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What is a rectifier?
A rectifier converts alternating current into direct current and holds a DC bus and its battery at a regulated float voltage. In telecom and substation systems the rectifier feeds the load continuously and keeps the battery charged, so when the AC input fails the battery takes over the DC bus with no break at all.
DC power systems are the quiet backbone of telecom and substations. No transfer time, no inverter in the critical path, and a battery that is always connected.
Where rectifier systems are used
Telecom sites standardise on 48 V DC for base stations, transmission, and core equipment. Substations use 110 V or 220 V DC for protection relays, breaker tripping, and control. Both share the same architecture: parallel rectifier modules on a common bus, a battery string floated across it, and a controller that manages charging, alarms, and low voltage disconnect.
Float, boost, and temperature compensation
Float voltage holds the battery topped up without overcharging, typically around 2.25 V per cell for VRLA. Boost or equalise charging is applied briefly after a deep discharge to restore capacity faster. Temperature compensation lowers float voltage as the room warms, which is the single cheapest way to protect battery life in a hot site.
Redundancy and sizing
Rectifier systems are sized as N plus 1: enough modules to carry the full load plus recharge current, and one spare. Recharge current matters, because a system sized only for the load will take days to bring a deeply discharged battery back. A common rule is to allow 10 to 20 percent of the battery capacity in amperes as recharge current on top of the load.
Frequently asked
- What is the difference between a rectifier and a UPS?
- A rectifier delivers DC to a DC load with the battery permanently connected. A UPS delivers AC, converting DC back to AC through an inverter. Rectifiers suit telecom and control loads, UPS suits AC equipment.
- Why 48 V in telecom?
- 48 V is high enough to keep cable losses reasonable and low enough to stay within extra low voltage safety limits, which simplifies installation and maintenance at unmanned sites.
- Do rectifier batteries still need testing?
- Yes. A floating battery gives no indication of remaining capacity. Impedance trending plus a periodic capacity discharge test is the only way to know the site will survive an outage.