Home Forums General Discussion Technical Questions Dynamic Breaking Resistors

Hello Group,

Have a question, in the 1990s (maybe later) some of the manufactures used DBRs on there AC drives. So far I see them on Otis GEM and Kone MP21. Are there any other companies that used them on their gear? Also has there been any retrofits to add thermal protection before they burn the building down. Or is it not a problem.

Work Safe You Guys

Jim,
MCE used then too. In most of the drive with DBR, I've always seen a mechanical overload with the contactor. Personally I always setup the overload protection in the drive as well. I will set the drive 2 or 3 higher. The function is there and I like the redundancy.

And yes, I've had them fail. The signs that led us to the DBR were the car shooting past the floor and/or tripping the overloads...

Most of the controller company use them when the system do not have the re-gen drive install. Some do have the thermal protection installed. And yes, when resistor open, the elevator drive will tripping the overcurrent most of the time during dec.

we had 2 motion cars nearly burn down a building due to braking units not shutting off

the building did a emergency generator early in the morning, when they switched over to the generator, all seemed well, they went about there testing, and about 20 minutes later, the fire alarm in the machine room went off, then both cars shut down, the braking resistors got so hot that they started the wiring in the controller and the gutter on fire, it was quite the mess, well after quite a few days of rewiring and replacing parts the car were up and running, the problem was that the generator output was to high, over 525 volts, this high voltage turned on the braking units, which started heating the resistors, until they erupted in fire, luckily the engineers were able to turn off the disconnects before more damage happened I'm with christy, we never realized this could happen, it had no thermal protection. there are plenty units out there that will do the same thing kind of scary if you think about it it was a giant toaster. this is something to keep an eye out for on older breaking units

Scott,

Thanks for sharing that story. I have a university that have two MCE units with DBRs. I'm emailing them your backup generator findings. I will ask them to include us on their next generator test.

Some VF drives have just the DBR directly connected to the drive but others are run via a drive resistor unit I think for the larger units. JKH can I ask where the typical thermal protection is located IE on the resistor or on the drive its self? Thanks in advance mate as I cant remember and if you use only lift supplier types(non commercial) they don't usually have them from my experience.

Brett,
I emailed you an example of how MCE used a DBR.

i think that they put a thermal protection device in the cabinet with the braking resistors, if it got to hot, it shut down the drive and braking unit.

We had a company that their thermal protection was tripping when nothing was wrong just heat build up in the cabinet. Their fix was to have us move the thermal protection from the top of the resistor box to the bottom!!!! It cured the problem but how well designed was the system to start with. And how hot will it get now????

true true, this is a slippery slope, how hot does it have to be to shut down, to hot, to late not hot enough and nuisance shut downs. i have noticed that most of the drives now have the dynamic braking circuit included in the drive. i wonder if this same scenario would still turn the output on? ac line volt to high, causing dc bus volt to climb beyond braking voltage and the continue to cook the resistors. anyone have any ideas on the new drive circuitry.