Thank you so much for the encouraging feedback. It seems that these posts have hit the spot.
I want to stop the theory now as it gets very deep and overburdened with maths after only scratching the surface with AC.
Today I would like to present multimeter safety and a few facts that Bunnings and Dick Smiths wont/cant tell you.
Multimeters are just that, multi purpose measuring instruments. They are made in 4 insulation classes, class 1 and 2 are about $30 from Bunnings and should NEVER be used to measure mains (240 volts) voltages. The MINIMUM class for mains is class 3. These classes can be seen at the base of the meter, if they meet Australian standards.
What they dont tell you.
Meters set to measure voltage are very high internal resistance and current meters are very low resistance. It is imperative for YOUR safety to ensure the meter is set to the correct scale and function for what you want to check, before you stick the probes in. When I was teaching, I would check the correct settings on meters of all students BEFORE they used it to check for mains voltage. After a few successful checks the kids would do this by themselves, we never had an accident.
If you set your meter to amps and put it in the 240V socket it will blow up and you may get a shock if the meter has no protection. I suspect the $30 Bunnings special has little or no protection.
Amp meters need to be in the flow of current, that means the circuit has to be broken, we should have little need to measure current, most caravans are fitted with devices to either regulate the battery charging current and display it for the curious. I have a fluke clamp meter which places a clamp around the wire to measure the current. OK this is not a cheap meter HOWEVER it is a class 3 up to 750VAC and 600VDC. It has idiot proof settings (auto ranging) to volts, ohms, amps and continuity.
I had a routine that I taught to apprentices and school students. ALWAYS check for the presence of voltage before you shove your maulers into any circuit. A simple "voltstick" can test for the presence of voltage but I dont believe they are that reliable, for me there is nothing safer than a good meter.
Although 12 volts is considered non threatening I beg to differ, if you are messing around with your caravan batteries and you accidentally short the terminals there is potential for massive current to weld whatever tool you have to said terminals and for the battery to overheat and go boom, making one unholy mess under the bed (that will pee off the bride no end). Needles to say it can mess you up as well. Acid on skin is not that nice.
Its fine to get these beasties on special and save some money, but for goodness and safety sake invest in a decent meter and learn how to use it safely it may save your life.
Take a peek at these
www.youtube.com/watch?v=m_yrfpD7tRc
www.youtube.com/watch?v=GPoWH5xH8q8
Once again I appreciate the encouraging PMs and posts. I will concentrate on safety and simple maintenance tasks in future posts.
Greetings Phil, Salutations all you Techies, I have been burdened with this problem, is a sense of Humour allowed in the tech's room,,,???? anyway Phil, catch you down the track , looking forward to comparing our Happy pills, Billeeeeeee
First off......Merry Christmas and a happy new year to every one.
Now where was I ??? Are yes, yep, I for got what I was going to say, craft again, must be old age!!!
One thing that I have always done when working on electrical equipment 12 Volt, 24 Volt, mains ( 240 Volt ) and even 3 phase ( 440 ~480 Volt ) I would stress that it is important to take off any rings, watch or even chain/ tie that is around your neck, lessions the risk of comming into contact with a live wire. While we should not be playing with mains voltage at all, and in this area has to be done by people with the correct qualification.
Rings and watches!!! well even low voltage ( 12 & 24 Volt ) while you may not feel a voltage get a wedding ring between 12 Volts and the earth of you 4x4 and you run the risk of the ring be comeing red hot in a very short time ( no pun intended ) Have seen it happen in real time. A bloke had some how got his wedding ring caught between the B+ terminal of a starter motor and the metal part of the starter motor. The ring went white hot in a matter of seconds and also had become ' welded' to geter. End results were that the auto elec lost a finger.
Battrey's and I'll talk 12 Volts here can also in a short cct have a very high Amperage capacity ( 100's of Ah ) and quiet often do when starting you diesel/ petrol motors.
First off......Merry Christmas and a happy new year to every one.
Now where was I ??? Are yes, yep, I for got what I was going to say, craft again, must be old age!!!
One thing that I have always done when working on electrical equipment 12 Volt, 24 Volt, mains ( 240 Volt ) and even 3 phase ( 440 ~480 Volt ) I would stress that it is important to take off any rings, watch or even chain/ tie that is around your neck, lessions the risk of comming into contact with a live wire. While we should not be playing with mains voltage at all, and in this area has to be done by people with the correct qualification.
Rings and watches!!! well even low voltage ( 12 & 24 Volt ) while you may not feel a voltage get a wedding ring between 12 Volts and the earth of you 4x4 and you run the risk of the ring be comeing red hot in a very short time ( no pun intended ) Have seen it happen in real time. A bloke had some how got his wedding ring caught between the B+ terminal of a starter motor and the metal part of the starter motor. The ring went white hot in a matter of seconds and also had become ' welded' to geter. End results were that the auto elec lost a finger.
Battrey's and I'll talk 12 Volts here can also in a short cct have a very high Amperage capacity ( 100's of Ah ) and quiet often do when starting you diesel/ petrol motors.
One to think about !!!!
Cheers for that one Valiant,
When I was in the RAAF it was a routine order (one you could get into deep sh1t if you disobeyed) that said NO rings, chains, watches etc were to be worn on or near aircraft (this applied to all trades). As an electrician it was expressly forboden, I saw some photos of a guy who slipped on an aircraft entry ladder, grabbed the sill of the ****pit and ended up with his wedding ring and most of the flesh on his finger left on the sill as he ended up on his butt on the wet tarmac.
Very important advice that some ignore, we are often our own worse enemy when it comes to personal OHS.
One thing that for got to mention was that the motor that the auto elec got his ring caught on was part of a portable gen set that had a capacity of 55 Kva,and powered by a big catapilar engine, so a pritty big gen set. As for the battery, two large 12 Volt jobs and at a guess in the order of 1200 scA's each battery, so 24 Volts at 1200 odd Amps, While the terminal voltage is not high ( 24 Volts ) the current capacity is off the scale.
Consider when you go to start your average 6 cylinder motor 400 ~ 600 Amps is what the starter motor would possably draw while starting the engine, so a little ring or a watch is not going to bother the battery.
Even when working on my own equipment in the cars / caravan etc I always take of any rings etc just in case. Even when working on fuse panels in the 4x4 and while the fuse panel may have a master fuse, still the current would only be governed by the size of the fuse and could sink enough Amps into your ring to heat it up a fair bit, before the fuse "blew'.
-- Edited by valiant81 on Sunday 28th of December 2014 02:43:12 PM
What he said plus; PPE - when I was working in GeoPhysics we were moving 12 batteries around all the time. If you accidentally get a spanner across the terminals it will get red hot quick so leather gloves and also you will get a big SPLAT of sparks so eye protection !!
