Supercharged UPS

[Kebast]

I've seen several DIY modifications for UPS (Uninterrupted Power Supply) where instead of using the small normal UPS batteries, the user replaces those batteries with a large (~100 ah) deep cycle battery. First off, I'm curious how safe this is? I guess if all the connections are made properly, and the UPS inverter can supply its rated power for the extended time it would be ok. In any case, I have a couple of UPS units that have dead batteries, and was thinking of attempting this (with extended monitored testing certainly). My plan was to put a couple of these (UPG UB12350 Amazon Link) in series (my UPS is 24 volt).
The PC I have connected only uses 114 watts max. The UPS has a display screen that tells me output volts and watts, so assuming 95% efficient inventor (is that valid?) my max current draw from the batteries would be 5 amps.


Anything off here? How safe is this?

[inetdog]

I've seen several DIY modifications for UPS (Uninterrupted Power Supply) where instead of using the small normal UPS batteries, the user replaces those batteries with a large (~100 ah) deep cycle battery. First off, I'm curious how safe this is? I guess if all the connections are made properly, and the UPS inverter can supply its rated power for the extended time it would be ok. In any case, I have a couple of UPS units that have dead batteries, and was thinking of attempting this (with extended monitored testing certainly). My plan was to put a couple of these (UPG UB12350 Amazon Link) in series (my UPS is 24 volt).
The PC I have connected only uses 114 watts max. The UPS has a display screen that tells me output volts and watts, so assuming 95% efficient inventor (is that valid?) my max current draw from the batteries would be 5 amps.


Anything off here? How safe is this?

My biggest concern would be whether the charger in the UPS is able to handle a larger battery and whether its set points are correct for the new battery type.

Although at the load you describe, recharging would not be an issue except after a long power outage, you still need to make sure that the battery does not get overcharged by an incorrect voltage set point. The only safety concern that I would have is that you include an external fuse to prevent a fault in the UPS from pulling the full short-circuit current of the larger battery. And of course, please protect the battery terminals from somebody dropping metal on them.

95% is a good figure to start from, although it might actually be lower. With the battery removed from the UPS housing, there would be a slightly lower concern about temperature rise when running for an extended time. Does it have a fan? If so, make sure to put the case back together enough to allow the original air flow path.

[Sunking]

Mostly a myth and wishful thinking. If your UPS cost less than $1000, it is likely a cheap standby UPS rather than Line Interactive or Dual Conversion. If you bought the UPS at a box store for less than $400, it makes a good boat anchor when the battery dies.

[Sunny Solar]

My plan was to put a couple of these (UPG UB12350 Amazon Link) in series (my UPS is 24 volt).Not sure what you trying to do here.. You have 2 12v UPS and want to series them to run of a 24v battery pack or they are 24v UPS and you want to series them to make them run from a 48v battery pack or lastly and this is not possible,You want to series the outputs to run something??? If the last question is what you want to do all you will end up with is 2 boxes of scrap metal and electronic components.
Most consumer UPS have the electronics designed for only very short time on. Less than 30 mins.

[Kebast]

Found specs

My UPS

Certainly not boat anchors, the batteries can be replaced. They just charge almost as much for the replacement battery pack as for a new unit. Hence this post

Found the specs for my UPS. Sunking, you're right 95% was way out of range. UPS is listed at 80% for full load and 84% at half load. I wish they provided the full curve since I only use about 20% of the rated load.

Sunny, don't let the Amazon link confuse you. I would only need two of the batteries from that four pack. That was just the first easy link I found. My UPS has two batteries (7.2 ah iirc) internally in series for a total of 24 volts. I would do the same with the 35 ah batteries. I have another smaller model that only has one battery inside (12 volt). The two UPS units would be isolated systems.

I checked the smaller 12 volt unit with a volt meter. The voltage going to the battery with the unit plugged into grid power was 13.7. So right at the float range for agm I think. The spec sheet for the UPS I linked listed the recharge time as 16 hours. If I ever have a power outage, I might have to hook up a stronger charger to fully charge the larger batteries.

[Kebast]

Runtime chart

This is a bit misleading since the test load used has a PF of 1.0, but listed time for a 115 Watt load is 55 min: Chart

Power supply for my PC is 85% efficient.

[Sunking]

The voltage going to the battery with the unit plugged into grid power was 13.7. So right at the float range for agm I think.

Correct all UPS use a single stage float charger.

The spec sheet for the UPS I linked listed the recharge time as 16 hours. If I ever have a power outage, I might have to hook up a stronger charger to fully charge the larger batteries.

This tells you a couple of things immediately.

1. It is a Standby UPS, not a Line Interactive or Dual conversion. If it were a Line Interactive or Dual Conversion the rectifiers can charge the battery in less than an hour, plus supply the UPS inverter with all its power.

2. It tells you the charger is very small of just uner 2 amps. It will charge a larger battery , but it will just take more time.

[Kebast]

Thanks

Thanks for the info. I might experiment with the small 12 volt unit (Back-ups ES 500 I think) before messing with the larger one. Here's the fine print about recharge time: **The time to recharge to 90% of full battery capacity following a discharge to shutdown using a load rated for 1/2 the full load rating of the UPS. Not exactly sure what to take from that, except that charge time depends on load.

The small unit is an old unused spare. The XS 1000 is still in use, although the batteries are at the point were I'm only getting about 8 minutes of run time during a power failure, was more than 30 when the unit was new. I'm using this PC to record and serve all the TV shows we watch (Ubuntu Linux, mythtv, using hauppauge 2250 TV tuner cards). Sucks to have a short power outage and miss recording shows because the computer has shut down.

Essentially the goal is to get the run time up near an hour without spending that $400 plus on an industrial unit. We had one of those in a lab where I worked. 8 hour run time for 4 pcs and a stereo lithography machine. Was the size of a small filing cabinet .

[Kebast]

one more thing...

1. It is a Standby UPS, not a Line Interactive or Dual conversion. If it were a Line Interactive or Dual Conversion the rectifiers can charge the battery in less than an hour, plus supply the UPS inverter with all its power.

I did notice, according to the spec sheet, the XS 1000 is a Line Interactive model.
The odd thing is I have another Back-UPS ES 550 that IS >95% efficient at all loads. Link. I'd play with that one, except it is newer and the battery is fine.

[Sunking]

Here's the fine print about recharge time: **The time to recharge to 90% of full battery capacity following a discharge to shutdown using a load rated for 1/2 the full load rating of the UPS. Not exactly sure what to take from that, except that charge time depends on load.

It means it is a Line Interactive UPS which is a Good Thing, very Good Thing.

A LI UPS has a static bypass switch (electronic rather than mechanical), and works in a Boost/Buck Operation. So under normal conditions Line AC power is supplying power to the loads. However the Inverter is operating in parallel with AC line power through a Buck/Boost transformer. If you have say a Line voltage dip (called Sag) the inverter will Boost to keep the voltage constant using battery power and rectifier power. If say the voltage goes high (called Swell) from the AC line side, the inverter will Buck the AC line and lower the voltage. Hence the name Buck/Boost transformer in the static bypass switch. If AC line power fails, the inverter immediately without any interruption supplies power via the battery and inverter. It is a seamless operation. Only Line Interactive and Dual Conversion UPS can do that. A standby UPS will have a power disturbance when AC line power fails.

OK as for battery size your UPS can handle should be very easy to find out. Look at APC website for your model and look for a added battery option. Most all of them off an expandable battery option as accessory equipment. That will tell you how large you can go. Or just call their product support number and ask.

[Kebast]

Thanks!

Thanks for the info about the expandable battery banks! I didn't know that was an option. I know one of the main issues people find when adding large batteries to their UPS units is after an extended power failure the inverter fails (melts, or other catastrophic events). If mine is already rated for a certain size extended battery that would certainly take that worry away.

[bstedh]

Inverters

I am currently doing what you described. I have several UPS' an have replaced their batteries with 100AH and or 70AH battery strings. All of my UPS' have provisions for extended external battery strings. You can usually tell this by locating a extended battery connector on the back of the UPS. However I did connect mine to the standard battery connection point on the front by putting a hole in the front Bezel to run the wires through.

I obtained these UPS' used because their batteries where dead or degraded and the companies where just replacing the entire unit. =] As these where designed for server racks and not just a single desk they have very nice power filtering and monitoring capabilities. 2 are APC brand 1000W monsters and 1 smaller APC brand and then another off brand. I was also able to get some telcom quality AGM batteries at a great price that will run one of these UPS' for an entire day. Unfortunately the batteries if you where to go out and buy them retail would run you about $400 each so that was a huge score for me to find them being gotten rid of because the owner didn't know what they had. I just offered to recycle them for them and gave them $10 each for 16 batteries....

Now that I have enough backup power to run the entire house for a day or more I need to figure on How I really want to wire it all into the house. I don't want battery stands in each room... I will probably have an electrician friend of mine help me wire a power backup rack in the garage that will feed different zones of the house. Even with out the battery backup the UPS' will provide a huge service in filtering the power as I am on a crappy co-op grid that has all kinds of spikes and short drop outs and flickers. With a total of 5 UPS', 4 car style inverters, and 27 total AGM batteries I should have a leg up in the Zombie apocalypse