Cessna 400 Series Voltage Regulator Upgrade Kit

mshac · #1 09-16-20, 06:20 PM

Problems with your alternators not properly sharing the electrical load? Alternator lights flashing on your panel during taxi or cruise flight? Airplane going through alternators like underwear?

Potentially eliminate these problems, and others, with the Cessna 400 series voltage regulator upgrade kit. Upgrade your aircraft to true modern "parallel" alternators!

Being in the aircraft parts business, I noticed I had several of these 400 series voltage regulators in inventory, so I thought I'd offer them to the 337 community.

This "kit" is nothing more than two used 400-series voltage regulators, step-by-step instructions and a wiring diagram I created, plus a copy of an actual 337 form that has been used successfully with several FSDOs. Installation is simple. Since a field 337 is required, YMMV.

Installation time is estimated at 1 hour. All existing wiring is re-used, with the addition of one new wire that allows the voltage regulators to communicate. This is the "paralleling" line that changes everything, at least as far as your alternators go...

You will not receive any 8130 paperwork (these are used parts), although there may be a "yellow tag" on the regulators. I will guarantee the Voltage Regulators for 90 days after delivery. My liability is limited to the price you paid for the kit.

Price is $499.95, with free 2-3 day Priority shipping anywhere in the lower 48. Fully returnable within 30 days, buyer pays return shipping. Order processing may take a few days.

Any questions, feel free to PM me.

Skymasterdriver · #2 12-23-20, 09:19 PM

Can we buy you wire diagram and 337 paper work and us zeftronics regulators or is the Cessna ones all we can use ?

california Sky · #3 12-27-20, 01:30 PM

Good morning

Looking to purchase the diagrams have a set of regulators available.

Please advise

mshac · #4 12-27-20, 01:58 PM

If you just need copies of all the FAA paperwork and the step-by-step instructions I wrote, plus tech support (if needed) its just $100. I will email everything immediately upon payment. Please PM me for payment details.

patrolpilot · #5 05-01-21, 07:32 AM

Another successful install mshac! My shop loved the package!

mshac · #6 05-01-21, 11:03 AM

Quote:

Originally Posted by patrolpilot

Another successful install mshac! My shop loved the package!

I'm very happy to know you're enjoying the upgrade to true parallel alternators!

Makes you wonder why Cessna didn't do it this way themselves, since they already had the parts and the design ready to go.

JAG · #7 05-09-21, 05:05 PM

Hi Mark,

Will your modification work for the 337A model as well? Mine has the two 30 amp alternators, and I have just replaced one of my voltage regulators and about to change the other...

These older planes have just 1 regulator for both alternators (the second one is just a spare), so one alternator is always carrying more load.

Thanks,
Jeff

mshac · #8 05-10-21, 02:07 PM

JAG, your alternators would work fine with this system. It would require 337 field approval, just like all the other installs, but I've yet to hear of anyone being denied the 337, as its a simple and safe upgrade.

EDIT:

There would be additional wiring required for the older airframes like yours. This upgraded system requires each alternator to have its own dedicated voltage regulator. I don't know how the wiring was done by Cessna on a 337A, but you would need independent circuits to each alternator.

I hope this helps. Feel free to PM me anytime.

mshac · #9 07-10-21, 10:34 AM

Quote:

Originally Posted by Skymasterdriver

Can we buy you wire diagram and 337 paper work and us zeftronics regulators or is the Cessna ones all we can use ?

This upgrade only covers factory Cessna voltage regulators. Its possible that a system could be designed using the Zeftronics VRs, but it may well be "a bridge too far" for an easy field 337 approval because it strays too far from the original design.

This modification takes an existing, approved system from 400 series aircraft and applies it to the Skymaster, with no changes to the POH or placards. The FAA seems to view this approach favorably.

vwisdom · #10 11-13-21, 05:20 PM

I would like to get a copy of the upgrade.

Thanks

mshac · #11 11-14-21, 12:49 PM

Quote:

Originally Posted by vwisdom

I would like to get a copy of the upgrade.

Thanks

PM sent with all details

CRDedrickson · #12 12-09-21, 05:52 PM

I came across this post and it might be related to an issue I have with low voltage when at idle. I have accepted that at low RPM (~1000) there may be insufficient voltage to charge the battery, but this always resolves at higher taxiing RPM and certainly always in flight.

My understanding is that the voltage regulators adjust the alternator field current to maintain the set voltage. Should I be able to achieve rated charging voltage at idle, nominally 1000 RPM? I don't think this should adversely affect the scenarios, but I'll mention that the alternators were upgraded to 60 amp units by a prior owner. I am seeking to understand if this low voltage at low RPM is a design limitation, or if there is a remedy (voltage regulator adjustment or model change)?

My most recent interest in this voltage is because I've added an electric air conditioning system that requires a voltage in the 24 +/- area to prevent an unplanned battery drain. So, at idle and while taxiing, the AC system may shut down. The system is Peter Schiff Aero's SOFIE system. It provides up to 18,000 BTU and rejects heat to the outside by liquid antifreeze piped to the condenser located in the rear engine compartment. The cycle is a freon system with electric compressor for the evaporator in the cabin.

Russ Dedrickson
N8CV 1973 T337G Pressurized Super Skymaster, standard TSIO-360 Continentals

mshac · #13 12-09-21, 06:06 PM

Directly from the POH:

"The ALT NOT CHARGING lights will normally stay out during idling and taxi operations. Occasionally a light may come on when electrical loads are at a minimum and one engine is operating at a much lower RPM than the other. If one light constantly comes on during idle or taxi with equal engine RPM, or during cruise, the voltage differential between the voltage regulators is too great and the regulators should be adjusted."

One of the last steps in my 400-Series voltage regulator upgrade installation is to adjust the new regulators to the same voltage output at 1600 rpm with a load on the electrical system. This, along with the new paralleling circuit, prevents the lights from coming on at any time unless there is truly a fault in the system.

Also, the trigger voltages for the high output and low output warning lights are fully adjustable. If all you have is the OEM amp gauge, get a cigar lighter digital voltage gauge so you can watch the actual voltage in real time. Here's one at Amazon that displays up to 30 volts and provides two USB power outlets: https://smile.amazon.com/dp/B01N00I4...XBN6VJS7V3F5P1 If you don't like that one, there are many other styles available.