Battery Backed 3HP AC drive system

[thekman]

We use a 3HP gp motor through a VFD to drive a transmission to move a 10,000 pound gate. I've been asked to make this work on batteries. I need to come up with the most cost effective means of doing this. In similiar smaller systems, I've gotten away with a DC motor, but I need 3HP. I'm trying to figure out if I should try and run DC into the VFD bus, although I'm guessing that's going to be a lot of batteries, or venture into the 180V DC motor world, to which I am a stranger. Any offerings while I exploit google would be tremendously helpful.

 

[ScottyUK]

DC motor sounds like the best solution. Could you mount a lower power DC motor onto an extension shaft of the AC motor which would allow emergency operation at a lower speed? That way you wouldn't need the full 3HP.

 

[thekman]

Having difficult time finding a 3HP motor and controls. Need to ramp up/down and reverse. Pretty sure dual motor configuration is out of the question (cost & complexity). Most of 3HP required for moving from stopped position, once moving, not so much power required, but starting from rest is part of every cycle.

 

[ScottyUK]

It will be hard to arrange for the DC link to charge the battery, so you'll need a separate charger.

 

[thekman]

ya, gotta cross that bridge too...

 

[itsmoked]

The simplest solution is to just buy a 5kW inverter and hook it up to the VFD thru a transfer switch. Run the VFD on single phase when in backup mode. Try to find an inverter that will crank 5kW using 12VDC batteries so you can charge the batteries with a vehicle if, say, the ZA has occurred.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mikekilroy]

google "remote gate actuators" or similar; there are a lot of companies who provide this already, why reinvent it? Add some solar (good app for this) to top of batteries in the 95% off time and you have a good well designed, debugged system - probably UL and everything already.

http://www.KilroyWasHere<dot>com

 

[jraef]

Most VFDs provide DC bus terminals. Even on those that don't, I've just put DC on two of the AC terminals and let it pass straight through the diodes. The only issue with that is that the diodes might not be sized to have all of the current pass through one diode per pole, so the VFD need de-rating. Many small VFDs 3HP and under are already sized to be capable of single phase AC input without de-rating, but that will put current through 4 or the 6 diodes, you would only have two. That's going to make a 3 phase rated drive need to be LARGER than 3HP, which then means you lose the no de-rate issue. So that leaves you with finding a VFD with DC bus terminals on it. They are out there, my employer makes them, specifically for this purpose.

So that just means getting the right voltage on the terminals, plus figuring out how much power you need to store, i.e. how many operations do you need to hold up for? Voltage wise, I'd go for finding a 200V rated motor, which will require that you get the DC bus voltage up to 280VDC or so, which boils down to 24 x 12V batteries in series. The drive we make will continue to operate down to 190VDC, which will become about 135VAC. What that means is that down to that level, the drive will have to limit itself to about 40Hz, so as the voltage drops, your gate may have to move slower, you need to work out those details. but once you know those limits, and what is expected of the backup system, you can then size the batteries.

When all of that is done, you will need a float charger for the batteries, the VFD will not do that for you.
Good luck.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[thekman]

Thanks Jraef,
Funny thing, the Leeson drives I use do have DC bus terminals (see 174279 for example)yet there's hardly a mention of them in the manual, and when I contact the rep/leeson, he is clueless. I think I read somewhere that these terminals were used for a braking resistor, but I never use them.
Anyways, I will not be able to suggest a battery bank, I will most likely be limited to a couple of marine batteries or similar.
I will most likely go with an inverter, and I've got a 5A (smart) charger I use in other designs.
I will most definitely be coming back here to give status and ask more questions, no doubt about that.
Your input is invaluable, thank you for the reply!
Mark

 

[jraef]

You cannot use terminals that are used for the Dynamic Braking option if the BD transistor is integral to the drive. Typically that will be the case on drives under 10HP. larger drives don't have the integral braking transistor, so they provide simpler terminals on the DC bus so that you can connect an external one. That type would be OK.

Now here's the prob;em. I have no idea which way they are doing it on those lenze / AC Tech / Leeson drives. The B+ and B- terminals are used to connect to an external braking module., Lenze part #845-206. If you read the quasi-manual they have available for that unit, it starts off describing what I would think is a stand-alone DB braking module where the DB chopper would be external to the drive. But later in the manual, they contradict themselves and even go on to say that the DB Brake module they sell is NOT capable of being used with another VFD, because the B+ and B- terminals are in come way "communicating" to the module. That implies that there is something else inside the VFD besides just a simple DC bus terminal there. Not very well written or described I'm afraid.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[mikekilroy]

Perhaps another alternative so you can use your 2pc 12v batteries and the Leeson inverter you know and love:

http://magnumenergy.com/

http://magnumenergy.com/wp-content/uploads/2013/07/MS-PAE_series_data_sheet_revc.pdf

We supplied a MS4024PAE to a customer for their 24vdc batt to run our 5hp servos for off grid testing..... IIRC, this 5kw output for 30 sec unit was only a couple thousand dollars?

http://www.KilroyWasHere<dot>com