Intermittent Electric Trim Actuator

[airlina]

John, I would like to have a backup rocker switch in my parts inventory, do you recall where you got your replacement switches and if so what the part number for the switch was. Also I will see if I can find out about the actuator for you. Thanks Bruce

[Birddog]

Bruce,

I actually ordered two types of DPDT switches from Granger on the Internet: <http://www.granger.com>
One was a Rocker for $21.89 and the other was a Toggle for $18.94 The Rocker is slightly smaller in length and width than the one provided by SkyStar. The Toggle uses a 1/2" mounting hole. They are both made by Hubbell Wiring Device-Kellems.

Rocker = Granger #3JC10 and Toggle = Granger #3HZ95

They are both rated at 15 amp inductive. I am not that impressed with with either of them, especially based on cost, and I think 15 amps is not suited for our application over the long haul. I just ordered a DPDT Rocker switch from Spruce A/C that is rated for 20 amps and at a cost of only $8.40. The Spruce P/N is 14-225. I will give that one a try. Note: all of the switches are spade terminal type, not terminal lugs.

I am seriously thinking of designing a relay operating trim system in an effort to reduce the current flow through the switch contacts. My failure modes have been pitted switch contacts. The switch will only activate the relay coils. That combined with the speed control you suggested ought to be the most reliable speed selected electric trim system. Finding the proper 12 VDC relays will be the biggest problem. I would mount the relays and ballast resistor in a small metal box with a terminal board attached somewhere behing the instrument panel with easy access.
Anyway, that's my current thinking.
--
John
Warrenton, VA
N993JK

[RandyL]

Good idea John, a relay sounds like a smart move and one that should extend rocker switch life given the constant use the trim actuator gets in a Kitfox (for trim rather than flaps as in an RV). Here is the relay board commonly used in RVs, seems like this would be perfect for our application.
cat-med_flap-board.jpg

$39.50 and available from Van's Aircraft .

[3kdscf]

Sorry to bump this 13 year old thread but thought I would post because its still an issue. I have a Series 6 and had this intermittent trim problem at around 90 hours flight time. This thread mentions two causes of the intermittent trim problem: 1) gunk in trim motor's commutator and brushes and 2) arcing in the switch.


First a warning. Although others seem to have successfully taken the trim motor apart, cleaned it, and put it back together, it's not for the faint of heart. As careful as I was during disassembly, four washers fell out leaving me scratching my head as to the proper order and I didn't want to guess. Other problem is that getting the brushes back properly is very difficult. My suggestion is to do what I did and just order another trim motor assembly from John McBean.


In my case, the problem turned out to be arcing in the switch (see photos). I was initially fooled into thinking the switch was fine because when I removed the connector to the trim motor and measured the voltages there I got +12V with down trim activated and -12V with up trim activated. The issue though was that because of the worn contacts, the resistance was too high. Replaced the switch, and all worked fine.


Since this problem has not been reported since 2008, my guess is that only the Skystar kits that had the old arc-prone trim switch. The new rocker switch from John McBean is different.

Attached are photos of the affected Skystar switch, the messed up contacts, the delicate brush assembly of the trim motor, and the washer assortment that fell out when I opened the motor up
trim-motor-washers.jpgtrim-motor-brushes.jpgtrim-motor-switch-contacts.jpgSkystar-switch.jpg