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Originally Posted by SirAlec Thanks for the insight. Thats what i learned in my high school physics, and that was long time ago.
any more insight or books, pdf on this new breed of Ammeter will be helpful.
Thanks again.
BTW best judge of that will be the time when you actually know you are in a dud car and its not cranking at all.
But temperature meter that i talked about is a dead serious issue, It actually will save the engine from cessation and hence will save money and time. |
Actually I learnt about ammeters and voltmeters from my father's high school books - mine didn't really have any details and my sister's (she is younger) almost skipped the two !
The books did talk about ammeter being connected in series and voltmeter in parallel, but then there were sections about how to measure voltage with ammeter and current with voltmeter (also sections on how to measure 50V with a 5V capable voltmeter and how to measure 100A with a 1A capable ammeter). The rest is just breaking apart the things and looking for yourself
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Digital voltmeters are actually analog to digital converters - they compare the voltage directly with a reference and have very very high impedance. A digital ammeters is a precision resistors across which a voltmeter is connected.
Coming to temp. sensor - very good idea and as I wrote earlier you may want to put one on the battery as well. Very hot batteries and very cold batteries do not work very well no matter what their state of charge is. Though of course if engine is running cold/hot (and you know about that) you can change your driving style. With battery there isn't a lot you can do.
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Originally Posted by Sutripta Great that some discussion on!
Think it is best if we go through some (very) basics. Then we can work out what expected behaviour should be, and therefore spot anomalies. Then we can correlate the anomalies with problems. |
This is what preventive maintenance is all about - keep looking for any unexpected or abrupt changes in behaviour.
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Originally Posted by Sutripta Also think it is best if explanation (initially at least) goes along lines of high school and college physics. This will also be of advantage to the large number of IT/ ITES personnel in this forum. |
Dada, my explanations were actually from Physics textbooks of 11th grade from the early 1960s (written in Hindi).
But I agree we must keep it as simple as possible for as long as possible.
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Originally Posted by Sutripta To start of with, the electrical system consists of a large number of loads, and two sources of power (battery and alternator. We shall discuss dynamos only if there is sufficient interest at the end of the thread). But instead of thinking that the loads are connected to the battery (through switches/ relays etc), and that the battery is charged by the alternator, I think it is conceptually clearer if we think that the loads are connected to a 'power bus', and that the power bus has two sources of power, the battery and the alternator, which are connected to it in parallel. The nominal voltage of this power bus is 14.4 volts, not 12. All loads, except self starter (and I suppose glow plugs) are designed to operate at 14.4 volts. |
Bus, relays, glow plugs ! How is this at a high school level
?
I don't know specifics of car eletricals so here's a question - is the battery directly connected to the "power bus" or is there a switch/relay mechanism in between?
also is there only one "power bus" or are there two or even more (perhaps different vehicles have it done differently)? From what I know car chassis is used as ground for all return currents (by the way, how does it work when chassis goes carbon/fibreglass)
If I were designing things I would define different "domains" - at least one for mission critical stuf - attached to the battery and another for non critical stuff (like ICE) directly connected to alternator with optional switch to battery, and perhaps more.
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Originally Posted by Sutripta The self starter, though logically connected to this power bus, is physically handled separately because of its very high current consumption.
Immediate question should be how can one connect two sources in parallel, which is what we are doing when we are connecting them to the same bus. More in the next post.
Regards
Sutripta |
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Originally Posted by Sutripta I've seen more AVR failures than I can care to remember. And most were that the output voltage went uncontrolled!
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It will be interesting if we can work out why cars evolved differently.
Regards
Sutripta |
First paragraph:
chip designers usually don't have a clue how unreliable their products are. I remember talking to a technician with British MoD once - their nuclear missile submarines used vaccum tube electronics from the 60s well into late 90s - because it was "boot proof" i.e. you kick it like hell with army boots and it will still work.
Second paragraph:
Cars did NOT eveolve differently. This has nothing to do with cars. But let me ask you a different question (if you want to stick to the "ammeter is series" theology) - if you want to measure the o/p current of a local substation's transformer, do you seriously believe you will put the "ammeter" is series?
As people wrote on other threads - at start the electricals take currents as high as 300A - the small thin wire of the coil in the ammeter will be glowing red in no time if anything like that passed through it. In fact it will be glowing red if the nominal 50A passed through it.