[VHFcontesting] Power budget

nosigma at aol.com nosigma at aol.com
Sun Mar 11 06:24:13 EDT 2018


The AC start up load should be in the specs.  If not, double the running current draw if its a bleed down unit, triple the running load if its not.

In the 90's I built and operated several shelterized instrumentation radars for use in deserts on generator power.  Generators had to package in the shelters for deployment.  Inverter generators did not exist back then.

AC was a pain.  Large random current draws and voltage drops on start up followed by voltage surges on shut down.  This wreaks havok on sensitive equipment.  To lesser extent resistance heaters and blowers did the same thing.

Much of the start up problem is due to commercial AC units not having a bleed down capability so they try to start up against a HEAVY compressor load.  Lots of insulation, white paint on the roof and a silver side up tarp over the roof for shade and an air gap minimized short cycling of the AC.  But the huge start up load was still there.

AC units with compressor bleed down and interlocks to prevent a loaded start up were special order, militarized mobile units back then.  This helped A LOT.  It may be a more common item on RV units today, check for this capabity. A home window unit probably wont have it.

Even with all of this I had to size the generator for twice the max current draw of the AC unit on start up stay over 100 volts so the electronics were not too unhappy.  Straight generators depend on rpm for gross voltage stability.  Inverters will still surge as the throttle opens under a big load spike, but to a much lesser extent.

The AC load will far and away be the biggest load on your system.  Once running I found that the AC generated an unacceptable level of noise on the power lines.  This led to a lot of filtering for the radar electronics.

Taken all together this resulted in an acceptable but far from ideal solution.

Ultimately I ended up with TWO 10kw generators.  One for electronics and one for support functions.  The shelters were rewired to isolate them from each other but the were still minor disturbances through the shared a.c. grounds.

When the radar was in standby the load was so low on the electonics generator I had to add a resistor bank to force the generator off idle to a stable 3600rpm level.  I could have used a smaller electronics generator but one is none and two is one, plus I would have to double up on spares.

Here is what I suggest:
An inverter generator for the electronics on its own circuit.
An AC unit with compressor bleed down.
A second generator (inverter or conventional) for the AC which is oversized by at least 50% for the start up load, 100% if the AC doesnt have bleed down, you dont care about voltage spikes on this generator as long as the AC can handle it.  Conventional generators are much cheaper at higher power levels.
Keep the grounds seperated.

With the second generator you can bring a coffee maker, small fridge, a microwave, lights, floods for set up and have all the comforts of home.  


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On Saturday, March 10, 2018 Dan Evans via VHFcontesting <vhfcontesting at contesting.com> wrote:
Hello group, I'm putting together a small (12') pull behind trailer for grid hopping / portable operations.  It's actually a 1967 Winnabago that I'm restoring / remodeling. Anyway, I would like to add a small window unit air conditioner to make summer operating bearable.  The original AC unit is long dead, so I was planning to install a 5000 BTU.  This is the smallest unit I've been able to find.  My question is how much generator am I going to need for this setup?  I know one of the small inverter types should be plenty to run my radio equipment, but will it handle the AC? I know there are plenty of guys on the list that have been down this road before, so I would appreciate your input! 73Dan -- K9ZF  Vice President, Clark County Amateur Radio Club,Amateur Radio Emergency Service, Clark County Indiana. EM78el The once and future K9ZF /R no budget Rover  ***QRP-l #1269 Check out the Rover Resource Page at:  List Administrator for: InHam+grid-loc+ham-books  Ask me how to join the Indiana Ham Mailing list! On Saturday, March 10, 2018, 12:31:28 PM EST, Mike & Becca Krzystyniak <k9mk at flash.net> wrote: Greetings All,     James, AF5EH is selling his pair of HP 8753C (3 GHz) & HP 8753D (6GHz) model network analyzers.     Both have their respective S parameter sets and fresh CRT's.     Anyone interested?  If yes, please contact James off list at james at jwarden dot com Thanks for reading this. 73's  Mike K9MK _______________________________________________ VHFcontesting mailing list VHFcontesting at contesting.com http://lists.contesting.com/mailman/listinfo/vhfcontesting _______________________________________________ VHFcontesting mailing list VHFcontesting at contesting.com http://lists.contesting.com/mailman/listinfo/vhfcontesting

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