12v lighting for my house powered by my van

[12vshocker]

Ok so the plan is: to power the the lighting circuit using a car battery via a pcu, that connected the the a/c via timer circuit, fit a diode to the battery pos, so not to waste electricity recharging the battery with a/c power supply.

Is there a better way to click over to the ac power? I.e. Monitoring the battery status and some sort of automatic switch over once the voltage drops?

Also how do you calculate how long the battery would last, I know I'd need to find out the consumption of that circuit per day, and battery ratings etc but what would the formula look like?

And if I connected the neg post of the battery to the met bar would it tap into the unused neutral current (probably not the right word). Also I suspect something terrible would happens under fault conditions.

 

[12vshocker]

Sorry I meant UPS not PCU, stupid TLA's

 

[davesparks]

But why do you assume the battery would be further away? He can't energise a circuit using a 12v battery that then feeds PSU's that have 240v on the primary.

Because there is only one battery which he wants to feed the whole circuit from directly and he wants to install a diode to prevent the 240AC getting to the battery, he clearly hasn't got much of a clue.

From what I can understand of the OP this is exactly what he is intending to do, feed a whole lighting circuit at 12V directly from a battery.

 

[Deuce]

Because there is only one battery which he wants to feed the whole circuit from directly and he wants to install a diode to prevent the 240AC getting to the battery, he clearly hasn't got much of a clue.

From what I can understand of the OP this is exactly what he is intending to do, feed a whole lighting circuit at 12V directly from a battery.

I just... Can't believe that. He must surely mean the elv circuit on the secondary side of the PSU. not the entire lighting circuit the PSU is on..

 

[davesparks]

I just... Can't believe that. He must surely mean the elv circuit on the secondary side of the PSU. not the entire lighting circuit the PSU is on..

I may have misunderstood completely but what I got from the first post is that he wants a 12V lighting circuit, doesn't want to use an inverter, wants to keep the existing transformers/drivers in place and use a diode to prevent the 240V AC getting to the battery.

 

[Richard Williams]

I got a headache reading that lot

 

[DPG]

I bet the novelty of swapping batteries between house and van every day soon wears off.

 

[PJElectricalSW]

Just use a 12vDC to 230vAC inverter, no worries about any DC volt drop, LED gubbins and secondary lighting circuits. Use existing cabling with a switch over rotary switch to go from 'mains supply' or from the invertor supplied juice.

Economy 7 users do not know what they are sitting on...

 

[Deuce]

Just use a 12vDC to 230vAC inverter, no worries about any DC volt drop, LED gubbins and secondary lighting circuits. Use existing cabling with a switch over rotary switch to go from 'mains supply' or from the invertor supplied juice.

Economy 7 users do not know what they are sitting on...

So this is where we're at.. the op is gonna drive his 12v DC van to power an inverter to charge a 230ac battery to then power 230ac psu's to power 12v DC lights?

This has reached insanity level. I invite the op to post again and let us all know what the hell their motivation is! I can only assume it's stealing power... Which is fine, I don't care - on the basis that in this case stealing the power seems to be at least as much effort as earning it legitimately

 

[12vshocker]

To carify I will be using an inverter of some sort, but how do I get it to switch over automatically to mains supply if the voltage drops?

 

[PJElectricalSW]

Insanity at new levels, I agree that it seems daft but if the OP has legit and honest intentions then surely we should offer advice.

And you'll be wanting a voltage drop relay, try Finder or Schneider for help on this one.

The cost of this setup is likely to reap little for you, it would be cheaper to buy solar torches/lamps and bring them in of an evening.

 

[DPG]

Remember car batteries are not intended to be deep discharged, so as PJ says above you will need some sort of voltage monitor to cut off before the battery voltage gets too low.

 

[Michael Sands]

Just use company fuel to power generator the set up you are suggesting is just insane and potentially kill someone by electrocution or fire
To calculate power usage it should simply be amps per hour 10 bulbs using 1 amp each would use ten amps per hour a simple calculation of ohms law will work fine to work out amps used per lamp
There are loads of channels on YouTube about power walls made from reclaimed batteries maybe that would be a better place to have your questions answered

 

[Deuce]

I've solved this.

Instead of transferring the power from the van... Just leave the 12v lights turned off. Then park your van, leave the engine running and headlights on hi-beam shining through your window

 

[Squid]

Work harder earn more money and then you don't have to worry about your electrikery bills, simples.

 

[Silly Sausage]

Work harder earn more money and then you don't have to worry about your electrikery bills, simples.

Just fiddle the meter

(Disclaimer: my posts are just opinions, not necessarily to be taken seriously )

 

[Squid]

Just fiddle the meter

(Disclaimer: my posts are just opinions, not necessarily to be taken seriously )

You worry me sometimes with your choice of words..........'o)))))

 

[Lucien Nunes]

Let's be clear about the economics here.

The average cost per kWh in the UK at the moment is around £0.14.
A 110Ah 12V battery stores (very approximately) 110x12/1000 = 1.3kWh or £1.85 worth of electricity. It's not exactly that figure because the voltage is not 12V over the full discharge, and the 110Ah is quoted at the 20-hour rate but will be less if discharged in less than a day. Let's assume a reasonably optimistic 80Ah representing 100% depth-of-discharge to 10.8V over a full life of about 400 cycles. We can't really push it any harder because of the fairly aggressive charging rate required quite apart from the discharge.

The OP must supply his own battery, even if he's stealing the fuel used to generate the power. To get the performance mentioned he will need a good quality battery. 110Ah non-traction AGMs range from say £120-200. If he spends £175 he will get a good brand that will hold up to this kind of use. A traction battery rated for discharge at C/5 will do better at correspondingly higher cost.

Each daily cycle saves him 80 x 11.5 x 0.14 = £ 1.29 in electricity but costs 175/400 = £0.43 in battery wear and tear. So the maximum possible saving on this scheme is around 86p per day. I would be surprised if, in real-world changing conditions, you would achieve half that.

To quote the wise words of Dave OCD's post:

Why even bother.

FWIW, you can use a pair of diodes to allow a backup mains-driven PSU to take over seamlessly when the battery gets low. You set the voltage of the PSU equal to the minimum voltage to which you want to discharge the battery. Whichever is higher does the work. Use big, low voltage Schottkys to avoid undue losses.

As mentioned above, heavy cables will also be needed to avoid yet more undue losses. For those unfamiliar with transmitting power at 12V, the power loss is 367 times greater than at 230V for a given power and cable size (230/12)². E.g. the headlamp feeds on my boat are 10mm² (tunnel lights) and 16mm² (spot lights). 24V makes a 75% saving in copper over 12V.

 

[Shoei]

Let's be clear about the economics here.

The average cost per kWh in the UK at the moment is around £0.14.
A 110Ah 12V battery stores (very approximately) 110x12/1000 = 1.3kWh or £1.85 worth of electricity. .....

Logic is spot on, you probably looked at your calculator in disbelief and unconsciously moved the decimal point. It's 18.2 pence for 1.3kWh.

If everything is 100% efficient and the batteries never degrade it takes about 5 years to break even, in real life, break even is approximately never.

 

[Lucien Nunes]

Yes, well spotted! Made a crucial slip there, I accidentally switched from visualising what the OP's single 110Ah battery holds, to what the battery complement on a recent project holds (just over 1100Ah) and subconsciously changed the numbers as I typed so that they made sense. As I've often used as an example, the average person cannot lift £1 of electricity stored in lead-acids.

So yes, the battery saves less than 20p of electricity per cycle but costs more than that in depreciation, hence the scheme makes a net loss.