I was thinking some more last night about how poor a fit the Herc black heating rods are to the Iris vv top and then it occurred to me that we can calculate what an ideal resistance would be for the Iris to drive based on a set of requirements. Here are the requirements I came up with:
- Provide the widest possible range of power to the Hercules given the Iris output voltage limits of 3.5 to 7.4 volts.
- Don't exceed 5 amps of current.
- Provide enough headroom for the Iris to maintain regulation for a "long" time with freshly charged batteries.
Any other resistance related requirements I'm forgetting?
If we look at max output we would want 5 amps at 7.4 volts which is 36.5 watts. This means that the heating rod resistance would be 1.5 ohms. At 1.5 ohms the power at 3.5 volts is about 8.2 watts. So with a 1.5 ohm heating rod you get a power range of 8.2 to 36.5 watts on the Iris.
Doesn't this sound ideal? The 37 watts allows me to vape my most stable waxes which I have needed on occasion. At 20 watts I get the power level of a black rod. At 12 watts, the power level of the old blue rod, I can experiment with vaping flowers in the Herc. As far as headroom, with a 30 watt setting (which I predict will become the most popular Iris/Herc power level) the 1.5 ohm rod needs just 6.7 volts, so with freshly charged batteries starting at 8.3 volts the battery voltage level would have to drop to 6.7 volts for the Iris to fall out of regulation. I consider this to be a lot of headroom and allows me to vape all day at a steady 30 watt output. You get all of this while safely staying within the 5 amp current limit.
Here is a table showing my work:
Notice the maasive current the 0.8 ohm black rod will try to draw if full voltage is accidentally applied.
And here is a summary table:
As Irises become more common people will be tempted to try it with all the different Herc heating rods so I think this information will become important. Also, I'm hoping to make the 1.5 ohm heating rod the standard for Iris use. It really is the best in this application. I'm glad I got plenty of spare 1.5 ohm rods for my SR-71!
Hedo
P.S. I can make any of my spreadsheets available to anyone who is interested in tinkering with them. Let me know.