Very Simple Low Voltage Battery Alert

#12

Joined Nov 30, 2010
18,224
This site comes up with cool circuits because dozens of good minds are presenting various points of view. No one person could do all this! Your usual internet stuff is generic. This site gets specific.

A 555 can be used as a window comparator if you want to investigate that.
Pin 5 can be used to alter the 1/3-1/3-1/3 ratio to change the switching points at pin 2 and pin6.

This isn't a cmos 555, but the basic internal diagram is the same.
 

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Thread Starter

iONic

Joined Nov 16, 2007
1,662
This site comes up with cool circuits because dozens of good minds are presenting various points of view. No one person could do all this! Your usual internet stuff is generic. This site gets specific.

A 555 can be used as a window comparator if you want to investigate that.
Pin 5 can be used to alter the 1/3-1/3-1/3 ratio to change the switching points at pin 2 and pin6.

This isn't a cmos 555, but the basic internal diagram is the same.
At this point the 555 will offer no additional benefit the the use of a dual comparator... which is not a problem.

So I could regulate the battery voltage to provide a stable operation for the comparator. I have a few very low If/Vf color LED's that would reduce power consumption.
 

#12

Joined Nov 30, 2010
18,224
I don't think comparators care that much about a stable power supply, as long as they can survive the highest charging voltage you might put on the battery. The battery will hold the supply for the comparator(s) quite nicely.

The cost of continuous LED current is very high for this circuit. I like it because the 555 will blink the LED. Then again, a comparator can be taught to blink, too.
 

Thread Starter

iONic

Joined Nov 16, 2007
1,662
I don't think comparators care that much about a stable power supply, as long as they can survive the highest charging voltage you might put on the battery. The battery will hold the supply for the comparator(s) quite nicely.

The cost of continuous LED current is very high for this circuit. I like it because the 555 will blink the LED. Then again, a comparator can be taught to blink, too.
Blinking is nice as it can offer a visual alert. The LED's I have are rated at:
Vf - 1.8V, If - 2mA. Perhaps they are so dim I wouldn't even know they were on! Haven't tried them.
 

SgtWookie

Joined Jul 17, 2007
22,230
Ken,
That 7-color LED you linked to takes 15mA to 35mA to operate it, is somewhat difficult to use, and Radio Shack doesn't supply documentation for it.
 

Thread Starter

iONic

Joined Nov 16, 2007
1,662
I keep thinking about the LM314 as a single chip solution. The only specification I would have to fight is the chips source voltage. This, I believe, could be overcome with the zener regulator to supply the Vin which should insure an accurate reading. The voltage indicator resolution would be far greater and I could even tie the outputs into pairs a 5 LED indicator.
 

#12

Joined Nov 30, 2010
18,224
How about a nice CMOS quad comparator with push-pull outputs that only eats 20 microamps? TLC3704CN

What I'm saying here is that current waste can make a battery monitor become the problem, not the solution.
 

Thread Starter

iONic

Joined Nov 16, 2007
1,662
How about a nice CMOS quad comparator with push-pull outputs that only eats 20 microamps? TLC3704CN

What I'm saying here is that current waste can make a battery monitor become the problem, not the solution.
You are right #12. I keep thinking only of the particular use for a particular battery which would deplete the battery fairly quickly, thus the need for a real efficient monitor is not necessary. However, if I was smart I would have a single design that would be as efficient and effective as possible and even span different battery voltages.

I was also toying with a quad comparator, the LM339 as that's what I have on hand at present, but the TLC3704 looks as though it can match the function of the LM339 and cut the power consumption by 20x. Nice choice.

The problem with just LED's as indicators is that you have to be within visual sight of the battery or detection circuit. My thought was to explore the possibility of a small Peizo as a pulsed audio alert. Not sure on the power consumption of such devices. Can the comparator be made to "blink" a peizo?
 

SgtWookie

Joined Jul 17, 2007
22,230
I keep thinking about the LM314 as a single chip solution. The only specification I would have to fight is the chips source voltage. This, I believe, could be overcome with the zener regulator to supply the Vin which should insure an accurate reading. The voltage indicator resolution would be far greater and I could even tie the outputs into pairs a 5 LED indicator.
LM314 doesn't seem to be a valid part number.

Did you mean something like an LM3914?
 

#12

Joined Nov 30, 2010
18,224
@ Ionic, answering your question,
A comparator can be taught to blink. Comparators can do any output that is "off" or "on" but they aren't so good in the middle. That's what op-amps are for, and there are cmos (very low supply current) opamps if you need middle stuff on the output.

Some piezo's have their own oscillator, but you can do an oscillator to make a piezo beep with a comparator. "Beep" is just audio frequency on/offs.
 

Thread Starter

iONic

Joined Nov 16, 2007
1,662
@ Ionic, answering your question,
A comparator can be taught to blink. Comparators can do any output that is "off" or "on" but they aren't so good in the middle. That's what op-amps are for, and there are cmos (very low supply current) opamps if you need middle stuff on the output.

Some piezo's have their own oscillator, but you can do an oscillator to make a piezo beep with a comparator. "Beep" is just audio frequency on/offs.
And now that I have come full circle again back tot the "comparator" the LM10
suggested by Audio-Guru looks like a decent option as it already includes a voltage reference. It seems a bit confusing to use from my first glance though.
 

Audioguru

Joined Dec 20, 2007
11,248
The LM10 has an adjustable regulated voltage reference from 200mV to almost any reasonable higher voltage. It also has a low voltage low power opamp.

The opamp can be a comparator with the voltage reference as its reference voltage.
When the supply voltage drops lower than its reference voltage then the opamp can drive a warning device.
 

#12

Joined Nov 30, 2010
18,224
Right, AG. I forgot to mention that an opamp can be used as a comparator. Somebody pointed out that an opamp configured as a comparator is pretty slow compared to a "real" comparator, but a millisecond here or there isn't going to be a problem with a battery monitor. With stuff this slow, I tend to think of opamps and comparators as interchangable (except for the "open collector" style comparators).

Eager to see a schematic, even if you need a few calculations to finish it. :)
 

Thread Starter

iONic

Joined Nov 16, 2007
1,662
I will re-read the datasheet one more time and come up with a circuit. ...Scratch that, the datasheet has no info....I will read the App notes.

 
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MrChips

Joined Oct 2, 2009
30,711
Just had a 48V battery charger fail to shut down and switch to float mode... totally destroyed four 12V 15AH SLAB (Sealed Lead Acid Batteries) worth $200 for an ebike.

Now if you are going to the trouble of having multiple comparators and LEDs, I'm thinking of using a micropower MCU. What I have in mind is a Freescale MC9S08QG4 or QG8 since I have these laying around. It has analog comparator and A/D converter.

For battery monitor, I will put it in stop mode and use the comparator to wake up the MCU when the voltage drops to a certain level. Then I will use the A/D to monitor the voltage at lower levels with intermittent LED flashes (no need to drain the battery any faster).

I can use a bi-colour LED using two output ports or I can use single LEDs on separate ports.

The MCU supply current under STOP3 mode is 6uA.

For monitoring overvoltage, of course, power drain is not an issue.

What do you think?
 

Thread Starter

iONic

Joined Nov 16, 2007
1,662
Just had a 48V battery charger fail to shut down and switch to float mode... totally destroyed four 12V 15AH SLAB (Sealed Lead Acid Batteries) worth $200 for an ebike.

Now if you are going to the trouble of having multiple comparators and LEDs, I'm thinking of using a micropower MCU. What I have in mind is a Freescale MC9S08QG4 or QG8 since I have these laying around. It has analog comparator and A/D converter.

For battery monitor, I will put it in stop mode and use the comparator to wake up the MCU when the voltage drops to a certain level. Then I will use the A/D to monitor the voltage at lower levels with intermittent LED flashes (no need to drain the battery any faster).

I can use a bi-colour LED using two output ports or I can use single LEDs on separate ports.

The MCU supply current under STOP3 mode is 6uA.

For monitoring overvoltage, of course, power drain is not an issue.

What do you think?
It sounds pretty nice. But when it comes to programming I am at a complete loss.
 
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