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Hacking UPS to last longer - adding large 12V battery


nick9
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I have read a bit about people wiring a large 12V deep cycle battery into their UPS to make it last longer (say a 100Ah or 2x100Ah if it is a 24V UPS). In theory the UPS already has a battery charger, small battery and inverter and so replacing the battery is a cheaper alternative to buying a whole new system to keep my PC going for the 2 hours of load shedding. The main reported problem seems to be overheating and therefore safety - how hot is too hot. I'd love to hear from people who've done this.

My UPS: The 800VA AP series from PSS (http://pss.co.za/wp-content/uploads/2017/06/PSS-Distributors-AP-Series-Brochure.pdf     http://pss.co.za/product/ap-series) which has 1 x 12V battery (9AH) in it.

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Jip, you can do that.

The one and only caveat is that you disconnect the larger batteries and re-charge them with a separate larger charger after use.

Why? Rule of thumb: Take the C20 AH rating, battery must be charged slow with 8% / 10% of AH rating / 13% of AH rating as the max.

The small UPS'es have extremely small chargers like 350mA - 1amp as per the specs on that link. That is the only reason why they cannot use big batteries.

An idea is to use Brad Harrison / Anderson connectors, one connector on the UPS for this extra batt, one on the batt so you can easily and safely disconnect and re-connect the larger batts to re-charge them.

 

 

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I'm going to warn against doing this, unless you know what you are doing. Quite often the transformer and other electronics in these small UPSes are not designed to run for any length of time (ie there is insufficient cooling). They get away with this because the battery is normally flat long before things overheat. Along comes Johnny with a bigger battery... :-)

If it's a nice large UPS running at part capacity, no problem. Possible add some fans (if it doesn't have some already), and I've seen some people even add thermal paste between the transformer and the case (a cheap way to get a heatsink) to keep it cooler for longer.

Eg, here is a video series where a guy does a conversion, blows it up, fixes it... etc :-) Around 13:00 he explains that things inside are really too small.

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Aha, I thought the powerforum might be the place to come! Got some good info at mybb, but not this level.

OK so let me see if I have it right. With a 100Ah battery, they need to be charged at around 10 amps - and the little UPS charger will only be able to charge at 1 amp max. So the UPS charger gets hot because it's running at max the whole time AND the battery is being treated badly with a charging current much lower than it wants, plus anyway it would charge v slowly and would not be ready for the next round of load shedding.

So really I'd only be saving on the cost of an invertor, which is something though. I am presuming the invertor doesn't mind having a bigger capacity battery feeding it?

Also, I have read mixed thoughts on the use of a modified sine wave invertor (as my UPS has) with a PC - some say the PC's PSU will handle it fine and others say you need a pure sine wave. There is also the PC monitor.

Like the idea of the connectors yes.

Any recommendations on a decent battery charger for the job?

And I was thinking of a Victron AGM or Gel (https://www.victronenergy.com/batteries/gel-and-agm-batteries) - is that a good idea?




 

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Quote

I'm going to warn against doing this

Just saw this as well.

I take your point - I don't know much about all this, and though I think I could learn sufficiently, I don't think I have the time to experiment. Plus it is quite a cheap UPS, so more likely to have the issues you talk of.

And it's only saving me the cost of an inverter, it may not be worth it.

Aside from getting a new system (e.g. was quoted around R20,000 from ExSolar for a full Victron system with very posh pure sine wave inverter) - is there an option of going second hand, perhaps via this forum? I don't have a device to load test a battery which means I wouldn't really know much, but I may not need this system for more than a few months so I don't want to spend too much.

 

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5 minutes ago, nick9 said:

Any recommendations on a decent battery charger for the job?

I like Optimate https://optimate-battery-charger.co.za/product-category/chargers/

Take heed of Plonsters overheating warning, my bad, I forgot to mention that. IF you do this, put a fan on the UPS to keep it cool ... and do not run at hard as per that video.

7 minutes ago, nick9 said:

PC's PSU will handle it fine

They do, they have been doing it for decades. PSU in PC's and laptops are quite robust.

But, if the cash is there, pure sine wave is always better.

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3 minutes ago, nick9 said:

So the UPS charger gets hot because it's running at max the whole time

No, this side is actually fine (even though the battery is not properly charged). The transformer runs at 10% of its normal capacity (so it won't get hot) and the switching transistor that makes AC is off while charging, so no problem at all. No, what I mean is that it will likely overheat during load-shedding, because it was only designed to work for a few minutes. For example, your typical 800VA APC has an 18ah 24V battery. That's 430Wh, which is like 20 minutes at 800W (reduced capacity because it's discharged at such a high rate).

Yours has a 9Ah battery, so it is more like 5 minutes.

If your load is around 50W-100W, typical laptop power, you might be fine.

9 minutes ago, nick9 said:

mixed thoughts on the use of a modified sine wave invertor (as my UPS has) with a PC

The first thing a switch mode power supply does is turn the input into DC. So it won't care.

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3 minutes ago, nick9 said:

... is there an option of going second hand ...

What is your goal?

You can get cheap 2nd hand 24v modified sine wave inverters with 15amp chargers, with fans built in, for R1000 - batteries excluded off course. :-) 

Or you can go and spend thousands on pure sine wave, and run the house. :-) 

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Thanks for all this great info.

My goal is to run my desktop PC (not my laptop) and one monitor and two powered external drive enclosures for 2 hours during load shedding & nothing else in the house. My alternative plan to that is to switch to my laptop when the power goes down, having saved my work during the 5 minutes I have on the UPS. And do without the drives, which is not ideal in my workflow. I am travelling in the UK at the moment so I can't test the power use of my set up, but I am estimating it at 500W. Not sure how accurate that is.
 

Quote

You can get cheap 2nd hand 24v modified sine wave inverters with 15amp chargers, with fans built in, for R1000 - batteries excluded off course. 🙂

Please can you point me in this direction!

If I am right at 500W, let me see if I can calculate the battery capacity I need correctly.

500W for 2hrs = 1000Whr at 12V
1000/12V = 83 Ah at C/20,      But at C/4, say 120Ah
And if I want to discharge battery to only 50%, it would be 240Ah

Is that right or do I also need to allow for power factor to get between VA and W?
 

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11 minutes ago, nick9 said:

Please can you point me in this direction!

One 24v modified sine wave inverter with 2 x 100ah batteries, should do it - as new they can handle it:

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I investigated this at length because I had an APC ups. They are generally considered the highest quality in the UPS industry, at least for home to small business UPS.

And overall they aren't designed to run longer than the battery allows

  • Heat
    • On the APC it has a fan that cools the mostfets so that won't overheat.
    • The only option was to add a heatsink to the transformer so the fan helped cool it down (on the APC on the Mecer the transformer got so hot it was exceeding the transformer heat rating)
    • I've taken apart both Mecer and Proline and they have even cheaper and smaller transformers so they'll produce even more heat (The reason they produce more heat if smaller is quite complex, I can add more detail if you are interested)
    • Transformer has a base load of 50w on the APC for example(meaning it ALWAYS draws 50w). The net effect is that the transformer will overheat if run for a longer period of time
    • If you don't have a fan in the UPS it will almost certainly overheat (ie> they are relying on the battery failing before it overheats)
  • Charger
    • Charger on the UPSs I looked at were pathetic to say the least
    • They don't trickle charge (so charged batteries are overcharged and cooked)
    • Discharged batteries don't charge fast enough and they can't even fully charge them
    • The APC charger was especially pathetic at 1amp charge current with a nasty sawtooth waveform
  • Efficiency sucks on UPS. Even the APC has really terrible efficiency of less than 80%

Overall when it is all said and done, you don't save by going the UPS route. Buying something like the cheapest Axpert inverter works out the same price for something far more reliable and higher quality in every way. It has a good quality charger, it can run 100% of the time, it is far more efficient.

And before you ask, I actually modded by APC so I know a great deal about how it works and the quality of it. Similarly I've had an Axpert open. The Axpert is just better in every way.

My 2c.

Edited by Gnome
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This is fantastic info, thank you.

Looks like it's definitely not worth it for me.

Is there an Axpert model you'd recommend I look at to go with 2 x 100Ah's and charging from mains, rather than solar? At this point I don't have a solar panel.

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With regard to battery types, and sealed vs non-sealed, do I need to worry much about that, especially as I work in a small room with limited ventilation. i.e. are the sealed battery types keeping any off gassing inside the box and the non-sealed letting off gases into the room?

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4 hours ago, nick9 said:

Is there an Axpert model you'd recommend I look at to go with 2 x 100Ah's and charging from mains, rather than solar? At this point I don't have a solar panel.

You don't need solar panels. I bought one only to use as a UPS. Used to be tons available for sale, but everything is sold out now: https://www.takealot.com/all?qsearch=axpert&_sb=1&_dt=all&_r=1&_si=958d81b135dd5f9f1fb81d0ce937c901

Everyone is gearing up for load shedding.

Of course prices have gone up also. In order of price

Note that they are all Voltronic Axpert. The first and second one are both quite old models but there are PLENTY of people here with some and they are really reliable.

The last one is a newer model, basically the same inside, just slightly nicer looking case and a few minor new features.

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To run a PC you can really go modified sine wave. The batteries are the costly part, no matter what inverter one gets.

Step up on modified inverter, add a MPPT controller and panel on the bank ... then you forget about Eskom as the batts are always charged properly daytime.

Make it all portable and there you go.

Non-sealed is a big no inside BUT one can make a plan and have them outside in a ventilated box, kept cool, cables though the wall with inverter inside. There is a plan for everything.

A positive for ventilated batteries is that you can see the water levels and top them up. A lot of sealed batteries die because one cell has dried up. Could have been prevented if one could check and top them up - obviously, once cut, they are not "sealed" anymore.

Titbit. Some of the "sealed" batteries you can cut off the label on top and get to the caps underneath. :-) 

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Well I guess that means my 48v 3kva APC ups should have died a long time ago. The current one has been in continuous service for about 3 years as the non eskom power for my house. Yes their efficiency sucks and the charger won't cope with the bigger batteries. But the ups is a workhorse . When I run the dishwasher it complains a little (just over 2kw draw) but otherwise no issues. It will happily run at half power all day . If you have it why not use it, and if it does what you want great. If you find something better or more suited , then by all means spend the cash.

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2 minutes ago, seant said:

3kva

Well, there is your answer. When you get into the upper power echelons, you can't fake it anymore, especially because these things tend to also end up in data centers and you don't want to tick those guys off...

The small ones though... like an 800VA one (allegedly) with a mere 9Ah battery. Not going to do the same thing.

Come to think of it: I have an old mecer-branded UPS in the garage. It was knocked off the table by a customer at a company where I used to work, I brought it home and found that all that was wrong with it is one TO-220 component got knocked loose. Resoldered it and it started right up.

So I could actually do a test... if I could be bothered that is :-)

Edited by plonkster
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The thing is at a lot of the e-waste guys aren't interested in keeping the larger rack mount UPS or any ups as the scrap value of the units are mainly the batteries and the transformers so if you look around  you can get 48v units with no batteries for next to nothing.  

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1 hour ago, seant said:

Well I guess that means my 48v 3kva APC ups should have died a long time ago.

I don't think any disputes the last a long time

1 hour ago, seant said:

Yes their efficiency sucks and the charger won't cope with the bigger batteries. But the ups is a workhorse

I don't really see it as a work horse. A work horse implies designed for 100% duty factor. Most APC UPS aren't. Only the APC UPS that have the port for extended run batteries are designed to run at 100% duty cycle.

But don't take my word for it: 

 

1 hour ago, seant said:

 When I run the dishwasher it complains a little (just over 2kw draw) but otherwise no issues. It will happily run at half power all day . If you have it why not use it, and if it does what you want great. If you find something better or more suited , then by all means spend the cash.

Are you feeding the UPS output into your house?

Or are you actually plugging the dishwasher into the unit?

Your runtime on battery with the dishwasher can't be more than a few minutes

1 hour ago, seant said:

If you have it why not use it, and if it does what you want great. If you find something better or more suited , then by all means spend the cash.

I had the same argument but when you think about modding it, it becomes a money pit. It just wasn't designed as an inverter.

Edited by Gnome
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@Gnome I have the UPS wired into the house running off a big enough battery pack which is charged by solar . I took into account the unit's inefficiency when I build the battery pack so I don't have any problems there. For what I use now it's just fine, sonewhere in the future I'll get a more efficient, larger inverter. I'd like the outback 8kva radian unit but they are a touch pricey.

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31 minutes ago, Gnome said:

Most APC UPS aren't.

Have used APC's for a very long time now. Always 24/7/365.

Never once a problem, ever ... bar batteries ... because they are the online versions, ports for extended battery packS, fans running all the time - that 50w you mention. ;-)

I used to use them as part of my changeover setup, to be the buffer between the off-grid inverter and starting fridge, freezers., the inverter feeding the APC.

And one APC saved all my devices, when a electrician cocked up the life/neutral connection of the lights, burnt out the APC's charger, APC worked till the last batt amp in the batts. Saved me a HUGE amount of damage, nut the APC was irreparable, no parts, too old.

Where I would agree with the "most APC" statement is if you refer to the smaller non-online cheaper "APC" ranges, APC and Schneider Electric somewhere got together, and the "cheaper" ranges became available while back.

So I would say "Most non-online UPS aren't."  :-) 

 

Any case guys, Nick9 is sorted. 

Edited by Guest
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@nick9 - Referring to your original question - I have done similar myself on almost all my UPS's at home, but it's the charger that's built into the UPS that is the issue. Most home/small UPS are 12V or 24V (usually 24) with two tiny 7Ah or less batteries. My own logic, with only experience and history of failures, is NEVER go more than double the built in Ah, and only with a decent quality UPS.

So, for example, I have a 2kVA ups that came with 7Ah batteries, which lasted less than 10 Minutes under near full load. Replaced the batteries with 14Ah and my time has jumped to 25min (mainly because the Voltage detection of the UPS can't kick in as quickly). I have tried on another UPS to go to 30Ah batteries, but they cannot recharge properly and eventually a circuit in the UPS died and popped the whole thing after a week.

If you are going to do it, only go double the internal batteries, and on a decent UPS. the cheapies/chinese stuff just can't handle the charge current.

Another alternative, which is only heresay since I haven't done myself - Get a seperate charger for the batteries, and then break or use a diode to prevent the UPS from trying to charge the batteries. Then apparently you can use huge batteries. Again, this is heresay from someone I know, but I have never seen their setup (or needed to try, since I have full house solar now).

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