Fitting a 1500W Inverter

DBK

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In this thread I asked for comments on a 1500W pure sign inverter. As the comments were favourable I went ahead and ordered one. :)
https://www.motorhomefun.co.uk/forum/threads/thoughts-on-this-inverter.155627/

When it arrived I tried it for size in my chosen spot in the PVC.

OI000181.jpg

This is very close to the batteries, which is good, but the space is very confined but I thought if it overheated I could add some PC cooling fans.

However, just before I started drilling holes I had a sudden realisation this wasn't going to work. :) The reason is this space is filled by the seat back cushion when it folds down to make one of the beds. Doh!

So back to some head scratching and after looking at other alternatives I decided the best option was to put it where all the other electrical stuff is in the space behind the wardrobe. This allowed me to mount it correctly but the cables going to it from the batteries are now very long at about two and a half metres which will create about a 3% voltage drop, which is high but at the upper limit according to what I could discover on the Internet. I am using 25mm cables and 35mm would be much better but they are considerably more expensive and stiffer.

OI000182.jpg

In the picture above you can see the two bits of wood I have screwed to the right hand side of the services space. The panel they are fixed to is 16 mm plywood, forming one wall of the bathroom. The left-hand side would have meant shorter cables but this is only very thin ply and not strong enough for the weight. The reason for the wood strips is because there is a ventilation opening right where I wanted to put the inverter. This ventilates the cupboard under the sink so I needed it to be kept open.

OI000183.jpg

The inverter fits quite well in this new spot and is now mounted as the instructions suggest with the fan at the top. I could have mounted it the other way up which would have reduced the length of the negative cable a bit but I wanted to fit an isolating switch and the best place for this means there would not have been any saving in the length of the positive cable by mounting it upside down. It is mounted a bit close to some water pipes but I think the risk is manageable.

This is where the isolating switch goes. It's the big red thing and isn't exactly discrete but it is easy to get at. :)

OI000184.jpg

This photo shows the positive cable routed through a 150 amp fuse. I'm not sure why I ordered a 150 amp fuse now as 1500W at 12 volts is 125 amps so I may change it later. These fuse ratings are slightly odd in that the stated current is their continuous working current, they blow at twice this. You can also see that I could have saved a bit of cable by mounting the fuse horizontally but it is a bit neater this way. :) I have some cable clips to add later to secure the cables in place.

OI000185.jpg

Following the discussion in the other thread and the very helpful advice from Eddie Vanbitz I bought a latching RCD which I will connect to the output of the inverter. Screwfix do one for less than £15 which I have fitted on one of the panels at the back of the wardrobe.

OI000186.jpg

You can see it above the 13A socket in the picture above. And yes, it doesn't quite line up, a bit more chiseling required. :) The box with the upside down yellow triangle is where the cables goings to the 13A sockets are. I will cut into these cables and add extra cable to reach the RCD and power relay using some junction boxes I've ordered.

My plan is to mount the power relay, which will automatically select the inverter if we are not on EHU and feed it's output to the 13A sockets in a pattress box behind the RCD. It fits, though the wiring is going to be a bit tight.

OI000188.jpg

The 47mm box isn't quite deep enough but Screwfix do a 10mm thick spacer which should give me enough room to include all the necessary wiring. You should be able to see the spacer in this picture of the back of the panel.

OI000187.jpg

I've successfully tested the installation using the sockets on the inverter with a 1200W hairdryer and I am now waiting for the bits to arrive for me to sort out the 240v side, which will be this weeks job.

More to follow, hopefully. :)
 

Lenny HB

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Looks good, one comment the fuse for the inverter should be at the other end of the cable as close to the batteries as possible.
 

mitzimad

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Im no electrician and im sure theres a reason why not but could the earth side not be returned via the body work ie earthed down to chassis which would surely have less resitance than a wire?
 
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DBK

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Looks good, one comment the fuse for the inverter should be at the other end of the cable as close to the batteries as possible.
That's food for thought, thanks. My idea was just to put it somewhere where it was easy to get at. :)

Im no electrician and im sure theres a reason why not but could the earth side not be returned via the body work ie earthed down to chassis which would surely have less resitance than a wire?
It's hard to get at the metal bits of the van body in our PVC. Cable is just easier run.
 

Don Quixote

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Not long enough, but a little common sense helps..........
That's a nice job and good to see using a good thick cable. The only thing I would change is that fuse a little to high for a 1500w, which on your length of cable ( should be fine ) would be around the 115amp out ish... (you should never get anywhere near drawing that much as your batteries will fall over in minutes) not hours and the heat would by extremely high. I have all my 240Volt sockets powered of inverter when not on EHU (thanks to Andy) also with RCD in line just in case.

Nice post as well.
 

QFour

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Its cheaper to buy ready made jump leads and cut the ends off (y)

Don't forget your voltage drop is based on the whole length of the cable .. There and back ..

You could have bought a double 13 amp socket with built in RCD which would have saved you a bit of wiring. Fuse is to protect the cabling so it should be at the other end. The inverter will have it's own internal fuse.

Looks very neat ..
 
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DBK

DBK

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Quick update, I've now moved the fuse to the battery end of the positive cable. Many thanks @Lenny HB for the suggestion. It makes sense of course. I must engage brain next time I do some wiring. I've also ordered a 125 amp fuse. :)
 

Don Quixote

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Not long enough, but a little common sense helps..........
Its cheaper to buy ready made jump leads and cut the ends off (y)

Don't forget your voltage drop is based on the whole length of the cable .. There and back ..

You could have bought a double 13 amp socket with built in RCD which would have saved you a bit of wiring. Fuse is to protect the cabling so it should be at the other end. The inverter will have it's own internal fuse.

Looks very neat ..
Please be very careful buying jump leads as many are cheap and have very little or no copper in them and will produce larges amounts of heat along the cable if used for prolonged periods of time ending up with melted outer, which if you cannot see because they are behind walls etc will be a fire risk. Buy good quality cable and be safe.
 

tonyidle

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Another point that might help with 'heavy' installations: for our purposes cable is usually sized to keep volt drop to a minimum. This means that it is often much larger than cable that's simply rated to carry the intended current. If there is difficulty making connections with the heavy cable it is perfectly OK to use a few inches of the smaller stuff at the ends of the run. Volt drop over the short lengths will be irrelevant.
 

Abacist

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Welding cable is much better than jump lead cables. I tend to over engineer stuff and used about 15 inches of welding cable between the batteries and the inverter with a suitable fuse.
 
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DBK

DBK

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I don't have the equipment to make up my own cables. The ones I've bought are soldered and crimped at the ends so should have a good electrical and mechanical connection. I'll list all the suppliers and bits used at the end when I've finished. :)
 

maxi77

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I would have said the 150 amp fuse was about right, you need to take into account the inverter efficiency when calculating the total DC load, and the one chosen claimed it was 85% efficient and you need to be able to cover the overload capacity also when things are started up one of the reasons most inverters have an up to 100% short term overload capacity.

I also agree with the comments about jump leads as permanent installation cable. Many are really crap I have seen them with aluminium cable and poor insulation too. They are a fire risk. Welding cable is good and well priced but usually only comes in black so the positive cable needs marked with red tape.
 
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All now more or less finished. The power relay was a tight squeeze.

OI000001.jpg

The three single wires waving about connect to the load terminals on the RCD which fits on top of this box. The relay isn't secured in this shot but I secured it with a zip tie going around the bottom of it which then pass out through the box mounting holes in the bottom left and right hand corners. I'm not sure it is essential to secure it but it made assembling all this easier if it didn't keep falling out. The two white cables you can see coming out of the bottom are for the EHU power in and the other goes to the 13A sockets. Not shown is a third cable which carries the 240V output from the inverter which is connected to the RCD input terminals.

OI000002.jpg

You can see all three cables and the relay securing zip tie in the shot above. I had to buy another 10mm spacer as though I managed to assemble it with one I felt there was a risk there were wires trapped between the relay and the RCD.

To connect to the sockets I had to cut the two cables which go to the sockets and extend them. I'm not really happy with the Screwfix junction boxes you can see in the shot below but some junction boxes I ordered from eBay, described as "three way" turned out to just have three terminals inside them! I had to fit a larger terminal block inside these Screwfix boxes to accommodate two cables coming in one one end but this was easy enough to do. I've used some zip ties to secure everything and I think they are safe.

OI000003.jpg

You may also see the earth which goes from the inverter metal casing to one of the junction boxes. I've joined all the earth cables together, EHU, inverter and sockets. I couldn't work out how the insulators on the inverter output terminals were fitted so I zip tied them on. Then when I was putting things away I found two plastic nuts in a bag - I will fit them when I take it all apart again to fit a new relay - see post below. :)

Confession time now. :) I incorrectly measured the negative cable and though it reached the inverter it did so in a sort of straight line with no chance of me securing it to anything. However, I wasn't the only one to make a mistake as the supplier made it using red cable instead of the black I ordered. They offered to replace it but I said no and ordered one 20cm longer but upped the cable thickness to 35 mm instead of the original 25mm. What I then did was to use the spare red cable I now had to double up on the long run between the fuse and the isolator.

You can see the two cables going to the fuse below plus the thicker negative cable.

OI000006.jpg
 
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DBK

DBK

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Relay looks neet but the NC contacts are only 720 watts at 240v and you have a 1500 watt inverter.
Well spotted! Bu**er! I need to look for a different one.
Many thanks - one of the reasons for posting this was to get advice and suggestions. Bizarre that the contacts are differently rated. I wonder what that would be for? :)
 
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Lenny HB

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I think the lower rating on the NC contacts is due to needing a lager are gap for higher currents to reduce the risk of arcing a compromise to keep the size down.
I found one on eBay with both NC & NO rated at 30 amp can't find any now.
RS do one that is 10 amp NC, 30 amp NO that will do, also try CPC, will probably need a bigger box.
 
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