Rework a UPS With Massive Capacity





Introduction: Rework a UPS With Massive Capacity

Those UPS devices you buy for your computer usually have a gel-cell battery that lasts for a few years. Less if your power goes out a lot. When you replace them, you pay a bundle, even if it's a standard cell. This short Instructable will demonstrate how to rework an older UPS for more capacity with cheaper battery power.

The picture shows some sample UPSs and an example of the gel cell from one of them. The UPSs come in various capacities and, although you can boost the capacity, the output power is fixed. When you start out, make sure that the UPS you're going to modify will provide the volt-amps and power that you need. Also note that the volt-amp rating is higher than the power rating. The difference is because AC powered devices have a power factor. Check online for more info about this. Another, similar Instructable, also warns against trying to max out the capacity of your UPS because some use transformers that will run continuously at the rated output. It really depends upon the quality of the UPS, but plan to run at not more than about 75% of rated output capacity.

Another thing to consider is whether or not your scrap UPS has AVR or Automatic Voltage Regulation. You'll want this if you can find it.

Step 1: The Guts

First, for safety's sake, unplug the UPS. This pretty much goes without saying. Also realize that the battery inside the UPS may be charged, so do not short circuit any metal parts inside the box.

When you open the UPS box, you'll usually find either one or two gel cell lead-acid batteries. You're going to replace it / them.

What you'll need:
1 scrap UPS - but it needs to be a WORKING UPS!
4 feet of #10 copper wire (2 feet of red and 2 feet of black if you can)
You may need to adjust this length, but keep it as short as you can tolerate.
4 spade lugs (two mating pair
2 ring lugs for single battery or 4 if you have two in the UPS
1 or 2 marine, deep-discharge batteries (85 - 120 AH capacity)

A drill with bit set
Crimper for the lugs
Wire stripper
Sandpaper or a small file to smooth out holes in plastic

Some notes on the parts: look at the pricing of the batteries and get the capacity that gives you lowest cost per amp-hour. Sometimes the 110-140 AH batteries are only a little more than the 70-90 AH ones. Check warehouse clubs for good pricing. Sometimes you can reclaim the core charge with an old motorcycle or car battery you have lying around. Make sure that what you get is a deep-discharge type battery. Some batteries are labeled as marine, but not deep-discharge.

Make sure that your battery has adapter studs that clamp to the lead posts. Then, get ring lugs from your hardware store, electronics store, or online store that will fit over the threaded studs and also accept #10 wire.

You can either get two pair of mating spade lug connectors, or get one set that are the mating connectors to the ones that come from the UPS. In the picture, these are the black and red wires that connect to the batteries.

Note the blue wire. The batteries are in series in this UPS, so it requires 24 volts (black terminal connected to red terminal). Do not try to power it with one battery if it comes with two! Get two more ring lugs if you need two batteries.

Step 2: Tap Into the UPS

Since the battery / batteries will not fit into the old case, you'll use the lugs and wire to extend the wires outside the case. In the picture here, I've replaced the spade lugs that previously connected to the gel cells with connectors that I know will mate together and accept #10 wire. It doesn't cost much and it's easier than trial and error, so spend the extra 25 cents.

Drill two holes in the side of the case. The holes only need to be large enough for the wire to pass through. You don't want the connectors to be able to sneak outside the case, to be safe. Make sure there are no sharp spurs or edges around the holes that might cut or damage the insulation. Thread the wires from the inside out, with the connection inside the case as shown.

As noted in the parts list, you'll want to keep the wires short to minimize voltage drop, but long enough that you can place the UPS and batteries comfortably near each other and the device you're powering (computer, stereo, etc.). Lay everything out, including battery box(es) if desired, and clip the wires to an appropriate length.

Step 3: Connect the Battery / Batteries

Here's where you connect up the battery or batteries. Remember that the batteries are likely charged and can supply a LOT of current. I think there's another Instructable that tells how to use them for welding. You do NOT want to do any welding, so make all crimped connections before you connect them to the batteries!

If you have two batteries, make sure to cut a short piece of wire before you add the ring terminals to the other end of the wires you connected into the UPS wires in the previous step. Make sure that this jumper wire is not too short if you are putting the batteries in containers (see end of article).

Note: You might have to ream out the inside of the ring terminals if you could not find terminals with the right inside diameter.

Once you know that the ring terminals will fit, crimp them to the red and black wire ends. If you have two batteries, make the jumper with the other two ring terminals and the small piece of wire you cut off.

Connect the red wire to the positive terminal of one battery. Connect the short jumper between that battery's negative terminal and the positive terminal of the other battery. Then connect the black wire to the negative terminal of the second battery. If you do not connect them this way, you will not get any power into the UPS.

Step 4: Use It

That's pretty much it. Simple, right? The hard part is finding the right parts and connecting everything in the right order without welding anything.

You should now be able to plug in the UPS and go.

Some additional thoughts and enhancements:

1. You are using lead-acid batteries. In the photo, I've shown a plastic layer under the batteries. Even though marine batteries are typically sealed, you do not want to take the chance of a leak. Spend $8 - $20 and get a plastic battery box for each battery you use. It will protect the batteries ... and your floor.

2. In the first step I claimed this would improve the capacity, massively. By how much you ask? The largest gel cells I've found in UPSs are 20AH. Others are more like 7 AH. Using an 85 AH marine battery to replace a 20 AH gel cell, you should expect to get at least four times the runtime. HOWEVER, do not plan to run the batteries down by more than 50% or you will severely shorten their life. Figure more than a doubling of capacity, but less than 4 times. If you use a 115 AH battery, figure at least 3 times the run time and a much longer battery life.

3. I have not had any problems with the UPSs recognizing the new batteries or keeping them charged. If you have the UPS monitoring software, use it and try some tests. See how long your new rig will run before hitting the 50% charge level.

Expect the total cost to be about $80 for a single battery setup with 85 AH battery and battery case. Double battery setup with 115 AH batteries should be about $160, max. These are using battery prices in summer 2009. Battery prices spiked briefly last year, but have come back down.



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Good idea to add a fuse inline somewhere in case something goes other. Otherwise you'll be welding something!



I have and APC 3000XL. I have a 1400 VA load on it.
Originally I only would get 8 minutes on backup.

Internally the APC 3000XL utilized 4 12 volt batteries in
series for 48 volts. I had first tried 4 12 volt group 29 marine batteries in
series. The provided me 100 minutes on backup with 1400 VA load. I have now
switched to 8 six volt deep cycle golf card batteries with 550 reserve capacity
@ 25 amps, in series to obtain the required 48 volts. I now get 500 minutes
backup time with 1400 VA load. I have no problem with charging the batteries or
overheating. I have utilizes this for seven years.

My recommendations are:

  • 1.Avoid parallel batteries as on bad battery will
    drain the other(s).
  • 2.Make sure there is a fuse between the batteries
    on the UPS.
  • 3.Use large enough wire to carry the expected
    load. I utilized #6 MTW.
  • 4.Fully charge the batteries before you start.

If you

Great supplemental information for this Instructable!

I modified an APC350 using a car battery with a 600CCA rating, just over 3 years ago. This unit runs on one of our shop computers, 5 days/wk - 24/7. Our area is prone to blackouts from 5-10 times per year on average and this "baby" never overheats and the battery still passes it's load test. I've never tested the true amount of time this UPS can keep our shop system running, until it dies but the longest power outage I've witnessed at 40 minutes and it was running just fine!

You are right. I'm doing this with APC ES550 at home. I took out the 12v 7Ah battery and used 3 12v 12Ah batteries in parallel. I think the UPC charging block is probably tickle charging the 7Ah battery because you need 16 hours to do the initial charging. But I left the one at home as is. If a 10A charger is used with a 12v 75Ah car battery then I would need a 12v 2A charger outside the box to replace/bypass the charging circuit. For the heat issue I would cut some vents and get a 12v dc fan and control circuit.

correction: 12v 6A charger instead of 2A. Probably the UL test for run time is at least 5x at max output which it passes so it could possibly be more.

This would be NO, even two 12 volt batteries in parallel would still represent only 12 volts. However two 12 volt batteries in series would be 24 volts. Batteries in parallel double the amperage capacity while keeping them at 12 volts. Batteries in series would double voltage, however it would also double the charge time, and not necessarily double the run time, but would be close to 1 and one half. Nature of batteries, as all batteries have an internal resistance that dictates the charge rate. Think of it as something like a capacitor and resistor in series.

There is one big problem with all of this and that would be the rated output of the charging circuit, most likes not enough to charge the higher VA (volt/ampere) rating. To maintain costs this circuit would be the minimum needed for the original battery! Also the wattage would still be the same output from the circuit.

Been there and tried this. Every time there is a slight drop in power coming in to the UPS alarm triggers and the computer shows an immediate loss in run time until shut down and a slow recharge, i.e. drops to 60% and is charging slowly.

The only real answer is to buy a higher rated UPS with more VA and wattage output. My 500 VA APC UPS does not work well on my HP 9400 that has a 1050 watt power supply! Often shuts down the computer when the Laser printer starts! AA real problem!!!

I have not experienced any problem with voltage drops and alarming with either the CyberPower 900AVR or the Power99/500VA UPSs that I've modified. Obviously I don't have a schematic and cannot analyze the charging circuit, but generally, charging circuits for lead-acid are designed to supply a given current-limited output and maximum voltage. If you increase the capacity of the batteries, then the recharge time will increase under these assumptions. But if you have outages that often, then you have other power issues to worry about that no UPS is going to resolve.

Why not connect the extra batteries with the original ups batteries in parallel if the voltage is the same?