Date: Sat, 29 Sep 2007 08:14:13 -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
In-Reply-To: <f06240800c3240ae16877@[192.168.1.102]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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.
>
