[Boatanchors] [ARC5] No-load current of dynamotors?

[Robert Downs]

That isn't too bad given that the front to back ratios of the Seleniums is
probably down to next to zilch.  Equates to roughly 35% efficiency.  

However, unless the selenium plates were actually made in the last 20 odd
years or less (very unlikely), you were damn lucky that the whole machine
didn't go up in a cloud of smoke.  I would not light it off again until you
have replaced the Selenium rectifiers with Silicon and equivalent heat
sinks.

Robert Downs


-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of Charles via ARC5
Sent: Friday, March 11, 2022 20:20
To: BoatAnchors Digest; ARC-5
Subject: [ARC5] No-load current of dynamotors?

Just wondering if anyone has measurements on the no-load input current 
of their dynamotors (of various sizes).

My Bendix 2 KVA aircraft inverter is rated at 115 amp full-load draw, 
per the nameplate. Now that I have a monster unregulated 24-28 volt 
supply, I have measured the idling current at 26V at 40 amps. 1/3 of the 
full-load current seems kind of high? I was expecting more like 10-20%.

The only 120 volt resistive load I had on hand was a 525 watt heat gun 
element, and the output voltage dropped only a few tenths of a volt, 
while the input current rose to 75 amps. Next data point will be a 900 
watt electric heater (the inverter is rated for 1 KVA single-phase), 
unless I rig up a three-phase load.

(The only other dynamotors I have are small ones for "ARC-5" receivers 
and I haven't checked them yet).

It does have two carbon-pile regulators, the original selenium 
rectifiers, and a couple of relays that draw a little here and there, 
but nothing's getting significantly warm except the air coming out of 
the rotating assembly (it has fans on each end cap that draw in, and 
exhausts from the middle). I can only assume that this is normal 
behavior? Thoughts?

Cross-posted to Boatanchors and ARC-5 lists.


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