Rectifier Questions

Grouch

Grouch

Senior Member
Location
New York, NY
I always come across rectifiers in old buildings in NYC, that provide DC power to elevators (both passenger and freight). AC power is on the input,
and the output is DC. I attached pictures of one such rectifier... the front view, side view, and nameplate data.

My question is, what is the top triangular piece for? All the rectifiers I come across have the same construction, with this top triangular metallic piece. It is some sort of heat sink? Or something else.

Rectifier_Front.JPGRectifier_Side.JPGRectifier_Nameplate.JPG
 
herding_cats said:
yes it is to dissipate heat while being a deflector shield for potential water etc. Or anything falling into it like a nut or bolt, particulates.
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How come regular transformers have a different construction? Such as these that we're all familiar with. Yes there's ventilation, but not like a rectifier with the metallic grated top. Is it because a rectifier generates more heat?
FR939_R.jpeg

hbiss said:
I would also say that it's to keep people from piling junk on top of it blocking the flow of hot air.
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So that's the reason for the pitched triangular roof?
 
Is there a heat generating device, like resistor, in the top hat? Clearly the slanted portion is intended to prevent/reduce entry into the ventilating slots on the top of the enclosure.
I have seen literature that says their rectifier device contains a 'regeneration absorption' circuit, which sounds like a marketing term for an edgewound resistor.
 
Elevator codes are more conservative in nearly every area. They want the elevator to keep working for as long as it can to get the passengers out. If there is a leak or sprinklers, they wouldn't want water to get in that rectifier or pool on a flat surface.
 
CoolWill said:
Elevator codes are more conservative in nearly every area. They want the elevator to keep working for as long as it can to get the passengers out. If there is a leak or sprinklers, they wouldn't want water to get in that rectifier or pool on a flat surface.
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The hood in the OP picture would not provide very much protection from a sprinkler, all of the sides are open for ventilation.
 
jim dungar said:
The hood in the OP picture would not provide very much protection from a sprinkler, all of the sides are open for ventilation.
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Any sideways water would be incidental. The rectifier is open on the top, so the hood most certainly does a great job at preventing direct water into the enclosure.
 
Those hoods looks like a field addition, not a factory part; could be a NYC requirement (to keep things off the top).

BTW, many rectifiers were installed by ConEd as part of removing their DC distribution system (which took something like 50 years to accomplish; that's a different topic).
 
Here's another example, from a different building. The top hat is taller. Also, you can see screws / supports coming out at the end, on the right... and there's some horizontal device within the grating that appears to be supported by them. Next time I'll try to peek in more. Any idea what these horizontal devices are? It seems that the top hat encases them.

IMG_1555a.JPG
 
LarryFine said:
As in dynamic braking?

I thought they used DC motors for the speed control-ability before VFDs became common.
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Elevators are similar to cranes.
In both cases you can have overhauling loads. Dynamic braking is one control method for these loads.
 
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