Machsupport Forum

Tangent Corner => Tangent Corner => Topic started by: Overloaded on March 13, 2010, 09:57:50 AM

Title: RESISTOR, VFD Braking
Post by: Overloaded on March 13, 2010, 09:57:50 AM

Hi,
  How to determine the required resistor for a given app. ?

What I have:
       1.5kw (2hp) Inverter Duty motor, Fugi 2hp VFD.

Looked at Automation Direct catalog for a GS2 2hp VFD and 2 hp motor for reference and they call for a :
GS22PO-BR (resistor) which is:  
230v/2hp,
Braking Torque ED 125%                                                                                                                                                                                                                              100 ohm
POWER 300W
Duty Cycle 10%

Is there any ill effect from using a higher wattage than listed/necessary ? (sometimes, higher wattage ones are cheaper)

Must the resistance be kept at 100 ? I notice as the HP goes up, the res. goes down... 1 hp = 200 ohm
2 hp = 100, 3=70, 5=40, 10=20...and so on..

How critical is the selection ?
Is there a simple formula for determination ?
I like to "mix n' match" where I can. :)
Thanks

Title: Re: RESISTOR, VFD Braking
Post by: NosmoKing on March 13, 2010, 03:39:07 PM

A higher wattage will not affect anything, the higher the HP the higher the BEMF energy so hence the lower resistance to achieve the same effect.
Your best to stick with the Manuf resistance value, anything alot lower and you may overload the electronic braking circuit.
Nosmo

Title: Re: RESISTOR, VFD Braking
Post by: Overloaded on March 13, 2010, 04:38:10 PM

Thanks Nosmo,
 That confirms much of what I found. Higher resistance than optimal would just take longer to stop. Lower could do damage.
 I finally found reference to the specific res/watt for this (similar) drive.
2hp, 40ohm, 400 watt.

See them on eBay, all sorts of values.
Automation Direct lists  a 40ohm 400w to go with their 5 hp drive.
All about what's in the drive I guess.
Thanks again,
RC