May the ceiling survive!
FYI - I bought a $10 50A current shunt - place it in series with the circuit, place a DMM across it and each 1mV is equivalent to 1A.
I've used it to test starter motor currents (140A & 240A) - the 50A rating is a long-term rating but it handles higher currents for short times - it's a thermal thing so as long as the thing doesn't melt (or get annealed etc).
One issue is that the shunt's "calibration" is via hacksaw-like cuts into its thick conductor. It will be these thinner
cut sections that will fuse (melt) but the surrounding conductor conducts heat away quickly. THe point is, a VERY large current may fuse it very quickly, but for $10... (100A for $20 was IMO too expensive - this was an interim "ammeter" until I got a 400-600A clamp-on AC/DC true-RMS ammeter or DMM.)
Though I intend to mount a few Hall-effect current sensors (up to 600A) in my vehicle, that's for experimentation etc. IMO such measures are useless for most.
What people want to know is "
is the charging system keeping up?" - or maybe "
how discharged is/are my battery/ies?", and a Voltmeter is best for that (an ammeter might indicate an underpowered alternator, and maybe a battery fault, but that's about it. (It doesn't even indicate the starter-motor current.)).
Ammeters are only useful to get an indication of a load (as I did for starter motors). Though once upon a time ammeters were fitted to many cars, they are useless in practice... [ it only tells the battery charge or discharge current, not if overcharging, undercharging, how long the battery will last or when you have reached the recommended 20% discharge limit (for crankers; 50% for deep-cycle), or if your battery has a collapsed cell or has reached its end-of-life. ]
... and until remote shunt versions appeared, were generally a hazard and a big voltage drop. [ The un-fused alternator-battery
ammeter cable was routed to the ammeter in the dash, and then back again (ie, alternator to ammeter to battery instead of a short alternator to battery cable) only to go back to the cabin & IGN switch & dash etc via fuses as per normal distribution. (The ammeter is fitted between the battery and loads-and-alternator. Hence you could not fit loads to the battery (the ammeter would show that as a -ve load current - ie, as if charging the battery by its
load current.)
Anyhow, even though shunts were later used {a dash-mounted voltmeter across the battery's GND cable or an inserted shunt resistor [eg, in the GND cable OR from the battery's +12V terminal - specifically between battery +12V and the alternator +12V output (often labelled B or B+) indicated "Amps" (eg, a 1V drop might mean 100A (10mV per Amp))], they lost favor due to their limitations. Apart from all the stuff a voltmeter could show, a voltmeter is cheaper anyway - an ammeter is a voltmeter PLUS a
shunt resistor.
Summary:
Most should survive with a high-current shunt. They can then use their true-RMS or any other DMM else voltmeter to measure the current.
Why measure currents long-term or permanently? (Data logging or "smart" diagnostic purposes etc excepted.)
If using an ammeter for some battery or charging-system intelligence, forget it. Forget how many Amps your battery is discharging at (assuming it's noticed, the old analog-meter scale is far from accurate!), wouldn't you rather know what State Of Charge your battery has?
A voltmeter also indicates under and over charging [above ~14.5V; below (say) 13V (idling and low-RPM excepted)], and the condition of the battery - though some knowledge is required (eg, 13.8-14.4V; 12.7-~11.7V; cranking and loaded voltages).