Building an Emergency Light

[juan123]

I am a newbie to electronics. I would like to build an emergency light for my house with a 5ah 12 volt battery. Does anyone have a simple circuit I could build? I would like it to be: when the electricity goes out, the emergency light goes on. Thanks for any help!

 

[bogdanfirst]

just a tip. it is good if you cand find a lead acid battery. they take it very well when overcharged. so you could have a circuit that will charge the battery with say, 500mA and then use a trickle charge, like 100mA or 50mA. this way the batt will always be full.
for the light, you could use an economic light. that way for 15W or even 9W you could get enought light, and still the battery will last enough time. there is, though the problem with the conversion. you could check this circuit: https://tacashi.tripod.com/elctrncs/inverter/inverter.htm
i have biult it and works ok. but i had the transformer already built.
if you are interested i cand design a cricuit for this. but maybe some have other solutions.

 

[stevez]

I'm not sure what you were planning but one thing I'd consider is that LEDs might be more efficient than traditional filaments. I know that doesn't solve your control problem.

 

[bogdanfirst]

leds are more efficient than incandescent lamps.
but if you just want some leds, why use such a high capacity battery?
anyway, please tell us more details of what you want...

 

[olly_k]

just a tip. it is good if you cand find a lead acid battery. they take it very well when overcharged

They also don't take it very well when disscharged lol!
one of my roles in a previous job was to check and service emergency lighting (seeing as knowone else had ever bothered :cry: ). It seemed only the larger twin lamp versions used Lead acid most used NiCad!
The simplest way to implement such a system would be to use a relay, driven off the main supply (via a transfromer if low voltage coil) and have the relay switch the lamp on when power is removed. Simple. Not efficient but simple! You could also use the transformer to trickle charge the battery if required.

 

[bogdanfirst]

so you say that NiCd batteries are better?
so the charging should be continous ? but with a low current?
20mA? maybe more?
now, i don't think that charging the battery should be fast right? i think that the electricity doesn't go off that often?

 

[olly_k]

so you say that NiCd batteries are better?

Not nescessarily better, just much cheaper and easier to maintain. You could even use normal batteries. Using a flourescent lamp will increase efficiency and therefore would mean a high capacity battery is not as necessary.
If trickle charging, I would suggest maybe in single figures, like 1 or 2 mA at most. Although I am no expert where rechargable batteries are concerned!

 

[bogdanfirst]

oky, NiCd are better than lead-acid. what about NiMH ???

 

[McGuinn]

NiCd are phased out due to the existance of posionious Cadnium within them. NiMH suffer from memory problems, so that leaves Lion... they are good.

 

[Oznog]

Flourescents are significantly more efficient than LEDs, also FAR cheaper for unit of light output. LEDs also are commonly driven with resistive ballasts which drops the power efficiency by around 30% right off the bat.

Check out these. They carry their own ballasts, run straight off 12V, and quite reasonably priced! I had a link to another supplier who sold them in small crates for only a little more than a single bulb, but I can't seem to find the link now.
https://www.oksolar.com/lighting/light_bulbs.htm

These kick ass over the straight tubes. Much more light output and better color.

NiCds weren't phased out so much because of the cadmium, but rather they had memory effect problems and NiMH just had more capacity.

 

[Crofty]

NiCd are phased out due to the existance of posionious Cadnium within them. NiMH suffer from memory problems, so that leaves Lion... they are good.

Ooops???... NiMH are the ones that 'Don't' suffer from memory effect That nasty is reserved for NiCads. Lion's require somewhat more complex charging circuitry. Stick to NiMH's

Steve

 

[bogdanfirst]

well, NiMh have greater capacity. but you need charging circuit.
they don't like when overcharged.
yet, lead acid, have the best price/capacity.
i'll go for NiMh. you could check in the link i mentioned, and power them from 6V. that's 5 cells. might work with 4 too.(or 4 alcaline batteries)