Using equity in property

[Wayde C Hall]

Hello everyone!  As someone new to real estate investing, I was hoping someone would be able to answer a question about a home equity line of credit.  

My question is if you have a house worth 150k and was purchased for 100k using a mortgaged and you make continuous payments for several years.  Assuming in this time you pay 20k from your existing 100k mortgage and no increase in the originals property value, would you be able to include that money paid over those few years into the equity of the home in comparison to the mortgage to get a larger line of credit (a total of 70k)?  

I understand that a line of credit takes the total value of the home from the purchase price of the home so I wasn't sure this would work since you'd be going against the mortgage instead of the value of the house itself.  Is something like that even possible?  

Thanks for any help!