How an earth can a new alternator be just shy of 4000 euros.
It’s a 120 euro car part after all
Yes 4k is crazy. Plus VAT too I bet. But this is the wrong alternator. The BC410 is the little backup alternator which some SR22s have although judging from that link not many people know it is there. I have that model installed in the TB20 as a backup too. It runs off a vac pump drive point. It does a clean 15A or so, thus requiring an AFMS and some instructions in the Emergency section of the POH for load shedding. And yes it costs about $2.5k… direct from B&C.
The core return on the BC410 is not a core as such. Only B&C can work on these. The whole old unit goes back to the US.
Anyway the pic in post #1 is the main alternator.
I still don’t get why these are so exposed. That kind of non-waterproofing went out of fashion in the 1970s, when roadsides were littered with broken down Vauxhall Vivas, with water in their electrics 
The water will corrode everything inside. Brushes (which are spring loaded with quite small springs), slip rings, the rectifier assembly… the whole lot. The cable has crimp terminations which will eventually perish due to being filled with water, which will be forced down the length of the cable all the way to the other end, between the strands (I have seen that process work; it’s quite impressive).
2019 I had a defect on my alternator. The whole thing was burned. We opened it and repaired it. So I could have a look inside. No visible corrosion at all. And you know, I`m flying in bad weather all the time. ;-) I would send photos, but with the new engine I got a new alternator too. :-)
Interesting comments. I don’t know anything about the expected long term condition of an alternator, but I wonder if the heat given off dries it quickly and thus mitigates the effect of water ingress. Certainly not ideal, but maybe not as bad as you might initially think?
Yes it is possible the temperature rise boils off the water but it would need to be really hot. Otherwise, at merely elevated temperatures, corrosion merely accelerates.
People do get alternator failures – it is a fairly common thing in GA – and I wonder why this Q never seems to be asked.
Bathman wrote:
How an earth can a new alternator be just shy of 4000 euros.
Well, my 1984 Audi Quattro had an alternator whose replacement cost was $900!
To this point, that probably (certainly should) includes a new drive coupling too. The front mount alternator arrangement is more because of the mechanical opportunity to drive it. The only alternative is off the starter adapter at the back of the engine, and some starter adapters are notoriously expensive and mechanically overworked anyway. The front mount alternator arrangement works well, with one vital pilot operating note:
The drive coupling is a silicone ring friction arrangement, intended to slip in the case of an alternator seizure. If the coupling has never slipped, they’re fine. Once they slip, a little bit of engine oil will find itself into the intended friction area, and the coupling will never transmit full torque again. Replacement of the coupling will be the only $$$$olution. The pilot can prevent slipping (other than alternator internal seizure) by managing the electrics better: (Peter will be better than I at this logic, but I did the math years ago)…..
You’re hurtling down final approach at night, everything turned on, carrying some power. All the electrics are drawing watts. Watts are RPM times torque. With the engines creating decent RPM, the torque stays low. You cross the threshold, and close the throttle(s). RPM drops to idle, watts stay the same, so torque goes way up. That increase in torque can be enough to momentarily slip the coupling, and introduce engine oil. After a few repeats of that situation, each less good than the last, the coupling is frictionless, and you’re wondering why the alternator light(s) are coming on under a “normal” electrical load.
Lycoming pilots, and some rear mount alternator pilots don’t have this problem, as the belt driven alternator will just slip the belt (though note that Lycoming alternator belt replacement requires the removal of the prop – unless you carry a special substitute assembleable belt).
I wish I’d known this back when I flew the C 310 and 340, in hindsight, my lack of this knowledge was occasionally abusive to the alternator drives in my night landings. The first solution is to replace all the lighting with LED, the current draw goes way down, and watts/torque problem solved. If you’re flying incandescent lights, consider switching the alternator(s) off on short final, until you clear the runway. Then landing lights off, RPM up, taxi light on, and alternator(s) on to top off the battery as you taxi in, monitoring the ammeter. Prior to LED lights, this is what I did in my C 150 (not the same coupling in an O-200, but still expensive). I’d monitor the ammeter after landing, and by the time I was in front of my hangar, the charge was topped off. I have never had any alternator problems with it.
As for the getting wet concern with front mount alternators, it’s imperfect, but many things are. I think they run warm enough to mostly boil the water off anyway…
Are we not all using a check list which ensures no avionics are exposed to the startup and shutdown of an alternator?
I’d be very unhappy to cycle my alternator on and off with a full panel of expensive toys powered up.
GA_Pete wrote:
I’d be very unhappy to cycle my alternator on and off with a full panel of expensive toys powered up
The Cessna cautions in this regard are with respect to turning on the alternator, that the avionics master should be turned off. Turning the alternator off will not cause a voltage spike. If operationally it’s not convenient to unload the torque on the alternator drive, consider reducing it, alone with keeping the RPM faster as possible. For my modestly avionics equipped planes I have not been too concerned about cycling the alternator with avionics on, but I do respect that this would be a much more important consideration for “well” equipped planes.
My caution is with respect to Continental direct drive alternator engines (knowing that some 470’s and 520/550’s are belt drive). Lycomings are all belt driven, and not affected. As I worked for many years in the engine shop repairing and later designing and approving replacement Continental starters, I saw the damage being done to the starter adapter shaft gears from torque overloading of accessories, and electrical consumption is within the pilot’s control. We tried for more than a year to develop a replacement improved drive coupling for the Continental front mount alternators, but could not produce the desired product improvement. We gave up. During this development, I came to understand what a pilot can do to reduce load and damage to the drive coupling. Happily, LED lighting will greatly reduce this problem in the future.
I do have an LED landing light but need to change the taxi light too.
Mine is wired such that selecting landing light actually selects both.
I’ve got a ‘ford escort’ looking alternator which is rear-of-the-engine belt driven so not too much of a worry. No idea how expansive they are, let’s hope I don’t need one for quite some time.
Yes, for sure, if you lower the alternator rpm then the regulator winds up the field current to maintain the bus voltage, and at a constant bus load the alternator torque is proportional (to 1st order approximation) to the field current.
There is much folklore about blowing up avionics by turning the alternator on/off (some previous threads I think) but unless the voltage regulator is defective the bus voltage should not exhibit any spikes. The main reason for turning avionics master off during starting is to protect from the massive spikes from the inductive behaviour of the starter motor. On some planes e.g. the TB20 the avionics buses are all interrupted when the starter is energised, but one isn’t supposed to rely on that.
Why can’t Conti engines have the alternator(s) underneath, and belt driven?
LED lamps help, at ~1.5A (at 28V) versus ~4A.
