DC Power Disconnect Alarm System

Posted by: @farzad_k

Hello.

I am looking to build a simple circuit that audibly warns when the current out of a 12v DC battery has been interrupted.

I use a circuit breaker on the negative cable coming into the battery from a charger and the breaker has a mechanical disconnect switch that sometimes accidentally can be pressed, breaking the circuit without any warning rendering the battery depleted after a while because it is not being charged but it is being loaded. I am looking into a simple circuit I can build that activates a buzzer which is powered by the 12v battery being charged. Maybe such a device already exists and I can jut purchase it and put it inline.

I have seen a few videos online but not very helpful ones. Aside from the buzzer, what else do I need (non-arduino) that can sense the power outage (V-in=0) and then activate the buzzer circuit?

 

Thanks for any suggestions.

The simple solution but with a caveat is to just install a 12v relay in line and attach the buzzer to a normally closed set of contacts. The caveat is that the relay is using power all the time.

A more modern approach is to use a Hall sensor or a suitably sized power mosfet. There are videos here that covers Mosfets.

As far as commercial products, if you have a battery you need to keep charged then get a battery monitor, it has many uses. I use a Victron Smart BMV-712 and if I needed an external alarm for a disconnected battery I could use the built in relay. 

I don't need to use that function as I have a full solar system and the battery is monitored in other ways including email and phone app. I attached a pic of the screen to configure the battery alarm.

@zander Thanks for the response. I am not sure if battery monitors are meant to alert of charge disconnect while you are not able to see the circuit breaker. I also have some of Victron's hardware and they are great. In this case it would be an overkill. I do like their shunts and will be using one of them to monitor power for my astronomy gear.

@farzad_k I am also an astronomer but I sold most of my gear. If you have the shunt, what are you using to read it? 

You could install an ammeter in the circuit, or a simple low power light bulb but if you can't see the switch, maybe you can't see either of those. If you can't see then as I said a relay with normally closed contacts connected to a buzzer and the battery will work.

BTW, as I showed you in the pic, my battery monitor can indeed sound an alarm. I don;'t use it since I have the same functionality in the main display. All the victron equipment is networked so it can be monitored centrally.

@zander This is what I am going to build:

@farzad_k That looks like it will work.

Thanks

@farzad_k You may also want to check out this

https://www.electroschematics.com/dew-heater-controller-telescope/

Lot's of ideas at Cloudy Nights of course

https://www.cloudynights.com/topic/786582-dew-heater-controller-diy/

Also

https://sourceforge.net/projects/arduinonanodewcontrollerpro/

and

https://stargazerslounge.com/topic/364099-diy-dew-heater-controller/

Good luck

@zander Thanks. The link to CN is to a discussion I started 😀 

@farzad_k I wondered if it was you, have you finished that project yet.

It's something up my alley so to speak, but I am in the last years of my life and my list of projects keeps growing. I wish I had started earlier. 

I would really like to see what you came up with finally.

@zander Sorry to hear about your last years - is that by choice? Of course we live forever, won't we.

I have hundreds of projects - so many electronic parts that I don't even know why I bought some of them 😀 

Yes, I finished it, I built two of them and I am very happy with the design. The final entry to the post talks about the ending. But while I did get all the hardware for the automatic dew heater controller I never initiated that work.

https://www.cloudynights.com/topic/786582-dew-heater-controller-diy/?p=11356196

@farzad_k Some days it seems nearer than others, but once you cross 80 a realistic person knows it's not a time for long range planning. I still enjoy good health, although some parts are wearing out but nothing terminal so that's a big plus. They say only the good die young, so I have a few hundred years left yet.

@zander My thinking is that it is better to die, fighting to live than live fighting not to die.

Enjoy your life - it will last forever.

@farzad_k Couple last thoughts from your past posts.

I need to run a test, but I think there is a software control over the LCD brightness. 

There are ESP32's with external antenna that might help with your range and data rate.

@zander One major source of discouragement, as I recall now, was the ESP32 controller was very difficult to program and to get it to run. I bought a few, loaded all the python and other very strange platforms and decided that I didn't want to deal with the ESP32. I don't even recall what my grand plan would have been except that the sensor would sense the temperature and increase of decrease the voltage - that is really all. One of these days I might get back into that.