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I seen few entries at instructables related to modification of existing UPS devices which explained via dangerous way. in some cases purchasing an used device might be more smart choice. but if you already have a lot of batteries, this entry shows how to use them without losing an eye or arm.

you will need:

+ plastic gloves

+ hot silicon stick

+ at least 1m cable which can handle high current

+ extra batteries which is same voltage & same capacity

Step 1: Preparing the Device

you need to wear plastic gloves first, it's capacitors can hold the electricity upto 24 hours which is still dangerous even if it's not connected to any power source

+ unpack it

+ remove the existing batteries

+ cut the heads of battery connectors

+ extend the battery cable

Step 2: Extend the Battery Cable

+ drill holes for previously extended cable

+ fit the cable from hole and fill the surrounding area with silicon. that's prevents the cable damage while moving the device.

Step 3: Connect Batteries in Parallel

if your ups uses single battery, you can just connect them in parallel. if it uses double battery, you have to consider two of them as a single while adding extra banks of batteries.

for example, my ups was using two 12v 7ah serial batteries which is makes 24v with 7ah capacity. if you attach another two in parallel that produces 24v with 14ah capacity.

you can add unlimited battery banks if they're match same voltage and capacity.

Step 4: Usage Notes

+ usually this kind of devices designed to work about 5-10 minutes, after 20th minute the voltage inverter coil and mosfet's getting hot even can melt the device's case. you have to install cooling fans if your ups made from plastic case.

+ you have to disconnect all batteries from each other when you're turning it off. while ups is active it's keeping the batteries alive by feeding them with "float voltage" (https://en.wikipedia.org/wiki/Float_voltage) otherwise they're try to charge themselves without ups connection and quickly die within few days.

+ DO NOT USE lead-acid (used in car-marine) batteries if you're using it indoor. these kind of batteries produces poisonous gases and there is risk of explosion on high loads. take serious that, i learned via hard way.

<p>Photo in Step 4: <em>Get some proper connectors.</em> :) Crocodile clips and spindly wire isn't much good -- FASTON terminals, crimped, are what are meant for these batteries. For larger batteries still, that use nut-and-bolt fixing, this is even more important. The currents involved are high, and poor connectors/thin wire are not appropriate.</p>
<p>maybe. i put a stress test until batteries completely drain at %90 load but didn't noticed any extreme temperature on cables or connections. but you right, the final connection cable which handles the load of all 8 batteries must be thicker than original one based on the battery count.</p>
<p>I did upgrade a cheapo UPS battery to a larger AH type, and it worked fine until sometime later the unit stopped (months) functioning properly, but it was worth the hack to get extra miles [kilometers] out of such junk.</p>
<p>few months ago i used 60ah lead-acid batteries with diodes to prevent charging by ups. and was charging them manually after a blackout happens. i decided to use this setup after a small accident with them.</p>
<p>Sorry to be the bad boy here, but you are wrong, re:&quot;you can add unlimited battery banks if they're match same voltage and capacity.&quot;</p><p>The UPS would not charge the batteries properly and all of it will die. Unless it is specially designed for higher capacity like the APC's XL series.</p>
<p>yes that's correct, charging time will be extended based on battery bank count. for example, that mentioned setup has 4 pairs of 12v batteries (8 total) which is charging in 2 days with this ups. consider that 4 days if you make it 16.</p>

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