[CentOS] Low random entropy

I am use to low random entropy on my arm boards, not an intel.

On my Lenovo x120e,

cat /proc/sys/kernel/random/entropy_avail

reports 3190 bits of entropy.

On my armv7 with Centos7 I would get 130 unless I installed rng-tools 
and then I get ~1300.  SSH into one and it drops back to 30! for a few 
minutes.  Sigh.

Anyway on my new Zotac nano ad12 with an AMD E-1800 duo core, I am 
seeing 180.

I installed rng-tools and no change.  Does anyone here know how to 
improve the random entropy?

thanks