How do I make a 12v UPS??

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headstrong

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Hi there

I want to make a backup power supply for my 12v wireless AP..... I cannot buy a UPS as no1 has stock in my area so I want to try the D.I.Y. route :D

My plan so far is to get a 12v car battery and connect it directly to the 12v wireless AP.....My concern is that when the battery gets flat, it will drop the voltage and damage my wireless AP... What could I place between the car battery and the wireless AP that will break the circuit once the voltage drops below 11v for example??

Thanks alot
 
If the battery goes flat it won't damage the wireless device. Most car batteries are more than 12V - about 12.5 - 13.5V. Depending on how sensative the wiresless device to voltage, I'd put a voltage regulator (7812) in the circuit. I reckon it would take days for the wireless device to drain a car battery!
 
the voltage will drop and your ap will continue to run as normal, probably find it works ok from 7 volts upwards...below that it'll just power off.

if you get a bench power supply with variable voltage you can see at what point it switches on. that'll be your cutoff voltage.

if you implement as gregg says, then it'll get a steady 12v irrespective of what the battery voltage is, until the regulator can no longer cope.

i have a 12v dc/dc power supply in my car, which still spits out 12v even when i am cranking the engine, these things are marvellous:-)

p.s. as i didnt design the circuit in your AP i'm generalising big time here based on *most* electronics. hence, dont sue me.
 
gregmcc said:
If the battery goes flat it won't damage the wireless device. Most car batteries are more than 12V - about 12.5 - 13.5V. Depending on how sensative the wiresless device to voltage, I'd put a voltage regulator (7812) in the circuit. I reckon it would take days for the wireless device to drain a car battery!
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thanks gregmcc.......What happens when a battery goes flat? Does it loose voltage or amps??....ie once the car battery goes flat will it still produce +-12v but with zero amps??
 
BiteMe said:
the voltage will drop and your ap will continue to run as normal, probably find it works ok from 7 volts upwards...below that it'll just power off.
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So the AP will not be damaged then?
 
headstrong said:
thanks gregmcc.......What happens when a battery goes flat? Does it loose voltage or amps??....ie once the car battery goes flat will it still produce +-12v but with zero amps??
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This question shows you have no understanding of electricity. I would, in the best of possible ways, suggest you get help from someone who does, otherwise you are probably going to create yourself a problem.
 
bekdik said:
This question shows you have no understanding of electricity. I would, in the best of possible ways, suggest you get help from someone who does, otherwise you are probably going to create yourself a problem.
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I have called Hamrads, Zakspeed, brights and personally visited and spoke to consultants at Midas and battery centre and no1 was able to help me...hence i'm asking the real experts on MyAdsl
 
ok you help me i help you.
car battery will work and you cannot damage anything if the voltage drop as thereare no spikes in the line,but if the voltage go up then you might have a problem.
 
You should probably get a deep cycle battery but just to be clear, if you buy a 45aH battery for example and the router is rated 12V@1A which is most common you have 45 hours of battery life before it dies. The voltage drop will be very low until it comes close to running out of power.

What exactly do you want to run from the battery and what's it's Amp rating.

Btw. the router itself will have a regulator IC built in, the power supplied by a unregulated AC->DC adapter set on 12v is closer to the region of 16-18volts.
 
I want to run a wireless AP which uses 12v @ 1 amp.....I used my multimeter and it confirms what gnome said about my AC/DC running at 16 volts instead of 12....

From what I understand the AP will only draw the amperage that it needs and so it shuldnt receive the full charge and blow itself up....right?
 
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dablakmark8 said:
high amps can blow your device,its not the voltage.
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that is blatantly wrong.
your amps needs to be either the same or higher..the device will draw the amps it needs to operate. like a big tank, you only take what you need.

volts, however, can be though of as "pushed" into the device. and too many volts will damage it.

where did you get your info from? a chappies wrapper?
 
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