Introduction #

Mini-Tamiya and Deans (also called T-connect or T-Plug) are the two most common battery plugs used in airsoft. While Deans is superior, many stock airsoft replicas come with a mini-Tamiya battery plug by default. There is an industry move towards Deans so in few years the inferior solution may disappear, for now, a lot of people are still using it and many are recommending the switch mostly to gain a better rate of fire. It is hard, however, to find the exact data about the advantages from the electrical point of view. So how much can we actually gain? We can get some datasheets for Deans plugs, like this AMASS clone, but I couldn’t find anything similar for mini-Tamiya so the only option is to do the measurements.

I decided to do a very practical test - I have measured the internal resistance of two batteries that I bought with mini-Tamiya plugs before and after rewiring them to Deans to check how that resistance changed and how that influences the actual voltage that the motor sees (and thus its speed).

In this experiment, I’m only focusing on the electrical advantages of Deans plugs (more precisely on the difference of resistance which translates to smaller voltage drop). There are other benefits of Deans, including:

• better reliability and longevity- they are less likely to break or wear out
• smaller size
• ability to handle larger currents without melting
• standardized polarity

The test #

For the test, I took two of my batteries that were barely used and quite new. The internal resistance was tested by my DIY measuring method with 1 mOhm load (giving around 8-12A on fully charged batteries) just before rewiring and just after rewiring the plugs, on fully charged batteries. The plugs I have used are made by AMASS.

Apart from measuring the IR, I have also made some calculations - voltage drop caused by the 30A current (the value we could expect when shooting on AUTO on a decently powered replica), the percentage of nominal voltage of the battery that drop is (to make comparisons easier) and I’ve measured rate of fire on one of my replicas.

Due to its construction, the mini-Tamiya is more prone to aging when used than Deans. I would expect that changing the plug on a battery that was used for some time already might yield an even higher difference in resistance (and thus, performance).

Turnigy Nano-tech 11.1V 1300mAh 25C #

Measurements #

The internal resistance of this battery is surprisingly high. A month ago it was much smaller but now it went very high. I’m not sure why.

Difference #

• Internal resistance drop: 9 mOhm
• The motor voltage at the 30A load increased from 7.92V to 8.19V, which is 3.4% increase
• The RoF increased from 15.2 to 16, which is 0.8 difference or 5.2%

Electroriver 7.4V 1100mAh 20C #

Measurements #

Difference #

• Internal resistance drop: 10 mOhm
• The motor voltage at the 30A load increased from 5.67V to 5.98V, which is 5.47% increase
• The RoF increased from 10.3 to 11.1 which is 0.8 difference or 7.7%

Conclusions #

We can expect that by changing the plugs we can achieve around 10mOhm drop in the resistance due to the plugs. A somewhat decent Lipo battery should have 30-50mOhm (depending on the number of cells and its current capabilities) of resistance on its own so we are talking about 16-25% drop. Note that the Lipo batteries with smaller internal resistance exist but they are unlikely to be sold with a mini-Tamiya plug. The difference in the price of the 20 mOhm battery compared to the 30 mOhm battery is an order of magnitude larger than the cost of the replacement plugs so its cheaper to change the plugs than to buy a better battery if you want to squish all the performance from your gun.

After changing the plugs, the voltage seen by the motor is 3.5 - 5.5% larger, and the motor speed is linearly related to the voltage so it should increase by the same rate. On top of that, due to smaller resistance and higher voltage, the current should also increase giving the motor extra torque which could also increase the RoF. In practice, when checking with a slow firing replica, there was 5.5-7.5 increase in RoF which in my tests was 0.8RPS in both cases, On a faster replica, with say 20RPS, the 7% could translate to up to 1.4 RPS.

A typical NiMH battery has 150-200mOhm of internal resistance so for them, the additional 10mOhm is not noticeable. For them, mini-Tamiya might have been historically a good choice and this is probably why so many replicas still use them (they provide NiMH battery with the gun).

If your replica already has Deans plug and you are using a mini-Tamiya battery with an adapter, that would add additional resistance so the gain you may expect bigger improvement from changing the plug of your battery to Deans.