William_H
Well-known member
A post by Jordanbasset on water cooled fridges mentioned that he measured voltage at the compressor as 12v however the terminal would not carry the current for the compressor.
It struck me that a reminder about digital voltmeters (DVM) might be in order.
Almost everyone has a DVM and uses them to check for 12v supply.
The DVM very accurately indicates the voltage that is present. However this does not always indicate a good 12v supply. The DVM draws a little current to measure. However this is incredibly tiny current like about 1/10 of a microamp. This kind of current can easily creep through a mass of corrosion or dirty contact.
However as soon as you seek to use the 12v supply so measured at some amps you get nothing through. You have been misled by the DVM. If however you measure the voltage while the device be it fridge or lamp is connected (and drawing current) you will get a more accurate picture of the voltage through the switch etc. ie none if it is faulty.
One way to overcome this problem is to connect a lamp of a few watts in parallel with the DVM. The current drawn by the lamp will be commensurate with the current the circuit is expected to carry so will give a more realistic assessment of the supply capability.
Or just be aware that voltage measured does not always mean a good supply. olewill
It struck me that a reminder about digital voltmeters (DVM) might be in order.
Almost everyone has a DVM and uses them to check for 12v supply.
The DVM very accurately indicates the voltage that is present. However this does not always indicate a good 12v supply. The DVM draws a little current to measure. However this is incredibly tiny current like about 1/10 of a microamp. This kind of current can easily creep through a mass of corrosion or dirty contact.
However as soon as you seek to use the 12v supply so measured at some amps you get nothing through. You have been misled by the DVM. If however you measure the voltage while the device be it fridge or lamp is connected (and drawing current) you will get a more accurate picture of the voltage through the switch etc. ie none if it is faulty.
One way to overcome this problem is to connect a lamp of a few watts in parallel with the DVM. The current drawn by the lamp will be commensurate with the current the circuit is expected to carry so will give a more realistic assessment of the supply capability.
Or just be aware that voltage measured does not always mean a good supply. olewill