Van Wiring System Off Of Leisure Battery

[Radventures]

Hi guys,

So basically I'm coming here looking for some friendly advice with the intention of eventually getting an electrician out to make sure I'm not messing anything up (I'm based near Swindon - recommendations welcome!). I just want to do as much of the prep as possible.

I've put together a wiring diagram based on what I've learnt on the web. The van is an LDV Maxus and the starter battery looks like the best thing to plug in to as the alternator is hidden away. Basically what I want to do is hook up some LED lighting and a couple of mains plugs which I can run laptop/charge camera batteries/phone etc from. The only thing I've bought so far is the 85ah leisure battery.

Based on the diagram could you kind chaps let me know if:

a) anything is going to cause a problem?
b) if anything could be improved? (I've read that the split charge relay isn't the most economical solution, but am struggling to find a replacement)
c) how I would go about working out what wires/fuses I need?
d) what size inverter should I choose? Is this even the best solution?
e) have I missed anything?

The other thing I was wondering was about the leisure battery. If using up a full charge is going to ruin it, is there some sort of mechanism I can implement to prevent this happening?

Thank you so much for your time and effort,
Scott

 

[Lucien Nunes]

The principle is OK but there are some bugs in your sketch there.

The coil of the split charge relay is shown as being permanently energised from the battery, i.e. the relay will stay closed instead of isolating the batteries as required. If you intend to use a straightforward relay, it should ideally be energised from the warning lamp output of the alternator (if it's machine excited) so it closes when the alternator is delivering output. If it doesn't have a suitable output, next best is an ignition feed that's off during starting, so that the batteries are linked when the engine is expected to be running. If you are intending to use an electronic voltage sensing-relay, this will do the switching automatically according to the engine battery voltage - it won't need the extra control feed.

The fuse in the relay contact circuit is unlikely to do much good, it might blow on the brief current surge when the batteries connect at different states of charge, and its resistance is undesirable. In fact the resistance of this part of the circuit should be kept very low.

I'm not sure why you've connected the mains sockets to the 12V circuit! Note also that the 'earth' of the mains sockets is a different animal to the 'earth' (i.e. chassis negative) of the 12V circuit. Keep mains wiring to a minimum and connect all three cores to the plug that is plugged into the inverter, not the chassis. There is a whole separate discussion you can have over earthing the inverter output. much advice will be wrong. Search this forum for info.

I had to laugh at the inverter symbol... that's the symbol for a binary logic inverter, not a box that converts 12V into mains!

Your q's:
a) As above
b) Voltage sensing relay to control split charge
c) Depends on loads you want to run and length of cables
d) From your description, a few hundred watts would be sufficient. A 600W unit would have an easy life without being much more expensive.
e) The devil is in the detail
f) The inverter will have under-voltage shutdown to prevent you over-discharging the battery, but it will not prevent you using it to 100% depth-of-discharge. Big expensive units allow you to set that limit too, but you might choose to add a voltmeter and just keep an eye on it. Voltage tracks charge state over a limited range and at low load, although varies with temperature. Once you get a feel for the available energy on (say) 60% discharge you can stop watching the VM. OTOH it's not a huge deal, one can spend too much time fretting about battery cyclic life instead of drinking beer and partying!

 

[PEG]

Pretty well covered by Lucien...small gripe would be the use of a 1960's split charge relay,in amongst all that 21st century tech

Your vehicle alternator will "see" those two paralleled batteries as one,and let the charging shananagins begin...

That relay will open the lock gates,even if the water level the other side,is 10 foot higher than your barge...and another holiday is spoiled

 

[Lucien Nunes]

I'd like to see you open the gates against 10'. The most I can manage is a couple of inches!

If the alternator is retrofitted with an intelligent or battery-sensed multi-step regulator, then I agree that paralleling batteries in different states of charge with a relay may not be desirable. But with a standard constant-voltage regulator I don't see much harm in it. The alternator will simply hold all of them at 14.4V or whatever, regardless of how many or their state of charge. If the aux battery is flat there will be a brief equalising current when the relay closes, not as much as one might imagine, and not enough in practice to damage the relay. I fitted dozens of Bosch 0-332-002-156 on systems with 200-300Ah and never knowingly had a failure. The relay serving the general domestic battery on my boat sometimes has to pull 440Ah of fairly-low and 300Ah of fully-charged batt together, it's only a basic Lucas SRB600 and it's lasted 20 years so far.

 

[Radventures]

Thank you for the information - it's immensely valuable!

So, I have readjusted the diagram based on what you have said to the best of my ability. I'm still not really sure where the inverter should be connected & have struggled to find information on wiring up the VSR online, so there may again be errors... If you could be so kind as to take another look?

Another thought - if I wanted to add another leisure battery into this system would that cause problems?

ps if I'm seeing 10' of water outside my van then the electrics will be the least of my problems haha!

 

[Lucien Nunes]

Remove the fuses from the relay leads. Give the relay a negative reference from the starter battery. The inverter is a box with 12V DC in at one end and 230V AC out at the other. Job done.

 

[ruston]

Here is some further information on the situations in modern vehicles with smart alternators.
Maybe not applicable in your situation , but may be of interest in general.

One thing to remember is that high and low voltages outside the tolerance of the ECU will cause problems
If the battery is+/-of the tolerance for instance the ECU will not open the injectors. You would not even be able to start the vehicle with a tow until the parameters have been satisfied.

http://www.12voltplanet.co.uk/auxiliary-battery-charging-in-vehicles-with-smart-alternators.html

 

[Radventures]

Awesome, thanks lads. 12voltplanet have so much useful stuff on there - the tip is appreciated.

 

[Radventures]

ps: any tips on how to calculate cable width/fuze size would be amazing.

 

[Radventures]

pps: is the 600w recommended the surge power or continuous power? Many inverters seem to about at either 220v or 240v, does this matter?

 

[Lucien Nunes]

I was thinking of a 600W continuous rating as being around twice the maximum power you were implying you might want - a laptop adaptor taking 120W (flat laptop batt) and a few other small electronic items at 50W each. Small battery chargers may not take this much and a fully charged laptop might only require 40W to keep it running. Do you have a definitive list of things you want to power?

Sizing cables depends on both current rating and voltage drop - the cable must be large enough to satisfy both requirements. Voltage drop depends on length and is very critical in 12V systems - for the same percentage loss at the same power consumption, cable resistance needs to be 400 times lower on 12V than 240V. With a battery discharged to 11V and an inverter efficiency of 85%, a 300W load will require 300/0.85/11=32A from the battery. Unenclosed 4.0mm² might appear to be adequate for current rating, however if the inverter is 3 metres from the battery the voltage drop would be 32 x 0.018/4 x 2 x 3 = 0.86V which is excessive. You might do well with 10mm² for the charging leads and the inverter, and probably 1.5 for the lighting, but you should check the numbers when you know the lengths involved.

 

[Radventures]

I see, I see. My laptop charger reads 85W & battery is around 15W if I remember correctly. Aside from this, just the LEDs, which would probably max out around 20W. I can't see anything more watt intensive than my laptop being used - especially not at the same time as my laptop and I don't own/plan to use much other electrical gear. The initial surge seemed like the only thing that could cause problems, but I couldn't actually discover if a laptop has this phenomenon.

Inverter should be adjacent to the leisure battery & both should be around 1.5/2m from the starter battery. Lighting may run up to 3m and mains plugs should be >1m, but I think using the information you've provided I should be able to google around work it out - thanks for spelling that out for me - immensely helpful as ever.

Out of interest, what are the cons in using wire that is too thick? Extra resistance?

 

[Lucien Nunes]

The main disadvantage of oversize cables is that sometimes they can be difficult to connect to the device terminals. It's self-defeating to use a really heavy cable but then make a poor connection that develops high resistance. Other than that, and within the bounds of sensible cost, bigger is better although the benefit diminishes exponentially once the voltage drop is below a few %.

Surge is negligible for the laptop adaptor. It sounds like a 300W inverter might be adequate for your very modest requirements then. Many of them are built right down to a price and not generously proportioned inside, so it pays to allow a bit of headroom. They contain highly stressed electronic components and have a high failure rate per hour of use when pushed to their full output.

Are you running the LEDs from the 12V circuit? You should be, unless you require some special type of fitting that can't be got in a 12V version. But from your wording it sounds like you are including them in the inverter output i.e. using a 230V driver or adaptor to feed them. This is inefficient - transforming the voltage up and down again - and might add 30% to their consumption from the battery.

 

[Radventures]

Great tip on the LEDs. I did not realise that. So I can wire it directly to the leisure battery with a fuse in between?

I plan to be using the inverter almost daily, so maybe something a bit more heavy duty would be a good idea then.

 

[Radventures]

Hello again! So, after some research and consideration, I think I'd like to go for a battery to battery charger for the increased charge times. From what I can gather I would just replace the VSR with the B2B - is this correct? Is there anything else I should be mindful of. Many thanks.

 

[Lucien Nunes]

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...

 

[amlu]

great deals in China on 12V leds...

http://www.aliexpress.com/item/20PC...ite-Red-Green-Blue-Waterproof/1896145024.html

bought a lot of 50 some 2 years ago, got them all over the workbench, back of the van, some in mates shed, all still work no problems.
runs of straight 12v dc, happy with 14v in the vehicles too no drivers needed
and fix anywhere with 2 little screws no sticky tape mess.

 

[Radventures]

Right you are... decreased charge times. Airspace and good connections - got it. Cheers again Lucien. Your second paragraph, however, is literal gobbledygook to me!

Those LEDs look perfect. Not sure about he 20-40day delivery though - don't still have some lying about you fancy selling do you ha?

 

[Dan]

great deals in China on 12V leds...

http://www.aliexpress.com/item/20PC...ite-Red-Green-Blue-Waterproof/1896145024.html

bought a lot of 50 some 2 years ago, got them all over the workbench, back of the van, some in mates shed, all still work no problems.
runs of straight 12v dc, happy with 14v in the vehicles too no drivers needed
and fix anywhere with 2 little screws no sticky tape mess.

Do you buy much stuff from there?

I've used www.dhgate.com a few times but most of it seems to be tat you'd see at a car boot sale.

 

[Radventures]

Almost installation day! Couple of things still bothering me if anyone would be kind enough to clear them up.

1. I understand that I can wire the earth for the battery to battery charger (and both batteries) to the van's chassis, but not the plug socket earth cables. How do I ground them?

2. What's the best way to attach the cable to battery positive/negative terminals? Do I simply screw it in? (something like this https://www.amazon.co.uk/Car-Batter...8&qid=1474736934&sr=8-1&keywords=car+terminal)

3. If I have 4 wires coming out of the inverter into the fuse box does it matter if they overlap? ie. have four wires connected to the same terminal? Is there an alternative? As well as these 4 wires I'll also have the cable coming from the start battery to contend with. I can foresee there not even being enough space to connect everything.

Thanks as always.