While the cat's away...

[azure]

LOL, I still don't think you have anything wrong. You have a bit of voltage drop in your system, that's the way the laws of physics work.

I know. What I saw yesterday would be FINE, if that was what I normally saw. Normally I see 13.2-13.3. Sometimes lower. I've even seen below 13.0 in flight. And my Sandel will go offline at about 12.4 (I think -- might need to be a bit lower, but it's somewhere around there).

Here's the thing, "Are you running out of electricity? Do you have breakers popping and the charging system going off line?

Yes. See post #231.

If you don't have a problem, it ain't broke. If it ain't broke, don't fix it. If these are long term accurate and stable readings on your instruments with no problems in operations, there is nothing to fix.

They aren't. The readings I saw yesterday were very different from what I've been seeing for over a year. And the NY A&P who maintained the plane for several years said that the lower readings were not what he had been seeing.

 

[Henning]

I know. What I saw yesterday would be FINE, if that was what I normally saw. Normally I see 13.2-13.3. Sometimes lower. I've even seen below 13.0 in flight. And my Sandel will go offline at about 12.4 (I think -- might need to be a bit lower, but it's somewhere around there).


Yes. See post #231.


They aren't. The readings I saw yesterday were very different from what I've been seeing for over a year. And the NY A&P who maintained the plane for several years said that the lower readings were not what he had been seeing.

But if I understand you correctly, since you went and pulled the battery leads and put the batter on the tender for a while, the situation has resolved itself and you now have good readings. Is this not correct?

 

[azure]

But if I understand you correctly, since you went and pulled the battery leads and put the batter on the tender for a while, the situation has resolved itself and you now have good readings. Is this not correct?

The battery has been on the tender intermittently before, since it's what my A&P uses. It was on the tender for a few days before I flew up north last Saturday. During that flight I noticed the usual low bus voltage readings. At the end of that trip the CB tripped. It was then on the tender again until yesterday. All of a sudden I see really decent, rock solid readings. For the first time, and so far for only about 0.1 tach hour. I think it's way too soon to pronounce the patient cured.

Sure, if this becomes the "new normal", then it would support what you've been saying. But (1) there's no real evidence that my charging system hasn't been keeping the battery up (since the voltage at the battery is at least 0.5 V above the bus voltage) and (2) I still can't fathom how a battery that's not quite fully charged could drag down a perfectly good alternator. Ship's ammeter does register a rightward deflection indicating a charge after engine start, but that's only for a couple of minutes. I don't see evidence of any charging load on the alternator during flight.

Oh yes, my Minder Plus just came. Now I've got to decide whether to put the battery on that, thereby changing another variable, or keep it on my A&P's Tender for a while longer.

 

[Dr. O]

First off, your batter is weak (probably a high resistance cell) and not capable of a full charge... A fully charged battery (after the surface charge bleeds off) is 12.70 - 12.75 volts (2.12 volts per cell)... At 12.60 you are already 10% - 14% discharged... Borrow a battery and swap it out for a quick test... Most modern batteries at rest will run 12.8 volts or a bit more... A weak cell will cause the battery to accept a charge only for a few minutes then act like it is fully charged because of the internal resistance of the bad cell...

(p.s. I just checked my two aircraft batteries - 12.82 not on charge within the past two weeks - and 13.02v off the float charger a couple of hours... It was setting on the welding bench and I am doing some welding today, so it was unhooked earlier...

You alternator does not seem to be able to feed the load as well as it should as the voltage sags off after a start when you turn on the avionics... Could be the regulator, or could be be a couple other things (not gonna do a tutorial here) Your 13.4 volts running seems to be low to me... I would expect 13.8 - 14.0 minimum (1 volt above a full charge at minimum) with no avionics turned on right after cranking the engine...

As far as testing a battery, it is done with a load meter, not a volt meter... I have two RG35 batteries from the airplane (changed out for new batteries on a schedule) that I use around the shop for odd jobs... Both will hold the loadmeter needle in the green for a full ten seconds at a 180 amp load - a battery with a weak cell will not do it - as I suspect yours will not...

Good luck...

denny-o

 

[azure]

First off, your batter is weak (probably a high resistance cell) and not capable of a full charge... A fully charged battery (after the surface charge bleeds off) is 12.70 - 12.75 volts (2.12 volts per cell)... At 12.60 you are already 10% - 14% discharged... Borrow a battery and swap it out for a quick test... Most modern batteries at rest will run 12.8 volts or a bit more... A weak cell will cause the battery to accept a charge only for a few minutes then act like it is fully charged because of the internal resistance of the bad cell...

I've been through this several times with my A&P... he seems to think it depends somewhat on the battery model, and that anywhere in that range of 12.5-12.8 is acceptable as long as it doesn't drop any further. There's also calibration error -- the 12.6 was my reading using my Fluke, but my A&P read 12.76 I think. Do you have a reference for 12.6 being under spec?

Unfortunately I don't have access to a battery I can borrow, certainly not one that is known to be good.

You alternator does not seem to be able to feed the load as well as it should as the voltage sags off after a start when you turn on the avionics... Could be the regulator, or could be be a couple other things (not gonna do a tutorial here) Your 13.4 volts running seems to be low to me... I would expect 13.8 - 14.0 minimum (1 volt above a full charge at minimum) with no avionics turned on right after cranking the engine...

100% agreed. And I DO see 14.0 after engine start, with no avionics running. Assume the JPI reads low, then it's probably 14.2. And during flight when I'm seeing 13.2-13.3, it's really 13.4, which I AGREE is too low. But how can it be the alternator, when it was keeping the bus voltage up at 13.8 yesterday (measured with a voltmeter, the JPI read 0.1-0.2 lower) under all normal loads, and just a smidge lower with the pitot heat on? Really the only difference from previous times was the guy in the right seat who was futzing with the rat's nest of wires and the connections to the bus.

As far as testing a battery, it is done with a load meter, not a volt meter... I have two RG35 batteries from the airplane (changed out for new batteries on a schedule) that I use around the shop for odd jobs... Both will hold the loadmeter needle in the green for a full ten seconds at a 180 amp load - a battery with a weak cell will not do it - as I suspect yours will not...

If I had my own load meter I would use it... but I don't. My A&P has one and he claims the battery passes.

Good luck...

Thanks.

 

[Henning]

If I had my own load meter I would use it... but I don't. My A&P has one and he claims the battery passes.


Thanks.

You can take the battery out and take it to Pep Boys or where ever (if you have a good auto electric place...) and have them toss it on their machine. Some of the places have pretty sophisticated stuff if you want a second opinion.

 

[denverpilot]

I think I've posted this before here in this thread, but a membership in the Cessna Pilot's Association and a call to John Frank out there will get you a step-by-step "you can't screw this up if you follow instructions" test plan that will remove all wive's tales, lack of A&P electrical knowledge, self-doubt, etc.

They've been through all the possible permutations and they have the schematics and know-how. Really, my membership in CPA pays itself off every year easily, just in their Tech documentation. They really should call themselves the Cessna Technical Association, since they've never offered one whit of information on how to *pilot* a Cessna. But their tech staff and in-house library are one of the best out there.

 

[azure]

They sound a bit better in that regard than CFO then... and CFO is pretty good.

I may go ahead and join, just for another set of technical minds and ideas. For the moment though, I'm starting to suspect this problem is nailed. 1.2 hours under the hood this afternoon, first time since December (and boy did I suck! ), 1.6 total, 1.4 on the tach. Not once in flight did I see the bus voltage below 13.6 on the JPI. A quick call to my A&P afterward confirmed that he had cleaned up some messy (and actually dirty) connections, especially where the alternator wire comes in, making (he hopes) a temporary fix permanent.

So I'll be watching it like a hawk, but I'm guessing this one is fixed.

And my Battery Minder seems to work like a charm. It started the automatic desulfation cycle within 10 minutes of being connected after flying, which means it thought the battery was fully charged. The docs say the battery voltage has to reach 14V before it will start the automatic cycle, and if the battery won't accept a full charge because of sulfation, you need to press the "maintenance" button to start it. So the Minder seems to like my battery... FWIW.

Now on to the next problem... ever since Ionia my gear warning horn is oddly muted. It's always something...