[bjb3013]

I flew yesterday and noticed thet my GRT EIS was showing from 14.2 to 14.8 volts after 45 min. I had the upper alarm set at 14.6 V so it kept coming in and out. It started on a decent when I throttled back and kept up the rest of the flight. I finally figured out that when the landing light (100Watt) was on, the volts went to 13.9.
With all electrics lights,pump etc. the volts went to 13.5 The amps seemed to be fine.

I have a lead acid battery so I will check the cells and dig into how old it is.
Is there anything else I should check before pulling the Alt. What is the Max output I should see. I was 40 deg and kinda slow to crank. Can a weak battery cause this?

BB

 

[lucky333]

Regulation problem?

Weak cranking is a result of low voltage at the starter. Could be a weak battery. Or if the battery is good, maybe its not getting properly charged variousl reasons.

Don't know if you have an internal or external regulator but the first thing to check is to see if all connections are tight and clean. Don't forget the grounds, alternator to engine, engine to firewall, firewall to battery.


Assuming that the regulator is good, remember that the it will drive the alternator to make the voltage it senses agree with its setpoint... so make sure that the sense wire is measuring near the battery and that its connections are good as well.

From your voltage readings, I would first look for a difference in voltage between where the alternator is sensing the system voltage and where the battery/bus is. Grounds, crimps etc. A wide swing implies that there is a voltage drop between what is on the busses and what the regulator is seeing or that there is resistance in the current path.

BTW Measure the voltage yourself rather than relying on the GRT. Nothing at all against GRT (I'm going that way too) but it takes one measurement error source out of the equation. Measure it with a good DVM and if it agrees with GRT, its good. If not, fix THAT and proceed..

You can check a wet battery by removing the caps and dipping your voltmeter probes into adjacent cells. (Engine off) From cell to cell, you should measure 2+ or more and they should all be close. Significant differences indicate degradation of the individual cells. Voltages less than 2 V/cell indicate a severly discharged cell or one on its way out. BTW, use cheap probes or wrap bare wire around your good ones when dipping.. sulfuric acid and all of that.

A bad battery can cause voltage excursions with load depending on lots of factors including the regulator and wiring.

If you think that all is well so far and have an external regulator you can measure the field voltage (which is what controls alternator output) against the loads. You'll have to start the engine for this one so don't walk into the prop.. You'll need the GRT and a voltmeter for this.

Add wire lengths to the voltmeter probes as required to be safe.

Clip a voltmeter to the (F)ield terminal to ground. Start the engine and run at a fast idle with minimal loads and let the battery voltage stabilize from the starting. Note the field voltage. It should be considerably below the battery voltage (4V-7V maybe). That's what the alternator/regulator thinks is necessary to run the system.

Now turn everything on, landing lights etc, and note the battery voltage on the GRT. It should be pretty close to before. The field voltage on your voltmeter should be HIGHER indicating that the regulator is pushing the alternator to deliver more amps to drive the additional loads. If its NOT, you have a regulator problem. If the field voltage is pushing close to the battery voltage with no increase from the alternator, then its the alt.

Finally, don't overlook other drops in the system. Are the contactors healthy or are pitted contacts causing resistance in the charging/supply system? Measure the voltage across the terminals when the system is under load. Depending on what you have between the alternator and the battery, you could have drops in the system that would prevent the battery from getting fully charged.

If it were mine, I'd:
Check the connections
Check the battery
Verify the voltmeter connection (is the GRT getting accurate voltages)
Then check the regulator.

Hope this helps

John

DISCLAMER: Nothing in this discussion should be construed to imply that normal, safe operating procedures should not be observed at all times. (dont walk into the prop, please)

 

[Geico266]

Max output can be anywhere from 14.0 to 14.8.

Your readings sound good to me, but the fluctuation concerns me, should be steady. Check connections, grounds, ect., like the previous posts says.

Try checking your battery before a flight, after it has sat for a min of 12 hours. Should read a min of 12.4 volts. If it is that or lower you may want to replace it, or invest in a good charger than can desulfate a battery. Battery Minder works well.

http://www.vdcelectronics.com/

I think Black & Decker makes a good desufating charger also.

 

[lucky333]

Or just buy a new battery..

Max output can be anywhere from 14.0 to 14.8.

Your readings sound good to me, but the fluctuation concerns me, should be steady. Check connections, grounds, ect., like the previous posts says.

Try checking your battery before a flight, after it has sat for a min of 12 hours. Should read a min of 12.4 volts. If it is that or lower you may want to replace it, or invest in a good charger than can desulfate a battery. Battery Minder works well.

http://www.vdcelectronics.com/

I think Black & Decker makes a good desufating charger also.

For my money, just buy a new battery. Geico266 is correct, there are desulfating chargers that can extend a battery's life but having designed a few, unless you want to maximize the service from a $10K-$20K forklift/pulltruck battery, its not worth it. There are lots of other wear/failure modes.

Nothing makes troubleshooting a charging system easier than a battery in the pink. If you get a new one and find out its something else, well.. you have a spiffy new battery to go with the fix.

John

 

[gmcjetpilot]

Not normal, could be simple fix

I flew yesterday and noticed that my GRT EIS was showing from 14.2 to 14.8 volts after 45 min. BB

I don't think you mention the alternator but with respect to the other post, it is not fine. Voltage should be within a very stable range, +/- 0.10v. You are seeing some big swings which meas the VR is not doing its job.

Others who have this issue found poor connections where the problem. Correcting it solved the issue. Check to make sure ALL connections are good. I would not fly if the voltage remains unstable and pull it off and have it checked by a alternator shop. Good luck.

If you have an Internally Regulated alternator like the Nippon Denso (ND) it should be locked on to either 14.3, 14.5 or 14.6 typically. 13.5 volts is low for most modern alternators, but with a lead acid alternator you can handle the lower volts better. The SLA type Odyssey battery needs about 14.3-14.5 volts ideally. I'd be curious to know what alternator you have.

PS I agree 100% with Lucky333, the battery is the heart or key to a healthy electrical system and as you even pointed out needs a good look at. I have had lead acid batteries stress tested at shops and given a clean bill but they died shortly there after. Some advocate preventative or proactive replacement of batteries, verses the fly till they die method that I use in my cars.

 

[bjb3013]

I checked the battery and 1 day after a 1.2 hour flight the voltage was 11.9 Charged battery fully at home and load tested. Failed the test so I will purchase a new battery then check the system further.

Thanks
BB

 

[Geico266]

I checked the battery and 1 day after a 1.2 hour flight the voltage was 11.9 Charged battery fully at home and load tested. Failed the test so I will purchase a new battery then check the system further.

Thanks
BB

Check out Odyssey dry cell batteries. The new AGM batteries (absorbed gas material) last a long time (5-10 years), and can't spill. Money well spent.

http://www.odysseyfactory.com/