12 Volt car battery emergency light

I agree that there are multiple ways to do a task. And using an AC relay for sure does the job and this is the solution am I leaning towards however still open to the diode approach but concerned that a diode normally drop by 1/2 a volt leaving my charging circuit at 11.5V instead of the expected 12V

Perhaps this is not an issue? Regardless I am grateful to you all for providing guidance.

Perhaps someone can validate?

photo

opale7000:
I agree that there are multiple ways to do a task. And using an AC relay for sure does the job and this is the solution am I leaning towards however still open to the diode approach but concerned that a diode normally drop by 1/2 a volt leaving my charging circuit at 11.5V instead of the expected 12V

Perhaps this is not an issue? Regardless I am grateful to you all for providing guidance.

No, a charger will put out about 13.8V to 14Vcharge the batteey, not 12v.
An automatic charger will taper the charger current as the battery comes up to charge.
What charger are you thinking of using?
Your pictured circuit will latch ON and the relay will not drop out when the charger stop due to current from the battery holding it ON.
Tom... :slight_smile:

TomGeorge:
No, a charger will put out about 13.8V to 14Vcharge the batteey, not 12v.
An automatic charger will taper the charger current as the battery comes up to charge.
What charger are you thinking of using?
Your pictured circuit will latch ON and the relay will not drop out when the charger stop due to current from the battery holding it ON.
Tom... :slight_smile:

I will be using a NOCO Genius G1100 Smart Battery Charger

When the AC returns, the charger will be powered and the relay should revert to original NO state, should it not? It is the 12V charger that controls the relay. If there is 12V present at the charger terminal when AC is present and no 12V if charger is not being supplied AC.

Regardless like you said the small voltage drop via the diode is insignificant thus your original solution look good with the added protection the diode provides. Thanks again TOM

Hi,
In your circuit when the relay turns ON the coil is connected to the charger AND the battery through the contacts, when the charger drops out the battery will keep the coil powered, instead of letting it drop out.

Tom… :slight_smile:

Hi opale7000,
The photo you put up is INTERESTING but unfortunately not going to work as you will have a path from the battery to the relay after the power goes off unless your relay can movefraster that the speed of electricity as the link from battery throught the relay to the charger is a complete circuit and as the power dies the voltage drops until the battery current begons to flow back through the relay contacts to the relay coil, holding it on.

Go back to the original circuit submitted as the diode stops the battery current from reaching the relay coil or as i said power the relay from another power pack.

The charger you have is rated at 1.1 amps getting a diode rated at say 3 or more amps will be very cheap an there are diodes that drop as little as 0.2 volts.

The voltage controlled relay idea was one i had contemplated but the down side is that the voltage must drop below a certain point before the relay will change, which means a delay before the lights come on. How long will depend on the battery as some batteries take a long time to drop from the charging volts. I had one that went fro 13.8 float down to 12.7 over an hour.

My parents currently run the shed and their veranda from 12v led lighting powered by a couple of 80ah batteries charging off 120 watts of solar panels. All bits and pieces i picked up in my travels and off ebay.
The lights on the veranda can be run on or off by switch or by a motion sensor ($5 off ebay) as they come home at night it turns on to light the way. It has a built in light sensor and adjustable sensitivity for both sensors and on time.

Tell me about the situation/setup you have and i can give you some pointers as running the lights whenever the power goes off seems wastefull especially if the power goes off say 3 hours before dark and the battery is dead soon after.

It would be good to know you skill set and level so we dont talk over your head or treat you like a dunce.
Im resonable at electronics good at fault finding and can make the LIGHT on an Arduino blink with EASE

Power a relay coil with a wall wart. When mains power goes out, relay switches state. Apply accordingly.

INTP:
Power a relay coil with a wall wart. When mains power goes out, relay switches state. Apply accordingly.

Agreed. There is a clear separation when using an AC relay to control the battery charger and led array load.

OK I now understand my faulty logic with the DC powered relay. :o Duh!

In regards to my skill level I have graduated in electronics back in the 80s then got into software development as a career. Now just tinkering and learning micro-controllers, linux and general electronics.

It make sense to add a light sensor and motion sensor to help maintaining the battery reserve. But I would think that a small 12 volt led array could go for several hours on a battery charge?

This backup light device will be used in my garage so that I can have at least some lighting during a power failure. I like the idea of not turn on if there is sufficient light already and that it only turns on on motion detection and turn on for a predefined time period.

1750mAh (aka 1.75Ah) will run a string of 300 3528 LEDs (5 meters @ 60leds/meter) for 1 hour.

Saying something like "But I would think that a small 12 volt led array could go for several hours on a battery charge?" is absolutely meaningless. You don't mention how big your battery is. :roll_eyes:
A 10Ah battery will give a little over 5.5 hours. A 75Ah battery gives like 43 hours. Optimistically, and depending on how deep you want to discharge that battery. And that's with the LED strip that I mentioned. You haven't mentioned what LEDs you're talking about.

Hi again,

The leds i settled on are the 5630s in they are bright and unlike the others i tried they are set to run at around 60% of there maximum unlike the 5050s that i have tried that seem to run at 120% to get the brightness.

The last 5 meter strip i bought cost me $11 off ebay and fitting them to a strip of alluminum to suck off the heat (the enemy of eletronic components) has them running here in Australia in 30 degree heat without burning out.

The seller was kobeedeal and i had no problems with him. He ships world wide.

The motion sensors are many and varied but just go for the physical fit and make sure it has light sensor, timer and adjustment for each. Helps to make sure it runs on 12v dc to.

The lights in the shed are currently made up of two strips one meter long fitted to a 20mm wide strip of aluminum. The stands hold it off the surface it is mounted to to allow heat dissipation and i have fitted a boost/buck to them as it holds the voltage stable (not really needed) and has current limiting to stop the strip from thermal runaway if the temps soar.

Boost Buck voltage and current adj. ebay

They light up around 4 square meters like its daytime. Takes around 1.5 amps to run but allow 1 amp per meter of leds untill you get an actual measurement.

Best thing is here you dont need an elecrtician to sign off on low voltage wiring. Dont forget to fuse it for heavens sake.

INTP:
1750mAh (aka 1.75Ah) will run a string of 300 3528 LEDs (5 meters @ 60leds/meter) for 1 hour.

Saying something like "But I would think that a small 12 volt led array could go for several hours on a battery charge?" is absolutely meaningless. You don't mention how big your battery is. :roll_eyes:
A 10Ah battery will give a little over 5.5 hours. A 75Ah battery gives like 43 hours. Optimistically, and depending on how deep you want to discharge that battery. And that's with the LED strip that I mentioned. You haven't mentioned what LEDs you're talking about.

you guys are good and accurate :wink: I'm out of the country at the moment and all I remember it is a Size 51 battery (Honda CRV brand) . This is a project I intend to build.

The led strip technical details will also will be provided in a future post on my return and will be 36" long. I will probably do a short youtube video demonstrating this project as a way of giving back to the community.

Thanks again for your support