Looking to do some AC-DC conversion

[nornrich]

All,

I am looking to set up a system that has 110VAC input and runs an inverter driven motor off of 110VAC 1PH. This is the easy part. I want to be able to provide battery backup to this system, so I need to convert the 110VAC to 24VDC and then be able to feedback the 24VDC back into 110VAC through the inverter. The motor is a 1 HP, 3 phs motor. Any suggestions would be helpful.

Regards,

Rich.....

Richard Nornhold, PE

 

[itsmoked]

Have you any idea what it takes, battery wise, to run a a one horse motor?

How long?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[nornrich]

itsmoked,

We aren't looking for continuous operation for hours on end. We need the unit to operate for one more cycle of around 30 seconds. We just need to be able to move the unit to the nearest station.

Regards,

Rich.....

Richard Nornhold, PE

 

[ScottyUK]

Look for a 1KW UPS. Probably badged as 1400VA or some such, but you'll need Watts and VA for this job.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[jraef]

Many off-the-shelf VFDs can accept external DC input, so all you need is enough battery power. The bigger problem is, most 1 phase motors of that size are not suitable for operating on PWM output. You motor needs to be a PSC or Shaded Pole design.

Is the motor decision cast in stone? If not, consider using a 3 phase 230V motor instead. There are lots of off-the-shelf VFDs that accept 120V 1 phase power input and provide 3 phase 230V output. Then just find one of those which provides DC link terminals, get an isolator and connect your batteries. You will need about 325VDC, so 14 24V batteries or 28 12V batteries in series.

 

[ScottyUK]

I just opened up my little APC 'Smart UPS' 1400VA to have a peep inside. Two 12V VRLA batteries, look about 20AH or so from the size. This one is 240V in and out but I'm sure there's an equivalent with 120V input in the US.



----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[nornrich]

All,

What if I took 110VAC input into a 12VDC battery charger, then hooked the battery pack into an DC-AC automotive inverter? This might sound like a lot of work, but this would give the battery backup I need and would keep the system on 110VAC during normal operation.

Regards,

Rich....

Richard Nornhold, PE

 

[ScottyUK]

Other than making more work, does that gain anything over buying a little UPS?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

You can do that. I would suggest that you need a VFD to run the motor as otherwise the starting current will trip or fry any inverter or UPS. Get a good cut-off battery charger. A 1,500W inverter and a 120V to whatever voltage your motor needs.

BTW I am talking about TWO separate things. I believe you are confusing an 'inverter' which can convert xVolts DC into xVolts AC with a 'VFD', which is a device that synthesizes a complex varying three phase signal for driving motors.

Follow the above definitions when reading my further above description. i.e. you may already have the VFD.(?)

Keith Cress
kcress -

http://www.flaminsystems.com

 

[nornrich]

itsmoked & ScottyUK,

Thanks. I do have a VFD for operation of the motor, as I figured that inrush current in any arrangement is going to fry my system.

Regards,

Rich...

Richard Nornhold, PE

 

[itsmoked]

Good!

BTW These are the best inexpensive chargers I've ever found.

http://www.batterytender.com/product_info.php?products_id=2

I also expect that you are not planning for the charger to run the motor, just bring the battery back up after running the motor occasionally.

Keith Cress
kcress -

http://www.flaminsystems.com