JPI reading voltage

[DonMuncy]

While flying with a couple of more knowledgeable guys than me, they noted my JPI "BAT" was reading 12.8 v. They thought this was too low.

I keep a battery minder on the plane anytime it is in the hangar. I have never seen a low voltage light come on, and have not had any issues like poor cranking.

What is the consensus here. What is everyone else seeing.

[Cruiser]

Well, it seems you are not having a problem so it may not be a problem however, the voltage regulator on a 12V system should be charging 13.8 to 14.2 volts output.

It might be an adjustment on the regulator but I am of the view that you don't mess with something when it is working OK.

[Bob_Belville]

Don, I have a JPI EDM 930 which logs BAT (voltage) every 6 sec. I just looked at a recent flight -- It was 14.0 while taxing and became 13.8 during take off roll. It stayed there thoughout the flight. FWIW, AMP was 6 for a short while after start up but became 3 in flight with an occasional 2 or 4 or 5 isolated reading.

 

(I do have a new PlanePower 70A alternator & VR.)

[bonal]

Look into Gill and Concord charging specs. you will note that charger and battery tenders for aircraft batteries are designed to charge at under 13 volts and they specifically point out that you should not use an automotive use charger or tender. The reason is that in order to be lighter and still produc ample power they have to usr a stronger acid. When this is given too high of charge voltage it will cause the plates to break down faster shortening the battery life and lowering its performance. if you look on Aircraf Spruce under bat chargers you will see a good explanation on this.  Your 12,8 is probly just right.

[carusoam]

There is a small amount of additional storage to be gained by charging to the higher level.

Then again, in the deep winter climes of Dallas, will you ever need it?

Balancing out the forces of don't fix what ain't broken and fixing something that isn't quite right...

Best regards,

-a-

[N601RX]

It should be at around 14, but the difference could be due to where the JPI is connected.  If its on the avionics bus turn everything else off and see what the JPI says. There could be some voltage drop on the bus with everything on. 

 

Here are the Concord RG series recommended charging voltages.

5-0324-rg-manual1.pdf

[ArtVandelay]

It should be ~14v when charging, if charged, it should be 13.2v to maintain it's full charge. You should check the voltage with a voltmeter, it could be there is a voltage drop on the sensor wires depending on how it is wired.

[orionflt]

all the above, but 12.8 is too low. 

 

brian

[laytonl]

That is low, but it may not be the actual battery voltage. You need to check the voltage at the battery. Lee

[PTK]

That does sound low for it to be charging voltage.

Could it be the alternator getting weak? Probably worth looking into.

I can only go by what I'm seeing which is 14v.

Here is an example.

[N33GG]

Last time I let low voltage like that continue, wondering if it was ok, I lost all electrical in solid IMC.

Might be ok, but might not. Get it checked. Get it resolved.

Good luck.

[DonMuncy]

Thanks for the input guys.

[BigTex]

Just pulled my JPI BAT and it's generally right at 14.1V and drops on occasion down to 13.6V.

[ArtVandelay]

Just pulled my JPI BAT and it's generally right at 14.1V and drops on occasion down to 13.6V.

Right, 13.6 is the float charging level, SOP is to start 14.1 unless you have a drain on the system like prop heat, etc, then when mostly charge it drops to 13.6, I stated 13.2 earlier, but 13.6 or 13.7 is the right float voltage.

Sent from my iPad using Tapatalk

[AdamJD]

Bumping up this old thread.  I am having the same issue.  Voltage has fluctuated between mid 13s and as low as 12.2 yesterday.  It has been doing this for a few months now.  I had a new regulator put on yesterday and then flew for 2.5 hours.  That didn't fix the issue.  I've had two separate mechanics look at and clean connectors. 

See below.  Notice that it started in the low 12s for much of the first hour.  Then spiked to the low / mid 13s for the second hour (only change was dropping 500' in altitude as I picked up an IFR flight plan).  Then dropped suddenly back to low / mid 12s for the rest of the flight.  Again, no real event that would have caused that.

Note:  Before I dropped the plane off for annual in mid-Feb, it was at 14 every flight.  The 1st flight after annual in mid-Mar it was between 13.2 and 13.5.  It has degraded since to what you see below.  There was no direct work to the electrical system during annual.  However, they did some extensive work which required dropping the exhaust system.  Could moving things around have caused anything?

Interested in anyone else's experience or thoughts.  Thanks!

[Ragsf15e]

I had the exact same issue.  It took 2 years and many thousands of dollars.  Finally found the corroded connection myself with a digital voltage meter.  I’m not saying this will do it for you, but it takes less than an hour and is easy…

Get a dvm.  Remove cowling.  Get alligator clips attached to the alternator output so you can stay away from the prop.  Have a friend stand on the brakes and start the engine.  Measure voltage at your cigar lighter to ensure it’s really low.  If it’s below 14v, then Measure voltage at the alternator output.  If you see 14v there, next check the voltage further back (i used the connection at a noise filter attached to the firewall).  If 14v, check it where power comes through the 60/70amp fuse in the cockpit.  If 14v, check it on the bus behind the circuit breakers.  You’re looking for the connector where voltage is 14v on one side and less on the other.

Mine was on the bus where the alternator input connected to the power bus.  Once you find it, it’s easy to fix.

[Ragsf15e]

4 hours ago, AdamJD said:

Bumping up this old thread.  I am having the same issue.  Voltage has fluctuated between mid 13s and as low as 12.2 yesterday.  It has been doing this for a few months now.  I had a new regulator put on yesterday and then flew for 2.5 hours.  That didn't fix the issue.  I've had two separate mechanics look at and clean connectors. 

See below.  Notice that it started in the low 12s for much of the first hour.  Then spiked to the low / mid 13s for the second hour (only change was dropping 500' in altitude as I picked up an IFR flight plan).  Then dropped suddenly back to low / mid 12s for the rest of the flight.  Again, no real event that would have caused that.

Note:  Before I dropped the plane off for annual in mid-Feb, it was at 14 every flight.  The 1st flight after annual in mid-Mar it was between 13.2 and 13.5.  It has degraded since to what you see below.  There was no direct work to the electrical system during annual.  However, they did some extensive work which required dropping the exhaust system.  Could moving things around have caused anything?

Interested in anyone else's experience or thoughts.  Thanks!

My above post is how mine was solved… here’s a 3 page thread on low voltage…

 

[AdamJD]

Thank you!  That thread is very informative.  I'm going to try and dig in and see what I can find.  My problem sounds very similar.  I haven't yet changed the alternator.  But have a new VR, so I'm pretty sure that is good.  I'm hopeful this is a connector / wire issue.  Will report back.

[Ragsf15e]

8 hours ago, AdamJD said:

Thank you!  That thread is very informative.  I'm going to try and dig in and see what I can find.  My problem sounds very similar.  I haven't yet changed the alternator.  But have a new VR, so I'm pretty sure that is good.  I'm hopeful this is a connector / wire issue.  Will report back.

If you crank it up and see 14v measured at the alternator, and less than 14v elsewhere, then the alternator isn’t your problem.

Be careful near the prop.

[AdamJD]

2 hours ago, Ragsf15e said:

If you crank it up and see 14v measured at the alternator, and less than 14v elsewhere, then the alternator isn’t your problem.

Be careful near the prop.

Is there a way to thoroughly troubleshoot without starting the engine?  I watched the Mike Busch 'All About Alternators' from 2016.  He recommended to measure from field terminal on alternator, to regulator, to switch, and back to circuit breaker with engine off, stating you should see close to battery voltage through that circuit.  He stated that if you have 12v at the field terminal on the alternator, then the circuit is not the issue - meaning a bad alternator.  I assume that's because in that case ~12v is flowing through that full circuit to the alternator.  Did you do that before you tested the alternator with the engine running?  Seems like a quick way to determine if it is the alternator, but I'm definitely no expert on electrical systems.

I supposed if the alternator is getting ~12v at the field term with engine off, I can do what you suggest (with really long alligator clips) and measure the out terminal from the alternator when the engine is running to confirm its bad.  Anything less than 14v (with a new regulator already installed) would mean the alternator is not doing its job, right?

Thanks for your advice!

[Ragsf15e]

33 minutes ago, AdamJD said:

Is there a way to thoroughly troubleshoot without starting the engine?  I watched the Mike Busch 'All About Alternators' from 2016.  He recommended to measure from field terminal on alternator, to regulator, to switch, and back to circuit breaker with engine off, stating you should see close to battery voltage through that circuit.  He stated that if you have 12v at the field terminal on the alternator, then the circuit is not the issue - meaning a bad alternator.  I assume that's because in that case ~12v is flowing through that full circuit to the alternator.  Did you do that before you tested the alternator with the engine running?  Seems like a quick way to determine if it is the alternator, but I'm definitely no expert on electrical systems.

I supposed if the alternator is getting ~12v at the field term with engine off, I can do what you suggest (with really long alligator clips) and measure the out terminal from the alternator when the engine is running to confirm its bad.  Anything less than 14v (with a new regulator already installed) would mean the alternator is not doing its job, right?

Thanks for your advice!

Yes, I did do that.  Both the Zeftronics and plane power sites have troubleshooting guides that lead you through pretty well.  You won’t have the full battery voltage on the field wire, but close.  The zef troubleshooting guide gives you a range (~11.5-11.8) or so.

Heres what I found… it’s relatively easy to find very small losses with just battery voltage and no draw.  You can spin your wheels (and I did) finding inconsequential losses.  A EE buddy of mine finally suggested following the voltage out of the alternator with the engine running.  V=i x r, so you see a bigger voltage drop across the same resistance with higher current.  It was pretty clear where the problem was and was not when I tried it this way (with avionics and lights on supplying draw).

I dont mean to say there are a few checks that are good to try first.  Definitely check the field voltage at the alternator (and the connections there).  Check the bus voltage at the cigar lighter to see if it matches your other low indication.  I might also try (because it’s easy) testing battery voltage and following that through the starter solenoid and to the bus, but remember that the alternator voltage is following that route TO your battery, not to the bus, so it’s more likely the problem is between the alternator and the bus if the bus is low.

[PT20J]

There aren’t that many connections. It might be an easiest to just check each one. You might also want to check the brushes in the alternator. 

[AdamJD]

Great info.  I'll report back later this week when I have chance to pull the cowl and start testing.  Thanks!

[AdamJD]

Still stumped. On my last flight, JPI reported volts in mid-12s most of the 2.75 hour flight.  Event went to 11.8 when I was low power and descending. 

Took a multimeter out today with a friend.  With engine OFF and master / alt field ON, measured ~12.5v at the field connection alternator.  Also checked at the VR even though it shouldn't be less than what it was at the field connection at the alternator.  My battery was fully charged as well.  

We then ran the engine and measured at the power buss.  It showed ~14v steady on the meter at the power buss, but showed 13.4v. on the JPI.  The JPI is powered from the avionics buss.  Ran out of daylight to measure voltage with the meter on the avionics buss while the engine was running.  I may go out and do that tomorrow.

1) If I have ~12.5 volts on the multimeter at field terminal on alternator with master / alt field ON engine OFF, then field path from battery through everything to the alternator is good, right?

2) If I have ~14 volts steady on the multimeter at power buss with master and engine ON, the alternator and VR are doing their job, right?

My JPI was installed in Nov 22 and had shown ~14volts in flight until 2 months ago after my annual.  Post annual, it's been fluctuating between 13.5 and 11.8 and trending downward.  Last flight was the first time it dipped below 12 on the JPI.

Open to any thoughts or ideas.

[Ragsf15e]

20 minutes ago, AdamJD said:

Still stumped. On my last flight, JPI reported volts in mid-12s most of the 2.75 hour flight.  Event went to 11.8 when I was low power and descending. 

Took a multimeter out today with a friend.  With engine OFF and master / alt field ON, measured ~12.5v at the field connection alternator.  Also checked at the VR even though it shouldn't be less than what it was at the field connection at the alternator.  My battery was fully charged as well.  

We then ran the engine and measured at the power buss.  It showed ~14v steady on the meter at the power buss, but showed 13.4v. on the JPI.  The JPI is powered from the avionics buss.  Ran out of daylight to measure voltage with the meter on the avionics buss while the engine was running.  I may go out and do that tomorrow.

1) If I have ~12.5 volts on the multimeter at field terminal on alternator with master / alt field ON engine OFF, then field path from battery through everything to the alternator is good, right?

2) If I have ~14 volts steady on the multimeter at power buss with master and engine ON, the alternator and VR are doing their job, right?

My JPI was installed in Nov 22 and had shown ~14volts in flight until 2 months ago after my annual.  Post annual, it's been fluctuating between 13.5 and 11.8 and trending downward.  Last flight was the first time it dipped below 12 on the JPI.

Open to any thoughts or ideas.

You still need to check the avionics bus and/or any other busses added over the years.  I believe the jpi is not sensing it’s own input, but has a separate Sense wire connected somewhere else.  Maybe someone else can confirm that or look through the jpi wire diagram from their website.

you’ve narrowed it down for sure.  Alt and vr are good.