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Date:         Tue, 28 Aug 2007 23:09:48 -0700
Reply-To:     Michael Elliott <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Michael Elliott <camping.elliott@GMAIL.COM>
Subject:      Re: Zodi Tent Heaters
Comments: To: Matt Roberds <mattroberds@COX.NET>
In-Reply-To:  <Pine.LNX.4.64.0708290001230.16976@birdbird.example.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I defer to the honorable Mr Roberds on the matter of the battery size. In my defense, the Zodi page I found didn't show the battery in enough detail to show its Ah rating. Mea culpa though, since I pulled the 7Ah guess out of my a ... er, my hat.

I, too, thought that running that fan much slower than the mfgr intended w/o some careful investigation into what bits might overheat and by how much could lead to trouble. But it appears that the amount of heat that the airflow sucks away from the heat exchanger is sufficiently trivial that even with a dead battery the exchanger bits will not melt down. The manual, which is full of nice warnings about horrible things that can happen and pointers on how to avoid problems makes no mention of needing to keep the fan running.

It also states that "The Hot Vent is designed to be operated in calm conditions with wind less than 5 mph. In windy conditions the burner will extinguish. If flame does extinguish, immediately turn off propane burner. Hot Vent is NOT intended to be operated during sleeping periods." That might be important depending on where you camp. Pretty much anywhere outdoors may be problematic. Inside a hanger?

-- Mike "Rocket J Squirrel" Elliott 71 Type 2: the Wonderbus 84 Westfalia: Mellow Yellow ("The Electrical Banana") 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano KG6RCR

Matt Roberds typed: >> 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 >


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