HELP for Designing UPS

[emalay]

hi, I am doing a project in which it is intended to design a backup power unit suitable for maintaining power for a small motor. If line power is loss it switches to battery powered inverter within less than 0.1 sec. The inverter output must be fully synchrionised to the line, so that there is limited inrush current when the switching takes place.the unit should wait atleast 20sec. I have got the querry that can I use A relay for controlling the time delays during the Switching operations. I have already designed the Inverter for converting 12V DC to 120V AC, but struggling with the Delay and switching operation , Please help me.

Thanks for your time and Consideration in advance!!!!

Malay

 

[Nigel Goodwin]

Why not run the motor permanently off the inverter?, and have the mains charge the battery - then if the mains goes off it will continue running off the battery with no switching required!.

 

[cadstarsucks]

hi, I am doing a project in which it is intended to design a backup power unit suitable for maintaining power for a small motor. If line power is loss it switches to battery powered inverter within less than 0.1 sec. The inverter output must be fully synchrionised to the line, so that there is limited inrush current when the switching takes place.the unit should wait atleast 20sec. I have got the querry that can I use A relay for controlling the time delays during the Switching operations. I have already designed the Inverter for converting 12V DC to 120V AC, but struggling with the Delay and switching operation , Please help me.

Thanks for your time and Consideration in advance!!!!

Malay

You do not say motor is... Some think a fractional horse is a large motor, but I work with 3HPs all the time. Are you locked in to an AC motor? Could you use a DC or a universal?

If a universal would work way is to simply run the inverter at low line levels and diode OR it with the rectified line.

D.

 

[cadstarsucks]

Why not run the motor permanently off the inverter?, and have the mains charge the battery - then if the mains goes off it will continue running off the battery with no switching required!.

I have one word for you - efficiency

D.

 

[Nigel Goodwin]

I have one word for you - efficiency

I have one for you - quality

 

[cadstarsucks]

I have one for you - quality

Which you apparently know very little about. Inverters are notoriously inefficient. That generates heat and heat creates failures. You would have him run a power supply at 80% max efficiency, IF he's lucky a bit more, into an inverter that is in all probability less than that for an overall of 50-60%.

If we take it to an extreme and say he is running it continuously at 1A@120V ( roughly a 1/10HP motor ) he is spending about $8.50/mo, or over $100/yr, to keep the motor running instead of $4.25. This is a US standard $0.10/KWHr estimate.

We will not bother going into the EU efficiency regulations involved about it.

D.

 

[Nigel Goodwin]

Which you apparently know very little about.

Perhaps it's you who doesn't?, it's how the higher quality (and more expensive) UPS's work.

 

[cadstarsucks]

Perhaps it's you who doesn't?, it's how the higher quality (and more expensive) UPS's work.

You must be referring to all those OLD designs that they are not allowed to sell to the public anymore due the the NEW laws about power EFFICIENCY!

D.

 

[Nigel Goodwin]

Perhaps you would care to design him a suitable switched inverter then?, one that's syncronised to the incoming mains as he asked for!.

You seem to be missing the point that this is a HOBBIEST forum, we're not offering solutions for production - just ideas for a 'one of' project. The solution I suggested would meet all his criteria cheaply and simply - whereas your 'suggestion' was simply to mock the idea - hardly very constructive?.

 

[cadstarsucks]

Perhaps you would care to design him a suitable switched inverter then?, one that's syncronised to the incoming mains as he asked for!.

You seem to be missing the point that this is a HOBBIEST forum, we're not offering solutions for production - just ideas for a 'one of' project. The solution I suggested would meet all his criteria cheaply and simply - whereas your 'suggestion' was simply to mock the idea - hardly very constructive?.

Perhaps you should read his original post where he states that he ALREADY has the inverter DESIGNED. If anything my suggestion would allow him to simplify his inverter design by making it pulsating DC instead of full AC.

Perhaps you missed my post where I said I started as a hobbyist AT 12. I know what it is like to want to do things and not have the money for parts.

 

[Hero999]

If it's powering a motor then the momentum should be enough to keep it running for the 5ms it will take for a relay to switch from the mains to the inverter.

 

[cadstarsucks]

If it's powering a motor then the momentum should be enough to keep it running for the 5ms it will take for a relay to switch from the mains to the inverter.

Most likely, but a lot depends on the amount of mass in motion combined with the amount of friction in the system.

D.