Al salaam a'alaykum Bob

24 Nov 03 10:24, Bob Lawrence wrote to David Drummond:

 DD>> Other disadvantages are:

 DD>> 1) Installing a second lot of wiring for the 6V;

 BL>  Remember to use thick wire...

Indeed, but how thick is thick?

 DD>> 2) The cells, solar panels and load are all wired via an
 DD>> "intelligent" regulator. It keeps track of current/time into
 DD>> the battery, and out and adjusts charge rate accordingly. It
 DD>> also disconnects the load if the battery voltage gets too low.
 DD>> This would not happen with 6V tapped straight off the three
 DD>> cells. 

 BL>  Jeeze! You don't muck around. I'm suspicious of an "intelligent"
 BL> device. Actually, it's only as smart as the dickhead who designed it.

It uses a PIC - doesn't Brenton work in that line?

 BL> Those words you quote sound like they were written by a salesman...
 BL> why on earth would they keep track of ampere-hours in and out? Are
 BL> your cells lead-acid? 

They're gel cells.

 BL> If they're NiCad it makes a sort-of sense, but even then it's pretty 
 BL> silly.

 BL>  My guess is that it disconnects if the voltage gets to *high* (to
 BL> prevent over-charging), with a limited current that drops to zero as
 BL> the battery gets up to 13.8 volts (2.3V per cell).

It uses PWM to adjust the effective charge rate.

 BL>  It *will* work with a 6V tap and half the cells run flat. The six
 BL> cells in series are never the same anyway, and this can be a problem
 BL> with NiCad batteries and the fancy gel-cells, 

yes?

 BL> but good ole lead-acid is pretty tolerant of being overcharged. The three 
 BL> non-flat cells *will* be overcharged at the beginning of the charge cycle, 
 BL> they will fizz more gas, 

These are not supposed to fizz - they're sealed.

 BL> but at the end of the charge, the bottom three cells will be fully 
 BL> charged. You can't over-charge a lead-acid battery. As soon as the 
 BL> charging current falls, so does the voltage. A single cell can be 2.5V on 
 BL> hard charge, but it slowly falls to 2.25V just sitting there (it leaks 
 BL> internally) and on use to 2.1V. A flat battery is 2.0V but it varies with 
 BL> temperature. 

There is a temperature sensor attached to one cell and wired to the regulator.

 BL> That's why the *best*way to test a charge battery is with a 
 BL> hygrometer (the float in a bulb).

Nowhere to stick the hygometer....

 BL>  Over a few years, the life of your top three cells will be reduced,
 BL> but you can only expect 5 years out of a battery anyway (whether you
 BL> put water in or not). 

These are guaranteed for ten, life expectance of 15....

 BL> If it worries you, swap the top three and bottom three cells around every 
 BL> six months.

The buggers weigh more than 20kg each. I'm not moving them any more than I have to.

Regards,
David

--- Msged/LNX TE 06 (pre)