Ammeter acting up...

b727plumber

b727plumber

1979 7GCBC, Frame-up restoration by ACA in 2022
Joined
Jun 24, 2020
Messages
93
Location
Centennial, Colorado
I picked up our 1979 7GCBC from ACA after a complete rebuild. Flying home, the ammeter started pulsing from zero to just under 30, frequency of about once per second. This lasted for under 5-10 minutes and then it went to zero (or maybe a slight discharge). I didn't notice this for quite some time and when I landed for a fuel stop, the engine wouldn't start.

I connected a GPU to test the starter itself and rule it out. Starter was good.

Put the battery on a 2 amp tender and charged it overnight. Next day, started right up, but the pulsing started again and then just went to zero. I was flying across the midwest, on the way to Denver area, so I just turned the master off and flew the old fashioned way. Saved the battery for starting & comm when necessary.

Thoughts?
 
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Given you just had it restored, my guess would be a short or wiring mistake. Definitely not just a gauge reading problem, or you wouldn't be dead battery after flight.

The factory should 100% be sorting this out for you.
 
Big Ed said:
Given you just had it restored, my guess would be a short or wiring mistake. Definitely not just a gauge reading problem, or you wouldn't be dead battery after flight.

The factory should 100% be sorting this out for you.
Click to expand...

I've got a message into them and hope to discuss on Monday.
 
Joe said:
I'd be looking for a loose connection. I've had a bad ground strap cause similar symptoms.
Click to expand...
Yeah, after thinking about it, I agree with loose connection. Alternator is not charging battery. Spikes in ammeter are when the loose connection makes momentary contact, causing the system to charge for a short period. Could be as simple as someone didn't tighten a terminal post nut and it loosened or fell off in flight. Or could be a defect in a wire, terminal, or component.

I would start by checking all terminal posts in the charging circuit for tightness. Check at the alternator, ammeter, battery, battery ground, master relay, and master breaker. Also check the alternator field circuit. That is the wire that runs from the master switch to the voltage regulator, and from there to the ammeter. Check all terminals on the voltage regulator, and the ground from the VR to the firewall. Also check connections at the circuit breaker behind the ammeter, and the breaker at the master relay.

If nothing obvious there, then you get into more methodical troubleshooting. First check continuity of wires and terminals. Then move on to defective components. A few possible culprits off the top of my head: alternator, voltage regulator, inline fuse holder from the bus to master switch, master switch, breakers at master or ammeter. I'll post a circuit diagram in a bit to help.

That sounds like a lot, but I bet you don't have to go that far. Betcha it's just a loose or missing terminal nut or screw.

Good news is you moved the battery to the firewall, so most of what you need to see is right there under the cowl or glare shield. Hurry up and beat the snow!
 
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Here is a schematic. I could only find one for an aft mounted battery. AFAIK the main difference would be lack of a firewall fitting for the starter cable. I would focus inspection on the connections circuits in yellow. Also shown is a drawing of the area under the glare shield. Would definitely check all these connections.
circuit diagram.webpunder glare shield.webp
 
Agree. I find wires pulling out of ring trrminals and butt splices. A gentle tug on the wire may show you which one.
 
The factory did perform the SL 418 - Electrical System Update.

My A&P came by the hangar today and we put a tester on the electrical system. We also checked the integrity of all of the wires and found that the ring terminal that connected the ground to the VR was barely hanging on - it felt like, if I pushed on it a few more times, it would have snapped off.

We redid the ring terminal and then tested the electrical system. It indicated that both the VR and the Alternator are bad, so I ordered a Zeftronics R1510L VR (to go along with the Electrodelta OV that was installed in 2006) and a Hartzell ALY-8520R O/H Alternator.

Hope to have the parts by this weekend and the work done early next week. Will post an update then.

Thanks to everyone for the guidance!
 
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Had an alternator failure about ten years ago - buddy in the business said “Plane Power.” Never been sorry. I did put in an alternator field switch, and am getting fairly good at remembering to turn it on.
 
So, the airplane is back in business! My A&P replaced the alternator with a Hartzell and installed a new Zeftronics VR. Works perfectly! Flew it 1.5 today before it snows again tomorrow night! Love this airplane!

Now, another question for the group. The factory installed a new cigar lighter on the crossbar and when I plugged a USB adapter into it, it doesn't work (I tested the same USB adapter in my truck and it worked just fine). My A&P thinks it might be that, when I had the high amperage problem momentarily before, it could have blown the shunt. Any ideas for where I should focus my troubleshooting of this newly installed feature?!
 
Where is it fused? Did the factory add one under the panel? Carefully check with a multi meter to determine if you're getting voltage to the center pin down inside the cigar lighter.
 
I like USB adapters. TSO ones are a bit spendy, but supposedly have less noise.
 
Well, since I'm not too smart on electrical systems, does it matter if that connector doesn't have a ground wire connected to it? Is the unit theoretically grounded already from being mounted in that crossbar frame? If that is the case, wondering where to look next to figure out why it's not working??
 
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