It is actually worst then that. Gensets put out volts and amps. The
combination of the two is KVA not KW. Gensets are rated on KVA not KW. To
get KW you multiply KVA by the power factor. A lot of manufactures assume a
power factor of 1 and do this conversion for you. But in reality you seldom
have a power factor of 1. By the way 1 is the best it can be.
Power factor is a measure of the phase shift of volts to current. The
things that cause a phase shift are inductive loads. Things like
transformers, airconditioner compressors, fans, electric drills, or a
battery charger (marine units are typically transformer isolated).
Resistive loads like resistance heaters do not cause a phase shift. The
inductive loads provide work by building and colapsing magentic fields.
These fields requires some reverse voltage (back EMF) to compeletly colapse
the field prior to building it in the oppsite direction. The back EMF
causes the shift in voltage and current. To fight this engineers add
capacitors to store some energy to counter this back EMF.
Capacitors increase size and cost money. Not a lot but some. In this
competive market most of us would buy a $1000 airconditioner vs a $1200
slightly larger AC. That said; I wish that the builders would offer power
factor correction capacitors as an option. Then the folks with gensets
could choose. (Mermaid A/C might by power factor corrected)
You can add capacitors to adjust you power factor but it is complicated,
requires test equipment that few people own, and requires disassembly of the
electrical devices to properally install. If you add to much capacitance
you can damage the genset. This requires the capacitance to come on when
the load comes on. Therefore it must be mounted at the load after its
on-off switch. Not a job for the weekend boaters but for a highly skilled
electrician who does this sort of thing. Not to many people do it so not to
many electricans do it. Why should they invest thousands in test equipment
for something they may never do in their lifetime.
Just a guess but some boats may lose 20% or more of their genset capacity to
lousy power factor.
For genset sizing I like to use the x2 factor (minimum). Add up all your
loads and x2 to get the genset size. Remember to start the biggest load
first. When adding up loads look at the input power not the output power.
A 100 amp battery charger may have an output of 100*12 = 1200 watts but the
input power can ge significantly higher. It would not suprise me if it was
15 amps worst case. That's 1.8 KVA. I don't think that this type of load
requires a high surge (or a high sudden in-rush) to start up so the x2
factor would oversize. But I would think that the Honda 2000 would be wide
open if your charger is pulling 100 amps.
Sometimes power factor gets worse a load drops so don't expect the Honda to
have an easy time it the charger is putting out 50 amps.
"Kelton" wrote in message
.. .
Doug,
you probably have a battery charger that puts out fewer watts that your
generator supplies. If you have a battery charger that is trying to
supply 100 amps to the batteries (1200 watts) and the generator can only
supply 1000 watts, you have a problem. If you have discovered a way to
do this, let me know. We will apply for a patent for perpetual motion.
Kelton
s/v Isle Escape
Doug Dotson wrote:
I'm confused about why there is some question about
running a battery charger off of a genset. I have run
mine for several years with no problem. The battery charger
runs off the genset the same as off of shore power.
Doug
s/v Callista
"engsol" wrote in message
...
I spnt a bit of web time googling marine battery chargers that
might work with the Honda EU1000 or EU2000 generators.
Here are some URLs...not an exhaustive list by any means...
http://www.charlesindustries.com/main/ma_chargers.html
http://www.newmarpower.com/
http://www.mastervolt.com/chargers/index.asp
http://www.progressivedyn.com/
http://www.majorpower.com/newmar/p3bc.html (interesting)
http://www.batterystuff.com/battery/...o/dual-pro.htm
I like the specs shown by majorpower.com. They give a
figure for power factor, which sems to be missing from
other manufs.
As a trial...assume a 100 AH gel battery. A PT14 charger will
charge 28 to 140 AH batteries at 14 amps maximum. 14 amps times
1.1 (efficeincy of 90%) times PF of .95 (spec at 115VAC) equals
about 16.2 amps. Adjust to 115VAC input and you get about 2 amps,
or 230 VA. A 25 amp charger might work even better without over
stressing the generator.
I called a couple of the charger manufs, and they concur
with the numbers. The trick is to get a charger with a rated output
compatible with the available input power. A 150 amp charger ain't
going to work with a EU1000. But of course the trade-off is longer
charge times.
Hope this helps.
Norm B