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?
hi,
Quick look at your charger.
Just curious, whats the device that the 12V 1.3AHr SLA has to power.?
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!!
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...
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.
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, when you tested this what happened when the battery
was disconnected? What did the buzzer do?
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.?
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.
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.
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.
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?
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.
- 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.
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.?
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