Jump to content

Inverter Question


Durbanite
 Share

Recommended Posts

We have a RING 300w modified sine wave inverter which we want to fit into the caravan however the leads to the leisure battery terminals are too short.

I want to buy longer runs of the cable, but I am unsure whether the cabling needs to be 3mm or more. The only current drawn from the inverter will be for a 19" TV & Sky HD+ digibox. The inverter is in the caravan which is in storage several miles away. Can any one advise please? Thanks.

Link to comment
Share on other sites

We have a RING 300w modified sine wave inverter which we want to fit into the caravan however the leads to the leisure battery terminals are too short.

I want to buy longer runs of the cable, but I am unsure whether the cabling needs to be 3mm or more. The only current drawn from the inverter will be for a 19" TV & Sky HD+ digibox. The inverter is in the caravan which is in storage several miles away. Can any one advise please? Thanks.

Personally any distance over a mtr from battery is going to need IMHO 6mm,, cable to prevent voltage drop. if under a mtr then 4mm.

 

Others will come on with other answers so this is just what I would do, also I would not go too far from battery, better idea would be to have inverter as close to battery "shorter 12volt cables" and extend the mains out

Edited by Mike&deb
Link to comment
Share on other sites

6mm would be ample for 25 amps I would of thought ?

 

 

Dave

Jeep Commander 3. 0 V6 CRD

Isuzu D- Max Utah Auto

Elddis Crusader Storm 2000 Kgs, Unipart Royal Atlas Mover .

 

Link to comment
Share on other sites

2. 0mm2 (D2. 8mm): up to 25A

2. 5mm2 (D3. 0mm): up to 29A

3. 0mm2 (D3. 4mm): up to 33A

4. 0mm2 (D3. 7mm): up to 39A

6. 0mm2 (D4. 3mm): up to 50A

 

. ..according to BS ISO 6772:2011 (low voltage auto cable)

 

2. 0mm2 should be fine for your scenario. Resistance per metre = 0. 00942ohms, therefore volt drop at full load = 25A x 0. 00942 ohms = 0. 2355V per metre. Double the cross sectional area, you approximately halve the resistance, therefore halve the voltage drop.

 

If there's anyway to extend the AC cabling (e. g. an extension lead), this would be preferable. ..significantly lower resistive losses.

 

Edit: Added volt drop & diameter details

Edited by tictag
Link to comment
Share on other sites

6mm would be ample for 25 amps I would of thought ?

 

I'm assuming you meant 6mm2? A 6mm diameter cable would support 70A! ;)

Link to comment
Share on other sites

I'm assuming you meant 6mm2? A 6mm diameter cable would support 70A! ;)

 

I meant 6mm2 that would give allowance of increasing the inverter at a later date if needed and save buying new cabling.

 

Dave

Jeep Commander 3. 0 V6 CRD

Isuzu D- Max Utah Auto

Elddis Crusader Storm 2000 Kgs, Unipart Royal Atlas Mover .

 

Link to comment
Share on other sites

2. 0mm2 (D2. 8mm): up to 25A

2. 5mm2 (D3. 0mm): up to 29A

3. 0mm2 (D3. 4mm): up to 33A

4. 0mm2 (D3. 7mm): up to 39A

6. 0mm2 (D4. 3mm): up to 50A

 

. ..according to BS ISO 6772:2011 (low voltage auto cable)

 

2. 0mm2 should be fine for your scenario. Resistance per metre = 0. 00942ohms, therefore volt drop at full load = 25A x 0. 00942 ohms = 0. 2355V per metre. Double the cross sectional area, you approximately halve the resistance, therefore halve the voltage drop.

 

If there's anyway to extend the AC cabling (e. g. an extension lead), this would be preferable. ..significantly lower resistive losses.

 

Edit: Added volt drop & diameter details

Thanks. It seems that the 2mm will be more than adequate for running the TV & Sky Digibox. All the rest can be plugged directly into the 12v system in the caravan. I guess it is off to Maplins or a DIY place to find cabling.

Edited by DeltaTIowner
Link to comment
Share on other sites

You have missed out volt drop. If your inverter cuts out at 11. 5 volt then at 7. 3 mV/A/m then 300W = 26A so 0. 2 volt drop per meter so at 3 meters 0. 6 volts so inverter will cut out at 12. 1 battery volts.

 

As to current carrying capacity this also depends on installation method in free air clipped direct 6mm sq which I am using as an example is rated 47A however same cable Method 100 (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) is rated at 34A. OK ratings designed for a house but if that cable can't get rid of the heat the current carrying capacity is reduced.

 

Personally having the inverter switch off at 12. 1 volts rather than 11. 5 volts for a TV is not a problem but I have guessed at the switch off volts it may be different. Likely 6mm is ample but I cringe at the simplistic answers given. I have gone on 6mm sq with 2. 5mm sq the value is 18mV/A/m so volt drop 0. 47 volts so would switch off at even higher voltage. Also method 100 amps = 21 amps and you are drawing 26 amps I would say 4mm sq min.

Edited by ericmark
Link to comment
Share on other sites

What is the distance between the inverter and the battery - if it's 3 metres then the cable run is 6 metres (one run of red and one of black). So with a voltage drop of approx. 0. 2355/m x 6 = 1. 4 volts. If you are only starting off with 12. 6 then all the inverter will see is 11. 2 when the battery is fully charged and a lot less as the battery discharges. If you want to extend the battery cables then you'd need 4mm2 at least. For low voltage work you need to take account of the voltage drop as well as the current rating.

 

You would be better advised to use an extension lead on the 240 side. 300 watts = 1. 25amps, you could go as far as you like without a significant voltage drop

2018 S-Max Titanium 2. 0 Tdci (177. 54bhp,180ps,132kw) Powershift + 2015 Unicorn III Cadz, Ventura Marlin porch awning

Link to comment
Share on other sites

Actually a though occurred to me. The inverter came with a cigarette type connector so maybe we can plug it directly into the 12v cigarette type socket in the caravan? Surely it should be able to handle couple of amps. Sure would save a lot of hassle and also conveniently locate the inverter.

Link to comment
Share on other sites

Actually a though occurred to me. The inverter came with a cigarette type connector so maybe we can plug it directly into the 12v cigarette type socket in the caravan? Surely it should be able to handle couple of amps. Sure would save a lot of hassle and also conveniently locate the inverter.

 

The TV plus the Sky box will be more than a couple of amps but even with the inverter losses well within the "lighters" 10 amp normal rating.

However the voltage drop issue will still be there, the wiring to the lighter will IMo be marginal for 10 Amps and certainly not sized for low voltage drop.

Dont think the 25 Amps plus losses the 300Watt inverter might one day draw will be good for the system.

Edited by JTQ
Link to comment
Share on other sites

You could, but don't try taking 300watts from it. The caravan wiring won't take it and if you are lucky you'll just blow a fuse.

 

Our 22" TV takes about 40watts and we have run it from a 150watt square wave inverter using the 12v van socket. Neevr tried an Sky box, however Sky HDboxes can take about 40watts when the disk drive is running, so you could be taking 80watts, plus another 10 watts for inverter inefficiencies. The consumption would be around 90watts = 7. 5amps.

Cigarette lighter sockets are supposed to be rated at 10amps but they can get quite hot with 5amps running through them. You'll also probably find that the caravan wiring is quite light as well. If your van is anything like mine the power supply from the battery to the distribution board is about 8 metres and then there's another 5 back to the 12v socket so the voltage drop could be quite considerable

2018 S-Max Titanium 2. 0 Tdci (177. 54bhp,180ps,132kw) Powershift + 2015 Unicorn III Cadz, Ventura Marlin porch awning

Link to comment
Share on other sites

So it looks like your options are, in order of preference:

  1. Extend the AC side, if possible, significantly lower losses/volt drop
  2. Use the internal aux socket but take care of current draw (total wattage / 12 must be less-than aux socket circuit fuse)
  3. Extend the DC cables but take care of both current capacity and the volt drop (4mm2 minimum is the recommendation)
Link to comment
Share on other sites

Just another point worth mentioning - SkyHD boxes still take a fair amount of power unless they are put into energy saving standby mode or turned off, so leaving one gently cooking to a bit of recording won't do your battery a lot of good, you could easily flatten the battery in 24hours just by leaving it on standby.

 

Running your TV & Skybox could take 6-8amps so a 3-4 hour nights viewing will give your battery a good bashing, two nights will flatten it.

2018 S-Max Titanium 2. 0 Tdci (177. 54bhp,180ps,132kw) Powershift + 2015 Unicorn III Cadz, Ventura Marlin porch awning

Link to comment
Share on other sites

Just another point worth mentioning - SkyHD boxes still take a fair amount of power unless they are put into energy saving standby mode or turned off, so leaving one gently cooking to a bit of recording won't do your battery a lot of good, you could easily flatten the battery in 24hours just by leaving it on standby.

 

Running your TV & Skybox could take 6-8amps so a 3-4 hour nights viewing will give your battery a good bashing, two nights will flatten it.

The extra cabling will be less than a metre in length as the supplied leads are far too short. TV uses less than 35w and the digibox about 45w maximum. Main battery is 110amp Numax and we have a 85amp battery as a back up just in case, but thanks for the heads up on consumption.

We are hoping to have a 120w solar panel installed before we go down the route of going non EHU sites. We are hoping to try non EHU sites for the first time this year. After that we have to consider the lights which are LED low lighting and water pump. Doubt if we will go off EHU if we have to use heating.

Link to comment
Share on other sites

Have you considered housing the inverter with the backup 85Ah battery as a stand alone powering system for the TV Sky unit?

Then connections are at mains voltage so cabling losses are minimal and if that battery is depleted the caravan's life support is able function from the van's battery.

Side issues are;

This battery can be recharged when out for the day using your car.

Then when/if you go solar you use a Duo controller that handles the two batteries needs totally in isolation.

 

That is the system we have with a few extra twists and it serves our off EHU needs well.

Link to comment
Share on other sites

You may also get problems using a modified sine, you will probably find a pure sine wave will work much better.

Our concern is buying one that is not made in China and is reasonably priced.

Link to comment
Share on other sites

Victron (high end) do a 180W inverter for around £96, 350W for around £123. Product info here: http://www. victronenergy. com/inverters/inverter-12v-24v-48v-800va-3kva/ Sales info here: http://www. onboardenergy. co. uk

 

note: the pricelist on their homepage is RRP, it'll be cheaper if you ask for a quote)

 

Edit: Hyperlinks disappeared :ph34r:


p. s. I am not affiliated to onboard energy - that's just where I bought the kit for my 'spanking new solar project'.

Edited by tictag
Link to comment
Share on other sites

  • 5 months later...

We are having the 120w solar panel installed at the end of the week so want them to connect up the inverter using the 27A mains cable from Maplin. I think 3 metres should suffice as the inverter can be mounted just the other side of the battery box. At a later date we will invest in a pure sine wave inverter.

Link to comment
Share on other sites

6mm would be ample for 25 amps I would of thought ?

 

 

Dave

The current isn't the only factor here, you need to consider cable length and volts drop, whilst 6 mm may be fine for the current it may not be ok if a long cable was needed.

Link to comment
Share on other sites

Aargh. After placing an order with Maplin for 3 metres of the 27A cable yesterday and paying for it, they have just sent a text saying not available! :angry: Now got to try and find another supplier, so maybe Screwfix?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...