GRAMEYER GRT7-TH4 R4 Analogue AVR - Analogue Automatic Voltage Regulator for GRAMEYER Alternators | OEM Replacement

GRAMEYER GRT7-TH4 R4. This is a Analogue Automatic Voltage Regulator from the GRAMEYER 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 5 A rated on TH4 and TH4 E, field resistance window 6-50 ohm at 20 degC, accuracy 0.5 per cent, working range -20 to +60 degC. Everything else on this page exists to explain how those four numbers decide whether the unit fits a particular alternator.

Excitation architecture. Self-excited, shunt fed. 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. 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.

Sensing. 160-300 Vac or 320-600 Vac single-phase sensing. 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. The cheapest diagnostic tool in excitation work is a DC ammeter in the field circuit. It turns a vague symptom into a number within seconds.

Power stage and field drive. Power input 170-300 Vac single-phase or two-phase, 50 / 60 Hz, output 76.5-126 Vdc. Field current rating 5 A rated on TH4 and TH4 E, forcing capability 7 A for 10 s on the 5 A builds, 10 A for 10 s on the 7 A builds, field resistance window 6-50 ohm at 20 degC. 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. 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.

Accuracy and response. 0.5 per cent steady-state accuracy, Dynamically adjustable from 8 to 500 ms, 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. 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.

Frequency behaviour. Rated for 50 / 60 Hz, with Adjustable under-frequency protection by trimmer. 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. Conformal coating is the difference between a board that survives a coastal site and one that corrodes quietly in eighteen months.

Paralleling. Reactive droop, 5 A CT for parallel operation with a PAR/5 controller. 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. 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.

Protection built into the regulator. Under-frequency, over-excitation, EMI filtered input. 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. 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.

What it fits. Leroy Somer, Stamford, Marelli and Mecc Alte alternators with 6-50 ohm fields. 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 GRT7-TH4 is the most widely fitted Grameyer board and it comes in four build variants: TH4 at 5 A rated, TH4 P at 7 A rated, TH4 E at 5 A rated with a +/-9 Vdc analogue input, and TH4 PE at 7 A rated with the analogue input. The analogue input is what lets the regulator follow a power factor controller or a remote voltage trimmer, so the E and PE versions are the ones specified on paralleled and marine installations. All four carry CSA approval.

Where this regulator does not belong. A GRT7-TH4 R4 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.

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 GRT7-TH4 R4 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.

Stability before accuracy. Set the stability adjustment until the voltage stops hunting on a load step, then leave it alone. Chasing the last tenth of a per cent of static accuracy by tightening stability is how a set ends up oscillating at 2 Hz under a resistive load and looking like a governor fault. The GRT7-TH4 R4 is specified at 0.5 per cent static; a real machine on a real load will not do better than that no matter how the trimmer is set.

Rewind caution. After a field rewind the resistance often changes by ten to twenty per cent, which can push a marginal regulator out of range. Whenever a machine comes back from a rewind, re-check the regulator against the new field resistance before returning it to service.

Voltage high and unresponsive. If the machine runs to maximum excitation regardless of the trim, disconnect the field and see whether the voltage collapses. If it does, the regulator has failed shorted; if it does not, the field is being fed from somewhere else, usually a shorted thyristor or a mis-wired paralleling circuit. Do not run the machine at full excitation for more than a few seconds while diagnosing, because the winding will not survive it.

Documentation. Insist on the wiring drawing for the exact suffix being supplied. Generic family drawings are the reason installations end up with the sensing on the wrong tap, and the resulting fault is indistinguishable from a faulty board.

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 GRT7-TH4 R4 that certainty comes from the combination of 5 A rated on TH4 and TH4 E, 7 A rated on TH4 P and TH4 PE continuous field current and the Dynamically adjustable from 8 to 500 ms response, and it disappears the moment the field resistance drifts outside the window the board was set up for.

Power and sensing are not the same circuit. The power input on a GRT7-TH4 R4 can come from a different winding from the sensing input, and on PMG machines it always does. Wire them as two separate circuits, fused separately, and label both. The single most expensive mistake on a PMG set is landing the sensing leads on the PMG supply, which gives the regulator a voltage reference that rises with speed and produces a set whose voltage tracks engine rpm.