VFD braking resistor (2024)

I don't have an explicit answer for you, but often those smaller VFDs (especially the new ones) have built-in resistors. Your unit is pretty small, so I'd check out the documentation to make sure that isn't the case for you.

Alan

I don't know about your VFD but my book on the 2 HP rated Magnetek GPD 333 lists 100 ohms 200 Watt resistor for a DB resistor. If your application involves stops of high inertia loads from high RPM better get a 500 Watt.

I have a total of 100 watts DB resistor on the VFD of my 10 HP lathe. Two stops from 2000 RPM's in rapid succession with the 10" three jaw get the resistor hot enough to sizzle spit (No biggie, it's ceramic and is safe to almost red heat).

[This message has been edited by Forrest Addy (edited 06-09-2004).]

People adding a DB resistor should shop around before they buy the factory part. The Magnetek (now Yaskawa) DB resistor for a 5 HP GDP 333 lists for $300. The same rated resistor from Newark Electronics is $16. Go figure.

For $286 I can build a little vented enclosure.

[This message has been edited by Forrest Addy (edited 06-09-2004).]

I took a trip to the local surplus electronics shop. I found a 40ohm 250W unit for less than $10 out the door. Should be plenty for my little 1hp mill if Forrest can get away with 200w on his 10hp lathe.

Chris

Chris, sounds like a great deal, but 40 ohms may be too low for a 1 Hp drive. The lower the ohms, the more current will be drawn by the resistor. The DB chopper circuit, especially if it is built-in to the VFD, may not be able to handle it. This could lead to damage of the DB circuit, or the drive may trip anytime the DB tries to turn on.

Typical ohm values for 1 Hp VFDs are usually in the 100-150 ohm range. 40 ohms is more in line for a 5 Hp VFD. If the VFD uses the same DB circuit for a 1 Hp as it does for a 5 Hp then you would be OK. I would ask the VFD manufacturer what their recommended ohms and watts ratings are.

Hey Jim,

Thanks for the input. This is for a Baldor BDI 1100 drive. According to the manual it needs a resistor with a resistance of 30 ohms or more. No other specs of course.

Once I get it I'll play with the braking function. Not sure I really need it, but it would be nice to not have to brake manually. I guess if it trips on braking I'll know why in advance. They had a few different sizes in stock. I could always swap it.

BTW: The braking resistor only switches in if the bus voltage goes over 375ish on a 240v drive right? So a 40ohm resistor across a 375v drop will pull 9.375 amps? Doesn't sound too bad. 3.5 kw peak? That should smell nice. :^)

Thanks,

Chris