Introduction: USB Lithium Re-chargeable DT830 Multimeter With Polyfuse

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About: There's always a better way, just keep recycling those brainwaves!

■ What I like about this meter

This DT830LN digital multimeter (DMM) offers
▪ A compact size
▪ 10A current measuring range
▪ Backlit display
▪ Low cost

The DT830D model is identical and more commonly available, but does not have the backlit display.

■ What I don't like about this meter!

There are a couple of things that annoyed me about this meter.

Firstly, switching it off means losing your range and function settings.

Secondly, there is no auto power off, so forgetting to switch it off and reaching out for it days later means swapping the 9v battery.

These are fairly common drawbacks on most low-cost rotary manual range type DMMs.

Using the backlit display does help remind me to switch it off, but this is quite battery hungry in itself.








Step 1: Custom Mods

So lets get to work on making some low cost custom modifications to tackle these issues:

My requirements:

+ Add an on/off pushbutton toggle switch, so you don't lose your function and range settings when powering off.

+ Use an internal lithium ion rechargeable battery pack for longer battery life.

+ Make it USB rechargeable

+ Disable the hold function button by hot gluing it in the off state. I never use this and its annoying when on.

+ All components to be self contained in the meter.

+ Environment friendly with no landfill for dead batteries!

+ Replace wired fuse with self resetting polyfuse.




Step 2: Tools & Parts

Tools:
+ Soldering iron
+ Drill
+ Hot glue gun
+ Mini file

Parts (£2 or less)
+ Miniature Push toggle on off locking switch. (About 5p each)

+ Flat ithium ion battery pack. I used a spare old mobile phone battery (BL194) which was in good condition (free or £1.50). Any flat lithium phone battery which fits will do.

+ MT3608 2A Step up adjustable voltage supply board (20p)

+ micro USB lithium charger board with current limiting protector (30p)

+ PP3 9v battery connector (optional, not required if you solder direct). Or you can recycle one from an old battery.

+ 250v 0.2A Polyfuse (35p each)

Step 3: Circuit Design

The general circuit schematic is as above, and will work with any other 9v DMM.

Note that the on/off switch is between the lithium charger board and the voltage supply regulator. This avoids battery drain by the voltage regulator when its switched off.

I also stripped the lithium batteries internal protection board. This can be done by prising off the plastic connector strip and board, then soldering direct to internal lithium battery lugs.

This is optional, but i decided to do this as my external charger board already does this, and it minimizes on voltage drop. It also makes the design more maintainable should the internal protection board fail.

Step 4: Assembly

Drill, file, solder and hot glue :-)

Power switch fits nicely above display. I trimmed the switch peg to give it a lower profile.

USB board fits in top rear panel

Battery fits in middle of rear panel. I removed the internal battery protection board (see earlier design notrs) this also helped it fit nicely in the rear middle compartment.

Step up board sits in compartment below probe terminal sockets.

The backlit display is semi transparent letting the red/blue charging leds show in the front lcd display. The dt830d non-backlit model is non transparent, so I drilled a viewing hole next to the usb socket.

Remove wired mini fuse and solder polyfuse in its place.

Step 5: Finished Product

So far very happy with my mods.
Lithium battery has plenty of capacity.

This is hopefully the last time the rear cover needs opening for a long time.

Please note it is not advisable to use the meter whilst it is being charged via the usb port. Please be careful not to measure mains AC or high voltage while the DMM is connected to USB as you will be connecting the mains voltage to the USB and there's a possibility of damaging the USB device that you are using to charge the DMM.You should only charge the battery when the DMM is not being used,.

Have now upgraded all of my dt830s including the larger yellow dt830 base model.

Happy battery free metering!