Home sized generators??????????

[JohnH]

I recall fuzzy language like that, but I'd go by their table. Unlike
motors, reactive loads don't neceessarily need long surge currents.

make that "resistive" loads

 

[Me]

Nick thank you.

As I interpret it, Honda is using 3x for starting "reactive" loads.

As I interpret your guidance, one should find the largest reactive
load, multiply it by 3 and add it to the base load.

As I interpret that method, it assumes that only ONE load will be
starting at a time.
And, to cater for a "worst case", the largest reactive load is chosen.
In our installation however, there are several motors, any of which can
start independently and randomly.

Is there any form of protection we can apply to prevent overload if we
have the "perfect storm" of multiple, simultaneous reactive load
starts?

Also, I note that some loads such as Compressors and Fridges seem to
use a 4x rather than 3x start figure.
Is it possible or even likely that some new higher efficiency fridges
need even more than the 4x?


Thanks for your help!
I'll try not to sleep through the answer.
Phil

In that case, why are you trying to "cheap Out" on the genset? If you
want Prime Power, why not buy yourself a Prime Power Generator? The
simple reason that Hondas, and most all 3600 Rpm Gensets, aren't
considered Prime Power gensets is they really don't have the rotating
mass nessesary to sustain inductive starting loads. They depend on
their internal governer/throttle to pickup the loads as they come online,
because they are designed to be light duty mechanisms. This is nothing
more than a design tradeoff that your system just can't deal with, so
either redesign your loads so that only one inductive load can come
online at a time, or buy a Prime Power Genset, and be done with it.

Me

 

[Me]

"..., or buy a Prime Power Genset, and be done with it. "

Why would a Prime Power unit have a higher surge capacity?
I understand that they will have a much longer rated life, but the ones
we looked at (Onan GNAB) had very little extra surge capacity.
The surge and Prime were within about 10% of each other verus the 80%
higher rated value of the Generac...

"The
simple reason that Hondas, and most all 3600 Rpm Gensets, aren't
considered Prime Power gensets is they really don't have the rotating
mass nessesary to sustain inductive starting loads...."

Again, I thought Prime power was the ability to run for extend periods
and not a measure of surge capacity.

A Prime Power Genset will have significantly more rotating mass,
and therefor significantly more enertia which will mitigate the
surge loads that are of short duration. (big flywheels and more poles
on the rotor)

Me

 

[Steve Spence]

But have you ever noticed that the first thing a person who can't
make their point, or is proven wrong does, is switch into insult mode?

That may be true of some folks, but Nick is rarely wrong, and never
insults someone when he is. He admits his mistake, and posts a
correction. He tends however, to not suffer fools gladly.

 

[Me]

I see.

I agree that they (the slower running generators) have more mass.

But, while energy is dependent on the mass of the object in motion, it
is also dependent on the SQUARE of the speed.
Do you agree?
If so, then an 1800 rpm generator would need to have 4 times the
rotating mass to have the same rotating energy as a 3600 rpm generator.
Do you agree?

It could very well happen that an 1800 rpm does have more rotational
energy than a 3600.
But how significant is it?
And
How much of that extra energy can be "tapped" to provide surge capacity
while still staying within the voltage and cycle limits?

How much do you mean when you say "significantly?"

it is the rotating mass that needs to be evaluated. Think Cranksaft,
Geartrain, Pistons, Connecting Rods, Generator Rotor, Ect. Now
look at both units. Which has more more rotating mass, and which
is made of Aluminum and which is CastIron? Which has 2 poles, and which
has 4 poles, with the associated copper for each pole. That 3600 Rpm
engine is going to have a short stroke crank, compared to the 1800 Rpm
engine, which will have a much smaller mass than it's slower counterpart.
If the load surge is just for a cycle or two the governer systems don't
even come into play, because none of them can react that fast to any
preceived load change. If the load surge is of longer duration, then
governer action does come into play. Now there are a whole bunch of
different things that need to be evaluyated when looking for surge
capacity. How close is the 3600 Rpm engine to it's topend throttle
position before the load hits, as compared to the 1800 rpm engine.
What is the Governers Feedback Loop Reaction Time for both systems?

Basically, this all boils down to: Lightweight 3600 Rpm Gensets are
design compromised to have more droop, and less surge capability
than the heavier 1800 Rpm Gensets. You pay for the Iron and Copper,
and the more you buy, the better the capability. Diesels will have
better surge than gas powered engines, and HP/Watt ratios are ALWAYS
a good indicator of how a genset will preform on surge and overload.

Me

 

[William P.N. Smith]

But have you ever noticed that the first thing a person who can't
make their point, or is proven wrong does, is switch into insult mode?

Of course we have, you fricking moron!

[Sorry, couldn't resist...] 8*)