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Andypairo 20th November 2003 02:35 PM

Battery monitor for TDA1543 DAC
2 Attachment(s)
While building a DAC mainly based on Doede's DDDAC I felt the need for a battery monitor.

I wanted some automatic functions (the most important is power cut-off when the battery is discharged), and ended up with something like this:

Andypairo 20th November 2003 02:50 PM

The image doesn't show it (why can't I attach the corrected file?), however the DAC supply is taken from the NO contact of the relay.

S2 is used for isolating the battery and for switching off the DAC

S1 turns on the DAC (the relay will latch until Vbatt goes below 10.5V)

The charger provides the supply for relay and leds, if it is missing the battery will power them through D1 (so the DAC can operate without an external supply).

If Vbatt > 11.5V the green led is on, otherwise the yellow one.

When Vbatt goes below 10.5V the relay will turn off; there is no need for hysteresys since the voltage being compared to the 5V reference is taken after the relay contact.

Any comments;) /suggestions:confused: / flaws to spot:smash: ?



Andypairo 21st November 2003 07:14 PM

2 Attachment(s)
I've made some refinements, maybe useful, maybe not.

Added a red led to signal undervoltage lockout/charge mode, re-wired the yellow led so that it switches off when the power is cut down and moved the pushbutton before the switch S2.

This way is possible to monitor the battery even if S2 is off by pressing S1, and also solved a relay vibration that happened when pressing teh button with S2 off or without the battery inserted.

Please let me know if you find it useful or if it has some flaws.



tiroth 21st November 2003 08:06 PM

Thanks Andrea. It is apropos because just the other day I forgot and left my active crossover on all night. :dead:

Andypairo 21st November 2003 10:12 PM

Let me know, in case you build it, how it works for you.

Take care not to sink too much current from the output that controls the relay, when I first connected the red led with a 1k5 limiting resistor it pushed the output of the opamp high enough to switch the relay on :xeye:

This is a characteristic of the LM358: it can source almost 20 mA but has problems sinking current :smash:

So you have a battery active x-over...can you tell me something more about it?



tiroth 22nd November 2003 01:03 PM

I am afraid I probably won't implement this any time soon due to the many other projects I have stacked up. ;) But someday...

I put together a page on my xo but have never taken the time to draw the schematic! But basically I just stuck a CCS on a JFET and used it as a buffer, cascading 1st and 2nd order filters. I found that +12V and -6V were more than sufficient, so I am using three batteries with Rod Elliot's charger.

Andypairo 24th November 2003 07:36 AM


I am afraid I probably won't implement this any time soon
You bad boy!:smash:

Well, considered its simplicity (you can easily assemble it on a veroboard in a hour or so) and the cost of batteries (!) I'd give it a try...



Ryssen 6th December 2003 12:49 AM

Will this work if battery is 7.2v and charger 9v?

Andypairo 10th December 2003 05:09 PM

Of course, but you'll have to change the relay and the thresolds.



Ryssen 10th December 2003 09:18 PM

How do I change the thresold?
Can I insert a VR somewhere?

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