Reducing power surge on AC adapter

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chessman
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Reducing power surge on AC adapter

Post by chessman » Thu Jul 15, 2004 7:30 pm

Quick and simple question:<p>I have an AC adapter for a laptop that's killing a 12V inverter. The power consumption of the adapter is well within specs of the inverter, yet the inverter is overloaded and shuts off due to an on-power surge.<p>How can I limit this surge?

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MrAl
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Re: Reducing power surge on AC adapter

Post by MrAl » Thu Jul 15, 2004 8:12 pm

Hello,<p>How many amps and what voltage does the
adapter put out?<p>Take care,
Al
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haklesup
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Re: Reducing power surge on AC adapter

Post by haklesup » Fri Jul 16, 2004 12:45 pm

You say the inverter circuit protection trips upon power up of the AC powered switching supply you have plugged into it. Does it power the PC ok after it is powered up or have you ever gotten that far.<p>If the Inverter were starved then you could put a cap in parallel with the DC input but that would only cause a short if used on the output. <p>Is it protected by a fuse or a curcuit breaker. If a fuse, use the same rating but find a slow blow type (you may be using fast blow instrument type now) If a circuit breaker try finding a replacement with similar slow blow characteristics or replace it with one 25% higher.<p>Or get a bigger inverter. Have you confirmed the inverter works for say a lamp.

cato
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Re: Reducing power surge on AC adapter

Post by cato » Fri Jul 16, 2004 1:47 pm

Plug in the adapter on a zero crossing of the power line :D

upsmaster
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Re: Reducing power surge on AC adapter

Post by upsmaster » Sat Jul 17, 2004 7:37 am

I don't think u can, The inrush is so high that the DC to Ac inverter stalls and won't start. Some short time fix could be the tempture of where u are operating the inverter cold temps will cause your problem and too small of wire size on the DC input side of the inverter. Had this same problem with a controller for placeing fiber optic cable for phone company. The inverter worked ok in side but when it was used outside in cooler to cold weather it would stall upon start up. Had to go to larger inverter to solve the problem. Both devices u are useing draw large slugs of current when they start up nature of the devices
joe

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MrAl
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Re: Reducing power surge on AC adapter

Post by MrAl » Sat Jul 17, 2004 7:52 am

Hello again,<p>Probably the reason for the higher inrush
is the same as with any rectifier and
capacitor ac to dc bridge...that is, the
caps draw very high peak currents around
the peak of the sine wave and zero elsewhere.<p>If the inverter is reacting to the initial
charge only, you may be able to simply
switch a small value resistor in series
for startup, then short it out after startup.
This will give the caps time to charge up
and so will reduce inrush (1 or 2 seconds).
If the inverter is responding to the cyclic
higher peaks, then you might need to keep
a resistor in series if the system will
tolerate this.<p>Those bridge rectifier / capacitor filters
always draw high current peaks.<p>Take care,
Al
LEDs vs Bulbs, LEDs are winning.

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dacflyer
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Re: Reducing power surge on AC adapter

Post by dacflyer » Mon Jul 19, 2004 1:54 pm

they do make inrush limit resisters...i forgot their specific name...i used to use a 120v 100watt lamp in series for circuits less then 100 watts.. the rush of current would be dissapated thru the lamp the lamp would light for a split second as the caps charged...then the power supply would be just fine..the power supply for your laptop doesn't draw hardly any power once it gets past the start up surge...
good luck,,

ng2aradiofunk
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Re: Reducing power surge on AC adapter

Post by ng2aradiofunk » Mon Jul 19, 2004 9:36 pm

"I have an AC adapter for a laptop that's killing a 12V inverter. The power consumption of the adapter is well within specs of the inverter, yet the inverter is overloaded and shuts off due to an on-power surge"<p>Ok,
the inverter 'shuts off' as it was probably
engineered to do...<p>1] due to fully engineered instantaneously acting low voltage dropout at about 10.5volts on the 12volt supply side, which will auto-reset upon
supply increase above that 10.5volts.<p>2] due to partially-engineered load-side over-current stopping of the inverter oscillator, from brute force core saturation, then 'latched-out'
until manually de-powered and re-powered.<p>3] due to specification of 'power handling'
They REALLY mean 100Watt absolute max, and
80watt max continous (with cooling beyond that
normally available). Hence, for a nominal
60watt computer load, you might want a 300watt
minimum sized inverter WITH SINE WAVE of course
Certainly there's nobody out there using something
bought at a flea market vintage 1986! <p>I'd guess low supply voltage to the inverter, as
result of excessive IR voltage drop. <p>Much bigger wire is required than you might guess, when the prime supply is vehicular 13.6volt nominal, or half-discharged lead battery at about 12.3volts. <p>With HOUSE wiring at 115/120volt nominal, 10 volts
drop is workable (but not safe with the fire marshal). <p>In this system, a drop from 12.3 to
10.5 volts, 1.8volts, is not workable.
Now,...we are talking about 10x the current
for the same power on a 12volt system,
simultaneous with 1/6 the allowable
voltage drop.<p>HENCE wire size of 10x6=> 60 times the
circular mils on a 12volt system for
the same POWER delivery.<p>So, delivery of say 80watts 12 volts
at 10 feet, on TWO wires (don't even think of chassis-return HERE) => 20 feet say 6.5 amperes
and max transmission loss about 50% of 1.8volts
(12.3=>10.5)= 0.9volts...ect..ect..ect..
Look it up in the wire tables..but basically
rule of thumb, #8 wire is ALMOST too small here. <p>A] You could validate this failure mode mechanism, with a storage scope on the DC side, not a meter. Or apply an absolutely SOLID 12-13.5 volts, using battery jumper cord direct to a known charged battery, better yet, vehicle engine 'on', giving hopefully 14.8volts
or so at the battery...14.8 if it is weak, 13.6-13.8 if fully charged and new/chemically correct.<p>B] Secondly, power-up with the laptop OFF, let
some seconds of time elapse, then bootup...where
and when in the bootup does the inverter 'shut off'<p>
SO,
That's where to look.
Even Random Looking, causes focus and even thinking ...<p>I'd tend to discount Equipment engineering failure/deficiency in either the inverter or
the converter....Neither would I expect a hard
'failure mode' in either....<p>a Soft Failure, due
to excessive heat in the environment, yes thats
likely...<p>And of course, your laptop battery would normally
act as a voltage stabilizer, preventing 'startup'
loads on computer bootup, disk drive/optical drive
seeks, ect. <p>Hence,
YOUR BATTERY is probably, ALSO a
contributor to this problem...It won't hold a
charge, so all startups are full dead load, INCLUDING the battery??<p>[ July 19, 2004: Message edited by: ng2aradiofunk ]</p>

ng2aradiofunk
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Re: Reducing power surge on AC adapter

Post by ng2aradiofunk » Tue Jul 20, 2004 9:07 am

go ahead, tell me ....<p>the supplied and installed 12volt line cord for the inverter is 10 feet of #16 or #14 <p>
Right?

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