GRAMEYER GRT7-TH2 10A Analogue AVR - Analogue Automatic Voltage Regulator for GRAMEYER Alternators | OEM Replacement

Position in the range. The GRT7-TH2 10A sits in the GRAMEYER regulator family carrying the designation Analogue Automatic Voltage Regulator. Its place is defined by the field current it can hold, 10 A continuous, against the field resistance it can drive, 6-50 ohm, 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. 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.

Sensing. Single-phase sensing, 160-300 Vac or 320-600 Vac. 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. Load sharing between parallel sets is set up with an instrument, not by ear. A droop adjustment made by listening to the sets will be wrong at every load other than the one it was set at.

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 10 A continuous, forcing capability 14 A for 10 s, field resistance window 6-50 ohm. 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, 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. 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.

Frequency behaviour. Rated for 50 / 60 Hz, with Adjustable under-frequency protection. 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 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. 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.

Protection built into the regulator. Under-frequency, over-excitation. 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. If two identical sets behave differently on the same load, swap the regulators before swapping anything else. The result tells you which side of the machine the fault is on.

What it fits. Mid and large frame 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. 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.

Field notes on this model. The GRT7-TH2 is the higher-current companion to the TH4. The suffix after TH2 is the rated field current, so a TH2-35A is built to hold 35 A continuously, which means a different power stage rather than a relabelled board. These are used on large frame alternators where a TH4 would run out of field current on a cold load step.

The retrofit case. Most GRT7-TH2 10A sales are retrofits, not new build. The machine is ten to twenty years old, the original board has failed, and the drawing is gone. In that situation the useful evidence is the exciter field resistance measured with a meter, the residual voltage measured at the AVR terminals with the machine turning at rated speed and no load, and the nameplate kVA. Those three readings will identify a compatible board even when the original part number cannot be found anywhere.

Field cable sizing. The field circuit carries DC at low voltage and high current, so volt drop matters more than ampacity. Size the cable so that the drop at 10 A continuous stays under about one volt, and torque the terminals to the manufacturer figure. A field circuit that loses half a volt in the cable is a regulator that cannot reach full forcing when the load steps.

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.

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 drifts with ambient temperature. If the voltage is correct cold and low hot, the thermal drift of the regulator and the temperature coefficient of the field are adding up in the same direction. The GRT7-TH2 10A is specified at 0.5 per cent static; a drift of a couple of per cent over a fifty degree swing is normal for an analogue board and is not a fault.

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.

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 GRT7-TH2 10A is rated for -20 to +60 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.

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-TH2 10A 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.