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#1
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Ongoing Arrow alternator/charging problem
Hi everyone,
This group seems especially knowledgable, I hope you don't mind a question about a friend's plane. Its a 78 Arrow and is being used by a FBO for training. For the last month or so, they can't seem to keep the battery charged. Started a month ago and the alternator was found not putting out anything. Swapped it for a rebuilt alternator and two weeks later -- dead battery again. Same thing -- no output. Took the alternator back to the seller who tested it and confirmed that it wan't putting out. Bought a brand new one and installed it. Seemed to be putting out, but pretty low amperage except at high RPMs (Arrow has a load meter, not charge/discharge meter) . Exactly two flight hours later -- dead battery. Apparently, the alternator isn't putting out again. And the A&P is at a loss. I suspected the voltage regulator, but he says he's had it tested. Has anyone else run into a problem like this before? Or can anyone offer a suggestion on where to look for the root of this problem? I'd like to help him get this fixed -- we're both working on Instrument time and we're splitting the time between his Arrow and my Cherokee. Thanks guys... Chuck |
#2
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Swapped it for a rebuilt alternator and two weeks later -- dead battery
again. Same thing -- no output. Just curious if anyone tried to figure out what failed in the original alternator? You might also have the battery checked too. -- Dr. Nuketopia Sorry, no e-Mail. Spam forgeries have resulted in thousands of faked bounces to my address. |
#3
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There's another box in the charge circuit, the overvoltage relay. It
could be tripping at too low a level. And if the battery is old or has been overcharged, it won't charge regardless. Put a voltmeter on the battery terminals, check the voltage. Then start the engine, turn on the alternator switch and check it again. With the engine at taxi speed, you should get over 13 volts if the regulator circuit and alternator are working. If you're getting 13 volts and the battery still dies, replace the battery. |
#4
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A couple of people on here hit on what we think was the solution --
the battery. Apparently, although not old, it had been discharged too many times recently. We swapped the battery out today and then took it on a 2.7 hour ride. Everything worked perfectly. So, although we don't know why the rebuilt alternator gave out so soon after installation -- the ongoing problem after replacing it the second time was the battery. Thanks for all the suggestions guys... Chuck |
#5
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An intermittent open circuit on the alternator output terminal can
kill the diodes in an alternator. You can play hope and poke for a long time and some day you may replace the correct item. or you can run a simple test. This is easy to test. For a 12 volt system apply a 12 ohm resistor between ground and the alternator output terminal to get about a 1 amp load. Turn on the master and measure with a DVM the voltage drop between the battery + and the alternator terminal. Shake, thump and move wires, amp meter circuit breakers, master relay etc and watch for any voltage change. If the voltage changes more that a millivolt or so find out what is loose and fix it. This method allows you to measure EACH crimp connection, each wire section and each item in the path that the 1 amp current is flowing in. V=IR If i= 1 amp then V=R One millivolt is one milliohm. The method is called a Kelvin 4 wire ohm meter measurement. The DVM must be able to read millivolts. Remember if the alternator outputs 60 amps then the voltage drop is 60 times what you measure with the one amp load. The voltage drop should be less than 1 volt at full output. John On Wed, 15 Dec 2004 01:28:50 GMT, Chuck wrote: Hi everyone, This group seems especially knowledgable, I hope you don't mind a question about a friend's plane. Its a 78 Arrow and is being used by a FBO for training. For the last month or so, they can't seem to keep the battery charged. Started a month ago and the alternator was found not putting out anything. Swapped it for a rebuilt alternator and two weeks later -- dead battery again. Same thing -- no output. Took the alternator back to the seller who tested it and confirmed that it wan't putting out. Bought a brand new one and installed it. Seemed to be putting out, but pretty low amperage except at high RPMs (Arrow has a load meter, not charge/discharge meter) . Exactly two flight hours later -- dead battery. Apparently, the alternator isn't putting out again. And the A&P is at a loss. I suspected the voltage regulator, but he says he's had it tested. Has anyone else run into a problem like this before? Or can anyone offer a suggestion on where to look for the root of this problem? I'd like to help him get this fixed -- we're both working on Instrument time and we're splitting the time between his Arrow and my Cherokee. Thanks guys... Chuck |
#6
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Another test trick with Lycoming belt driven charging systems is to drive the alternator only with a 1/2 hp or more hand held electric motor instead of using the engine. The direction of rotation isn't critical. If you want to have "variable" speeds, put a cone pulley on the motor. This makes it a lot easier and safer to work around. Disadvantages are getting access if your cowl doesn't split, but of course that is always a problem. Recognize though that in service the alternator spins probably close to 10,000 RPM. |
#7
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Following up on the follow up. Two days after replacing the battery,
it died again. Man, was my friend ****ed. This plane is used as a trainer and flown a LOT. The A&P pulled the cowl and when he looked at the alternator -- he found the spring that holds the brushes against the stator sticking out of the top and the hold-down screw gone. They took the alternator out and back the the place that just rebuilt it. I understand there were more than a few harsh words about shoddy repairs, multiple tries, and loss of revenue. They (of course) rebuilt it again and didn't charge for it. It came back and was put in yesterday. This morning, he and I flew it for 3.5 hours. No problems. HOPEFULLY this is the end of the power problems. Chuck On Thu, 16 Dec 2004 05:44:30 GMT, Chuck wrote: A couple of people on here hit on what we think was the solution -- the battery. Apparently, although not old, it had been discharged too many times recently. We swapped the battery out today and then took it on a 2.7 hour ride. Everything worked perfectly. So, although we don't know why the rebuilt alternator gave out so soon after installation -- the ongoing problem after replacing it the second time was the battery. Thanks for all the suggestions guys... Chuck |
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