Solar charger current divider/regulator?

[mikem]

I have a 14V solar panel which puts out about 200mA on cloudy days
and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

If one battery is at 13.25V, then all of the current should be
diverted to the the other battery, until it too reaches 13.25V.

If either battery is disconnected, then all of the available solar
current should be available to the remaining battery.

If either battery is discharged, or develops a shorted cell, then
at most half the available solar panel current should be used in
an attempt to charge it to 13.25V, leaving the remaining current
for the other battery.

If both batteries are at 13.25V, then the excess solar current can be
shunted to ground.

Any ideas?

MikeM

 

[Luhan Monat]

I have a 14V solar panel which puts out about 200mA on cloudy days
and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

If one battery is at 13.25V, then all of the current should be
diverted to the the other battery, until it too reaches 13.25V.

If either battery is disconnected, then all of the available solar
current should be available to the remaining battery.

If either battery is discharged, or develops a shorted cell, then
at most half the available solar panel current should be used in
an attempt to charge it to 13.25V, leaving the remaining current
for the other battery.

If both batteries are at 13.25V, then the excess solar current can be
shunted to ground.

Any ideas?

MikeM

Hi,

Most of your requirements are met by using an lm317 voltage regulator to
produce 13.75 volts. The output of the regulator goes thru a diode to
each battery. This will give all the charge to the battery that is not
yet up to 13.25v.

The requirment that a 'bad' battery not be given power is more tricky.
This requires a microcontroller reading both battery voltages and power
transistors to send charge voltage only to good batteries.

Luhan

 

[Rich Grise]

They do this all the time in the RV world. You use what's called
"isolation diodes." You'd want to do a little digging to find
diodes with the lowest possible forward drop - Schottky (sp?)
comes to mind, but there may be others.

You certainly don't need any 3-terminal regulator: lead-acid
batteries _love_ a full-float charge.

And if the batteries and the load don't need all the current
that _can_ be supplied by the panel, it's not necessary to
throw the excess away - do nothing with it, and the excess
current simply won't flow.

Good Luck!
Rich

 

[Luhan Monat]

Yo,

I lived in an RV for 6 years --- 5 each 5 amp pannels.

What you say is fine execpt if one of the batteries has a bad cell and
wont come up to 13 volts. It will jjust suck all the power.

 

[Madis Kaal]

I have a 14V solar panel which puts out about 200mA on cloudy days

and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

one current-limited switching regulator for each, zener for shunting if
it happens that there is excess energy... Something like this:

http://www.nomad.ee/micros/solar/index.html

 

[Robert Monsen]

I have a 14V solar panel which puts out about 200mA on cloudy days
and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

If one battery is at 13.25V, then all of the current should be
diverted to the the other battery, until it too reaches 13.25V.

If either battery is disconnected, then all of the available solar
current should be available to the remaining battery.

If either battery is discharged, or develops a shorted cell, then
at most half the available solar panel current should be used in
an attempt to charge it to 13.25V, leaving the remaining current
for the other battery.

If both batteries are at 13.25V, then the excess solar current can be
shunted to ground.

Any ideas?

MikeM

Use a timer to switch the charge current back and forth every second or so.
This will ensure that both batteries get charged even if one of them is
damaged or gone.

If one of the batteries is at full charge, shunt its 'turn' to the other one
(although this complicates the issue)

There are various ways to do this.

I'd use a little 8 pin microcontroller to sense the voltage (using its
analog to digital converters,) and use two output pins to control some P
channel MOSFETS. That would be 2 P MOSFETS, 2 BJTs, about 10 resistors, a
7805, and a little code. However, that appears to be my answer to everything
these days.

Not using a uC would probably mean a cmos 555, a couple of zeners, a couple
of comparators, and a few power mosfets (plus assorted resistors,
capacitors, etc.)

Regards,
Bob Monsen

 

[Fred Bloggs]

I have a 14V solar panel which puts out about 200mA on cloudy days
and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

If one battery is at 13.25V, then all of the current should be
diverted to the the other battery, until it too reaches 13.25V.

If either battery is disconnected, then all of the available solar
current should be available to the remaining battery.

If either battery is discharged, or develops a shorted cell, then
at most half the available solar panel current should be used in
an attempt to charge it to 13.25V, leaving the remaining current
for the other battery.

If both batteries are at 13.25V, then the excess solar current can be
shunted to ground.

Concept- view in a fixed-width font such as Courier.



- +----+ +
+-----| PV |------+-----------------------+
| +----+ | |
| | |
| e e
| \| |/
| |----+--------------+
| /| | |\
| c | c
| | | |
| +------+ |
| | |
| --- ---
| SD \ / \ / SD
| --- p-ch's ---
| | |
| +-------------+------s d --- d s------+---------+
| | | | | | | | |
| | | --- --- | |
| | | 100k | | 100k | |
| | +-/\/\--+---+---+--/\/\-+ |
| | | |
| | \ * | * \ |
| +------|<|----+ +---+--+ +----|>|--+-----+
| | \ | | | | \ |
| | 13.0V | c c | 13.0V |
| | _ | |/ \| | _ |
| ----- _| +-----| |------+ _| -----
| --- | |\ /| | ---
| | / e e / |
| | 1k | | 1k |
| | / | | / |
| | \ | | \ |
| | | | | | |
+---+-------------+-------+------+--------+---------------+


* active zener's

 

[Fred Bloggs]

Fred Bloggs wrote:

Maybe like so:

Please view in a fixed-width font such as Courier.



- +----+ +
+-----| PV |------+-----------------------+
| +----+ | |
| | |
| e e
| \| |/
| |----+--------------+
| /| | |\
| c | c
| | | |
| +------+ |
| | |
| | |
| | |
| SD | p-ch's | SD
| | |
| +----|<|------+------s d --- d s------+---|>|---+
| | | | | | | | |
| | | --- --- | |
| | | 100k | | 100k | |
| | +-/\/\--+---+---+--/\/\-+ |
| | | |
| | \ * | * \ |
| +------|<|----+ +---+--+ +----|>|--+-----+
| | \ | | | | \ |
| | 13.0V | c c | 13.0V |
| | _ | |/ \| | _ |
| ----- _| +-----| |------+ _| -----
| --- | |\ /| | ---
| | / e e / |
| | 1k | | 1k |
| | / | | / |
| | \ | | \ |
| | | | | | |
+---+-------------+-------+------+--------+---------------+


* active zener's

 

[MikeM]

Hi Fred,

Thanks for the suggested circuit. I understand the current mirror and
the shunt voltage detectors across each battery, but dont get what
the two p-fets in series do?

Also, what is an "active zener"?

Tnx,

Mike M

 

[MikeM]

Tnx Luhan,

Most of your requirements are met by using an lm317 voltage regulator to
produce 13.75 volts. The output of the regulator goes thru a diode to
each battery. This will give all the charge to the battery that is not
yet up to 13.25v.

I understand how to use Shottky diodes to isolate one battery from the
other, and that the current will flow to the battery with the lower
voltage, but I really want to preclude a battery with a shorted cell
from hogging all the current.

The requirment that a 'bad' battery not be given power is more tricky.
This requires a microcontroller reading both battery voltages and power
transistors to send charge voltage only to good batteries.

Using an uController sounds more complicated than it ought to be...

Tnx

Mike M

 

[MikeM]

Use a timer to switch the charge current back and forth every second or so.
This will ensure that both batteries get charged even if one of them is
damaged or gone.

Doing this now, using a 555. Lower battery gets at most half available
panel current.

If one of the batteries is at full charge, shunt its 'turn' to the other one
(although this complicates the issue)

There are various ways to do this.

I'd use a little 8 pin microcontroller to sense the voltage (using its
analog to digital converters,) and use two output pins to control some P
channel MOSFETS. That would be 2 P MOSFETS, 2 BJTs, about 10 resistors, a
7805, and a little code. However, that appears to be my answer to everything
these days.

I have used 28 and 40 pin PICs. Which one has an A/D converter in an 8
pin pkg?

Not using a uC would probably mean a cmos 555, a couple of zeners, a couple
of comparators, and a few power mosfets (plus assorted resistors,
capacitors, etc.)

It gets complicated fast...

MikeM

 

[Robert Monsen]

Doing this now, using a 555. Lower battery gets at most half available
panel current.


I have used 28 and 40 pin PICs. Which one has an A/D converter in an 8
pin pkg?

The PIC12F675 has 4 10 bit A/D converters... in an 8 pin package. Very cool
chip.

 

[Robert Monsen]

Hi Fred,

Thanks for the suggested circuit. I understand the current mirror and
the shunt voltage detectors across each battery, but dont get what
the two p-fets in series do?

Also, what is an "active zener"?

Tnx,

Mike M

I hesitate to speak for Fred, but I spent about an hour studying this
circuit today, trying to figure it out...

The p-fets in the middle are a shunt between the two sides of the current
mirror. When the shunt is turned off, both sides get the same amount of
current due to the mirror effect.

The shunt is turned on when either of the voltages on the battery sides of
the shottkeys get to be greater than 13V.

An active zener is just a 3 pin device that is programmed by a couple of
resistors, and which has a sharp knee so that the detection of the 13V
condition suddently turns on the shunt. If your source isn't very stiff, the
active zener doesn't matter all that much, ie, the shunt still works
properly. I think you can simulate one of these pretty easily with a BJT, a
few resistors, and a normal zener.

The two BJTs in the center are actually a 'nor' gate, the output of which
feeds the p-fet's gates. So, if either of the batteries is at 13V, the
active zener becomes a short, which raises the voltage of the base of the
BJT. That turns it on, which drags the voltage of the gate of the pfets
down, which turns on the pfets and enables the shunt.

Now, the shunt is actually pretty cool. It causes the side of the circuit
that has the lower battery to get all the current. This happens because the
area containing the shunt drops to a diode above the lower battery, shutting
off current to the higher one.

Very cool circuit, and simple! No silly PWM to worry about. I think it does
everything you need.

Regards,
Bob Monsen

PS: This guy pops em out like waffles. I wonder if he had this sitting in
some drawer, or if he just designed it on the fly for you?

 

[mikem]

I hesitate to speak for Fred, but I spent about an hour studying this
circuit today, trying to figure it out...

Its amazing what you can learn by posting a question here...

The p-fets in the middle are a shunt between the two sides of the current
mirror. When the shunt is turned off, both sides get the same amount of
current due to the mirror effect.

I guessed that this is the case...

The shunt is turned on when either of the voltages on the battery sides of
the shottkeys get to be greater than 13V.

Without the shunt, wouldn't the current mirror shut down the current
to the "right" battery if the "left" battery reaches 13.xx V first?

An active zener is just a 3 pin device that is programmed by a couple of
resistors, and which has a sharp knee so that the detection of the 13V
condition suddently turns on the shunt. If your source isn't very stiff, the
active zener doesn't matter all that much, ie, the shunt still works
properly. I think you can simulate one of these pretty easily with a BJT, a
few resistors, and a normal zener.

Ok, I was thinking that it is a purchasable device, rather than a
sub-circuit...

The two BJTs in the center are actually a 'nor' gate, the output of which
feeds the p-fet's gates. So, if either of the batteries is at 13V, the
active zener becomes a short, which raises the voltage of the base of the
BJT. That turns it on, which drags the voltage of the gate of the pfets
down, which turns on the pfets and enables the shunt.

Now, the shunt is actually pretty cool. It causes the side of the circuit
that has the lower battery to get all the current. This happens because the
area containing the shunt drops to a diode above the lower battery, shutting
off current to the higher one.

Very cool circuit, and simple! No silly PWM to worry about. I think it does
everything you need.

It seems that in its present configuration, it will not stop charging
when the second battery reaches 13.xx V. If the 1K resistors were
lowered to a few tens of Ohms, then would the entire panel current be
shunted to ground after the second battery is charged?

MikeM

 

[Robert Monsen]

Its amazing what you can learn by posting a question here...

I guessed that this is the case...


Without the shunt, wouldn't the current mirror shut down the current
to the "right" battery if the "left" battery reaches 13.xx V first?

No, thats the beauty of a current mirror. Since the base voltage is the
same, the current through each of the transistors is the same (more or
less).

Ok, I was thinking that it is a purchasable device, rather than a
sub-circuit...

It is, look for TL431. I just meant that if you didn't have one, you could
probably get away with it by either hacking one together, or maybe
altogether if your solar source tends to droop when you draw current from
it.

It seems that in its present configuration, it will not stop charging
when the second battery reaches 13.xx V. If the 1K resistors were
lowered to a few tens of Ohms, then would the entire panel current be
shunted to ground after the second battery is charged?

When the voltage of the shunt is less than or equal to the voltage of the
battery, the current will stop flowing through the diode. So, as the battery
reaches 14V - Vf1 - Vf2, (where Vf1 is the forward voltage across one of the
current mirror PNPs, and Vf2 is the forward voltage across the shottkey) the
current will stop flowing.

MikeM

You know, AFAIK, I might have all of this wrong. I'll let the designer speak
for himself from now on.

Regards,
Bob Monsen

 

[[email protected]]

I have a 14V solar panel which puts out about 200mA on cloudy days
and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

If one battery is at 13.25V, then all of the current should be
diverted to the the other battery, until it too reaches 13.25V.

If either battery is disconnected, then all of the available solar
current should be available to the remaining battery.

If either battery is discharged, or develops a shorted cell, then
at most half the available solar panel current should be used in
an attempt to charge it to 13.25V, leaving the remaining current
for the other battery.

If both batteries are at 13.25V, then the excess solar current can be
shunted to ground.

Any ideas?

MikeM

Found one Electronics Now October 1997
But you might want to try
www.goldmine-elec.com

we can buy the Solar panell here for are cars or whatevver they just
plug into the cigarette lighter to recharge

let me know if what article and smhc
Logan

 

[[email protected]]

I have a 14V solar panel which puts out about 200mA on cloudy days
and 400mA in brite sunlight. I want to "float" two lead-acid batteries
in parallel (not series), each battery to be held at 13.25 V as long
as the sun shines. The minus side of the two batteries are tied
together; the positive terminals are isolated.

If one battery is at 13.25V, then all of the current should be
diverted to the the other battery, until it too reaches 13.25V.

If either battery is disconnected, then all of the available solar
current should be available to the remaining battery.

If either battery is discharged, or develops a shorted cell, then
at most half the available solar panel current should be used in
an attempt to charge it to 13.25V, leaving the remaining current
for the other battery.

If both batteries are at 13.25V, then the excess solar current can be
shunted to ground.

Any ideas?

MikeM

Found one in Electronic Now October 1997
might also try
www.goldmine-elece.com
also have Sun Tracked made with LED'S
and a Solar power supply in Encyclopedia of Electronic circuits Vol 6
page 312
we can by them here Solar pannell and they just plug into cigarette
lighter 75.00 Canadain so about 45.00 US to recharge your car
battery
logan

 

[Ted Wilson]

Fred Bloggs wrote:

Maybe like so:

Please view in a fixed-width font such as Courier.



- +----+ +
+-----| PV |------+-----------------------+
| +----+ | |
| | |
| e e
| \| |/
| |----+--------------+
| /| | |\
| c | c
| | | |
| +------+ |
| | |
| | |
| | |
| SD | p-ch's | SD
| | |
| +----|<|------+------s d --- d s------+---|>|---+
| | | | | | | | |
| | | --- --- | |
| | | 100k | | 100k | |
| | +-/\/\--+---+---+--/\/\-+ |
| | | |
| | \ * | * \ |
+------|<|----+ +---+--+ +----|>|--+-----+
| | \ | | | | \ |
| | 13.0V | c c | 13.0V |
| | _ | |/ \| | _ |
| ----- _| +-----| |------+ _| -----
| --- | |\ /| | ---
| | / e e / |
| | 1k | | 1k |
| | / | | / |
| | \ | | \ |
| | | | | | |
+---+-------------+-------+------+--------+---------------+


* active zener's

Hi Fred

How about a modification to your circuit along the following lines:


- +----+ +
+-----| PV |------+-----------------------+
| +----+ | |
| | |
| e e
| \| Rb Rb |/
| |-+--^^^^-+-^^^^--+-|
| /| | | | |\
| c / | / c
| | \Rf | Rf\ |
| | / | / |
| | \ | \ |
| |___|_______| | |
| | | ____________| |
| | | | |
| +-------------+ | | +---------+
| | |___|______ |
| | | | |
| | | | |
| | | | |
| | | | |
| | \ * | | * \ |
| +------|<|----+ | | +----|>|--+-----+
| | \ | | | | \ |
| | 13.0V | c c | 13.0V |
| | _ | |/ \| | _ |
| ----- _| +-----| |------+ _| -----
| --- | |\ /| | ---
| | / e e / |
| | 1k | | 1k |
| | / | | / |
| | \ | | \ |
| | | | | | |
+---+-------------+-------+------+--------+---------------+


* active zener's

Would need to give some thought to the required values for Rb/Rf to
provide orederly change-over, but I reckon this would do the job.
(Nice thing is it makes the PNPs work for their living and handle the
change over as well as defining the two charge currents).

Regards

Ted

 

[[email protected]]

GOT what need shmc
your e-mail adress didn't work

 

[[email protected]]

Found one in Eleectonics Now October 1997
Also one Enyc electronic Circuits volume 5 page solar power supply
Plus a Sun Tracker made with LED'S
in canada we get buy the pannell that just plugs in to your car
lighter to recharge
But i heard www.goldmine.elce-com
might have what your lookig for
hope this help
logan