GRAMEYER GRT7-TH4 R2 Analogue AVR - Analogue Automatic Voltage Regulator for GRAMEYER Alternators | OEM Replacement

Position in the range. The GRT7-TH4 R2 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. 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. 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. 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.

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. 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, 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. 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.

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. 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.

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

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. 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.

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.

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 R2 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.

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 R2 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.

Paralleling setup. With two sets on the bus, adjust droop until reactive load divides in proportion to machine rating, then check it again at half load. A droop setting that looks right at full load and wrong at half load is usually a CT ratio error rather than a regulator fault.

The forcing margin. A regulator that can only just hold rated voltage at rated load has no forcing margin left, and the machine will dip on every load step. The GRT7-TH4 R2 is specified with a minimum field resistance of 6-50 ohm at 20 degC; staying comfortably above that minimum, rather than exactly at it, is what leaves the forcing margin that makes a set feel solid rather than merely adequate.

Voltage low under load only. This is the classic field current limit symptom. Measure the field current at full load and compare it with the 5 A rated on TH4 and TH4 E, 7 A rated on TH4 P and TH4 PE figure for the GRT7-TH4 R2. If the board is at its limit, either the board is too small for the alternator or the field resistance has risen. A rewind, a corroded terminal or a long cable run will all produce the same reading.

Delivery and packing. Regulators are static-sensitive assemblies and should arrive in a sealed bag with foam, not loose in a box with a heatsink. Inspect on arrival and photograph the packaging before opening if there is any sign of crush damage.

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 GRT7-TH4 R2 the first thing to check is whether the 5 A rated on TH4 and TH4 E, 7 A rated on TH4 P and TH4 PE 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.

Mounting orientation and cooling. Most AVR boards are convection cooled and assume the heatsink fins are vertical. Mounting a GRT7-TH4 R2 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.