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Machine Overview and Electrical System
The Grove RT-60S is an 18-ton rough terrain crane powered typically by a 391 cubic inch Ford V8 engine with a 4-speed power shift transmission. Its 24-volt electrical system includes an alternator rated around 55 amps that charges the batteries while the engine runs. This system supports the crane’s demanding electrical load, including safety, control, and operational systems.
Charging Behavior and Observations
It is common for operators to observe the alternator’s output voltage fluctuating with engine RPM. In this case, the battery voltage hovers around 12.5 volts at idle—barely enough to maintain charge—and rises to approximately 13.5 volts when the engine is revved higher. Since an alternator needs a certain rotational speed to generate sufficient charge, low RPMs may not provide enough excitation or speed.
A fully charged 24V battery system typically reads around 12.8-13 volts with the engine off, increasing to about 13.8-14.4 volts during normal charging conditions when the engine runs. Voltages below 13.5 volts at running RPM suggest the alternator might be underperforming or the charging system faces mechanical constraints.
Potential Causes
An operator reported a similar issue on a 30,000 lbs forklift and resolved it by fabricating a smaller diameter alternator pulley on a lathe, effectively increasing alternator speed at idle without modifying engine speed. This custom solution improved low-idle charging performance dramatically.
Cost-wise, swapping to a high-quality rebuilt alternator could also improve volts output, but unless the pulley ratio or belt condition is addressed, the problem may persist.
Normal and Acceptable Charging Ranges
Glossary
While it is somewhat normal for alternators to produce lower output at engine idle, Grove RT-60S operators should expect voltages closer to 13.8-14.5 volts for efficient battery charging. Adjusting mechanical aspects like pulley sizes and maintaining alternator and belt condition are effective ways to improve charging performance. Swapping to a rebuilt alternator may also help but pairing it with optimal pulley ratios ensures the best results.
The Grove RT-60S is an 18-ton rough terrain crane powered typically by a 391 cubic inch Ford V8 engine with a 4-speed power shift transmission. Its 24-volt electrical system includes an alternator rated around 55 amps that charges the batteries while the engine runs. This system supports the crane’s demanding electrical load, including safety, control, and operational systems.
Charging Behavior and Observations
It is common for operators to observe the alternator’s output voltage fluctuating with engine RPM. In this case, the battery voltage hovers around 12.5 volts at idle—barely enough to maintain charge—and rises to approximately 13.5 volts when the engine is revved higher. Since an alternator needs a certain rotational speed to generate sufficient charge, low RPMs may not provide enough excitation or speed.
A fully charged 24V battery system typically reads around 12.8-13 volts with the engine off, increasing to about 13.8-14.4 volts during normal charging conditions when the engine runs. Voltages below 13.5 volts at running RPM suggest the alternator might be underperforming or the charging system faces mechanical constraints.
Potential Causes
- Alternator Pulley Speed: The pulley ratio affects the alternator’s rotational speed versus the engine’s crankshaft RPM. A larger engine pulley or smaller alternator pulley increases alternator RPM and improves charging at idle. An undersized or stock pulley may result in inadequate alternator speed at low engine RPM.
- Alternator Condition: Aging or damaged alternators may undercharge, especially at low speeds. Though a replacement alternator is on hand, wear in brushes, bearings, or diodes can reduce efficiency.
- Battery State and Load: Batteries nearing end of life or with high electrical loads (lights, hydraulics, sensors) may require higher alternator output to maintain charge.
- Belt Tension and Condition: Loose or worn belts result in slippage, reducing alternator RPM and charging output.
An operator reported a similar issue on a 30,000 lbs forklift and resolved it by fabricating a smaller diameter alternator pulley on a lathe, effectively increasing alternator speed at idle without modifying engine speed. This custom solution improved low-idle charging performance dramatically.
Cost-wise, swapping to a high-quality rebuilt alternator could also improve volts output, but unless the pulley ratio or belt condition is addressed, the problem may persist.
Normal and Acceptable Charging Ranges
- Engine off: Battery voltage ~12.8-13.0 volts (fully charged)
- Engine idle: Alternator output ideally 13.8-14.4 volts
- Engine revving: Voltage should remain in above range, not surpassing 15 volts
Glossary
- Alternator: Electrical generator converting mechanical engine energy into electrical power to charge batteries and supply electrical systems.
- Pulley Ratio: The size relationship between engine crankshaft pulley and alternator pulley, affecting alternator rotational speed.
- Excitation Current: Initial electrical current to energize alternator field coil to start charging.
- Voltage Regulator: Controls output voltage of the alternator to keep within safe charging range.
- Belt Slippage: Loss of effective rotation between the engine pulley and alternator due to improper belt tension.
- Check belt tension and condition; replace if worn or loose.
- Consider custom pulleys to increase alternator RPM at idle.
- Test or replace the alternator if electrical output remains insufficient across RPM ranges.
- Monitor battery health, as poor batteries increase charging demand.
- Consult OEM specifications for pulley ratios and alternator output for the RT-60S.
While it is somewhat normal for alternators to produce lower output at engine idle, Grove RT-60S operators should expect voltages closer to 13.8-14.5 volts for efficient battery charging. Adjusting mechanical aspects like pulley sizes and maintaining alternator and belt condition are effective ways to improve charging performance. Swapping to a rebuilt alternator may also help but pairing it with optimal pulley ratios ensures the best results.
