VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #1  
Old 07-13-2021, 09:12 AM
RV8iator's Avatar
RV8iator RV8iator is offline
 
Join Date: Nov 2006
Location: Saint Simons Island , GA
Posts: 1,619
Default Diminishing voltage?

I noticed a few flights back that upon start and early into the flight my system voltage was 14.2, right where it should be. As the flight time increased, the voltage decreased down to 13.8. If I loaded it up by turning everything on it would hold at 13.7. Iíve changed the alternator (ND 14870(14824)) twice and they all 3 canít have the same problem. Iíve cleaned the main ground strap from the engine to airframe and other ground wires with no affect. All connections have been pulled and wiggled and canít find anything loose. Next Iím going to check resistance of the main feed from the alternator to see if it may be internally corroded. If that is not it, Iím stumped. Where should I look next?
__________________
Jerry "Widget" Morris
RV 8, N8JL, 3,100+ hours on my 8.

VAF #818
Saint Simons Island, GA. KSSI
PIF 2007 - 2022

I just wish I could afford to live the way I do
Reply With Quote
  #2  
Old 07-13-2021, 09:16 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,179
Default

Connect a temporary multi-meter to the system. This will tell you if your installed voltage meter is the issue - as in the reading changes with time/temp. If both change, then look for something else changing with temp - like high resistance connections.

Carl
Reply With Quote
  #3  
Old 07-13-2021, 12:19 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,539
Default

Is the belt tight? A slipping alternator belt can drop the voltage; The greater the load, the greater the slippage. I would expect that slipping would increase as heat increases. Do you have an ammeter tied to the alt output? If so, what is happening to the current when the voltage drops?

Resistance in the system should create a high voltage from the Alt, not a low one, if the alt gets it voltage sense from the B lead. If it has a separate voltage sense terminal, then resistance on the B lead can cause a low voltage on the main buss. Easy to test. With engine off and master on, measure voltage at the battery and then voltage at the B lead on the alternator.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 07-13-2021 at 12:26 PM.
Reply With Quote
  #4  
Old 07-13-2021, 02:05 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,771
Default

I would suspect this behavior is coming from the voltage regulator. Where is yours mounted (internal?). Some regulators include temperature compensation (as temperature goes up ideal charging voltage goes down) so itís possible the regulator is behaving normally (although running warm). Is your battery fully charged at the end of these flights?
Reply With Quote
  #5  
Old 07-13-2021, 03:01 PM
rv8ch's Avatar
rv8ch rv8ch is online now
 
Join Date: Feb 2005
Location: LSGY
Posts: 4,140
Default Battery

Why do you want the voltage to stay so high? If you have a gel battery, it should not stay that high for very long, but come down, at least according to some stuff I've read on the Internet - and now I'm an expert!


http://www.chargingchargers.com/tutorials/charging.html

Quote:
Three Stage Battery Charging
The BULK stage involves about 80% of the recharge, wherein the charger current is held constant (in a constant current charger), and voltage increases. The properly sized charger will give the battery as much current as it will accept up to charger capacity (25% of battery capacity in amp hours), and not raise a wet battery over 125į F, or an AGM or GEL (valve regulated) battery over 100į F.
The ABSORPTION stage (the remaining 20%, approximately) has the charger holding the voltage at the charger's absorption voltage (between 14.1 VDC and 14.8 VDC, depending on charger set points) and decreasing the current until the battery is fully charged. Some charger manufacturers call this absorption stage an equalization stage. We don't agree with this use of the term. If the battery won't hold a charge, or the current does not drop after the expected recharge time, the battery may have some permanent sulphation.
The FLOAT stage is where the charge voltage is reduced to between 13.0 VDC and 13.8 VDC and held constant, while the current is reduced to less than 1% of battery capacity. This mode can be used to maintain a fully charged battery indefinitely.
Can you see how much current you are pulling from the alternator? That might give you some clues.
__________________
Mickey Coggins
http://rv8.ch
"Hello, world!"
Reply With Quote
  #6  
Old 07-13-2021, 03:21 PM
Walt's Avatar
Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 6,278
Default

Quote:
Originally Posted by rv8ch View Post
Why do you want the voltage to stay so high? If you have a gel battery, it should not stay that high for very long, but come down, at least according to some stuff I've read on the Internet - and now I'm an expert!
http://www.chargingchargers.com/tutorials/charging.html
.
I'm pretty sure that Odyssey batteries recommends 14.2 to 14.5 for charging voltage.

If you go to the Technical manual they recommend 14.7 for a max charge rate.
I use 14.6 -14.7 personally at a set point for the B&C reg.

RAPID CHARGING OF ODYSSEYģ
BATTERIES
All ODYSSEY batteries can be quickly charged. Figure 7
on the next page shows their exceptional fast charge
characteristics at a constant 14.7V for three levels of inrush
current. These current levels are similar to the output
currents of modern automotive alternators. Table 6 and
Figure 7 show the capacity returned as a function of the
magnitude of the inrush3 current.

Standard internal combustion engine alternators with an
output voltage of 14.2V can also charge these batteries.
The inrush current does not need to be limited under
constant voltage charge. However, because the typical
alternator voltage is only 14.2V instead of 14.7V, the
charge times will be longer than those shown in Table 5.

Table 5 shows 10A and 20A times as:
PC680 2.7 hours 1.5 hours
__________________
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154

Last edited by Walt : 07-13-2021 at 03:40 PM.
Reply With Quote
  #7  
Old 07-13-2021, 03:43 PM
RV8iator's Avatar
RV8iator RV8iator is offline
 
Join Date: Nov 2006
Location: Saint Simons Island , GA
Posts: 1,619
Default

Thanks guys for all the comments.
I have EarthX batteries. The amps look like they always have. Up to 35-45 immediately after start then slowly drops to 5 to 10 depending on lights, fuel pump etc. usage. All that looks like it always has. I’ve been running the ND alternators for 3000 hours so I have a pretty good baseline of how they have performed.
Belt is correct tension with no indication of slippage, black dust, noise..
Since 3 alternators are all behaving exactly the same I’ve pretty much ruled them out.
I’m on a trip for a few days but will measure voltage at batt and b lead when I het back.
I’m wondering if the internal regulators may be different than the ones I got 5 years ago and before. Could they be set to drop voltage when amp load goes down like auto’s do? Just a thought. None of my cars ever maintain over 14 volts after the batt is fully charged.
I’ll let you know if I find a smoking gun.
And..
Can I hurt anything running it like this?
PS. I put the proper earthX charger on both batteries about twice a month nad let them do there thing for a couple days each.
__________________
Jerry "Widget" Morris
RV 8, N8JL, 3,100+ hours on my 8.

VAF #818
Saint Simons Island, GA. KSSI
PIF 2007 - 2022

I just wish I could afford to live the way I do

Last edited by RV8iator : 07-13-2021 at 03:47 PM.
Reply With Quote
  #8  
Old 07-13-2021, 05:02 PM
guccidude1 guccidude1 is offline
 
Join Date: Mar 2008
Location: Reno NV
Posts: 554
Default Diminishing voltage?

Do you have an avionics switch? I the same problem, same alternator, same exchanges. Not until the avionics switch completely failed; toggle came out of the switch breaker in my hand, did I discover the true culprit. Changed the avionics switch breaker to higher amperage and problem solved. Hope this helps, Dan from Reno
Reply With Quote
  #9  
Old 07-13-2021, 06:49 PM
RV8iator's Avatar
RV8iator RV8iator is offline
 
Join Date: Nov 2006
Location: Saint Simons Island , GA
Posts: 1,619
Default

Quote:
Originally Posted by guccidude1 View Post
Do you have an avionics switch? I the same problem, same alternator, same exchanges. Not until the avionics switch completely failed; toggle came out of the switch breaker in my hand, did I discover the true culprit. Changed the avionics switch breaker to higher amperage and problem solved. Hope this helps, Dan from Reno
Good thought but no. I have one EFIS wired to main bus, and 2 backups to the stby bus. My 650 has itís own switch.
__________________
Jerry "Widget" Morris
RV 8, N8JL, 3,100+ hours on my 8.

VAF #818
Saint Simons Island, GA. KSSI
PIF 2007 - 2022

I just wish I could afford to live the way I do
Reply With Quote
  #10  
Old 07-13-2021, 07:21 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,220
Default

Quote:
Originally Posted by lr172 View Post
Is the belt tight? A slipping alternator belt can drop the voltage; The greater the load, the greater the slippage. I would expect that slipping would increase as heat increases. Do you have an ammeter tied to the alt output? If so, what is happening to the current when the voltage drops?

Resistance in the system should create a high voltage from the Alt, not a low one, if the alt gets it voltage sense from the B lead. If it has a separate voltage sense terminal, then resistance on the B lead can cause a low voltage on the main buss. Easy to test. With engine off and master on, measure voltage at the battery and then voltage at the B lead on the alternator.

Larry
The belt shrinks when it gets hotter, it has a negative coefficient of thermal expansion. Slip will still exist but somewhat self compensating until it wears excessively.
__________________
Bill

RV-7
Reply With Quote
Reply


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 12:50 AM.


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.