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Post by cye on Apr 7, 2011 16:43:36 GMT -5
Check out the postings of outtasight on the navitron forum www.navitron.org.uk/forum/index.php/topic,8368.0.html all we need now is someone fluent in electronics (Norman, Conor,...?) to explain some of the trickier bits of this to us lesser mortals to enable us to safely cobble together this type of arrangement ourselves. |
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Post by cye on Apr 7, 2011 17:17:47 GMT -5
I think I understand outtasight's 'embedded shunt' ammeter bodge.
Perhaps someone wiser will confirm if I'm on the right track about how his bodge works and why it's good to use this type of device to read amperage. Here goes:
Heavy duty booster type cable is good for rigging up 12v and 24 PV systems because it has low resistivity, won't heat up no matter what. A side benefit of it never heating up is that the cable will always have a constant resistance per mm in all conditions.
The one electronics formula I haven't forgotten is V=IR.
What this means is that with the R (resistance/ohms) fixed by studying just a short fixed-length section of the cable, then V (voltage/volts) is always proportional to I (current/amps). The trick with the outtasight embedded shunt ammeter bodge is that he uses the cheapo digital multimeter (£7) to measure the voltage drop over a short length of cable, and, with the short length being a fixed/constant resistance, the current flowing through the cable at any time can be inferred by reading volts rather than amps.
Why not just use the ammeter function of the cheapo voltmeter? I think this is because the cheapo meter can't read high currents, and even if it did, one would have to break the circuit (cable) to fit the traditional ammeter in series. This in turn introduces 2 extra potential points of failure. More connections in any circuit is generally to be avoided because this increases the risk of a poor electrical connection (i.e., a high resistance connection) which will heat up and either waste power or torch the place.
The problems and expense of a traditional ammeter are therefore avoided by only reading voltage (in parallel) rather than amps (in series). We can therefore infer the amps from the voltage because we know the resistance.
The cheapo meter's cables are soldered onto drawing pins embedded in the cable and these are used to measure voltage drop rather than chopping the cable to fit an inline expensive ammeter.
Hope I have understood this correctly?
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