Re: Battery charging with intermittant power source

On a sunny day (Sat, 10 Jan 2009 14:51:34 -0800 (PST)) it happened
"miso@xxxxxxxxx" <miso@xxxxxxxxx> wrote in
<f0f151e9-9761-4cd4-b906-93aceb6a14f4@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:

I just did one, there is a flashing alarm when the battery drops below 10=
.7 V,
and a switch off, using power MOSFET, when 10.0 V is reached, also with a=
larm.
There is current limit and voltage limit on the charger.
There also a a time limit on the charge (24 h for sealed lead acids).
Also the Ah hours is calculated from the current.
I guess I could make some assumptions, and limit charge on Ah hours too,
but then would need to monitor temp as well.
You can get as sophisticated as you want with a PIC :-)

Before I start any home project, I carefully search the commercial
market. Not often is it cheaper to DIY unless your time is free. I
generally build it myself when the price savings is large or I can
achieve better specs.

Yes, sure, never design or build something you can buy for a fraction of the price.
That is often the case with things like amplifiers, TV's, NiMH chargers, what not.
Still it may be fun.

Anyways, I just took the gel battery specs, it told me the max charge current,
charge time, charge voltage, and a lot of other interesting stuff.
I already had the power MOSFET switch part (you cannot buy that), the PIC
with plenty of analog inputs, so on suggestion of somebody here, I used the
voltage drop over the MOSFET to measure current (it is almost exactly 20 milli Ohm).
And the rest is just basic math in the same PIC (that also drives a 4 line text LCD display).
I dunno total cost, but I think I can match that 600 $ price tag on
http://www.blueskyenergyinc.com
This gel battery has now had about 1200 full charge / discharge cycles,
with very little decrease in performance I can see, so I must be doing something right,
If something does not work, then I can fix it, an other advantage of DIY.
And in this project, using proto board, the design was practically rebuild 2 times..
If I have some idea I can just try it out, added a second PIC a few weeks ago.
It has remote control from the PC via RS232, and manual control too.
I can read battery status from anywhere in the world, and control it too.
(It powers an amateur radio transmitter).
I can even make it play audio files from anywhere in the world, as the audio
comes via the PC, digital processor.
Or have the receiver record something....
Also on a timer (using crontab).
Now that is something you cannot buy anywhere...



I want to set up some gel cell charging scheme where the 3rd row of my
SUV resides when folded. [That is, yank out the seat and have a shop
build a lid, then recover the space for electronics.] There are plenty
of battery isolators on the market, but most charge controllers from
the solar and wind market can't handle the low drop out of being
charged from an alternator. However, the Blue Sky products look
promising:
http://www.blueskyenergyinc.com/
The trick with all these chargers is to interpret their nebulous
datasheets.

You want to run that car on gel batteries?
Or just use the car to charge those?
.

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