GRAMEYER GRT7-TH4E 5A Analogue AVR - Analogue Automatic Voltage Regulator for GRAMEYER Alternators | OEM Replacement

Position in the range. The GRT7-TH4E 5A sits in the GRAMEYER regulator family carrying the designation Analogue Automatic Voltage Regulator. Its place is defined by the field current it can hold, 5 A rated on TH4 and TH4 E, against the field resistance it can drive, 6-50 ohm at 20 degC, at 0.5 per cent accuracy over -20 to +60 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. 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. The trim potentiometer is not a calibration device. If rated voltage is not reachable near the middle of its range, the sensing tap is wrong.

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. 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.

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. 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.

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 spare is being held, hold the drawing with it. A board without its wiring diagram costs a shift of production time to install.

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. 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.

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 cheapest diagnostic tool in excitation work is a DC ammeter in the field circuit. It turns a vague symptom into a number within seconds.

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. 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.

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. On a machine that has been standing for months, check residual voltage before condemning anything: a winding that has lost its remanence will not build up on any regulator.

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.

Matching the board to the duty, not to the label. Two GRAMEYER alternators of the same kVA can need different regulators if one is specified for motor starting and the other for a resistive load. The GRT7-TH4E 5A is specified at 0.5 per cent static 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.

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 GRT7-TH4E 5A 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.

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-TH4E 5A 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.

Series resistance is not a fix. Adding a resistor in series with the field to bring it inside a regulator window costs forcing current exactly when the machine needs it most. If the field resistance is outside the window, change the board, not the circuit.

Spares strategy. Keep one regulator of each family in stock rather than several of one. A failed AVR takes a set off line in seconds and the replacement lead time is measured in days, which is why the cost of the spare is trivial compared with the cost of the outage.

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 GRT7-TH4E 5A 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.

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 GRT7-TH4E 5A 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.