Replacing my battery - just because

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Rich
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Replacing my battery - just because

Postby Rich » Tue Oct 10, 2017 9:38 pm

The RG24-15M has soldiered on for about 8-1/2 years now. But I have no ready way to perform the recommended load test to confirm how it would serve in flight in an alternator-failure scenario. It cranks the plane for starting just fine, but I don't get into extended-cranking scenarios, so no real stress test there. And that's not the kind of test that matters.

For the last couple of years it's had a babysitter in the form of the requisite Battery Minder when in the hangar. It has generally led a fairly low stress life, as extreme temperatures with said Battery Minder were very rare. There was a period in 2012 when I had starting problems and it got drained down a few times and it had to be recharged.

So it might be fine, but might not :scratch: Before pulling the current one out I will try a crude load test. Turn on stuff to give it a 13-amp load and see how quickly the voltage drops down.
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Re: Replacing my battery - just because

Postby rwtucker » Wed Oct 11, 2017 3:11 pm

I got about the same time out of my first RG24-15M and I credit BatteryMInder (no way to be sure).

I like your mid-load test idea and have never liked (and haven't done) the full load test because of its destructive impact on the battery, even when you do it once. You could add landing and even taxi lights to make the text more conservative or to test for night time capability. Either way, add the load to a fully charged battery and see how many minutes it takes to drop to a target voltage. On an AGM battery, 2.0 volts per cell represents ~75% discharge (25% remaining). I don't think I would cycle it lower than that. If you want to put less stress on your battery, you could stop the experiment at 2.3 volts per cell, which is about 50%. The result is likely to be very conservative because the G1000 will probably function normally down to ~18 volts or less since the components are running from regulated power supplies delivering 5.0 volts and +/- 12 volts. Maybe someone here has had a real life experience with that.

Post your test conditions and findings. When I get time, I'll do the same on my two year old battery. Maybe we can collect a bunch of test data.
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Re: Replacing my battery - just because

Postby Rich » Wed Oct 11, 2017 10:43 pm

Before putting the new battery in today I did this with the old one (ambient temperature about 45 degF):
1. Unplug the battery minder.
2. Turned on the master. Noted system voltage at 26.2.
3. Turned on my normal daytime flying load (avionics plus strobes). This is about 9 amps.

And here's how the system voltage progressed:
Dropped to 24 volts within a minute.
Held at 24 volts for about 25 minutes.
Began a slow drop to 22 volts. This took about 7 minutes.
Started a precipitous drop. Hit 20 volts in just a couple of more minutes. I

I terminated the test at this point after a total of about 35 minutes. Everything was still operating.

After installing the new battery I took the old one home. After about an hour after disconnecting the old battery I read the Open Circuit Voltage of it as 25.3 volts.
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Re: Replacing my battery - just because

Postby rwtucker » Wed Oct 11, 2017 11:09 pm

I don't know enough to interpret that weird voltage curve with the long 2.0 volt/cell plateau but it looks like you would have got a decent 30 minutes out of your 8.5 year old battery, maybe even a minute or two for a landing light.

I think that normal discharge curve voltages are close to linear until you reach 45-50%, then they begin falling off rapidly. What you saw might be the behavior of batteries that have accumulated sulphates over the years.

Anyway, not bad when the hangar talk is that we are doing well to get five years from our batteries. Good battery, good BatteryMinder, or both! Might be worth keeping the old one in the shop for avionics tests, etc.
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Re: Replacing my battery - just because

Postby gordsh » Thu Oct 12, 2017 12:32 am

May I ask what model BatteryMinder you all recommend for the DA40? I know its one of the 24 volt models but not sure of the Amperage. A few of them are labeled "Aviation Calibrated". Also I am assuming you connect the BatteryMinder to the airplane via the GPU socket or...do you have it wired directly to the battery of the aircraft? I have a couple Battery Tenders that I used for my motorcycle and lawnmower but they are 12 volts only.
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Re: Replacing my battery - just because

Postby Rich » Thu Oct 12, 2017 12:50 am

gordsh wrote:May I ask what model BatteryMinder you all recommend for the DA40? I know its one of the 24 volt models but not sure of the Amperage. A few of them are labeled "Aviation Calibrated". Also I am assuming you connect the BatteryMinder to the airplane via the GPU socket or...do you have it wired directly to the battery of the aircraft? I have a couple Battery Tenders that I used for my motorcycle and lawnmower but they are 12 volts only.


It's the one specifically recommended for the Concorde batteries: 244CEC1-AA-S5 and I have the BM-AIK2 kit. Somewhere here is a thread on the latter installation possibilities. I'll see if I can find it. But basically the connector is wired to the battery and sits inside the Ground Power access door.

Here's a post on a thread about this viewtopic.php?f=8&t=4390&p=59657&hilit=batteryminder#p59632
Check out the thread for more ideas.

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