There are two voltages in the power supply system of the RM4200D: 5 Volt and 24 Volt. Both voltages are supplied by slide-in power supply units on the right side of the DSP frame. At present, there are two types of power supply modules, “old” und “new” ones. The reason for this update are the improved technical data of the new modules. Current DSP frames are shipped by DHD with the new power supply units, but you can order the old ones as spare parts if required.

Until the change-over, the old power supply units RM420-82 (24V) und RM420-085 (5V) have been used. After that, they have been replaced by the new modules RM420-084 (24V) and RM420-083 (5V) ersetzt. All power supply modules have a power output of 75 Watt.

Figure 2: “Old” power supply module (RM420-82 and RM420-85). To be recognized from the outside by two small LEDs.

Figure 3: “New” power supply module (RM420-84 and RM420-83). From outside to be recognized by one big LED.

	Warning
	Never use both types of power supply modules in one DSP frame! Although they have the same connectors, the modules have different control signals that are not compatible. Keep this in mind, otherwise you can damage the DSP frame modules!

The following table shows answers to some FAQ concerning power supply units:

Question	Answer
What is the difference between “old” and “new” power supply unit?	The “new” power units can be used worldwide, since they can work with input woltages between 94V and 253 V AC. The“old” power supply units can work with input voltages of 200-250V AC only. In addition, the “new” power supply units have a Power Factor Correction (PFC).
What does Power Factor Correction (PFC) mean?	In the “old” switching power supply units, the current intake from the AC power line is non-sinusoidal. On rare occasions, this can lead to failures in the AC power line. Power Factor Correction compensates for this effect and is necessary to comply with the EN61000-3-2 standard.
Can “old” and “new” power supply units with the same voltage be used together in a DSP frame?	Warning No! Do not try this! Although the plugs are mechanically compatible, the control signals are different. If you do not consider this, modules in the DSP frame can be damaged!
Can “old” and “new”power supply units with different voltages (5V and 24V) be used together in the same DSP frame?	Yes. The power supplies for 5V and 24V are independent from each other. Thus you can use e.g. two “old” power supply modules for 5 V with two “new” modules for 24V together in the same DSP frame. In the same way, you can use “old” modules for 24V with “new” modules for 5 V. Make sure that all modules of one voltage are of the same type!
Why have the “new” modules been introduced at all?	There have been several reasons: Occassional, there were problems accquiring the components for the “old” modules. The “new” modules can be used worldwide due to the wider range of input voltages. The “new” modules have Power Factor Correction and comply with the EN61000-3-2 standard. The “new” modules use energy more efficiently.

The following list contains the most important specifications for the used power supply modules. All values are stated for the “new” modules, the values in brackets refer to the “old” modules.

When mounting power units to a DSP frame, you have to make sure that the power supply modules are passively cooled correctly. Therefore, it is necessary to allow air flowing unrestrictedly through all used power supply modules.

	Warning
	If you are mounting the power supply modules in a way that air convection is blocked, the modules can overheat and do not work correctly any longer. In certain cases, the modules in the DSP frame can even be damaged! If you have questions concerning the arrangement of power supply modules, please ask your DHD vendor!

The following figure illustrated how heat accumulates if the power modules are not mounted correctly:

Figure 4: This arrangement of power supply modules causes overheating. Do not use this arrangement!

If you need more than one power supply module for the DSP frame (e.g. to supply for several modules or for redundant power supply), make sure the units are operated with sufficient ventilation. In this case, use a second module carrier to mount in the rack additionally. The following figure shows a possible way:

Figure 5: For several power supply modules use an additional module carrier to ensure convection.