quick charge

[ronv]

Lots of people seem to be looking for lead acid battery chargers for batteries bigger than can be charged fairly fast with the regular 317 chargers, so I thought I would try one for 5 to 20 amp hour batteries. My thought was to try to keep it simple but still try to keep it safe and fast.
Compromise I guess.

Maybe you all could look this one over.
Some notes:
I added the caps to the 317 to get it stable.
The transistor in the voltage feedback loop is for some ambient temperature charge compensation.
I think the initial Vbe variations are taken out by adjustment, but I'm not sure how accurate it will be at the two current levels.
On a side note... Anyone have ideas for a better battery model?
I don't have any plans to build it so any help would be appreciated before I post it as a solution.

 

[Mr RB]

Re the battery model, I don't use a simulator but in hardware I sometimes simulate a lead acid battery on a charger by a big electro cap in parallel with a resistive dummy load.

 

[alec_t]

The transistor in the voltage feedback loop is for some ambient temperature charge compensation.

The LM317 output voltage change over a 10-50°C range seems slightly greater with Q1 than without it (at least, with the two different 317 models I've got).
Since the LM339 is a quad package I'm wondering if, instead of Q3, a comparator plus a ref voltage derived from the TL431 might give less drift?
BTW, how come your pic occupies only the top half of a tall sheet?

 

[ronv]

With Q1 the voltage goes down as the temperature goes up, which is what you want with SLA batteries. Without it the voltage goes up with temperature which could result in overcharge.

I'm not sure what happens with my paint pictures.... There seems to be room for 2 screen shots.

Thanks Mr RB, That's kind what the sim does too.

 

[alec_t]

I've had a play with your asc file. Replacing Q3 with one of the '339 comparators reduces output drift by a factor of ~3. I was able to get it down much further, to ~25mV, by using a thermistor instead of Q1. In the attached mod of your charger I've used a Darlington as the current amplifier for the 317 and added a settable current limit (up to ~10A). Selection of R1/R2 sets the max current and the bulk charge termination current for both battery capacities.
I'm no expert on lead acid battery charging, so some of the values (e.g. output voltages for bulk and float charging) may need adjusting. Do 'leisure' batteries need a different charging regime from normal car batteries? Or are all lead acid batteries (including SLA) charged the same way?

Edit: I feel that for high current charging a switcher might be more cost-effective (taking into account heat-sinking) than a '317-based charger.

I'm not sure what happens with my paint pictures.... There seems to be room for 2 screen shots.

Paper portrait/landscape orientation? Paper size?