Date: Mon, 7 Jan 2008 08:39:35 -0800
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: Now charging of house batteries Re: New fridge replacement
option for the Dometic
In-Reply-To: <2B17A919-BBDA-4EE2-969A-311137DEC112@newclear.us>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi Kai,
Cool. There are a number of ways to go about charging house batteries from
the alternator which may provide deeper charges than just strapping the
alternator to the battery. Your idea (laptop power supply > small solar
charge controller) looks interesting, but not very fast, as you say. For
example, my laptop's power supply is rated for 19VDC/3.8A, and the little
Sunguard solar charge controller you linked to can handle up to 30VDC
input and 4.5 amps. This could take quite a while to charge up a bank of,
say, four 22Ah wheelchair batteries. Other, beefier, solutions, like
stronger power supplies running into stronger controllers could work. The
ham radio kits you suggested may fill the bill, the first says he's used
it with 450W of panels, which could output 25A of current I suppose. This
is a field for experimentation.
I'm not certain what you mean when you wrote "maybe let the controller see
just 30 amps (for 4 33ah batts) of the alt for a couple or 3 hours?" --
like connect the input of the controller to the alternator directly?
--
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 1/7/2008 5:42 AM Kai Mei wrote:
> 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.
>>>
>
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