Home > VansAirForceForums

- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

Old 07-08-2019, 02:44 PM
ILikePike ILikePike is offline
Join Date: Jan 2011
Location: Eatonton, GA
Posts: 210
Default Potential electrical issue

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.
Jeff Green
2016 RV-8 #82985
1968 E33C Aerobatic Bonanza
Pleased to donate Dec 2019
Reply With Quote
Old 07-08-2019, 02:53 PM
nzrv8's Avatar
nzrv8 nzrv8 is offline
Join Date: Jun 2009
Location: Australia and NZ
Posts: 175

You state zero amps shortly after startup - what is your voltage reading at that same time?
Paid up - Sep 2019
Reply With Quote
Old 07-08-2019, 03:23 PM
pilotkms pilotkms is offline
Join Date: Mar 2007
Posts: 330

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.
RV 7A RV #9700 May 2017
N325KS the Flying K
Built in SoCal KCCB, now in GA @ KPXE
430+ Hours & 7X cross the USA
OSH flyin 2018 & 2019 & Petit Jean 2019
Reply With Quote
Old 07-08-2019, 05:18 PM
bjdecker's Avatar
bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 103
Default It depends...

...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?

Retired Firmware Guy and Airplane Builder

2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned
1998 RV-8 QB -- Started, Sold
Aided and abetted building a number of other RV's.

Last edited by bjdecker : 07-08-2019 at 05:34 PM.
Reply With Quote
Old 07-08-2019, 05:38 PM
thinkn9a thinkn9a is offline
Join Date: Nov 2007
Location: Mississippi
Posts: 259
Default From Odessey Technical Manual (2016)

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.
Wallace & Marietta Goodloe
9A -QB
Phase 2 has started!
Thanksgiving time, is dues time for us
Reply With Quote
Old 07-08-2019, 09:39 PM
ILikePike ILikePike is offline
Join Date: Jan 2011
Location: Eatonton, GA
Posts: 210

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.
Jeff Green
2016 RV-8 #82985
1968 E33C Aerobatic Bonanza
Pleased to donate Dec 2019
Reply With Quote
Old 07-08-2019, 09:46 PM
Mich48041 Mich48041 is offline
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,940

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.
Joe Gores
RV-12 Flying
Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -6. The time now is 10:19 PM.

The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.