# APC Battery Backup - Extending Run Time with BIG Battery Bank



## homerb

I just bought an APC BN1250 UPS battery backup from craigslist for $40 bucks. It's a 1250 VA / 780 Watt system that has an advertised runtime of 90 minutes when the power goes out.

This is technically an "electrical" thread rather than a PC thread, but since it's supposed to be a PC component, I'll post it here.

I plan on using this battery backup for my home theater system that includes a 55" LG LCD TV, Comcast Cable Box, a Media Center PC, and a pair of end table lamps with compact florescent bulbs in them.

The guy I bought this backup from says that the batteries are good as new, but I'm not sure if I believe him. Regardless, $40 isn't a bad price, even if it needs batteries. Here's why:

I plan on extending the run time using two, perhaps four deep cycle marine batteries. Since this particular inverter runs on 24 volts, I'll need at least two batteries wired in series to get the 24 volts. I was even thinking of running four batteries in a massive series-parallel configuration. 

The unit comes with two 12V 9aH batteries for a total of 18 amp-hours. An Optima Yellow Top battery has 55 aH, or two for 110 aH. That's 5.1 times (510%) more capacity than the battery that comes in the UPS. Using this equation, assuming 90 minutes of runtime, I could theoretically get 459.9 minutes of runtime with two Optima Yellow Tops. 

While I'm not going to get Optima Yellow Tops for this project, the "cheapest nice generic" batteries for a boat or RV would have similar output. I'm going to try to find sealed batteries so they don't emit hydrogen gas when charging.

I'm going to test the system as-is for a baseline. The specs claim 90 minutes of runtime with half load, so I'll see if I can push it for an hour running the TV and Cable Box. If it goes longer than an hour, I'll be happy. I won't risk it by running it completely out of juice. 

There have been some issues with increasing the battery capacity in these APC battery backups in the past. Mainly with the inverter. Some of the smaller ones are only designed to be run for 10 minutes, and after that they start to heat up. Seems like this one is designed to be run at least 90 minutes, and it has a cooling fan built in. I could certainly add extra cooling fans inside with the extra space cleared by getting rid of the internal batteries. 

Another issue is with the internal computer and the capacity it "thinks" it has. Some have reported that they won't run more than the time they originally ran with the old batteries because they are used to having smaller capacity, and you have to go in and change some of the parameters. 

We'll see about that.

Has anyone done this before? Good results?

Homer


----------



## Yoyizit

The only kink may be, the apparent battery capacity depends on how fast it's drained.
For 9 Ah the 'C' rate is 9A, and it will drain to some agreed-upon cutoff voltage. 
At C/100 you will pretty much get full capacity. A lot of batteries are tested at C/20.
And, a constant current load is not the same as a constant resistance load. Your batteries may be drained by all this electronics at a constant power rate.


----------



## Scuba_Dave

Why try to extend this to run a TV ?
You would be better off putting the $$ towards a generator setup


----------



## homerb

Scuba_Dave said:


> Why try to extend this to run a TV ?
> You would be better off putting the $$ towards a generator setup


Good question. 

I have a Generac 7500W / 13,500 W portable generator that runs the whole house except for the A/C, Furnace, and Electric Stove. I bought that generator at a pawn shop for $250 bucks. Sweet!

But that thing is LOUD! I don't want to be running it late at night. It'd be cool to have a battery backup on the TV, Cable Box, and living room lights (or whatever) until I can go get the generator started and hooked up, or for after I have shut off the generator. The cable box is most important to keep running, because as soon as power gets cut to that, it takes a good 5-10 minutes to start back up.

The APC backup will work just fine as-is, but this forum isn't called "Leave Things The Way They Came Chatroom", it's called "DIYChatroom". With that being said, I want to make it run as long as possible, and if I can do that with some cheap car batteries, that'd be awesome. 

Plus, when the generator is getting warmed up, it sometimes revs up and down which creates a very inconsistent voltage. The cable box with the hard drive doesn't like outages and brownouts very much. 

It might also be important to stay low-key and keep some lights on without attracting the type of attention that a loud generator creates. I could run a few extension cords from the UPS to run a few lights in other rooms too. 

But when you think about it, I don't "need" any of this. None of us "need any of this". I could do just fine during an outage with some candles and flashlights and no creature comforts. An outage is a good excuse for me not to have to check all the annoying work emails anyway.

But it's fun to do. I like projects like this. I like having a few options. 

Homer


----------



## Yoyizit

homerb said:


> one of us "need any of this". I could do just fine during an outage with some candles and flashlights and no creature comforts. An outage is a good excuse for me not to have to check all the annoying work emails anyway.


I flip a coin. 
Heads, you go without power for a day. Tails, you have a backup.

How much would I have to pay you, lump sum, for you to be completely indifferent as to which way the coin lands?

That's what the backup is worth to you, today.


----------



## PortlandRemodel

*Battery*

I've used this unit before and it's great. The extended battery life is worth it but you still have to have the computer set up for automated shut down in the event of a power failure. APC has this software that interacts with their units and will do it the right way. It is not a replacement for a backup. Backup and UPS's are really like casino odds in reverse. It's possible but unlikely you'll lose everything and more likely something less terrible will happen. But with a UPS and backup, it is super unlikely you'll experience any of the problems.
www.portlandhomeremodeling.com


----------



## Yoyizit

Forgot to mention that in general paralleling batteries is tricky.


----------



## homerb

Yoyizit said:


> Forgot to mention that in general paralleling batteries is tricky.


Thanks for the disclaimer.:thumbsup: I'll take that into consideration. 

Even if you have a basic knowledge of how electricity works, you'd be able to wire batteries in parallel or series. Or series-parallel.


----------



## Yoyizit

homerb said:


> Thanks for the disclaimer.:thumbsup: I'll take that into consideration.
> 
> Even if you have a basic knowledge of how electricity works, you'd be able to wire batteries in parallel or series. Or series-parallel.


Yes, but will the batteries object, sometimes explosively?
Also, charging vs discharging brings up different problems.

School buses have a 24 battery for cranking the engine and a tap @ 12v for accessories. Charging/discharging this arrangement requires a complex interface.


----------



## homerb

Yoyizit said:


> Yes, but will the batteries object, sometimes explosively?
> Also, charging vs discharging brings up different problems.
> 
> School buses have a 24 battery for cranking the engine and a tap @ 12v for accessories. Charging/discharging this arrangement requires a complex interface.


I see what you're saying. You're right, it is important to make sure you've got the batteries sized correctly, and to make sure they are wired properly for the application.


----------



## Yoyizit

homerb said:


> I see what you're saying. You're right, it is important to make sure you've got the batteries sized correctly, and to make sure they are wired properly for the application.


No, there's more to it. 
You don't ever want heavy currents to flow *between* batteries, and it's hard to say all the ways that this can happen.


----------



## homerb

Yoyizit said:


> No, there's more to it.
> You don't ever want heavy currents to flow *between* batteries, and it's hard to say all the ways that this can happen.


I know there's more to it. I just don't feel like explaining it because it's beyond the scope of this thread. 

I'm not a novice when it comes to wiring up batteries and doing these types of projects. I worked in the 12 volt industry for six years and I'm an MECP master installer. I wouldn't even consider doing these types of DIY projects if I weren't so experienced with electronics, I'd just go out and spend the extra money on something with the capabilities I'm looking for instead of using my knowledge to save money.

I've seen lots of threads in this forum where people are constantly challenging other people's intelligence and knowledge about the topics that are being discussed. Before the original topic is even discussed in sufficient detail, there's always someone going off on a tangent about the risks and dangers of the topic at hand because they think the people discussing it don't know enough to consider the risks. It makes people not want to read the thread anymore, and it discourages people from starting their own projects. 

Safety first, but let's all do ourselves a favor and instead of assuming that other users of the site don't know what they are doing, assume that they know what they are doing and that they have enough skills and intelligence to consider the safety precautions. There are always people that screw things up, but that doesn't mean every thread needs a disclaimer. There's already a disclaimer on this site somewhere. I'm sure the administrators of the site could set up a "disclaimer" bot for each thread if they wanted to.

I don't mean any disrespect to you or anyone, (and I thank you for being so kind as to post on my topic and share your knowledge with me) but I would appreciate it if people assumed I knew what I was doing. Of course, I don't know everything and that's why I ask for advice. But if I wanted someone's opinion about the safety precautions, I'd ask for it. I think I speak for most of us in the forum. If anyone disagrees with me, please feel free to explain why you think I'm wrong for what I just discussed. :thumbup:

Thanks. 

Now, can we please get back to the topic at hand? Have you ever "hot wired" an APC battery backup?

Homer


----------



## PortlandRemodel

homerb said:


> Now, can we please get back to the topic at hand? Have you ever "hot wired" an APC battery backup?


Do you mean by hot wire just that you don't have the correct connections? Or that you plan to make batter connections from home made designs? APC has wiring diagrams that are not difficult so I don't think it's a problem at all. When APC sells case shells they are just that - shells that have the batter connectors. You could also alternatively buy a shell with a wiring harness.
www.portlandhomeremodeling.com


----------



## homerb

PortlandRemodel said:


> Do you mean by hot wire just that you don't have the correct connections? Or that you plan to make batter connections from home made designs? APC has wiring diagrams that are not difficult so I don't think it's a problem at all. When APC sells case shells they are just that - shells that have the batter connectors. You could also alternatively buy a shell with a wiring harness.
> www.portlandhomeremodeling.com


Using the proper connections, heavy gauge wiring, and using larger capacity batteries in the proper sequence and voltage in order to dramatically increase the run time of a used battery backup way beyond what APC had originally intended in order to save money over using an APC designed battery pack.

A decent APC battery backup system might have battery capacities of anywhere from 7-21 amp-hours. Enterprise class APC battery backups might have battery capacities of 50-100 amp-hours in stock trim and have connectors for external batteries in either 12, 24 or 48 volt configurations.

One of the enterprise class APC battery backups would be the best to start with because they have built in cooling fans, sine wave output, large capacity charging circuits, etc. 

You can get a "good cheap" deep cycle marine battery with 100 aH capacity for $50-$60 bucks. 

You could extend the runtime of a 750 watt APC backup with a couple large capacity deep cycle batteries to several hours, perhaps days depending on what's plugged in, and how many batteries you have.


----------



## PortlandRemodel

You mean they aren't really worth the hundreds of dollars they charge? That's gonna make the UPS snake charmers upset... (ha ha)


----------



## vsheetz

Rather than kluge a APC, consider equipment designed to do the job:

Switches automatically from AC/DC power supply to battery power, charges pretty much whatever battery bank you want to connect:
http://www.westmountainradio.com/SuperPWRgate.htm

Run the output to a DC to AC inverter, such as from Tripplite.

Commonly used for ham radio emergency power.


----------



## homerb

vsheetz said:


> Rather than kluge a APC, consider equipment designed to do the job:
> 
> Switches automatically from AC/DC power supply to battery power, charges pretty much whatever battery bank you want to connect:
> http://www.westmountainradio.com/SuperPWRgate.htm
> 
> Run the output to a DC to AC inverter, such as from Tripplite.
> 
> Commonly used for ham radio emergency power.


Thanks for showing this! It's not that expensive, either. 

I have an 800W cont 1600W peak AC inverter and a 1.5 amp "battery tender" trickle charger. I don't think I'll leave it running continuously with things plugged into it, like with an APC. But, it's still good for emergencies.


----------



## homerb

Sorry to revive an old thread. Coincidentally, it's been almost exactly a year since I started this thread! 

Just had an outage during a storm and this system I made ran perfectly. It ran everything in my living room including my LCD TV, DVR, Cable Modem, Router, Computer, and Table lights (CFL's), An approximate 600W load for 4 hours straight until the power came back on. It probably had another 2-3 hours left in it before the batteries died. 

I didn't even have to fire up my generator. My Generac 7500 EXL is really loud and I'm afraid it would bug the neighbors. I'll only use that for extended outages when the battery backup goes dead and when I need to keep the fridge and hot water heater going. 

This is the first real "test" of my system. Now that I know I can have at least 7 hours of runtime (probably more with a lower load), I can use the battery backup at night to avoid attracting attention, and then use the generator during the day.

Has anyone else done anything similar?

Homer


----------



## RandomEE

homerb said:


> Sorry to revive an old thread. Coincidentally, it's been almost exactly a year since I started this thread!
> 
> Just had an outage during a storm and this system I made ran perfectly. It ran everything in my living room including my LCD TV, DVR, Cable Modem, Router, Computer, and Table lights (CFL's), An approximate 600W load for 4 hours straight until the power came back on. It probably had another 2-3 hours left in it before the batteries died.
> 
> I didn't even have to fire up my generator. My Generac 7500 EXL is really loud and I'm afraid it would bug the neighbors. I'll only use that for extended outages when the battery backup goes dead and when I need to keep the fridge and hot water heater going.
> 
> This is the first real "test" of my system. Now that I know I can have at least 7 hours of runtime (probably more with a lower load), I can use the battery backup at night to avoid attracting attention, and then use the generator during the day.
> 
> Has anyone else done anything similar?
> 
> Homer


That's awesome, thanks for the post.

I have a similar backup unit plugged into my Linux server. I can only get about 20 minutes of run time on it, which seems kind of short for having only one computer on it.

In my garage I have a couple of massive APC 3750 Watt, 5000 VA backup units, but they both require 220V inputs. Unfortunately for me that means about $450 to run a new circuit to a new breaker, as I'm out of spots in my panel.

Your post makes me want to wire up 2 or 4 of the batteries that are just laying there collecting dust. I would be curious to know more about what you ended up doing for your setup.


----------



## Red Squirrel

Great to hear that it worked out. I've been thinking of doing this for a while now. They do make inverter chargers which are made for it, problem is the switch-over time is too long, most equipment would still go down. Making a dual conversion UPS would be nice too, but good luck finding a 300 amp battery charger to keep up with the load.


----------



## Marty1Mc

Have you considered how you're going to re-charge these batteries? I am sure the APC unit doesn't have the capacity to re-charge two car batteries in series/parallel to the unit.


----------



## homerb

Marty1Mc said:


> Have you considered how you're going to re-charge these batteries? I am sure the APC unit doesn't have the capacity to re-charge two car batteries in series/parallel to the unit.


The smaller APC units that only have a 12V system have a pretty weak charging circuit. 

However, the larger units that have the capability to be expanded with a separate battery pack have a more robust charging circuit. As far as the APC is concerned, it just thinks it has the "add on" battery pack. Nevertheless, it's still a small trickle charger. They don't need to be charged up fast anyways.


----------



## Red Squirrel

I would imagine it would take a while, but I'm sure it would eventually still charge up fully. You could possibly add another charger to the circuit so you can charge em faster after an extended outage, though I'm not sure what effect that would have on the UPS's charger. They'd probably do funny things with each other. Could keep the system offline and charge separately I guess. Would only need to do this when it's been completely depleted. 

Would probably take a couple days to charge with just the UPS, but unless you get tons of outages, this is probably acceptable. 

Though, I wonder if an inverter charger like this would be better than an APC:

http://www.ebay.ca/itm/8000W-Pure-S...AU_Boat_Parts_Accessories&hash=item5d302e2abc

It has a transfer time of <8ms which I imagine is acceptable for computer equipment. It's 220v though, but there are more, and cheaper ones too. Idealy a 240/120 unit would be perfect as you could just hook up a small sub panel to it and wire circuits in directly and have both 120 and 240 voltages.


----------



## homerb

Sorry to resurrect an old thread, but has anyone thought of this lately?


----------



## dazium

*Battery bank*

I too have been trying to do the same. i am runninf 6 12/12 sl;a batteries for 72 ah and 12v. when i attached the paralelles bank to the ups, the shunt vaporised, in thoery this should have not happened because the voltage has remained the same. i have email apc about this and am still awaiting a reply from them. i did replace the trace shunt with copper wire. upd works again on single battery but still not the bank. Yes i am getting 12.6 v tested from the bank. no its not overvolted. yes i did fix the shunt, works now. when plugged into wall, and with single battery but not the bank??? any ideas?


----------



## homerb

dazium said:


> I too have been trying to do the same. i am runninf 6 12/12 sl;a batteries for 72 ah and 12v. when i attached the paralelles bank to the ups, the shunt vaporised, in thoery this should have not happened because the voltage has remained the same. i have email apc about this and am still awaiting a reply from them. i did replace the trace shunt with copper wire. upd works again on single battery but still not the bank. Yes i am getting 12.6 v tested from the bank. no its not overvolted. yes i did fix the shunt, works now. when plugged into wall, and with single battery but not the bank??? any ideas?


If it's a 12 V system, make sure that all of your batteries are wired up in parallel like you mentioned. That means that all of the positive wires are hooked up to the positive leads in the battery and all the negative wires hooked up to the negative leads on the battery, as opposed to running them in series where you go from positive to negative to positive to negative and so on. And make sure you test the output voltage of the entire bank before you hook it up to the APC unit. Output voltage of the entire bank should be nearly identical to the output voltage of a single battery. 

If that is the case, the APC shouldn't even be able to tell the difference between one battery two batteries or three batteries and so on. Because you have increased the capacity and the amperage rather than the voltage by wiring them in parallel.


----------



## dazium

*Mr*

They are all paraleled. I have made banks before. i also have a custom ebike runing 88-96 v with lithium packs. 24s. I custom buikt the wiring harness for both. do you think that maybe the precharge from the batteries to the unit. charging the caps with lots of current, could have fried the fuses. i will be adding an online fuse to the pack to keep the current below 30amp. other than that, idk what is wrong with the ups. this is a small battery bank for me.


----------



## homerb

dazium said:


> They are all paraleled. I have made banks before. i also have a custom ebike runing 88-96 v with lithium packs. 24s. I custom buikt the wiring harness for both. do you think that maybe the precharge from the batteries to the unit. charging the caps with lots of current, could have fried the fuses. i will be adding an online fuse to the pack to keep the current below 30amp. other than that, idk what is wrong with the ups. this is a small battery bank for me.


You said that you were able to get it to work with just one battery. Hook it up with that first battery and let it charge and run. Then, add more batteries to the bank when the first one is still hooked up. That way you would gradually be increasing the capacity of the bank without introducing a sudden jolt or charge that might be exaggerated by a bank of more than one battery.


----------



## Yoyizit

dazium said:


> I too have been trying to do the same. i am runninf 6 12/12 sl;a batteries for 72 ah and 12v. when i attached the paralelles bank to the ups, the shunt vaporised, in thoery this should have not happened because the voltage has remained the same. i have email apc about this and am still awaiting a reply from them. i did replace the trace shunt with copper wire. upd works again on single battery but still not the bank. Yes i am getting 12.6 v tested from the bank. no its not overvolted. yes i did fix the shunt, works now. when plugged into wall, and with single battery but not the bank??? any ideas?


Post a schematic of your intended network. The number of spurious current paths can be large and resistances can be extremely low.


----------



## Red Squirrel

Seems odd it would have vaporized as even though there is more current available, the system is only going to draw what it needs. Could it be that there is a very momentary short circuit that happens during the switch over? Maybe the relay is make before break and during the transition period it is shorting the batteries. So with a small battery not a big deal, but with a huge bank, then it is. Just a guess though.


----------



## Ravenworks

PortlandRemodel said:


> You mean they aren't really worth the hundreds of dollars they charge? That's gonna make the UPS snake charmers upset... (ha ha)


:thumbsup::thumbup:


----------



## KD7LRJ

I have been doing this with many different UPS units (including some just like the one you have). I wrote this article a while back and have modified dozens of UPS units to run on external batteries.

I have several 1500 VA units that are similar to the ones you have. They too have fans in them (unlike the 1000 VA models). In addition, they have a port at the top rear of the unit to plug in an external battery. This is essentially the SAME THING you are talking about doing; adding more capacity than just the internal batteries. I use the external port on mine to attach more capacity.

While these units are great, I have mostly stuck with using the older ones (which I get free at work when they throw them out) which run on 12 volts instead of 24. I mod them and then give them to local Ham Radio people to keep their emergency batteries for their radios charged up. And, bonus for them, they work as regular UPS units as well.

Other UPS related articles on my blog.


----------

