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11-08-2016, 10:50 AM
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Join Date: Dec 2015
Location: Long Beach, CA
Posts: 370
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need help with electrical problem
Lately I've been having a hard time starting the engine - it would always start, but I had to crank a lot longer than normal. We checked the timing and load tested the battery and both seem ok. (the load tester read "weak", but not bad enough to "replace").
Yesterday, just to see if it's a weak battery that was causing my problems, we used an external battery to directly crank the starter - it started up right away. Probably one of the easiest starts I've ever had on my -4.
But here's the interesting/ difficult part - when I turn on the master switch, I can see the battery voltage dropping right before my eyes and within 15 seconds, I'm down to about 12.3volts (starting at 14.0). And my ammeter shows that something is drawing about 8amps as soon as the master is flipped on. Engine not running. (nothing else running. lights, radio, etc. all off) The only thing that the master turns on is the turn coordinator, which I cant imagine would draw 8amps. So this would explain my hard starting problem - I turn on the master switch, it drains the battery, and by the time I'm ready to crank the engine, there's not enough juice left to start the engine. But the question is WHY is my battery getting drained just from the master being on?
So do I have a short somewhere in the system? Is it normal for my system to draw 8 amps just sitting with the master switch on?
I have a very simple panel with steam gauges and radio/ transponder/ lights and manual flaps, trim. No EFIS or other electronics.
I have charged up the battery three times and every time it would charge to full, but as soon as I flip my master switch, it would run down.
Not sure if it's related, but a month ago, I dropped a screw into the area where the circuit breakers are and tried to locate and retrieve the screw but just could not do it. I thought to myself, "I hope that screw doesnt make contact with the terminals in the breaker and cause a short". It's in a super tight space and really hard to get to. I will check that next.
Any ideas, guys??
Last edited by 1flyingyogi : 11-08-2016 at 10:51 AM.
Reason: more details
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11-08-2016, 11:11 AM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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How old is the battery?
I suggest that you take all of the positive and negative electrical connections apart between the battery and starter and clean them and then put them all back together.
The master contactor can draw up to 1 amp. And its contacts might be dropping some voltage. The alternator field can draw 3 amps or more. The ammeter might not be accurate.
Measure the voltage between the battery positive terminal and the starter (positive) while cranking, the lower the better.
Measure the voltage between the battery negative terminal and the engine block while cranking, the lower the better.
__________________
Joe Gores
RV-12 Flying
Last edited by Mich48041 : 11-08-2016 at 12:28 PM.
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11-08-2016, 11:22 AM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Quote:
Originally Posted by 1flyingyogi
Yesterday, just to see if it's a weak battery that was causing my problems, we used an external battery to directly crank the starter - it started up right away. Probably one of the easiest starts I've ever had on my -4.
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OK, but where did you hook up the external battery?? You said "directly crank"----does that mean you hooked jumper cables to the starter directly? What about the ground cable??
If that is how you hooked up your external battery, all you proved was that the starter is good.
Unless you used the same wires/connections/contactors/switches etc as are normally used with the onboard battery, you did not do much to identify the problem.
Do you have a good clean ground connection?? do you have a ground strap between the engine and the firewall??
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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11-08-2016, 11:26 AM
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Join Date: Jun 2006
Location: Vero Beach, FL
Posts: 881
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How old is your master relay? I would attempt to eliminate the master relay as the culprit. Not sure why you're seeing 14 volts on the battery initially, that's pretty high. Can you pull all the breakers/fuses on all your equipment except the starter and see if there's any difference? I would also check your engine ground to make sure there's no corrosion on the terminals. Or add a temporary engine ground wire in addition to the one you have. See if that makes a difference. Next thing I would check is your start relay especially if it's got some age on it, however that wouldn't explain the current drain you're getting. Good luck, let us know what you find.
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11-08-2016, 12:55 PM
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Join Date: Dec 2015
Location: Long Beach, CA
Posts: 370
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Thanks for everyone's input. The battery is about a year old. I fly regularly (about twice a week) and never felt the need for a battery tender and have never had a problem until now.
The reason why I hooked up the external battery directly to the starter is to rule out a bad starter or a bad battery. I actually did not even know I had an electrical problem at this point. I was just have difficulty starting, so that's why we checked the timing, then load tested the battery, then cranking the engine with an external battery directly hooked up to the starter (grounding it on the frame). I was in the cockpit holding the brakes and manipulating the throttle and mixture while my friend on the outside touched the cables to the battery/ starter to start it.
Once it started right up, we knew that it was not a problem with the starter/ mags/ timing. Then we shut the engine down and tried it with the ship battery and that's when I noticed the voltage drop and unusually high amp draw. I was able to start the engine back up a second time with the ship batter (took a lot longer cranking). I then checked to see that the alternator is charging the battery and it did. With engine running, it quickly climbed back up to about 14.1volts. As soon as I shut off the engine, (but master still on), the voltage again quickly dropped to about 12.3. It probably would have dropped to even lower if I kept the master on.
I'll be out at the hangar again tomorrow and will try your suggestions. Thanks!
Brian
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11-08-2016, 01:41 PM
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Join Date: Jan 2006
Location: Vonore, TN
Posts: 369
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Quote:
Originally Posted by 1flyingyogi
I then checked to see that the alternator is charging the battery and it did. With engine running, it quickly climbed back up to about 14.1volts. As soon as I shut off the engine, (but master still on), the voltage again quickly dropped to about 12.3.
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Isn't his normal? The battery is 12 volt in a 14 volt system. With the alternator off you should only see a little over 12-volts on a charged battery.
__________________
John Tierney
Vonore, TN
RV-7A - N777JT Flying
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11-08-2016, 03:03 PM
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Join Date: Dec 2015
Location: Long Beach, CA
Posts: 370
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Quote:
Originally Posted by Pat Hatch
How old is your master relay? I would attempt to eliminate the master relay as the culprit. Not sure why you're seeing 14 volts on the battery initially, that's pretty high. Can you pull all the breakers/fuses on all your equipment except the starter and see if there's any difference? I would also check your engine ground to make sure there's no corrosion on the terminals. Or add a temporary engine ground wire in addition to the one you have. See if that makes a difference. Next thing I would check is your start relay especially if it's got some age on it, however that wouldn't explain the current drain you're getting. Good luck, let us know what you find.
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My master relay is was probably installed when the plane was built in 2006 (I'm not the builder). It has 411hrs on it now. How do I check the master/ start relay? I will pull the fuses on my equipment and see what happens and also check my engine ground my next trip out to the hangar.
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11-08-2016, 03:14 PM
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Join Date: Dec 2015
Location: Long Beach, CA
Posts: 370
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Quote:
Originally Posted by John Tierney
Isn't his normal? The battery is 12 volt in a 14 volt system. With the alternator off you should only see a little over 12-volts on a charged battery.
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I'm not sure. But technically, a "12-volt" battery is actually supposed to be 13.2 volts b/c each cell is 2.2volts x 6 cells. So under no load, fully charged, a "12volt" battery should read 13.2volts, correct? And I guess the 14volts is what it will read as it's charging?? Someone more knowledgeable can confirm?
But the thing that bothers me more is the 8amp draw when the master switch is flipped (with nothing running).
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11-08-2016, 03:44 PM
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Join Date: Jun 2006
Location: Vero Beach, FL
Posts: 881
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Best way to check your battery/start relays is to borrow a couple of new ones and change them out. If that's not possible, on the battery relay, I would pull all of your CBs, turn the master on, and measure the voltage on the battery side of the relay (measure from the terminal post to any firewall ground) and compare it to the output side of the relay. Should be about the same. Next, push in all of your CBs and see if there's any difference in the readings. If you have a voltage drop with the CBs in, try to isolate the equipment that is causing the problem by pushing the CBs in one at a time. For the start relay, first disconnect the wire from the relay to your starter and be sure to isolate the loose end of the wire. Please be careful! Now you can check the voltage drop across the relay in much the same manner as you did the master relay. Have someone push the start button and measure the voltage from the battery side of the relay to ground and then from the starter side of the relay to ground. Again, should be about the same. If you get a significant drop across either relay, I would suspect a bad relay.
Do the easiest stuff first: check your battery connections and your engine ground wire. Adding a second engine ground can tell you a lot if there's a difference in the cranking. If you have a bad engine ground, the starter will seek a ground through your engine controls, like the throttle or prop cables, and in extreme cases can melt the cable housings. Feel around for any heat in the wires or relays after you've made a couple of start attempts.
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11-08-2016, 03:44 PM
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Join Date: Jul 2007
Location: Taylorsville, Ga
Posts: 798
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I normally will see some battery voltage drop with minimum instrumentation on ie Dynon ifly gps and of course the master solenoid. But cranking is normally no problem even with 10v DC indicated. Maybe a look at the starter would be in order. Then a weak battery just accelerates the down hill spiral. Thinking you may find your problem either in the battery or starter. Good luck troubleshooting and stay clear of that prop while all that's going on.
__________________
DRRhodes
2020 VAF Supporter
RV9 N908DR
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