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G8MNY > TECH 16.07.03 00:35l 71 Lines 3235 Bytes #999 (0) @ WW
BID : 5757_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: Simple SCR Regulated Charger
Path: DB0FHN<DB0RGB<OK0PPL<RZ6HXA<SP7MGD<GB7YKS<GB7MAX<GB7YFS<GB7TUT<GB7CIP
Sent: 030715/0711Z @:GB7CIP.#32.GBR.EU #:5757 [Caterham] $:5757_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
This is a simple SCR controlled charger. It was made to give 27.5V at 15A for
charging a train carriage's 500 AH 24V battery lighting system. It is not
suitable for use with electronic equipment that can't operate on hummy
supplies!
Using a dual winding transformer or a single one with 2 other diodes so the
SCRs form part of a bridge... Or 1 SCR arm following a bridge rectifier.
SCR1
AC1 __________________!\!____________________
! _____ !/!\ !
!____!\!__!1K !_____!__!\!__ !
!/! !____! !/! ! !
! !
SCR2 ! !
AC2 __________________!\!___________________!
! _____ !/!\ !
!____!\!__!1K !_____!__!\!__! ! +
!/! !____! !/! ! __!__
__!__ ===
/ \ ' ! BATT
--- !
AC RETURNS ZENER ! !
________________________________!_________!
__!__
/////
The Zener can be a virtual one for voltage adjustment with current limiting
changing the voltage as well.
!
----------------------------
VIRTUAL ZENER WITH ! ! ! !
CURRENT LIMITING ! + c \! POT c \!
--- !------>10K !---------
100uF === e /! ! e /! ! !
! ! ! ! !+ !
! ---\ ! ! --- 1K
! / \ ! ! === !
! --- ! ! !10uF !
! ! ! ! ! !
-VE ret ---------------------------------------\/\/---- Batt return
SHUNT
The Zener can be 5-10V (12v system). Both transistors are NPN. Set the voltage
pot so that the Zener action is 1V higher than the required Battery voltage.
Make the shunt resistor (thick wire link eg a few inches of coat hanger) so at
the maximum current wanted the 2nd NPN conducts to limit the trigger voltage &
hence the current.
The transformer must deliver an RMS voltage slightly greater than the battery
voltage plus diode & wiring losses. If too low triggering the SCRs can be
difficult, but a 2nd 2v winding put around a toriodal/leg of the transformer to
feed the trigger circuit can keep the unit working well on low mains (the train
PSU had to deal with mains of less than 200V AC at times).
This circuit is very efficient, only the transformer heats up with the high
pulse current, & SCR losses, no half power lost in dropper regulator! So a
thermal trip mounted on the transformer in case it overheats in heavy loading
conditions is recommended.
For recharging 12V batterys use 14.5V DC setting, for float (infinite charge
rate) use 13.8V, with sealed types use 13.5V MAX.
/QSL
73 De John, G8MNY @ GB7CIP
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