The ARCO Zeus A4000-24V LTO is a 24V high-output alternator built to charge well at low engine speed. LTO stands for Low Turn On: it starts producing power at lower RPM than a conventional high-output unit. That suits boats and vehicles that spend long periods idling or at low revs, and installations where belt load has to stay modest.
Ratings are at 27.5V and at the alternator shaft (engine RPM × pulley ratio):
| Peak, cold (9,000 alt RPM) | 144 A (about 3.96 kW) |
|---|---|
| Sustained hot, cruising (6,000 alt RPM) | 130 A (about 3.58 kW) |
| Sustained hot, idle (3,000 alt RPM) | 108 A (about 2.97 kW) |
| At 2,000 alt RPM | about 87 A (2.4 kW) |
| Just under 1,500 alt RPM | about 51 A (1.4 kW), continuous |
| Starts charging at | about 1,070 alt RPM |
| Max continuous operating temperature | 212°F (100°C) |
As a worked example from ARCO: a marine diesel idling at 750 RPM with a 2:1 pulley ratio still gets over 1.5 kW from this alternator.
This is an external-regulation alternator. It uses a native 24V rotor and needs an external regulator such as the ARCO Zeus regulator, which is also what lets it charge lithium correctly. Background: Can my alternator charge lithium batteries? and 24V vs 48V: which is right?
Choose the housing that matches the alternator you are replacing:
| 1–2″ single foot | Most domestic single-foot alternators (e.g. Motorola, Prestolite). |
|---|---|
| 3.15″ J180 saddle | Most small-case saddle alternators (e.g. Hitachi, Lucas, Mitsubishi) and most Yanmars. |
| 3.15″ saddle, rear-exit B+ (common rail) | Required on Yanmar common-rail engines after 2013. |
| 4″ J180 saddle | Most Volvo Penta 4″ J180 mounts, and many larger industrial-based engines. |
| Vortec / GM pad | Mando-type alternators with Vortec/GM feet (many MerCruiser and Volvo Penta gas engines). |
| N62 with clutch pulley | The factory second alternator on many Sprinter-based RVs. |
Not sure? Send us a photo of your current alternator’s mounting feet and we will match it.
Like every Zeus alternator it is built in the USA by ARCO Marine of Pensacola, Florida, and is SAE J1171 certified (ignition-protected for marine engine rooms). Inside: a 16-pole rotor, a large-frame 138 mm stator, dual cooling fans and avalanche-rated diodes, with the rectifier outside the housing to keep heat away from it.
Planning a 24V system? Call us on (410) 216-2907 or start with the Power Guide.