Date: Mon, 7 Jan 2008 08:42:00 -0500
Reply-To: Kai Mei <kai@NEWCLEAR.US>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Kai Mei <kai@NEWCLEAR.US>
Subject: Now charging of house batteries Re: New fridge replacement option
for the Dometic
In-Reply-To: <46FE6BC5.40600@gmail.com>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
Here's another take on it:
Solar controllers and 18 v power supplies.
Charge the deep cycle batteries with a Laptop power supply and a
controller like
http://store.solar-electric.com/sg-4.html
18v supplies are cheap for 12v or 120v and you could add solar with
no added costs (or borrow?)
doesn't quite solve the long, long charging times tho, maybe let the
controller see just 30 amps (for 4 33ah batts) of the alt for a
couple or 3 hours? is 1/3C too much too send to wheelchair batteries?
You could have a charging system that takes decent care of the deep
cycle batteries, for under $60.
Another solar controller is only avail. as a kit. Here's some info.
The solar controller is designed to charge a gel cell or wet cell 12
volt
battery with a solar panel. Panels from 1 to 200 watts can be used and I
have used one with 3 panels equaling 150 watts total with no problems as
well as a small 3.5 watt panel charging a small 2.8 amp battery. The kit
comes with a 2x3 fiberglass silk screened and solder masked circuit
board.
All parts for the board and instructions and app notes.
The price is $30
The kit includes: FR-4 type fiberglass circuit board with solder mask
and=
silkscreen similar to Elecraft boards (1.8"x2.9"). All parts that
mount =
to the board including all resistors and capacitors diodes, a 65 amp
powe=
r FET, 8 amp shottkey blocking diode, red LED, heat sink and mounting
har=
dware for FET and a 4 pin terminal block for connections to the
battery a=
nd panel. Assembly instructions and schematic drawings. Application
note=
s and possible modifications for more current or using with an
external p=
ower supply rather than a solar panel to charge the battery. =20
Hi
Bob is right on this. The controller kit I sell is a series mode
controller
but uses a 45 amp P channel FET so it is turned on by pulling the
gate to
ground. A switching supply is not required for this circuit so there
is no
RF generated that may get into the receiver. The heat sink on my
controller
is a small TO220 type and is really only needed if the panel is over 100
watts. The real limiting part in the design is the reverse current
diodes
and I use 2 8 amp shottkey's in parallel. The controller IC has a
precision
band gap reference and 2 precision comparators and I provide 1% metal
film
resistors in the measuring circuit so there are no adjustments required.
There is also a LED that indicates when the panel is charging the
battery
and when the battery is fully charged. The controller operates by
connecting
the panel to the battery and monitoring the voltage. When the battery
voltage reaches 14.0 volts the panel is disconnected and a wait period
starts of about 4 seconds. At the end of the wait period the battery
voltage
is checked again and if it is below about 13.8 volts the panel is
reconnected to the battery. The controller will maintain a 13.8 volt
level
on the battery.
Don Brown
KD5NDB
I should mention that my controller operates the same as the MicroM+
but I
use a different circuit and different IC. The circuit is much simpler
and
more accurate because of the precision band gap reference and precision
comparators in the IC. Also the LED on my controller will not light
if the
panel is not providing enough voltage to charge the battery. The kit
is $30
and includes all parts and fiberglass circuit board.
The Pc board is 1 7/8" X 2 7/8" X ~1/2"
It works the same as the Micro M+ but uses a different circuit that
is mu=
ch simpler. The circuit is made up of 8-resistors 1-8 pin IC 1-power
FET =
1-Shottkey diode 1-led and 3-capacitors. A terminal block connects
to th=
e battery and solar panel.
The design is for a 12 volt SLA gelcell or wet cell battery I have
used t=
he charger with a 2.8 amp battery and 5 watt charger and a 70 watt
solar =
panel with a 35 amp SLA battery.
I haven't researched this but it may work with NiMH or NiCads with
some r=
esistor changes
There are no rf generating circuits. The charger operates as a switch
app=
lying the full power from the solar panel to the battery until the
termin=
al voltage reaches the trip point then the current is switched off.
Once =
off there is a 4 second delay before the current can switch back on.
When=
the battery is fully charged a very short pulse of current is
applied to=
the battery every 4 seconds to keep the battery toped off as long
as the=
solar panel output is above the battery voltage.
The power FET is rated at 64 amps so with the proper heat sink the
contro=
ller will handle just about any solar panel. The limiting component
is th=
e Shottky diode in series with the battery. The diode is rated at 8
amps =
so the max power is about 75-85 watts. The power FET and a larger
diode c=
ould be mounted off board on a heat sink for a larger solar panel.
The board is small enough to mount inside the K2 with KBT2 or it will
fit=
in an EC-1 enclosure with a 2.8 amp 12 volt SLA battery. You can
also us=
e a 1 amp 15-18 volt wall wart power supply with a 5-10 ohm 5 watt
resist=
or in series in place of the solar panel to keep the battery charged
from=
the mains.
Don Brown
KD5NDB
On Sep 29, 2007, at 11:14 AM, Michael Elliott 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.
>>
