White Exec wrote: ↑Thu Jan 13, 2022 5:11 pm
Test it by supplying (off the car) a 5W bulb or a 21W bulb, which should draw approx 0.42A and 1.75A respectively from a known 12v source. A 55W headlight buld should pull approx 4.58A, but that could be a stiff test for some DMM's, and should only be done for 10-15secs max, for the reason below...
DMM's easily get their higher current ranges 'cooked' by mild abuse, when the internal series resistance gets heated up without actually blowing the internal fuse. Also worth checking that internal fuse (and its holder), as, if oxidised, it will affect current readings. All should show up with the test above.
citroenxm wrote: ↑Thu Jan 13, 2022 5:38 pm
How can a bulb give me a current draw reading.....?
I e since put a new battery in the meter.. Still had 0.300 amp draw in 10amp range. But got that down to 0.113 amps on 10amp range.
I've had chance to read this so will paraphrase to hopefully explain.
What White_exec is saying is that a DMM isn't reading current at all, when used as an ammeter, it is actually a voltmeter measuring the voltage drop across an internal resistance of known value.
You can check the accuracy of your meter by connecting to a known external resistance being fed with known voltage and unrestricted current.
e.g. 12v battery, 5W bulb.
Power = IxV, which extrapolates to P/I = V and P/V = I.
Using I = P/V.
P = 5W
V = 12v.
5/12 = 416mA, or 0.42A
One can test the accuracy of their Dmm by checking the current flowing through a set of known wattage bulbs.
If the meter has been run close to it's maximum current allowance, or for an extended duration, either the internal shunt, or the switching may have overheated and changed resistance, so the meter might give incorrect readings, hence testing against known values (various bulbs of known wattage) can be used as a check of the meters accuracy (calibration).
If you don't have a working ammeter, a voltmeter and load of known resistance will give voltage drop values, which can be converted into Amps flowing through the circuit.
This is how measuring voltage drop across the fuses detects current passing through a circuit. The fuse has a small resistance, so any flow of electricity causes a voltage drop. Even a piece of wire has some resistance.
If there is no current flow, no voltage drop occurs.
This negates the need to pull fuses out, which is advantagous on cars that use CAN, as they take upto 30 minutes to shut off again once the module has been activated, which it will be by pulling out and replacing a fuse.
Your meter appears to have a 10A input and also a mA input for current readings less than 1A.
Typically the more sensitive selection will be more accurate for the very low readings. Do not test a current of more than 999mA through the sensitive input, or the meter will be damaged.
I've not tried this on a circuit containing components and current leakage, only on checking continuity of power supply, or Gnd, but it means that if one didn't have a Dmm to check for current leakage, a selection of bulbs could be used.
A circuit passing 0.4A, will illuminate a 5W lamp, but not a 21W lamp.
The risk is the lamp itself will provide resistance which may restrict current flow enough to stop illumination.
12v, 5W lamp has 28 ohm's resistance.
12v, 21W lamp has 6.9 ohm's
12v, 55W lamp has 2.6 ohm's
12v, 1W lamp has 144 Ohm's resistance and will draw 83mA of current, which is enough to drain the battery fully in 35 days, so no start after about 18 days.
iirc, your draw is currently about 100mA, so should be enough to illuminate a test lamp, or dashboard warning bulb.