How do i charge a LEAD ACID battery.

[AtomSoft]

hey ! a PB137 is like a LM317 set to 13.7v heh

dropout is about 2v to 2.5v so at 13.7+2.5 = 16.2v

so a 19v supply should do

 

[audioguru]

If you charge your little batteries at 2.4A (the typical output current of a PB137) then they might be destroyed.
With a 19V supply it will dissipate [(19V - 13.7V) x 2.4A=] 12.7w and will need a pretty big heastsink.
But if your batteries are old and discharged then they will not charge.

 

[AtomSoft]

who said i was charging at 2.4A? the max is 2.1A so i assume... 1.5A is good enough... hence the LM317
[(19V - 13.7V) x 2.4A=] 12.7w

would then be

[(19V - 13.7V) x 1.5A=] 7.95w

but dont i have to account for the 2v dropout?

19v-13.7v-2v*1.5A = 4.95w

 

[audioguru]

Sorry, the PB137 and the LM317 both have a typical output current of 2.2A, not 2.4A. I read the graph wrongly in the datasheet.
Their minimum guaranteed output is 1.5A.
The max current of some LM317's is 3.4A. That will blow up your little batteries.

 

[AtomSoft]

heh hence current limiting resistor.

 

[audioguru]

heh hence current limiting resistor.

Then why do you need a voltage regulator? Use a resistor and a big zener diode.

 

[Mark_R]

check this out ==>> **broken link removed**
An interesting micro controller charger module

9-36V input, temp compensated.
I'm thinking about trying one of these out.

 

[AtomSoft]

Nice find... Ima have to a better look into it

 

[Mark_R]

The project I'm working on requires a 7AH battery in long term service outside, summer and winter. Considering the temperature swing I figure temp comp is important so I don't cook the battery (or worse, cause it to vent) on a 100 degree day. I looked at all kinds of schematics from simple to exotic but once I found the silvertel unit I quit looking.