Struggling Battery in Tail

[0TreeLemur]

Our "new" J had a new Concorde battery installed one year ago.   After every flight I connect the battery minder, and every time it indicates less than full charge.   After a while on the minder it indicates full charge.

This doesn't seem normal to me.  It seems to me that when the engine is running, the alternator will easily power for the avionics, and have plenty left over to keep the battery topped off, even when taxiing back to the hangar.

Didn't have this problem in our C, where the battery was just forward of the firewall and we had a generator that didn't keep things charged while taxiing.

I'm suspecting a bad connection somewhere in the battery circuit.   Anyone agree?   How to diagnose?

Thanks,

Fred

[EricJ]

Mine does that, too, and I can measure the batt voltage with a DVM and it's always fine.   I don't know what criterion the minder uses to indicate the battery level, but I've just learned to ignore it.

 

[RLCarter]

You might be looking for a problem that doesn’t exist…

[Will.iam]

Yes my minder will go through the levels even if i just unplug it leave it off the battery for 10 mins and then plug it back in. The difference is how quickly it jumps from low middle and full stages. After a flight it will start off on low and within a min jump to the middle stage where it hangs out there usually for 15 to 30 mins before jumping to the full stage. 

[0TreeLemur]

7 hours ago, RLCarter said:

You might be looking for a problem that doesn’t exist…

That fits.  I'm a solution looking for a problem. 

One question for those of you with alternators.  Our J has no alternator field switch other than the CB.   I gather this means that any time the master switch is on, the alternator field is energized unless the CB is pulled?  How many A is that?  Our J has an "Electrodelta" voltage regulator, looks original.

I remember the Cessna's I used to fly had split master switch, half was the master and the other half was the alt. fld. switch.  Why doesn't my '83 J have a field switch?  Is the VR smart enough to know that the engine isn't running and not energize the field?

Thx.

Fred

[slowflyin]

Same, mine always shows less than 100% after a flight.  

[RLCarter]

@0TreeLemur when I went to an alternator on my E it came with toggle switch & light for the field. When we went to an alternator on the 172 there was no mention of installing a field switch. In the 1500+ hrs put on the Cessna since installing the alternator we’ve had it go off-line maybe 4 times in flight, turning off the radios and cycling the master switch (single switch, not split) it comes back online and starts charging again. Honestly not sure why a field switch is needed or not needed, but I’ve flown other planes other than mine and some do and some don’t 

[0TreeLemur]

51 minutes ago, RLCarter said:

@0TreeLemur when I went to an alternator on my E it came with toggle switch & light for the field. When we went to an alternator on the 172 there was no mention of installing a field switch. In the 1500+ hrs put on the Cessna since installing the alternator we’ve had it go off-line maybe 4 times in flight, turning off the radios and cycling the master switch (single switch, not split) it comes back online and starts charging again. Honestly not sure why a field switch is needed or not needed, but I’ve flown other planes other than mine and some do and some don’t 

The only reason I can think of to switch off the field is while running electrics on the ground with the engine stopped.  If I switch the master on and pull the CB's on all the avionics, something is still causing a negative deflection of the ammeter .  Having the field coil energized full time seems to draw something like 4 or 5 amps.  Accurately reading the ammeter used in the J is really difficult.  I guess I should pull the alternator field CB and see if that is causing that draw.

Definitely want to pull that CB in the case of an alternator failure in flight to preserve battery.

[GeeBee]

The Battery Minder does a "topping charge" which your alternator does not and cannot do. That is why you never see it "fully charged" when you plug it in to the Battery Minder.

 

[A64Pilot]

There is no need for a separate alternator switch, automobiles don’t have them and we have the same or similar electrical systems.

I’m nearly certain anytime the master is on, the VR is powered and therefore there is current to the field on the alternator, nothing that I know of is smart enough to not power the field circuit when the engine isn’t running.

Only thing a split master gives you is the capability of turning the alternator off, without pulling the field CB.

Cessna’s I’ve flown have those obnoxious CB’s that are flat when on and you can’t pull them, so you can’t de-energize anything with the CB, so you have to have a switch.

However I guess not having a separate switch means the pilot has to know that the field CB is the way to turn off the alternator if they ever need to.

[DonMuncy]

I'm trying to think of a reason why I would ever need to turn off the alternator. I suppose if I ever saw the ammeter peg to the right, I might.

[Pinecone]

The split master switch is/was to start the engine without the alternator being on.

The Battery Minder display is sort of odd.  It shows what looks like levels, but it really just telling which mode it is using.

The one that looks like like the battery is under 1/2 is not saying it, it is saying the unit is in Constant Current charge mode, which is where it starts to see if the battery needs a bulk charge.  Bulk charge is used to get the battery up to about 80% charged

In many cases, it switches quickly to Constant Voltage mode (logo looks like about 2/3 full), that is used to top up the battery to about 95% charged.

And then full looking indicator is really about full, as it means over 95% charged and in maintenance/float mode that takes it up to the 100% level.

I plugged mine in today, and it started in Constant Current and quickly cycled to Maintenance/Float.  So the battery was over 95%, but the unit still started with the Bulk Mode, with the logo that looks like the battery is very low.

IMO, they should take off those logos.

[GeeBee]

From the M20R AFM:

ALTERNATOR OUTPUT LOW
(Alternator annunciator warning light flashing)

REDUCE ELECTRICAL LOAD.

If annunciator light still flashes:
AlternatorFieldSwitch ........................................................ OFF 

1. Reduce electrical load, as required, to maintain essential systems.

2. Continue flight and LAND, when PRACTICABLE, to correct malfunction.

[A64Pilot]

37 minutes ago, Pinecone said:

The split master switch is/was to start the engine without the alternator being on

Why would you want to do that? As evidenced by all the aircraft without a split switch, it’s not necessary

All chargers switch from constant current to constant voltage, which is really a misnomer, even cheap single voltage chargers don’t actually switch, but they are initially current limited because they don’t make enough current to raise the battery to the voltage set point, once the battery is charged enough to hit set point then it “switches” to constant voltage, but not actual switching is going on, just it can now hold set voltage is all, then because it can hold voltage set point, current begins to decrease

But there is no switching going on, it’s simply hitting its voltage set point is all, just like an alternator.

”Three” stage chargers really only have two voltage set points, the bulk phase is where the charger is current limited, absorption is where it finally hits absorption voltage, then when amps drop to the set point the charger switches to float voltage, but other than the max the charger can make there is no current limits.

A “three” stage charger does have two voltage set points and DOES switch from one to the other

I think marketing has gotten to battery chargers and a lot of fancy claims are made for sales

Now chargers that you can set max current do exist, but they are usually let’s call them professional chargers, way more expensive than most would pay.

Alternators are set between absorption and float voltage, so they actually slightly overcharge a battery, but obviously batteries are tough enough to handle it.

[T. Peterson]

43 minutes ago, A64Pilot said:

Why would you want to do that? As evidenced by all the aircraft without a split switch, it’s not necessary

All chargers switch from constant current to constant voltage, which is really a misnomer, even cheap single voltage chargers don’t actually switch, but they are initially current limited because they don’t make enough current to raise the battery to the voltage set point, once the battery is charged enough to hit set point then it “switches” to constant voltage, but not actual switching is going on, just it can now hold set voltage is all, then because it can hold voltage set point, current begins to decrease

But there is no switching going on, it’s simply hitting its voltage set point is all, just like an alternator.

”Three” stage chargers really only have two voltage set points, the bulk phase is where the charger is current limited, absorption is where it finally hits absorption voltage, then when amps drop to the set point the charger switches to float voltage, but other than the max the charger can make there is no current limits.

A “three” stage charger does have two voltage set points and DOES switch from one to the other

I think marketing has gotten to battery chargers and a lot of fancy claims are made for sales

Now chargers that you can set max current do exist, but they are usually let’s call them professional chargers, way more expensive than most would pay.

Alternators are set between absorption and float voltage, so they actually slightly overcharge a battery, but obviously batteries are tough enough to handle it.

I know nothing of electrical systems beyond basic switchology ( on/off ) and am just trying to learn something. If the split switches are for the purpose of starting, is it possible the engine starts easier if one of the split switches is off?

[Guest]

3 hours ago, DonMuncy said:

I'm trying to think of a reason why I would ever need to turn off the alternator. I suppose if I ever saw the ammeter peg to the right, I might.

If the alternator started making electrical noise in your avionics, you may want to turn it off.

[PT20J]

I think the primary purpose of the field switch is to reset the over voltage protector if it trips.

I believe Concorde recommends constant voltage charging at as much current as the battery will accept. 

[Fly Boomer]

1 hour ago, PT20J said:

I think the primary purpose of the field switch is to reset the over voltage protector if it trips.

I believe Concorde recommends constant voltage charging at as much current as the battery will accept. 

During constant-voltage charge, the Concord CMM says:

NOTE:  THE OUTPUT CURRENT OF THE CHARGING EQUIPMENT SHOULD BE SET AS HIGH AS POSSIBLE.  RG SERIES BATTERIES CAN ACCEPT CHARGING RATES UP TO 8XC1.

For my RG35AXC batteries, that's roughly 280 amps.

[0TreeLemur]

So, I've learned a lot.   Mostly that I've got the best kind of problem, a non-problem.   Thanks to all for the comments.   Quite a lively discussion!

[Pinecone]

13 hours ago, A64Pilot said:

Why would you want to do that? As evidenced by all the aircraft without a split switch, it’s not necessary

All chargers switch from constant current to constant voltage, which is really a misnomer, even cheap single voltage chargers don’t actually switch, but they are initially current limited because they don’t make enough current to raise the battery to the voltage set point, once the battery is charged enough to hit set point then it “switches” to constant voltage, but not actual switching is going on, just it can now hold set voltage is all, then because it can hold voltage set point, current begins to decrease

But there is no switching going on, it’s simply hitting its voltage set point is all, just like an alternator.

 

In some aircraft, the checklist has you start the engine, then turn on the alternator.  Other have you turn them on before start.  My 252 POH calls for only the Master on for start, then turn on the alternators.

Agreed, but the Battery Minder tells you which charge phase it is in, even if there is no switching of operation.

My point was, the little icon showing a batter with a level inside is NOT telling you the state of charge of the battery.

[cbarry]

A simple reason for a slightly depleted battery charge after a flight is the alternator likely will not be producing adequate output to offset the draw under low rpm operations—such as low power/rpm  taxi.  

[PT20J]

A capacity test is the only way to know for sure the health of the battery. 

[A64Pilot]

Every good battery charger I’ve run, and I lived aboard a sailboat with a 660 AH Concorde battery bank with 4 Very good programmable chargers, when first turned on will initially start out at absorption voltage, even a fully charged battery will initially accept a high charge rate, but very quickly it begins to diminish, Ideally when the batteries acceptance rate hits 1/2 of 1% of the batteries rated capacity the charger will then drop to float, which happens after a few minutes.

If you have a golf cart their charger usually has a meter and you can see charge rate, and many other chargers have a meter also.

The battery is not being overcharged having a 1.25 or so amp charge for a few minutes, most maintainers are actually very low power chargers, because of course their purpose is to maintain a charge, not to charge a low battery.

To see this, unplug your battery minder, tender or whatever on your fully charged battery, then plug it back in, it should start out at absorption voltage for several minutes then drop to float.

[Will.iam]

I think if it was a problem starting the engine with the alternator already engaged mooney would have made all airplanes with alternators have a separate switch. My 252 has 2 alternators and in the event i need to isolate one or both of them i have a nice split switch to control each of them that you use to also test them individually during preflight. Since i have to turn them off anyway during runup, it just makes sense (from a minimum number of switching on and off) to start the engine with them already in the off position. I then switch on the engine direct driven alternator first at idle and slowly increase rpm until i see the voltage on the battery increase then i turn on the 2nd alternator that is belt driven as it spins faster than the engine driven one so the voltage jumps even higher when turned on at same rpm. Thus a save an extra switching of the first alternator switch to off and back on during the test.