The power tray of the Heitz System 4 has DC/DC converters charging batteries with circuitry very similar to Sprint 3.
Five batteries in series are used to provide the (nominal) 60V power to the servo amplifiers. A sixth battery is used for stable “System12V” power. Each of the six batteries are charged by DC/DC converters using input power from the vehicle 12V battery. “System12V” and “60V) are therefore isolated from CAR12V by the DC/DC converters.
The left side of the front panel has BNC connectors for ABORT, Raw SPEED, Raw DECEL and TEST. These signals are fed to a connector at the rear D/Sub, and to each tray through a vertical rear interconnect board. The front panel also has a D/Sub connector for analog external command signals for each tray, fed around to the vertical rear interconnect board.
All of these signals except "ABORT" have a common "External Ground", which is converted to internal signal ground by isolation amplifiers in each tray. SPEED and DECEL are "raw" inputs which are scaled appropriately in each tray.
Batteries are Heitz-designed Lithium batteries, assembled with high power "intrinsically safe" cells with Nanophosphate® lithium iron phosphate (LiFePO4) technology. They have current-time characteristics superior to, and have about one-third the weight of the Sprint 3 batteries.