Pfannenberg FLZ 700 Peltier Unit Thermostat, DC Changeover

The thermostat that drives Peltier cooling and heating

The Pfannenberg FLZ 700 is a DIN-rail thermostat designed specifically for Peltier (thermoelectric) units. It reverses the DC polarity to the unit so the same Pfannenberg PCM device can cool the enclosure when it is too warm and heat it when it is too cold, with no separate heater.

A Peltier unit has no compressor and no refrigerant. Its cooling and heating direction is set by the polarity of the supply, so an ordinary on/off thermostat is not enough. The FLZ 700 provides the polarity changeover, a variable hysteresis and an energy-saving gap mode in one small controller.

Technical specifications

Hysteresis and gap mode

In hysteresis mode the controller works like a conventional thermostat around one set point, with a switching difference adjustable from 1 to 10 K. In gap mode, selectable from 1 to 40 K, the unit does nothing while the enclosure temperature lies between the lower and upper limits, and cools or heats only when the temperature moves outside that gap. For an enclosure that can safely sit anywhere between, say, 15 and 40 °C, gap mode saves energy and reduces the number of reversals the Peltier modules see, which extends their life.

The manufacturer lists the FLZ 700 as the controller accessory for the PCM 55 and PCM 70 Peltier units (article 17270802070) and states automatic cooling and heating changeover and demand-driven operation as its main features. The Pfannenberg PCM 70 is the matching Peltier cooling unit.

Selecting and wiring the controller

The 15 A contact rating and the 540 W DC limit define what can be connected, so check the supply current of the Peltier unit against them. The PCM 70 is rated 24 V DC with 108 W power consumption in the manufacturer data, well inside the limit. With gap mode, set the lower limit above the dew point of the site air, so that the cabinet is not driven into condensation, and the upper limit below the maximum permitted temperature of the electronics inside. Mount the FLZ 700 on the profile bar inside the enclosure, where its sensor sees mixed enclosure air, and keep the low-voltage DC wiring short and of adequate cross-section.

Before ordering, confirm that the load is a DC Peltier unit and not a fan or an AC heater; for those, use one of the FLZ 5xx bimetal thermostats instead. Confirm the supply voltage and the polarity-reversal wiring with the unit documentation.

How the Pfannenberg FLZ 700 works

A Peltier unit cools or heats depending on the direction of the DC current through it. The FLZ 700 senses the temperature and reverses the polarity of the supply to the unit. When the cabinet is too warm, the unit cools. When the cabinet is too cold, the controller flips the polarity and the same unit heats. No compressor, refrigerant or separate heater is needed.

Where the FLZ 700 is used

• Control cabinets with Peltier cooling units
• Enclosures that must be cooled and heated
• Sites with wide day and night swings
• Small enclosures with low heat loss
• Systems with a Pfannenberg PCM 70 unit

Selection checklist for the FLZ 700

• Peltier unit supply current within 15 A
• DC power within 540 W
• Hysteresis or gap mode
• Switching gap from 1 to 40 K
• Ambient temperature up to 70 degrees C
• Space on the DIN rail
• Terminal size of 0.5 to 2.5 mm2
• Matching PCM unit

Installation, commissioning and maintenance notes for the FLZ 700

Snap the controller onto the 35 mm DIN rail. Wire the DC supply and the Peltier unit to the screw terminals, keeping to the current limit. Set the mode and the temperature on the controller. Watch the first cooling and heating cycle. Keep the enclosure sealed so that humid air does not enter.

Requesting a quotation for the Pfannenberg FLZ 700

Please send the Peltier unit, the supply and the quantity. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

FLZ 700 contact type

The contact reverses the DC polarity.

FLZ 700 hysteresis mode

In hysteresis mode the switching difference is adjustable from 1 to 10 K.

FLZ 700 gap mode

In gap mode the controller does nothing between the limits. The gap can be set from 1 to 40 K.

FLZ 700 switching tolerance

The switching point tolerance is 3 K.

FLZ 700 switching power

The contacts carry 15 A, and the DC limit is 540 W.

FLZ 700 temperature range

The operating range is minus 20 to plus 70 degrees C.

FLZ 700 article number

The article number is 17270802070.

FLZ 700 size and weight

The unit measures 59 by 81 by 38 mm and weighs 90 g, in RAL 7035.

Controller records for the FLZ 700

Record the mode, the set points and the date of fitting.

Choosing the right FLZ 700 mode

Use gap mode when the cabinet can sit safely between two temperatures, so the Peltier unit reverses less often.

Documents and quotation

The Pfannenberg FLZ 700 product sheet is attached to this page and is the manufacturer’s own document, not a Seven Star summary. It lists the switching modes, ratings and dimensions. Cooling hardware is in Cooling.

State the Peltier unit it will control. Seven Star LLC, an independent supplier in Muscat, quotes the FLZ 700 against your application data; send the enclosure size, ambient temperature, supply voltage and quantity so the correct variant and article number can be confirmed before an offer is issued.