ups hacking for fun and extended runtime

An uninterruptible power supply, (UPS for short) is an electrical apparatus that provides emergency power to a load when the input power source, (typically the utility mains), fails.

A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near – instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and or by means of diesel generators and flywheels for high power users.

The on-battery runtime of most uninterruptible power sources is relatively short. 5 to 15 minutes being typical for smaller units, but sufficient to allow time to bring an auxiliary power source on line, or to properly shut down the protected equipment.

Today I decided to change that, since I need to be able to run off batteries for a lot longer. 🙂

As may of you know, I am planning on going on the road for an extended period of time with the mighty warbusaur, and I will most likely be spending my summers in the pacific northwest, and my winters somewhere warmer… 🙂

So of course I have an epic plan involving solar panels, and wind/tidal/current generation techniques as well.

That stuff is all coming. but in the meantime, as I give the warbusaur (my pd4501 greyhound super scenicruiser) much needed love, I find that I need to run a large number of electronics when there is no power to do so…

I have a generator, but running a generator (even my super awesome honda EU3000is) just to charge my laptop and cell phone, with fuel being $3.95/gal right now, is frankly retarded…

So, how to store power for later usage?

I figured I needed something like 12 hours of runtime, but more is always better (go big or go home) and easier on the batteries, since they won’t discharge as far (deep discharges are what kill batteries)

Hmmm. Batteries.

I know I have some deep cycle trolling motor batteries in the van, but lets see if we can solve a couple problems at once, since batteries don’t like to sit, and my bus has a pair of really big (1400cca!) batteries in it, that are not being maintained properly.

so, I’ll pull them out of the warbusaur, and temporarily use them for this. 🙂

That my friends is a pair of Interstate Workaholic 1400cca 8d batteries…

Amps: 1750
Cranking Amps: 1750
Cold Cranking Amps: 1400
Voltage: 12
Weight: 130
Width: 11
Length: 20.75
Height: 9.63

They are heavy (260 lbs!), and they aren’t deep cycle, but they are as industrial as they come, and will work fine for what we are doing here. 🙂

So after much herculean effort, I managed to pull the batteries, and get them on my trusty cart, and drag them the 150 feet or so to the front of the shop.

A bit of work with a terminal shaper, and a scrub brush and some water, and they look as good as new. 🙂
Well, except for that…

In the depths of time there is a story about argyle pushing a 55,000 lb bus by himself…

We were on our way back from Pennsic, and overnighted in a rest stop up in the rocky mountains.

We awoke to 35 degrees outside, and the warbusaur won’t start. She turns over fine, but that 8v-71 jimmy diesel is just not having any of it.

We were on flat ground, so I dropped it in gear, let out the clutch, and bumped it with the starter, the idea being that if I can get her to move a little, we can just roll down the mountain and pop start it on the exit road from the rest area…

Well, when you walk a 55,000 lb scenicruiser about 50 feet on the starter, it creates a whole lot of current draw, and that in turn creates heat…

The above is what happens when your battery cables get hot enough to melt their jackets off and melt into the battery case…

I can see the plates through the holes on one of these, so I need to do something about it…

Duct tape is tacky, so I got out my trusty hot melt glue gun and did a bit of plastic welding…

Hot melt glue is awesome stuff when you need to fill gaps and stick things together permanently. I am constantly using it for things.

This is the bigger of the two holes in the casing. you can actually see the lead plates through this one.

5 minutes later, the patch is done, and cooling down. after it cooled down I used a utility knife blade and shaved the patch down so it was flush with the rest of the case.

Topped the cells up with distilled water, and put them on my 10 amp slow charger to see if they will take a charge (they should, but they are completely dead, so it may take a bit of cajoling)

So now comes the fun part 🙂
I can charge these with a battery charger, and discharge them with a small power inverter, and it will work just fine, and the losses are acceptable, but the only inverter I have here isn’t big enough to run my workstation, and it’s a pretty long drive to go fetch it.

But I have a lot of random bits floating around the shop, and we may be able to come up with something a bit more… creative. 🙂

This is one of those times I wish my solar panels were here, instead of sitting in Arizona waiting for me to buy them 🙂

So I rummaged around the shop and came up with a pile of dead computer ups systems.

Most dead ups systems aren’t actually dead. usually they work just fine, but the batteries are hosed.

Most of them will have smart chargers in them, and handle the failover from mains (shore) power to battery backup, automagically, as well as do unattended shutdowns of attached equipment (with a bit of creativity).

(although for this instance, I only need that if I’m running my workstation)

So, lets see what we’ve got, shall we? 🙂


Exhibit A: Powerware Prestige 1250p2
Google says:
True on-line, double-conversion, powerline isolated, with Cell Saver Technology™ (charges batteries only when necessary, resulting in up to 50% longer battery life)

1250VA, 875 Watts
Runtime at full load (875 Watts) 5.2 minutes
Runtime at half load (437 Watts) 14.6 minutes

Looks promising so far…
(giggles to himself at those runtime numbers)

now that is interesting.
5 gell cells in series? 5 x 12v = 60 volt dc rails.

Sad day, this won’t work for our needs, because I don’t have 5 batteries.

Interesting design though, looks to be pretty well thought out. Notice the lack of a big transformer?

Upon further inspection, if I had 5 batteries this unit could probably handle it.
There is lots of good stuff in here, it looks like this thing is built out of high end parts and it’s done right, and the cooling design is excellent (which matters a whole lot when you’re going to put it under the kind of stresses that (5) 1400cca 8d’s will put it under).

Alas, I had to put it back on the “I’ll use it sometime” pile. We need something with a 12 or 24 volt rail.


Exhibit B: Smart Power Systems SS1250RM
Google says:
Fully digitized microprocessor controlled, AVR boost, Advanced battery management, Cold start (DC power on), Automatically charging when UPS off.

That cold start ability is handy (although most ups’s, you can do the same thing by plugging them into themselves if you have to)

1250VA / 750 Watts.
Voltage (on battery) Pure sine wave at 120V ±5% -10% of nominal after low battery warning
Voltage Regulation (AVR)
AVR automatically increases output voltage 15% above input voltage if -9% to -25% of nominal.
AVR decreases output voltage 13% below input voltage if +9% to +25% of nominal.
Transfer Time 2-4 milli seconds, including detection time
Typical Recharge Time 4 hours (to 90% of full capacity)
Run Time (minutes) Half Load 32.4

Nice. AVR is good, but most ups’s have that, (exhibit a does, because the output can be greater than the input for short periods according to the spec sheet)

The run time and recharge numbers are nice, but for my purposes, I would expect to be drained down to more like 70%, and our batteries are so much bigger that it’s meaningless to us (except when comparing to other units)

This is worth a look…

Hmmm… paydirt! 🙂 24 volt rail… (2) 12 volt batteries wired in series, then wired in parallel with another pair. (series you add the voltages together, parallel the voltage remains the same) so we’re good to go…

Note the large transformer.

The charging circuits on this unit seem to reflect that aforementioned recharge time.
Keep in mind that these systems are designed to slowly charge up over time, not to do it every day.

The charging circuits here look pretty whimpy, especially compared to Exhibit A, and they may die if we put a real battery bank on it, but this unit will do the job.

Lets keep looking…


Exhibit C: American Power Conversion Smart-ups 650)
Google says:
650VA / 410 Watts
Typical recharge time 6 hour(s)

This is a small, low end unit, but I know people that have used a car battery with one, so lets check it out.

12 volt rails, so we can use 1 battery, or 2 in parallel. This appears to be a pretty robust unit.

410 Watts is enough for my cell phone and laptop, but it won’t run my workstation.
I may put this on a car battery to run my laptop and cell charger, since this unit is a bit more efficient than the big ones (no cooling fans)

This unit works fine, but apparently apc decided to change their powerchute software and remove the old versions from the internet, because I can’t talk to the stupid thing to turn off the “hey!, I’m on battery power!” alarm.

Setting it aside, Wrong tool for the job.


Exhibit D: American Power Conversion SU3000RM
Google says:
3000 VA / 2250 Watts
Typical recharge time 3 hour(s)

Let’s pop the top and see what we have here..

This just makes me smile.
Big transformers, beefy construction throughout.

This will do 🙂

Errr. or not. 8 batteries in 2 series parallel banks of 24 volts each, for a 48 volt dc rail.

so i need to buy 2 more batteries, or move on. 🙁

The temptation to buy 2 more batteries is very very high… 🙂

I mean, just look at those transformers 🙂

Woot! it’s even got the smartslot card in it. 🙂

And that brings us to our last contestant…


Exhibit E: American Power Conversion SU1400RM
Google Says:
1400 VA / 950 Watts
Typical recharge time 3 hour(s)

This is a similar design to the last unit we looked at, so here’s hoping 🙂

Pull the faceplate, Pull the battery Plug out…

Pull out the battery drawer…
If this unit is done like most 4 battery apc units are, we may be in luck 🙂

60 amp fuses on the dc side of things, there are two of them, so that means series parallel 🙂

And this is what series parallel 24 volt rail wiring looks like 🙂

Like the other apc units we’ve seen so far, the build quality and the layout are well thought out. I think we have a keeper 🙂

Looking good so far 🙂

Nice, well thought out parts layout and cooling…

Mock it up for testing…

So far so good…

You can plug a lot of things into one of these. it’ll run your microwave or your coffee pot all day 🙂

(The 3,000 va one will do both at the same time all day)

Now I’m going to leave the ups unit charging the batteries all night and see if it blows up or not… 🙂

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1 comment to ups hacking for fun and extended runtime

  • avatar William Lehman

    nice concept for a hack, looking at the final product, I think you’re going to need bigger copper in the long run. Frankly, you can never go wrong by going bigger on the copper.

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