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
6V Battery Charger Schematic
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.
Observe that the voltage divider is different in all cases.
The 2N7000 does not have adequate voltage rating for use in a 48V system, so a higher voltage MOSFET is specified (ZVN2110A).
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.