Main Battery Lasted Over 3.25 after Main Tie Trip

[Lance Murray]

What app did you use to draw that diagram? I have a few diagrams that I need to draw.

[Steven]

An alternative solution to a depleted DA40 battery popping breakers (e.g., after a hot start):

Run the engine on the ground at *low* RPM for a few minutes, setting RPM with the throttle just high enough that the alternator output stays below 25 Amps. The alternator won't provide full amperage at lower RPMs. As amps drawn by the depleted battery go down, gradually increase RPM with more throttle to again stay below 25 amps.

After about 10-15 minutes as the battery charges you'll be able to increase throttle to run-up RPM (where the alternator can provide full output) without popping any circuit breakers. Then it's safe to go flying.

This is the correct procedure.

Someone should come up with a fix so that a perfectly functioning alternator and a low but not fried battery does not trip the breaker (and also deal with the high output alternator tripping the breaker issue).

I recently had this problem and I can confirm that this solution works. I let the battery charge at about 15A, gradually increasing the RPM on the ground for 20 minutes. No further problems.

[Sandy]

A few weeks ago, I had a mechanic install a new battery in my plane. As I always keep my plane in a hangar, connected to a BatteryMinder, I was surprised when I taxied out to the run up area and got a low battery warning. While taxiing the MFD went blank, and the ESS Tie breaker popped. I reset it, but it kept popping, while I noted that the current draw was close to 40 amps, whereby the 25 amp ESS Tie breaker's value was exceeded. I note that while others have referred to the popping of the Main Tie breaker, the ESS Tie and Main Tie breakers are connected in series, so I guess that whichever of them actually pops at the lower current will be the one that pops when the alternator is trying to charge a low battery.

Back in the hangar I took off the upper cowling and did some checks, only to find that there was no continuity through the BatteryMinder harness to the positive battery terminal. I removed the 10 amp fuse from the BatteryMinder harness and it was good, but there was no continuity from the fuse holder to the positive battery terminal. It turned out that when the mechanic uninstalled the old battery the BatteryMinder harness wire that goes to the positive battery terminal had pulled up, inside the positive battery boot, and he never realized it. After I reconnected everything, with the BatteryMinder properly connected to the positive battery terminal, and then plugged in the BatteryMinder, it appeared that the battery was recharging, properly.

I now wonder why Diamond does not include a current limiting circuit between the Main Buss and the Main Tie breaker (which is connected in series with the ESS Tie breaker) to limit the battery charging current, even when at full power, to less than 25 amps, as that would allow for a low battery to be charged, even when airborne, without popping either the Main Tie or ESS Tie breakers, each of which is rated at 25 amps.

Sandy

[Kyle]

Sandy,
I'm curious why your battery required such a high current to charge. It seems that even without a battery minder connected, the battery voltage on a new battery shouldn't drop that much even if it was sitting for a couple of weeks. Had you been using the avionics in the hangar assuming that the battery minder would keep the battery charged?

Kyle

[Sandy]

Yes, Kyle... I had wrongly assumed that I could run the G1000 in the hangar, as I believed that the BatteryMinder was keeping it charged.

Sandy

[rbickford]

I just posted a similar story today, but now see this post. I can also confirm that you can charge the low battery, at a lower RPM, until the draw at higher RPMs stays below 25 amps. Just takes a little patience to get the battery charged up while you are on the ground. This is not intuitive and I was wondering if this is a design flaw or if there is a limiter in my charging system that is failing.

[Sandy]

There is no current limiter included that will limit current to something under 25 amps. Above 25 amps either the ESS Tie or Main Tie CB, each rated at 25 amps and connected in series, can trip. To the extent that they "limit" the current, by tripping and bringing it to zero, that's what happens. However, there are solid state current limiters available that could limit the current to 25 amps or less, so that the issue could be avoided.

Sandy

[rbickford]

HI Sandy. Thank you for the input. When it happened the first time, for me at least, it was not intuitive. I did not connect the dots between the low battery and the amperage draw. Maybe this is a common thing with aircraft charging systems. It would not be acceptable in an automobile charging system design. I am surprised that this issue has not be 'engineered out'. Maybe it has in later models.

[Ultrapilot1]

I wonder if they changed something in the circuit for the DA40's that are airconditioned because they have much larger alternators and a larger current drain on the battery.