Can a Dead Batttery Cause Avionics to Recycle once Engine Running

[carrollm]

My battery was dead but my hanger neighbor had a quick-jump that allowed me to get engine started, and I went flying to let it charge. On short final, I keyed to talk to tower and all my avionics recycled, this continued on and off in the pattern so brought it down and landed. I tried to repeat the problem and was successsful by turning on landing light. Each time I turned the light on, avionics recycled. During each of the these recycles my engine monitor was showing good voltage and amperage readings (AMPS solid at +2 and voltage solid at 13.5 volts.) So my question is, are the avionics runing off the battery or off the alternator charge? If the battery won't hold a charge I can understand why the avionics were cycling on and off, but if the avionics draw from the alternator/voltage regulator power, and all the amperage and the voltage are in the green, not sure what is happening.

 

[Clip4]

Doing a jump of an aviation battery rarely has good results because you are charging the battery at very high amps.

In a Cessna, the electrical items are powered by the battery.

How old is the battery? 2 amps sounds very low, could be a regulator or the battery. Also your voltage should have been >14.

 

[ircphoenix]

My battery was dead but my hanger neighbor had a quick-jump that allowed me to get engine started, and I went flying to let it charge. On short final, I keyed to talk to tower and all my avionics recycled, this continued on and off in the pattern so brought it down and landed. I tried to repeat the problem and was successsful by turning on landing light. Each time I turned the light on, avionics recycled. During each of the these recycles my engine monitor was showing good voltage and amperage readings (AMPS solid at +2 and voltage solid at 13.5 volts.) So my question is, are the avionics runing off the battery or off the alternator charge? If the battery won't hold a charge I can understand why the avionics were cycling on and off, but if the avionics draw from the alternator/voltage regulator power, and all the amperage and the voltage are in the green, not sure what is happening.

Yes it can. Happened in my Cherokee 140. Radios and 530 both misbehaved.

 

[GRG55]

My battery was dead but my hanger neighbor had a quick-jump that allowed me to get engine started, and I went flying to let it charge. On short final, I keyed to talk to tower and all my avionics recycled, this continued on and off in the pattern so brought it down and landed. I tried to repeat the problem and was successsful by turning on landing light. Each time I turned the light on, avionics recycled. During each of the these recycles my engine monitor was showing good voltage and amperage readings (AMPS solid at +2 and voltage solid at 13.5 volts.) So my question is, are the avionics runing off the battery or off the alternator charge? If the battery won't hold a charge I can understand why the avionics were cycling on and off, but if the avionics draw from the alternator/voltage regulator power, and all the amperage and the voltage are in the green, not sure what is happening.

If the battery is completely flat it's usually best to use a battery charger and not try to recover it with the airplane charging circuit.

Most often jump starting, or hand propping, the plane means there's still not enough juice in the battery to hold closed the main contractor on the battery. If the contactor remains open then you are running everything off the alternator but the battery isn't charging because it's not in the circuit. That may be what happened to you. As soon as you added a significant load, the radio transmit or the landing light, the momentary voltage drop was enough to drop out the avionics, especially if you have an avionics master switch relay.

If the alternator has to charge a dead battery it may actually be trying to put out more amps than it is rated for. That is particularly hard on it when you are still on the ground and there's little air going through the alternator cooling blast tube.

 

[bnt83]

Sounds like you may have an avionics relay in the airplane, that was a great idea on paper when cessna installed all those but never did really work as intended. It should be wired through the ignition switch and the external power receptical (if installed). The idea was that this relay would remove any power for the avionics bus when external power was plugged in or when the ignition switch was in the "START" position.

Durring engine cranking the starter put such a high load on the ectrical system the relay would skip is my understanding. So if your battery was already very low that could be what's going on.

I'd throw it out and use a standard switch in its place.

 

[Stewartb]

Alternators require battery voltage to excite the field. Perhaps your alternator was cycling on and off? What did your ammeter or voltmeter indicate?

 

[kgruber]

Best to properly charge your battery before flight, on the bench.