Upgrading to a large external UPS battery

[shiftline]

Is there any issues with adding a much larger battery to my UPS?  I have an older APC 1500 ( with 2x 7AH batterys)  I want to hook it up to a 147AH sealed led acid battery.. its the same chemistry and should eb the same float/charge voltages.

Aside from taking ages to re-charge would there be any issues doing this?

[alank2]

I've done it with no problems.  I had a large SLA battery and decided to put it to good use.

[johansen]

if you install a ferrite inductor in series with the secondary (low voltage side) of the main transformer in your apc unit you will save about 10$ a year in electricity. last time i did this i used 7 turns on a 1 inch diameter ferrite core, with a paper thin air gap.

also recommend replacing the 10 gauge battery cables with 8 gauge if you load it more than 1kw.

[shiftline]

Thanks for the tips.  Sounds like there shouldn't be any issues.   Good tip on increasing efficiency!

[nctnico]

I'd check the charge voltage. APC UPSs are notorious for cooking the batteries due to a way too high charging voltage. AFAIK there is a mod for this.

[wblock]

I'd check the charge voltage. APC UPSs are notorious for cooking the batteries due to a way too high charging voltage. AFAIK there is a mod for this.

The crappy "home" units are famous for that.  And maybe the really old higher-end units.  But my Smart-UPS 1500 from 2003 was dead on, and so are the few other Smart-UPS units I've checked.  Still, knowing for sure is worthwhile.

[BradC]

I'd check the charge voltage. APC UPSs are notorious for cooking the batteries due to a way too high charging voltage. AFAIK there is a mod for this.

The crappy "home" units are famous for that.  And maybe the really old higher-end units.  But my Smart-UPS 1500 from 2003 was dead on, and so are the few other Smart-UPS units I've checked.  Still, knowing for sure is worthwhile.

Pretty much all Smart-UPS units were dead on from the factory. Unfortunately over time the voltage divider resistors drift and it does not take much drift to push the voltage up a couple of hundred mV. They all have a resistive divider which provides the battery voltage into the charger ASIC. This must be 5.00V at your desired float voltage. It's a pretty cheap fix for an older unit to replace the divider resistors with newer and more precise units. There are plenty of web pages around with instructions on how to change the float voltage in software, but they are all pretty much wrong. They'll change the way it reports voltage, but the charge voltage is set in hardware.

[Don Hills]

Not all UPSes can use a higher capacity battery. Many small units don't have proper heatsinking - they use a block of aluminium instead of fins and a fan, and depend on the battery giving out before the heatsink gets too hot. If you increase the run time, it will overheat.

[station240]

Get a suitable DC rated circuit breaker to put near the batteries. That way there is a safe way to isolate them for testing or relocating everything.

[cs.dk]

if you install a ferrite inductor in series with the secondary (low voltage side) of the main transformer in your apc unit you will save about 10$ a year in electricity. last time i did this i used 7 turns on a 1 inch diameter ferrite core, with a paper thin air gap.

I'm just courious, but what different does it make to stick a ferrite on the secondary? I don't understand it

[SeanB]

A caution is many of the cheap UPS devices also have no isolation, so the battery is connected to either one side of the mains, or is on a rectified mains supply. Treat the battery cabling as if it is mains connected, and put the external batteries in a plastic box suitable for mains use.  In the space vacated by the battery put a high value electrolytic capacitor, 10 000uF 25V or so for a 12V unit, to provide local decoupling for the UPS, and use 4mm wire to connect the external battery pack. Inside there is now room to add a 12VDC 80mm fan, powered by the battery, to cool the inside of the unit. Place so the fan cools the transformer and the heatsink of the power devices, and if you have the ability add an extension to the heatsink to improve the cooling, but make sure it does not foul anything.

Still not going to be a great UPS, just a better cheap one, which will run longer. Done that, and it has improved runtime to around a hour, though I am using 10 7Ah SLA packs in parallel, used ones but still reasonable.

[wblock]

Pretty much all Smart-UPS units were dead on from the factory. Unfortunately over time the voltage divider resistors drift and it does not take much drift to push the voltage up a couple of hundred mV. They all have a resistive divider which provides the battery voltage into the charger ASIC. This must be 5.00V at your desired float voltage. It's a pretty cheap fix for an older unit to replace the divider resistors with newer and more precise units. There are plenty of web pages around with instructions on how to change the float voltage in software, but they are all pretty much wrong. They'll change the way it reports voltage, but the charge voltage is set in hardware.

Hm, just checked my SUA1500 and it has drifted up.  Haven't disconnected it yet, that'll be a project.  From photos, the original resistors were standard 1% precision types--what would be a better replacement?

[edpalmer42]

I agree with Don Hills.  When you add bigger batteries, the heatsinking may not be adequate.  Also, the charging circuit probably won't be able to recharge the batteries in a reasonable time.  The charger could actually burn out trying to charge a big battery!

The problem with trying to set the charging voltage is that it's temperature dependent.  Cool room, warm room, idling, full load, what voltage do you use?  Better UPS systems use a different charging method.  The typical system uses a current limited charge, then constant voltage (aka float) charge.  The better systems cut off the constant voltage charge after a couple of weeks and then just monitor the battery voltage and recharge as necessary.  Instead of a battery life of maybe two years, you get a battery life of more like 5 to 7 years.

I think I heard that some of the newer APC units used this type of modified charger, but I haven't looked into it.

Ed

[johansen]

if you install a ferrite inductor in series with the secondary (low voltage side) of the main transformer in your apc unit you will save about 10$ a year in electricity. last time i did this i used 7 turns on a 1 inch diameter ferrite core, with a paper thin air gap.

I'm just courious, but what different does it make to stick a ferrite on the secondary? I don't understand it

further testing should be done to investigate, you can read about my experiments here:
http://www.fieldlines.com/index.php?topic=148266.0

oztules, reports that adding an inductor to his custom wound toroid transformer (in his 6kw inverter, but it might be 15, i cant recall) reduces no load idle watts from 200 to 20 watts.

[BradC]

Hm, just checked my SUA1500 and it has drifted up.  Haven't disconnected it yet, that'll be a project.  From photos, the original resistors were standard 1% precision types--what would be a better replacement?

A pair of 1% resistors that are closer to value

Oddly enough one of the schematics I have for an SUA2200 has the main high value divider listed as a 0.1% resistor (I suspect its a typo but it's there). My 2200 is currently reading the load about 30% high, so grossly underestimating the runtime. It looks like the capacitor in the CT burden circuit is drying out, so when I take it down to service it I'll do the divider resistors at the same time. Mine is less than 100mV up and I have 4 years on this battery set so far.

Outside of gross over or undercharge, the biggest factor on UPS battery life is the quality of the battery. Generic replacements just are not as good as either CSB or Vision batteries. I seem to get better life out of CSB.

[DanielS]

Generic replacements just are not as good as either CSB or Vision batteries. I seem to get better life out of CSB.

When you compare the 15 minutes rating of CSB batteries to most other generics, it becomes quite obvious that most generics are simply not intended for applications more intensive than 1-2h discharge - they lose effective capacity two or three times as fast.

[wblock]

After swapping out my SUA1500 floor model for an SUA1500RM2 rack-mount, it appears that the only schematics I've found might have nothing at all to do with this model.

Can anyone point me to a schematic of the SUA1500?  Or at least verify exactly which resistors and values are the voltage divider in this model.  Right under VR1, R118 is 22.6K (label 2262, so pretty good), R119 is an inch away next to the QFP and labeled 1002.  It's only reading half that, but it's in circuit (no, I'm not going to pull it without a replacement and a reason to believe it's the right one).  R124 is right next to R118, labeled 1302 but reading 12.86K.  1.1% high, maybe it... Another chance to use this smiley: 

Photo: (yes, the solder on R118 looks a little dented from probes being jammed through the flux on it):

[BradC]

I can't help you with a usable schematic I'm afraid. My small unit is a SU1400 which is the model before yours and the schematic I have is for the model before mine. It will be a 24V unit though, so your divider resistors are 22.1K & 100K. My schematics have them listed as R118 & R119, but that's not right on my unit either. My SU2200 is the last through hole version (schematics are correct for that) and the SU1400 is the first SMD version (I don't have an accurate schematic for that).

See if you can find the charger ASIC and have a poke around pin 13. That is the voltage input after the divider. Maybe you can work backwards from there.
When you find the 100K resistor, you should have ~27.x volts on one side and 5.00V on the other. The 22.1K will have 5.00V and 0V respectively.

[moya034]

For a while now I've been using a 12v battery bank with a Samlex Battery Charger (configured to charge a battery bank with a load attached) as a "DC UPS" for my ham radio gear, LED lighting in the shack, and just about anything else that can run off 13.8v Samlex makes these units in 15, 20, 50, and 80 amp models. You can have as big of a battery bank as you can afford!

I have been wanting to use another large battery bank and higher current Samlex Charger to run my FiOS gear, networking equipment, and servers as follows:

• Power Stream makes ATX PSU's that accept a 9-18 VDC input voltage.
• For mini-ITX motherboards there are the Mini Box 160 watt PSU's. These however require a 12v REGULATED input as the 12v input goes right to the +12v power rail, so you would need a DC-DC converter to hook it up to your battery bank.
• All your other devices like switches or WAP's that have wall worts, may run off 13.8v directly or custom power supplies can be made.
• Anything that absolutely must have have 110v ac can run off a Power Inverter. (Only thing I can think of in my application is the monitor)

[wblock]

See if you can find the charger ASIC and have a poke around pin 13. That is the voltage input after the divider. Maybe you can work backwards from there.
When you find the 100K resistor, you should have ~27.x volts on one side and 5.00V on the other. The 22.1K will have 5.00V and 0V respectively.

I did find a schematic by searching on the board number, 640-7732H... Aha, pin 13 of IC21, like you say, goes to R216, 100K, 1/8W, 1% to VBAT, and R184, 22.1K, 1/8W, 1% to ground.  R184 is reading 20.62K.  R216 is reading 69.7K, but that's in circuit.  Now to decide whether to patch on some nice higher wattage stick-through resistors, or do it neatly with SMT 0805s.  Thanks!

[shiftline]

So I popped open my UPS and it had the 2 batteries wired in series for 24v (I guess I need to add a second giant battery!)
 The cooling seems a little lacking. I may put a 120mm of fan in the old battery area to provide some better cooling. The two exhaust fans are pretty tiny

The heat sinks are solid chunks aluminum and seems Cool to touch however I feel a lot of heat coming from the transformer. 
Is there anything I should be enhancing for cooling aside from a possible fan addition?







If I add a fan or two into the battery compartment would it be better to push air in it suck it out?

[BradC]

So I popped open my UPS and it had the 2 batteries wired in series for 24v (I guess I need to add a second giant battery!)
 The cooling seems a little lacking. I may put a 120mm of fan in the old battery area to provide some better cooling. The two exhaust fans are pretty tiny

The heat sinks are solid chunks aluminum and seems Cool to touch however I feel a lot of heat coming from the transformer. 
Is there anything I should be enhancing for cooling aside from a possible fan addition?

That does not look like any SmartUPS I've seen. Is it a BackUPS by any chance?

There is a significant difference in firmware. The BackUPS is hard-coded to work with the battery capacity it is designed for. The SmartUPS is adjustable for battery capacity. The problem with the BackUPS is the thermal design is for a very limited runtime, and without significant upgrade you will literally cook it both charging a big battery bank and running an extended runtime. The transformers in the BackUPS are designed right on the thermal limits, and as you see there are tiny little heatsinks on the switching FETs. The SmartUPS transformers have a significantly bigger core with both more thermal mass and a larger surface area to dissipate the heat, and the switch gear has heatsinking designed to be efficiently air cooled rather than relying on convection and thermal mass.

If you plan on putting bigger batteries in that unit, you want as much airflow over both the transformer and the heatsinks as you can muster, and both for charging and discharging. Additionally, the on-battery runtime is going to be a bit unpredictable as the firmware won't and can't adapt to a larger battery, so it relies solely on voltage. If you use the comms interface to remotely shutdown your systems, you might find the systems shutting down well before the battery is exhausted as the firmware knows that at X load you get Y runtime from the designed battery capacity.

I tried extending a BackUPS 650 for a while, but ended up picking up an old SU1400 on E-bay. A much better solution for an extended runtime when you want the software to do what it is supposed to do, properly.

[shiftline]

Yes it's a BackUPS


So it's hard coded to to turn down after a specific time rather than the the actual battery voltage?

Well that may be a problem!

The actual load would be low as its running fish tank pumps which I could wire directly the batteries. (2x 12v pumps and 1x 24v pump.) a controller and possibly a heater or led light would be the only thing plugged into ups for a draw

I'm sure this isn't much better but I also have one of theses. BackUPS as well


Or would I be better off just using a trickle/float charger and wiring the pumps directly to the battery(s) and skipping the UPS?

[BradC]

So it's hard coded to to turn down after a specific time rather than the the actual battery voltage?

No, its just that the runtime estimation is a relatively complex calculation and the battery capacity component of that is generally hard coded in the BackUPS series, so it's not likely to get it right. As I said before, it's only important if you are using the comms interface to remotely shutdown a PC. The UPS will keep on running until the battery goes flat, and for a dumb load (like your fish tank gear) it should all keep on trucking quite nicely.

With such a low projected load, the issues I raised about heat will be a lot less while in discharge mode, but you'll have heat problems while charging so you'll still need some good cooling. You might be better with a smaller unit (like my aforementioned 650) as they are 12V units and you'll only need the one battery. Cooling problems are the same though.

[shiftline]

Is it worth going the float charger route instead?  I could run the essentials off 12v the 24v stuff is more of a nice to have.  The max load of nice to have on outlets would be a couple hundred watts and the rest could run off batteries

Assuming I use the UPS
For cooling I could do a fan blowing (or sucking ) across the transformer and possibly one on top of if the unit



Or if you think I'm better off with a single battery unit this 550 ($25!) would prob work?  I really only need the charging circuit and some plugs to run a few hundred watts of dumb load. 


Or spend 120 on a used smart ups..

I just want to make sure I come up with something reliable and safe


Ps thanks for all the help on figuring this out