What would cause random voltage spikes to around 17 volts? on 1990 Chevrolet 1500 Pickup

I am getting about a 17v voltage spike during the first 10-15 minutes after start up. They will hold for a few minutes then drop, and return again. After the engine warms up, they seem to go away.

Any thoughts as to the cause?

3 answers 1 comment
take your alt in to a auto parts store to be checked if its good then it could be your voltage regulator
alternator. repair it before it damages your computer

Roy
Thanks! I was thinking this or voltage regulator...
1990 Chevy 1500 4.3 V6 Kept having to get a jump to start it so I replaced the battery and after a few days it started needing a jump again to start it so I took the positive off the battery while the truck was running to see if it was the alternator and the truck stayed running with the positive off the battery so I said it can't be the alternator and just yesterday I got a jump and right after the truck died after about 5 minutes of running and now it won't start back up I don't have a lot of money to replace this part or that part The truck sounds like it's dead when you try to start it and after 3 times of trying to start it It has no juice in the battery Can someone help me with this problem I'm a woman and know a little about motors and has to fix it myself just don't have money to replace parts that are not the problem