Inverter + UPS question

[StNick]

Hi all,

We have two servers that sit on 2 x 1400kVa Meissner UPSes. These are able to give approximately 45 minutes of power during load shedding.

We have recently bought a 1kVA inverter (modified sinewave type) and a 102AH battery with the grand idea that when the power goes off, we simply plug the two Meissner UPSes into the inverter and power it up, thereby avoiding the need to reboot the servers.

HOWEVER, our plan is flawed... When we power up the inverter, the two UPSes do not accept this as a "sufficient" input signal, and they refuse to switch back over from battery to AC. I am assuming that this is due to the fact that our inverter is putting out a modified sinewave rather than a true sinewave.

If we take the UPSes out of the equation, the inverter powers the servers just fine for about 3.5 hours, but I would ideally like to avoid having to shut down three times a week.

Can someone in-the-know advise me if there is anything that I can do with our current setup to achieve the best results.

 

[.Froot.]

It is a lot safer to use a pure-sinewave rather than a modified sinewave signal (the extra price is worth it, as the frequency and everything is exactly as the AC power should be).

What is the power consumption of the two servers? The inverter should be about 15-30% (preferably 50%) more powerful than the power required (ie if the two servers use 500W each then you need 1000W+~50% = 1500W or 1500VA inverter). The problem could be due to insufficient current flow in your circuit.

<This topic has been discussed here>
Another solution to your problem, but which however I cannot professionally advise because it would void your UPS'-warranties, is to replace the UPS batteries with the 102AH deep cycle batteries. This would in effect create a superlong-online UPS which would otherwise work as normal.

 

[PrivateInSa]

Yhe UPS requires 1.5 kva x 2 to charge = 3KVA your invertor is only pushing 1 KVA and therefore the UPS's wont charge, try it the other way around

 

[StNick]

Thanks for the info... I've considered the 2nd option of yours before, but would the charger in the UPS be sufficient to charge the big 102AH battery?

 

[.Froot.]

It should be able to, it will just take a really long time (A UPS usually has a charge time of 3-4 hours depending on the battery), so say about 12hours maybe. The UPS's documentation might say what it's charging current is (in Amperes). So divide the 102AH/Charging current==time in hours).

 

[StNick]

Okay, lemme fiddle. I'm sure I can sacrifice a UPS for this experiment.

Thanks again!

 

[.Froot.]

Okay, lemme fiddle. I'm sure I can sacrifice a UPS for this experiment.

Thanks again!

No problem. You can't really mess this up, just disconnect the small batteries and connect the deep cycle battery in the same way. Just don't reverse the voltage and you should be fine.

 

[killadoob]

how much do inverters cost?

 

[.Froot.]

how much do inverters cost?

JFGI. I did it and here's an answer. http://www.bushpower.co.za/products.asp?pc=3

It depends on whether you go for a modified or pure sinewave signal (pure is better for electronic equipment such as clocks, computers, anything that uses clock signals, etc). Then it also depends on the power it can supply. If you need something to power a 500W appliance, add 30-50% and thus you need a 750W/ 750VA inverter.

 

[StNick]

Okay, so we connected one of the 102AH batteries to a 650va UPS and it worked just fine... There was a BIT of smoke from the cables we used (lol), but after doubling up on those, it wasn't too bad. This was a REALLY cheap UPS btw.

I'm now running BOTH batteries in series on a 1kVa UPS, and so far it has been going for just over an hour without any sign of giving up the ghost. I might add a little fan to move some air over the heatsinks on the transistors. That should do it.

The only question-mark that remains is whether this UPS will be able to charge these two batteries...

 

[.Froot.]

The UPS will be able to. Go YouTube it and see. Many people do this. A retailer I talked to said he would "advise me to use the bigger battery in the UPS although it would void the warranty (thus at my own risk)".

One thing I did not mention, and my apologies for that. You need thicker cables to connect to the batteries. Have a look at jump-start cabling or even welding cables if you want to. The current is too high for the puny wiring the UPS has installed.

 

[StNick]

Well, I'm over it.

The UPS we used crapped out. It just got too hot and started making TOO much noise for me to feel safe about putting it in our server room as a realistic alternative.

Anyone wanna buy some virtually brand-new equipment?

 

[Gnome]

Well, I'm over it.

The UPS we used crapped out. It just got too hot and started making TOO much noise for me to feel safe about putting it in our server room as a realistic alternative.

Anyone wanna buy some virtually brand-new equipment?

Classifieds FTW

 

[.Froot.]

Did you replace the battery cables with super-thick cables? Because if you don't you pretty much have a 4A current that is bottlenecked by a ~1A cable and that creates heat. This is the only change that has to occur if you want to use the deep-cycle batter in the UPS.

 

[StNick]

I admit, we didn't change the cables, and you ARE right...

However, the heat from the transformer alone was melting the plastic! I just don't think it is designed to operate for such a long period of time without extra cooling (ie. better heatsinks + fans).

Anyway, we just bought ourselves a 50kVA generator at an auction, so that should do it.

 

[.Froot.]

Sounds like a plan.... Just get a voltage stabiliser or a decent surge-protector. Generators are notorious for irregularities when it comes to voltage and as I can see you only want the best for your servers.

 

[Gnome]

Sounds like a plan.... Just get a voltage stabiliser or a decent surge-protector. Generators are notorious for irregularities when it comes to voltage and as I can see you only want the best for your servers.

Depends on the generator, Honda generators generally provide more stable power than power station do down in the US. At least the review I saw that was apparent from the oscilloscope and it was second only to a APC sine wave UPS.

Also 50kVA units aren't the cheap crap you buy from Builders Warehouse, likely a Diesel Volvo unit or similar, doubt the power coming from that thing is going to be outclassed by Eskom's power as of late.

 

[StNick]

This thing is a beast. It's getting wired up today, so I'll let you know if we fry our entire office. :-/