Re: inverter problem and current limiting

From: Fritz Schlunder (me_at_privacy.net)
Date: 12/07/04 

Date: Tue, 7 Dec 2004 09:36:01 -0700

"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.

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