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6, 24 & 48V Battery Charger System

6V, 24V, 48V External Battery Charger Control

This is an extension of the previously published External Battery Charger Control (12V). It adapts the control for 6, 24 & 48VDC systems. Some of the differences are subtle so pay close attention. The occasion for this article is the requirement of a reader who has a 48V system. At the same time, I thought it logical to also include 6 & 24V versions.

Please note that while the 12V version was tested, these are not tested. While I believe that everything is OK, there is always a possibility for some minor errors.

This External Battery Charger Control applies line power to the motor of a 1kW motor-generator set via a high current relay contact. Upper and lower voltage limit (UL & LL) potentiometers provide full control of the On /Off voltage thresholds thus preventing both battery overcharging and over-discharging. Note that this can also control a static battery charger instead of the M-G set, or even an actively generating solar panel.

24 & 48V Battery Charger Schematic

24 & 48VExternal Battery Charger Control

6V Battery Charger Schematic

6V External Battery Charger Control

System diagram

6, 24 & 48V Battery Charger System

Voltage pre-regulator

In order to support the higher voltage of a 48V system that float charges at about 58V, an LM317HV regulator is required. The “HV” version is rated for 60V, so in this circuit the total input voltage rating is 70V. Note that the LM317 regulator does not have a ground pin so the maximum voltage that it can support is actually added to the regulated output voltage.

Voltage divider

Observe that the voltage divider is different in all cases.

Relay Driver

The 2N7000 does not have adequate voltage rating for use in a 48V system, so a higher voltage MOSFET is specified (ZVN2110A).

Power Relay

The Omron G8P series relay is available in almost any coil voltage rating. Note that the 6V version is not stocked by DigiKey. However there are numerous 5V versions in stock and should work OK on 6V with the addition of a 5.1Ω, 0.5W resistor.

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