Thorp Air Command - T18.net

So I have having mid 15 volts and spiked at 16v over the last couple of weeks. Pulled my automotive regulator and after opening it one of the coils had a burnt winding. It's stamped 06 71 on the inside so I assume 1971.

I can post a picture but it's a black box with 3 mounting holes, 2 on the side with the 4 blade connector and 1 mounting point on the non connector side.

Looking things up it looks similar to VR715 or VR714 type from wells. I can't find any specs on what makes them different and their pin out is the same but slightly different than mine.

Currently mine has 2 small wires from the alt that go to pin F and pin 2 then my alt field wire from the switch connects to #4. #3 has nothing connected to it. The above mentioned ones show wiring diagrams of F (field), 2 is stator, 3 "ignition" and 4 is a lamp indicator. So that means I would use 1,2,3 but not 4.

My other question is how do I know which wire is what from the alt on the 2 small wires? I'm going to leave it connected because it obviously has been working although since I didn't have anything to check volts (only had ammeter) maybe it was dead a long time ago. I don't see markings on the alt and the 2 spades the wires come from are right next to each other.

What auto regulator is everyone using that might fit my description? Should I go with the VR715 or 714 since it looks similar and just has 1 pin switched? Even though these are cheaper (20-50$ range) I don't want to keep burning them up if I wire them incorrectly.

Alternator was replaced 1 year ago before I purchased the plane. Have been flying it without knowing voltage for this year.


Thanks!

PS: I checked every last piece of info in the logs last night with no mention of part numbers on the alternator or the regulator. Gotta love poor documentation. At least put the part number in when you document a replacement!

Most auto parts stores are useless anymore unless you can supply them with a make and model. It's been a long time since I could show the guy behind the counter a part and he just walk in back and get a replacement without looking anything up. Now if it can't be found on the computer it doesn't exist. Heaven forbid they actually have to open a book.

Other than fitting your existing connections, I don't think it would matter which regulator you used. We've removed the strip connectors and gone to single spade connectors on some aircraft because the connectors wore out, broke or simply would not fit an "updated" regulator. A person just has to label the wires and/or pay attention to what they are doing when changing parts.

If those wires are all the same color then chasing the wires by hand or disconnecting them and checking each one for continuity are the best ways I know of to determine which wire is which.

There are a lot of variables which make it difficult to help from here. If it would help, I can post some wiring diagrams tomorrow night.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Well I only have 2 wires that come from spades on the alt next to each other. I think the field wire is supposed to be 2.5 ohms when checked between ground but I can't remember if more than or less than. I have no idea what the other wire is on the next spade but it was hooked to pin 2 on the regulator. The alt field wire is easy to identify because that's the one I installed when I rewired the plane. I didn't touch the ones from the alt and just left them in the same position.

I also have spade connections because the black connector for that regulator was junk.

So it sounds like I should just leave the 2 wires where they are on field 1 and pin 2 then hook my alt switch field wire to whichever pin is for the ignition on the automotive reg. Correct?

Anything I should check on the alt to make sure that the 1 year old alt didn't kick the bucket?

Sounds reasonable to me. If you took the alternator and regulator to someone knowledgeable who has a test bench they could check it all out and label the connections for you without risking anything on the aircraft.

I attached a troubleshooting document I thought you might find helpful.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I would think any automotive electrical shop could do that ?

RB

I think so. The system is the mostly the same. Field wire on separate switch instead of the key. Minor differences in over-volt protection, if any. Parts stores are more hit and miss. Many have the equipment but not always the knowledge to use it.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I bought a duralast (wells) VR715. This thing is a fraction of the weight of the original as it is solid state. Looking at the back, the grounding wire that was on my "field switch" pin is still on the 4th pin of this new one like my original one. I assume that means pin 4 is the one that I attach my field switch wire. I'll upload the picture I took.

Tomorrow I'll go out and test the continuity of the Alt F1 and F2 wires like stated in that PDF and see if they are within 3-7 ohms. Since everything was working fine but just higher voltage (and I found a broken wire in the coil on the VR) I think I just have a dead VR. It is stamped 6-71 for a date on the back so it had a good run.

Well, it won't let me upload my picture. It opens the window and just sits there saying "uploading" then takes me back and there is no image. Anyways, the worst case scenario if my field switch wire is on the wrong pin it just won't activate my alt when i flip the switch, correct?

The only downfall that bugs me about EAB is the lack of standard things used in the build. Seems like every plane is just slightly different.

I have had the website do that to me. It seems to happen if I try to post a picture that is too big.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Custom built airplanes are just that, custom built. If it is standardization you want, buy a Cessna. These things are as much a work of art as they are transportation. Along with the good things (speed, affordability, ect.), comes the responsibility to learn. That is the foundation of the amateur built classification.

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Bob Highley
N711SH
SN 835
KLAL

Ya, depending what task and mood I'm in I love it or hate it! When it came time for all the ADs on my Cherokee I was hating a certified bird but it's nice when things fail there is a standardized replacement. I think more so because I'm still learning the airplane ways and the local fbo doesn't work on many experimental so I have to bug everyone on the forums or David read down in olney. I enjoy some of the work and having a lot more freedom. The fast speed for fuel burn doesn't hurt as well!

Update:

Installed a Wells VR715 solid state regulator. Had to put a jumper between Pin4 and Pin3 so they both receive 12v. Works like a champ!