What can you tell me about jump starting my plane? How can I tell whether the alternator is charging properly, following a jump-start? How does the Ammeter work? Any problems I should watch out for?
Search strings: jump-starting, alternator output, amp meter, amp-meter, overload, over charge, over-charge, low battery, weak battery, dead battery, under charge, under-charge, voltage regulator, electrical failure.
From a Mike Rellihan Forum post:
Alternator and/or regulator failures can occur following a jump-start (due to a low or dead battery) because the units typically have a lot of time on them, and simply are not up to the demand that is applied under those conditions. When a plane is jump-started, the units not only have to supply the operating loads, but also have to apply a full charge rate to the battery for an extended period of time. Normally the charging system has to run full bore only for 30 to 60 seconds to replace the starting current, after which it begins to taper off. You can see this occur on the ammeter.
After a jump start, the charging system will be operating at full bore for as long as 30 minutes, before it tapers off (assuming that the battery is still good and is accepting a full charge). You can also see this occurring on the ammeter. This generates considerably more heat in both the regulator and the alternator; neither of which is designed for sustained full output (in the original stock units). And in fact, a 60A Ford or Prestolite unit won’t even produce more than 80% output after it gets hot; which in the case of a jump start is probably within 5-10 minutes or less. That’s why we don’t have constant trips on a 50A alternator output breaker connected to a stock 60A alternator, during high load conditions.
On many modern aircraft, the alternator is already taxed just providing operating power for well-equipped planes. When the charge rate drawn by a very low battery is added to this load, and the parts are operating for an extended time at high output and high temperature, it pushes some percentage of them over the edge.
The old original generator systems are a bit more tolerant, but only because of two of their inherent shortcomings. They are much heavier; and that added mass of iron helps them deal with heat. They also typically have a much lower output rating (typically only 30-35A), so they simply can’t generate as much added heat. On the other hand, they will take much longer to bring back a dead battery.
I have read some analyses that claim that a fully discharged battery cannot be brought back to its original fully charged state by a typical mobile charging system. Those writings claim that restoring full capacity to a fully (or nearly so) discharged battery requires bench charging, using a temperature-monitoring smart charger. The charging method and pattern varies by battery type and size. Restoration also depends on whether there is any internal battery damage, such as sulfate flaking or plate shorts from warping. While I can’t say with certainty that this is true, as opposed to being esoteric charger marketing hype, personal experience tells me that it may well be true. In many cases involving conventional (refillable) lead-acid batteries, I have seen that a battery never regains full amp-hour capacity after a complete discharge. In fact, many automobile owners have had this same experience; leaving the headlights on just once, until the battery is dead, leads to a need to replace the battery in short order even when it is only a year or two old. A fully discharged battery will often charge up to full indicated voltage; but often will no longer produce the same number of amps for the same length of time, as compared to an undamaged battery of the same age. This can be seen on a simple load tester, without benefit of the more expensive battery testers.
You can reduce the risk of a post-departure charging system failure by leaving a power cart or jumper cables connected for at least fifteen minutes before trying to start, so that the battery gets partially restored. This works far better when jumping from something like a car with a running engine (held at 1,500 RPM minimum), so that full charging system voltage is being applied. Using a charging system can get the battery up to 13V or more; especially if conditions allow keeping the jumpers attached during engine start. Pre-charging works far less well with something like a power cart containing one or more batteries, simply due to the lower voltage available to transfer charging current. A battery cart typically can’t get the battery back to much above 12.5V, despite being connected during the starting process.
This inherent weakness in the old original charging systems is one of the key reasons why we recommend the Plane Power alternator and the Plane Power or Zeftronics voltage regulator conversion, when the opportunity arises. These are our preferred replacement products that we install at KLUX. So far, so good.
Of course, the moral in all this is, DON’T DO JUMP STARTS!. Remove the battery and charge it properly on a bench. This also avoids the risk of a battery box explosion from hydrogen gassing in the battery compartment. It isn’t uncommon to have a small spark in one of the battery connections when the starter is engaged, or during a high charge rate, especially when the battery isn’t receiving enough maintenance attention. Far better for this to occur on a bench, if at all. Removing and reinstalling the battery also helps preclude the possibility of a connection that might spark during starting or high-rate charging.
Courtesy of BAC Member Bill Sciscoe:
That was a beautiful explaination of this system, its inner workings, anomalies and short comings.
You do not have to be a student of aviation very long to learn, that accidents, fatal accidents, occur because of a cascading chain of events. Like, a dead battery, a quick jump start, “we are late now, let’s jump back in the aircraft and go.” Follow this with skipped items on the checklist and skip over the amp meter in your instrument panel scan. Then you takeoff and climb into a complete electrical system failure, without a fully charged battery to power any of the essential items necessary for a safe decent to an airport and landing (quite possibly at night with the shorter days we have this time of year, speaking N. hemi, you ozzies). I have heard of people flying home on a 496 panel display. I would not really want to though.
I do not know a pilot with more than 1 hour of logged time that does not “often” skip over the amp meter in their scan. There are no color markings on the darn thing. So, I am pretty sure that 90% of the pilots out there could not tell you what the darn thing means anyway.
We have 3 primary circuits in our aircraft electical system.
1. The Batt circuit, provides power to the starter and emergency power to Main Bus (our ampmeter is in this circuit, only). This is a two way circuit that accepts power back to the Batt, for recharging. Our ampmeter swings both ways to show us which way the power is going, in this circuit.
2. The Voltage Regulator circuit, provides excitation power to the Alternator, from the Main Bus (Batt). This is a one way circuit.
3. The Alternator circuit, provides power back to the Main Bus supplying the aircraft system electrical load. This is a one way circuit. (If we had a true ampmeter, it would be in this circuit showing the true aircraft system electrical load.)
Amp Meter or Not an Amp Meter?
When is an ampmeter not an ampmeter? The answer is, when it is wired the way it is in our aircraft.
An ampmeter must be wired in the circuit to measure the load, between the power source and the load. An ampmeter placed in a circuit will tell you how many total amps of load is being drawn from the power source, by the load down stream of the ampmeter.
In our aircraft the ampmeter is wired between the Battery and the Main Bus Bar (the Load). It is not in the circuit between the Alternator and the Load.
So, in our aircraft the ampmeter is an ampmeter only when the Batt Master Switch is on and the Alt Switch is off (or the Alt / Voltage Regulator are defective).
During Normal Ops, with both switches on and Alt / VR circuits and all components are working, our ampmeters then become an “electrical system & battery health meter”. The Alt circuit is carrying the aircraft system load with no ampmeter in that circuit to indicate to the pilot what that total aircraft electrical system load is.
Our aircraft “electrical system / Batt Health Meter” is now telling us one of four things.
1. The needle is centered or very, very slightly right (+) of center, the Alt / VR circuits are good, supplying the power for the aircraft electrical system load and providing a slight trickle charge back to the Batt which is also, good. This is Normal Ops and what we all want to see.
2. The needle is far right (+) of center, the Alt / VR is working hard to repay a pretty discharged Batt. This condition should improve, with the needle coming back towards the center. If it does not, we have a problem.
3. The needle is left or far left of center (-), the Alt / VR circuit is not healthy or it is dead, with the aircraft Batt carrying the load of the electrical system and discharging (the Batt is bleeding to death). Do not takeoff or if you are airborne land asap. Our aircraft ampmeter is a true ampmeter at this time. Because it is between the only power source (the Batt) and the total electrical system load. The good news is you have a true ampmeter, the bad news is, you will not have anything electrical for very long.
4. The needle is left or widely fluctuating, the Alt / VR circuit is not able to handle the total load of the electrical system and is tapping the Batt for power. We have a problem, hung starter, cycling gear pump hyd. motor, short to ground, defective Alt / VR circuit, the Batt has a shorted cell, etc….
This is my interpretation of our electrical system and our limited human / pilot interface with it.
I hope this is more clear than mud and helps our understanding of this system.