A meca mod (box or tube) is a simplistic device, without any electronics or regulation, delivering all the power of the battery to the directly installed assembly. The coil value is therefore fundamental. Indeed, it will determine the current drawn from the battery. It is therefore essential to know how to calculate this value and the real performance of the batteries in order to stay within the limits and not play with your safety.

Ohm's law 

A powered electrical circuit is characterised by four values:

- The voltage (volts) 

- Current (amps) 

- The coil (ohms) 

- Power (watts) 

These four values are all related, and can therefore be calculated in relation to each other. The diagram below summarises all the possible calculations with these four values, and among them, the ones you will use most often:

I = V / R (current = voltage / resistance)

or its counterpart :

R = V / I (resistance = voltage / current)

Batteries and limits 

The maximum voltage of a battery is 4.2V. This voltage will decrease with use, but this value of 4.2V will be used for all calculations to maintain a safety margin. For use on mechs, the constant discharge value of the battery (CDR or CDC) will be the only value to be taken into account, as it determines the minimum coil of the assembly. The maximum discharge (MDR or CDM) has no legitimacy and should never be used as a reference.

Never rely on the values indicated on the wrap (almost always the maximum discharge), but only on the real values communicated by Mooch after extensive testing of the batteries. As a reminder, the most common batteries, with their real CDC and the limit coils (formula R = 4.2V / CDC).

- Sony/Murata VTC6: 15A, R ≥ 0.28Ω

- Sony/Murata VTC5, LG HG2, Samsung 25R: 20A, R ≥ 0.21Ω

- Sony/Murata VTC5A & VTC5D, Molicel P26A, HOhmTech Work 2: 25A, R ≥ 0.17Ω

- Samsung 20S: 30A, R ≥ 0.14Ω

- NCR2070C, HΩ Sherlock 2: 30A, R ≥ 0.14Ω

- Samsung 40T: 25A, R ≥ 0.17Ω

- Molicel P42A, HOhmTech Run XL: 30A, R ≥ 0.14Ω

- Samsung 30T, HOhmTech Run: 35A, R ≥ 0.12Ω

Parallel and Serial 

In the case of dual battery mods, these can be arranged in parallel (box) or in series (tube stacked). For your calculations, two rules to keep in mind:

- parallel : the voltage remains the same but the current is added

- series : the voltage is added but the current remains the same.

In other words, with a stacked tube, the calculations will be done with a voltage of 8.4V, which implies a double coils value to stay within a reasonable limit (around 0.5Ω in general). Using Ohm's law, another formula will allow to calculate the power delivered according to the circuit: P = V² / R. And thus, with a coil of 0.5Ω in stacked :

P = 8.4² / 0.5 = 141.12W 

That seems to be more than enough, doesn't it?  

Voltage drop 

Voltage drop is a loss of voltage due to the coil of the mod itself. Some argue that it is possible to exceed the theoretical limit calculated, never having 4.2V real with a battery. However, Mooch's tests on various mech mods show that this loss is on average less than 100 mV; in other words, this loss seems totally negligible.

Mechatronic Mods 

Some tubes like Armor Prime, Fush or SoulKeeper are wrongly called "semimecha". A real aberration, since a device can only be mecha or electro. No more, no less. We prefer the term "mechatronics" for these tubes, operating as a mecha (without regulation) and with just electronics for minimal protection (temperature, inversion, short-circuit, overload, etc). In fact, Ohm's law applies, as the electronics do not limit the current drawn from the batteries.