if the "squelchy" sounding problem was related to it, as I haven't found time to fly it since I got it fixed.
 
stsavios said:
Turns out it was the Alternator field wire. Came loose while running up the engine, and would sporatically charge. System is charging great now.

I'm just wondering if the "squelchy" sounding problem was related to it, as I haven't found time to fly it since I got it fixed.
Click to expand...

Good job. I have "fixed" both of my Cherokees electrical gremlins by simply tracing every wire going to the alternator, and making sure the connections were/are clean and tight.
 
stsavios said:
Turns out it was the Alternator field wire. Came loose while running up the engine, and would sporatically charge. System is charging great now.

I'm just wondering if the "squelchy" sounding problem was related to it, as I haven't found time to fly it since I got it fixed.
Click to expand...

If you mean static, probably. Arcing things make tons of RF noise. Spark-gap transmitter, Marconi style.

Squelch is by definition, silence. A squelch circuit is meant to "squelch the noise".

So I don't know what something sounding "squelchy" is, but I can guess that you're saying there was enough signal/noise present in your receiver to defeat the squelch circuit and open the audio path to your headphones. :)
 
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