LEROY SOMER R449 Analogue AVR - Analogue Automatic Voltage Regulator for LEROY SOMER Alternators | OEM Replacement

Position in the range. The R449 sits in the LEROY SOMER regulator family carrying the designation Analogue Automatic Voltage Regulator. Its place is defined by the field current it can hold, Field current limited by P5, against the field resistance it can drive, Matched to the exciter field, at +/-0.5 per cent accuracy over -40 to +70 degC. Where a machine falls outside either of the first two figures, a different member of the same family is the correct answer rather than a workaround.

Excitation architecture. AREP or PMG. 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. 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.

Sensing. 5 VA through an internal isolating transformer: 0-110 V terminals cover 85-130 V, 0-220 V cover 170-260 V, 0-380 V cover 340-520 V. 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. Where a board has been superseded, the replacement usually fits the same footprint but not the same terminal numbering. Read the drawing, do not read the old wiring.

Power stage and field drive. Power input 95-520 Vac, 50 / 60 Hz, output Up to 110 Vdc into the exciter field. Field current rating Field current limited by P5, forcing capability 15 A limit, folding back to 2 A after 10 s, field resistance window Matched to the exciter field. 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. The measurement that settles most arguments is the field current at full load, taken with a clamp meter, compared against the rating on the board.

Accuracy and response. +/-0.5 per cent steady-state accuracy, Fast response with the Load Acceptance Module active, 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. 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.

Frequency behaviour. Rated for 50 / 60 Hz, jumper ST3, with Under-frequency knee at 47.5 Hz on 50 Hz or 57 Hz on 60 Hz, Load Acceptance Module included. 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 set that runs at reduced speed will show low voltage on any regulator. Check engine speed against the nameplate before touching the excitation system.

Paralleling. Reactive droop via P1, 5 per cent at rated power factor 0.8. 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. Field current limit P5, 15 A fuse of the gG 10/38 type, over-excitation fold-back after 10 s. 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. Where a board has been superseded, the replacement usually fits the same footprint but not the same terminal numbering. Read the drawing, do not read the old wiring.

What it fits. Leroy Somer LSA 40 / 42 / 43 / 44 / 46 / 47 / 49 alternators. 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. 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.

Field notes on this model. The R449 is the bigger brother of the R438: same sensing architecture and the same Load Acceptance Module, but a 15 A field current limit instead of 8 A, which is what the larger LSA frames need. Bench setup is straightforward. Disconnect the sensing leads, feed 200-240 V into X1 and X2 through the 0-220 V tap, put a DC ammeter in series with the field, turn P5 fully anticlockwise, then bring P2 up until the field current stabilises before setting P5 to the target current.

Reading the application backwards. Most regulator problems arrive described as engine trouble. A set that hunts on load, or whose voltage sags for two seconds after a contactor closes, is usually reporting a field current limit rather than a fuel problem. On a R449 the first thing to check is whether the Field current limited by P5, factory set at 7.5 A figure is being reached on a cold morning, because field resistance rises with temperature in the opposite direction to copper and a board that is marginal at 20 degC can be comfortable at 50 degC or the other way round depending on the winding.

Fusing. Fit the fuse the manual specifies and nothing larger. A bigger fuse does not protect the regulator better, it protects it later. On a R449 the fuse is there to clear a field short before the thyristor is destroyed, and a 20 A fuse in place of an 8 A one turns a cheap board replacement into a rewind.

Bench test before installation. Where a spare board is available, test it on the bench with a variable AC supply into the power input and a resistor bank as the field load. A board that cannot hold a steady output into a resistor will not hold it into an exciter either, and finding that out on the bench costs nothing.

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.

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.

Counterfeits. Where a board is widely copied, buy from a source that will state the country of manufacture and stand behind it. A counterfeit regulator usually works for a month and then fails on the first cold morning, and by then the machine has a reputation problem rather than a parts problem.

Parallel operation is a different animal. A single set on an island load only has to hold voltage. Two sets in parallel also have to agree about reactive load, and that agreement is made or broken by the droop circuit, not by the voltage accuracy. If a site is going to parallel, the regulator choice has to be made with the droop method in mind from the beginning, because retrofitting load sharing onto a board that was never specified for it costs more than buying the right one.

Mounting orientation and cooling. Most AVR boards are convection cooled and assume the heatsink fins are vertical. Mounting a R449 flat on its back inside a sealed box shortens its life even though the ambient temperature reads acceptable, because the local air around the thyristor is far hotter than the box average.