It has to be a minimum of 4V because the boost chips used in these things have to have what is called "headroom". Usually it is 1.5v, so your 3.7v battery becomes 5.2v output. Most of these mods then drop this back with a diode in series with the atomiser, hence the 4v.
The only way you can get a wide voltage spread is to use two 3.7v batteries in series, for 7.4v and then use a PWM buck chip to cut back the voltage. Unfortunately, this approach only works in a box mod. Can you imagine the length of a tube that holds 2 18650s in series?
You can make your own VV box mod on these principles for around $50, if you don't want to shell out for a Provari, Darwin or Eclipse.
PS: Sorry, just realised that the Eclipse is a box type device, not a tube.
The only way you can get a wide voltage spread is to use two 3.7v batteries in series, for 7.4v and then use a PWM buck chip to cut back the voltage. Unfortunately, this approach only works in a box mod. Can you imagine the length of a tube that holds 2 18650s in series?
You can make your own VV box mod on these principles for around $50, if you don't want to shell out for a Provari, Darwin or Eclipse.
PS: Sorry, just realised that the Eclipse is a box type device, not a tube.
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