power supplies and battery chargers

7/27/2019 Power Supplies and Battery Chargers

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DISCLAIMER : - The drawings, proceedures and words are for information only.No claims are expressed or implied as to the safety, usefulness, or accuracy of this

information. I will not accept any liability for any damages caused to people or property

from the using of this information or from any associated links. Your actions are your

responsibility - VERIFY and CHECK information out before proceeding, and don'tattempt anything without the required skills, if you cannot agree to this, leave this page

now . . . . . . . Chris.

The circuit below is a switchmode power supply that is one of my favorites. I have built many of these

and they can tolerate an absolute hiding. (Some of you may believe switchmodes are faint hearted ,

well , some are! ) This unit would be ideal for converting power from say 24v to 12v in solar power

installations. The number of series pass transistors you use will depend on your "current"

requirements. , (sorry!). It uses an LM317 which is rated at 1.5 amps and has short circuit outputprotection. It can have an output input differential voltage of 60 volts, and has a voltage adjust

terminal which allows an output voltage as low as 1.2 volts. Operation briefly - The LM317 operates

as a regulator delivering the voltage required as set by it's adjust voltage resistor string to ground and

the 240 ohm to o/p. When current is drawn from the output terminals of the supply the LM317

attempts to deliver the power which creates a voltage drop across the 30 ohm resistor on the 317s

input leg. This biases the MJ2955 on which then biases on the bank of MJ15003's to feed power to

the output via the toroidal inductor. Energy is stored in the inductor during this phase and released

into the load via the free wheel diode when the transistors turn off. (This circuit will operate as a

linear regulator as well by removing the inductor and diode). Regulation is maintained via the 240

ohm resistor on the output, this is the voltage "sense" input, and the wire should be connecteddirectly to the output terminal of the supply. Ripple can be surpressed by monolithic caps across the

output and using much C. I have built a number of these and can honestly say they have been

absolute workhorses, and rarely have they blown up. (switching ripple may be a problem for some

amateur radio gear however).

wer supplies and Battery Chargers http://www.freewebs.com/acselectronics/buildregs.html

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This is a traditional shunt regulator circuit using an LM723, they do a good job but once the battery is

charged they sit there and get hot dissipating the power from your solar panel. I recommend the next

circuit below this one. The 723 can output 150mA of current to control the external transistors. It cantolerate voltages up to 40v and is adjustable from 2 to 37 volts. This circuit works by comparing the

voltage set at pin 4 (inverting input) which is derived from the internal reference (pin 6 - 7.15v) and

adjustable via the 1k trimpot, pot midpoint = 5.87v), and that of the voltage on pin 5 (non-inverting

input) which is the sampled battery voltage (via 6K8 and 4K7 for 12v operation). For operation at 24

volts change the 6K8 for 18K, and ensure the shunt transistor can handle the load and is adequately

heatsunk. (parallel transistors as necessary).


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Below is another shunt regulator , with a difference. This uses an LM358 op amp. (it's a dual op-amp

with 1 package unused - take the unused inputs to + and - supply to ensure chip stability). This uses

the inverting input as the reference voltage (7.5volts) and is compared against the battery voltage

which is sampled by resistor strings , 10K, 20Kpot, 10K for 12 volts or 47K, 20Kpot, 10K for 24 voltoperation. (select appropiate links - "red" link set for 12 v). When the battery sample voltage rises

above the reference voltage the output (pin1 ) goes high and switches on the FET and allows power

to be diverted to a "load". The FET gate is protected against overvoltage by a 16 volt zenner for

operation on 24 volts, the LM358 can handle voltages up to 32 volts. ( if you wish put an additional

100 resistor and 30 volt zenner on the chip supply line). This sort of regulator is good because you

have the option of using this "diverted" power for something you may want instead of just warming

the corner as with traditional shunt regulators. Again use a number of power fets in parallel to

increase your power capability. Use enough fets to double the watt rating of the solar panels so it

won't get hot . Look on the battery disconnect project or PWM DC controller project to how to parallel

more FETs. The 1N5401 is there to protect the circuitry from a load that may generate back EMFs.

An inductive load such as a motor has the potential to destroy components with this high inducedback voltage.


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This next regulator uses the comparators within an LM555 timer chip. Basically the trigger input if it

goes below 1/3 of the applied Vcc the associated comparator goes high and sets the internal flip

flops output (Q=high, not Q = low) which drives the output amplifier (inverter) high. (pin 3 = high).When the threshold input goes above 2/3 Vcc then the reverse takes place. The trigger and

threshold inputs are connected to sample the battery voltage so the Threshold input sets the "off"

voltage setpoint, and the Trigger input sets the "on" setpoint, while the control voltage is set to 6v8

volts. (pin 5). The output is used to turn on the FET in the negative lead of the solar panel and

battery. (switching takes place on the negative line, the battery and solar panel positives are tied

together). Operation is possible for a 24 volt system using a 7812, 7815 or 7818 regulator to supply

the 555 and limit the applied gate voltage. Sampling pots are tied to a 6K8 resistor to the 24v battery

terminals. The circuit below show the 12 volt operation.


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Next is a series pass regulator for providing 12 volts to small appliances such as "getto blasters" ,

"Laptops" , "Lights" , "small TV's " , etc from a solar panel. Obviously the solar panel isn't running at

it's most efficient and I can't vouch for the laptop if a cloud passes over. Needless to say the solarpanel has to be large enough to run the appliance and the series pass transistor and heatsink

capable of dissipating the "headroom " energy of the panel array.


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The next ccts are good for gel cells and the like. They use an IC from Unitrode Corp. They have built

in smarts and indication so you know whats happening, again use as many series transistors in

parallel for your current needs.


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This one is good for small current applications that require a positive and negative rail or perhaps a

negative rail off some other supply you have . It uses a LM555 to drive a couple of transistors that

alternately charge up caps in series , so doubling the voltage 12 to 24 , 18 to 36, 9 to 18 volts ,

whatever. It is suppose to deliver 200Ma , I have used this once, but I didn't require that higher

power.

.


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This is a simple, good "solid" battery charger for 12 volt lead acid batteries. The design is a bit old

and the pot may be difficult to source. (If you have difficulty finding the scrs, use around a 15 amp 80

volt for scr1 and a 2 amp 80 volt for scr2 ). When the battery is low scr1 fires through R and the

unlabeled 1amp silicon diode. When the voltage reaches the desired level set by the 500 ohm pot

the zenner fires turning on scr2. This causes a voltage across both 27 ohm resistors and removes

the firing voltage from scr1 which stops the charging. If the battery voltage falls below the preset

value the zenner diode will block, turning off scr2 and charging will resume through scr1. This type ofcharger is probably best for battery charging as it charges in "pulses" as it uses unfiltered full wave

power. ( Don't be tempted to hang an electro of it, to smooth it otherwise the scr's won't turn off ! )

Good luck Chris.

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