LEROY SOMER R723 AVR Accessory Module - Sensing or Paralleling Support | OEM Replacement

LEROY SOMER R723. This is a AVR accessory or sensing module from the LEROY SOMER range, supplied as a direct replacement for the same model number in the field. The figures that matter are printed in the table above and repeated here so the page can be read on its own: field current rating Not published for this model - ask us, field resistance window Not published for this model, accuracy Not applicable, working range -40 to +70 degC. Everything else on this page exists to explain how those four numbers decide whether the unit fits a particular alternator.

Excitation architecture. Not applicable, accessory module. That single sentence decides most of the regulator's behaviour in a fault: whether the field survives a close-up short circuit, whether the machine builds up from residual voltage on its own, and how much the terminal voltage dips when a large motor starts on the same bus. Field resistance is a temperature-dependent number. A reading taken on a cold morning and a reading taken after an hour at load are both correct and both different.

Sensing. Three-phase voltage detection or paralleling sensing depending on the module. The sensing circuit is the regulator's only view of the outside world, so its wiring matters as much as its specification. A voltage error introduced by a loose terminal or a long run of untwisted cable is indistinguishable, from the regulator's point of view, from a genuine voltage error on the alternator. Terminal boxes are hot, dirty and vibrating. Anything mounted inside one should be judged on how it behaves in year eight, not on how it reads on the bench.

Power stage and field drive. Power input Supplied from the AVR, output Control signal to the AVR. Field current rating Not published for this model - ask us, forcing capability Short-term forcing current available for load steps, field resistance window Not published for this model. These are not independent numbers: the output voltage ceiling and the field resistance together set the maximum current the board can actually deliver, and the continuous rating is only reachable at the low end of the resistance window. Vibration kills more regulators than heat does. If a board has failed twice in the same machine, look at the mounting before looking at the supplier.

Accuracy and response. Not applicable steady-state accuracy, Not applicable, thermal drift Low thermal drift. In practice the accuracy figure is the least interesting of the three. What an operator notices is recovery after a load step, which is governed by response and by available forcing current, and what a maintenance engineer notices after two years is drift, which is governed by the reference circuit and the ambient temperature inside the terminal box. Any AVR that has been in service for more than ten years is running on borrowed time, and the failure always happens at the least convenient moment.

Frequency behaviour. Rated for 50 / 60 Hz, with Not published for this model - ask us for the nameplate data. The frequency-sensitive function exists to protect the prime mover, not the alternator: as engine speed falls the regulator reduces excitation so the alternator stops demanding torque the engine cannot supply. Without it, an overloaded engine is dragged down until it stalls, and the alternator is blamed for a fault that belongs to the fuel or governor system. A voltage that is correct at no load and low at full load is almost never an accuracy problem. It is a current limit, a resistance problem or a cable problem.

Paralleling. Reactive droop set-up for parallel operation. On a single set this circuit does nothing. On two or more sets it is the only thing that stops the machines from exchanging reactive power in a slow oscillation, and it is the first place to look when a parallel installation shows a circulating current that nobody can explain. Where a spare is being held, hold the drawing with it. A board without its wiring diagram costs a shift of production time to install.

Protection built into the regulator. Module-level protection only. These functions protect the alternator and the regulator, not the installation. Downstream protection, loss of mains and reverse power all belong to the controller, and a site that relies on the AVR for them is a site that will eventually trip in a way nobody can explain. A regulator is a closed loop with a slow plant attached, and the plant is a large inductance. That is why the stability adjustment exists and why it is set after, not before, the voltage is correct.

What it fits. R438 / R449 / R450 regulator family. Lifecycle status: In production. Both halves of that sentence matter at order time. A board that fits perfectly but has been discontinued is a different commercial decision from one that fits and is in current production, and the price difference rarely reflects the difference in risk. If the machine will not hold voltage at all, disconnect the field and measure the sensing voltage first. That one reading separates a sensing fault from a field fault.

Field notes on this model. The R7xx boards are not regulators. R731 is the three-phase voltage detection module, R734 is the paralleling sensing module and R726 is the interface board for external control. They wire alongside an R438-class AVR. If a machine with an R731 fitted reads the wrong voltage, the fault is usually in the module sensing fuses rather than in the AVR itself.

Matching the board to the duty, not to the label. Two LEROY SOMER alternators of the same kVA can need different regulators if one is specified for motor starting and the other for a resistive load. The R723 is specified at Not applicable regulation accuracy, which is the number that matters when the load is a mix of drives and lighting. For a purely resistive load even a looser board is invisible to the customer, and paying for accuracy that nobody measures is the most common way money is wasted on a rebuild.

The terminal box is a hostile place. Engine vibration, radiant heat from the exhaust and conductive dust all arrive at the same panel. Mount the R723 on the resilient side of the box if there is a choice, keep it off the hottest wall, and make sure the lid actually closes over the wiring rather than pinching it. A regulator that is mechanically stressed will eventually crack a solder joint, and the resulting fault looks exactly like a failed semiconductor.

What to record. Write down the sensing tap used, the field resistance cold, the field current at no load and at full load, and the voltage trim position. Those four numbers turn the next service visit from an investigation into a comparison.

Temperature drift of the field. Copper rises about 0.4 per cent in resistance per degC, so a field that measures 12 ohm cold will measure around 15 ohm at a 70 degC winding temperature. A regulator set up on a cold machine and never re-checked will therefore be running at a different operating point every time the season changes, and the symptom is a voltage that is correct in winter and low in summer.

Symptom first, board second. A set that will not build up voltage has one of four causes: no residual magnetism, a broken sensing circuit, a failed regulator, or a field circuit open. Test them in that order, because the first two are free to check and the third is not. Flashing the field with a battery through a resistor will separate a residual problem from a regulator problem in under a minute.

Warranty and what it covers. A one year warranty on a regulator is meaningful only if it covers a field-side failure and not just a dead-on-arrival check. Ask whether a board that fails after six months in service is replaced without argument, because that is the failure mode that actually happens.

Where this regulator does not belong. A R723 is a voltage regulator, not a protection relay and not a governor interface. If the site needs loss-of-mains detection, reverse power protection or synchronising, those functions live in the controller, not here. Expecting the AVR to carry them is how installations end up with a set that holds voltage beautifully and still trips the site on a mains failure.

Field cable sizing. The field circuit carries DC at low voltage and high current, so volt drop matters more than ampacity. Size the cable so that the drop at Not published for this model - ask us for the nameplate data stays under about one volt, and torque the terminals to the manufacturer figure. A field circuit that loses half a volt in the cable is a regulator that cannot reach full forcing when the load steps.