lml@lancaironline.net Mailing List Archive

Bill,

There have been numerous problems with intermittent relays. I have copied just one email on that topic:

Mailing List lml@lancaironline.net Archived Message #26236

From:	Sky2high@aol.com
Sender:	"Marvin Kaye" <marv@lancaironline.net>
Subject:	Re: [LML] Landing Gear Relays
Date:	Thu, 21 Oct 2004 11:24:06 -0400
To:	lml@lancaironline.net

In a message dated 10/21/2004 8:16:32 AM Central Standard Time, ChasNelson@aol.com writes:

I own a Lancair 360 with the more recent electrohydraulic power packs. I believe one of my landing gear relays have gone bad. Does anyone know the source of this component?

Symptoms: Pump does not come on and low pressure side is not pressurized. Voltmeter measurements: 12V at low pressure switch, 12V at low pressure relay control post, 12 V at high current input to low pressure relay, 0 volts at high current output, Relay is hot.

The gear retract fine.

Try:

http://www.aerocraftparts.com/ItemForm.aspx?item=5481-001

You may have wired the circuitry per Lancair's directions and that can lead to this problem

1. With the down circuit engaged (gear down sw), the gear motor breaker open and the hydro pressure low enough, the master switch was turned on for a long time.

2. The relay power fuse or breaker was not open.

3. Thus, the down relay was powered but there was no panel indication from the gear in transit light since it is powered from the motor power circuit.

4. Since it is an intermittent relay under power for a long time, it overheated and, after the power was removed, the melted coil insulation goo cooled and locked the plunger in the open position.

Consider this wiring:

1. the relay coil power circuit breaker or fuse should be connected after the motor breaker so that when the motor breaker is pulled all power to the entire electro-hydraulic system is removed.

2. the indicator light circuit should be isolated by diodes so that power is not backfed to the other relay. If the diodes are small enough they should blow before the small indicator wire starts a fire should it become is shorted and is asked to carry the 50/60 amps of the motor circuit. Otherwise, an inline fuse would help.

Scott Krueger AKA Grayhawk
N92EX IO320 Aurora, IL (KARR)

In a message dated 5/7/2012 6:58:06 A.M. Central Daylight Time, super_chipmunk@roadrunner.com writes:

I took Paul Miller’s suggestion and tested the windings on the 50A Leach and the Lancair- supplied contactors.

I connected a 24V power supply to the coil terminals without any load across the points and after 36 hours continuous the Leach case was slightly warm to the touch. All of the terminals checked out- electrically isolated from the case, low resistance across the points.

The Lancair contactor was very different. Within about 15 minutes the case was too hot to hold comfortably. The winding and contact terminals grounded to the case in an apparently random fashion with changing values of resistance and voltage. When the unit cooled down the terminals were electrically isolated and coil resistance was as new so the coil wasn’t shorted internally and the unit seemed to be fine. As power was reapplied and the coil began to warm the process repeated.

I haven’t heard of any problems on the LML so these contactors seem to be adequate for the job. Oildyne says the pump is intermittent duty (no percentage given) so it might be toasted before any problem with the contactor showed up. OTOH the contactor is relatively heavy and seems marginal- people using them might consider something different.

–Bill Wade