SMT1500 - battery drop when switching to backup

[Anonymous user]

Sorry if this has been asked before, I couldn't find a thread on it.

On my UPS the battery will read 100% whilst it is plugged in to mains - but as soon as it is unplugged the battery will then read 55-65%. Is this normal behaviour?

Cheers,

[BillP]

Hi,

That is not normal behaviour. How old is the battery pack and how old is the SMT? If the battery pack is more than 3 years old you should replace it. 

[Anonymous user]

Batteries are new, fitted to a second hand UPS. 

[BillP · Accepted solution]

Hi,

What is the load on the UPS while testing? It is possible that the batteries will discharge quickly with a heave load but not normal behavior to drop 40% in seconds. 

[Anonymous user]

Hey, so a load of maybe 4-600w, likely on the lower end of that. 

I do suspect however that it has something to do with load, at the moment I have a very small load (under 1%) and the same problem does not happen .

[BillP]

My SMT did this, when I checked the voltage it read 5 volts out so it wasn't charging properly, had to replace it.

[Anonymous user]

Cheers Gareth, how/where do I check the voltage? 

Cheers, 

[BillP]

Ideally with the covers off but on my smt2200i I could take a reading off the front battery packs and times it by 2 (you wouldn't have to times it by 2 on the 1500)

If you can't get probes into the battery plug you will need to take the covers off at your own risk remembering how much of it could kill you if you touched anything!

Compare the readings to the display values and work out the drift.

[Anonymous user]

Cheers Gareth,

I think I should be able to take a reading from the battery connection so I will give that a go before running it with its top off - I am roughly aware of the kind of current build up that must go on inside a UPS so shall have my sensible hat on should I have to run it without the top.

[Anonymous user]

Hi Gareth, 

Had a look at this today and with the unit plugged in my multimeter reads 27.69v. When unplugged the multimeter slowly drops quite quickly at first then slows down to about 25v. Dropping much more slowly after this point.

What display values should i be looking at and how do I work out drift. Sorry for the questions, trying to figure out of it needs to go back (it was cheap) or if it's fixable. 

Edit: should also mention the battery is showing 50%ish at the moment with no drop observed (but with no load). I will test again when it is at 100% with load. 

[BillP]

Compare the multimeter reading to the readout the UPS gives for the battery voltage, if it varies that is your drift.

[Anonymous user]

Thanks Gareth, 

So on mains the unit reads 27.3 and the multimeter 27.62. 

Similar drift when on battery. 25.6 on the multimeter 25.2 on the ups. 

I had left the unit charging as it was on roughly 50%. After just a few hours the unit read 100% charged, this seemed a little odd as lead acid takes time to charge. In any case I then left the unit unplugged before testing it again and when I then plugged it back in it was back down to reading around 50%. 

So something is definitely up here. 

[Anonymous user]

Just grabbed a quick video demonstrating what happens - it seems the battery percentage the unit reports is being affected by the size of the load on the unit.

When on battery turning the load on and off causes the battery charge status to go down and up.

Here is the vid:

[BillP]

May as well return it, not right when the battery drops like that.

[BillP]

Just to add, when mine was broken the battery pack would be 47 volts but the UPS thought it was 54 volts, you have no drift just knackered batteries by the looks of it.

[Anonymous user]

FWIW I don't think it's the batteries. The ups was bought without and they are new batteries from a reputable supplier here in the UK. 

I'll talk to the seller about a return. 

[Anonymous user]

From the UPS Front panel, did you tell the UPS that it had New batteries?

See what the UPS say the last battery change date was.

[Anonymous user]

Hey, yea new battery installed and date changed to reflect this.

I am just waiting for it to read 100% so I can do a run-time calibration via PowerChute as well.

[Anonymous user]

I ran a calibration test with roughly 50% load - the UPS this time dropped to around 50% (47 to be exact) like normal, but has not immidiately returned to 80+% upon removing the load - it has remained at 47% and charging.

So that's different at least - fingers crossed it means something. Not done the runtime calibration yet. 

[Anonymous user]

So... after the above mentioned Calibration test and then a runtime calibration the unit is much better... so much so that I think it will probably do me for the price I paid (under £80).

Now, with a 50% load if I unplug the mains the unit doesn't immediately drop, but over a few seconds drops to 85ish% - much better than before.

If I switch the load off and then back on again the unit does initially drop to 45-50%, but then builds back up again to around 85%.

I'll grab a quick video of the above to see if it looks more 'normal'.

[Anonymous user]

Here is the video of how it is behaving now: