Who likes big resistor banks?

WaterSparky · Feb 20, 2014

Not really anything of much importance was just replacing a cutler & hammer resistor bank recently thought people may like a look. Motor can't remember entirely was around 75-100kw i think.

I know of sort of how a resistor bank works, that its switched in series for start up to reduce current & increase start torque but how does it do that exactly?

[ElectriciansForums.net] Who likes big resistor banks?

Geordie Spark · Feb 20, 2014

Your uncles Tony & Engineer 54 will be able to tell you all about them while wandering down memory lane ........

Bobster · Feb 20, 2014

That's not big. Haha.

Slip ring motor by any chance?

WaterSparky · Feb 20, 2014

Ill wait for them to get up from their evening nap! :cheesy: Hehe. Well compared to 0.5W resistor it is no?

Yep, that the only use for them i think? Doesn't work with induction motors, wound rotor motor for a screw pump driving a gearbox via belts. Rough estimate of size is 3M in diameter and about 15M long. Needs the initial torque to get the thing moving i suppose.

Geordie Spark · Feb 20, 2014

WaterSparky said:
Ill wait for them to get up from their evening nap! :cheesy: Hehe. Well compared to 0.5W resistor it is no? Yep, that the only use for them i think? Doesn't work with induction motors, wound rotor motor for a screw pump driving a gearbox via belts. Rough estimate of size is 3M in diameter and about 15M long. Needs the initial torque to get the thing moving i suppose.

I had my nap a bit earlier today so now I'm primed & ready for action again ........ I think.

Bobster · Feb 20, 2014

You can use resistor banks in closed transition star delta starters, not very common. In fact I've only ever seen one. The resistors have to take full short circuit current.

belts can need a deceiving amount of torque to start, depending on weight and incline, so yes I'd agree they could be using if for starting in. Or a primitive way of speed control.

Knobhead · Feb 21, 2014

Where’s the FLT to move it around?

Motors and resistors:
1/ Primary resistance, mainly American. I’ve only ever seen two in the UK. Both on lifts
2/ Closed transition star delta, as RoB says not common. Only had dealing with three of them, they scared the siht out of me if they went wrong. Each starter had its own 800KVA transformer.
3/ That leaves us with a slipring motor which looking at it is the most likely. The various tappings give it away.

There’s a better way with slipring motors, it’s old technology but I think Rob will agree with me a vapourmatic give a very even start up.
The beauty of SR motors is high torque from start up without massive inrush currents.

mechelec · Feb 21, 2014

Looks like it could be a closed transition star delta starter resistor as already stated. I had pump that had been cycling up 60 times in an hour due to clogged weed screen and failed cleaner. It burnt the resistors out. White powder from the galvanised coating all over inside the panel.
i fitted delay restart timers to overcome the problem.

Darkwood · Feb 21, 2014

Here's a similar resistor at the end of its shortened life... was used as an inrush suppressor on a 22kw dol lathe - well until some ill educated bloke who thought he knew what he was doing added a inching option to machine and overheated them to the point they melted.

As is the OP's its a Cutler Hammer and does look similar albeit lacking the sheen!

Bobster · Feb 21, 2014

What did you end up replacing them with?

Darkwood · Feb 21, 2014

The banks had various connection tappings it looked like the original inch option had been removed as the extended resistor bank had failed which was used in inch coupled with main bank. The main bank was fine and but had damaged the connections and overheated them and melted all the insulation off because the original failure had been adapted to start-up main bank only and inch removed ... someone had come along added it again with realising the inching bank had been shorted out. Thus the cables and resistor banks got quite hot on repeated inching.

I removed the inch and replaced cables to get it working as customer was selling it as seen. So cheapest option done.

Knobhead · Feb 22, 2014

mechelec said:
Looks like it could be a closed transition star delta starter resistor as already stated. I had pump that had been cycling up 60 times in an hour due to clogged weed screen and failed cleaner. It burnt the resistors out. White powder from the galvanised coating all over inside the panel.
i fitted delay restart timers to overcome the problem.

Thermostats work a lot better. A timer can’t take thermal build up in to account.

I’ll almost guarantee that resistor is off a slipring motor, look at the tappings. Pity the OP doesn’t not know what the drive was.

Engineer54 · Feb 27, 2014

I’ll almost guarantee that resistor is off a slipring motor, look at the tappings.

I'll happily second that!!

Geordie Spark · Feb 27, 2014

WaterSparky said:
Not really anything of much importance was just replacing a cutler & hammer resistor bank recently thought people may like a look. Motor can't remember entirely was around 75-100kw i think.

I know of sort of how a resistor bank works, that its switched in series for start up to reduce current & increase start torque but how does it do that exactly?

View attachment 22968

We had things like that controlling the Waltzer and other fairground rides ............... The louder you scream girls, the FASTER it goes!!!

We also had this: Spirit In The Sky Norman Greenbaum - YouTube playing endlessly!!!

It ain't Rockabilly baby, and that's when I knew I had had enough of fairgrounds.

WaterSparky · Feb 27, 2014

Tony said:
mechelec said:

Looks like it could be a closed transition star delta starter resistor as already stated. I had pump that had been cycling up 60 times in an hour due to clogged weed screen and failed cleaner. It burnt the resistors out. White powder from the galvanised coating all over inside the panel.
i fitted delay restart timers to overcome the problem.

Click to expand...

Thermostats work a lot better. A timer can’t take thermal build up in to account.

I’ll almost guarantee that resistor is off a slipring motor, look at the tappings. Pity the OP doesn’t not know what the drive was.

I dont follow you Tony?

These have stats in them cut them out when too hot but some 'electrcian thought it was a clever idea to start and stop these and when the stat did what it supposed to and interlocked the pump from starting again be then bloody bypassed it!!!