# How to test UPS battery capacity to judge replacement?



## lumen aeternum (Nov 1, 2012)

Slightly OT... I have several Uninterruptible Power Supplies for computers and they have replaceable batteries (sealed Pb acid ???) since they go bad after a year or three.

So what is the easiest way to see how many amp hours capacity they still have? Hook up an incan bulb & time it? Something faster? (how many Amps is a 60 watt incan anyway...).


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## ChrisGarrett (Nov 1, 2012)

I replaced an APC 500 7Ah battery a month back and ran an 100w ican for 20 min before the alarm started spazzing out.

W/voltage = current

60w bulb at 120v is .5 amps. Remember, you'll be losing some energy through heat, but I'm not sure that matters too much.

A 100w bulb draws .833 amps, IIRC.

Chris


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## lumen aeternum (Nov 1, 2012)

100/120 = .833, yea.

But 7/.833 = 8.4 hours. So why did your low batt alarm sound after only 20 minutes?

Searching for replacement batteries I find a site that sells 4 different "smart" SLA chargers, for different Ah capacity ranges. A user review says it has a light that indicates a bad battery... wish I could find something that tells me the actual Ah it charged to.

Know any brands of UPS that have a button to silence the alarm? The new ones all seem to beep every 30 seconds. I have a very old APC brand with a button (& a test button too).

Need one UPS on the DSL modem and another on the TV & DVD recorder, because we get frequent momentary power dropoffs that are just enough to reset the moden, lose the channel lock, and screw up a DVD being recorded.

How can I recharge these things from a car battery? Have a marine battery hooked to an inverter/switch to keep the pellet stove working, but its far away from where the UPS are needed. Hate to plug in a charger to the inverter -- what a waste going from marine battery DC to AC then right back to DC...


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## AnAppleSnail (Nov 1, 2012)

Why are you charging a UPS from a battery? In an extended power outage I think it's worth switching to ” that” battery.


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## LowLumen (Nov 1, 2012)

lumen aeternum said:


> 100/120 = .833, yea.
> 
> But 7/.833 = 8.4 hours. So why did your low batt alarm sound after only 20 minutes?
> 
> ...



You have to convert that current (at 120V) to the 12 volt battery source current (*10),, .... + extra current for the inverter efficiency of less than 100%


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## Lynx_Arc (Nov 1, 2012)

I think you have to first figure out the battery configuration of your UPS some have 1 single battery some 2 in series and perhaps some even more. I have a UPS that uses 2 6v batteries in series and some that use single small 12v batteries and another that uses 2 12v 7Ahr batteries. Once you figure out how the batteries are set up that is your reference voltage be it 12, 24, or more. A UPS tends to output about 120v but you can measure the output of yours to make sure. Take a known load and using it see how long it runs and then get the watt hours or volts*amps*hours and then divide by the battery setup voltage reference. For example if you have 120v for 30 minutes at 1 amp that is 120*1*0.5 or 60watt hours. if your source is a single 12v battery dividing it by 12 gives you 5 which would be amp hours. If the reference is 24v then it would be 2.5 amp hours. 5Ahrs may be fine as there is some efficiency lost and batteries age but 2.5Ahrs would be no good for a 7Ahr battery setup.


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## Norm (Nov 1, 2012)

lumen aeternum said:


> 100/120 = .833, yea.
> 
> But 7/.833 = 8.4 hours. So why did your low batt alarm sound after only 20 minutes?



.833A at 120V, don't forget your drawing current from a 12V battery not from a 120V supply. You also need to allow for losses in the UPS.


Norm

Looks like Lynx_Arc beat me to it.


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## Lynx_Arc (Nov 1, 2012)

lumen aeternum said:


> How can I recharge these things from a car battery? Have a marine battery hooked to an inverter/switch to keep the pellet stove working, but its far away from where the UPS are needed. Hate to plug in a charger to the inverter -- what a waste going from marine battery DC to AC then right back to DC...



I don't see a point in trying to recharge batteries most UPS' have charging circuits in them to do that if your power is going to be off longer often time to get a larger ups on the items that cannot last long enough. Most likely the built in charging circuit will take half a day to recharge a UPS that uses up all its power such that trying to run an inverter to power that UPS to recharge it will have the power back on before you are done. I don't recall the max speed you can recharge SLAs but if you try and charge them too fast it reduces the life of them and for the most part their lives are seemingly too short anyway for the most part.


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## lumen aeternum (Nov 1, 2012)

AnAppleSnail said:


> Why are you charging a UPS from a battery? In an extended power outage I think it's worth switching to ” that” battery.



Because the stove is in a different part of the house from what I need to power with the UPS (the DSL modem).

WRT recharging the UPS battery in an outage... yea the unit itself or a dedicated SLA charger would probably be very slow if I plugged them into the inverter. That's why I'm asking if there is a setup to hook the dead 12V UPS battery to the marine battery with suitable diode or current limiting electronics in between.

The SLA charger seems inexpensive, and I could keep a spare UPS battery charged up, and hopefully get one fancy enough to tell me when the battery is only holding 75% of its charge, which would probably be worth buying a new one.


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## mattheww50 (Nov 2, 2012)

Several points. 
1). SLA chargers tend to be pretty simple devices, basically constant voltage supply with a series resistor to limit current.
2). SLA's don't like being fully discharged, in fact it is often 'fatal', so most UPS's will shut down before the batteries are completely discharged.
3). SLA's have a very finite life expectancy. Charging slowly removes electrolyte from a battery that doesn't have a lot to begin with, and lacks anyway to replenish. 
so with age the capacity drops off, until at somepoint between 3 and 5 years the battery will be essentially useless. IF the battery gets used extensively, the life tends to be even shorter.

I suppose the good news is SLA's are pretty cheap compared to more exotic battery technologies.

There are 'faster' chargers for SLA's, or at least are designed to be capabled of properly charging them at reasonably high rates. Check out the Schumaker SSC-1000A, which has a specific setting for Sealed Gel Cell (SLA) batteries.


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## glasssplinter (Nov 2, 2012)

Some other points to consider as well. 

If this is a smaller unit most of them do not have fans in them. Hooking up a battery with 10 times the capacity will certainly warm the unit up beyond what it's made to handle. You need to start with a good APC unit that can handle extra battery packs first or has internal cooling.

The unit can't handle charging the larger battery. Could be remedied if you're using another charger on it but it is already becoming complicated.

Overall if you're running into issues where you have extended outages, I think the best option would be to get a unit that powers everything for 20 mins or so. APC powerchute software will automatically calculate it based on load. Then get a small generator that you can plug everything into. Batteries to run things for extended periods start getting real expensive real fast and you still have the problem that they only last 3 years or so.

APC also has models that will display runtime on them and also test the batteries.


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## lumen aeternum (Nov 2, 2012)

Glass : Well, I'm not proposing hooking up the marine battery to the UPC in place of the SLA battery. Not gonna hump that monster up the stairs! Want to charge the SLA battery by hooking to the marine battery.
***

Maybe the best solution would be to figure out how to hook up my Ryobi power tool Lithium or NiCad battery packs to the UPS instead of the SLA???

The "One Battery To Rule Them" concept -- can the Ryobi power everything I might need?
***

The SLA chargers say "The Smart charger is designed for small to mid sized 12 volt lead acid batteries with 3-stage charging control to ensure the battery is charged fully without damage." Not sure if I'm allowed to show the link to the seller...
A reviewer said:
"2 Color Indicator Light

3 Stage Charging
Overcharge Protection

We require several uninterruptible power supplies (UPSes) for our various computers and equipment, from basic to deluxe multi-cell systems. We always keep at least a few replacement batteries on hand, and switch them around for wear leveling of have them as spares. To protect the sealed lead acid (SLA) cells from discharge and sulfation, while sitting in storage, we periodically hook them up to a charger. This little top-up charger is a nice addition or backup to our regular SLA charging system.

Unplugged, attach the clips and the LED indicator will show if it's still good. Plugged in, the indicator light is red when charging, and green after it has fully charged and has stopped."


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## lumen aeternum (Nov 2, 2012)

Arrggh... a little after dinner electrical math... what's killing me here is the gross inefficiency of converting the APS battery to AC so I can plug in a transformer that outputs DC to the modem...

The modem transformer outputs 10.5 V at 900 mA. So tiny draw from the modem. Not efficient at all; transformer draws 16 Watts to give 0.9 !!!

How can I just hook up the 12v APS battery directly to the wire (tapping into the transformer wire) ? I presume I want to limit the voltage so I don't fry the modem with 12 V.

Or better, the 18V Ryobi battery pack.

Can I buy a piece of equipment that will take 12v and allow me to select the output voltage, up to some not very high wattage?


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## Norm (Nov 2, 2012)

lumen aeternum said:


> How can I just hook up the 12v APS battery directly to the wire (tapping into the transformer wire) ? I presume I want to limit the voltage so I don't fry the modem with 12 V.



Search Ebay for "Lm2596 power step-down module dc 4.0-40v to 1.3-37v adjustable led voltmeter 2A"

Norm


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## Illum (Nov 2, 2012)

UPS's don't have a dedicated charger for its batteries, it seems after the first cycle the batteries never seem to match its initial performance... as if the battery never gets a full charge. APC, cyberpower, etc... don't matter. Now I manually top off my UPS battery following an extended outage. For bigger batteries [>10AH], I charge it with a 3A charger to bring it back up as quickly as possible.


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## lumen aeternum (Nov 2, 2012)

Norm said:


> Search Ebay for "Lm2596 power step-down module dc 4.0-40v to 1.3-37v adjustable led voltmeter 2A"
> 
> Norm



Fantastic. Found a site a bit cheaper than ebay too, but the operating logic seems a bit different. Also they have different configurations for the min/max voltages.

So is this the guts of a car flashlight battery charger?


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## hank (Nov 2, 2012)

> hook the dead 12V UPS battery to the marine battery
RV setups for multiple batteries are worth a look. This is expensive but meant to keep a poor battery from killing a better one when left unattended: http://www.redarc.com.au/products/product/dual-sense-smart-start-sbi-12v-100a/


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