Dynamic Braking Resistor

[thestelster]

I finally decided to put a braking resistor onto the Hitachi WJ200 VFD for my Ex-Cell-O 602 milling machine which has a 2hp motor.

Previously I had a 3s acceleration phase, and a 3s deceleration phase. Trying to stop any faster than about 2.5s and it would trip and coast to a stop. The 3s was never a problem except when power tapping, which can be daunting at times.

So I ordered a 50ohm 500w power resistor and hooked it up. Now I set it for 1s, and doesn't trip. I'm sure I can stop faster, which I will determine later, but 1s is quick enough for now.

I was going to buy a heat sink to set the brake on, but it was too expensive, so I just put the brake on a piece of 16g. aluminium sheet. Only time will tell if I need a heat sink, or maybe use of a small fan.

Next is to order one for my lathe.

 

[Susquatch]

Hey Stell,

What's going on here? Looks like connectors. What do they connect to?

I'm thinking you prolly don't need a Big heat sink or a fan. How hot does it get to the touch?

 

[Upnorth]

Loads of heat sinks are available for cheap. They can be salvaged from electronic equipment. Any piece of aluminum with some mass and preferably fins will act as a heat sink. Because you are using the resistor on a mill and not something with a lot of inertia like a lathe or a conveyer belt the heat load of the resistor should not be much. My 2hp mill braking resistor is not even on a heat sink and it works fine.

 

[thestelster]

Hey Stell,

What's going on here? Looks like connectors. What do they connect to?

View attachment 37541

I'm thinking you prolly don't need a Big heat sink or a fan. How hot does it get to the touch?

That's just an aluminium cable gland. There's a tapered rubber bushing inside which supports the VFD cable coming from the line reactor. Tightening the nut will squeeze the bushing around the cable. It's pretty much just a strain relief connector.

The wires behind that are from the brake resistor, but the leads were too short so I had to splice longer TGGT wire with butt crimp connectors, and then used double wall shrink tubing. It's not pretty, but it's quite solid and it works.

I just installed it last night, and only tested it a couple times, so it didn't get hot at all.

 

[thestelster]

Loads of heat sinks are available for cheap. They can be salvaged from electronic equipment. Any piece of aluminum with some mass and preferably fins will act as a heat sink. Because you are using the resistor on a mill and not something with a lot of inertia like a lathe or a conveyer belt the heat load of the resistor should not be much. My 2hp mill braking resistor is not even on a heat sink and it works fine.

Yeah, that's why I opted out of buying a finned heat sink until I determined if I needed one or not.

I was contemplating whether I should use a thin sheet of aluminium or a thick piece. I figured a thick piece would just hold the heat into the resistor, while the thin piece would dissipate the heat faster. So I decided to use the thin sheet.

I also ordered some thermal paste from Amazon to go between the resistor and aluminium sheet for better heat transfer.

 

[Upnorth]

I wouldn't worry too much unless you see smoke or smell something burning.

 

[Susquatch]

The wires behind that are from the brake resistor, but the leads were too short so I had to splice longer TGGT wire with butt crimp connectors, and then used double wall shrink tubing. It's not pretty, but it's quite solid and it works.

The wires behind that is what I was asking about. Nice camouflage making it look like there was something fancy going on there!

it didn't get hot at all.

Good. I didn't think it would. Lots of mass and surface area there already. No heat sink needed.

Do you have a link to the resistor?

 

[thestelster]

The wires behind that is what I was asking about. Nice camouflage making it look like there was something fancy going on there!



Good. I didn't think it would. Lots of mass and surface area there already. No heat sink needed.

Do you have a link to the resistor?

I ordered it from Mouser Electronics in Kitchener. Free shipping and delivered next day, (and it came from Texas!!)

 

[Susquatch]

I ordered it from Mouser Electronics in Kitchener. Free shipping and delivered next day, (and it came from Texas!!)

Nice! Excellent specs on the resistor!

 

[thestelster]

And I just received a braking resistor for my lathe.
18ohm @ 1.5kw. My lathe motor is 5hp.

 

[Susquatch]

And I just received a braking resistor for my lathe.
18ohm @ 1.5kw. My lathe motor is 5hp.

Nice!

Even nicerer than the one you got before!

Did you get this one from Mouser too?

 

[thestelster]

Nice!

Even nicerer than the one you got before!

Did you get this one from Mouser too?

Yes. I ordered it online yesterday at 3pm. Came from Texas, cleared customs, to my door today. Custom clearance and shipping included in the price.

 

[Susquatch]

Custom clearance and shipping included in the price.

Wow! Sounds like there are two in my future too!

 

[thestelster]

I just installed the braking resistor. Set the parameters to 3s acceleration and 1 second deceleration. With the 6" chuck at 1000rpm...no problem.

I changed to the lowest speed in high gear 250rpm, and reduced the frequency to 20hz which gives me around 80rpm, to simulate threading speed. Stops almost instantaneously!!

 

[Susquatch]

I just installed the braking resistor. Set the parameters to 3s acceleration and 1 second deceleration. With the 6" chuck at 1000rpm...no problem.

I changed to the lowest speed in high gear 250rpm, and reduced the frequency to 20hz which gives me around 80rpm, to simulate threading speed. Stops almost instantaneously!!

Wow. Couple that with a stop-switch wired to the VFD and voila! Thread reliefs are suddenly a thing of the past......

Too many projects........ But this one will be much higher on the priority list than most!