EarthX requires we install an automatic over-voltage protection (crowbar) for alternator type charging systems.  According to EarthX, "In the event of a charging system failure where the voltage increases to above 15.5V, the resistance to charging current increases, and above 16V the charging current is completely blocked. The time delay for this feature is 1 second to allow the aircraft alternator’s over voltage protection (crowbar circuit) to activate first. This design offers charge voltage protection greater than 40V. The discharge current (current out of battery) is unaffected in this situation. EarthX requires having automatic over-voltage protection (crowbar) for alternator type charging systems (not required for <20 Amp pad mount standby alternators)."

We are looking to use a Over Voltage Module (OVM-14), but not sure of the best way to install it.  Using the Viking Wire diagram, I believe the OVM-14 may work if inserted as shown in the other diagram.  Any suggestions would be appreciated.

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Do not install anything in the alternator circuit  of the sophisticated ND alternator brand. 

You can be assured the designers of the internally regulated unit are smarter than you.   Because some idiot - I was one for a short time - believed the Chinese copies of the alternator where of the same quality, destroyed the EarthX faith in alternators, is not the same as the Japanese branded units not having the guts already built in to protect you.  

In 30years of using these, there has NEVER been an issue, of any kind, with the Japanese built ND alternators or their sophisticated voltage regulators.   

This agrees with what Robert Paisley told me. Robert is a very smart guy, an electrical engineer, and a pioneer in converting Lycoming engines to electronic ignition and fuel injection. Because his engines are electrically dependent, he is fully aware of the need to have a solid electrical system. I asked him once about over voltage protection. Here is his response:


Modern Denso type alternators are not known to have over voltage issues. So we generally do not use over voltage protection. 


Based on the above comments by Jan and Ken, I'm satisfied that EarthX's concern for installing over-voltage protection on our aircraft is unnecessary.  One more item removed off our to-do-list.  Thanks for all the input.

Now, I will tell you what the most likely problems regarding alternator installs are:

  1. Broken / partially broken, main alternator lead as it is attached to the alternator.  The best remedy for this is to use a section of dead soft #8 cable with a heavy duty ring terminal in addition to serious strain relieving of the cable as it leave the alternator terminal.  The first support of the cable must be on the alternator itself
  2. See #1 above 

Me and Robert go as long way back.  Whatever he say's I would go with it.  

Just to make the point, in case some don't know, the difference with the Viking engine is the internally regulated alternator.

My Lycoming engine has an external voltage regulator that do have occasional failure problems. For this reason, OVP is important for an EarhtX battery if you have an external regulator.   

Just curious, what difference is there between a new internal and external voltage regulator that would make the external more prone to failure?  

I don't know because I never had an external one.  However, my gut feeling is:


  • Old style
  • Mechanical junk
  • Exposed wire connections
  • Corrosion issues
  • Vibration failure prone


  • Just works
  • Solid state integrated circuitry
  • Modern
  • Meets the reliability retirements of a modern Honda  

(I take that back, I did work on these in A&P school.  Easiest way to repair them was to get a Chrysler replacement unit from a local auto parts store.  Old technology stuff)   

Most of the alternators sold today for experimental aircraft are internally regulated and have built-in overvoltage.  You can look at B & C Specialty and PlanePower (owned by Hartzell) as two examples.  They are expensive $1,000.00 and at least for the PlanePower not terribly reliable.  My third PlanePower alternator just failed, all three in 300 hours.

The alternative is to purchase an older style NipponDenso alternator and connect it to an external regulator.  But older regulators do not have over voltage protect, so that needs to be installed.  That works for a Lycoming but probably not for the Honda / Viking engine.

The real question is, does the alternator in the Honda engine have overvoltage protection within it?


I should have included that over protection is important for all the glass panels we install in our aircraft; Dynon, Advanced Flight, Garmin, GRT etc.  But modern cars are loaded with microchips and screens that would also need protection from a runway alternator.  I haven't read of any recalls or complaints about Honda alternators taking out microchips by the hand full.


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