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Anonymous

hi everybody ,
dont meen to stir up a hornetts nest Embarassed

but everybody says keep the battery/invertor connections short , if this is not practical how do you prevent loos [how much over what distance ] what size cabble does one need.

what is the loss on the 240v side if a long cable is used ?
does anybody know how to work out the start up requirements for a tv on say a 40w model?

sorry to get the old grey brain cells working but iam getting nowhere fast.

cheers tramp Razz

DABurleigh

Tramp,

What size inverter is it?

Dave

Anonymous

hi dave, thanks for he quick reply spec as follows input volt-10-15v
output wave form modified sinewave 50hz
out power 300wt continuos
peak 600w.
also what is a choke and what does it do.

tramp

AutoK

tramp.
Not sure how you prevent loos but to minimise loss,
yes keep LT cables as short as you can and use thick cable I would probably use the type of cable the van manufacturer uses on the leisure battery conections, sorry I can't rember the actual diameter cables.

As for the secondary 230v side don't worry about voltage drop, it wont make much difference at 230v.

If your tv is a normal (CRT) type then at swith on the auto degause circuit could draw about 3 or 4 amps surge this does vary a bit from set to set.

LCD tvs don't have to be degaused.

Hope this helps.

AutoK

DABurleigh

Tramp,

A choke is an inductor that inhibits changing voltages. Often they are inserted into the leads near equipment or as the leads connect to a printed circuit board, in order to stop radio frequency interference getting into the equipment.

I have knocked up a little formula for you to play with regarding cable lengths and thicknesses.

For copper cables, 12V inverter output W (watts), cable length L (metres) from battery to inverter, metal cable diameter D (millimetres), acceptable voltage drop Vdrop (volts):

L < (554 x Vdrop x D x D) / W

Many electrical design rules suggest a maximum voltage drops of 6%. For motorhome use, I would keep to lower drops if at all possible to get most use out of the batteries before applications fail.

So, for a voltage drop of no more than 0.5V in a 300W inverter with copper cable diameter of 2mm, the cable length should be less than 3.7 metres. Vary to suit.

Some applications are more sensitive to voltage than others. Beware if your inverter is not plugged directly into the battery but merely into a 12V socket in the van; many motorhome manufacturers and converters skimp on internal wiring specifications.

As has already been pointed out, the mains cable length is far less critical as the current is so much lower, the voltage drop in the fixed resistance of cable is correspondingly lower.

HTH,

Dave

Brambles · Last edited by Brambles on Fri Nov 19, 2004 12:47 am; edited 1 time in total

Hi Dave,

I am not critisising your calculations but have you taken into account how invertors operate and the input is in effect oscillating. I am not sure of the duty cycle but would suspect the current spikes drawn from the battery are at least twice the average current. Sorry if I am throwing in a spanner.
Jon.

edit - nah, forget it, they will have filtered inputs and capacitors to take care of it or else the invertor would be creating a serious RF frequency problem. Too late at night to figure it all out.

DABurleigh

Jon,

I'm talking about just the 12V DC bit between battery and inverter Smile

Dave

Brambles

just edited my post, before I saw your reply - was not quick enough.

Anonymous

hi everybody
thanks for the help it all makes kind of sense, the misse says she can choke me if it would have the same effect Twisted Evil

it will give me somthing to play with this weekend, if i don`t freeze to death first.

tramp