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G8MNY > TECH 23.03.15 12:30l 119 Lines 5489 Bytes #999 (0) @ WW
BID : 25832_GB7CIP
Read: GUEST
Subj: Small Alafontronica 500W UPS
Path: IZ3LSV<IK6IHL<IK7NXU<IW7BFZ<I3XTY<I0OJJ<GB7CIP
Sent: 150323/1012Z @:GB7CIP.#32.GBR.EURO #:25832 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Dec 14)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This small UPS, is supposedly up to 500W of power. It is a 50Hz pulse width
stepped square wave mains inverter all from small 7AH 12V battery when in
backup mode (e.g. 55A @ 11V ?)
FRONT INTENAL SIDE VIEW
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ heatsink ______
³ÚÄÄÄÄÄÄÄÄÄÄÄÄÄ¿³ ÜÜÜÜÜÜÜ reg Freq Volts ³RELAYS³ DATA
³³ùOn On[]³³ =====================================================PORT
³³ùBackup ³³ Ûßßßßßß __
³³ùCharge Off[]³³ Û ³~~~~~~~~~~~~~~~~³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄ¿
³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÙ³ Û ³ __________ ³ ³ ³
³ ³ Û ³ ³ ³ ³ ³ ³
³ ³ Û ³ ³ MAINS ³ ³ ³ ³ IEC
³ ³ Û ³ ³ TRANS- ³ ³ ³ 12V BATTERY ³ OUT
³ ³ ³ ³ FORMER ³ ³ ³ ³
³ ³ ³ ³ ³ ³ ³ ³
³ ³ ³ ³ ³ ³ ³ ³ FUSED
³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ³ IEC
³ ³ ³ ³ ³ batt fuse ³ IN
³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
DESCRIPTION
The transformer has tapped primary & 2 secondaries, one into a bridge & SCR for
charging. And the 2nd is the centre tapped inverter input winding. Two relays
control the mains side, one for mains tap & other for mains connection.
On power fail the mains relay releases & the 2 large Tab FET switching
transistors sandwiched in the heatsink, run at 50Hz giving the waveform below.
On mains return the 50Hz is 1st phase locked to the mains, before switching off
& connecting back to the mains. Another relay als changes the output tap on
backup mode.
OUTPUT WAVEFORM with load (ringy from transformer & filter)
+340V´ ÚÄÄÄ¿ Peak Voltage depends on Battery state & Load current!
+230V³ ³ ³ Pulse width varies to get 230V RMS?
³ ³ ³
0V ´ÄÄÙ ÀÄÄÄ¿ ÚÄ
³ ³ ³
-230V³ ³ ³
-340V´ ÀÄÄÄÙ
USES
Mainly for computerised kit, that might suffer file corruption or even HDD
damage on some power fails. But note a non "on line" UPS can still be fooled by
bad "brown outs", where the mains voltage does not go straight out, but has a
few cycles close to the kit's PSU safe minimum voltage (e.g. drops to 150V for
1 second while someone is blowing a fuse & then out!) So kit PSU becomes
desperate for power & the UPS does not cut in, in time to stop the kit's PSU
giving illegal & corrupting voltages.
UNMANNED SITE MODIFICATIONS
As with most UPSs, this UPS is not suitable for an unmanned site. This is
because when the battery is emptied/fails on a long discharge, not only does
the output fail, but the UPS then stays in OFF mode with no output power, even
when the mains power restores!
So I designed 2 modifications to solve this...
1/ OUTPUT FAIL BYSASS RELAY
By adding a small 5A double pole mains changeover relay (low current 30Kê AC
winding) to the load side, when the output fails, the relay releases & the load
is then connected direct the mains. But nothing is that simple, as my relay did
not operate correctly & tended to Buzz on UPS changeover.
Mains L ÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿nc
ÚÁÄÄÄÄ¿ \_____ L
³ ÃÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÙ
³ ³L 10k LOAD
³ UPS ³out- Ú´>ÃÄÁÄ´>ÿ WITH
³ ³put ÃÄÄRELAYÄÄ´ UPS
³ ³N À´>ÃÄÂÄ´>ÃÙ BYPASS
³ ÃÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄ¿ _____
ÀÂÄÄÄÄÙ / N
Mains N ÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙnc
So I added a 4 diodes bridge & a series R of 10K (do not use series cap on
square wave mains!) This slowed down the action OK, from 10mS to <100mS.
2/ AUTO RE-START
Having done above, I now wanted the UPS to come back in when the battery is
recovered. On scoping around, I found the ON button was just a -ve on a low
current 12V circuit, to the ON logic. There was also a pulsed +ve 18V charging
waveform feeding the charge LED via 1kê, that diminished to 1V when the battery
was OK. So a little scratching of head I came up with this circuit...
18V 100Hz
Charge ÄÄÂÄÄ220Ä´>ÃÄÂÄÄÄÂÄ´<ÃÄÄÄÂÄÄÄÄ>ON
Pulses 1K ³+ ³ ³ ON
_³_ 10u=== 100k /button
Chargeð\_/ ³ ³ ³
ÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄ -12v
When the pulses reduce, the 10u discharges through the 100K to level were the
12V ON electronics starts up, doing a self test & back on. Although this does
not come straight back on when te battery might be usable, after a UPS
exhaustion event, leaving the load on normal unprotected mains via my 1/ mod.
However tt does come back automatically eventually & hopefully with a usable
battery.
A label was added to warn of the modification & how to turn the unit off.
e.g. POWER OFF UNIT WITH MAINS ON & then disconnect input mains.
SAFETY WARNING
This UPS has the DC battery -ve on the neutral, not mains isolated! I did all
my testing with an isolated mains supply & a scope earthed to battery -ve.
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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