High Voltage Battery Charger Circuit

The post details a simple automatic High Voltage Battery Charger Circuit which can be used for an automatic charging control of any preferred high voltage battery bank such as a 360V battery bank. The idea was requested by "resonance".

 The Request

Hello yonder,
I found all your circuit and projects interesting but
please I need a special assistance. I want to build a Low and high
battery full cutoff that can handle about 360VDC (30 Batteries in
series) such that when battery is full at 405VDC charging Voltage will
cutoff and when battery drop to like 325VDC it also cutoff battery low.
Please, do share this experience with me.

The Design

The figure above shows a straightforward configuration for achieving the proposed automatic high voltage battery charger circuit in the order of 360V.

The idea is based on the standard opamp based comparator principle, which is also implemented in many of the earlier 741 based battery charger circuits.

The circuit functionality can be understood as explained below:

The 360V is achieved by adding 30 nos of 12V batteries in series, which constitutes 430V level as the full charge threshold, and 330V as the full discharge level threshold.

The battery bank voltage needs to be controlled within these limits for ensuring a safe charging environment for the batteries.

The opamp circuit is configured for implementing the above mentioned high voltage charging control as indicated in the diagram.

The 360V is stepped down to a suitable proportional level for the opamp sensing input at its non-inverting pin#3 applied via a 10k preset. This is done through a potential divider network using a 220k and a 15k resistor.

The inverting pinout of the opamp is clamped at 4.7V through a zener diode for providing a reference to its complementing pin#3 sensing input.

The operating supply voltage for the opamp pin#7 is extracted from one of the batteries associated with the negative line of the system.

The preset is adjusted such that the opamp output pin#6 just becomes high and triggers the transistor when the battery voltage reaches at around 430V.

The above action forces the relay to operate and cuts off the supply charging voltage to the battery bank.

As soon as this happens, the battery voltage tends to go down a bit which normally prompts the opamp to trigger back the relay ON, however the presence of the feed back resistor connected across pin#6 and pin#3 holds the opamp situation, and prevents this from happening.

This is also called the hysteresis resistor which temporarily latches the opamp to a certain voltage range depending on the value of this resistor (Rx).

Here it must be selected such that the opamp stays latched until the voltage of the battery bank drops to about 330V, after which the opamp could be expected to restore the relay back in its N/C position initiating the charging process for the batteries.