SLA battery: Connectivity detection

Hi Eric and MrAl,

I have read the little discussion between you both (hehe).
MrAl, thanks for joining this thread and giving your input.

When I initially put the circuit together, I had already removed the R4 for the LM358 as I thought it was not needed. I also knew about the missing resistor for the base of the transistor (I'm using a BC548 instead of 2N2222 by the way)... but thanks! I haven’t yet tried your ‘diode’ suggestion though.

Guys, I cannot replicate! Maybe I’m having a blonde day, but this is starting to do my head in! Perhaps I don’t understand the diagrams, or maybe it’s because you haven’t included a battery when you were testing it (which could explain why I’m having problems).

I was kindly wondering if you could do another schematic and this time include my fuse/switch/diode/battery setup and show me how you wire up the LM358 to it, and also the LM317. It sort of works and it sort of doesn’t??

A couple of questions for you:

1) I really don’t understand why I need to connect the LM358 power pin to the battery and not to the LM317 output. Connecting it this way is causing problems… If you observe my existing circuit (see attachment), the ‘Charging’ LED will come on thinking that the battery is drawing current when it’s not, when in fact it’s the LM358 drawing the current.
Also, multimeter shows a huge voltage drop because of this (I don’t like it!).
Connecting the LM358 to the LM317 instead eliminates both of these issues.

2) What is supposed to happen when say, the fuse blows? Is the buzzer supposed to turn on straight away? What if the fuse is replaced? Is the buzzer supposed to turn off straight away? Or do I expect a delay?

By the way, I have attached my existing power supply/charger schematic for you to observe.

Thanks again so much.
Jason.

hi Jason,
I'll have another look at the circuit with the part you have posted added to it.

You have realised that the LM393 is open collector output so the R4 is not required but a resistor in series with the BC548 is required. OK.

If you connect the LM358 power supply pin to the output of the LM317, if the mains fails then the circuit will not be active. Also R2 and RV2 will not see any voltage change if connected to the same point as the two 10K's [far left].

In other words the circuit will not be 'fail safe' in the event of a mains failure.

If wired as I understand it [ if the LM358 is powered from the battery] would appear as a 'disconnection' and the buzzer would sound, likewise if SW1 was opened.

What level of float charge current is charging the battery.?
The R3 39R seems to limit the current to about 50/75mA.

MrAl said:

Hi Eric,

Anyway, i didnt mean to say that the circuit doesnt
work, only that i spotted a few things that might
improve the circuit a bit. Let me go into a tiny bit
more detail now.
I appreciate any comments you may have on my posts.

First, the basic connectivity. If the battery becomes
completely disconnected, the way the circuit is drawn
it looks like the LM393 is getting it's power from
the battery so now it wont get any power and wont be
able to power the buzzer alarm. Correct me if this
interpretation is not correct.
Jason dosnt want the buzzer to sound if the mains fails.
The LM358 is powered directly from across the battery terminals

Second, when switching to LM358 we should think about
the output current to ground through the transistor
BE junction.
Again Jason is aware of the these two resistors when using a LM358 substitute


Perhaps you can do me a favor here since you already
have the circuit built up...
Maybe you could do a test where you force both op
amps to drive the transistors BE junction by forcing
their inputs to force the outputs to go 'high', without
the 1k resistors. You'd have to leave it run for a
good hour or two, then come back and feel the ic
chip to see how hot it got.
For you have I tried shorting out the base resistor, no observable problems, however I wouldnt recommend doing it.

Repeat with 2.2k resistors on both outputs in series with
the base of each transistor. Compare the heating results.
Would be nice to hear about this test. It's a little hard
to simulate this kind of thing.
Likewise with LM358 part 2, its recommeded a series resistor be fitted.
Thoughts?

Click to expand...

hi Al,
I am somewhat puzzled with the results that Jason has, but I'll see what I can do with regard to his 'extra LM317' bits.

Regards

hi Jason,
I'll have another look at the circuit with the part you have posted added to it.

You have realised that the LM393 is open collector output so the R4 is not required but a resistor in series with the BC548 is required. OK.
yep yep; taken care of!

If you connect the LM358 power supply pin to the output of the LM317, if the mains fails then the circuit will not be active. Also R2 and RV2 will not see any voltage change if connected to the same point as the two 10K's [far left]. Yeah at this point in time, I am not worried about the 'Low Battery' warning. I am mainly concerned about the battery detection

In other words the circuit will not be 'fail safe' in the event of a mains failure.
That's fine. I'm going to be adding another circuit to this later on that can detect too high or too low a voltage, with an automatic cut-off relay.. but that's a new cattle of sheep.

If wired as I understand it [ if the LM358 is powered from the battery] would appear as a 'disconnection' and the buzzer would sound, likewise if SW1 was opened. With a battery actually connected the way I have it (common ground with the LM317), I think it doesn't quite work the same as without a battery... according to my tests... unfortunately.

What level of float charge current is charging the battery.?
The R3 39R seems to limit the current to about 50/75mA.
If I calculated correctly, according to Ohm's Law, R = V/I, so R = 13.5 / 0.39A = 34.6R ... closest value being 39R. 0.39A is the max initial current according to my battery. I have tried the current limiting a while back with a 5W globe, and multimeter gave me a reading of just under 300mA I think.

hi,
Quick look at your charger.

Just curious, whats the device that the 12V 1.3AHr SLA has to power.?

ericgibbs said:

hi,
Quick look at your charger.

Just curious, whats the device that the 12V 1.3AHr SLA has to power.?

Click to expand...

Anything up to the maximum the battery and/or charger can supply... heatsinks and everything taken into consideration of course.

I really have a 12V (3A) regulator connected at the Load which I've omitted out of the diagram to keep it simpler. Basically it could be an emergency lighting system (using LED's) or an alarm, or something like that. Many uses!

BTW, some of the voltage and current notes you wrote on my diagram don't quite look right (I am sure you know what you are doing and I respect you fully), but I am getting satisfactory results on my end, and have been testing it for a few weeks without fail. What the!!

jst3712 said:

Anything up to the maximum the battery and/or charger can supply... heatsinks and everything taken into consideration of course.

I really have a 12V (3A) regulator connected at the Load which I've omitted out of the diagram to keep it simpler. Basically it could be an emergency lighting system (using LED's) or an alarm, or something like that. Many uses!

BTW, some of the voltage and current notes you wrote on my diagram don't quite look right (I am sure you know what you are doing and I respect you fully), but I am getting satisfactory results on my end, and have been testing it for a few weeks without fail. What the!!

Click to expand...

hi,
You say you are driving a 12V 3A reg from the output of the 'circuit/battery',
how is that possible with a 12V battery and the LM317 set to 14.2Vout...

ericgibbs said:

hi,
You say you are driving a 12V 3A reg from the output of the 'circuit/battery',
how is that possible with a 12V battery and the LM317 set to 14.2Vout...

Click to expand...

Well the LM1085 12V is a low drop-out one, so I can get close to 12V when the charger is working (as long as the load is not too small), but slightly less than 12V when the battery is in use... I understand I won't get 12V during mains failure.

The reason I have it there is because 13.5 might be too high for some applications (better safe than sorry), otherwise I wouldn't bother with it.

Do you have a better suggestion?

Hi again,


Eric and Jason,


I didnt seen any post that mentioned base resistors so i suggested either
1k or 2.2k. Now that i see that Jason is going to use them i can again
sleep at night

The way i read this thread is that Jason wants the buzzer to sound if
the 12v battery becomes disconnected. If i am wrong let me know.

Now if you want the buzzer to sound, you have to turn on the NPN
transistor that drives it. In order to turn on the NPN transistor you
have to have a 'high' output out of the associated LM358. In order to
get a 'high' output out of the LM358, you have to have some
POWER connected to the supply pin of the LM358. Any power
just about, but 12v would be great. The problem is, when the 12v
battery (which is powering the LM358) goes away (disconnects)
the LM358 no longer gets power, and so can not produce a 'high'
on it's output and so can not turn on the NPN and so the buzzer
remains silent.
The solution is to connect the LM358 power pin to the LM317,
and connect the buzzer also to the LM317. This way if the
battery goes out the buzzer sounds, but only if the mains is
still alive.

Eric, when you tested this what happened when the battery
was disconnected? What did the buzzer do?

MrAl said:

Hi again,


Eric and Jason,


I didnt seen any post that mentioned base resistors so i suggested either
1k or 2.2k. Now that i see that Jason is going to use them i can again
sleep at night

The way i read this thread is that Jason wants the buzzer to sound if
the 12v battery becomes disconnected. If i am wrong let me know.

Now if you want the buzzer to sound, you have to turn on the NPN
transistor that drives it. In order to turn on the NPN transistor you
have to have a 'high' output out of the associated LM358. In order to
get a 'high' output out of the LM358, you have to have some
POWER connected to the supply pin of the LM358. Any power
just about, but 12v would be great. The problem is, when the 12v
battery (which is powering the LM358) goes away (disconnects)
the LM358 no longer gets power, and so can not produce a 'high'
on it's output and so can not turn on the NPN and so the buzzer
remains silent.
The solution is to connect the LM358 power pin to the LM317,
and connect the buzzer also to the LM317. This way if the
battery goes out the buzzer sounds, but only if the mains is
still alive.

Click to expand...

Hey MrAl,
Yes you are right about the buzzer sounding when battery is disconnected, but mainly if the fuse blows or switch is "off". If the battery isn't there at all, well, you're right, how will the LM358 operate. That's one of the reasons why I was asking the question earlier (but also because I experienced another problem) - why does it have to be powered by the battery and not the LM317 - but Eric has explained this.
This is all becoming too confusing for me now Arrghh!

jst3712 said:

Well the LM1085 12V is a low drop-out one, so I can get close to 12V when the charger is working (as long as the load is not too small), but slightly less than 12V when the battery is in use... I understand I won't get 12V during mains failure.

The reason I have it there is because 13.5 might be too high for some applications (better safe than sorry), otherwise I wouldn't bother with it.

Do you have a better suggestion?

Click to expand...

*Scratches head* Wait, come to think of it, the low drop-out probably only applies when the 3A has been reached, as per the datasheet: "...with a maximum dropout of 1.5V at 3A of load current."
It appears I overlooked it.

I am trying to keep the output as close to 12 volts as I can, whether mains is present or not. Maybe I can try a zener diode setup??? Never done this before though.

MrAl said:

Hi again,
Eric, when you tested this what happened when the battery
was disconnected? What did the buzzer do?

Click to expand...

hi Al,
The original request was to detect when the battery became detached from the LM317 charging input.

So the logic behind my design was to power the LM393 directly from the battery and use the 10k/10k divided input from the output of the LM317 as the sense voltage.

When the charger was connected to the battery, the voltage at the 10k/10k sense resistors and the RV1 set would be such that the LM393 would be low. [no buzz]

When the LM317 to battery line was broken [open] the slight rise on the output of the LM317, as it was no longer on load and the slight drop in battery voltage, as it was no longer being charged would be detected by the LM393 and the LM393 output would go high [buzz on]

This happens on the test rig here.

As havn't seen a diagram on how the complete system is interconnected I cannot explain why it dosnt work for Jason.

Perhaps it would be useful if you back track over the original requirement in case i have overlooked something.
It maybe because of the other circuits he has connected.?

ericgibbs said:

hi Al,
The original request was to detect when the battery became detached from the LM317 charging input.

So the logic behind my design was to power the LM393 directly from the battery and use the 10k/10k divided input from the output of the LM317 as the sense voltage.

When the charger was connected to the battery, the voltage at the 10k/10k sense resistors and the RV1 set would be such that the LM393 would be low. [no buzz]

When the LM317 to battery line was broken [open] the slight rise on the output of the LM317, as it was no longer on load and the slight drop in battery voltage, as it was no longer being charged would be detected by the LM393 and the LM393 output would go high [buzz on]

This happens on the test rig here.

As havn't seen a diagram on how the complete system is interconnected I cannot explain why it dosnt work for Jason.

Perhaps it would be useful if you back track over the original requirement in case i have overlooked something.
It maybe because of the other circuits he has connected.?

Click to expand...

Hi, the "complete system" is what I just posted, only I didn't include the 12V reg and any potential loads at the LOAD output terminals. There's nothing else connected.

I don't know if this makes any difference, but the LM317 is powered from a --regulated-- 18V DC source, as opposed to unregulated, for reliability (I've run into a few hiccups with an unregulated one before, but let's leave that one alone).

Technically your LM358 circuit operation makes sense in my mind, but I don't know why it's not working well on my end

I am trying to come up with another solution... I honestly didn't think this'd be so hard.

Jason.

Hi again,

Jason:
Try connecting the power pin of the LM358 to the output of the LM317 and
see if that helps. If not, you will have to draw up an entire schematic of
how *you* have everything connected so we can see what else is wrong.

You can also help by stating what exactly isnt working and what is working.

MrAl said:

Hi again,
Jason:
If not, you will have to draw up an entire schematic of
how *you* have everything connected so we can see what else is wrong.

You can also help by stating what exactly isnt working and what is working.

Click to expand...

Hi Al,
You beat me to it.!

I'm sure you are aware that the LM358, configured as the two part Comparator is a standard circuit and it should work, IF connected correctly and Jasons charger and other modules are where we expect them to be.

Have a quick look at the charger/battery circuit with the voltages I added, it looks as though the charge current is quite low.

ericgibbs said:

Hi Al,
You beat me to it.!

I'm sure you are aware that the LM358, configured as the two part Comparator is a standard circuit and it should work, IF connected correctly and Jasons charger and other modules are where we expect them to be.

Have a quick look at the charger/battery circuit with the voltages I added, it looks as though the charge current is quite low.

Click to expand...

Guess what, I have some good news, I think. I just rewired everything, and it appears that I had a bad breadboard jumper/wire that snapped without me knowing... geez I hate it when that happens!

I am just testing it out properly at the moment before I get back to you and say Yay or Nay.

As with the charge current, as I mentioned in a previous post, I replaced the battery with a 7W globe with a multimeter in series set to tell me the current drawn by the globe, and it gave me a reading of just under 300mA (and my battery can handle initial current up to 390mA), so I'm not sure why you calculate it as being only 69mA

hi Jason.
First of all you will not get the same results using a lamp in place of the battery as a charge load.

Looking at your mv circuit.
The LM317 output is set tp 14.2V, there is a 0.7V drop across D2, so that gives 13.5V at the junction of D2/D3.
At this point the 13.5V will not power a 12V 3A regulator.

Now assume the battery is fully discharged at 10.8V [for a SLA]
that means there is a voltage difference of 13.5V - 10.8V= 2.6V across the 39R.

Ohms law, Ichg = 2.6/39R = 0.067A [ 67mA Max]
as the battery voltage rises to say 12Vnominal, there is only 13.5V -12V = 1.5V difference across R3 [39R].
So Inom = 1.5V/39R = 0.038A [38mA]

So for a 1.3AHr discharged battery, assuming an average charge current of 40mA, will take 1.3/.04 = 32hours at 100% eff, as the eff% is more like 60%, this means its going to take about 50hours to fully charge the battery.!!

Also the D3 diode will reduce the effective battery voltage from 12V down to 12-0.7 = 11.3V, which will not power a 12V 3A regulator.[LOAD connection]
BTW: the LM317 IIRC is rated at 1.5Amax.

The D1 LED charge lamp indicates CHARGING with currents as low as 15mA, which could be misleading.

Hope this covers your question.

EDIT:
I cannot understand you concern over the point, if the battery is not there how will the LM358 work.???

What would be the point of have a battery charger disconnection circuit, without a battery.

ericgibbs said:

hi Jason.


EDIT:
I cannot understand you concern over the point, if the battery is not there how will the LM358 work.???

What would be the point of have a battery charger disconnection circuit, without a battery.

Click to expand...

Hi Eric,

Is this a question for me?

I thought the buzzer was supposed to buzz if the battery was
disonnected and the mains power was still alive?
Is this correct?

MrAl said:

Hi Eric,

Is this a question for me?

I thought the buzzer was supposed to buzz if the battery was
disonnected and the mains power was still alive?
Is this correct?

Click to expand...

hi Al,
No its for Jason.

Its the definition of 'battery disconnection' that I thinks causing the problem.

I need a small "add-on" circuit that will warn me (perhaps with an LED) when/if the battery is disconnected from the charger. Possible scenarios:- Battery connection becomes loose; the fuse blows due to a short or incorrect polarity; or the 'Battery On/Off' switch is "Off") - otherwise there is no way of telling that the battery is connected or not.

Click to expand...

As I understand the ORIGINAL requirement was:
If the battery becomes 'disconnected from the charger lead', the buzzer sounds.
So the battery is always there to power the LM358, but if its not connected to the charger for some reason, the buzzer sounds.

Jason then said he didnt want the buzzer to sound if the charge lead connection was good when the mains failed.

- what happens if the main power supply fails due to AC failure? The buzzer would sound due to the huge voltage difference, yeah? I don't want the buzzer/LED to come on during a power failure.
So thats why the high side of the buzzer goes to the high side of the LM317.

Click to expand...

I hope that clears it.

BTW: did you have chance to look over the charger circuit.?

ericgibbs said:

hi Al,
No its for Jason.

Its the definition of 'battery disconnection' that I thinks causing the problem.



As I understand the ORIGINAL requirement was:
If the battery becomes 'disconnected from the charger lead', the buzzer sounds.
So the battery is always there to power the LM358, but if its not connected to the charger for some reason, the buzzer sounds.

Jason then said he didnt want the buzzer to sound if the charge lead connection was good when the mains failed.


I hope that clears it.

BTW: did you have chance to look over the charger circuit.?

Click to expand...

OMG, this is confusing the crap out of me now.

*If* we connect the LM358 power pin to the LM317 *instead of* to the battery directly, like originally suggested, and make any other necessary adjustments, then the LM358 would still operate because it's powered from the LM317 - even if the battery has been taken away.

Please let me reiterate what I want, as there still seems to be some confusion (and I may be to blame):
- If the battery has been removed from the charger (intentionally or unintentionally) when AC is present, warn me**.
- If the fuse blows for whatever reason, when AC is present, warn me**.
- If the switch has been turned off when AC is present, warn me**.
- It does *not* need to warn me of any problems during an AC failure (to keep things a little simpler).

** It's to warn me that the battery has lost connection to the charger, causing it to self-discharge, and that the load will not be powered during an AC failure if the problem is not corrected.

Shall we start a new thread so I can explain it all precisely all over again? Sorry, I'm becoming annoyed over the whole thing now. *breath in; breath out Jason*