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

[Charles]

Relax everyone, those seleniums are (relatively) small-signal, they only 
handle the small coil current to the carbon pile regulators (not the 
whole inverter output!). It's on the order of 100 ma. This isn't my 
first rodeo :)

In any event I probably have half an hour of run time so far, with 
multiple starts, and they aren't at all hot or smelly and the load 
regulation is excellent, as I noted. I'll probably replace them with 
silicons at some point, but everything's working as designed and I hate 
to mess with it. Especially in the tight quarters of the circuit box 
atop the rotating assembly.

The full load efficiency for 1 KVA single-phase is supposed to be 50%, 
and for 2 KVA three-phase 55%. I don't have a spec for zero-load current 
though (and the only manual I can find is on ebay for $142, over four 
times what I paid for the inverter...)

David, I don't know what a PE-73 is, but this unit (Bendix 1518-1) 
weighs 40 lbs, as I'd expect from a 2 KVA motor-generator pair. Don't 
look now but the peak inrush current is 420 amps! =8^O


On 3/12/22 01:49, Robert Downs wrote:
> 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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