multimeter doubt, lost the test leads - can use simple wire?

[aj_silverthunder]

multimeter doubt!

guys i have a multimeter but i have lost the test leads...
but i want to measure volts,ohms...etc.i used simple wire and somehow plugged it to the probes of the multimeter!
my problem is that --i used to measure the DC volts from a LM7809 ,but i got the result as 7.5 V
,even with the 7812,i got 9V!
is it the problem with the test leads!
it shows high precise with measuring the ohms...
what is the problem here!

 

[hameeds01]

Re: multimeter doubt!

measure it with another meter if it shows some different readings then the probes r faulty & replace them

 

[pranam77]

multimeter doubt!

If you are refering to a substandard multimeter which looks like the one in the picture, you bought for 300/- Rupees or 6$, it is worth for what you paid. You'll get better quality and accuracy but for a price...Cheers

 

[bwana1]

Re: multimeter doubt!

usually the measuring chain differs between voltage, current and resistance measures, in that to accomplish a resistance measure a current source is needed.
So the input circuits for this kind of measure aren't the same that when measuring voltages. This implies that input attenuators used for voltage aren't used in a resistance measure. So, if your tester was prone to input overload in a former voltage measure it's very likely that the attenuator's resistors that were inserted have been damaged and no more give the expected attenuation ratio, while the intact resistance chain continues to give true results. Another possibility is that your tester has some way to calibrate it, and that a re-calibration is needed.

 

[Audioguru]

multimeter doubt!

I have an excellent quality (fairly expensive) Fluke multimeter and a cheap Chinese one. They both read voltages about the same.

Maybe you dropped your cheap meter and its cheap trimpot used for calibration has moved.
Or maybe its battery is almost dead.
Or maybe the input voltages to your voltage regulator ICs are too low (their input voltage must be at least 2V higher than the output voltage).

 

[aj_silverthunder]

multimeter doubt!

guys but i measured the output voltage from a nokia charger (5.7V/800mA) and the meter read 5.8V...
this shows it is working well,but when i measure the DC volts from a LM7809 , i got the result as 7.5 V
,even with the 7812,i got 9V!

 

[Audioguru]

multimeter doubt!

Post the schematics of the LM7809 and LM7812 power supplies so we can show you what causes their voltage to be too low.
If their input voltage is too low then their output voltage will also be too low.

Maybe your meter is wrong. The output of the 5.7V charger will be 5.7V only when it has its full rated 800mA load current. Its voltage could be 7.3V or more without a load but your meter wrongly shows 5.8V.

 

[aj_silverthunder]

multimeter doubt!

i think the problem is because i didnt use the test leads,instead i use two wires..
and another thing is that it gives very accurate readings of resistors..when i tested a 6.8K resistor i got readings as 6.8K !

 

[Audioguru]

multimeter doubt!

A different part of the circuit in a multimeter measure resistance. Using proper leads or wires won't make a difference to voltages.

 

[aj_silverthunder]

multimeter doubt!

guys at last i repaired my multimeter!
i kept the probe to a nokia charger(5.7V)i opened the multimeter and and changed the pot inside it till i get the readings as 5.7..and i got it!
and to further test it i connected it a SMPS 12V...
and i got very very precise and accurate readings as 12V!
now my multimeter is perfect and fine
...
but the other thing is that i said u before that i got 20V from a 12DC....
the real thing is that i have a 12V AC/1amp converter....
i used a bridge rectifier of 1n4007 and converted the AV to DC...
but when i measured the output i got 20V!
the multimeter was perfect..
and i came to know that the converter is the problem!
can u tell me what could be the problem!

Added after 4 minutes:


this is my multimeter!

 

[Audioguru]

The peak of 12VAC is 17V. The rectifier drops 0.6V or 0.7V then the resulting 16.3V charges the filter capacitor and the output is 16.3VDC.

 

[aj_silverthunder]

so how do i get a perfect 12V DC from a 12AC(1amp) power source!

 

[Audioguru]

A power source might not be regulated so its output voltage could be very high without a load.

Meters are calibrated by adjusting them to read the same as an accurate standard one.