| |
G8MNY > TECH 14.07.05 21:50l 71 Lines 3619 Bytes #999 (0) @ WW
BID : 54263_GB7CIP
Read: GUEST OE7FMI
Subj: Mains Power Protection.
Path: DB0FHN<DB0CL<DB0PDF<DB0SM<DB0EA<DB0ACC<DB0GOS<ON0AR<ON0AR<GB7CIP
Sent: 050714/2038Z @:GB7CIP.#32.GBR.EU #:54263 [Caterham] $:54263_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
After a topic raised by Lodewijk PA3BNX, here is my proposed design for a
protector. Athough spike suppressor plugs etc act fast & do protect to a
ceratin point by blowing fuses, they don't act untim the voltage is over 400V.
The problems about high mains are often due to the neutral having high
resistance at the substation, so if the 3 phase street loads are balanced,
there is little current so nothing gets hot. But when there is abnormal loads
on the other phases you can get 300V mains quite easily! This certainly may
happen if a neighbour blows a 30A fuse, and you get a large pulse on the other
2 phases. This may be enough to blow up a SMPSU etc.
It is also jolly useful on generator supplies!
Unlike mains spike protectors that attempt to snub voltages above 450v this
protector works like an ELCB/RCB (eg an old one could be used as a starting
point) & shuts power off to the load, if the voltage is too high or too low.
____________________________________________________________ N
³ PROTECTED
L ÄÄÄÄÄÄÄ)ÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo\______ L LOAD
POOR ³ Ào-oÄÂÄ´>ÃÄÂÄÄÂÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ¿ FAST
MAINS ³ Fuse_³_ _³_ ³ 47K 47K 100K 8W Lamp RELAY TRIP
< 219V ³ /_\ /_\ ³ ³ ³ ³ ³
or >253V ³ ³ ³ ³ 100K 47K 100K RELAY
N ÄÄÄÄÄÄÄÁÄÄÂÄÄÄ)ÄÄÄÄÄÙ ³ POT<Ä¿ ³ POT<Ä¿ aÃÄÄÄ¿
_³_ ³ ³ ³ NEON1 ³ ³ NEON2 g_³_ ³
\_/ ³ ³ ³ ³ ÃÄ´>ÃÄ)ÄÄÄÁÄÄÄÄ\_/ o ,
³ ³ 1uF ³ 22K ³__³/ ³ ³k / RESET
³ ³ 400V === ³ ³\e 10K ³ ³ PUSH
ÀÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÙ
SET LOW SET HIGH
TRIP TRIP
For 230V ñ10% the RMS max is 253V which is 358V peak. So using a bridge
rectifier & small capacitor, one can determine the voltage. This can be on the
mains direct with dangerous voltages as here, or using a transformer which is
rated for 260V (before saturation!)
The release relay here is a ZAP system, eg an SCR puts 350V DC into a 110V
relay via a Resistor (small) lamp from the 358V DC. This gives very fast mains
break times & the lamp reduces the hold current to a nominal level.
To trigger the SCR you just need a resistor chain with a pot across the 358V DC
with a small 80v neon lamp NEON2 (or zener) from slider to the gate. The neon
will tell you if the mains is still over voltage & the Lamp that the relay is
operated disconnecting the load.
UNDER VOLTAGE
For under voltage consider if voltage is below 230 -10% = 292V peak. The same
idea with pot & a NEON1 to an inverting low voltage NPN transistor then via a
diode to the same SCR gate as before. The trouble with this is that very low
voltages will let the relay release & apply low mains to the kit. If this is a
concern then a release relay system could be used but these are slower!
A push switch does the SCR reset as well as the lamp test.
2 WIRE MAINS
Another power problem affecting hams is the use of 2 wire mains system, were
no earth is used, they call the neutral the earth!! This is OK with plastic
water & gas pipes, but very dangerous if you have a real earth. Houses have
been burnt down by that, as the 30A earth wire used foe bonding to earths,
can't take the whole 200A street neutral imbalance current!!
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
