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Date: Tue, 19 Nov 2013 08:26:59 -0500
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Subject: Hydraulic pump suppression diode follow up
From: Jack Morgan <jmorgan1023@comcast.net>
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Hi Angier...... All,

The best suppression protection for the hydraulic motor solenoids is a =
1N5400 series silicone diode. Any from the series 5400 through 5408 are =
fine. The striped end of the diodes should go to the motor leads and the =
plain end to the third ground lead near the motor. They are good for a =
200 amp surge which gives plenty of margin for the less than 35 amp or =
so pump motor. The diodes prevent the voltage  across the relay contacts =
from exceeding main buss voltage plus a volt or so. Any accidental over =
voltage the aircraft might suffer will not harm the diodes unlike a =
zener/surge diode type solution. The energy suppressed is contained in =
the motor rather than in an external surge diode providing best =
reliability.

The solenoids provided by Lancair are very robust and I see no reason =
not to use them. I would include a 1N4001 series diode across the relay =
coil to protect the pressure switches. The solenoids can also be =
purchased from any auto parts store. Make sure to get the continuous =
duty solenoids rather than the starter solenoids. I have no beef with =
electronic relays except for the experimental and unproven nature of =
such one off solutions.

Jack Morgan