Voltage Regulator Tripping

[pulse1]

Last September we replaced the old dynamo on our Continental 0-200 with a new alternator, a voltage regulator and a new battery. After this change, we flew the aircraft for about 5 hours with no problems and then started to have problems with the overvoltage trip.

Most times, the overvoltage tripped about 2 minutes after engine start. Occasionally it would reset and work OK for the following flight. Mostly it would trip again after reset.

We have monitored the voltage across the battery and, after start, it steadily rises from 13.4V to about 16.5V when it trips. Loading the battery with, say, a landing light, delays the trip.

After extensive voltage monitoring we were convinced that the voltage regulator was faulty and we were supplied with a new replacement. This was fitted at the w/e and intially worked properly, with the voltage remaining stable during a 10 minute taxying test.

However, 10 minutes into the first flight, the overvoltage tripped again.

We are now baffled and don't know what to do next. We have a qualified electronics engineer in our group and he has done most of the testing so we are satisfied that connections and the wiring are correct.

We would be grateful if anyone out there can suggest any further checks we can do. The alternator and regulator were supplied by B and C. Has anyone else had similar problems with B and C regulators?

[411A]

You might check the alternator itself, sounds like to me it might well be an intermittant short in a field winding...IE, when the alternator case gets good and warm.

[Sallyann1234]

It's worth checking the new battery as well. If it has a faulty, high resistance cell, it will not take as much charging current as it should and the terminal voltage will rise unusually high. The fact that the additional current taken by the landing light holds the voltage down lends credence to this.
If the battery does have this fault then it can quickly be proven by leaving a load such as the landing light on, but without any charge being applied. It will run down much more quickly than it should.

[pulse1]

Thanks for a couple of good suggestions.

Sallyann1234,

During our testing, 16V across the battery gave a current of 3 - 5 amps. I thought that was about right and suggests the battery is OK.

[cwatters]

Poor earth on the regulator?

[Sallyann1234]

During our testing, 16V across the battery gave a current of 3 - 5 amps. I thought that was about right and suggests the battery is OK.

Depends upon the battery size. How many AH is it?

[al_uk]

Alternator is a B&C 200G. Battery is a small Odyssey.

Alternator is Permanent magnet, so no field windings.

During testing the 1st regulator, we measured DC&AC voltage between regulator casing and the engine. This was 0V, indicating earth is ok. Resistance was also 0 ohm.

Regulator is mounted on a block of wood (casing not earthed) on the engine side of the firewall. I don't believe it gets hot, but may need to check.

There is a 10,000uF electrolytic smoothing cap on the DC side of the regulator. The troubleshooting notes on the B&C website suggest that this is critical to correct operation. Next steps will be as follows;

1. Triple check the wiring
2. Test the smoothing capacitor
3. Test the voltage/waveform on the AC side
4. Try a different battery
5. Check the temp of the regulator during operation

Anyone any other ideas?

cheers,

Al

[pulse1]

Thanks Al. The battery is a Odyssey 680, 16 amphour motorcycle battery.

[SNS3Guppy]

If the voltage is running away, this isn't a battery problem; it's either a regulator problem or an internal regulation (excitation) problem. A battery with an internal short may take an increasing current, but not an increasing voltage. The voltage regulator, internal or external, determines what voltage output is possible. Regardless of the current demand on the alternator, that voltage should never vary outside the tolerances prescribed by the voltage regulator.

Either the regulator is being fed too much field current by the regulator, or it has an internal short in the field winding or winding to case, but if you have verified that the regulator is good, then you're left with the alternator.

Incorrect placement of the field wire on the alternator will also create a similiar problem.

You're probably using a repackaged ford regulator; it's an automotive regulator with a different data tag on it, and they aren't known for their high quality, longevity, nor excellence out of the box. I've seen several of them bad right out of the box. The only difference between what you're sold, and what you buy from an auto parts store is the data tag, and the price. Generally about five times the cost for the "aircraft" part.

Again, if you're not seeing a runaway current, then you've got an excitation issue going on Improper internal wiring may well be the case, or you've got something else delivering voltage directly off the battery without proper regulation in place.

[Sallyann1234]

Is that a continuous measured current into the battery under all conditions? It's the right level of current to charge the battery when it's been discharged, but too much to maintain as a continuous current when the battery is full.
The regulator should be reducing the current considerably under full charge conditions, with very little going into the battery and only supplying enough current to replace any equipment load.
Going back to the original post, you say that 'the old dynamo has been replaced by a new alternator' and I'm wondering if the combination of the new alternator and the voltage regulator are just pushing too much charge into the battery. Is the regulator adjustable?

[Sallyann1234]

Guppy, we posted at the same time and are thinking along the same lines. Re the battery, I was suggesting that the battery might have a high-resistance cell rather than a leaky one, but the current disproves this.

[al_uk]

Hi Guppy, Sallyann, thanks for the replies. The alternator is permanent magnet, so no field windings/excitation.

Just to clarify - I'm one of the members of the group.

I'm going to try testing the original regulator on the bench with AC and a 12V battery to see if it still regulates.

The regulator should have a stable output of 14.4V under normal conditions.

cheers

[The Flying Pram]

If it's a permanent magnet alternator with no separate field windings then the regulator has to either:
1/ shunt the excess output, or
2/ chop (to varying degrees) the A/C waveform to limit the output. The former was common with British motorbikes 20-30 years ago, and was done with a LARGE Zener diode mounted on a heatsink. Wasteful but simple. The second approach would need more circuitry and would give rise to considerable harmonics on the output, hence the capacitor to reduce this.

The Rotax 2 stoke engines can be fitted with regulators to provide DC battery charging, but 2 types are available, the cheaper version needs a minimum load to work correctly. It may be that your regulator is not capable of switching off sufficiently to keep the voltage within limits unless, as you seem to have found, a small load is applied. A basic magneto equipped aircraft, unlike a car, doesn't need much power to run its systems, so this could explain the voltage rise after a few minutes. Indeed with a conventional regulated alternator it is quite possible for the field to switch off for several seconds if there is no load on the electrical system.

[Sallyann1234]

Just a further thought. You may already be aware of this, but it's possible to get a misleading voltage reading on the regulator output. If the capacitor is not doing its job properly there will be a heavy ripple on the output and unless your meter is one of the 'true RMS' variety it could well follow the peak value and therefore give an false high reading. If you can lay your hands on a 'scope to hang across the battery you will see what the voltage actually is and if the electrolytic is properly smoothing the regulator output.

[Rokbski]

Any solution to this issue?

The voltage regulator dumps excess voltage (>14.4v) as heat through its case. That is why it is metal and looks like a heat sink!
It needs more heat sinking though i.e firmly bolting to something metal like a firewall.

The piece of WOOD you say you have fixed the regulator to is the worst place possible for it!

[No Fly Zone]

One early contact should be an engineer (not a sales type) at the manufacturer's head office. Tell him/her everything you've discovered and ask for suggestions. Odds are that they have heard of this before and probably understand what is happening. When in doubt, consult the best expert you can find and LISTEN to their suggestions.