Ugh - I'm not doing this again, at least with grapes. First you have to wash and pluck all the grapes, making sure you remove stems, then you have to poke a hole in each and every grape to let the water escape. Then you have to run the dehydrator. And run it and run it. I'm at 20 hours and still going. Youtube is telling me it might be 36 hours. Plus it's making the AC turn on from, as Mike mentioned, the generated heat. I was going to do it in the garage, but was afraid of attracting mice.
With the time and electricity, I could probably buy 100lbs of raisins for what it will cost me to generate a couple of pounds.
I prefer my dad's method. He just stuck them all in the sun and picked the raisins when they were done. Sadly, as I mentioned, it's not hot enough here by the time the grapes ripen. If it were a month ago, I could have done it. I'll have to look at grape jam or something for next year.
On the other hand, I first tested the dehydrator with bananas. Five minutes to cut the bananas, set the timer for ten hours in the evening, wake up the next morning to tasty dehydrated banana chips. I'll definitely still use the dehydrator, just not for grapes. I might play with beef jerky in a couple of months when the excess heat generated will be beneficial.