I was tired of constantly replacing the batteries in my multimeter, so I modified it to be rechargeable. Now, the battery lasts for about 2-3 months before needing to be charged again. Many newer Multimeters have an always-on backlight, which can drain the batteries quickly. However, with the modification I made, the battery lasts much longer.
In this article we will read how we can covert ordinary multimeter to a reachable also it’s quite simple project to do. Let’s see how can do this.
- First you need to take apart the multimeter basically you have to remove the back cover. For most multimeters after you remove the back panel you will have access to the battery holder and PCB of the multimeter.
2. After that you need to make room for installing the rechargeable Li-ion battery, this can be done by removing the existing battery holder. For this multimeter after removing the battery holder, there is quite a bit of space left for new battery. Do this according to your multimeter, as different multimeters will have different designs.
3. Now, the next step is to find a suitable Li-ion battery that fits in the multimeter and you can also close the back cover without any issues. For this I used an old mobile phone Li-ion battery as it was small and thin, also is has high capacity of 1450 mAh. You can also use Li-Po battery from an old MP3 player.
Note: Please do not connect the battery directly to the multimeter, we have to do some calculation before we can connect it safely to the multimeter.
As we can see this multimeter uses 2x AAA cells and they are connect in series (1.5V each), so they have 1.5v+ 1.5v=3v, so the operating voltage for this multimeter is 3v.
But, if you notice the Li-ion battery can go up to 4.2 volts after they are full charged . So if you connect the cell directly to the multimeter it can be damaged.
For the solution you can use a a buck converter that reduces the voltage, but there is a big issue that if you connect it with battery it will always be on and will drain the battery. So what we can do now?
Well, I came up with a really good idea. If you use a diode in series, we can decrease the voltage by 0.7v as most of the general purpose diodes have 0.7v voltage drop (make sure to use 0.7v drop diode).
4.2v – 0.7v =3.5v
Now the voltage is still little bit high, but this is safe as I measured the voltage on two series AAA cells and the voltage was 3.2v not quite 3v so 3.5 v will not be big issue. Well, I also tried two diodes in series but the voltage was very low. Finally I decided to go with the single diode. You can experiment with 2 diodes first.
After hooking up the diode the multimeter worked fine without any problem. For finishing the circuity I added the Li-ion battery charging module to recharge the battery, it also has micro USB connector so I can connect any phone charger and recharge the battery.
Now, everything is done we just need to close the back lid to finish the project.
For recharging I will have to unscrew the battery cap and the then I would be able to connect the charging cable.
Now, the multimer is ready to rock . The best part is it lasts for 2 to 3 months. So, basically I don’t have to worry about recharging this quite often, this is why I didn’t add any charging connector on the body of the multimeter.
The cool thing is that, I can re connect the old battery holder in case I need to ; also there is no modification done on the body of the multimeter so it looks good and same as before.
For me this was a fantastic project and very useful one too. I hope you liked the project and you should give it a try. 🙂
