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Date:         Sat, 29 Sep 2007 11:00:37 -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: New fridge replacement option for the Dometic
Comments: To: Roger Whittaker <rogerwhitt1@gmail.com>
In-Reply-To:  <ccd73a10709290951i4f85a052gef18744d91b7ee65@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Jigging and poking are both favorite activities hereabouts. If you want to use 120VAC to power the DC-DC charger (http://www.powerstream.com/WC.htm) you'll want a 120VAC > 12VDC converter that can handle the current the charger is trying to put into the battery. I'm not sure that a 12V/1A video camera supply is beefy enough. The specs for that DC-DC charger are confusing -- it says

"Continuous Charging Current: 15 Amps or 7.5 Amps depending on the front panel switch position (High-Low)",

and

"Charge Current Options: The peak charge current can be adjusted to 1-10 amps by internal trim pots. "Hi" and "Lo" limits can be changed independently."

Whatever that means. But it's more than 1A. I think.

Since it's 12 in and 12 out, the input current will most likely be a little higher than the output current.

All that's needed is a cheap and easy unregulated 12VDC supply capable of, I guess, 10A. This is hardly a difficult circuit to build -- a transformer, diode bridge and capacitors, fuse or two -- the brute-force method -- but making it UL/CSA approved for electrical and fire safety raises the cost and isn't stupid. Commercially-available products are the RV 120VAC>12VDC converters. I'm seeing those in the 30 - 40 amp range (too much for this application) and $150 cost range (also too much).

A cheap battery charger to do the conversion? Like http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=45005 ?

These things can be noisy, so if you plan on sleeping in the van and charge the house battery from shore power it might not be a good idea.

But the scheme for charging from shore power using a cheap battery charger (CPC) or converter would be

120VAC > converter > DC-DC charger > house battery.

Probably easier to use a decent 120VAC smart charger to charge the battery when on shore power, and a DC-DC charger to charge it when on the road.

(It's at this point where someone who hasn't followed this thread from the beginning will not know that this is about charging those small wheelchair batteries which cannot be charged by connecting them to the alternator and is about to ask, "Why not connect the house battery to to the alternator?")

-- 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

On 9/29/2007 9:51 AM Roger Whittaker wrote:

> for those who like doing jiggery pokery stuff... > i recently picked up a 120v to 12v power supply at a second hand store > it was designed to run an intercom system ... > anyway the output is 1Amp and will make an excellent trickle charger ... > the old panasonic 12 v power supply for broadcast video camera works > the same way > this added to the inverter and one could charge very well ... > just information for ther jiggery pokery sorts > yours > > On 9/29/07, *Michael Elliott* <camping.elliott@gmail.com > <mailto:camping.elliott@gmail.com>> wrote: > > I have eyeballed that wheelchair battery scheme and agree that charging > has to be handled carefully. strapping them to the output of the > alternator is just asking for trouble. They need smart, not dumb, > charging. > > For on the road charging, there are a couple possibilities, both of > which > add an additional layer or two of jiggery-pokery. The first is the > obvious > one: run an inverter off the alternator and use it to power a 120VAC > smart > charger, i.e., > > alternator --> inverter --> 120VAC/12VAC charger --> house battery. > > If the normal and recommended battery disconnect relay or separator is > shown it would be: > > alternator --> relay --> inverter --> 120VAC/12VAC charger --> house > battery. > > That's two layers of complexity, and not super efficient but it gets its > power from the alternator that's no worry. Advantages include: you can > connect your charger to shore power if such is available, and 120VAC > from > the inverter for household current appliances, although it's powered > from > the alternator/engine battery so it should only be used while the engine > is running (or only very lightly). > > A second approach to smart-charging the batteries is to use a 12VDC car > charger for wheelchair batteries, such as > http://www.powerstream.com/WC.htm -- it's a four-stage charger which > takes > the output of the alternator ((10-15 volt) and uses that to charge the > batteries, i.e., > > alternator --> relay --> 12VDC/12VDC charger --> house battery. > > Only one layer of complexity and about the same price, or lower, than an > inverter+smart 120VAC charger. Disadvantages include: no way direct > way to > use shore power to charge the batteries, and no 120VAC available > anywhere. > > -- > 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 > > > > On 9/29/2007 7:09 AM David Etter wrote: > > > Hi Warren: > > Just be careful that these Wheelchair Batteries when > parallel > > linked require special charging technology. They cannot be charged by > > the usual direct alternator input. They require a much lower and > > slower charge rate and will overheat and die an early death if > > charged at normal battery rates. > > I was planning the same 4 - 6 battery system until I read the > > charging requirements. I'm not saying it can't be done, it's just > > that you would have to arrange another layer of "jiggery pokery" > > (technical term for fiddling around) in the Westy system. > > If you ask someone who regularly uses these batteries you > > will find that they traditionally plug them in for overnight charging > > on a 2- 3 amp 'brick' style adapter. > > Good Luck and if you do come up with a good satisfactory SIMPLE > > system , please let me know as I still believe that the small 12 volt > > Wheelchair batteries are a good idea. > > > > Regards! > > David > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > > >> Karl, > >> > >> This looks identical to the "Isotherm CR65" unit I bought a few > months > >> ago. I first saw one of these in Eric Abercrombie's Syncro at > Syncro de > >> Mayo a few years ago. > >> > >> It's a little shorter than the Dometic but volume is much better > due to > >> extra depth. 2.3 cu ft. I believe. > >> > >> I think you may be a little optimistic about how long it will > run on a > >> given battery charge though....unless you've had it in long > enough to test > >> it in actual use. "4 days" seems very optimistic. > >> > >> The Danfoss compress draws a max of 2.7 amps. I "bench tested" > mine with > >> some food inside and based on how often it cycled I estimated it > would use > >> somewhere between 18-22 amp hrs daily. It ran a used but > charged, starting > >> battery we had around to "dead" in about a day and a half. I > estimate > >> that the popular 55ah Optima...if drawn down to 50% of its > capacity (to > >> preserve life), or 27.5 amp hrs useable, would only last about a > day and a > >> half. > >> > >> Seems we will need more deep cyle battery capacity...or > supplemental solar > >> charging for a weekend camp out. > >> > >> A few months ago Mark Drillock and I were discussing use of > several 22ah > >> wheelchair batteries linked in series. Only 2.9" wide and 6.8" > tall, four > >> would fit under the driver's seat for 88hrs, enough for 2+ > camping days. > >> Mark plans a bank of six in a tray under the van near the > sliding door. > >> I'm considering 4 more in the engine bay....I want to avoid the > expense > >> and hassles of solar charging. > >> > >> Some of these wheel chair batteries can be drawn down to 80% of > capacity > >> instead of 50% and recharging life will be reduced, but the > >> reduction ...to something like 225 re charges...instead of > 500...seems > >> like something I can live with..(at the number of trips I take > >> annually)....for the benefit of the extra useable amp hours. > >> > >> What's your real world experience been like? > >> > >> Warren C. > > > > > > > -- > roger w > There are two kinds of jobs in the world: > Picking up garbage and telling people things. > Successful people do both, with the same good attitude. (riw) > ----------------------------------------------------------- > View the growing list of video work at: > http://one.revver.com/watch/376349 > http://one.revver.com/watch/357909/qt/affiliate/10 > <http://one.revver.com/watch/357909/qt/affiliate/10> > http://one.revver.com/watch/345572/qt > http://video.google.com/videoplay?docid=-7135104650374818257 > <http://video.google.com/videoplay?docid=-7135104650374818257> > http://video.google.com/videoplay?docid=3259745150182742364


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