Just wanted to let you know that I have been using this 500W floodlight bulb as a cheap braking resistor for intermittent motor braking. It is easy to solder to and provides useful visual indication.
They are rated at 500W on 230V European grid voltage but have about 9 Ohms cold state resistance. Of course it would increase to 100+ Ohms when heated up to full brightness. However it works great for quick brake action preventing switched mode PSU from tripping due to a sudden overvolatge.
I would guess that if you see it glowing bright then you need to get a proper braking resistor with a heatsink.
In the US you probably need to connect two 250W in series to get the same result.
Last edited by LBodnar; 05-15-2009 at 10:30 AM.
Goodday. I use ac motor 380 VAC 15 HP for my cnc lathe spindle motor replacement and Hitachi VFD 11 KW. Internal braking resistor is only 20% duty cycle as per manual. So that I need external braking resistor. As in the manual of VFD, they recommend to use 150 ohm braking resistor. When I will purchase the resistor, there are several choice of power, 150 ohm 300 watt, 150 ohm 400 watt, 150 ohm 1000 watt and so on. How to get the right choice of this wattage that I need? If I do not use external braking resistor as recommended, maybe I will burn the VFD? Thanks.