Ok boys, few things to go through today
Firstly sorry for the lack of updates lately but we've been on half term then review week... i'd much rather just get on with it
So. Batteries.
2 types.....
maintenance free:
Conventional type (note the 6 ''cells'' on top of the battery in addition to the posts):
It appears that if you have a maintenance fee battery, as per its title, theres nowt you can do if you run in to a problem where it wont maintain charge and its the battery thats faulty; bin it and get a new one!
the cpnventional type seem a lot better because the cells contain the sulphuric acid. if your problem is cos one is low, top it up with distilled water. simplez.
to test the quality of the fluid in each cell there is a battery hydrometer. when testing you're looking for consistency. if you got one cell that is down but the rest are fine the chances are you have a short circuit in that one cell and the whole batt. will need replacing.
the battery hydrometer readings per cell are:
Fully discharged - 1.130 to 1.170
Part charged - 1.170 to 1.270
Fully charged - 1.270 to 1.31
not sure if anyone has one at home? use it much?
to test for battery voltage, put your multimeter to DC Volts on the ''20'' scale. red lead on positive terminal, black lead on neg terminal and this will give a ''static'' reading. this should be between 12.6 and 13.2.
checking it for dynamic voltage is doing the same but when the car's running and should be around 14.2 (correct this if i'm wrong as i was rushing notes a bit).
to check for ''amp draw'' whereby you can see what ''consumers'' (things using the batt. current) you need to get into the circuit. one way to do this is to make your multimeter part of the circuit and read the amps... dosconnect either battery terminal. connect to your MM on the amps scale, join the leads to the post and the battery cable and take the reading,,,, thats how much ampage your cars using just sitting there with everything off
the purpose of the battery is SLI.... starting, lighting and ignition.
so now we move on to circuits. got to be honest i was rubbish at science and even this basic stuff i'm semi-struggling with
Well this is what i learned.... if i have any Q's myself ill ask in red.... please put in stoopid terms though otherwise i wont get it
firstly the basic rules of electricity:
1. electricity will always look for an earth (ground).
2. it will get to earth (ground) via the quickest route.
3. if temperature increases from the current the resistance will increase too.
not sure why though 
voltage - ellectrical pressure
amps - electric current flow
ohms - resistance to current flow
ohms law:
''1v of electrical pressure is needed to push 1 amp of current through a resistance of 1 ohm''
so based on this theory....
so using the above lets look at this simple ''series circuit'' and apply the law...(sorry if this comes out really big)
so the box looking thing being the battery supplying 12 v and the light bulb having a resistance of 2 ohms... using the triangle to work this out 12 volts divided by 2 ohms = 6 amps (i equalling amps... not sure why).
What i dont get and where this triangle doesnt seem to work is where there is 300 amps going to the starter motor supplied by a battery voltage of 12v......300 divided by 12 = 25. so does that mean theres 25 ohms of resistance at the starter? characteristics of a ''series circuit'':
1. voltage shared between each consumer (e.g. if there was 12v and two bulbs voltage going to each would be 6v)
2. current is constant (i.e. doesnt alter if more thab one bulb)
3. one bulb goes out, all the others go out (which is why theyre not used that often in cars)
charcteristics of a ''paralell circuit'':
1. constant voltage
2. current is shared etween consumers
3. one bulb goes out, others stay on
if someone can explain the paralell circuit that would be great as again i didny understand it 
so thats enough theory for today. head really hurting. i know you guys prob think this is very simple but i was always crap at science in school (15 years ago) and its been ages since i did it anyway. so bear with me
today we've been getting front and rear clusters out and testing voltage. we also checked using the MM to see if bulbs were good or bad (even if they looked ok).
how to check a singe cap, single fillament bulb...
how to check a double cap, double fillament...
keep your vlack lead on the earth and check one cap at a time with the red lead.
when i say ''checking'' youre just checking for continuity.... no beep equals its bad and needs changing
NOW i know this is lots and as said you probably think this is silly basic.... but as said i'm struggling to get my head round stuff.... especially paralel circuits and how to work out ampage, voltage, resistance etc.
any help you can give me would be greeeeeeay
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Topic: Mechanic School Blog (Read 95986 times)