Inverter: long cable = increased consumption?

[demonboy]

Good morning,

I was just wondering if by installing a longer cable from my inverter I am increasing the workload (i.e. increasing the amp draw). My inverter is wired to my batteries with very thick cable about 3m long but I've wired in a cable and socket from the inverter to reach the other end of the boat and so that cable is a good 5m. That cable isn't as thick as I'd like it (big expense).

It's a 1000w modified sine wave and is now drawing 1amp on standby. I'm sure it was around 0.3 amps before I put in the longer wiring

 

[wotayottie]

It shouldnt (I would have said can't ) make any difference to the current draw on standby. Nor should it make a difference to the current draw in use, though slightly less of the output power will get to whatever you are using as a bit of the power is used to heat up the wire.

Is any part of the wiring getting hot to the touch? Might not be very tecchie but checking for warmth is a simple basic way of checking for power loss .

 

[st599]

Can't understand why standby current would increase, unless the circuit was energized.

Also, surely you work out the required current carrying capacity of the cable (with de-ratings for how fastened, multiple conductors, location etc.) and hence, diameter, and the required circuit and personal protection (as per 17th ed.) rather than the maximum cable cost.

 

[andythilo]

Good morning,

I was just wondering if by installing a longer cable from my inverter I am increasing the workload (i.e. increasing the amp draw). My inverter is wired to my batteries with very thick cable about 3m long but I've wired in a cable and socket from the inverter to reach the other end of the boat and so that cable is a good 5m. That cable isn't as thick as I'd like it (big expense).

It's a 1000w modified sine wave and is now drawing 1amp on standby. I'm sure it was around 0.3 amps before I put in the longer wiring

What is your cable size? For a 1kW invertor I would think 10mm2 as a minmum for short length. For a long length either 16 or 25 would be preferable.

 

[VicS]

For the 240volt cable running from the inverter to the socket there is no need for it to be any heavier than you would use for a domestic appliance appliance with the same power rating (1000watts)

0.75mm² would be adequate but 1.0mm² would be a sensible choice.

For the 12 volt connection from the battery to the inverter a very heavy cable is required and the longer the cable run the heavier it must be to avoid excessive volts drop.

I would expect the inverter manual to give some advice but for a 3m run you should be looking at no less than something like 2 AWG or around 30mm², based on a max volts drop of 3%

 

[demonboy]

OK, problem solved. It wasn't drawing 1 amp in the first place or, if it was, it isn't now. Cable from battery to inverter, btw, is 10mm2. Thanks to those who took time out to respond.

 

[VicS]

Cable from battery to inverter, btw, is 10mm2

No where near heavy enough for a 3m distance. That would be the absolute minimum size of cable that could be used and would only be suitable for a cable run of less than 1m

 

[tobble]

OK basic fizix - power = volts x current. power loss in cable is a function of current.

on the 12V side you'll need lots more amps to deliver a certain power than on the high voltage side of the inverter. so you need less diameter of cable, or can get away with longer cable, on the 230V side.

so in answer to your question, if the lead on your 230V appliance is OK for normal domestic (land lubber) use, it's ok to plug into your inverter.

a different question would be is the cable on the 12V side fat enough to handle 1000W.

sorry that's a slightly rubbish explanation, if I think of a better one I'll update this...

 

[demonboy]

No where near heavy enough for a 3m distance...

...and...

is the cable on the 12V side fat enough to handle 1000W.

The only thing being plugged into the extension cable from the inverter is a router that draws milliamps so thanks for answering that, tobble. Larger items that plug directly into the inverter come in at around 300w like juicers and food processors. Also the cable from the battery is probably closer to 2m.

I am, however, concerned that this is not adequate based upon Vic's reaction. When I originally installed the inverter I used battery cable and had no problems but it sounds like I should be using the heavy duty stuff again. I do not have a user manual and I am not an electrician, hence the OP.

New question: so I can put this in perspective, what is the area of the core on a standard battery cable (about as thick as ones forefinger)? 30mm2?

 

[andythilo]

Have a look here, confirms for a 2m run you should be using 50mm2

http://www.windandsun.co.uk/Components/sizing_cables.htm


Thats a hell of a cable to run through a boat. However you can get the cable easily from eBay. Use welding cable is it's VERY flexible :

http://cgi.ebay.co.uk/WELDING-CABLE...al_Components_Supplies_ET?hash=item518d7eaddf

Then you gotta crimp the bad boy and that'll mean a hydraulic crimper. You can borrow mine if you live near me.

 

[VicS]

what is the area of the core on a standard battery cable

Battery cable could be one of several sizes; typically;

6AWG or 13mm², which has core diameter of approx 4.1mm
4AWG or 16mm², approx 5.2mm diam
2AWG or 32mm², approx 6.5mm
1AWG or 40mm², approx 7.3mm

 

[tross]

OK, I'll ask the stupid question. Why did you want to move the inverter? You will experience far less losses if you extend the 240 volt side of things ?

 

[VicS]

Why did you want to move the inverter?

He didn't ... at least my understanding is that the inverter is between 2 and 3m from the battery. He has run a 240 volt supply some 5m to power a router which has current consumption of only a few milliamps ... I assume therefore that's router as in a bit of computing hardware rather than as in a woodworking machine.

A pity the inverter is not closer to the battery but there you go!

 

[demonboy]

OK, I'll ask the stupid question. Why did you want to move the inverter?

That's not a stupid question, I just didn't bother explaining why I'd moved it. Because the inverter is powering a (wifi) router it means it's on for some time whilst I'm sitting at the laptop, which is in the nav area. It's a fairly noisy fan on the inverter and it was starting to annoy the hell out of me as it was sitting close to the chart table. I moved it to my 'airing' cupboard so it's out the way.

Vic, the inverter is no further away than its previous position to the battery. It's just a lot further away from the chart table, hence the long 240v extension cable. You'll be pleased to know, however, that I purchased some 50mm2 cable yesterday.

The power consumption whilst on stand-by may still be an issue, however. Half way through this thread I stated that it wasn't but I realise I'd bypassed the ammeter and so it wasn't reading anything when I switched it on.

I'll post again once cables have been installed and wired via the ammeter. We're about to leave for Port Said (400nm) so got a long list of things to do but I'll try and get it done today.

 

[Gypsy]

Why not a Smaller Inverter?

A 1kw inverter is a big boy for the small job of powering your WiFi router. I would expect the router to consume about 15-20w (about 90mA @ 220V). Why not buy a small 150-200W inverter for this application. It will probably not have a fan and will certainly be more efficient and produce less heat than the 1KW. Alternatively, if the router accepts DC from a plugpack you could look for a DC-DC converter such as used for PC's to run directly off 12V....even more efficient.

Leave the 1KW guy for the 'heavy lifting' it was designed for.

 

[whipper_snapper]

The only thing being plugged into the extension cable from the inverter is a router that draws milliamps so thanks for answering that, tobble.

There is probably a simple way to power that from your 12Vdc. The one in my house actually takes 12V, but I know many are 5V. If it was me, I would prefer that to running a big inverter to power a tiny router via its own power brick which takes it back down to a few V dc.


[That's strange. Gypsy seems to have said the same thing 6 hours before I did. But I am sure it wasn't there when I posted! Is there a time zone issue as well as pure time setting issue on here at the moment ?]

 

[cozzykim]

OK basic fizix - power = volts x current. power loss in cable is a function of current.

on the 12V side you'll need lots more amps to deliver a certain power than on the high voltage side of the inverter. so you need less diameter of cable, or can get away with longer cable, on the 230V side.

so in answer to your question, if the lead on your 230V appliance is OK for normal domestic (land lubber) use, it's ok to plug into your inverter.

a different question would be is the cable on the 12V side fat enough to handle 1000W.

sorry that's a slightly rubbish explanation, if I think of a better one I'll update this...

Not exactly rubbish, but power lost in the cable is actually I²R (IOW, Amps squared X resistance of the cable) and is basically why the national grid is high voltage/low current

EDIT: agree with WS, run a router & laptop if possible directly from 12V D.C. My D-Link router is 12V D.C. What's O.P's

 

[demonboy]

Why not buy a small 150-200W inverter for this application... Leave the 1KW guy for the 'heavy lifting' it was designed for.

Not sure you read my post correctly, Gypsy. I also use the inverter for powering food processors and other heavy loads.

Cozzykim: the router is actually a 24v system. My boat is 12v.

I do have a smaller inverter but I don't want to permanently install this one as it 'floats' around the boat as and when I need it. I don't have the money to purchase any more (and trying to source one on the Suez Canal could be problematic!).

Anyway, all of this has nothing to do with my original post! I have now installed 50mm2 cable and everything is good. Thanks for your comments and suggestions.

 

[cozzykim]

Cozzykim: the router is actually a 24v system. My boat is 12v.

"Bummer"

 

[Gypsy]

I thought you were worried about the current drawn. Using the 1KW unit when only loaded with the router is very inefficient and a small unit for the router would draw less current and produce less noise and heat. It is probably left on for significant periods so it can all add up. The juice extractor and other stuff is the 'heavy lifting' I was referring to.