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battery discharging in flight

JRo

Well Known Member
Airborne & homeward bound today, my battery began to discharge. It showed around -6 amp, and voltage dropped from 12.9v to 11.8v in the course of a 40 minute ride home. The only system control I could locate in the cockpit was the 30 amp fuse for the generator, which I checked and found OK.

As it was a beautiful day and homeward bound, didn't think an unscheduled landing was called for; pressed on without further incident.

Any ideas?

Thanks,

Jim R.
 
Jim-

The first thing I would check is to make sure the plug into the voltage regulator on the lower engine side of the firewall is pushed in all the way.
 
There are some suggestions at this website:
Testing the Rotax Regulator
In addition to the tests mentioned, I would also measure the DC voltage between terminal "C" and the regulator case (with master switch on and engine off). The voltmeter should read battery voltage on terminal C. A more meaningful voltage measurement can be made while doing this test if an automotive brake lamp is connected between terminal "C" and ground. The lamp will load the circuit to make any high resistance connections more noticeable. If all of the above tests do not indicate a problem, but the system voltage is less than 13.5 with the engine running, then replace the voltage regulator.
Joe Gores
 
Replaced Regulator

Had similar problem but would indicate a charge for 10 to 15 minutes during flight but would then start discharging. Replaced the voltage regulator and haven't had a problem since.

Jersey
 
Settings

Since reading this post, I made it a point to monitor my voltage during a flight this morning. I noticed the voltage to be 13.4/13.5 but it was in the yellow below the green area. I think 13.4/13.5 is good but puzzled why it would be in the yellow range. WHAT should the voltage reading be during cruise with everything turning on??
 
Since reading this post, I made it a point to monitor my voltage during a flight this morning. I noticed the voltage to be 13.4/13.5 but it was in the yellow below the green area. I think 13.4/13.5 is good but puzzled why it would be in the yellow range. WHAT should the voltage reading be during cruise with everything turning on??

What is your normal voltage reading and how much are you drawing (i.e. all the electronics turned on) during the flight? It is possible that you are taxing your alternator a bit too much.

I think most regulators in alternators are set to about 14.1-14.5v. If you start drawing more amps than the alternator can easily handle, then the voltage comes down in relation to the draw. I would think mid 13v would be fair to judge it as the upper part of the yellow, since the 14.x would be the green and 12.x volt would be considered red or near red.
 
I thought Dynon had a low bus voltage alarm. My bus volts are usually about 13.8V, and my ammeter usually shows a trickle charge of1 or 2 amps.
 
Pulled the cowl and began testing. About an hour in, we went to remove plug from regulator/rectifier, and found it loose. One of the 2 securing clips was apparently never seated properly from the get-go! My bad. Once properly "clipped in" all systems normal.

Although I feel foolish, really relieved it was an uncomplicated fix. Whew! I had set aside a whole day for the problem, ended up with the rest of the day free. When does that ever happen, right?!

Jim R.
 
Jim, glad to hear it was a minor issue. Now get that new fuel pump and you should be good to go for a long time.
 
I like reading about the simple fixes. I file them away as stuff to try first if I have a problem. --- like the statue in Animal House said "Knowledge is good"! :)
 
Jim, that is good news. A process of trouble shooting... following the links and finding a solution. And, it is really fun when it turns out to be simple.
So many times that day you set aside.... isn't even enough.
 
Regulator problems......maybe?

If my battery is fully charged and I only have the D180 turned on (everything else is off) and at 4000 rpm my voltage is 12.2 and amps is -2, does this point to a bad regulator? I've checked the connections and they are good at the regulator. I disconnected plug at regulator and checked the connector pins for signs of shorting and none found.
Could this be an alternator/generator issue??
Your replays are appreciated.
Thanks
 
Steve, the regulator could be bad. But test the aircraft wiring before replacing the regulator. Do the tests described HERE. Then use a low wattage 12 volt lamp and connect one lamp wire to the regulator case (not to aircraft ground nor to battery negative). And connect the other lamp wire to regulator terminals B and R and C, (one terminal at a time). The lamp should illuminate brightly. Also measure the voltage across the lamp while it is on. The voltage should equal battery voltage. Again, use the regulator case as a voltage reference, not aircraft ground. If no problem is found with aircraft wiring, then replace the regulator. Loading a circuit with a lamp will make problems show up that might not show up with just a voltmeter alone.
Other possible causes of low voltage could be an open alternator circuit, or a blown main fuse, or a half-bad master switch. If you replace the regulator, use heat-conductive grease between the case and the airframe.
Joe Gores
 
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It was charged after my last flight with battery charger. The reading I had today was with a fully charged battery and a ground run-up to 4000 RPM. Voltage showed 12.2 and amps showed -2 amps at 4000 RPM.
 
Bad regulator

I followed the tests that Joe Gores recommended earlier in this thread on the aircraft's wiring today and everything checked out OK. Everything points to regulator problem.
Thanks Joe for your help.
 
Heat is the enemy of electronics. The heat from the regulator needs to be dissipated both by cooling air and by conduction to the airframe. Use heat conductive grease to help conduct the heat away.
 
Steve, looks like your regulator is dying at about the same point mine did. I moved my new one to the new location away from the heat. Very happy I did. FWIW department.
 
New location

Thanks John. Is the new location inside the instrument bay? Any pictures of new install location? Steve
 
Resurrecting an old thread but it seems the most appropriate place. Sorry for the lengthy post ...

First a bit of history. I've been struggling with voltage regulators, seemingly forever. I had a Ducatti fail early on (65 hrs), probably a problem with the connector. (I currently have almost 300 hrs on the plane.) Another Ducatti went to a low voltage charge and I decided to try the John Deere VRs. I've tried a couple of them but they seemed to have a lower than recommended charge rate (13.3v or so). I tried boosting that a bit by adding 1 or 2 diodes to the VREG CNTRL line to the VR (the signal that goes to the "C" terminal of the Ducatti & the IGN terminal of the JDs) with some success but generally have been barely able to get up to the 13.8v - 14.2v that I think is more normal. I do not know whether any of this is related to my current problem below.

I just had another Low Voltage alert from SkyView with a John Deere AM101406/MIA881279/JDR1406 VR. I swapped in another VR and the result was the same - not charging at any RPM. I put the battery on a battery charger and it was down to about 35% capacity. I measured the voltage on the VREG CNTRL wire at the VR and it was only 1.75v. That was measured between that wire (disconnected from the VR) and airframe ground with the engine OFF and Master ON. I had previously (back in 11/2015) measured that at 11.52v when shooting another problem. I think that should always be near battery voltage, right? All fuses are OK.

I looked at the RV-12 schematics and that VREG signal looks like a pretty straight shot from the VR, through the AV-50000A Control Module, the AV-50002 Ignition and Start module & Master SW, to the AV-50001 Switch & Fuse module. It goes through a 1A fuse in the S & F module but it seems like I'd get a 0v reading if that fuse were blown, not 1.75v.

Not exactly sure how to shoot this problem. Next time I go out I intend to:
  • Back up from the VR, through the AV-5000x modules and check the VREG voltage at each connector. At some point I should find something near battery voltage.
  • Joe pointed to a "Testing Rotax 912/914 Generator and Regulator/Rectifier" article some time ago that I'll try but until I can find the issue with the VREG line I doubt this'll be productive.
  • ?????

I'm pretty much at a loss here about any other approaches. Any thoughts about anything else I can do to shoot the problem?
 
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Install a new-style DUCATI R/R under the avionics shelf as recommended by Van's. At the risk of jinxing my unit, my replacement/relocated DUCATI R/R seems to be surviving for the past 380 hours.
 
Install a new-style DUCATI R/R under the avionics shelf as recommended by Van's. At the risk of jinxing my unit, my replacement/relocated DUCATI R/R seems to be surviving for the past 380 hours.

Sorry, should have mentioned that. Already inside under avionics shelf. Has been there since the build ...
 
If there is not battery voltage on regulator terminal "C", then the circuit MUST be open. There is either a bad connection or else the 1 amp fuse is blown. Yes, the fuse can be blown even with 1.75 volts on terminal C. The voltage could be coming through the regulator from terminal B. Remove the small yellow wire from the regulator, then measure the voltage on the yellow wire.
Try taking the AV-50001 SWITCH & FUSE MODULE D-Sub connector apart and measure voltage that comes from the 1 amp fuse. If the fuse is OK, then other possibilities are a loose or broken D-Sub connection or a bad master switch.
 
Thanks Joe.
If there is not battery voltage on regulator terminal "C", then the circuit MUST be open. There is either a bad connection or else the 1 amp fuse is blown. Yes, the fuse can be blown even with 1.75 volts on terminal C. The voltage could be coming through the regulator from terminal B. Remove the small yellow wire from the regulator, then measure the voltage on the yellow wire.
Sorry, I wasn't clear. The 1.75v was measured on the disconnected small yellow wire (yellow wire to airframe ground).
Try taking the AV-50001 SWITCH & FUSE MODULE D-Sub connector apart and measure voltage that comes from the 1 amp fuse. If the fuse is OK, then other possibilities are a loose or broken D-Sub connection or a bad master switch.
I'll do that next time out. Sure hope it's not the Master - I had an intermittent Master a year or so ago that I replaced - the lead time for the switch was 6 weeks :(
 
Did you buy the master switch from Van's?
To check the master switch, disconnect the D-Sub connector from the AV-50000A that goes to the IGNITION MODULE. Then turn the master switch on and measure continuity between pins 13 and 14.
If the master switch is bad and you do not want to wait until a new one is delivered, regulator terminal "C" can be jumpered to terminal "B". The disadvantage of doing that is that in case of smoke in the cockpit while flying, the master switch will not shut down the electrical system. It would be necessary to pull the alternator fuse.
 
Did you buy the master switch from Van's?
Good question. I got it from Mouser. Not sure why I didn't get it from Van's. I would have thought that I would have tried them first - don't remember why, it was a while ago.

To check the master switch, disconnect the D-Sub connector from the AV-50000A that goes to the IGNITION MODULE. Then turn the master switch on and measure continuity between pins 13 and 14.
If the master switch is bad and you do not want to wait until a new one is delivered, regulator terminal "C" can be jumpered to terminal "B". The disadvantage of doing that is that in case of smoke in the cockpit while flying, the master switch will not shut down the electrical system. It would be necessary to pull the alternator fuse.
I saw that in the picture in the "Testing a VR" you posted earlier. Wasn't sure what that was for. Good to know ...
 
Suggestion

When my kids were in college, I maintained a fleet of four well used but pretty reliable small 1996 Oldsmobiles for them. I grew pretty good at finding and solving electrical problems with that fleet of four. Initially when there was an electrical problem, I searched for open grounds or broken wires, bad fuses, etc. This was effective and solved most of the problems.

On one car with an apparently unsolvable problem (b.o. radio), I pretty much gave up - but then I removed all of the fuses and replaced them. Problem solved.

So, I have learned to be suspicious of fuses. I recommend that you replace the appropriate fuses even if they check ok. Do the cheap and simple things first. Sounds to me like a blown fuse or two or bad ground has haunted you for quite a while.
 
Digital voltmeters can be misinterpreted. Supposing that a digital meter is used to measure the voltage at the downstream side of a blown fuse and the meter reads 1.75 volts. Is it really 1.75 volts? If a load is connected that requires 1.75 volts, would it work? No, it would not. So is the meter lying? No, it is displaying exactly what it sees. If a digital meter has, say, 5 megohms of resistance and it is connected in series with a blown fuse with a resistance of 30 megohms, an infinitesimal amount of current flows from the source through the blown fuse and through the meter back to the source. If the source is a 12.75 volt battery, then 11 volts are dropped across the blown fuse and 1.75 volts are dropped across the digital meter. The meter reads 1.75 volts.
If a 5 watt, 12 volt, indicator lamp is connected as a load, now the meter will read zero because the infinitesimal current is flowing through the lamp instead of the meter. I like to test a circuit when it is under load to get more meaningful meter readings. By the way, the definition of infinitesimal is the distance that an aircraft carrier sinks in the water when a fly lands on its deck. :)
Fluke Meter pdf talks about input impedance.
 
Not much progress today ...

I still haven't been able to isolate my problem. Here's what I did/saw today:
  • The battery seems to be holding a charge OK (12.75v).
  • Checked and verified good continuity all the way from the small yellow wire at the VR (VREG CNTRL) to the Switch & Fuse Module (AV-50001) via:
    • Control Module (AV-50000A) WH-00063 (21) & WH-00030 (14)
    • Ignition & Start Module (AV-50002) WH-00030 (14) & WH-00030 (13)
    • Control Module (AV-50000A) WH-00030 (14) & WH-00031 (23)
    • Switch & Fuse Module (AV-50001) WH-00031 (16)
  • Checked and verified that the Master Switch correctly made & broke continuity of the VREG signal between pins 13 & 14 of WH-00030.
  • Confirmed battery voltage (12.75v) on the Battery input of the Switch & Fuse Module.
  • ?? With 12.75v on the battery input of the Switch & Fuse Module and with the D-Shell disconnected, measured 9.7v on the VREG WH-00031 (16) S & F module output.
  • Just to verify another S & F module output, I checked the Fuel Pump output (WH-00031 pin 1) and it was at 12.75v.
  • Also measured 9.7v on pin 23 of the Control module end of WH-00031.
  • ?? I couldn't figure out how to measure intermediate voltages between the Control module VREG input, WH-00031 (23), but the voltage at the small yellow VR wire continued at the 1.75v I previously saw.
  • Visually checked the 1A VREG fuse on the S & F module. There was no visual difference between that fuse and the other two fuses on the circuit board but I have no idea if there's any visual indication if these fuses blow.

So, I'm still at a loss. Tomorrow I guess I'll go out and see if I can see some way to check intermediat voltages between the Control module that's at 9.7v to try to see where it drops to the 1.75v I see at the small yellow wire.

I don't understand the drop to 9.75v S & F module VREG output.
 
Instead of using a voltmeter, use a 12 volt test light. The test light should NOT have an internal battery. It should have a light bulb that lights up when connected to the aircraft battery. The wattage of the test light should be 3 watts or less. Any larger than that risks blowing the 1 amp fuse, if it is not already blown, which is a good possibility.
Does the tester illuminate when connected to the voltage regulator output from the switch and fuse module?
 
Bad fuse(s)...?

Tomorrow I guess I'll go out and see if I can see some way to check intermediat voltages between the Control module that's at 9.7v to try to see where it drops to the 1.75v I see at the small yellow wire.

I don't understand the drop to 9.75v S & F module VREG output.

Cat troubleshooting rule #1...always start with the obvious. 9.75v is not right.

Follow electrical safety precautions.

Keeping your meter negative lead (common port) at the same grounding location. Probe to good metal contact with your meter positive lead (V positive port), meter selection on DCvolts.

Unit powered up, and connector disconnected...

Probe all three soldered on fuses, first at their power in lead. Then at their power out lead.

All 6 test points should read Battery voltage. (your 12.75v)

If it drops at all across the fuse, the fuse is bad. If the power in is low, the problem is further upstream. If they all check good, your problem is downstream.

Remember, a bad fuse is a result of a problem. Typically not the problem itself.


Regards,
 
Does the tester illuminate when connected to the voltage regulator output from the switch and fuse module?
Ok, the tester does not illuminate on the vreg output on the back of the s & f module. It does illuminate on other outputs (fuel pump) so the tester is working. If I understand the schematics correctly, that pretty clearly points to the 1a fuse?
 
Jumper the fuse and re-test pin 16. Check pin 23 while your at it... Caution this assumes the short(s)to be elsewhere. (Out of S&W module.) Quick amp draw check?

Recommend testing points in my previous post.
 
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I don't think I have a good way to test those points without a bench setup for the module. The fuses are mounted on circuit board where the module has to be disssembled to get at them.
 
Battery Lead?

You may have checked this, but my battery began to discharge on my 6A in flight; then, the alternator would charge fine when I was on the ground. Turned out to be a loose crimp on the battery lead at the alternator. John
 
If I understand the schematics correctly, that pretty clearly points to the 1a fuse?
I agree. The problem is definitely within the Switch and Fuse module. Since the fuse is the weak link, that is most likely the problem.
As an educational experiment, connect the test light between ground and the yellow "C" wire. The test light will load the circuit. Now measure the voltage coming from the Switch and Fuse module. Notice that the voltage is no longer 9.7, but has dropped to zero. More meaningful voltage test results are obtained when circuits are under load.
 
I don't think I have a good way to test those points without a bench setup for the module. The fuses are mounted on circuit board where the module has to be disssembled to get at them.

Roger that.

Tom you going to send this somewhere to be repaired?

What caused the fuse to blow? Was it the reg? Short in the wiring?
 
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