Date: Thu, 3 Jun 1999 19:54:34 EDT
Reply-To: Ssittservl@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: S Sittservl <Ssittservl@AOL.COM>
Subject: Re: Electrical - '90 Westy
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> From: sales@RALPHOTO.COM (Ralph P. Geho)
> To: vanagon@GERRY.VANAGON.COM
>
> Help Please - any of you electrical types out there.
>
> I am purchasing a 1000w Honda EU1000 generator. Its Specs are:
>
> AC output: 120v 1000w (1.0kva) max., 900w (0.9kva) rated
> DC output: 12v, 100w (8.3a) for charging 12v batteries
>
> I would like to be able to run the fridge and water pump, and maybe a
> 40w light bulb in the Westy on the 120vac from the Generator.
>
> The fridge says 120v, 7.0 / 0.7 amp
>
> Should the generator be able to handle this load?
>
> Thanks
>
> Ralph
The basic equation to figure this out is:
amps * volts = watts
kva is (I think) "kilo volt-amps", which is to say, 1000 watts.
The next thing to know is that the Westfalia's 12V and 120V systems
are completely independant (unless you've modified your electrical
system). Plugging the 120V output from the generator into the van's
"shore tie" won't power the 12V stuff at all. (It does on most RV's -
typically they have a 120V-to-12V power convertor - but not the Westfalia.)
The only things on the 120V system are the fridge and the 120V outlet
by the back seat. Everything else is 12V - that includes the pump,
the interior lights, the radio, etc. It also includes a little cooling
fan in back of the fridge, that runs on 12V regardless of whether the
fridge is on propane, 120V, or 12V.
Since your generator's 12V output is meant for charging batteries, I
supopose you could theoretically hook that 12V output up to the van's
battery (with jumper cables, I guess), and power the 12V stuff that
way. I doubt it's worth the trouble, but I'll assume you're going to do
it, so we can look at your "worst case" power usage.
First, to give you a rough sense of how much power your generator's
supplying: a typical home circuit breaker is 15 amps, and it typically
feeds all the lights and outlets in one or two rooms. At 120V (house
current), your generator can supply 1000 watts, or 8.3 amps. So, that's
enough to comfortably run all the electrical stuff you might put in
a small living room, for example.
Now let's add up what your 120V stuff draws:
The 40 watt bulb draws, well, 40 watts.
My fridge is marked: "Volts: 12/120 Amps: 7.0/0.7"
I take that to mean that it draws 7 amps when running on 12V, and
0.7 amps when running on 120V. That makes sense, I think - it's
84 watts either way.
So, between the fridge and the light bulb, you're using 124 watts.
That leaves you an extra 776 watts (of the 900 conservatively available)
to use to power the microwave, the big-screen TV, and the Jacuzzi.
As for the 12V stuff, should you choose to power it, too:
I think the tiny fridge fan uses something like (very roughly) 0.1 amp.
That's a little over 1 watt.
I don't know what the pump uses, but a much larger RV pump I found
on-line draws about 3 amps, so the little Westfalia pump surely
draws no more than 2 amps. (That's only in infrequent, short bursts,
of course, but we need to make sure we've got enough amps when everything's
all running at once.) That's 24 watts.
I don't know exactly what the interior lights draw, but I'd be surprised
if it was more than 2 amps, if you had everything on. That's another
24 watts.
That's a total of 49 watts, out of the 100 you have available.
Plenty for hooking up the 12V popcorn popper, the 12V hair dryer, and
the 12V flashing neon "Welcome to our campsite" sign.
So, the short answer is: you've got plenty of power.
As to whether the 12V hookup is worth while:
Battery capacity is measured in "amp-hours" - that is, how many
amps the battery can supply for how many hours before the battery
is dead. So, a 10 amp-hour battery could supply 1 amp for 10 hours,
or 2 amps for 5 hours, or 10 amps for 1 hour, etc. My van's starting
battery has a "reserve capacity" of about 30 amp-hours; I suppose
I'd be comfortable drawing about 20 amp-hours from it before I'd worry
about being able to start the engine. (But I'm not a battery expert,
so I don't know how much it's a good idea to draw).
Anyway, if we use the 20 amp-hour figure, that would mean you could run:
- The pump for 10 hours straight (probably not good for the pump, and
you'd have to refill the water tank a few dozen times), or
- The fridge fan for over a week, or
- All the interior lights for 10 hours.
That's pretty conservative, because I think the amperages I estimated
are on the high side.
-Steven Sittser
