Essential Bus breaker tripping issue

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Paul
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Re: Essential Bus breaker tripping issue

Post by Paul »

With a working alternator and a low battery, the essential bus will trip under load. The alternator puts out more power than the CB likes to see. Once this happens, you're just running on battery power. A classic DA40 gotcha is having a hard time starting but finally succeeding. Now the battery is low but you taxi under relatively low power and no issue. Then either on the run up or takeoff roll, when you add power, the essential bus trips.
Last edited by Paul on Thu Jul 28, 2016 3:27 am, edited 1 time in total.
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Steve
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Re: Essential Bus breaker tripping issue

Post by Steve »

Paul wrote:With a working alternator and a low battery, the essential bus will trip under load. The alternator puts out more power than the CB likes to see. Once this happens, you're just running on battery power. A classic DA40 gotcha is having a hard time starting but finally succeeding. Now the battery is low but you taxi under relatively low power and no issue. Then either on the run up or takeoff role, when you add power, the essential bus trips.
My recollection is that the MAIN TIE breaker is the one that trips in this situation, not the ESSENTIAL BUS. I'm not sure what could cause the OP's symptoms.

Steve
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Paul
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Re: Essential Bus breaker tripping issue

Post by Paul »

Yes I think you are correct and I am not. It's been a while since I flew a Diamond although I'm scheduled for multi engine DA42 training in two weeks.
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Veldung
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Re: Essential Bus breaker tripping issue

Post by Veldung »

I brought the plane back in the shop this morning and I hope the mechanic listens this time. It has been in the shop twice because of these issues and they could never find anything wrong with it. I'll keep you guys posted what they find. Or at least I hope they find....
Last edited by Veldung on Thu Jul 28, 2016 2:25 pm, edited 1 time in total.
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Rick
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Re: Essential Bus breaker tripping issue

Post by Rick »

How old is the alternator? If it has more than a couple hundred hours on it, I would have the mechanic at least look at the brushes. Your is a 2005 - I'm pretty sure you can pull the brushes on the OEM Kelly Aerospace alternator without removing it.
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Veldung
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Re: Essential Bus breaker tripping issue

Post by Veldung »

I believe it is the still the OEM alternator. I will give the shop a call and let them know to check that first. They think it might be a corroded wire somewhere but I don't really believe that.
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Veldung
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Re: Essential Bus breaker tripping issue

Post by Veldung »

Getting a little bit frustrated here... My mechanic couldn't find anything wrong with the electrical system. Again! That was now the third time in the shop for the same issues and "nothing wrong" with the plane. I asked him if he can replace the brushes and he said he would have to pull the alternator off to do so. I assumed you could change the brushes on the Kelly Aerospace alternator without taking the alternator off.
I guess I need to get the brushes myself and find another shop who is willing to put them in. If that doesn't help the voltage regulator might be next. Its just frustrating that they can't whats causing the issues.
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Re: Essential Bus breaker tripping issue

Post by rwtucker »

When I was reading the beginning of this discussion, I was thinking of an off-beat problem like a belt that was somehow slipping after heating up. After I looked at your graphs, and assuming that the drops do not coincide with your switching on an electric Hibachi, your alternator/regulator system is failing by definition. You can get this kind of erratic behavior from a few different causes. One cause is a failing electronic component in the regulator that is triggered by a specific threshold of heat and/or voltage. It might be OK initially at 2700 RPM but then, when hot, fail at 2350 RPM but be functional again at 2250 RPM, or a slightly different load, etc.

Whatever the problem, any shop who looks at your graphs ans says "nothing wrong" is by definition incompetent. Your graphs define something wrong. Full stop. It is no surprise that the system may check out OK on the ground but fail in the air. Real mechanics know this and implement a strategy that might involve substituting parts.
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Re: Essential Bus breaker tripping issue

Post by Tim H »

I decided to replace the alternator brushes during an annual two or three years ago. After 610 hrs TTSN, one of the brushes was worn almost to the wear bar and the other was 1/8" above the wear bar.

Took the A&P less than 1/2 hr and he did not have to remove the alternator. (Kelly Aerospace P/N ALU-3045BS for the brushes)

2005 DA-40 with G1000.
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Re: Essential Bus breaker tripping issue

Post by Sandy »

Steve said:
My recollection is that the MAIN TIE breaker is the one that trips in this situation, not the ESSENTIAL BUS. I'm not sure what could cause the OP's symptoms.
In my case, when I taxied out with a low battery it was the ESS Tie breaker that popped. Looking at the schematic, the ESS Tie and Main Tie circuit breakers (each rated at 25 amps) are connected in series (as long as the ESS Switch is OFF), so I think that the one in any given plane that actually trips at the lower current will be the one that trips first.

I've been looking at the various threads that relate to a low battery voltage followed by excessive current flow causing the tripping of the ESS Tie or Main Tie circuit breakers when the alternator tries to recharge the battery with a higher than 25 amp current. The recommendation that makes sense on the ground is to adjust the idle to keep the charging current under 25 amps until it is possible to go to full power without exceeding 25 amps.

I wonder why Diamond does not include a current limiting circuit in series with the Main Tie and ESS Tie breakers, to limit the current to below 25 amps, so that a low in-flight battery does not cause the breakers to pop.

BTW, did we ever hear from Valdung as to what his problem turned out to be?

Sandy
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