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beenthere 06-02-2007 07:21 PM

Project: Battery charger regulator
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This circuit comes from some years ago as a part of a project we did to make it possible to keep a charger on a battery continuously without it overcharging.

It's mostly a junk box project, at least as far as the components used in the one I held onto. This is like late 1970's technology grafted onto 1960's.

The regulator board is a replacement for whatever was in an old Monkey Ward (that is properly Mongomery Ward) charger, rated at 15 amps. The components labelled T1, D1 & 2, Q3, SW1, the ammeter, and the circuit breaker are all part of the charger.

Other components:

Resistors R1 - 7 - 5% carbon 1/2 watt (1/4 watt should be fine)
Resistors R8 & 10 - 1% 1/4 watt. Oops, R10 should be 2.26K
Trimmer R9 - any multi-turn trimmer will do. Single-turn is not good.
Op amp Z1 - any Op amp should do, as long as it's better than a 741. It's used as a comparator, so good input impedance is better. The CA3140 was the hot op amp back when.
D3 - any 2.5 volt reference diode will do.
D4 - any 1N400X will do.
D5 - this is a 4.7 volt zener. $00 mw is fine - no tolerance necessary.
Q1 - we had cases of 2N1613's. Used them for everything. It's a switch, so 2N2222 is a good sub.
Q2 - had bunches of these, too. Just about any PNP will sub.


The output from the full wave rectifiers is pulsating DC. The diode D4 isolates the op amp from these pulsations, and C1 filters it. Z1 is set up as a comparator with the D3 reference diode presenting 2.5 volts to pin 3. As long as the voltage on pin 2 is less than that, the output will be high.

In operation (with the switch in the regulated position) the voltage on pin 2 will reflect the charge on the battery during the low portion of the rectified waveform. If it is less than 2.5 volts, as set by the R9 trimmer, then Z1 output wil be high. That will turn on Q1. In turn, that will turn on Q2. As the rectified voltage increases, so will the voltage between R6 & 7. This will gate Q3 and allow charge to flow to the battery.

When the battery is up to charge (ideally, 13.6 volts), the voltage on pin 2 of Z2 will be high enough to make the output go low. This will leave Q1 & 2 off, and the SCR will not gate again until the battery charge falls a bit lower.

By using a meter, R9 may be adjusted for a very precise charge on the battery.

SgtWookie 01-24-2008 02:26 AM

Was there a schematic? :confused:

beenthere 01-28-2008 11:40 PM

Yes, and I have reposted it. Good 1960's technology there.

alexuma 06-24-2008 09:07 PM

I was wandering if we can replace IC CA3140E with other subs. Any suggestions ?
I am trying to develop a regulator-rectifier circuit for automobile engines but cost was major issue. I really want to bring it as down as possible.
Any feedback on it will be highly appreciated.

mozikluv 06-24-2008 11:46 PM

part substitution
as what "beenthere" has recommended, anything better than a 741 will do as sub and a comparable high input impedance.


jmanna032003 07-06-2008 03:51 PM

the value of Q3?

SgtWookie 07-08-2008 09:41 PM


Originally Posted by jmanna032003 (Post 78173)
the value of Q3?

Good question, actually.

I'll suggest that the current rating of the SCR you choose should be based upon the current rating of the transformer that you select. Double the current rating for long life. Voltage rating is up for grabs, but just about anything over 50v should do fine.

theamber 07-09-2008 08:39 PM

However this circuit is ok for NiCd or NiMH batteries.
But best way to charge a Lead Acid battery is with a current limited voltage regulator. This way sets a maximum current of the reg. that will flow to charge the battery. If the current rises over this set current, the regulator will put out a lower voltage. Since voltage drops, so will the current; hence current limited.
While the battery is charging, the current should decrease slowly while voltage starts to increase. In the end the current will be next to zero and the voltage will be equal to the set voltage.
Here is a simple schematics at the bottom of this page.

Or you can go simpler with this however cannot go unatteded:

mozikluv 07-11-2008 01:12 PM

lead acid battery charger with float
1 Attachment(s)
here's a design by "tony van roon" on a lead acid battery charger with float.


alexuma 07-11-2008 04:35 PM

Best way to Switch ON/OFF SCR
What would be the best way to switch ON/OFF a SCR ?

I wanted to use it as a switch in a 12V lead acid charger circuit; i.e when battery voltage goes 14.2 V, STOP charging when it comes down 12V start charging with some 10-15 Apms charging Alternator (after rectification) !

I was thinking to use comparator (IC 741) based switching circuit. I want to make it robust with fewest number of components.

Any ideas will be appreciated.


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