Low Voltage Problem - Any Suggestions?

[luv2flypilot]

I am 2 hours away from the 40 hour mark and entering phase II and I have recently started experiencing low voltage problems with the 60 amp breaker in line with the alternator tripping intermittantly. I have a Vertical Power VP-200 which monitors every piece of my electronics equipment and have had no problem with any of the circuit breakers tripping within the VP unit as well as can individually monitor each device and its load. Some things I have checked that seem a little out of the norm to me are are the following:

1) With the engine stopped I turn on the VP-200 unit and the activate the switch to the Field and get a 4.0 amp draw. This circuit breaker is rated at 5 amps and this seems a bit high to me since typically you would have a breaker that is rated 125% of the load. Could this be because of something wrong with the alternator creating a higher load internally?

2) With the engine stopped and the field turned on, I get almost 1 volt difference between voltage metered on the field input and alternator output. I was getting around 12.8 V on the alternator output with about 11.7 V on the alternator Field input.

I have a Plane Power AL12-EI160 60 amp internal regulated alternator and speaking with them on Friday, they said that to try and do the test with reading the voltage at the field input and alternator output and there should be no more than a .2 V difference. They said that if it is higher, then it could be something wrong or a short on my field circuit. I have traced and metered the circuit from the alternator field input to the VP box and have no shorts, chaffing, etc. I can monitor the entire current load of the panel from the VP-200 screen and the max I have ever seen is around 33 amps at take off with landing lights, strobes, boost, at everything running. Seems strange that this 60 amp breaker is intermitantly tripping. Maybe I have a bad breaker? Not sure what the chance of that could be? I also want to note that I have checked my Odyssey PC680 battery and spoken with them as well and do not think I have a battery issue. Any suggestions or help would be greatly appreciated.

[647jc]

I would replace the 60 amp breaker. Not too difficult to do and not too expensive. If it does not solve the problem.... you will just have a spare.

[rvator51]

My Plane Power Alternator pulls about 4 amps when the engine isnt running. Once the engine is running, it drops to under an amp. When I talked to the Plane Power support person, he said that was expected behavior. I resized my VP-100 CB to 6 amps just in case.

The other thought I have is that I wonder if the 33 amps you are monitoring on the VP-200 also includes the amps that are going directly to the battery to recharge it from the Alternator. When you include that, could it sometimes to tripping the breaker? I may be remembering it wrong, but I seem to recall that you want your main breaker sized larger than the max amps put out by the alternator to eliminate nuisance tripping but I could be wrong.

[luv2flypilot]

Thanks for your posts and suggestions. I have traced out the field wiring, verified proper wire gauge and everything seems to be correct with no short, etc. I also notice that the field does drop from 4A to about 2A draw once the engine is running as you also indicated Tom with your VP-100 and Marc Ausman at Vertical Power said this is normal. In speaking with Plane Power they stated that their 60A alternator will put out more than 60A, however they do not recommend running it continously at more than 60A to ensure it does not heat up and/or cause internal damage. With this being said, I plan on keeping it the breaker at 60A since with full power requirements to my panel with everything running the maximum draw is around 32-35 amps max and Plane Power told me that even with a very low battery, the alternator should not put out more than an additional 10 amps to try and charge the battery.

I have a new Odyssey PC680 battery coming on Friday and will try to see if that makes any difference. I am wondering if it is possible that a battery cell(s) could be shorting out at high current loads, therefore causing a higher resistance and output from the alternator above 60A? Oddyssey told me that they recommend using their charger to maintain and charge the battery and that a trickle charger under 2A could actually damage the battery. I have been using a 1.25A battery tender/charger and just found this out by speaking with them. When I test the battery with a battery load tester, it indicates that the total AH load is only around 6-7 AH when the battery is listed to be 16 AH. The battery is strong enough to start the engine, however maybe something is going on with it once a large current is applied on main power circuit. If this does not correct the problem I will replace the 60A breaker to see if maybe it is faulty. I am also going to call Plane Power tomorrow to see what they think about the input voltage being almost 1 volt difference between the field input and the alternator output when the field is turned on. They told me last week that this voltage should be be only a .2 volt difference at max with the field turned on and the engine not running, however ohms law would tell me that there could be a 1 volt difference due to the higher load from the field being turned on. The alternator has also been pulled and checked out as OK. I will try one thing at a time and will let you know what I find.
__________________
Bryon Graves
Discovery Bay, CA
RV-7A, N507RV - Stuck @ 38 Hours / Flying Phase I

[luv2flypilot]

As suggested I replaced the 60 amp circuit breaker mounted on my engine firewall with a 60A fuse I purchased at Kragens (Aircraft Supply ) and temporarily secured it in the engine compartment using one of the mounting studs on the circuit breaker for support. Test flew tonight for 45 minutes staying close to the airport with no issues. Seems as through the 60A circuit breaker purchased from Spruce Aircraft ( http://www.aircraftspruce.com/catalo...es/6070amp.php ) only lasted 37 hours and must have been failed due to the heat in the engine compartment. I was hoping to get some feedback on whether people used a circuit breaker or fuse to protect their circuit and alternator and where others installed theirs?

[luv2flypilot]

Here is a photo of the location of my 60A circuit breaker to protect the alternator and charging circuit. Seems as though it failed after 37 hours due to possibly heat. I was hoping to get some feedback on whether people used a circuit breaker or fuse to protect their circuit and alternator and where others installed it?

[John Clark]

I must agree that the problem is heat related, looking at the mounting location it is going to get quite warm. Circuit breakers are heat sensitive, in fact that is what causes them to trip. Unless the breaker is "heat compensated" the amperage required to trip the breaker will become dramatically lower at a high temperature. $15 ACS breakers are not intended to be in the engine compartment.

John Clark
RV8 N18U "Sunshine"
KSBA

[luv2flypilot]

If I mounted an ANL fuse holder with an ANL60 fuse in the same location within the engine compartment, would it be possible for heat to effect it?

[ronschreck]

Originally Posted by luv2flypilot

If I mounted an ANL fuse holder with an ANL60 fuse in the same location within the engine compartment, would it be possible for heat to effect it?

Fuses are mounted in the engine compartment all the time with good results. Go for it!