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need help with electrical problem

1

1flyingyogi

Well Known Member
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??
 
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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.
 
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1flyingyogi said:
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.
Click to expand...


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??
 
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.
 
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
 
1flyingyogi said:
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.
Click to expand...

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.
 
Pat Hatch said:
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.
Click to expand...

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.
 
John Tierney said:
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.
Click to expand...

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).
 
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.
 
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.
 
1flyingyogi said:
But the thing that bothers me more is the 8amp draw when the master switch is flipped (with nothing running).
Click to expand...

What kind of switch are you using?

Cessna style split switch------are you only hitting the batt side or also the alt side.

As I recall, a bad diode in the alt can cause your 8 amp draw if you happen to be turning on the field at the same time as the master.
 
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Nominal cell voltage for a lead-acid battery (flooded or AGM; same thing) is 2.0 Volts when fully charged. 2.2V per cell is roughly the threshold to *charge* a lead-acid battery.
https://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery
8 amps is quite a bit for 'idle' current, unless you've got a lot of mechanical stuff that's live in addition to the master contactor (1-2A typical).

I'd certainly find that screw. Even if it isn't your current (pardon the pun) problem, it might well be your problem in-flight at some point.

I really don't understand why anyone who's doing their own electrical work doesn't follow the Matronics Aeroelectric list, and have a copy of 'the book'. (It's a free download.)

Charlie
 
How do I check the master/ start relay?
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By measuring voltage drop while the circuit is under load. The greater the load, the more current that flows and the greater the voltage drop, which makes it easier to find problems. You mentioned using a battery load tester in post #1. Disconnect the starter and connect the battery load tester in its place. Energize the starter contactor and quickly check for voltage drops. I say quickly because the starter contactor is not made for continuous duty, and because the heavy load will be running the battery down.
Most people will connect their voltmeter black lead to aircraft ground or battery negative. That works, but an easier way is to connect the voltmeter red lead to the battery positive terminal and test the positive half of the loaded circuit with the black meter lead. Or connect the voltmeter directly across a suspect component like a contactor.
 
So I had a bit of time at the hangar yesterday and here's what I found out:

When I removed the alternator from the circuit breaker (disconnected it), the amp draw problem went away! So again, with master switch on (everything else off), my ammeter shows 8-9amps being drawn. With the alternator disconnected from the system, when I flip the master, I only get about a 1amp draw. I was told that I could have a bad diode in the alternator. What do you guys think?

I checked my battery again with a load tester and it seems the battery is fine. After a full charge on the battery tender, voltage shows 13.5volts and under load drops to about 10.8 to 11.1volts. Returning to about 12.5volts after load removed and slowly climbing to about 13.x volts.

After this, I pulled the plane out and tried starting it. I noticed that ALL the nuts holding the wires on top of the plugs were loose! I tightened them all and the engine started up right away! I shut down and waited 10 minutes and it started back up again. So that was the cause of my hard starting problems - I hope??

When running, everything seems fine. Alternator charging the battery (reading 14.0volts, and ammeter shows current going into the battery).

Brian
 
1flyingyogi said:
When I removed the alternator from the circuit breaker (disconnected it), the amp draw problem went away! So again, with master switch on (everything else off), my ammeter shows 8-9amps being drawn. With the alternator disconnected from the system, when I flip the master, I only get about a 1amp draw. I was told that I could have a bad diode in the alternator. What do you guys think?


Brian
Click to expand...

Yep, diode issue by the sound of it.
 
Starting problem

If a starter solenoid had inadvertently been used instead of a master solenoid would that cause an extraordinarily high amp draw? Just Askin'
 
update

I got some help from another RV guy at my field and tested my alternator and said it had an internal short. So I pulled the alternator and had it rebuilt, but did some research and found that a brand new one at Autozone was only $43, so I bought a new one and installed that (I had to use the old pulley b/c the new one was too small and would spin too fast).

But... problem not solved. When I turn the master switch, the ammeter still shows an 8amp-9amp draw! With alternator field wire disconnected, the draw went away. We tested the alternator again just to make sure and it's a good alternator.

So my friend tells me that the ONLY other thing it could be is the regulator. Here is a photo of my old regulator:

https://drive.google.com/open?id=0B3XXrCYpP8guYjRfRllNdFhONUU

And bought this new one here (which apparently a lot of VAF guys are using). Part numbrer VR730:

https://drive.google.com/open?id=0B3XXrCYpP8guczV3RC10QWYxNmc

The only thing is I don't know which terminal is used for what. I called the tech line and got a bit of help, but just wanted to be 100% sure before I install it. Can someone please confirm?

Here's what I got from the tech guy at Duralast:

He said that the far left terminal (apart from the other three) is for an indicator light - not used in my application. The next one over is for the "switch battery voltage" - same as my red wire on my current regulator? Next to that is for the "stator terminal" - not used in my application?? And the last one over is the "field winding" - wire that goes on the top terminal in my current regulator that connects to the field on alternator. Is this right??

Thanks again for all your help!

Brian
 
When the engine is not running, the voltage regulator will allow maximum field current to flow, usually 3 to 5 amps depending on the size of the alternator. 7 or 8 amps is excessive for the size of alternators used in homebuilt aircraft.
 
problem fixed!!

Finally!! I was getting pretty frustrated and was going to just give up and pay an A&P to figure it out for me if I couldn't make any progress today. But after installing the new voltage regulator, it worked perfectly. Amp draw now is about 2amps as soon as I turn on the master switch and then settles down to about 1amp.

Thanks again for everyone's input. Now, I just gotta put the plane back together and hopefully go flying again by this weekend!! :D
 
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