Two Voltage Regulators?

[MartinPred]

Ever since I installed my brand new lycoming O-360-A1D engine with my old 60-AMP alternator, I've had low voltage problems. The alternator just isn't producing more than 12.5 volts--barely enough to keep the battery charged enough to start the engine.

I've removed the alternator, sent it to the shop for a rebuild, and reinstalled it with no improvment. So now I'm thinking it may be the regulator(s). Last year, I replaced the original 25 amp alternator with a new automotive 60-amp internally regulated one. But I left the old external voltage regulator in place. Didn't seem to make much difference, and the alternator put out about 13.5 volts.

Now with the new engine, I'm wondering if having two regulators is causing me problems. Should I just remove the external one from the system and see what happens? If there anything else i should check?

-Matt
402BD

 

[Ironflight]

Hmmm....intereating - I never thought about what would happen if you had both an internal and an external VR in the same system. I could conjecture a lot of issues between the two, but that is just speculating based on knowing that the internally regulated alternators do not like having their excitation voltage turned on under a load. The external regulator is probably doing just that - and you could have killed the internal regulator. the only way to know for sure would be to take the alternator in to a shop and have it tested. If it is bad, get a new one, if it's good, bring it home. In either case, I'd try disconnecting the external reg entirely, wire the internally-regulated alternator properly, and see if that works.

I'd say there is a non-zero chance that having the two regs killed the internal one - I don't know the probability, but it is non-zero....

Paul

(Oh, and search for some of GMCJETPILOT's posts on alternators....if nothing else, they are educational!)

 

[David-aviator]

Ever since I installed my brand new lycoming O-360-A1D engine with my old 60-AMP alternator, I've had low voltage problems. The alternator just isn't producing more than 12.5 volts--barely enough to keep the battery charged enough to start the engine.

I've removed the alternator, sent it to the shop for a rebuild, and reinstalled it with no improvment. So now I'm thinking it may be the regulator(s). Last year, I replaced the original 25 amp alternator with a new automotive 60-amp internally regulated one. But I left the old external voltage regulator in place. Didn't seem to make much difference, and the alternator put out about 13.5 volts.

Now with the new engine, I'm wondering if having two regulators is causing me problems. Should I just remove the external one from the system and see what happens? If there anything else i should check?

-Matt
402BD

It would seem 2 regulators would confuse the system, like who's in charge of the charging?

I would remove the external regulator from the circuit, it does not have to be physically removed, just disconnect its wires.

My guess is you will see about 14 volts if the internal regulator has not been assassinated by the external unit in a war over who is in charge of charging.

 

[Ted Johns]

Last year, I replaced the original 25 amp alternator with a new automotive 60-amp internally regulated one. But I left the old external voltage regulator in place. Didn't seem to make much difference, and the alternator put out about 13.5 volts.

Wow... just... wow.

Internally regulated alternators do not make the field wire available for an external regulator to control. The internally regulated alt. needs a control signal to turn it on, and a voltage reference to tell it what to regulate. The two wiring schemes are not compatible.

I suggest you decide between the two alternator system types, and make the wiring correct for the one you pick.

A modern IR alternator should put out a bit over 14 volts. If not, something needs fixing.

 

[MartinPred]

Removed the External--no change

As suggested, I removed the external regulator from the circuit--no change. I'm still getting at most 13.1 volts.

So do you think it's a bad alternator? How about the battery? It's an Odyssey that's at least six years old--maybe older.

What should I try next? New alternator or new battery--or something else?

Thanks,

-Matt
402BD

 

[Ironflight]

I still think that you could have done some damage to the alternator Internal VR by controlling from an external one - if it were me, I'd pull the alternator and take it to an Autozone (or clone) and have it tested.

The thing is, if you're getting more than 13 volts, it's doing something! An old battery isn't going to drag the voltage down unless it is badly shorted.

Paul

 

[breister]

As suggested, I removed the external regulator from the circuit--no change. I'm still getting at most 13.1 volts.

So do you think it's a bad alternator? How about the battery? It's an Odyssey that's at least six years old--maybe older.

What should I try next? New alternator or new battery--or something else?

Thanks,

-Matt
402BD

If you have a local automotive shop that can test alternators, they will be able to tell you if the alternator is bad. Many internal regulators are epoxy'd in these days making it impossible to repair, so most of the problems with internally regulated alternators require replacement.

 

[Ted Johns]

As suggested, I removed the external regulator from the circuit--no change. I'm still getting at most 13.1 volts.

So do you think it's a bad alternator? How about the battery? It's an Odyssey that's at least six years old--maybe older.

What should I try next? New alternator or new battery--or something else?

Thanks,

-Matt
402BD

If the battery still cranks the engine reasonably well the battery is not your problem.

Is the DMM accurate and trustworthy?

What is the measurement from the alternator case to the output stud?
What is the measurement from the alternator case to the reference pin?
What is the measurement from the alternator case to the negative battery terminal?
Referencing the above measurements to the case is important because there may be bad ground connections.

What is the measurement across the battery terminals?

If the measurement from case to reference pin is an honest 13.1V, then the alternator should be putting out at least 60 amps, trying to raise the output voltage.

 

[MartinPred]

If the battery still cranks the engine reasonably well the battery is not your problem.

Is the DMM accurate and trustworthy?

What is the measurement from the alternator case to the output stud?
What is the measurement from the alternator case to the reference pin?
What is the measurement from the alternator case to the negative battery terminal?
Referencing the above measurements to the case is important because there may be bad ground connections.

What is the measurement across the battery terminals?

If the measurement from case to reference pin is an honest 13.1V, then the alternator should be putting out at least 60 amps, trying to raise the output voltage.

Those seem like tough measurements to take with the engine running and the prop six inches away. But I did confirm that my local autozone can do a bench test. I'm going to pull the alternator and run it over there this afternoon. If it's bad, I'll grab the popular 87' Suzuki Samurai 55 Amp alternator off the shelf and give that one a shot.

-Matt
402BD

 

[Ted Johns]

Those seem like tough measurements to take with the engine running and the prop six inches away.

A set of 2 meter test leads with alligator clips puts you well out of harms way.

I like to know what's broken before I start to remove parts. That's what works for me.

Without measurements, it's a guessing game. I'm not a fan of this approach. Finding a bad connector after replacing several hundred dollars of hard parts is annoying.

 

[MartinPred]

A set of 2 meter test leads with alligator clips puts you well out of harms way.

I like to know what's broken before I start to remove parts. That's what works for me.

Without measurements, it's a guessing game. I'm not a fan of this approach. Finding a bad connector after replacing several hundred dollars of hard parts is annoying.

I did as advised and measured the voltage at the alternator. It matched my E.I. meter in the cockpit. So I pulled the alternator and took it to a local shop. They could only get about 11.2 volts out of the alternator. So now I'm thinking that it's obviously a bad alternator. I go to my local Autozone and pick a brand new one (the popular 1987 Suzuki Samurai model). I take it back to the hanger, install it, and pull the airplane out for an engine run.

No change. 13.0 is about the max voltage I can get. And the engine barely starts because the battery is clearly not fully charged.

I'm thinking it may be the battery because I put the charger on it for an hour and it prior to this attempt. So the next thing I can think to try is a brand new Odyssey battery.

-Matt
402BD

 

[Ted Johns]

I'm thinking it may be the battery because I put the charger on it for an hour and it prior to this attempt.

What is your charger rated at? If the battery was flat, 1 hour is not likely to be enough. If the battery charger is rated at 6amps, give it at least 5 hours for a flat battery.

Do you have landing lights?
A fully charged PC680 should power two 50W bulbs for over 25 minutes before it falls below 10.5volts.
A fully charged PC680 should power two 75W bulbs for over 20 minutes before it falls below 10.5volts.

If it can do this, it's fine.

 

[MartinPred]

What is your charger rated at? If the battery was flat, 1 hour is not likely to be enough. If the battery charger is rated at 6amps, give it at least 5 hours for a flat battery.

Do you have landing lights?
A fully charged PC680 should power two 50W bulbs for over 25 minutes before it falls below 10.5volts.
A fully charged PC680 should power two 75W bulbs for over 20 minutes before it falls below 10.5volts.

If it can do this, it's fine.

I'll try that test (I have the PC925 in there so I might get even more time than that). But assuming the battery is fine, what on earth could the problem be? A short somewhere in the circuit? Wouldn't that kill the whole system or pop a breaker vs. suck voltage?

That battery is over seven years old, so it wouldn't surprise me if it's on its last leg.

-Matt

 

[AltonD]

Ever since I installed my brand new lycoming O-360-A1D engine with my old 60-AMP alternator, I've had low voltage problems. . . .

Just in case: Do you have a good ground from the engine case to the firewall/Battery negative terminal?

 

[Ted Johns]

But assuming the battery is fine, what on earth could the problem be?

What is the output current of the alternator when the landing lights are on and the engine is running?
What is the voltage from the alternator case to the output stud?
What is the voltage from the alternator case to the reference pin?
What is the voltage from the alternator case to the negative battery terminal?

As soon as you give me those four measurements, I'll tell you what the problem is.

Hint: It's likely to be bad wiring.

 

[MartinPred]

What is the output current of the alternator when the landing lights are on and the engine is running?
What is the voltage from the alternator case to the output stud?
What is the voltage from the alternator case to the reference pin?
What is the voltage from the alternator case to the negative battery terminal?

As soon as you give me those four measurements, I'll tell you what the problem is.

Hint: It's likely to be bad wiring.

Hmm. I didn't write down the voltage with the landing light on but I don't seem to remember much of a fluctuation when I turned things on and off. So I'll go out tomorrow and take a few more measurements. I was getting a discharge light anytime the load was greater than five amps.

Just to make sure I'm on the same page, you're talking about clipping the negative alligator clip to anywhere on the exterior of the alternator, and the red clip to the output stud which is the threaded post that's connected to the bus? After that move the red clip to the reference pin which is the connection to the wire that leads to the ALT switch?

My battery is inside the firewall under the radio stack between the brake pedals, and it's a pretty solid connection to a ground post. But I'll double check it.

Thanks,

-Matt