One solar panel, multiple charge controllers?

[Tad]

You might also consider a small panel that sits on the dashboard/roof
of the vehicles.  VW uses(d) them while shipping vehicles.  They are
all over EBay.  Even harbor freight sells small panels to maintain
batteries.

I vote for a trench as well.  You'll be able to run the angle grinder
there if you need to, or a real battery charger, or the block heater,
etc.  Then you can either permanently mount a $20 smart charger to
each vehicle, or get a multi-bank unit and use longer DC leads.  I
vote for the former.

-Tad

On Thu, Mar 20, 2014 at 12:05 PM, Nan and Sandy Sanders
<radiodog77 at pobox.com> wrote:
> HI Rob. It should work but..... Keep in mind you will only need one or two
> hundred Ma max to keep the batteries charged if you start out charged so a
> 250 watt panel is over kill. The other thing you will have to be careful
> about is rfi. Long connecting wires and switching regulators will be real
> easy to hear on your HF rig.
> One other thing. It will not take long to approach the cost of a few hundred
> feet of 10-2 and an outdoor outlet box (digging a trench is good exercise).
>      Sandy
>
>
>
>
> At 09:24 AM 3/20/2014, Robert Seastrom wrote:
>
>> Hi guys,
>>
>> I'm trying to think through an engineering problem and would like to
>> solicit some thoughts.
>>
>> Living in the country as I do, there's a tendency to accumulate vehicles.
>> If you want them to start when bidden (particularly the diesel trucks with
>> two 12v lead acid batteries in parallel so they can self-discharge through
>> each other) it's a great idea to have them on a battery tender of some sort.
>>
>> The current count of vehicles I'd like to support is three, and it's
>> cost-prohibitive to run electricity over to where they're parked (at least
>> until at some point in the distant future when I build a shop over there, at
>> which point the whole discussion is moot).
>>
>> Decent size solar panels, along the lines of a CS6P, are available for
>> reasonable prices.  I have a post hole digger and can easily set a timber
>> with a panel mount on top at an appropriate angle facing south.  Now the
>> question is what to do with the output of the panel.
>>
>> The panel in question is 37 volts open circuit and 30 volts optimal
>> operating voltage, 250 watts.  That oughta be enough
>>
>> I suspect that just having one single charge controller and paralleling
>> two trucks with lead acid batteries and a trailer with a small gel cell that
>> runs its lights isn't the swiftest idea.  Besides, theres i2r losses to
>> consider when running tens of feet of 12v (maybe not that big a deal at
>> battery-tender level amperages, but still).
>>
>> Perhaps just fusing the panel output and running a drop to each vehicle
>> and regulating it down with a charge controller (series type not shunt type
>> obviously) on each vehicle would do the right thing...  but then I worry
>> about what might be inside the regulator - here in the future with switching
>> power supplies being the norm, several buck regulators on the output of one
>> current source might end up fighting each other.  But maybe not a big deal
>> if there was a decent sized cap across the solar panel?
>>
>> Any thoughts on the right approach (optimally one that might involve
>> maximum application of off-the-shelf components rather than from-scratch
>> construction) would be greatly appreciated.
>>
>> Thanks,
>>
>> -r
>>
>>
>>
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