simple battery backup for the board of education question
firealarmfreak
Posts: 105
hey is it possible to make a VERY SIMPLE battery backup for the boe?
I thought I could use a relay, wire it so the relay ran from an ac-dc adapter and when the relay losy power, it closed the battery circuit.
I only worry that if the relays power shorts out, but all other power remains on, the boes 9 volt adapter plus the battery circuit will be closed, resulting in 18 volts being put into the boe
over voltaging it and killing it.
is there a safe way that would avoid that, thats simple that i could use, i only want the boe to be backed up so i dont want to bother buying a ups. Also, i want it to be simple.
Thanks,
Chris.
I thought I could use a relay, wire it so the relay ran from an ac-dc adapter and when the relay losy power, it closed the battery circuit.
I only worry that if the relays power shorts out, but all other power remains on, the boes 9 volt adapter plus the battery circuit will be closed, resulting in 18 volts being put into the boe
over voltaging it and killing it.
is there a safe way that would avoid that, thats simple that i could use, i only want the boe to be backed up so i dont want to bother buying a ups. Also, i want it to be simple.
Thanks,
Chris.
Comments
You'll need a NC (Normally closed) 5volt relay that's connected to the battery and the BOE... then when power is applied via the ac-dc adapter the relay breaks the connection... when
power goes out, the relay returns to its normal state and keeps power flowing.
The only problem is there is going to be a several usecond delay between the sources, so you'll need to put a fairly large cap in the circut to keep power during the switch over.
These are the words of a newbie, I have no idea if this will work or not... its just what I've been thinking.
When the AC power goes off, the relay kicks in and disables that
circuit while enabling the battery at the same time. Use a larger
capacitor, a small capacitor to filter spikes, and a diode for back
EMF across the relay coil. I built a circuit like this and it ran
continuously for several years until I moved.
humanoido
You have started subjects on this matter several times now.
http://forums.parallax.com/showthread.php?p=760234
http://forums.parallax.com/showthread.php?p=757367
http://forums.parallax.com/showthread.php?p=758823
http://forums.parallax.com/showthread.php?p=755624
What more do you need?
You were given a few ways to go the·last time,·but you made no replies, had no follow-up questions.· Carl's·second suggestion there was "very simple."
Do us all a favor and Press "Subscribe to this thread" to bookmark this subject for yourself.
Post Edited (PJ Allen) : 2/1/2009 2:20:36 PM GMT