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Decreased charge time, surely! B2BC's used to be expensive but are perhaps better value now and the better charging performance worth the investment. I still tend to think in marine terms where an engine might run for 12 hours a day and there might be charging current available from somewhere - genset, aux or propulsion, for much of the daily load cycle. As such it's not so important to get charge into the service batteries quite as fast. In wiring terms the only real difference is that it will require more substantial negative connections than the low-current sensing wire of the relay. It will also probably require free airspace for cooling.

OT but does anyone remember Lucas 4BD split charge diodes in oilfilled cans like ignition coils? Found a few of those in my old service stock the other day dating from the mid 70s, including a pos-earth (common cathode) one. Only any good with a battery sensed regulator of course, and sure enough there were battery sensed 4TRs, 14TRs etc in the kit. And even a NOS 3AW warning light relay for the venerable 11AC. But I digress...

I do,vaguely,the 11ac was standard on some Jags,and various small Perkins,etc...what a mass of components,compared to today's gear.
Control units,field relays,and a bumble-bees heart of an alternator buzzing away at the end!

I appreciate your scenario re split charge relays,but with limited depletion,and use by your good self,problems would be rare.

In situations where there is not a "dedicated" charge alternator,as such,say just a vehicles standard fitment,and the aux batteries are flattened by a liverie's kid's laptop and lighting use...the 40A it tries to pull when that relay closes,plus the vehicles ancillary use,just murders the poor alternator.

Found one 2 year old MAN 18 tonne truck,with a 45A alternator as standard! Retro-fitting a 120A upgrade,was £850,12A current limited B2B unit was £70,so,customer had change for a new Stubben (saddle)

As a kid,i used to stalk an old auto-electrician,he had a very bad hunchback,and temper to match,but i learned many things...one was his reluctance to clip a Durite ammeter on,when testing charge rates,preferring to ask "can yer keep yer 'and on the casing,more than a couple of seconds?" ...a "yep" would mean no further discussion ;)

As for my lock gate analogy,it IS possible to open them against a filled lock,or the upper level...just requires a Yale strongback or pull-lift,slung across the gate beam ends...don't ask...all i remember was THAT was the easy bit,removing all the old safes and shopping trolleys obstructing the sluices was a messy pain:)
 
Still some confusion there. You do not need a fuse box on the AC output of the inverter, the 230V loads should plug directly into its 13A output socket. Whether you provide any additional AC earthing / grounding depends on how the inverter is internally configured, we cannot answer that without knowing and on small low cost units they don't tend to tell you in the blurb like they do on professional ones. You can test it with a meter.

The term 'earth' in 12V vehicle wiring, such as 'earth connection' or 'negative earth' simply means 'common return conductor' and has nothing to do with safety earthing. Using the vehicle chassis or 'earth' as one pole of the circuit is simply an economy measure to save cable. Whereas the term 'earth' in mains voltage 230V wiring means 'safety equipotential conductor' and has nothing to do with carrying the operating current of the device. Two very different things.

I don't understand your 'four wires' bit at all.

Those battery terminals are OK-ish but the cables need to fill the terminal before you do up the screws otherwise they will just fall out again. There are better versions of the same, or ones with a captive terminal bolt and nut to which you can connect a crimped lug. Or you can get pre-made cables with crimped terminals.

Very rough sketch attached of what I think you're trying to achieve

Van Wiring System Off Of Leisure Battery DSCF4804.JPG - EletriciansForums.net
 
Thanks Lucien.

By four wires I mean the two LEDS circuits & two mains circuits. (I realise now I only have one LED drawn, but there will in fact be two on separate switches).

I don't understand why I don't need a fuse - shouldn't each of the LED/mains circuits be fused? Could you kindly explain that to me?

Thanks for clearing up my earthing confusion. How then, shall I earth the inverter? Photo attached.

Van Wiring System Off Of Leisure Battery 20160925_181928 - EletriciansForums.net
 
Compared to household mains supplies which can deliver thousands of amps in the event of a short-circuit, the maximum output of a 600W inverter is around 2.6A. It simply does not have the capability to produce higher currents, and for its own protection against damage it will shut down if overloaded or short-circuited. The smallest fuse any piece of mains electrical equipment normally requires for adequate protection is 3A, most are fine with being protected at 13A or 16A. As the inverter output cannot reach this level, there will never be enough current to blow such fuses hence no point adding them.

You attach a pic of the B2BC but ask about the inverter earthing. When you have the inverter you can double-check the internal connection of the output socket earth pin by measuring its resistance to the case and DC input negative. There will then be some debate about the best configuration according to what kind of wiring you propose to connect to the output.
 
I opted for a 1200w inverter in the end, as I didn't want to worry about overloading it. So the maximum output would be around 5A and should still be fine. Thanks.

Yeah, I can't explain that one away - it had been a long day! There will either be 2/3m of cable between the starter battery and leisure battery and >1m cable from the leisure battery to the inverter, or it will be the other way round. It depends on how I can rejig the space for the leisure battery under the bonnet.
Van Wiring System Off Of Leisure Battery 20160926_133700 - EletriciansForums.net Van Wiring System Off Of Leisure Battery 20160926_133708 - EletriciansForums.net Van Wiring System Off Of Leisure Battery 20160926_133716 - EletriciansForums.net
 
I expect that will do fine for your requirements, given the size of the unit and its terminals I would be sceptical about its ability to support 1200W for very long. Keep the cables short and fat consistent with keeping the inverter cool.

If you want to think about earthing on the 230V side, you will need to measure the resistance from the earth contact in that evil multi-hole socket to the neutral contact, the DC input and the case (I note it doesn't have a separate earth terminal.) What you do then will be a matter for discussion, there might not be one single recommended method as there are pros and cons of floating supplies etc. Or you could do what most people do and ignore it completely as an insignificant risk with so few pieces of equipment connected.
 
I missed these - thanks for chipping in. Insignificant risk = no hassle in my books.

Could you clarify what you mean by a distribution point spinlondon? Do you simply mean a means to distribute more sockets etc in the future should I wish to?
 
Okay sure. Logistically, I was wondering how I'm going to turn a single live wire from the fuse box into four and it makes sense to use the fuse box as you suggest, but do I need another part. Like I know you can get 2,3,4 way battery terminals - is there something similar I need here?
 
I'm un-stumped! Managed to figure out a way if I drill a new hole behind the fuse box. I've worked out I'll need around 2.7m of cable to run from the starter battery to the battery to battery charger. Where, conveniently, is a shelf which I should be able to store everything else. So I'm tying to work out cable size:

Max cable current at an inverter efficiency of 85%, 600w max load and battery discharged to 11v: 600/0.85/11 = 64A from the battery.
Volt drop is then a distance of 2.7m, volt drop figure is 2.8v for a 16mm2 cable (from https://www.tlc-direct.co.uk/Figures/Tab4.7.htm) and the 64A from cable current: 2.7x4.4x64A = 0.484. In a 12v system this is just over 4% voltage drop right? If I can find a 3 or 4 core 16mm2 cable then (according to the linked table above) I can get the voltage drop down to 0.414 which should be okay right?

Is there anything else I'm forgetting? Thanks!
 
Hi - just looking at the pics of your invertor in post #25 and LN comments in #26. The manufacturer supplied 12v lead looks like it might be 4mm2. Sometimes the supplied cables can be a bit light duty, but I'm not sure investing in multiple 16mm2 cables will be worth your effort. Your calc of about 0.4V drop for 64A over 2.7m of 16mm2 copper looks about right. But I just don't see that invertor in your pic being able to sustain that draw. Of course I can't read the spec etc so I may well be wrong. If you want, you could try connecting to 12v car battery and loading the 230V AC side with some lamps via a plugboard and see how it performs?
 
There seems to be some confusion here! You say the 2.7m is the length of the B2BC input cable, but you then calculate the VD using the inverter current, not the B2BC input current. As it happens the maximum is a similar figure (60A) but that is only coincidence - they are separate circuits working at different voltages and currents. The B2BC will only be operating when the alternator is running, so the launch voltage at the starter batt should be >14V. So long as the VD doesn't reduce this below the minimum input voltage of the B2BC at 60A, the voltage at the inverter batt will always be correct. Decreasing VD a few more % will simply increase maximum output current from the B2BC by about the same amount so it's not worth busting a gut for.

The VD is likely to be a few % less than the tabulated value because the cables won't be running at full temp, because the current is limited below their CCC by the VD.
 
Hey Wilko, thanks for chipping in. I was thinking 10mm2 for the inverter & leisure battery cables. Think that's about right? The 16mm2 I meant just for the starter battery > B2b charger (and b2b negative cable). Inverter is rated for 600/1200w. I've tested a couple of bits off of the 12v lighter and seems to be okay handling loads up to 300w so far. Can't imagine I'll be loading much more than that.

Lucien, I admit I struggled superbly with the calculations so that would explain the confusion. Although I am getting the gist a bit now after some research & your help. Thanks for clearing things up (again). Would you be so kind as to clarify what you mean by 'CCC'?
 
I would normally use Tri-rated AWG 4 or 35mm2 for battery to starter cables.
Although, that's on Harley Davidson motorcycles, so it may be different for vans and other vehicles?
 
Thanks for chipping in guys. I've started putting some wires in (unconnected) and cutting cables to size. A few questions have cropped up and I would be very grateful for some help. I'll upload pics for ease of explanation.

1. I'm wondering how I am going to take a single live wire from this inverter plug and turn it into two wires for two mains sockets? Also, if I leave the negative/ground for this plug unconnected it shouldn't matter right? The inverter negative will be linked to the battery terminal (from the 12v cable on the other side) I'm technically just using it as a live output from the inverter?

Van Wiring System Off Of Leisure Battery 20161012_163423 - EletriciansForums.net

2. What's the best way to hook up this pair of wires? I've noticed in a lot of the circuits in the car there's a clip system. What are these called, as I'm struggling to find these online? Or is there a better way? Should I remove the two wires attached to the LEDs and solder on the 2.5mm2 wire I'm installing?

Van Wiring System Off Of Leisure Battery 20161012_163500 - EletriciansForums.net

3. Is it best to return the earth (in this instance the negative cable if I'm right?) to the leisure battery negative (which will be earthed to chassis). I remember Lucien saying not to take this to the chassis earth so I'm a little confused.
Van Wiring System Off Of Leisure Battery 20161012_165925 - EletriciansForums.net
4. This is the B2B charger. In the instructions it says if I 'link' the two connections here labelled 'battery' & 'temp' I activate the feature where the charger turns off and on automatically (pretty desirable right?). By link I assume it means simply connecting a wire between the two with the screw in sockets. Am I right/if so, what thickness should the wire be?
Van Wiring System Off Of Leisure Battery 20161012_163658 - EletriciansForums.net

Many thanks!
 
Also, I've just opened a thread asking for an electricians help with overseeing the installation at some point over the next week. If anyone in the Swindon (Broad Town specifically) area can help out (or you can recommend someone) that would be great.
 

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