On Sat, 26 Sep 2009 20:54:17 +0100, "Dave"  wrote:

>Hi and thanks for reading this.  I have two inverters, 150W & 350W and use 
>an 85aH Leisure battery.  The load is a notebook computer and small fretsaw. 
>Both are rated at 240v MAX 1amp each.  Im getting a maximum of 2 hours use 
>before the battery goes down. Its the same whichever inverter I am using. 
>Is this usage usual ?   Some years ago I used a standard car battery with a 
>television running at more than 2 amps (240v) and got well over 5-6 hours 
>use. Sometimes over 8 hours.  What can I realistically expect from an 
>inverter and leisure battery ?  Or is it back to the generator ?
>Thanks in anticipation
>Dave 
>
OK, here's my thoughts:

Firstly you must verify that when you believe your battery is fully
charged, it really IS fully charged.  The only reliable way to be sure
of this is with a hydrometer to check the specific gravity of the
electrolyte in each of the six cells.  The electrolyte level in each
cell should be very similar and to the correct level(covering the
plates).  All six should measure nearly the same, and a  reading of
anything less than 1.28, is less than fully charged.  Variation in
readings between cells indicates a problem in one or more cells.

Secondly, it is only possible to know what current is being drawn at
any time by your appliances, is by measurement.  Your appiance ratings
are maximum ratings - e.g. your TV will only draw the full 240watts
with the colour turned up, the brightness turned up and also the
volume turned up - an experiment I did many years ago showed
significant variation in current drain if the sound was turned OFF.  

One thing I can be certain of is that you would not have got
"sometimes over 8 hours" running  TV at 480watts from a car
battery(usually 65Ah).  As someone has already said here assuming 1amp
of battery current for ever 10watts of appliance power(which is a very
good rule of thumb!), if the TV was actually running at  2 amps.

2amps at 240v = 480watts = 48amps current from 12v battery for 5 hours
is 240Ah!

Thirdly, what do you mean by "the battery goes down"?  If you mean
that a point is reached where the inverter will not start up when
switched on, then this will not necessarily mean the batery is flat.
All the inverters I have ever used have drawn a fairly hefty current
on start-up.  Very often unless the battery was freshly charged, this
surge would cause the voltage of the battery(or more correctly the
voltage at the inverter input) to drop to the point at which the
inverter would shut down(somewhere between 10.5 and 11.0volts).  It is
also relevant that a car starter battery is constructed to supply a
heavy current for short time, whereas a leisure battery is not.  This
might explain why you appeared to have longer battery life from a car
battery than the leisure one!  If your appliance usage is a lot of
ON/OFF swirching of the inverters I can well believe it being only a
short time before the inverter refuses to power-up.

Lastly it cannot be over-emphasized the importance of the wiring
between the inverters and the battery.  The cabling should as short as
practical and the connections as good(permanent) as possible.  Plugs
and sockets are notorious for causing unwanted voltage loss, as are
loose or dirty fuses and holders.

In conclusion it is only really possible to make predictions of
battery life with continuous monitoring of battery voltage and current
drain

HTH

Neil

(Reply via group please)

You dont state if the inverter is sine wave or square wave or modified 
square wave.
While the laptop power supply may be switch mode, it may take as much as 20% 
greater power on MSW inverter compared so sine wave inverter. The extra 
power is in heat so if the laptop power supply is getting hot you know it 
does not like the inverter.

If the fret saw has a universal motor then a MSW inverter does not matter, 
but if the fret saw has a normal induction motor then you are looking at 25% 
greater power load, plus another penalty for the motor drawing more power to 
try and develop the power that is needed.
A universal motor is a motor with brushes like the majority of hand power 
tools.

Thankfully my 410w of solar panels keeps everything going.

"Neil Pearson"  wrote in message 
news:rVixm.44719$ze1.11130@news-server.bigpond.net.au...
> You dont state if the inverter is sine wave or square wave or modified 
> square wave.
> While the laptop power supply may be switch mode, it may take as much as 
> 20% greater power on MSW inverter compared so sine wave inverter. The 
> extra power is in heat so if the laptop power supply is getting hot you 
> know it does not like the inverter.
>
> If the fret saw has a universal motor then a MSW inverter does not matter, 
> but if the fret saw has a normal induction motor then you are looking at 
> 25% greater power load, plus another penalty for the motor drawing more 
> power to try and develop the power that is needed.
> A universal motor is a motor with brushes like the majority of hand power 
> tools.
>
> Thankfully my 410w of solar panels keeps everything going.



410 Watts   wow

a. clarke wrote:
> 
> "Neil Pearson"  wrote in message 
> news:rVixm.44719$ze1.11130@news-server.bigpond.net.au...
>> You dont state if the inverter is sine wave or square wave or modified 
>> square wave.
>> While the laptop power supply may be switch mode, it may take as much 
>> as 20% greater power on MSW inverter compared so sine wave inverter. 
>> The extra power is in heat so if the laptop power supply is getting 
>> hot you know it does not like the inverter.
>>
>> If the fret saw has a universal motor then a MSW inverter does not 
>> matter, but if the fret saw has a normal induction motor then you are 
>> looking at 25% greater power load, plus another penalty for the motor 
>> drawing more power to try and develop the power that is needed.
>> A universal motor is a motor with brushes like the majority of hand 
>> power tools.
>>
>> Thankfully my 410w of solar panels keeps everything going.
> 

> 410 Watts   wow

He's just bragging about the size of his roof!

Well in total I have 910W - 410W on the caravan and 330W on top of my 
vehicle and 2 x 85W portable when I want air-conditioning in summer.  Never 
go onto a pitch and only freedom camp. Cost of solar panels is chicken feed 
compared to what I have saved in paying.

Dump excess power into 22L hot water system. Seldom have fire up the gas for 
hot water.  Power my inverter LG air-conditioner in summer directly from the 
array with a custom MPPT inverter I built that interfaces into the LG 
electronics.  The LG then delivers the amount of power it can from the solar 
panels down to 93W.  One of the 110W panels keeps the 12V batteries on 
float.  Webasto diesel heater keeps me warm in winter.
I would never ever let a vehicle alternator or mains powered battery charger 
near my system for battery life.


"Dougal"  wrote in message 
news:t7KdnYrDW7a4s1vXnZ2dnUVZ8rWdnZ2d@eclipse.net.uk...

> He's just bragging about the size of his roof!