lead-acid battery charging circuits wanted

[Roy J. Tellason]

I'm looking to build some battery chargers, preferably sometbing that I can
leave hooked up and powered all the time, for a number of different sized
lead-acid batteries I have on hand here (mostly gels). The sizes range
from 2AH on up to a group 27 that'll handle 20A charging currents.

I'd like to be able to control currents, and taper as needed, ending up
with a float charge voltage. My goal here is to promote battery longevity
as much as possible.

Assuming I have transformers and rectifiers, it's what I hook up to it from
there that I need to build.

Any URLs or other pointers to circuits that would be appropriate for this
use would be much appreciated.

 

[Ian Stirling]

I'm looking to build some battery chargers, preferably sometbing that I can
leave hooked up and powered all the time, for a number of different sized
lead-acid batteries I have on hand here (mostly gels). The sizes range
from 2AH on up to a group 27 that'll handle 20A charging currents.

I'd like to be able to control currents, and taper as needed, ending up
with a float charge voltage. My goal here is to promote battery longevity
as much as possible.

Assuming I have transformers and rectifiers, it's what I hook up to it from
there that I need to build.

Any URLs or other pointers to circuits that would be appropriate for this
use would be much appreciated.

Art of electronics has it.

Read the manufacturers specification sheets.
Around 13.8V is more-or-less right.
Does reducing the float voltage by .1V or so increase service life?

 

[TCS]

I'm looking to build some battery chargers, preferably sometbing that I can
leave hooked up and powered all the time, for a number of different sized
lead-acid batteries I have on hand here (mostly gels). The sizes range
from 2AH on up to a group 27 that'll handle 20A charging currents.

I'd like to be able to control currents, and taper as needed, ending up
with a float charge voltage. My goal here is to promote battery longevity
as much as possible.

Assuming I have transformers and rectifiers, it's what I hook up to it from
there that I need to build.

Any URLs or other pointers to circuits that would be appropriate for this
use would be much appreciated.

All you need is a power resistor and a linear supply.

When the battery is discharged current is:
I=E/R

When the battery is fully charged (say 13v), current is:
I=(E-13)/R

For example, E=15, R=10,
Idischarged=15/10 = 1.5A; Icharged= (15-13)/10 = 200ma

 

[budgie]

I'm looking to build some battery chargers, preferably sometbing that I can
leave hooked up and powered all the time, for a number of different sized
lead-acid batteries I have on hand here (mostly gels). The sizes range
from 2AH on up to a group 27 that'll handle 20A charging currents.

I'd like to be able to control currents, and taper as needed, ending up
with a float charge voltage. My goal here is to promote battery longevity
as much as possible.

Assuming I have transformers and rectifiers, it's what I hook up to it from
there that I need to build.

Any URLs or other pointers to circuits that would be appropriate for this
use would be much appreciated.

Google for the data sheet for the Unitrode (TI) UC3906. Great chip
for care & feeding of SLA's.

 

[budgie]

All you need is a power resistor and a linear supply.

When the battery is discharged current is:
I=E/R

When the battery is fully charged (say 13v), current is:
I=(E-13)/R

For example, E=15, R=10,
Idischarged=15/10 = 1.5A; Icharged= (15-13)/10 = 200ma

Now there's a recipe for cooked SLA's ....

 

[Paul Burridge]

Now there's a recipe for cooked SLA's ....

Yeah, 200mA is too much to leave on for an extended period, even on
one of the larger batteries.

 

[Tim Shoppa]

I'm looking to build some battery chargers, preferably sometbing that I can
leave hooked up and powered all the time, for a number of different sized
lead-acid batteries I have on hand here (mostly gels). The sizes range
from 2AH on up to a group 27 that'll handle 20A charging currents.

I'd like to be able to control currents, and taper as needed, ending up
with a float charge voltage. My goal here is to promote battery longevity
as much as possible.

Assuming I have transformers and rectifiers, it's what I hook up to it from
there that I need to build.

Any URLs or other pointers to circuits that would be appropriate for this
use would be much appreciated.

For just float-charging batteries things aren't too critical. The float
voltage is temperature dependent, but the battery manufacturers give you
the equation for their cells. There is also a max current into the battery.
In the end, any off-the-shelf voltage-regulated and current-limiting power
supply will do just fine if you twiddle the knob for the tempco.

Charging for cyclic use is a different matter. You give up longevity for
rapid charge. The best chargers measure both discharge and charge integrated
currents while also watching endpoint voltage and cutting off discharge
if the battery nears the endpoint. But all these complications are
needless if you only need float charging.

Tim.

 

[TCS]

Yeah, 200mA is too much to leave on for an extended period, even on
one of the larger batteries.

then recalculate it for different parameters. It still doable with
just a resistor and a fixed power supply.

 

[mikem]

I'm looking to build some battery chargers,

Here is a URL which nicely explains battery charging.

http://batterytender.com/battery_basics.php

Their products are cheap enough that it hardly pays to DIY.

MikeM

 

[Roy J. Tellason]

Here is a URL which nicely explains battery charging.

http://batterytender.com/battery_basics.php

There is some interesting info there, all right...

Their products are cheap enough that it hardly pays to DIY.

MikeM

Cheap is a relative thing, particularly when one is unemployed _and_ has a
well-stocked junk box, including several different battery chargers, some
functional, some not. I used to run a retail battery store and collected
these for parts when somebody bought a new one, figuring that at the very
least the transformers would be worthwhile. Turns out that most of the
ones that didn't work had bad diodes, and I also happen to have some 25A
bridge rectifiers that I'm not otherwise using...

The one "automatic" charger that I've actually been able to trace out was a
little 6A unit, 12V only. I have *no* idea where that bit of a schematic
got to, but there was an SCR, a zener diode, a resistor or two, and a
cap in there.

On thinking about this since I made the original post, I'm thinking that an
adaptation of your typical crowbar circuit might work here. The top end
going to the positive supply, and the bottom end going to the battery's
positive terminal -- if the voltage is below a certain point, then it
triggers the SCR and dumps some charge into the battery for that half
cycle.

I'm guessing that the "6A", "10A", and similar chargers I've got to work
with here are limiting current based on the design of the transformer.
When there's a battery that's *really* dead but not been that way long
enough to become sulfated, they'll draw up to 15A from a "10A" charger,
and the gauges these come equipped with often reflect this.

On the output end of such a circuit, I'm thinking that maybe an LM317 or
perhaps one with a boost transistor set up as a current regulator would be
a good thing to use, particularly with some of the smaller batteries I
have on hand here (2AH - 10AH for example).

Maybe some comparator circuitry could be added to this to allow for
detecting when there's a shorted cell, though I'm not sure how well it
would distinguish between that cnodition and one where the battery is just
_that_ far run down. Got a few LM3900 (?) or whatever that quad comparator
chip is, too.

I'm also not sure how such a setup would convert to "float" charge, either,
though I do have some power supplies which just happen to have some
13.8V/5A 3-terminal regulators on them...

Anybody else care to jump in here?

 

[budgie]

then recalculate it for different parameters. It still doable with
just a resistor and a fixed power supply.

If you expect any decent life from the SLA, it's a tad more
complicated than that in real life.

The nearest you could get is a regulated voltage source that equals
the long-term float voltage recommended by the SLA maker. Then
current limit either with a proper circuit *or* a series impedance.
This will not give optimum recovery time *or* achieve a proper SOC in
any sort of reasonable time interval. If it were that simple,
dedicated SLA charge controller IC's wouldn't exist.

 

[Anantha Narayan]

this will ensure long life of lead acid batteries
it is a old generic circuit based on thyristors

http://delabs.tripod.com/cirdir/power1.html

100 circuits at http://delabs.tripod.com/

{
note to spammers
if you spam me
then
1. your hard disk will crash
2. your monitor will go up in smoke.
}

 

[TCS]

On 04 Nov 2003 17:06:13 GMT, TCS
The nearest you could get is a regulated voltage source that equals
the long-term float voltage recommended by the SLA maker. Then
current limit either with a proper circuit *or* a series impedance.
This will not give optimum recovery time *or* achieve a proper SOC in
any sort of reasonable time interval. If it were that simple,
dedicated SLA charge controller IC's wouldn't exist.

they exist because trickle charging is slower than rapid charging

 

[budgie]

they exist because trickle charging is slower than rapid charging

Nope, they exist because the simplistic approach you offered roots
SLA's in short order, just like the compromise recharging used in most
desktop/domestic UPS equipment.

 

[TCS]

Nope, they exist because the simplistic approach you offered roots
SLA's in short order, just like the compromise recharging used in most
desktop/domestic UPS equipment.

I've never had a SLA last less than 8 years being trickle charged.

It's leaving them around self discharging that kills them.

 

[Roy J. Tellason]

It's leaving them around self discharging that kills them.

That's why I want to _do_ something about the ones I have on hand here...!

 

[budgie]

I've never had a SLA last less than 8 years being trickle charged.

It's leaving them around self discharging that kills them.

That might be a bit hard to argue. A few months back I pulled a tower
computer apart and discovered a Yuasa NP8-6 (6v 8Ah) inside. This box
had been sitting in my shed for eight years or so, and the battery
date code is 8703031 so it is now over 16 years old. It was DEAD
FLAT, and I assumed it had sulphated away.

After three cycles on my UC3906-based charger it now delivers more
than 80% of rated capacity, even after charging and then standing for
a month.

But then, if you want to treat your batteries the way you described
why should I care?