Idiots guide to electrics

whitevanwoman

Guest
Please could someone either point me in the direction of a good website or post explaining about electrics to a complete dummy re electrics?

All I know is that houses run on 240 volts and car batteries run on 12volts but I don't know the difference between volts / amps / watts etc and don't know where to start to try to calculate how much electricity my various appliances would use on mains hook up. I know that the higher the wattage, the more elec is required eg old style 100w light bulbs use alot more elec cos they are brighter, than old style 40 w bulbs, and that low energy bulbs only use about 11 w and so are much more economical.

But how do I calculate my consumption when not all accessories say on them what wattage they require - sometimes it just says volts and amps. All I know about amps is that 3amps is the bog standard fuse in a house plug and that a kettle or hairdryer needs a higher fuse like 13 amps - or have i got that the wrong way round?

At the moment I have a leisure battery (no idea what size but it says its a heavy duty auto / marine battery, second hand donated by a friend with caravan so no idea of age / condition ) which isn't wired in and so I am just running 12 v appliances direct off that and am trying to work out how long it would last.

The 12 volt various appliances I have are :

laptop - requires 19v, got an incar charger for it which works fine
mini car heater / fan - says 150 watts on the packing, works when plugged direct into cig lighter but it blew my 4 way adaptor
mobile - incar charger
AA & AAA high speed battery charger (charges flat batteries in approx 20 mins) - has both 240v lead and 12v incar charger
mini oven
mini kettle
mini fridge - it works with a fan and can apparently used to keep food hot aswell but I guess is would use more elec, it has both 12v and 240 volt cables, it's effectively an elec cool box, fits a couple of milk cartons in or 4 pack of beer


Do I need to have the engine running for some of the things eg mini oven, mini kettle (I remember from school that things that heat up consume much more elec)?

The various items I would like to use if I had hook up (I have a hook up extension cable with 2 sockets, not wired directly into battery) are :

a small 2 bar elec heater which I had in my caravan (only 1 bar works, am guessing it's probably about 800w)
laptop charger
leisure battery charger (apparently it's a fast charger?)
a light with a low energy bulb (11w)
AA battery charger (fast charge)
mini fridge

I also have a small work top 240v oven which would be useful

I have 2 sockets in my hook up adaptor, what combination of the above 240v items should I avoid using - presumably I shouldn't use the heater and oven at same time, but what about the leisure battery charger and /or mini fridge with other things?

I have a 4w solar panel trickle charger but from what I've read, this isn't going to be much use except to stop the battery from discharging if not used for a while. Is it worth getting a second one and can I use 2 clipped onto the leisure battery at the same time?

Any explanation needs to be very very simple - a friend once tried to explain using the analogy of a river and the width of the river, speed of the flow of water etc but I got very confused.

Thanks.
 
Jess
you will find a load of information on here, if you go to motorhome problems or knowledge and do a search there, maingate has posted many responses about this, if you cant find anything pm him, i cant help you cos i get confused about it too, lol
 
kimbowbill said:
Jess
you will find a load of information on here, if you go to motorhome problems or knowledge and do a search there, maingate has posted many responses about this, if you cant find anything pm him, i cant help you cos i get confused about it too, lol
Click to expand...

I spent a couple of hours last night reading back through various threads but didn't find anything from within the past year or so. I'll try doing a search now, but I'm guessing that if I search for "electrics" I'll get loads of results.

Any suggestions as to a more specific phrase to search for?
 
John Wickersham has written books on all aspects of doing as self build

Amazon sell them cheaper than elsewhere. Maybe some members have one they could sell you cheap.
 
Hi Jess

I bumped a thread which I posted on this,

http://img137.imageshack.us/img137/305/movanowiring.jpg

movanowiring.jpg

The diagram shows how the 240V system is separate from the 12V.

Also a formula you will find useful is Watts = Volts x Amps

For example at 240v 40W(Bulb) = 240V x 0.166A

at 12V 40W(Bulb) = 12V x 3.25A

The way you can use this practically is take the wattage of your appliances and divide by the voltage and it gives the current drawn

eg 40W/12V = 3.25A So you know if you run this bulb for 8 hours you need 8x3.25Ah = 26 Ah of supply. You can compare this to the Ah capacity of your battery(s).

(Edit On the wiring diagram, if you prefer to have a split charge relay, just replace switch A with the relay, and if you want to wire your fridge so it works on 12V while the engine is running, replace switch C with a fridge relay. If I need to run my fridge while moving I usually just plug it into my inverter on 240V. I find it works better off 240V and gas)
 
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maingate said:
John Wickersham has written books on all aspects of doing as self build

Amazon sell them cheaper than elsewhere. Maybe some members have one they could sell you cheap.
Click to expand...

Thanks for this, will check it out, sounds just the job. Would be very glad of any second hand copies.
 
Firefox said:
Hi Jess

I bumped a thread which I posted on this,

http://img137.imageshack.us/img137/305/movanowiring.jpg

View attachment 4114

The diagram shows how the 240V system is separate from the 12V.

Also a formula you will find useful is Watts = Volts x Amps

For example at 240v 40W(Bulb) = 240V x 0.166A

at 12V 40W(Bulb) = 12V x 3.25A

The way you can use this practically is take the wattage of your appliances and divide by the voltage and it gives the current drawn

eg 40W/12V = 3.25A So you know if you run this bulb for 8 hours you need 8x3.25Ah = 26 Ah of supply. You can compare this to the Ah capacity of your battery(s).

(Edit On the wiring diagram, if you prefer to have a split charge relay, just replace switch A with the relay, and if you want to wire your fridge so it works on 12V while the engine is running, replace switch C with a fridge relay. If I need to run my fridge while moving I usually just plug it into my inverter on 240V. I find it works better off 240V and gas)
Click to expand...

Brilliant, thanks v much.

But aaaggghhh, maths equations!!! I failed my maths o level (showing my age now) 4 times, I finally got a CSE grade 1 at 18. Dropped physics and chemistry at 13. Even Brian Cox's explanations of science stuff confuse me though I'm interested - did you see him on Jonathan Rosss last night, he put half a million volts? watts? amps? through Ross in a mini Hadron collider type thing and made his hair stand totally on end, amusing but I couldn't understand why a) ross wasn't electrocuted (was he standing on a rubber mat?) b) how touching Ross or the collider thing with a wooden stick decharged them c) why it was dangerous for Ross and Cox to touch each other whilst Ross was still charged.

And Brian Cox is the best science teacher I've come across so if I can't understand his explanations, that's why I need an idiots guide.

All I really know about H&S for electrics is that during a thunderstorm the safest place is in the van or lying flat in an open area away from trees, tent poles, brollies etc, and that I should do all my lawn mowing with the flymo and any DIY involving electric sockets / lights (eg, rewiring a lamp, plug, changing bulb etc) in my wellies.

I once had to have all the wiring (the coil?) in my 2CV replaced because I was using silver foil instead of a fuse which had blown - lesson learned the expensive way but I still don't understand what appliance needs what type of fuse in a house plug.

Tonights homework will be to sit down with pen and paper and work through this info you've given me - I might actually start putting together a "camper" file with info and notes etc about this sort of stuff plus some of the other hints & tips from other threads - after the RH meet, I realised that I needed a "Pre-trip check list" and a "Post-trip check list", a Packing list, print outs of info about Trannies, tyre pressures, type of oil, etc. Also my dad told me when I got my first car that I should do a POWER check each week (I never have but its good advice which I'm going to try to start doing) POWER = Petrol, Oil, Water, Electrics, Rubber (although both my vans are Diesel but Dower doesn't work as well as POWER - and putting in petrol instead of diesel is another story for the next meet...)

Am quite proud of yesterday afternoon's efforts which saw a deluxe version of my "bucket with a lid on it" loo - it is now disguised in an old laundry box with a hinged wooden lid which can double up as a seat and, instead of an inflatable neck cushion for a seat, I have a plywood commode type arrangement and there is space in the laundry box to store spare wood shavings, loo roll and air freshener :D

Have been giving some thought to a foldaway bunk instead of an air mattress on the floor... it's hard to explain if you haven't seen inside my van, but I'm thinking along the lines of adapting a camp bed / sunlounger, so am on the look out for a second hand one (I'm quite handy with a sewing machine so can replace / recover canvas) if anyone has got one destined for the tip / car boot sale / ebay - happy to give you a few quid for it, cheapest new one I've seen is about £20, and am not even sure that my idea will work so I don't really want to buy a new one just yet.
 
Hello,

I would also like to point out that some sites also have restrictions in how much they supply in Amps. Many a time have I witnessed a person hitting the switch on a kettle, then tripping the site!! However the best one by far I saw was someone in there caravan awning with a huge George Foreman Grill, wondering why every time he turned it up fully, he was throwing the trip.

Go with Maingate's suggestion with John's book for understanding the fundimentals with using your bus.

The only alarm bells ringing from my point of view, is how you wish to use the van when wilding, without making sure you have enough power to do the jobs you want to do. The best calculation I have used (but this is purely a guide/guess and has worked for me so far) is take the wattage of the object in question (e.g a 700W Cooking Power microwave, which uses 920W total when in use), divide it by the supply voltage, divide again by 60 (this puts in a time element of consumption), then times it by the length of time you wish to run the object.
So for purpose of demonstration;

940W divide 12V = 78.3A (please note that a use of an inverter is used in this, so will use approx 20W for it's own operation based on a 1500W unit)
78.3A divide by 60 = 1.305
1.305 times by 10 mins (the average time for a Jacket Spud) = 13.05ah of power used.

Now you have a rough idea of consumption, PLEASE also bear in mind of battery capacity, as one 100ah battery will not give you 100ah of usable power. Most batteries only have a certain percentage of operation over 12v (the average is 25%), hence on all previous posts I have ever made, I've always dummed on about battery capacity (even before suggesting on how you charge them). Again as an example, one 100ah battery may only give 25ah of usable power, so as you can see from the above calculation, one jacket spud has killed half of your usable battery capacity!!!
 
here is a zig wiring diagram hippy-1.jpg

as regard heater get a small oi;ed filled heater 700 watt then if you on hook up you can leave it on low overnight should warm up van nicely and it only small draw i did a post on here about dunelm heater ony i think 15 pounds
 
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oldish hippy said:
here is a zig wiring diagram View attachment 4115

as regard heater get a small oi;ed filled heater 700 watt then if you on hook up you can leave it on low overnight should warm up van nicely and it only small draw i did a post on here about dunelm heater ony i think 15 pounds
Click to expand...

Cheers, I got one of the Dunelm heaters (and said thank you), not used it yet, it was for my bedroom but it's not been below zero here except once or twice this winter.

I had the other heater in my caravan and it's really light, and I thought one bar would be sufficient to warm up the van pre bed time. I wouldn't have a heater on overnight because, as yet, the van isn't insulated so it would just be a waste, and I'm used to sleeping in an unheated bedroom in Cumbria, 200 m above sea level, and I have a mountaineering down sleeping bag so am not likely to be cold once in bed.

Plus, the dog provides me with an XL "always on" hot water bottle! ;)
 
Even Brian Cox's explanations of science stuff confuse me though I'm interested - did you see him on Jonathan Rosss last night, he put half a million volts? watts? amps? through Ross in a mini Hadron collider type thing and made his hair stand totally on end, amusing but I couldn't understand why a) ross wasn't electrocuted (was he standing on a rubber mat?) b) how touching Ross or the collider thing with a wooden stick decharged them c) why it was dangerous for Ross and Cox to touch each other whilst Ross was still charged.
Click to expand...


I didn't see the Ross item as I don't watch TV :lol-053: Current (amps) is what kills you. It sounds like Ross was charged up very slowly using a high voltage, and ended up with a static charge. Since the current wasn't flowing anywhere fast it is safe. I think if he was discharged quickly there could be a problem but the wood stick being a poor conductor could discharge him slowly. Even a stick can carry current if the pressure (voltage) is high enough.

Voltage is electrical pressure. It doesn't flow through anything but you put it across (either side of an object) it makes the current flow. The voltage can be high or low, but if the current is small it is safe in personal terms. Voltage = Current x Resistance is another equation, but the useful one for motorhome electrics is Watts = Volts x Amps.

You will often see newspaper journalists get it wrong when they say "the man was killed when 40,000V went through him". He was actually killed by the current going through him caused by the electrical pressure of 40,000V, but the trouble is that misleading statements are not much good to help understand the difference between current and voltage :rolleyes2:
 
Firefox said:
I didn't see the Ross item as I don't watch TV :lol-053: Current (amps) is what kills you. It sounds like Ross was charged up very slowly using a high voltage, and ended up with a static charge. Since the current wasn't flowing anywhere fast it is safe. I think if he was discharged quickly there could be a problem but the wood stick being a poor conductor could discharge him slowly. Even a stick can carry current if the pressure (voltage) is high enough.

Voltage is electrical pressure. It doesn't flow through anything but you put it across (either side of an object) it makes the current flow. The voltage can be high or low, but if the current is small it is safe in personal terms. Voltage = Current x Resistance is another equation, but the useful one for motorhome electrics is Watts = Volts x Amps.

You will often see newspaper journalists get it wrong when they say "the man was killed when 40,000V went through him". He was actually killed by the current going through him caused by the electrical pressure of 40,000V, but the trouble is that misleading statements are not much good to help understand the difference between current and voltage :rolleyes2:
Click to expand...

trying to digest this, word by word, to understand...
 
If it helps (or confuses!!), coulombs is charge (or electrons). What Ross had was a lot of charge. So this has to be let off slowly through the stick to keep the current low.

Current is the flow of charge (or rate over time). If 1 coulomb flows in 1 second that is called a current of 1 amp, or put another way 1 Amp = 1 coulomb per second.

Volts = Joules/coulomb and Amps = coulombs/second . If you multiply J/C X C/S, the C cancels out and you get Joules/second = power = watts.

Hence Watts = Volts X Amps

A current of 0.3A to 1A could kill someone if it went through the heart or brain as it messes up all the very small body currents which keep us going.
 
Firefox said:
If it helps (or confuses!!), coulombs is charge (or electrons). What Ross had was a lot of charge. So this has to be let off slowly through the stick to keep the current low.

Current is the flow of charge (or rate over time). If 1 coulomb flows in 1 second that is called a current of 1 amp, or put another way 1 Amp = 1 coulomb per second.

Volts = Joules/coulomb and Amps = coulombs/second . If you multiply J/C X C/S, the C cancels out and you get Joules/second = power = watts.

Hence Watts = Volts X Amps

A current of 0.3A to 1A could kill someone if it went through the heart or brain as it messes up all the very small body currents which keep us going.
Click to expand...


That explains it perfectly, thankyou. So Sue Ellen didnt shoot JR then, who'd a thunk it! :confused:
 
You can still see last nights' Jonathan Ross Show on ITV Player, here.... (To see Brian Cox electrify him, fast-forward to approx 39 minutes).

Video - ITV Player

There's some useful info on this thread, but a lot of it will be much too confusing for a novice. As others have already said, the best thing would be to get a basic grasp of Ohms Law which states (in basic laymans terms):

Power (in Watts) is equal to Voltage (Volts) multiplied by Current (Amps).

So Watts = Volts multiplied by Amps.

Volts = Watts divided by Amps.

Amps = Watts divided by Volts.

(The voltage, as you know, will normally be 240volts in your house (in UK), and 12volts (usually) in your car or motorhome).

If in any doubts about electrics it's always best to ask advice or let a competent person do the job.... They're not called "killer-volts" for nothing!

And remember, when you apply Ohms-Law to campervans, it's known as " Motor-Ohms Law"!!
 
scampa said:
There's some useful info on this thread, but a lot of it will be much too confusing for a novice. As others have already said, the best thing would be to get a basic grasp of Ohms Law which states (in basic laymans terms):

Power (in Watts) is equal to Voltage (Volts) multiplied by Current (Amps).

So Watts = Volts multiplied by Amps.

Volts = Watts divided by Amps.

Amps = Watts divided by Volts.
Click to expand...

Actually the above Watts law.

Ohms law is the other equation I gave : V= IR or Voltage = current x resistance

Otherwise, all present and correct :lol-053:

For those who have problems with W = VxA, V=W/A, and A= W/V.... think off 6=3x2, 3=6/2 , and 2=6/3

Sometimes putting in example numbers instead of letters helps to see the relationship :cool1:
 
if i were you Jess, i would try the "trial and error" method go out in your van, use you power and roughly time it how long you get, for eg, when i went to RH i used my lights, water pump and tv over 4 days on 2 leisures
 
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