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G8MNY > TECH 22.05.26 16:26l 62 Lines 2602 Bytes #5 (0) @ WW
BID : 60413_GB7CIP
Subj: Battery Backup PSU
Path: JH4XSY<IW0QNL<HB9ON<DK0WUE<PI8ZTM<CX2SA<ED1ZAC<GB7CIP
Sent: 260522/0717Z @:GB7CIP.#32.GBR.EURO #:60413 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Sep 07)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is my design for a backup PSU suitable for a repeater etc. It offers a
different approach to just paralleling up a battery with a PSU.
FEATURES
Trickle charges battery @ 14.2V boost or 13.5V normal @ up to 1A peak.
A flat battery does not hold repeater off air/blow up PSU.
LED indicator shows "battery present" when mains is on.
CIRCUIT
Fuse +20V _____
ﾄo-oﾄｿ ﾚﾄﾄﾂﾄﾄﾄﾄｴ>ﾃﾄﾄﾂﾄﾄﾂﾄﾄﾄﾄｴ13.8Vﾃﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ______Tx Power
)ｺ( ﾃﾄｴ<ﾃﾄﾄｿ ｳ ｳ+ ｳ Reg ｳ +ｳ100u /Relay 1-3A
MAINS )ｺ( ｳ ｳ ｳ === ~~ｳ~~ === ﾚﾙ
)ｺ( ｳBridgeｳ ｳ ｳ10mF ｳ ｳ ｳ
)ｺ( ｳ ﾚｴ<ﾃﾄﾁﾄﾄ)ﾄﾄﾁﾂﾄﾄﾄﾄﾄﾄﾁﾂﾄﾄﾄﾄﾁﾄﾄ0V ｳ
ﾄﾄﾄﾄﾄﾙ ﾃﾄﾄ)ﾄﾁﾄﾄﾄｴ>ﾃﾄﾙ __ｳ__ u1 ｳ u1 boostｳ
15V ｳ ｳ ｳrelayｳ ﾚｴﾃﾅﾄｴﾃｿ ﾚﾄo/ﾄﾄｴ
4A ｳ ﾀﾄﾄｴ>ﾃｿ ~~ｳ~~ ｳ _ｳ__ ｳ D7 ｳ ｳ
ﾀﾄﾄｴ>ﾃﾄﾄﾄﾁﾄﾄﾄﾄﾄﾂﾄﾁﾄﾄﾄﾄﾁｴ7815ﾃﾁﾄﾄｴ>ﾃﾄﾁﾄｴ>ﾃﾂﾁﾄﾄo-oﾄ +Battery
D5 D6 e\ｳ in ~~~~out D8 ｳ Fuse
PNPﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ68Kﾄﾄﾄﾄﾄﾙ
/ｳ
ﾀﾄﾄﾄﾄﾄ1K5ﾄﾄｴ>ﾃﾄﾄﾄ0V
D5-8 1N4002 || LED
Main regulator & Mains & Battery
7815 on heatsink Present
OPERATION
The +13.8V PSU is quite conventional as needed, but with the addition of D5 &
D6 supplies raw DC power to the mains fail relay, which connects the battery
instead of the PSU when it is released. Extra "no drop out diodes" could be
placed across the relay contacts if absolutely no power break is required
e.g. to feed a uProcessor PCB.
This raw DC is also used to charge & maintain the lead acid battery. The charge
voltage is either 1 or 2 diode drops less than the 15V regulator output as
needed.
On the battery going flat after a long mains failure for example, the 15V
regulator limits the battery recovery current to 1 amp (why it needs to be
heatsinked), which stops the battery from taking down the PSU, so the repeater
will come back on as soon as mains is restored even on a shorted battery.
N.B. This is the opposite to some strategies (UPS) that wack in full current
into the battery in case of another power failure.
The LED battery indicator shows the presence of the battery when the battery
voltage is less than the raw DC rail voltage by turning on the PNP transistor.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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