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Charging Question (Electrical - Not Credit)
Looking for some opinions and I know that there are no shortage of those
here. I just returned from a little night ride to get my three landings and noticed what appears to be an abnormal reading from the ammeter. When on the ground, preparing for takeoff, I see a significant rise on the ammeter when I switch the landing light and fuel pump on. I know that this is normal, particularly with the landing light drawing a good bit of juice. The question is...When applying full engine power for takeoff, the ammeter rose off the scale. Not a sudden pop of the needle, but a pronounced rise as the RPM went up. When throttling back to cruise power, the meter drops to a more normal reading? Opinions??? Thanks Mike |
#2
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Generator or alternator?
Mike MU-2 Helio Courier "Michael Bremer" wrote in message ink.net... Looking for some opinions and I know that there are no shortage of those here. I just returned from a little night ride to get my three landings and noticed what appears to be an abnormal reading from the ammeter. When on the ground, preparing for takeoff, I see a significant rise on the ammeter when I switch the landing light and fuel pump on. I know that this is normal, particularly with the landing light drawing a good bit of juice. The question is...When applying full engine power for takeoff, the ammeter rose off the scale. Not a sudden pop of the needle, but a pronounced rise as the RPM went up. When throttling back to cruise power, the meter drops to a more normal reading? Opinions??? Thanks Mike |
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On Tue, 30 Nov 2004 00:01:03 GMT, "Michael Bremer"
wrote: Looking for some opinions and I know that there are no shortage of those here. I just returned from a little night ride to get my three landings and noticed what appears to be an abnormal reading from the ammeter. When on the ground, preparing for takeoff, I see a significant rise on the ammeter when I switch the landing light and fuel pump on. I know that this is normal, particularly with the landing light drawing a good bit of juice. The question is...When applying full engine power for takeoff, the ammeter rose off the scale. Not a sudden pop of the needle, but a pronounced rise as the RPM went up. When throttling back to cruise power, the meter drops to a more normal reading? Opinions??? Thanks Mike Is this in a Piper? If so, could be a faulty regulator. z |
#4
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Michael Bremer wrote: Opinions??? What type of aircraft? George Patterson If a man gets into a fight 3,000 miles away from home, he *had* to have been looking for it. |
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Opinions??? What kind of ammeter? The one that shows alternator output; or the zero-center kind that shows battery loss/gain? With the first, what you describe is possible. The load is heavy, exceeding the available output at low RPM. At high RPM, you have more output. Of course, there are lots of factors -- how high did it get? Did it drop off when you turn off the landing lights? -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
#6
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Well...I guess I should have given more info, sorry.
It is a Piper Cherokee 180 (1968). We are talking about an alternator (pretty sure it is a Chrysler). The ammeter shows total load as opposed to charge/discharge. I also have a volt meter which shows steady at all RPM and loads. When I turn on the light the meter rises. It appears to be a stock meter that doesn't have a lot of numbers, basically "0" on the left, "30" in the center and "60" on the right. If I extrapolate/interpolate/guesstimate the readings, it is about 45-50 amps with everything turned on at idle RPM. At takeoff power, the needle swings as fat to the righ as it will travel. As the power is reduced, the needle settles back to the same 40-50 area. Thanks Mike "Michael Bremer" wrote in message ink.net... Looking for some opinions and I know that there are no shortage of those here. I just returned from a little night ride to get my three landings and noticed what appears to be an abnormal reading from the ammeter. When on the ground, preparing for takeoff, I see a significant rise on the ammeter when I switch the landing light and fuel pump on. I know that this is normal, particularly with the landing light drawing a good bit of juice. The question is...When applying full engine power for takeoff, the ammeter rose off the scale. Not a sudden pop of the needle, but a pronounced rise as the RPM went up. When throttling back to cruise power, the meter drops to a more normal reading? Opinions??? Thanks Mike |
#7
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Michael Bremer wrote:
Looking for some opinions and I know that there are no shortage of those here. I just returned from a little night ride to get my three landings and noticed what appears to be an abnormal reading from the ammeter. When on the ground, preparing for takeoff, I see a significant rise on the ammeter when I switch the landing light and fuel pump on. I know that this is normal, particularly with the landing light drawing a good bit of juice. The question is...When applying full engine power for takeoff, the ammeter rose off the scale. Not a sudden pop of the needle, but a pronounced rise as the RPM went up. When throttling back to cruise power, the meter drops to a more normal reading? I'd say it's seems like a fairly flat battery being charged. How long was it since that A/C was flown for a reasonable amount of time ? All batteries self-discharge at various rates depending upon their chemistry. |
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MC wrote in message ...
Michael Bremer wrote: Looking for some opinions and I know that there are no shortage of those here. I just returned from a little night ride to get my three landings and noticed what appears to be an abnormal reading from the ammeter. When on the ground, preparing for takeoff, I see a significant rise on the ammeter when I switch the landing light and fuel pump on. I know that this is normal, particularly with the landing light drawing a good bit of juice. The question is...When applying full engine power for takeoff, the ammeter rose off the scale. Not a sudden pop of the needle, but a pronounced rise as the RPM went up. When throttling back to cruise power, the meter drops to a more normal reading? I'd say it's seems like a fairly flat battery being charged. How long was it since that A/C was flown for a reasonable amount of time ? All batteries self-discharge at various rates depending upon their chemistry. Batteries tend to sulphate as they age. The lead sulphate that forms on the plates as a result of normal discharge is usually converted back into acid during charge, but a small amount always remains, and if the battery is left in a low state for any length of time, the sulphate becomes more permanent. Eventually it breaks off and piles up in the bottom of the cells, shorting them a bit and causing a huge charge rate. Best bet is to try another battery. If the regulator was shot, the lights would get much brighter as RPM came up. Dan |
#9
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Michael Bremer wrote:
: It is a Piper Cherokee 180 (1968). We are talking about an alternator : (pretty sure it is a Chrysler). The ammeter shows total load as opposed to : charge/discharge. I also have a volt meter which shows steady at all RPM : and loads. I've got more or less the same plane. The stock ammeter doesn't show total load, but rather total current supplied by the alternator. If the voltage is high enough so the battery isn't providing any current, it is the "total load." How accurate is the voltmeter? A 0.5V difference makes a *big* difference in how much current the battery is taking. : When I turn on the light the meter rises. It appears to be a stock meter : that doesn't have a lot of numbers, basically "0" on the left, "30" in the : center and "60" on the right. If I extrapolate/interpolate/guesstimate the : readings, it is about 45-50 amps with everything turned on at idle RPM. At : takeoff power, the needle swings as fat to the righ as it will travel. As : the power is reduced, the needle settles back to the same 40-50 area. Remember that alternators can't put out their full rated current at low RPMS. It's quite likely that there's a slight discharge of the battery at idle RPM and full load. Between that an a healthy but low battery, I could envision seeing LOTS of current at high RPM with everything on. Remember that the 60A (or 80% of it anyway) is a rating for continuous load... not continuous load + low-battery charging. The 45A reading at idle seems a bit high. My mechanic has been ferreting out a similar problem with his Arrow. We're suspect that the ammeter is reading too high on his, but haven't been able to measure it directly. Any corrosion on the current shunt in the ammeter would cause it to read too high. I would say put a digital voltmeter on the battery/bus and see how much the voltage changes between idle and full RPM. If it's less than 12.0V at 600-1200 RPM under full load or over 14.5V at full RPM under full load (or not full load for that matter), there's a charging problem. Bus voltage will tell all (unless there's a bad wire somewhere), but the current is hard to judge where is coming from/going to. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#10
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"Michael Bremer" writes:
Well...I guess I should have given more info, sorry. It is a Piper Cherokee 180 (1968). We are talking about an alternator (pretty sure it is a Chrysler). The ammeter shows total load as opposed to charge/discharge. I also have a volt meter which shows steady at all RPM and loads. Actually total alternator OUTPUT, *not* load. {At least in any 12vdc electrical system I've seen...} If the load exceeds available alternator capacity, it draws from the battery. When I turn on the light the meter rises. It appears to be a stock meter As you'd expect -- more load, mode demand, more output... that doesn't have a lot of numbers, basically "0" on the left, "30" in the center and "60" on the right. If I extrapolate/interpolate/guesstimate the readings, it is about 45-50 amps with everything turned on at idle RPM. At takeoff power, the needle swings as fat to the righ as it will travel. As the power is reduced, the needle settles back to the same 40-50 area. So the alternator is putting out 60A at TO rpm. That part sounds OK -- part of that 60A is supplying the lighting load, fuel pumps, avionics, whatever; the rest is recharging the battery from the drain of starting, and other past deficits. My only question: is that ~50A load rational? You can add up the numbers and see... -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
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