Date: Tue, 27 Mar 2007 09:31:03 -0700
Reply-To: "mike ." <mwmiller@CWNET.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "mike ." <mwmiller@CWNET.COM>
Subject: Re: Trickle charging battery with 1.8W solar panel = failure
In-Reply-To: <46092923.20707@gmail.com>
Content-type: text/plain; charset="US-ASCII"
Rats and mice will chew anything, and I do mean anything, insulation
included.
On 3/27/07 7:24 AM, "Michael Elliott" <camping.elliott@GMAIL.COM> wrote:
> I was going to post some ideas about Martin's issue but I'm glad I held
> off -- Matt's response is much more in-depth and useful than anything I
> would have posted. However, Matt continues to promulgate a tired and
> pernicious stereotype when he recommends fusing the panel's wires to
> protect them from melting due to shorts if they are gnawed on by "... a
> hungry squirrel." C'mon guys -- a few wires get chewed on by some inbred
> hick distant cousins and suddenly all the squirrels in the world are
> ravenous insulation munchers?
>
> --
> Mike "Rocket J Squirrel" Elliott
>
>
> Matt Roberds typed:
>> On Mon, 26 Mar 2007, Martin Jagersand wrote:
>>> Trying to find a reason I measured the output of the charger at two
>>> times: 1pm under full Alberta sun: 40mA, at 4pm 10mA. That makes
>>> only 480mW and 120mW. Far from the advertized 1.8W.
>>
>> The solar panel probably really does make 1.8 W, if you are lucky enough
>> to be using it on 21 June at the equator. In Alberta in March, getting
>> only 0.48 W doesn't seem out of line. Also, you were probably getting
>> a little more than 0.48 W, because if the panel was putting out exactly
>> 12.0 V, it would never charge the battery - the voltage from any charger
>> has to be a little bit more than the battery voltage or it will never
>> work. If you were getting 13.0 V at 40 mA, that'd be 0.52 W.
>>
>> Also, the manufacturer may be cheating a little - the raw panel itself
>> may indeed put out 1.8 W in full sun, but because it's used as a battery
>> charger, there is almost certainly a diode in series with the panel
>> to prevent the battery from discharging through the panel at night.
>> This diode will drop something like 0.5 V to 1.0 V - if the raw panel
>> puts out 0.138 A @ 13 V (1.8 W), the diode will use 0.07 to 0.14 W of
>> the available power. It doesn't sound like much, but you don't have
>> much to start with.
>>
>> There are different ideas on what a good long term key-off load is for
>> a car battery but I seem to recall something like 20 mA being discussed.
>> If your key-off load is that high, your solar cell must _average_ at
>> least that much output to keep the battery charged. This means that
>> the actual peak output at your location probably needs to be something
>> like 3 or 4 times that, because of cloudy days, night, etc.
>>
>> You could measure the key-off drain on your battery. Make sure
>> everything is shut off, then disconnect the negative cable at the
>> battery. Set your meter to measure current, then put the red lead on
>> the free end of the negative cable and the black lead on the negative
>> battery terminal. If you get something much over 20 or 30 mA, you may
>> want to investigate your electrical system.
>>
>> If you find a device that draws a lot of current with the key off but
>> otherwise appears to be working properly, you might be able to reduce
>> the load on the battery by pulling the fuse for that device when you
>> park the van for a long time. You might tape the removed fuse to the
>> steering wheel or shifter so you remember to reinstall it when you
>> come back. This way, any charger you use doesn't have to power that
>> load as well as trying to charge the battery. Another alternative
>> is to disconnect the battery from the van completely and connect the
>> solar panel right to the battery terminals. If you do this, include
>> a small fuse (5 A or so) in the positive solar panel wire right at
>> the battery terminal - this will help stop the solar panel wires
>> from melting from the battery current if they get shorted for some
>> reason, like a hungry squirrel.
>>
>> If I had to store a car outdoors in the winter for a long period of
>> time, the first thing I'd try with the battery is to take it out of
>> the car and store it in a heated location indoors. If there was power
>> available, the next thing I'd do is hook up something like a Deltran
>> "Battery Tender" or Schumacher "Battery Companion" or similar. These
>> are "smart" chargers which will charge the battery and then keep it on
>> a small enough charge to make up for any discharge but not overheat
>> the battery and cook off the electrolyte. Even if one of these chargers
>> was drawing 2 W average from the AC line, running it for six months
>> straight would use about 9 kWh, or around US$0.60 to US$1.80 at current
>> rates.
>>
>> Most so-called "trickle chargers" are not smart enough to reduce the
>> charging current to a low level and will happily cook your battery if
>> you leave them on long enough. They are good for slowly charging a
>> battery overnight or for short-term maintenance, but not for long
>> term. If a charger like this was the only thing available, I'd see
>> if I could come up with an electromechanical lamp timer to run the
>> charger for something like an hour a day. This would give the charger
>> a chance to correct any self-discharge of the battery, but not let
>> it stay on long enough to start cooking off the electrolyte.
>>
>> If there was no power available, but there was sunlight, I might try
>> to use a solar cell. In support of solar energy, both the US and
>> Canadian governments have done a lot of research into how much sunlight
>> ("insolation") you actually get at various places throughout the year.
>> Using that information, and data sheets for the solar cells, you could
>> pick out a size of solar cell that would definitely keep the battery
>> topped up.
>>
>> If there is no place to keep the battery inside, but there is power
>> available at the car (like maybe at a camp site), I'd probably still
>> disconnect the battery cables, and then hook up an AC-powered charger.
>> Having a camper makes this easier, but if you do it on a non-camper,
>> do something so that you don't forget you have a charger plugged in!
>> Disconnecting the battery is one clue - when you put the key in,
>> nothing will happen. A simple thing is to loop the extension cord
>> for the charger through the driver's door handle, or around the
>> driver's outside mirror, or similar. If you don't do this, you will
>> eventually drive off with the charger still connected, and end up
>> buying a new charger, a new extension cord, or maybe a new outlet.
>>
>> Matt Roberds
>>
| 
