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Date: Thu, 28 Nov 2013 16:56:30 -0500
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From: John Cooper <snopercod@comporium.net>
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Subject: [LNC2] Oildyne Hydraulic Pump Inrush
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Today I inserted a 75A / 50mV shunt in the power lead to my hydraulic 
pump in order to measure the current draw. I connected my Fluke 87-V 
digital voltmeter on the 600mV range across the sense terminals of the 
shunt . With the pump running in the "gear down" direction and the 
equalization valve open, the motor was drawing a steady 29 Amps. I then 
shut off the pump, closed the equalization valve, and with the Fluke in 
the "250 uS peak" mode, measured the inrush when the pump started up 
again briefly. Would you believe 135 Amps!  (Disclaimer: I purchased the 
shunt on eBay and can't vouch for its calibration.)

Next time the plane is up on jacks, I'll re-do this test in both gear up 
and gear down directions. Also, I intend to temporarily remove the ZNRs 
across the hydraulic relay contacts and measure the voltage spikes with 
no protection.