LEROY SOMER R713 AVR Accessory Module - Sensing or Paralleling Support | OEM Replacement

What the R713 is. A AVR accessory or sensing module built by LEROY SOMER for brushless excitation systems. On paper the specification is a list; in service it is a set of limits. The current the board will hold indefinitely is Not published for this model - ask us; the field resistance window it will drive without exceeding its output voltage is Not published for this model; the tightest voltage band it can maintain is Not applicable; and the ambient range in which all of that remains true is -40 to +70 degC.

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. Counterfeit regulators are a real problem on the widely copied boards. Buy from a source that will state where the board was made.

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. Static accuracy is measured on a resistive load at constant frequency. Real loads and real governors are neither, so treat the figure as a comparison between boards rather than a promise.

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. An alternator that has been rewound needs its field resistance re-measured, because a rewind commonly moves it by ten to twenty per cent in either direction.

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 regulator rated for a minimum field resistance of a few ohms will not drive a high resistance field to full current, however good its specification looks on paper.

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. Take a photograph of the terminal block before removing anything. Wiring drawings for older machines are frequently wrong, and the photograph is the only reliable record.

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. 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.

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. Take a photograph of the terminal block before removing anything. Wiring drawings for older machines are frequently wrong, and the photograph is the only reliable record.

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.

Standby versus prime power. A standby set runs a few hundred hours a year and its regulator spends most of its life cold; a prime power set runs continuously and its regulator spends its life at operating temperature. The R713 is rated for -40 to +70 degC, which is fine in both cases provided the terminal box has any ventilation at all. What changes between the two duties is the capacitor ageing inside the board, not the semiconductor, so a prime power machine should have the regulator inspected on a schedule rather than on failure.

Wiring practice that prevents most call-backs. Run the sensing leads as a twisted pair, separate from the field cables, and land them on the terminals the drawing names rather than on the ones that happen to be nearest. On a R713 the sensing input draws very little current, which is exactly why it is vulnerable: a loose terminal adds resistance that the regulator reads as a voltage error and corrects by pushing the field up, so the machine runs hot and high for no visible reason.

Commissioning sequence. Start with the machine at rated speed, no load, and the field disconnected. Confirm the sensing voltage at the AVR terminals is inside the window the board expects, then connect the field with the voltage trim at minimum. Bring the trim up slowly and watch the field current, not the terminal voltage, because the terminal voltage will look correct long before the field current has stabilised on a cold winding.

Measure, do not assume. Nameplate field resistance figures are nominal at 20 degC and are frequently wrong after a rewind. Take the measurement with a four-wire meter if one is available, because a two-wire reading on a low resistance winding includes the lead resistance and can be off by twenty per cent.

Intermittent loss of excitation. Intermittent faults are almost always mechanical: a crimp that was never properly made, a terminal screw that was tightened onto insulation, or a board that is flexing. Wiggle-test the harness with the machine running at no load and watch the field current meter.

New, old stock or refurbished. Discontinued regulators are available as new old stock, which is genuine and works, and as refurbished, which is a gamble on how the board was stored. Ask which one is being quoted. A board that has spent ten years in a damp warehouse has aged electrolytics even though it has never been installed.

What the customer is actually buying. When a regulator is quoted as a replacement, the buyer is not purchasing a circuit board. They are purchasing the certainty that the set will hold voltage on the next load step. On the R713 that certainty comes from the combination of Not published for this model - ask us for the nameplate data continuous field current and the Not applicable response, and it disappears the moment the field resistance drifts outside the window the board was set up for.

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 R713 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.