Harbor Freight Meter Modification

Revised  11-21-07

On a recent visit to Harbor Freight I discovered that their small volt ohm meters were on sale for $1.99! 
Being freed from concerns of damaging an expensive meter I experimented a bit and made an interesting discovery that you might find useful.



Some time ago I took two of the Harbor Freight meters, which cost nearly $5.00 at that time, and put them on a board wired so that one would continually show voltage readings while the other showed current.

This worked well and it comes in handy when testing circuits and engines.

Here is the wiring diagram for the above setup. 

I like the above setup but wondered about modifying a single meter so that it could be easily and quickly switched between showing voltage and current.
This is normally something of a chore as voltage is measured by putting the meter in parallel with the load on the circuit as in the diagram below.

Measuring current requires that the circuit be broken and the meter inserted in series with the load.


I surmised that I would have to add a switch to make the change between measuring voltage and measuring amperage. 

After a bit of experimenting I made an interesting discovery.  If you wire the meter as in this diagram you can measure voltage by putting the selector in the DC volts range and current by moving it to the 10 Amps range.  No other switching is needed!

This works because you are always routing the power to the motor through the shunt that connects the command and 10 amp plug.  I have moved the selector through the full set of ranges and have noted no damage to the meter.

Give it a try and see what you find with your meter.  No guarantee that it won't cook your $500.00 Fluke but it sure works well with my $2.00 Harbor Freight!