Fuses ratings

Chip Fetrow tacos at fetrow.org
Thu Jul 26 18:40:04 CDT 2012

I have a portable Honda generator that actually generates DC, but that  
is followed by an inverter that makes pretty pure sine wave AC.  It  
produces several orders of magnitude less harmonic distortion that  
most portable and even stand-by gen-sets.

This series of portable generators have an economy mode.  There is a  
switch on them that reads "Full" in one position, and "Ecco" in the  
other position.  In the Ecco position, the gas engine runs to match  
the load.  In general, in my usage, it runs very slowly.

The problem is the refrigerator.  The first time we had an extended  
outage, I decided that I would take the four hour recommendation and  
connect the refrigerator.  When its thermostat called for cooling the  
engine came to a very abrupt halt.  Not the moan normally heard from  
an overloaded gen-set, but a stop like someone threw a large crowbar  
into the gears.  I didn't ever want to hear that again as I am afraid  
it might cause major engine damage.  So, I don't plug in the  
refrigerator.  When enough time (about two to four hours) has gone by,  
or someone has had the door open too long, I go outside, flip the Ecco  
switch to FULL, then plug in the refrigerator.  I then go outside and  
flip the switch to Ecco.  Once the refrigerator thermostat is no  
longer calling for cooling, the engine will drop greatly in speed (and  
noise), at which point I unplug it from the generator.

My first thought was to add a small capacity battery to the inverter  
input to hold up the inverter until the engine could spin up, but a  
339 Volt battery wouldn't be small, even if made up of AA cells.

My next thought was a feed forward idea you write about here.  The  
idea would be to delay the compressor by five or ten seconds, while  
the thermostat directly switches the generator to FULL.  Then, after  
about 30 to 60 seconds, the generator would be allowed to go back to  

I have no fear about modifying the generator, but a bit of concern  
about modifying the refrigerator.  I suppose I could have a mechanical  
switch to allow me to switch my circuit out...  I really DO like the  
idea of the refrigerator not coming on right away when a power failure  
is restored.  Already, my heat pump has a five minute time delay.  It  
holds off for five minutes on power restoration.  My hot water heater  
holds off for 20 minutes.  That will never be an issue because it is  
super insulated and 80 gallons for two people.  I shut off the water  
and the water heater when we leave home for more than a day.  We can  
return home after four days out of town and still take a hot shower,  
even though the hot water heater won't be on for a while.

I last bought a home HVAC unit in 1996.  Two stage compressors were  
available, though not common on units 3 tons and up.  I wanted to down- 
size my unit from 3 to 2.5 tons because I like low humidity in the  
Summer.  Variable speed indoor air blowers were common.

Today, two stage compressors are very common, but inverter run  
compressors are available if you don't buy the entry level units.   
Having a 3 ton unit running at one ton can really help with both  
energy costs and humidity.  Additionally, they make much less noise.


On Jul 26, 2012, at 1:00 PM, tacos-request at amrad.org wrote:

> Message: 4
> Date: Wed, 25 Jul 2012 19:00:26 -0400
> From: Mike O'Dell <mo at 131.ccr.org>
> Subject: Re: Fuses ratings
> i worked with a company which used the HVDC approach for marine  
> systems.
> since everything has a switching PS today, driving one with an  
> inverter
> simply puts two in series plus the bulk rectifier. So all the big  
> loads
> were designed to use BLDC motors with wide-range controllers. the air
> conditioning didn't have a bang-bang thermostat - it simply spun at
> the right speed to maintain thermostasis. likewise the refrigeration
> and othere big loads.
> the thing that made it *really* interesting, however, was the
> feed-forward control loop done with a CAN-bus. the large loads would
> announce to the generators how they would be ramping power and
> then after an ack from the generator controller, they could start
> the run-up. before the ack, however, the controller goosed the
> diesel(s) so they could run-up smoothly with the load ramp.
> [...]
> the system was called a "load-following generator" which is
> inaccurate from a control-system viewpoint, but the fact that
> the generator didn't have to run harder than necessary to
> maintain load was "load-following".
> 	 -mo

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