Do It Yourself (DIY) UPS / Inverter

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netfreak

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I am trying to figure out how to create an UPS for things like DSL modems and Wireless phones.

These things run of 12 , 9 or 6 Volt DC and we can wasily get batteries that will last hours.

For example, if we put 10 of these batteries

MAHA / POWEREX 11,000mAh D NiMH Rechargeable Batteries 2pcs pack

We get 110 AH of power.

We should be able to run a PC for 4 hours with that much power (but that will require Power in AC form). A typical UPS that costs ~2k has a 7 AH battery and runs PC for 15 mins.





Question is does anyone on this ofrum have a come across a way to create a DC to DC UPS ? This UPs can take input from a AC - DC converter and have some kind of switching to charging / discharging batteries as and when required.
 
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Have you read this ?

..and the follow-up
 
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netfreak

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Yup, that the first one Google turned up :)Thing is, this guy is trying to create a AC -> AC UPS. That requires inverter and thus $$$ :(
 
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I might be mistaken here, but dont the devices you want to run off the batteries *expect* an AC signal.So i'm wondering how you can avoid the inverter at all ?
 
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netfreak

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dont the devices you want to run off the batteries *expect* an AC signal.

Actually these devices (DSL Modem, Wireless phone, WiFi router) run off DC.

They come with AC->DC adopter that generates 12 volts DC.
 
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DOH..of course
 


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boygr8

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Anything that works of 12 V DC like ADSL modem can be in my opinion be connected to a 12 V battery.....though I am not an expert in this field...........but I think it will draw the require amperes it requires......u just have to match the voltage.I think even if u connect ur ADSL modem to a truck battery ( both rated at 12 V), i think the modem wont get fried.
 
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netfreak

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Yaa it should not get fried.And thats one part of solution.Another part is how to design a circuit that keeps charging the battery [but does not feed voltage to modem itself].
 
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did you find a solution yet?i use two ups batteries of 12v 7.5 Amphere batteries in parallel to get 12v 15Ampheres and made a small circuit so switch to the batteries manually!using just a the modem stays on for around 5 hrs and using two batteries in parallel i get 10-12hrs!the damn bsnl modems have huge current drains (12v 1.2AH WTF??14.4watts per hour)my wireless router has double the range double the speed and yet it only draws 3.3v at 2AH - 6.6watts per hourhighly ineffiecient!