RE: (ET) Solar charging, part 2

["harry landis" <hlandis hotmail com>]

Say there is a constant 1 amp load on the battery pack while the panels are 
trying to charge it. Say the panels can put out 5 amps. Say the batteries 
are fully charged. As soon as the controller turns off the panels, the 
battery voltage will fall a little below the quiescent voltage of 38 volts, 
so the controller reconnects the panels for 5 minutes. Now the battery is 
being charged at 4 amps net. This will repeat as long as the panels can put 
out power. So the panels will be connected essentially continuously, and so 
the batteries will get overcharged.

My controller expects to be looking at the resting voltage of the pack. If 
it is looking at some other voltage, like the resting voltage minus some 
voltage drop due to current being drawn, it will not be able to do its job 
correctly.
The current draw is a few milliamps.

Harry Landis



From: "Humphrey, Timothy" <HumphreyT neads ang af mil>
To: "'elec-trak cosmos phy tufts edu '" <elec-trak cosmos phy tufts edu>
Subject: RE: (ET) Solar charging, part 2
Date: Tue, 22 Apr 2003 21:19:57 -0000

I know it's your charger, you built it so you should know how it works. 
But,
I'll have to disagree that it will over charge an in use battery.

If the battery is being drawn from, I agree it's voltage will be low and as
such your control will either stay on or keep turning on. But, if that is
happening, then it is not charging the battery. It is merely causing the
charger or solar panels to share the load with the battery. As soon as the
load is removed the controller will start to function as required. You 
can't
charge a discharging battery.

One question I have about using it on solar panels though, is how much 
power
does the controller consume itself? If it turns on at night, what kind of
drain will it present to the battery. It gets it's operating power from the
battery, right? I know it could probably run itself for a decade or two on
the ET's pack, but should those using solar panels consider a dimlight
disconnect, in order to keep what they just put in?

Oh, and by the way, you'll be receiving my order for one soon.

Stay Charged!

Hump



-----Original Message-----
From: harry landis
To: elec-trak cosmos phy tufts edu
Sent: 4/22/03 4:29 PM
Subject: Re: (ET) Solar charging, part 2


I think my controller would work fine with a DC solid state relay
instead of
the AC one. As it happens, I have some DC SSRs available. So if anyone
wants
a controller with a DC SSR (30 amps, I think) just ask. Same price ($40
including shipping). Note: this control scheme won't work on a normal
solar
installation. It only works in applications like the ET where there is
essentially no power drain on the batteries while charging. If there is
significant current being taken from the batteries, the battery voltage
is
no longer the rest voltage, but is lower due to the drain. So the
controller
thinks the battery is always low, and ends up overcharging it.

Harry Landis





From: Jeremy Gagliardi com
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) Solar charging, part 2
Date: Tue, 22 Apr 2003 16:04:28 -0400 (EDT)

On Tue, 22 Apr 2003 16:00:07 -0400, "SteveS" wrote:
 > Yes, at the relatively low currents that we are talking about (5A or
so),
 > there are inexpensive controllers one could make or buy. Now, where
do we
 > buy cheap (err, inexpensive) solar panels?
 > SteveS
 > E12Ss
 > E20

Okay, now the next question is who can build one (Harry Landis, are you
up
to
the task)?  I haven't dabbled in electronics since I took a required
course
in
college for my CompSci degree.  That was 11 years ago, and I don't
remember
a
lick of it.  Although, if someone drew up a schematic, I might be able
to
follow
it.

--
Jeremy
E20

 > > This makes me wonder if it would be simpler to build a simple DC
 > controller,
 > > similar to the Landis model.  The Landis Controller is a solid
state AC
 > relay
 > > with a simple DC monitor (when batteries go below 38V it turns on
the
AC
 > relay
 > > to the charger).  Can't a similar controller be built that monitors
the
 > > batteries in the same exact way, but opens up a DC relay from the
solar
 > panels?
 > > The Landis Controller is only about $40.



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