The 521 Tab From Coilmaster – A Must Have For Vapers That Build Their Own Coils?

The Coilmaster 521 Tab promises to be the very best ohms reader available, and an extremely useful tool for building your own coils with.

It boasts an accurate ohms checker, an OLED display, voltage checker as well as the ability to measure voltage drop and it is powered by a single 18650 battery, that you can charge via the USB port.

An excellent feature is that you can actually fire your coils whilst on the deck, which means you can pinch and adjust them without having to remove your atomizer from the 521 tab and place on a mod!Coilmaster 521 Tab Reivew

Is the Coilmaster 521 the ultimate platform for building your own coils on? Let’s find out!


  • Large, stable platform for building
  • OLED Screen
  • Checks resistance from 0.01-9.99 ohms
  • Checks voltage from 0.3-9.99 volts
  • Measures voltage drop
  • Powered by one 18650 battery
  • USB charging port
  • Reverse battery polarity protection

Kit Contents

The Coilmaster 521 Tab comes in a pretty hefty box, inside there is:

  • 1x Coilmaster 521 Tab
  • 1x Voltage Meter
  • 1x USB charging lead
  • 1x Set of alligator clips
  • 1x instruction manual
  • 1x authenticity card

Coilmaster 521 Tab build quality

On first impressions, it almost looks like a glorified DJ turntable! But what you have here is a very well made ohms checker that does so much more than just read the resistance of your build, and we will go into more detail about the functions in the section below…Coilmaster 521 Tab Reivew

It’s manufactured from very durable and heat resistant ABS plastic, with a large fire button and a clear OLED screen that shows resistance or voltage depending on what you are using it for at the current time.

There is a stainless steel 510 with spring loaded brass connector pin at the top, and I’ve never had any sort of issue with anything I’ve screwed into it. Around this is a ring of LED lights and this will light up in red when in resistance reading mode, and blue when in firing mode.

It looks cool and is also a good visual reminder!

At either side of the 521 Tab you will find a USB port for charging, and the button which you choose to select either resistance reading mode or firing mode.

The battery cover at the base of the 521 tab is held in place with magnets and this area was the only downside for me with the overall build quality, as mine felt wobbly and never felt like it was secure, I don’t know whether that was just an issue with my unit however! Coilmaster 521 Tab Reivew

Other than that, I had no issues with the build quality, it feels very solid.

Using the Coilmaster 521 Tab

First things first you need an 18650 battery in order to power the 521 tab, and you want to ensure you have a battery capable of handling an amp draw of 20A minimum, a good bet is to purchase a Sony VTC4 or a Samsung 25r from a reputable vendor.

This needs to be inserted by removing the magnetic battery cover at the base and inserting it into the battery slot. There is reverse polarity protection so if you insert it the wrong way round, you are protected. Coilmaster 521 Tab Reivew

Battery life is great too, the 521 tab saw me through a pretty heavy week of rebuilding and the USB charging port on the side makes for quick and easy recharging.

As the 510 connector is spring loaded you shouldn’t have any issues with any atomizer connection, however don’t fire any atomizers with a flat or recessed 510 pin as this could cause a dangerous hard short!

Setting the 521 tab to resistance mode will display the resistance of your current build on screen- if this is jumping around then you know you need to adjust your build. Resistance is read accurately from 0.01-9.99 ohms.

By setting the 521 tab to firing mode you can actually fire your build whilst on the 521 tab, as long as the resistance is above 0.2ohm. I wouldn’t recommend doing this unless you are certain no short is present in your build as there is no short circuit protection built in here!Coilmaster 521 Tab Reivew

It’s not just a gimmick though, it actually comes in very handy for making adjustments to your build and tidying up your coils- I’d recommend a good set of ceramic tweezers in order to do this safely.

You have a separate voltage meter included which plugs into the two holes next to the 510 connection. This means that you can screw in a mechanical mod (with battery), fire it and get an accurate voltage drop reading, however this won’t work with hybrid mechanical mods as the mod will not make connection.Coilmaster 521 Tab Reivew

The leads with an alligator clip can be clipped on to either side of a coil to get a resistance reading, and they come in very handy for measuring atomizers with a hybrid connection or those rare units that don’t have a 510 connection, as you can clip these leads on and get an accurate resistance reading.Coilmaster 521 Tab Reivew

Performance is brilliant overall, apart from adding a few safety features such as short circuit protection to give newcomers a bit of added protection, I couldn’t ask for any more from the 521 tab.

What I Like

The option to fire your build and make adjustments without removing it from the mod is excellent, using a pair of ceramic tweezers (to avoid short circuits) whilst firing your coils makes for some very tidy builds. If you wish to test the build out, you can actually vape it whilst on the 521 tab!

It’s extremely accurate at reading resistance, one of the most accurate ohms readers available.

Measuring voltage drop is a huge plus point if you are a mech mod user, enabling you to identify any potential issues with voltage drop on your build.

USB charging is included which means you simply need to plug in the external USB charger and charge away, handy if you are building on the move!

What I Dislike

It doesn’t fire builds under 0.2ohm. If you are building super low, or using a Temp Control build, the Coilmaster 521 Tab won’t be able to fire it for you to make adjustments to the build. This is also probably a good thing, as anything 0.2ohm or under will put undue stress on most single 18650 batteries…

Another thing of note is that the battery cover under my unit seemed wobbly, and whenever I slotted it back into place it never felt like it was a secure fit. I don’t know if it was an issue with my unit or whether there is a wider issue

There aren’t any safety features built into the 521 tab that I am aware of to protect against short circuits. I wouldn’t recommend this for people new to rebuilding, as if your coil is shorting against the deck or your atomizer has a recessed 510 pin for example, you could find yourself in a lot of trouble if you fire the 521 tab.

Further reading: Beginners guide to RBA’s

Final Coil Master 521 Tab Review Verdict

It’s an incredible all in one kit that is absolutely perfect for coil rebuilding, and with the ability to fire and adjust your build, measure voltage drop, get accurate resistance readings and even have a test vape on your build, the 521 tab really has it all!

That being said, with the lack of safety features I wouldn’t recommend this to beginners, however for experienced coil builders it is absolutely perfect and a kit that offers the full package at a very reasonable price.


  • Can fire your builds whilst on the deck
  • Very accurate resistance reading
  • Measures voltage drop
  • USB charging
  • Clear OLED screen
  • Easy to use
  • Build quality in the majority is very good
  • LED lights look cool!
  • Good battery lifespan from an 18650 battery


  • Doesn’t fire under 0.2ohm
  • The battery cover at the base of the unit is wobbly
  • There are no safety features built in that I am aware of to protect against short circuiting, so this may not be ideal for beginner coil builders
  • If your atomizer has a recessed 510 connection, firing it on the 521 tab could cause a dangerous hard short
  • Hybrid mechanical mods will not work with the voltage meter
Been vaping full time for three and a half years, started on cigalikes for a fair while then curiosity got the better of me and I moved onto an ego/ce5 set up after, a month or two later I was seeing people walking around with these interesting shiny tubes and I thought 'I gotta get one of those'. Before I knew it a trip down to my local B&M got me my first VW mod, an Innokin SVD, paired with an iClear 30, and I was hooked. Soon after that I was jumping to VW mods both box and tube shaped, before I then made the jump to rebuilding and thus sub ohming, with my first RDA and mech mod. These days I'm still preferring mechanical mods, but using VW mods with both RDA's and tanks alike whilst on the move, most importantly I am still loving vaping!


  1. Looks as if this is what every coil builder needs, a great time saver and accurate ohm reader as well. Brilliant piece of kit again from coilmaster

  2. i have been wanting this gadget for a long time. i was thinking about getting the friday morning burning tab, but i cant find it sold anywhere in my country.

  3. I have wanted one of these for a very long time. I’m on a tight budget since my back surgeries &wrist surgery. If I won this I’d be the happiest woman alive!!


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