Help! Circuit Design Comparator (Battery Equalizer) High Cell Discharger

[toxsick]

Hi,

I have a project I need help completing.
I have a 24v bank of batteries and am always keeping an eye on them as over time one set of 12v string will be alot lower

I was thinking of some sort of circuit that can detect the voltages of say 2x 12v or even 4x 6v strings using a comparator design
I would like the following features
High Performance
*I need the output to be triggered because once a load is on the batteries that voltage would drop causing the comparator to change
Such as the highest voltage battery would trip a timed relay (say runtime of 2minutes) , so I can connect a any load such as a light or anything else to aid in discharge
* After the run of 2 minutes let things settle for 5 minutes then repeat process.
*I would like sensitivity control of the compared voltages

Low Performance
I might build a second circuit that is always Live perhaps a switch from Highperformance into Low performance that will constantly run a load of minimal watts


I hope someone here can help me with what I would need to complete this circuit.

 

[MikeMl]

TL431 is a very inexpensive, simple, precision voltage level detector capable of lighting a LED or pulling in a relay. You could have one per 6V battery, and offset three of the detectors using opto-isolation...
I will post a circuit when I get to another computer later today...

as promised:

This version has no hysteresis. Not hard to add if needed. This one turns off the LED when voltage drops (kinder to battery). It is simple to reverse the logic if needed.

 

[toxsick]

Hi MikeMI,

thankyou so much for your reply.. I cannot believe you came up with this so quickly...

so this circuit will make a light turn on at a Set voltage? almost like a voltage switch? (can be used as a Low Voltage DIsconnect?) which I wouldn't mind making!!!

anyways, if that is so that might not be so ideal since my batteries (solar use, which discharge daily) will activate that light with a typical discharge?
I need to detect the voltage difference of 2 batteries say if there is a difference of more than 0.05-0.1v to activate the Light/Relay
or

maybe I understand wrong? I am not really able to follow electronics flow path and whats going on inside that circuit!

 

[ronsimpson]

What is the size of your batteries?

Here is a way to test if the batteries are balanced. (same voltage)
R1, R2 are good 1% or better resistors used to make a 1/2 voltage point.
Battery1 and Battery2 have a center point that should also be at 1/2 voltage.
The opamp (almost any type) has a gain of 10 (or 100 by R4=1k).
The output of the opamp should at at 1/2 voltage if the two batteries are the same voltage.
If there is an error it is amplified by 10 or 100.
The red and green LEDs will be off if the batteries are balanced.
LEDs turn on at 1.5 volts. With a gain of 10 the LEDs will just turn on with a imbalance of 0.15V.
LEDs turn on at 1.5 volts. With a gain of 100 the LEDs will just turn on with a imbalance of 0.015V.

 

[toxsick]

Wow, this is looking very good and perhaps exactly what I require.
your explanation is very appreciated

Can I assume the Red LED will turn on for Battery 1 and Green LED will be Battery 2
as you said no LED means battery is balanced.

if this is so, would it be difficult to configure the LED into a relay?
I have heard of opto-relay (Can use the LED to trigger a relay.. might be simplest way)
or should I use a transistor with an output leg to power a relay?

 

[ronv]

Wow, this is looking very good and perhaps exactly what I require.
your explanation is very appreciated

Can I assume the Red LED will turn on for Battery 1 and Green LED will be Battery 2
as you said no LED means battery is balanced.

if this is so, would it be difficult to configure the LED into a relay?
I have heard of opto-relay (Can use the LED to trigger a relay.. might be simplest way)
or should I use a transistor with an output leg to power a relay?

Usually you balance batteries when you charge them. In other words you steal some power from the ones that are fully charged, but allow the ones that are not to continue to charge.
It probably isn't a very good idea to discharge them all to the weakest one.

 

[ronsimpson]

Charge, discharge, balance, etc:

I once worked on a design for 24 volts batteries in buses. (and tractors)
We used two 12V batteries. Some loads were 12V and some are 24V. The charger is 24V.
The batteries had problems in that both batteries say the 24V charge and 24V load, BUT the bottom one also saw the 12V load. There is an imbalance that will kill one or both batteries.

My battery balancer has a error amp much like in post #4. It ran a PWM that took power from the "high voltage" battery and put it in the "low voltage" battery. It worked all the time (charging and discharging) You probably don't need a 50A balancer! but a small version could be designed.

If you have a 1A load probably 100mA balancing will work well.

Again: What is your load current? What is your charge current?

 

[toxsick]

Hello,

My batteries are 4x 120Ah 12v Marine Calcium Batteries

Charge voltage is 28.2-29.6v and floats around 28.2
but have it set to equalise at 29.6 for 6 hours daily due to the calcium batteries requiring higher voltage... because my charge unit has max float of 28.2..

I have approx maximum of 40A going into the batteries.

----------------------------

i have another question.. my batteries charge upto 29.5v and early morning I see 20-30A rate even higher by midday the batteries maximum charge rate goes down to 2-4 A

considering I have 4 120A batteries thats 240Ah @ 24v but i dont see why it wont take more amps?! do you think calcium needs much more volts?

I cannot go above 30v because Inverter over volt kicks in!!

 

[ronv]

I think this is along the line of what Ron is talking about. It is a switched capacitor balancer. I used one like it on my golf cart.
I didn't include the clock circuit but can if you want to build one. You only need enough for 2 batteries so you can cut the schematic off there.
Basically it just charges a large capacitor from one battery and discharges it into the one with lower voltage. Runs during charge and discharge.
I don't think your calcium batteries are that much different to charge. If in doubt for a few dollars you can buy a hydrometer to make sure they are getting fully charged.

 

[ronsimpson]

Hi RonV,

Interesting. What I did is using an inductor in place of a capacitor. I can see placing a cap across one battery for mS then moving it to the other battery for mS. That is very much like connecting one end of an inductor to the 12V point. Then connecting the other end to 24V for uS and then to 0V for uS.
I see the capacitor version does not need an error amp.
The inductor version, if run at 50% duty cycle, could probably work with out an error amp. I used current limit and error amp because......

 

[ronv]

An inductor. Why not. I would have never thought about it. Yes, It might not be pretty if the clock stopped and there was no current limit.

 

[spec]

Hi,

I have a project I need help completing.
I have a 24v bank of batteries and am always keeping an eye on them as over time one set of 12v string will be alot lower

I was thinking of some sort of circuit that can detect the voltages of say 2x 12v or even 4x 6v strings using a comparator design
I would like the following features
High Performance
*I need the output to be triggered because once a load is on the batteries that voltage would drop causing the comparator to change
Such as the highest voltage battery would trip a timed relay (say runtime of 2minutes) , so I can connect a any load such as a light or anything else to aid in discharge
* After the run of 2 minutes let things settle for 5 minutes then repeat process.
*I would like sensitivity control of the compared voltages

Low Performance
I might build a second circuit that is always Live perhaps a switch from Highperformance into Low performance that will constantly run a load of minimal watts


I hope someone here can help me with what I would need to complete this circuit.

Hi toxsick,

Just intrested: how did all this turn out- have you solved your battery inbalance problem?

 

[ChrisP58]

Some time ago I was doing some work on a city bus that had a lot of 12 power running on the 24 volt battery system. They had a 100Amp version of this to keep the two 12 volt batteries balanced.
https://www.vanner.com/battery-equalizers/

 

[spec]

I bet those balancers are expensive