Axpert inverter switchover times

D

Deckert

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Jan 13, 2004
Messages
386
Hi,

I was doing some run-down testing on my inverter today (for those that want to know, I got ~7.5 hours on an avg load of 900W with four 170AH lead-crystal batteries - yes I fully discharged them for this test).

However, I also grabbed my oscilloscope and measured the switchover times (from Eskom to inverter and back). Also measured the delay time the UPS includes before it switches back to Eskom.

Now, in UPS mode, the manual quotes 10ms switchover, but here are my results (have a look at the delta-T values in the top-left corner):

Switchover from Utility to Inverter

axpert-switchover-time.jpg

Fallback from Inverter to Utility

axpert-fallback-time.jpg

As you can see, both times are 28ms. Longer than what the manual quotes, but it seems good enough for all my electronic kit to survive the switchover time. Note the slight ramp-up in voltage when the Inverter gets going.

The inverter introduces a 6 second delay before it switches back to mains after Utility power is back. Presumably (and sensibly) this is done to wait for the Utility power to stabilise, as I've seen some horrible spiking on the mainline when the power comes back to 20,000 houses all at the same time:

axpert-fallback-delay.jpg

I didn't do any tests in APL mode (really don't see the need to). I used a 28V isolated step-down transformer to measure the output (hence the slightly distorted sine wave). The inverter sine wave output is 100% pure.

What is also interesting is that it appears that there is some sort of phase-sync going on (the Utility waveform is in phase with the inverter output). I repeated the test 3 times just to be sure - maybe I was just lucky in that the inverter wave clock happened to be in sync with Eskom.

--deckert
 
Last edited:
S

Scavenger

New Member
Joined
Oct 12, 2006
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2
Hi,

Interesting. The Axpert will be fine for general home appliances, but for a PC, server or other sensitive electronics the transfer time is too high. I'd rather go with a UPS that has a transfer of 2-5ms as I have a large media/file server in my house with 2x gaming PC's.

So much for getting the Axpert. So far I am looking at a Tescom SSPRO3000VA and it comes with either 3 or 6 x 102ah batteries. It has a 4ms switchover, which is great.

Thanks, you've answered my question about which to get now!
 
Gnome

Gnome

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Getafixx

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Scavenger said:
Hi,

Interesting. The Axpert will be fine for general home appliances, but for a PC, server or other sensitive electronics the transfer time is too high. I'd rather go with a UPS that has a transfer of 2-5ms as I have a large media/file server in my house with 2x gaming PC's.

So much for getting the Axpert. So far I am looking at a Tescom SSPRO3000VA and it comes with either 3 or 6 x 102ah batteries. It has a 4ms switchover, which is great.

Thanks, you've answered my question about which to get now!
Click to expand...

My Axpert powers the TV, router, wi-fi, PC, PS3 etc. No problems with switch-over.
 
The_Traveller

The_Traveller

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Aug 9, 2008
Messages
3,476
Deckert said:
Hi,

I was doing some run-down testing on my inverter today (for those that want to know, I got ~7.5 hours on an avg load of 900W with four 170AH lead-crystal batteries - yes I fully discharged them for this test).
Click to expand...

7.5 hours is not really grand for Lead Crystal if the claims are you can fully discharge them. You'd get 6 hours with a VRLA discharged to 50%-60% of capacity.

You sure your batteries were fully discharged or your inverter just cut off at a certain voltage ( 10.5V / 42V ) ?
 
D

Deckert

Well-Known Member
Joined
Jan 13, 2004
Messages
386
Scavenger said:
Interesting. The Axpert will be fine for general home appliances, but for a PC, server or other sensitive electronics the transfer time is too high. I'd rather go with a UPS that has a transfer of 2-5ms as I have a large media/file server in my house with 2x gaming PC's.

So much for getting the Axpert. So far I am looking at a Tescom SSPRO3000VA and it comes with either 3 or 6 x 102ah batteries. It has a 4ms switchover, which is great.
Click to expand...

I run a server cabinet (Cisco kit, D-Link switches, two servers and a firewall) on the Axpert and they have no issues with the switchover time. My desktop has always had an APC UPS, even before I added the Axpert - added protection. Think of it this way: 28ms is just over one cycle, which happens 50 times a second. If your kit cannot withstand that, maybe you should be looking at alternate kit? ;-)

Is the Tescom switchover time tested or are you going on the marketing material?

--deckert
 
D

Deckert

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Joined
Jan 13, 2004
Messages
386
The_Traveller said:
You sure your batteries were fully discharged or your inverter just cut off at a certain voltage ( 10.5V / 42V ) ?
Click to expand...

The battery has a very extensive datasheet. The 100% DoD data shows a lifetime of >600 cycles - so this was a once-off test. Lesser depth of discharge renders substantially higher cycle times:

170ah-lead-crystal-life.jpg

The datasheet also lists the end-voltage per cell (each battery has 6 cells). At 8 hours and a constant current discharge of 20.15A, the end-voltage per cell is listed at 1.85V, which totals 11.1V per battery. That's where I stopped my test, when the set reached 44.4V. During my test the discharge current was slightly higher than 20A.

--deckert
 
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