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Anyone have any experience adding additional batteries to a UPS system for home use? Lots of info out there but what is safe/smart?

VERAULT

VERAULT

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Joined
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Connecticut, USA
So I have a few older APC UPS systems and lots of extra batteries. Where I live we get frequent brownouts. I have a SMART UPS 1500 with two batteries in it currently but I wanted to try wiring in some external batteries to it. I am assuming I need to add them in parallel as its currently running off the paired 24v battery system but I don't know for sure. Can I just add two more batteries in series to the two inside the unit?

I would love to here from anyone having experience with this type of thing. I know there are lots of articles about people connecting car batteries etc and I am not going that route. These are 12V UPS batteries that are not new by any means, I just want to get all the use out of them before they permanently deplete.

Would love anyone's take on on this.

There are tons of "tid-bits" on the internet about this but what is safe?:

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If you add additional batteries in series, this will increase the terminal voltage of the battery combination. This will damage the internal inverter.

I suggest that you don't go down this route.

Adding further batteries in parallel could be an option. However, the batteries will be charged by the unit, so consideration must be given to the maximum potential charging current.

A further problem with batteries in parallel could be circulating currents when the individual batteries have different terminal voltages.

These are all problems we also experience in the radio controlled model fraternity with high-powered Li-Po batteries...

Dave
 
From a safety standpoint, I would be concerned about the UPS being unable to monitor the temperature of external batteries. I have had a couple UPS shut down after the batteries went dead and it kept trying to charge them until they got too hot. Which is a crappy design for sure, but a lot of consumer grade UPS are sketchy like that.
 
I did that for years with a big 1400 VA Elgar sinewave UPS (still have it, if anyone wants to pay shipping). I replaced the 8 6V AGM cells with 4 12V garden-tractor batteries. I got about 5 years per set of batteries, which I guess is decent. When the utility moved the distribution facility just down the road from me, outages became pretty rare. I sold the gas backup generator that hadn't been used in years and took the big UPS out of the picture.
At about that time, my telco dropped their direct-to-CO copper hookup and installed a fiber-fed terminal. I went to VoIP for phone service because the telco was exempted from providing continuous service. That is, I couldn't make a POTS or VoIP phone call more than about an hour after power failure. I use a cell phone for emergencies--I get about a bar and a half 4G LTE, so talk and messaging work, but browsing is just about impossible. Hence, no need for round--the-clock TCPIP connection.
I do have another NSSI UPS that takes 3 6V AGM batteries, but I haven't bothered with it.

On my porch, I have 2 garden-tractor batteries that are trickle-charged by some PV cells, so if I get desperate, I can always hook an inverter to them and run that way.
 
Yeah Chuck I went the inverter route a couple years ago. We were away on vacation and we had a friend watching the house. They failed to tell us the power was out and the generator was running. Dont know how they could have missed the noise. Anyway, IT ran through most of our propane and ran for so long it burned up alot of oil. I had to get my generator rebuilt (generac) IT was an expensive situation and took a few weeks or maybe a couple months I forget to get fully operational again... We had a powerout yesterday and the generator stopped working again... ITs always something.
 
Chuck(G) said:
I got about 5 years per set of batteries
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That's about what I get from an electric lawnmower using lead-acid batteries. Been using one since the 90s, and 5 years seems pretty consistent. My current one uses three batteries, and it turned out that a box of four batteries cost only like two bucks more, so I need to find a use for the fourth. And while my current VDSL modem has a slot for a custom battery, I'm using one of those Belkin things instead. AT&T sent out a lot of them back ten years or so ago.

As for adding more batteries, series is of course Just Wrong. Parallel works when the batteries are charged, but now the charger has to charge twice as many batteries. At best this means twice the time to full charge, but at some point you could possibly overload the charging circuit into early failure. Lead-acid is probably more forgiving about unbalanced voltages, but usually it fails with one cell shorted, which is 2 volts difference. Lead-acid doesn't have overheating problems as far as I know, but lithium-based batteries definitely need thermal monitoring.
 
Bruce Tomlin said:
As for adding more batteries, series is of course Just Wrong. Parallel works when the batteries are charged, but now the charger has to charge twice as many batteries. At best this means twice the time to full charge, but at some point you could possibly overload the charging circuit into early failure. Lead-acid is probably more forgiving about unbalanced voltages, but usually it fails with one cell shorted, which is 2 volts difference. Lead-acid doesn't have overheating problems as far as I know, but lithium-based batteries definitely need thermal monitoring.
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The double charging time is what I assumed. I suppose initial shock of charged vs spent batteries was an issue. I had thought that maybe wiring them in Parallel and letting them equalize before connecting to the UPS charger would be a good idea,, but that might not really work.
 
VERAULT said:
So I have a few older APC UPS systems and lots of extra batteries. Where I live we get frequent brownouts. I have a SMART UPS 1500 with two batteries in it currently but I wanted to try wiring in some external batteries to it. I am assuming I need to add them in parallel as its currently running off the paired 24v battery system but I don't know for sure. Can I just add two more batteries in series to the two inside the unit?

I would love to here from anyone having experience with this type of thing. I know there are lots of articles about people connecting car batteries etc and I am not going that route. These are 12V UPS batteries that are not new by any means, I just want to get all the use out of them before they permanently deplete.

Would love anyone's take on on this.

There are tons of "tid-bits" on the internet about this but what is safe?:
Click to expand...

What is the load you are trying to power from this UPS, and how long would you like it to run for when the power goes down? These UPS units are all powered by 12V SLA batteries, and are only designed to run a few minutes. Yes you can extend their run time by connecting external batteries in parallel to their internal battery - but it takes a lot of batteries to get a substantial amount of run time if you are trying to power anything but a very light load. Unfortunately, these UPSs are also relatively inefficient when powering a light load.

To give you an example from my experience - I have a rack mount "extended run time" APS UPC that is specifically designed to be connected to external rack mounted battery cabinets. Mine is connected to two external battery cabinets, so there are a total of 50 12V 5.5Ah batteries powering this UPS. This powers a small desktop PC (no monitor) and 5 network cameras with a runtime of around 20 hours.

As you pointed out there are only tidbits of information posted on the internet from people who have extended the runtime of a small UPS unit by adding external batteries. The descriptions I have seen have involved use of APC's more robust 1500VA units, and not the smaller 700VA unit you are using. Powering these UPSs with a number of external 12V SLA batteries is safe, when those batteries are powering the UPS. What is harder to predict is what will happen when the power comes back on and that little UPS unit tries to recharge all the batteries connected to it - at best it will work but will just take a long time, at worst the UPS will fail because it is unable to supply the required charging current. As has also been pointed out good UPS units are usually designed to monitor their internal temperature as a safety measure, and will shut down if a high temperature (possibly due to a battery failure) is detected. The likelihood of this occurring is apparently small with 12V SLA batteries, but nonetheless you do lose this safety measure by using external batteries.
 
And while my current VDSL modem has a slot for a custom battery, I'm using one of those Belkin things instead. AT&T sent out a lot of them back ten years or so ago.
Click to expand...

I'm still using a Technicolor 2000 for my modem. A good reliable one, but I don't use the network hub in it, nor the WiFi AP. I use a separate router for that. Is yours the "bare modem" model? Does it work well on VSDL2? Do you think it'd work on a CenturyLink ISP connection?
 
hmb said:
What is the load you are trying to power from this UPS, and how long would you like it to run for when the power goes down? These UPS units are all powered by 12V SLA batteries, and are only designed to run a few minutes. Yes you can extend their run time by connecting external batteries in parallel to their internal battery - but it takes a lot of batteries to get a substantial amount of run time if you are trying to power anything but a very light load. Unfortunately, these UPSs are also relatively inefficient when powering a light load.

To give you an example from my experience - I have a rack mount "extended run time" APS UPC that is specifically designed to be connected to external rack mounted battery cabinets. Mine is connected to two external battery cabinets, so there are a total of 50 12V 5.5Ah batteries powering this UPS. This powers a small desktop PC (no monitor) and 5 network cameras with a runtime of around 20 hours.

As you pointed out there are only tidbits of information posted on the internet from people who have extended the runtime of a small UPS unit by adding external batteries. The descriptions I have seen have involved use of APC's more robust 1500VA units, and not the smaller 700VA unit you are using. Powering these UPSs with a number of external 12V SLA batteries is safe, when those batteries are powering the UPS. What is harder to predict is what will happen when the power comes back on and that little UPS unit tries to recharge all the batteries connected to it - at best it will work but will just take a long time, at worst the UPS will fail because it is unable to supply the required charging current. As has also been pointed out good UPS units are usually designed to monitor their internal temperature as a safety measure, and will shut down if a high temperature (possibly due to a battery failure) is detected. The likelihood of this occurring is apparently small with 12V SLA batteries, but nonetheless you do lose this safety measure by using external batteries.
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It runs my primary PC as well as my switches, router, cable moden. I get about 20 minutes off it now (with no monitor) Id like to double that.
 
hmb said:
As you pointed out there are only tidbits of information posted on the internet from people who have extended the runtime of a small UPS unit by adding external batteries. The descriptions I have seen have involved use of APC's more robust 1500VA units, and not the smaller 700VA unit you are using.
Click to expand...

Not sure where you got that info, as pointed out in the thread #1 I am using a APC Backups 1500
 
VERAULT said:
It runs my primary PC as well as my switches, router, cable moden. I get about 20 minutes off it now (with no monitor) Id like to double that.
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Your SmartUPS 1500 already has a couple of 12V 18Ah batteries. Adding several additional 12V SLA batteries in parallel to double the number of Ah (and double the run time) should be quite safe to do.
 
Chuck(G) said:
All of the VDSL2 modems I've seen for purchase seem to come with CenturyLink firmware, which is why I asked.
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I have a Pace/Arris modem (apparently they have Motorola heritage?) with wireless and voip. It has a tendency to freeze up every few months (won't even give dial tone), and sometimes it doesn't want to route between wireless and ethernet. Part of the routing problem is it will cache temporary IPv6 addresses, so on anything that I want to SSH into, I disable IPv6 randomization.

The past year or two it hasn't been so bad, so maybe some of that is updates, or maybe it's just me proactively rebooting the modem before I need it to behave. (I have times when I want to keep a certain game connected 24/7 for a couple of weeks, and that's when the modem loves to flake out.) It also takes like five minutes from cold boot to moving packets around.
 
Absent power outages, my Technicolor modem has never been (intentionally) rebooted. We had a brief power glitch a few months ago, so my modem uptime reads 100 days, 22 hours. Same reliability for my mailserver - a little headless Orange Pi PC running Debian.
 
I've had a bigger flooded battery hooked up to my APC backups 350 for the past 4 or 5 years. Seems to work just fine, only it seems there is a timer in the unit that will limit the run time, instead of running the battery dead. I think I only get about an hour or so out of it before it shuts off, and the battery appears to be well charged still. Maybe there's a setting to change that?
 
Bentendo64 said:
I've had a bigger flooded battery hooked up to my APC backups 350 for the past 4 or 5 years. Seems to work just fine, only it seems there is a timer in the unit that will limit the run time, instead of running the battery dead. I think I only get about an hour or so out of it before it shuts off, and the battery appears to be well charged still. Maybe there's a setting to change that?
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I cant speak for your unit but that seems strange. These things are meant to deplete down to almost nothing.
 
Problem with doing this on the smaller UPSes especially is they're not designed for continuous duty, they're only designed to run for a few minutes at most with a modest load on them.

Cyberpower units especially are bottom of the barrel garbage. I've had to repair more than a few of them with blown mosfets because they either didn't have heatsinks on them and were run too long, or had heatsinks but the factory didn't install thermal paste.

The bigger units with fans in them are better suited for running for extended periods of time, just make sure the fans aren't locked up, because they often get that way.
 
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