Potential electrical issue

[ILikePike]

I am running a PP AL12ei60/b alternator and PC680 battery with VP-X. I am getting 14.6v with a short decreasing charge after start up then 0amps for the remainder of flights. Should I be getting a couple of amps charge to the battery for the duration of flights? Should the system voltage run more like 14.2v? I plan to check all connections at the next oil change particularly the troublesome plug into the alternator.

[nzrv8]

You state zero amps shortly after startup - what is your voltage reading at that same time?

[pilotkms]

I have same setup. Mine does the same. Settles on 0 or +1 for most flying. Only higher at first startup. Mine reads 14.6 out of the alternator and 14.4 out of the battery.
Had a strange reading of negative 7 amps in the middle of the desert. Alternator & battery readings remained at 14.6 & 14.4. Continued on. Cleaned shunt fuse connections at destination. Reading back to 0 for 50 happy hours.

[bjdecker]

...on how the VP-X is wired to sense voltage (V) and amps (A). Remember Amps <> Volts.

It sounds like the VP-X is wired to measure/report the state of charge or drain on the battery -- which is usually 0 when in-flight and everything is working correctly. It will indicate a discharge if the alternator drops offline.

Nominal system voltage (V) with the alternator running is ~14.3Vdc.
With the alternator offline, the system Voltage will drop to ~13.8Vdc and then continue to decrease over time, depending upon load, battery technology (lead acid, AGM, LiFePo, etc.) etc.

Do you have an aircraft electrical system schematic handy?

B

[thinkn9a]

Cycling tests conducted on an ODYSSEY PC545 battery demonstrated the impact raising the charge voltage from 14.2V to 14.7V has on the cycle life of the battery. The results are shown in the graph at right.


Samples 1 and 2 were charged at 14.2V while Samples 3 and 4 were charged at 14.7V. All batteries were discharged at 2.3A until the terminal voltage dropped to 10.02V and charged for 16 hours. In this particular test, a capacity of 11.5Ah corresponds to 100% capacity and 9.2Ah is 80% of rated capacity and the battery is considered to have reached end of life at that point.


The message to be taken from this graph is clear ? in deep cycling applications it is important to have the charge voltage set at 14.4 ? 15.0V. A nominal setting of 14.7V is a good choice, as shown by the test results.

[ILikePike]

The ammeter shunt is wired to measure current to the battery. Sounds like 14.6v is a good VP-X bus voltage. As for the current it charges and discharges as expected. I have almost 300 hours on the plane now and I believe until recently there was always 1 or 2 amp charge current after recharging from the start rather than zero. I have seen -1 or -2 amp discharge a couple of times. The zero and occasional negative charge is what has recently caught my attention. The voltage has always been consistent at 14.5-14.7v.

Thanks for the comments.

[Mich48041]

If the alternator is putting out 14.6 volts and if the alternator output is connected to the battery, then the battery IS being charged.