Hi I've been using the Nautilus mini for about 1 week now & love it. I went and bought a five pack of the new bvc coils & for some reason they burn out after about 2 hours of use. I have also put them in the regular nautilus & they don't seenm to last longer than 3 hours in that one. I am using them on an MVP2 at 8.5 watts. Do you think I may have gotten a bad box?