What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

electrical gremlins negative amps

M

magyarflyer

I'm New Here
asking for some help after a frustrating week. My rv-8 with a backup B+C alternator after 200 hrs TT one morning decided to have a dead battery. So i charged it and checked for function. All ok, recharged, went flying. During flight battery depleted slowly with -11 amp reading. Shed instruments (GTN 650 Dynon A/H, garmin comm) still reading -7 amps. Got stuck at Sherman where i had to recharge battery to come back home.
So far we replaced the alternator with a new one, the battery with a new one, the voltage regulator with a new one, guess again: - 11 amps. We checked the fuses and circuits but cannot come up with an answer. Any ideas will be appreciated. I have an air-power brand new alternator, odyssey 680pc battery and a new automotive voltage regulator that we piggy back into the system since i was not sure the b+c alternator was faulty. So far lots of screws and wires around but no joy
safe flying
 
You do have the alternator belt installed, right?? ;) :D (I know... probably not in the joking mood - sorry...)

It sounds you've replaced everything in the charging circuit except the circuit breaker to feed power to the alternator ('field supply'). Is it supplying power??

What do you have on the B-lead/alt output? OV crowbar and/or a big breaker of some sort?
 
Amp draw

It sounds like the alternator isn't putting out amps or they are not getting where they belong.
Internal/external regulator
Field wire
Field breaker and switch?
I've heard of lots of broken or loose field wires. Test the circuit from end to end and pull on connectors.
Check the "B" lead circuit.
Take the alternator somewhere to test it. I've seen out of box failures.
Just my old guy automotive opinion.
 
YellerDaisy said:
You do have the alternator belt installed, right?? ;) :D (I know... probably not in the joking mood - sorry...)

It sounds you've replaced everything in the charging circuit except the circuit breaker to feed power to the alternator ('field supply'). Is it supplying power??

What do you have on the B-lead/alt output? OV crowbar and/or a big breaker of some sort?
Click to expand...

good catch, i do have the belt installed
B-lead has a crowbar OV
maybe is time to set fire to the thing....:)
thanks
 
As Carl said the voltage is much more useful than the current.
If the bus voltage is at 12 (or 12.x) then the battery is supporting all the electrical loads and nothing is getting from the alternator to the bus.
If the bus voltage goes up to 14 at first and then drops back what is getting hot and stopping the power from reaching the bus?
Do you have any soldered joints that are breaking down?
Do you have any breakers that are misbehaving?
Look at each component in turn until you find the culprit.
Use a digital voltmeter to confirm what the aircraft is telling you.
 
Had this happen to me. Had us all shaking our heads. I decided I'd recheck every wire. First wire I pulled off was the B lead. It all looked good BUT when I twisted it, the connector came off in my hand. The original crimp was good enough for the first ten years but over time, it had been arcing inside the connector just enough to slowly fail the connection reliability. Put a new B lead connector and wire on it and all was well. Give everything a good tug and twist in addition to just looking at it.
 
magyarflyer said:
varies 14 volts when i start then drops to 12 after battery discharged when running idle for a bit losing voltage obvious
Click to expand...

At 14V the alternator is working. Then stops or output declines. Sudden or gradual drop to 12.8V?

If sudden then sounds like the OVP crowbar may be firing, but your alternator breaker doesn't pop?

If gradual maybe slipping alternator belt? Or bad connector or bad alternator (rectifier bridge) -- something heat-related?

Finn
 
electrical problem

My rv-8 with a backup B+C alternator after 200 hrs TT one morning decided to have a dead battery

Why doesn't your backup alternator work? That may be a separate problem.

You need to check why the battery went dead while aircraft was sitting or did you just not notice it on the last flight. If it was working on the last flight, you need to find why it drained the battery.

Check the voltage at the B terminal on the alternator with the master on. Should be 12 volts. Some builders put a fuse in the alternator line.

If you don't have an amp meter, take off the negative lead on the charged battery. You should get a spark if there is a drain somewhere.
 
Last edited:
Do you have an ANL fuse in the charging path (alternator to battery) and if so, have you confirmed that it is not blown?
 
anl fuse is not blown, altenator output is adequate, still getting negative amp read on the g3x garmin -11 to -9 amps when running the gtn and g3x
 
Voltage is important, not amps!
Likely that the power being generated by the alternator is not reaching the bus.
Get a thick wire, bolt it to the alternator output terminal and to the bus, don't use connectors just wrap the wire around the studs.
Does it solve the problem?
If yes remake all the connections in your wiring.
 
magyarflyer said:
anl fuse is not blown, altenator output is adequate, still getting negative amp read on the g3x garmin -11 to -9 amps when running the gtn and g3x
Click to expand...

The negative reading is not helpfull unless we know how the shunt is wired. It can be set up three different ways with three different meanings. Suggest you follow the wires from the shunt and see where they go.

Larry
 
Can I suggest that you ensure your earth points are ok and that there is no corrosion causing a high resitance in the relevant circuits. Especially the earth point for the Regulator if you have a separate one mounted on the airframe. Additionally, I recommend you replace the Master Switch (if it controls the Alternator) or the Alternator Switch as high resistance across the switch will upset the field voltage and can cause the Alternator to generate a lower output. Depending upon the switch itself, you might be able to open it up and clean it.

Cheers,
 
Link to B/C wiring diagram

https://bandc.com/wp-content/uploads/2018/05/sb1b-14_dgm_rev12-14.pdf
https://bandc.com/wp-content/uploads/2018/05/sb1b-14_technical_manual_revC.pdf

Test SB1B-14 stand by regulator.
Make sure you have continuity, 0 OHM between pin 4 and pin F on the stand by alternator. Pull the 5A field circuit beaker to Normal alternator.
With master ON and engine OFF you should see 12 V and about 3 A on the
alternator Field wire connected to pin 4 on the stand by regulator.
With master ON and engine ON you should see 13 V and about 1 A on the alternator Field wire connected to pin 4 on the stand by regulator IF battery is properly charged.

Good luck
 
You must log in or register to reply here.
Back
Top