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Is the Alternator Switch an Antique?

car alternators

Paul;

I think I understand your point? It is true that the automobile alternator doesn't have a field switch, but it does have an accessory position for the ignition switch, for listening to the radio. For instance, how would you turn on the radio and listen to ATIS before contacting Ground? I operated out of an international airport for years and the convention was to acquire ATIS before contacting Ground Control. We didn't run the engine first for a variety of reasons. The taxi was a mile and a half, so we didn't need to warm up the engine for instance. Wouldn't you just be heating up the alternator, without having a switch?
 
Ironflight said:
So Fred, if I understand your argument, you are essentially arguing against the ND alternator, not the concept of using the circuit breaker on the field as a switch - is that correct?

Certainly that is a valid topic for discussion - not the question I asked of course, but one that would be worthy of it's own thread. realistically, if we are depending on the human to turn off the Master switch at the smell of smoke, we can also rely on him or her to pull the field breaker - there is more time lost in going "what's that smell?" than in operating two "switches".
Click to expand...

I think, that from a safety standpoint, having the pilot to need to perform two functions instead of one, to clear an electrical issue, is more of an issue to me.
The ND alternator certainly performs the required alternator function, but at the price of other safety related issues. No pilot control, and no over voltage control are what you are giving upp.
Yes, those issues are probably far and few between, but, when they happen, can be dangerous. I'd rather spend a little more $$ and install a field controllerable alternator (with built-in over voltage control) that only requires one switch to disable it....
 
Automotive Alternators

Lux Wrangler said:
Paul;

I think I understand your point? It is true that the automobile alternator doesn't have a field switch, but it does have an accessory position for the ignition switch, for listening to the radio. For instance, how would you turn on the radio and listen to ATIS before contacting Ground? I operated out of an international airport for years and the convention was to acquire ATIS before contacting Ground Control. We didn't run the engine first for a variety of reasons. The taxi was a mile and a half, so we didn't need to warm up the engine for instance. Wouldn't you just be heating up the alternator, without having a switch?
Click to expand...

There are a few different electrical designs out there for automotive alternators. Most begin to putput current after the "Field" becomes active the first time, but will continue to output current even after the "Field" input goes dead. This results in non-positive control of the alternator by the pilot. From my experience, most of teh ND alternators fall into this catigory. (Some of these designs can be modified to have positive output control, but it results in a non-off-the-shelf solution.)
Other automotive alternator have a design that results in the field having the ability to shutdown the alternator output once the field goes dead. I've not been able to confirm that the regulator electronics in these units have an explicit over-voltage function to kill the alternator output when an over-voltage condition exists.
Again, I preferr to have positive pilot control of the alternator output. I fly hard IFR so want the maximum safey in my electrical designs....
 
I have 1200 hours on a ND internally regulated alternator which is commonly used on Kubota tractors. No failures. I found a regulator schematic for it (albeit in Japanese) and verified there is OV protection. I am able to switch off the alternator in flight with the field switch.

From my notes:

1-2436-01ND
(Ref. Num. 12189N)
Alternator - Nippondenso IR/IF
40 Amp/12 Volt, 1-Groove Pulley

Used On:
Kubota A28 Engine, Thermo King UMD
Replaces:
Daihatsu 27060-87201
Kubota 15881-64200, -64201
Nippondenso 100211-161, -163, -164, -469, -248
Thermo King 41-0749, 5D36221G01
Lester Nos:
12189

On my rocket I am using the same alternator, and have no alternator switch in the panel. I can get these alternators locally for $105 brand-new.

Found it here for $90: http://www.amazon.com/New-Alternator-Kubota-Thermo-King/dp/B003V1BN60
 
Hey Fred, thanks for the clarifications and contributions. I like threads where we get a lot of data out there - folks are going to make their own decisions regardless, but at least the information can be presented!

Fred.Stucklen said:
Again, I preferr to have positive pilot control of the alternator output. I fly hard IFR so want the maximum safey in my electrical designs....
Click to expand...

I agree! I guess we might differ on how that positive control is achieved, but that's OK...just two different methods.

Paul
 
Ironflight said:
So in summary, I see two good reasons to delete the switch - less chance of accidental activation and the saving of critical panel space (the -3 is a small cockpit).Paul
Click to expand...
Three additional good reasons:
  • Eliminates a point of failure
  • Simplifies the electrical system
  • One less wire to run and hole to drill and switch to mount
 
Over Voltage

Don't underestimate the risk of over voltage. The day my regulator stuck on full output, the alternator put out 19.5 volts. Both the Electronics International Volts/Amps gauge, and the screen on the Garmin 250XL warned of over voltage and the displayed the number 19.5. I killed the field switch and the buss voltage fell to battery voltage of around 12 volts. I fried the regulator in the R C Allen DG.

I had already installed the B&C 40 amp alternator, but was still using Van's cheapo regulator. The B&C regulator cost $228 dollars, but offers linear control, and over voltage protection. I didn't buy it with the alternator because Van's regulator had always worked ok, so why spend the extra money? Right?

Well, the repair cost $400 bucks to fix the DG and another $228 dollars to fix the problem! As it turned out, I hadn't save anything by not buying the B&C regulator in the first place.

Over at Jay Pratt's RV Central there was an RV-8 that had experienced the exact same problem as the Doll with one big difference. Every radio in the panel was fried. Cost??????

I like the ability to kill the field and therefore the output of the alternator while leaving everything else powered up on backup battery power. If IFR, you wouldn't want to kill all power on the main buss to address a fault with the alternator.
 
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Update on my possible over voltage event. The alternator has been run several hours with zero indication of a problem. I tested the backup alternator and it appears to be fine.

So my current view is that the indication of an over voltage on my Rocky Mountain system was in error. If true, then either it was an engine monitor problem or a wiring issue.

Since I just installed a smoke system which required me fumbling behind the panel to get power and a ground source, odds are that I messed up some wiring. I gave a cursory glance in the area today and saw nothing but need to look more closely.

I am leaning towards maybe a disconnected ground and secondarily a pulled wire.

I am still looking for an aftermarket over voltage protection system that is separate from the alternator and not integral to an EXP bus or similar system.

As of today, I see no need to get rid of my alternator field switch.
 
rocketbob said:
I have 1200 hours on a ND internally regulated alternator which is commonly used on Kubota tractors. No failures. I found a regulator schematic for it (albeit in Japanese) and verified there is OV protection.
Click to expand...
Does the schematic have enough detail to be sure there is no failure mode that could lead to OV and also kill the OV protection? You would also need to review the physical layout of the circuit to be sure there were no failure conditions that could come into play due to the location of components or traces. For example, I am aware of a pitch trim system on a type-certificate aircraft that had trim runaways on several aircraft due to corrosion on circuit boards that shorted out adjacent traces, leading to a failure mode that could not have been predicted just from studying the schematic, as the traces that shorted appeared to be completely independent in the schematic.

The nice thing about a separate OV protection is that it should still provide protection no matter what the failure mode is.
 
Thanks Dennis. I need to talk to him to verify a few things but that may be the OVP that I get.
 
I'm in no way trying to suggest that accounts of runaway voltage aren't real, but how come I've never heard of it happening in a modern car? Again, I'm not saying it doesn't happen, just that I've never heard of it.
 
Kevin Horton said:
Does the schematic have enough detail to be sure there is no failure mode that could lead to OV and also kill the OV protection?
Click to expand...

I haven't been able to locate the paper schematic I have but as I remember there is an ASIC that has a field sense, and the field is controlled via a MOSFET. If the voltage exceed a threshold it would shut the field off. Looking up the regulator part # I have found some data on the ASIC that says it has "rotor short protection". In layman's terms this is equivalent to overvoltage protection since a short in the field to ground would cause an overvoltage condition. Obviously an external OV circuit can't hurt except for the additional parts that can fail. I have a friend who has had a master contactor fail in-flight. With that said its probably more likely to encounter a failure in the external OV circuit than it is of a regulator failure. Early on when I first flew my RV-6 ten years ago I had the cheap Van's 1980 Honda Civic 35A alternator, an external regulator, and an Aeroelectric crowbar OV circuit which between the three had nothing but problems until I removed them in favor of the internally regulated alternator.

I personally know of several failures of PlanePower alternators, the last one occurring about a month ago. The $90 alternator I use has worked perfectly for almost 1200 hours. I would say that the OV protection of the IR alternator is probably not space-shuttle quality but I personally have had great luck with them and have not heard of anyone having a IR alternator running away.
 
Integrated Circuit

rocketbob said:
I haven't been able to locate the paper schematic I have but as I remember there is an ASIC that has a field sense, and the field is controlled via a MOSFET. If the voltage exceed a threshold it would shut the field off. Looking up the regulator part # I have found some data on the ASIC that says it has "rotor short protection". In layman's terms this is equivalent to overvoltage protection since a short in the field to ground would cause an overvoltage condition. Obviously an external OV circuit can't hurt except for the additional parts that can fail. I have a friend who has had a master contactor fail in-flight. With that said its probably more likely to encounter a failure in the external OV circuit than it is of a regulator failure. Early on when I first flew my RV-6 ten years ago I had the cheap Van's 1980 Honda Civic 35A alternator, an external regulator, and an Aeroelectric crowbar OV circuit which between the three had nothing but problems until I removed them in favor of the internally regulated alternator.
.....
Click to expand...

Perhaps it was this one?

http://www.datasheetcatalog.org/datasheet/CherrySemiconductor/mXtuwrw.pdf
 
Hi Paul,
I'm jealous of your fleet.
One thing to be sure of in selecting ANY alternator is overvoltage protection. I've had several sad conversations with owners who had to replace/ repair expensive avionics because of an overvoltage surge.
Best of luck.

Damon
Plane Power Alternators
RV 6
 
55 or 60 amp IR alt WITH ON OFF FIELD WIRE

Great thread, hope this is not too far off . I have OVP from periheliondesign, which works as long as field wire can turn on off IR alt. It seems some ND or other alternators will do this, (Currently have Mark Landoll Alt) does anyone have model seriel numbers for one of these. Rocket Bob had 40 amp but 55 or sixty would be better for me.


Thanks All
 
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