Date: Wed, 29 Aug 2007 00:34:21 -0500
Reply-To: Matt Roberds <mattroberds@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Matt Roberds <mattroberds@COX.NET>
Subject: Re: Zodi Tent Heaters
In-Reply-To: <20070828184547.RHGY15942.fed1rmmtai104.cox.net@fed1rmimpi04.cox.net>
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> From: Troy <colorworks@GCI.NET>
> Date: Mon, 27 Aug 2007 21:37:48 -0800
>
> It appears that either one or two of the ubiquitous 1 pound propane
> bottles bottles can be used, and that they can also be dimmed or
> turned down, as 20K BTU is probably way overkill for a westy interior.
I ran some numbers for heating up the back of a Bus (splitty) from 0 F
to 77 F (-18 C to 25 C), which may give you some perspective. The
calculations I made are very simple and it will almost certainly take
more heat than this, but it might give you an idea:
http://www.type2.com/archive/vintagebus/043445.html
> I don't see why a person couldn't adapt a cigarette lighter adapter
> plug-in though.
It would be pretty easy. What I would do is to cut the provided wire a
foot or so away from the battery clips, and install either some
insulated push-on connectors (the 0.25"/6.3 mm wide tabs) - if, on one
cable end, you put a male connector on one wire and a female connector
on the other wire, you can't get them mixed up. You could also use a
two-pin connector; the FLAPS and/or an RV shop sells one that's basically
half of a common four-wire flat trailer connector that would work fine for
this. Then I'd get a cigarette lighter plug and put about a foot of
wire on it - if there isn't a fuse in the plug, I'd put an inline holder
in the wire. On the end of the lighter plug wire, I'd put connectors to
match the wire to the fan motor. This way you can easily change back
and forth between the battery clips and the cigarette lighter plug.
For camp sites where you have shore power, you could buy or scrounge a
12 V, 2 A or so power supply and run the fan from that. Anything from
about 12 to 15 V at over about 1.5 A should work; if you have a defunct
older laptop, its power supply may be suitable. You could also run the
fan from a battery per the below, but make sure there's a fuse near the
battery if you do this.
> The fan itself I doubt drawls even .5 amps.
I hate to disagree with the estimable Rocket J - in his defense, he's
probably more interested in chewing on the wires than on reading the
label on the battery - but the battery they sell looks more like the
4.5 or 5 Ah size. This means that the fan draws about 1 amp. I don't
think I'd run it all night on a van with just one battery, but it might
be OK on a van with a dual-battery setup. There's no reason why you
couldn't use a bigger gel cell; the nominal 7 Ah size (very common in
small UPSes for computers) would let you get about six hours, and the
nominal 12 Ah size would let you get about 11 hours. Mouser sells bare
Power-Sonic gel-cell batteries for $16 (4.5 Ah), $20 (7 Ah), or $41
(12 Ah) plus shipping. Your local big-box home center may have a few
gel cells in the electrical department, as they are also used in
emergency lights and exit signs.
The simplest way to get more battery time would be to use a 6 V battery
that won't run the fan as fast. You have to be careful playing this
game, because the heater may overheat and either shut down (if it is
designed to) or melt (if it isn't). You could have two 6 V batteries
and run them in parallel for a long low speed run or in series for a
shorter high speed run. The fancy way is to use a PWM controller for
the fan, but I don't know of any sanely priced off-the-shelf modules to
do this.
Matt Roberds
