Batt Back AC or DC Motor?

[derekpulis]

I have designed a 1HP VFD. I now need battery backup motor control for the same power range. I also have a solar requirement which keeps the battery voltage at 12V (24V solar is an option but less popular). I have two options:
1. 'Step-up' the battery voltage to the VFD DC voltage through an inverter.
2. Design a 12 DC motor control.
Both have advantages and disadvantages. I plan to use a PM-SCR type motor for the DC approach. My research has produced some questions:
1. Why are 90 and 180V PM motors so popular?
2. What is the difference in price from a 1HP AC induction and an equivalent PM-SCR?
3. Is the ‘Brushed’ Motor that much less reliable?

Any feedback is very much appreciated!

 

[dpc]

You should look into using an automotive motor that will run on 12V. Then you won't need a drive at all. Just a battery charger.

Just curious as to the application. You will need quite a large battery to run a 1 hp motor (746 watts is 62 amps at 12V) for any length of time. This would also be a large solar array - even when the sun is shining.

 

[IRstuff]

Assuming a solar converter efficiency of about 8% and about 500 W/m^2 useable solar flux, you'd need at least 18 m^2 of solar cell.

TTFN

 

[derekpulis]

Thanks for the feedback – keep it coming!

The application is controlling a gate. There are a lot of different power requirements. Not all will need solar, but all will need battery backup (as an option). Solar panels would only be used on fractional HP model. I mention the solar cell only because it limits me from connecting 4 batteries in series and using a 90V motor at half speed when in battery mode.

In reference to using a 12V (automotive) motor – The battery is actually an option. I will need to operate the motor without a battery also.

 

[purplepete]

As a side issue, to keep your battery charged correctly its voltage needs to be maintained at 13.5 to 14.5 volts. If you regulate the charger (solar, mains or whatever) to 12 volts only, the battery will not retain much charge at all.

 

[jbartos]

Suggestions: derekpulis (Electrical) Jul 22, 2002 marked ///\\I have designed a 1HP VFD.
///Congratulations! Please, would you post its principle of operation?\\ I now need battery backup motor control for the same power range. I also have a solar requirement which keeps the battery voltage at 12V (24V solar is an option but less popular). I have two options:
1. 'Step-up' the battery voltage to the VFD DC voltage through an inverter.
///DC voltage is normally stepped-up (or -down) by DC-DC converters. The inverter normally inverts DC to AC.\\2. Design a 12 DC motor control.
Both have advantages and disadvantages. I plan to use a PM-SCR type motor for the DC approach. My research has produced some questions:
1. Why are 90 and 180V PM motors so popular?
///This is probably linked to the voltage resulting from energy conversions.\\2. What is the difference in price from a 1HP AC induction and an equivalent PM-SCR?
///Visit

http://www.thomasregister.com

and type Motor or Drive or what you actually have in mind under Product or Service. This will return companies that you can directly contact for info.\\3. Is the ?Brushed? Motor that much less reliable?
///It depends on its maintenance and application.\\Any feedback is very much appreciated!

 

[derekpulis]

"13.5 to 14.5 volts" -> Yeah, the batteries and solar systems are advertised as 12V. A battery that has a no load voltage of 12V is useless.

"Principal of operation" -> VFD = varies motor speed. Application = Gates.

"DC to DC Converter" -> Add a rectifier to an inverter and you get a DC to DC Converter.

"It depends on its maintenance and application." -> What application is a brushed motor more reliabale?

 

[jbartos]

Comment on "What application is a brushed motor more reliabale?" Lets look at DC series brush motor. It has such attractive torque speed characteristics, that it is only somewhat matched by fairly sophisticated electronic control of other types of motors, e.g. special designed induction motors.