Canadian Flag Blowing In The Wind Ron Leclerc Zenith CH701 Construction Log


Zenair CH701 STOL Aircraft...
CH701 STOL

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701 Electrical System: 1 |   
 

701 Electrical System...

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November 21, 2011
Electrical Wiring Tools - Terminal Town...

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November 30, 2011
CH701 Electrical System
Drawing for Externally Regulated Alternator... Electrical Drawing

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November 30, 2011
CH701 Electrical System
Drawing for Internally Regulated Alternator... Electrical Drawing

 

Alternator - Internal Regulator Modification...
It is well known, Internal Regulators are fairly standard these days in the Automotive world. Although Internally Regulated Alternators are fairly reliable, there is still a failure mode that is not acceptable for use in aircraft. This failure mode occurs when the regulator fails internally and puts the alternator in full output mode regardless of battery charge. This leads to an over voltage condition and eventual (if not instant) battery failure... and is not good for the electronics.

What’s worse, even if you were aware that the alternator was overcharging, you would not be able to shut it down by removing the field voltage via fuse or breaker. The only recourse would be to turn off the master switch — provided you have the alternator wired into your system correctly or have a separate breaker in your panel for the Alternator output that can be turned off.

Now the risks of an uncontrollable runaway for Internally Regulated Alternators is very low but is not zero. Commercial offerings of automotive conversions for Aircraft either modify the alternator for EXTERNAL Regulation and OV protection or have to get modified to accept external OV protection.

At any rate there are thousands of Internally Regulated Alternators flying without any OV protection that have never experienced a runaway failure, but there have been a few . . . with predictable results. Controlling power to the 12V IGN lead will place the Alternator OFF/ON-line while the engine is still running. It's not an unsafe or risky thing to do. However, there are failures internal to the Regulator that cannot be controlled by the switched 12V IGN lead alone.
So check out what can occur here! -

So, it is usually recommended to install Externally Regulated Alternators in Aircraft. This not only eliminates the type of failure mode caused by Internal Regulators, but also allows the use of Over Voltage shutdown circuits that will interrupt the field voltage to the Alternator and shut it down automatically before any damage can occur.

So this is what has to be done with the Option #1 alternator... convert it to an Externally Regulated unit!
 

Option #1 - Chevy Mini(5.50lb) Denso - Internally Regulated Alternator...
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July 13, 2014
Model: 12180N
Ser.No: AL 1481
Front View - 50Amp Chevy Mini(5.50lb) Denso - Internally Regulated Alternator 1-WIRE - $90 on eBay! This Alternator will be modified to work with an External Regulator! Will need Over Voltage Protection...

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July 13, 2014
Rear View - 50Amp Chevy Mini(5.50lb) Denso - Internally Regulated Alternator 1-WIRE - $90 on eBay!

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July 13, 2014
#VR166 AMC/FORD/Mercury - External Voltage Regulator C3SZ-10316A - $15.50 on ebay!

 

Option #2 - PM(Permanent Magnet) Alternator...
The use of a [PM]Permanent Magnet Alternator or Rectifier has been used by the Experimental Aviation industry for a long time! It is simple, light weight... will turn left or right and easy to install.
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August 27, 2014
Model: AM877577
John Deere Lawn Garden Tractor or YANMAR - PM ALTERNATOR Front View - 20Amp 12Volt. Weights 4.5lb, can be used either way, left or right. Will need Over Voltage Protection...

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August 27, 2014
John Deere Lawn Garden Tractor or YANMAR - PM ALTERNATOR Rear View - 20Amp 12Volt. Weights 4.5lb, can be used either way, left or right

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August 27, 2014
AM101406
John Deere Lawn Garden Tractor - PM Rectifier Voltage Regulator

 
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August 27, 2014
John Deere Lawn Garden Tractor or YANMAR - PM ALTERNATOR and rectifier/Regulator

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August 27, 2014
John Deere Lawn Garden Tractor or YANMAR - PM ALTERNATOR

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August 27, 2014
John Deere Lawn Garden Tractor or YANMAR - PM ALTERNATOR

 

Electrical Battery Contactors:
There’s a lot of mis-information circulating around the aviation community as to whether or not and how a spike-catching diode should be included in the circuit controlling the coil of any large relay, contactor or other inductive load. Common practice for years has been to place a diode across the contactor’s coil that would conduct heavily and stop this spike from propagating out to the rest of the system. Here’s what happens when you add the diode. When a plain-jane toggleswitche is used to control the contactor. . . nothing noteworthy happens when the switch opens. Voltage across the coil falls to zero and stays there. No fire, no spike.

Now let’s head off another myth at the pass. . . many folks shudder at the idea of 300 volt “spikes” roaring about the airplane wreaking havoc along the way. The energy from a collapsing contactor coil is going to be used up where ever the circuit resistance is the greatest - ACROSS THE OPENING CONTACTS OF THE CONTROLLING SWITCH. A tiny fraction of it might make it out onto the bus but not enough to be a significant threat to any other system components. Now by adding a diode benefits the controlling switch. The rest of the system doesn’t care if the diode is there or not.
 
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May 30, 2015
Spike Suppression Diodes - #1N5402... to be installed on Battery Contactor to protect against voltage spikes. Purchased on eBay from a company in Bangkok Thailand for. . . now get this, for $0.99. eBay

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May 30, 2015
Package of 10 #1N5042 are the type of diode used when placed across the coil of the Battery Contactor. Now If you buy a new Starter Contactor the... diode should be installed internally... so check with your vendor to ensure that it is!

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May 30, 2015
Spike Suppression #1N5402 placed across the coil of Battery Contactor! Note the jumper is required with this type of Battery Contactor. Note the direction of the gray line on the diode... this end is the positive direction!

 
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May 30, 2015
Spike Suppression #1N5402 placed across the coil of Battery Contactor! No jumper is required with this type of contactor! Note the direction of the gray line on the diode... the end is the positive direction!

 

 
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