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UPS fast Switching than inverter

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ismu

ismu

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Can anyone say How will ups switch faster than inverter to prevent PC restart,
How can it change in switchig section on microcontroller programing when compared to inverter.
 

Dear ismailpp2008
Hi
In fact we have 2 family for UPS systems that are off line and online . for PC , we have a time about 5ms to prevent turning off ( the delay of relays is about 50 ms , so relays are not good . ) you can use triacs or IGBT collections to recover the PC.
Best Lucks
Goldsmith
 

Sir
But Now there are somany varietys of UPS in market , all are by using MOSFET (for ac pulse generation) and relay (For switching).How can it possible , i mean i want to know how a ups can switch to battery backup when main supply at OFF, fastly
without reboot PC.
 

Again Hi
As i know , it is impossible to use relays , as fast switches ! ( perhaps the type of relays are different ( e.g at speed ) and i don't know).
And about mosfets , many of UPS , systems , are based on IGBT (for very high powers ).
Best Lucks
Goldsmith
 
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Most common UPS-es use MOSFETs for the power converter section and relay for switching. There are relays that can switch fast enough to prevent the PC from shutting down.

In the coding section, you need to check the mains periodically - if it is present, if the voltage is adequate, etc. You may do this every 1ms and then decide if you need to stay in mains mode or switch to inverter mode.

In simple inverters, what is commonly done is - mains is checked, then all actions are done for one cycle, eg generation of both PWM signals for AC generation in inverter mode or required actions for charging in mains mode, then again, mains is checked. By this time, there has been more than enough time for the PC to shut down.

Hope this helps.
Tahmid.
 
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All PC SMPS supplies have big filter capaciors at Input. These Capacitors hold charge from 25 ms to 45 ms on load of 300 to 500 watts. When the mains power goes off relay switches battery power to inverter and inverter gets on, generating its own mains supply. And this happens with in 20 to 25 ms which is much shorter than capacitors holdup time of SMPS. Hence PC has contineous supply hence PC doesnt reboot. try changing the two 3300uf capacitors of SMPS to lower value of 1000uf. and then try it with your Lineinteractive or offline UPS, your PC will surely reboot. if you use online UPS this experiment will fail as online UPS doesnt interrupt power to output and its inverter is always ON.
 
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Dear Tahmid
Hi
Can you tell me more about those high speed relays , please ? ( about their specifications and price and ...)
Thank you
Goldsmith
 

To my knowledge (11 years of UPS development) the typical intervention time for a well designed line-interactive UPS can be not more than 5-7ms (using 50Hz mains).
10ms of intervention time was the MAXIMUM time we could tolerate.
The relays were the typical ones certified for UPS use but driven with some small tricks (higher coil voltage for about 1-2 seconds).
BTW, it all depends on your algorithm used to identify the loss of mains: it have to check the mains voltage at least 1000 times/s


P.S.: Personal messages regarding the development of UPSs will not be answered!
 

Dear bepobalote
Hi
I don't think those relays are good for high powers , e.g 10KW . ( are there any higher power relays with that speed available ?)
Regards
Goldsmith
 

You were not referring to max power, so I have shown you one UPS specific relay.
Yes, we were using some relays on our 6000VA UPSs, but (I left those work 2 years ago) now I'm not sure of its exact characteristics.
IIRC it was a model similar to T9A: http://relays.te.com/schrack/relays/pcb.asp which has max 15ms of intervention time (can be reduced with the trick I described earlier).
In some UPSs (not ours) the relays contacts were put in parallel mode, but you have to be careful because in some particular conditions the contacts can "stick": this is one of the reasons you have to use relays developed expressly for UPSs.
I see you are from Iran, so MAYBE you have not to follow the strict requirements needed here in Europe, even if I WARMLY suggest you to be really careful designing devices like UPSs.
 
Dear bepobalote
Hi again
Thanks for your guide and advice . I have designed many UPSs , successfully until now but i didn't use relays for them until now ( i used some other elements e.g Triacs and .... etc ) . but now , i'll try to use those relays in my designs .
Thanks again.
Respectfully
Goldsmith
 

goldsmith said:
Dear Tahmid
Hi
Can you tell me more about those high speed relays , please ? ( about their specifications and price and ...)
Thank you
Goldsmith
Click to expand...

I asked in the market for relays to be used for UPS. I got them there. They were available in current ratings of 10A, 15A, 30A, etc. Price wasn't high, just slightly higher than normal relays.

Hope this helps.
Tahmid.
 
One such was Songle SLB relay rated for 20A/30A with an operation time of max 5ms and release time of max 3ms. I haven't used it though for the low voltage rating. The ones I used were mostly non-brand Chinese parts.

Hope this helps.
Tahmid.
 
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Please take care about using those relays: the contact distance is not specified!
From what I think it will be 0.8mm which is deprecated for UPS usage.
This small distance is surely the reason for the fast (few ms) switching speed: this relay is not even specified for voltage higher than 125V!!!!

BTW, my previous experience told me to not trust what was written on datasheet, so we always checked/characterize/certify all of the relays we were using.
 

@ismailpp2008
the relay for fast switching is in a separate circuit without any capacitors in the circuit of the relay section to cause any delay in switching on or off of the relay hence you get a 5ms-7ms switching speed and so the PC restart is prevented
 
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