Re: inverter problem and current limiting
From: Roger Hamlett (rogerspamignored_at_ttelmah.demon.co.uk)
Date: 12/07/04
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Date: Tue, 07 Dec 2004 16:55:08 GMT
"Fritz Schlunder" <me@privacy.net> wrote in message
news:31m4f0F3dfq03U1@individual.net...
>
> "Dave Moore" <dave.m.moore@baesystems.com> wrote in message
> news:41b5d694$1_1@baen1673807.greenlnk.net...
> > Hi All,
> > Ok, this is my problem. I need to run 2 laptops from a 12v
'leisure'
> > battery via an inverter. The battery is a 12v 110Amh item and the
inverter
> > is a 600W continuous/ 1500W surge item.
> >
> > The trouble starts when plugging in the laptop AC/DC adaptor into the
> > inverter output. Even without the laptop connected, this trips out the
> > inverter, which then starts to click (sounds like a relay switching)
in
> and
> > out. During this period of about 20 seconds or so it appears that the
> > inverter is trying to supply enough current but fails and retries. The
LED
> > on the laptop adaptor gets increasingly bright, and then (say after 20
> > seconds), the inverter stops clicking and works correctly. I can then
plug
> > the adaptor into the laptop and then all is well.
> >
> > Whilst this gets me running, I'm not happy with this. It appears that
the
> > adapter is pulling a lot of current when power is applied. Once the
laptop
> > is up and running the current load is much less. Does anybody have any
> cheap
> > suggestion as to how I might get round this?.
> >
> > I can think of 2 approaches:
> > 1). Try to limit the current to the adapter. This would have to be
done in
> > the 240V AC part of the system and frankily I'm a bit scared of
playing
> > around with this!.
> >
> > 2). Alternatively, I could replace the 19v laptop adaptor with
something
> > else which doesn't require such a large start-up current.
> >
> > Any ideas?.
> >
> > Thanks,
> > Dave
>
>
> Hi there.
>
> What is the condition of the lead acid battery? Is it in good
condition?
> Is the low voltage wiring connections to the battery using appropriately
> large wire and oxidation free connections? The inverter surely includes
an
> input undervoltage lockout feature of some kind. If the battery is
quite
> weak and is in need of charging or replacement (or the wiring/connection
> resistance is too high), then the inverter will quite possibly cycle
like
> you suggest.
>
> A 1500W surge rated inverter hooked up to a good battery with low
resistance
> connections should have no trouble juicing up a little laptop power
adapter.
The simplest way to limit the maximum current, is to add a thermistor in
series in the power line.
The input of a laptop switching supply, in it's simplest form, can often
present very large currents during startup, but most should have their own
current limiting circuit to prevent this being too 'silly'. However the
current could easily be perhaps 5A (at the mains voltage) during the
starting phase.
I'd be inclined to think that the most likely reason (like the poster
above), is that something is preventing the invertor from working as it
should. It is worth realising that the '600W continuous' rating will
require over 50A from the battery, while the 'surge' rating, will hit over
125A. I'd suspect that if this is driven from a 'cigar lighter' connection
on a 'leisure' battery, the supply is just drooping too far...
Best Wishes
- Next message: Leon Heller: "Re: accerelometers"
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- In reply to: Fritz Schlunder: "Re: inverter problem and current limiting"
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