I do not know any thing about the John Deer alternators. The Diehl alternator consists of permanent magnet array bolted to the fly wheel, a set of coils with iron cores bolted to the Diehl adapter case and a quite small regulator usually mounted on the firewall. Two wires from the adapter case hookup to the regulator. One wire is for the field and the other wire is for the alternator output. Without the field wire connected, the alternator has no output. The field and output returns are through the grounded adapter case. A rectifier array in the case converts the alternating current from the coils to direct current. The only moving part is the magnet assembly. The regulator is all solid state; it does need some cooling and does get that in conjunction with the electronic ignition module cooling air blast. There are no bearings or brushes in the system. The VW crank shaft bearings are used as the alternator bearings. The Diehl alternator is rated for 20 amps output continuous operation. The alternator can produce higher outputs, but will incur overheating problems resulting in insulation breakdown and rectifier burnout. My installation allows air to enter at the magneto mounting location and exit at the starter pinion area on the engine transmission mounting flange. The spinning motion of the fly wheel does pump a lot of air past the alternator. My Dynon D10A has a system voltage readout. An instrument panel mounted load meter displays current output from the alternator. The regulator holds the system voltage to a consistent 14.2 VDC at full battery charge.
With every electrical item on line, transponder and VHF radio transmitting, and engine WOT the current output from the alternator is 18 amps. The batteries are still floating. Granted, charging a down battery while running full electrical load may tax the alternator. However, the electric fuel pump is only needed for starting the engine. WOT is limited to 2 minutes at a time due to engine over heating, as recommended by Steve Bennett. Landing lights are not used continuously. With those considerations and at 75% power, the system current load goes to 10 amps. I consider that a reasonable continuous operation design. What could go wrong? Could get excess current outputs by shorting the output to ground, battery failure or alternator failure. If the output current goes high enough the 35 amp circuit breaker would trip and take the alternator and regulator off line. For what ever reason, such as overvoltage, I can disconnect the alternator from the system by manually pulling the breaker. Power is only produced if there is a current flowing. Inductive voltage spikes can be destructive to the system. Batteries do a great job limiting voltage spikes. Using a crowbar type circuit protection is definitely not recommended: that will short out the battery. Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ---------------------------------------------------------------------- What kind of alternator is that VW Diehl alternator? Is it field regulated aka most cars or a permanent magnet dynamo with regulator aka the small John Deere or Kubota tractors? Cheers John John Martindale 29 Jane Circuit Toormina NSW 2452 Australia ---------------------------------------------------------------------------------------- Cc: Sid Wood I have used the Expbus for 5 years on my KR-2. I added a 35 amp circuit breaker for the VW Diehl alternator rated at 20 amps. .....sheep shears -------------------------------------------------------------------------------------- Hmmm, in which case having a 35amp circuit breaker in its unregulated output is pointless. It will never trip because the dynamo at 20 amp rating is incapable of supplying that current in the first place unless it goes into substantial overspeed. What should be included is over-voltage protection across the regulated output that breaks (or shunts) the circuit in the event of regulator failure. Breaking unregulated output by circuit breaker or simple switch generates huge voltages in the dynamo coils that could break down the insulation around the wires in it because the power from the coils spinning in the non-adjustable non turn offable magnetic field has nowhere else to go. You should never spin a dynamo without somewhere for the excess power to go.......even if it just literally a "crowbar" across the output. Alternators are very different because the coils are energised to produce the field (as opposed to magnet) and can thus be turned off. Spinning of the armature thus has no output and no adverse impact. John Martindale ----------------------------------------------------------------- From: <brian.kraut at eamanufacturing.com> It is a permanent magnet generator. If I recall correctly it is a John Deer part. -------------------------------------------------------------------------------
