Multiple Battery Charger Circuit using Dump Capacitor

In this article I have explained how to build an automatic battery charger circuit using dump capacitor concept for self detecting and charging a multiple set of batteries. The idea was requested by Mr. Michael.

Circuit Objectives and Requirements

1. My name is Michael and live in Belgium.
2. I found your site thru google during my search of a battery trickle charger.
3. I've checked all 99 battery chargers but couldn't find one that maintains multiple batteries.
4. I'm still looking for a good circuit, therefore I hope maybe you can help me out.
5. At home we have a variety of lead acid batteries and during the winter most of them get neglected.
6. Resulting in spring, a check which battery made it and which one didn't.
7. Problem is the variety of batteries I'm a biker, my brothers has a small excavator and tractor, we have 2 vans with 2 caravans and we ( I, mother, sister, 2 brothers and there girlfriends) all have a car.
8. So you see a WIDE variety of batteries, in the past I've bought a smart 7stage charger but it is impossible to take care of all batteries using only one charger.
9. So I ask if you could design a circuit for me.
10. With the following specs:
11. Maintain at least 5 or more batteries simultaneously.
12. Checks voltage if low dumps a capacitor into the battery.
13. Able to handle capacities as low as 3 Ah up to 200Ah.
14. Safe to operate 24/7 with no user input.
15. Some of the things I've given some thought:
16. With the use of a cap dump, there's no need for a heavy mains transformer, because the load for transformer is under control.
17. A selectable capacitor depending on the capacity of the battery.
18. A problem for me was to find something that could activate multiple outputs on a time base(using a lm311 to sense the voltage, a 555 to dump using mosfet).
19. An indicator of some sort, which will indicate which battery needed the most dumps or immediate dumps, and locate bad batteries.
20. If you believe I've made some errors, or my requirements are impossible please let me now.
21. If you could implement extra features or safety features, I didn't think of do not hesitate to add or modify:)
22. I'm a student getting a bachelor in Electro Mechanics, I'm a electronic enthusiast, have a room full of components and parts to play with.
23. But I lack the designer skills for building circuits for my needs.
24. I hope to have drawn your interest in this problem and hope you find the time to design something for me.
25. Maybe this circuit could become number hundred on your site!
26. Also great job with your site and hope al the best for you!

The Design

The discussed circuit concept for automatically charging multiple batteries using dump capacitor can be fundamentally divided into 3 stages:

1. opamp comparator detector stage
2. IC 555 ON/OFF interval generator
3. dump capacitor circuit stage

The opamp stages are configured to maintain a continuous sensing of battery charge level, and correspondingly execute the cutoff /restoration of the charging process across the batteries attached with their relevant inputs. The charging process is carried out through capacitor dump system.

Let's undersatnd the various stgaes elaborately:

Self Regulating 4 Battery Opamp Charger Circuit

The first stage within this design is the opamp battery over charge detector circuit, the schematic of this stage can be seen below:

Parts List:

opamps: LM324

presets:10K

zener 6V/0.5 watt

R5 = 10K

diodes = 6A4 or as per the charging specs

We will consider only 4 batteries here, and therefore use 4 opamps for the respective over charge cut offs. A1 to A4 opamps are taken from the quad opamp IC LM324, each configured as compartaors to detect the attached corresponding battery over charge levels.

As can be seen in the diagram the non-inverting inputs of each of the opamps is configured with the relevant battery  positives for enabling the required sensing of the battery voltages.

The positives of the individual batteries are connected with the capacitor dump output, which I will elucidate in the later part of the article.

The inverting (-) pins of the opamps are designated to a fixed reference level through a single common zener diode.

The presets attached with the (+) or the non-inverting inputs of the opamps and are used for setting up the precise full-charge trip points with respect to the corresponding (-) pin zener reference levels.

The presets are set such that when the relevant battery voltage reaches the full charge level, the proportionate value at the pin(+) of the opamp just goes above the (-) pin zener reference level.

The above situation instantly turns the opamp's output from its initial 0V to a high logic equal to the supply voltage level.

This high at the opamp output triggers an IC 555 atable circuit so that the IC 555 is enabled to produce a periodic ON/OFF intervals over the attached capacitor dump circuit...the following discussion have explained us the proceedings:

IC 555 Astable for Generating periodic ON/OFF

The following schematic shows the IC 555 stage configured as an astable for the intended periodic ON/OFF switching generation for the subsequent capacitor dump circuit.

Parts List

IC = IC 555

R2 = 22K

R1, C2 = calculate to get the desired charge dump cycle rate

As shown in the above diagram, pin#4 which is the reset pinout of the IC 555 is connected with the output of the relevant opamp stage.

Each of the opamps will have its own separate IC 555 stages along with the capacitor dump circuit stage.

While the battery is in the charging process and the opamp output is held at zero, the IC 555 astable stays disabled, however the moment the relevant attached battery gets fully charged, and the concerned opamp output turns positive, the connected the IC 555 astable becomes activated, which causes its output pin#3 to generate a periodic ON/OFF cycles.

The pin#3 of the IC 555 is configured with its own individual capacitor dump circuit, which responds to the ON/OFF cycles from the IC 555 stage and begins the process of charging and dumping a capacitor across the relevant battery.

To understand how this dump capacitor behaves in response to the IC 555 ON/OFF cycles we may have to go through the following section of the article:

Capacitor Dump Charger Circuit:

As per the request the battery is required to be charged through a capacitor dump circuit, and I came up with the following circuit, I hope it would do the job as per the expectations:

The circuit functioning of the above shown capacitor dump charger circuit can be learned following explanation:

• As long as IC 555 stays in the disabled state, the BC547 is allowed to get the required biasing through its base 1K resistor, which in turn keeps the associated TIP36 transistor in the ON position.
• This situation allows the high value collector capacitor to get charged to its maximum allowable limit. In this position the capacitor is armed in the charged stand-by position.
• The moment IC 555 stage gets activated and begins its ON OFF cycle, the OFF periods of the cycle switches OFF BC547/TIP36 pair, and switches ON the extreme left side TIP36, which instantly closes and dumps the charge from the capacitor into the associated battery positive.
• The next ON cycle from the IC 555 reverts the situation into the previous conditions and charges the 20,000uF capacitor, and yet again, with the next subsequent OFF cycle the capacitor is allowed to dump its charge via the relevant TIP36 transistor.
• This charging and dumping operation is carried out continuously until the corresponding battery becomes fully charged, forcing the opamp to turn OFF itself and the whole proceedings.

All the opamps work in the similar manner, by sensing the attached battery condition and self starting the above explained procedures.

This concludes the explanation regarding the proposed automatic multiple battery charger using capacitor dump charging, if you have any questions or doubts, do not hesitate to communicate through comments...