[Jens Rekker]

I have a Curtis 1221 PO51, which is an early (1994?) transition from the 120VDC 1221 to the 1231C for 144 VDC. I am running it at 144V within a very conventional series DC configuration as per the Curtis manual wiring diagram, with the except of the A2 plugging motor lead for forklifts being left out.

My problem is that besides the usual initial squeal of the controller that goes away once you are rolling, mine is developing an intermitent squeal at higher speed. The squeal kicks in suddenly at moderate, steady throttle positions. It is often after a longer journey or heavy load (+200A). It may be associated with warmer temperatures (it's summer down here in New Zealand).

The higher speed squeal last for about 10 seconds and may respond to changes in throttle. But, I am worried if it indicates that the controller is degrading.

[Carroll_1]

The Curtis controller will emit a tone and reduce power in an overheat condition. My 1231C did this when the controller's cooling fan leads accidently became disconnected. If I backed off on the throttle for just a few seconds, it would cool down, resume power, and the tone would go away.

Here's an excerpt from the Curtis manual:

Noise
Controller operation is normally silent, with three exceptions: (1) A 1 kHz tone may be heard during plug braking. This noise is normal and indicates that plugging is taking place. The noise will stop when plug braking stops. (2) The same noise may indicate overtemperature. The controller shifts frequency during overtemperature from its normal 15 kHz to 1 kHz (1.5 kHz on “C” controllers), providing an audible tone to alert the operator to the overtemperature condition. (3) The frequency shifting feature on “C” controllers produces a 1.5 kHz tone during the first 15% duty cycle of the PWM output. This tone may be heard during low throttle, slow speed maneuvering.

Hot Controller
If the controller gets hot, it does not necessarily indicate a serious problem. Curtis PMC 1209B, 1221B, and 1221C controllers protect themselves by reducing power to the motor if their internal temperature exceeds 75 ｰC (167ｰF). The 1231C controller begins reducing power at 85ｰC (185ｰF). Power output will be reduced for as long as the overheat condition remains, and full power will return when the unit cools.

It sounds like you may be running near the limit on overheating. I'd consider adding additional controller cooling with either more heatsink or cooling fan capacity.