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  #51  
Old 12-22-2010, 08:56 AM
Lux Wrangler Lux Wrangler is offline
 
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Default 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?
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  #52  
Old 12-22-2010, 09:11 AM
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Fred.Stucklen Fred.Stucklen is offline
 
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Quote:
Originally Posted by Ironflight View Post
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".
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....
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  #53  
Old 12-22-2010, 09:23 AM
Fred.Stucklen's Avatar
Fred.Stucklen Fred.Stucklen is offline
 
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Default Automotive Alternators

Quote:
Originally Posted by Lux Wrangler View Post
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?
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....
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  #54  
Old 12-22-2010, 09:48 AM
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rocketbob rocketbob is offline
 
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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.../dp/B003V1BN60
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  #55  
Old 12-22-2010, 09:58 AM
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Ironflight Ironflight is offline
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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!

Quote:
Originally Posted by Fred.Stucklen View Post
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 agree! I guess we might differ on how that positive control is achieved, but that's OK...just two different methods.

Paul
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  #56  
Old 12-22-2010, 11:19 AM
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MauiLvrs MauiLvrs is offline
 
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Quote:
Originally Posted by Ironflight View Post
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
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
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  #57  
Old 12-22-2010, 04:31 PM
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Danny King Danny King is offline
 
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Location: Southlake, Texas
Posts: 626
Default 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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Last edited by Danny King : 01-16-2011 at 11:56 AM.
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  #58  
Old 12-22-2010, 04:55 PM
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Ron Lee Ron Lee is offline
 
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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.
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  #59  
Old 12-22-2010, 05:21 PM
DGlaeser DGlaeser is offline
 
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Location: Rochester Hills, MI
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Default Here you go . . .

Quote:
Originally Posted by Ron Lee View Post
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.
http://www.periheliondesign.com/lovm.htm
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  #60  
Old 12-22-2010, 06:02 PM
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Kevin Horton Kevin Horton is offline
 
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Location: Ottawa, Canada
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Quote:
Originally Posted by rocketbob View Post
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.
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.
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