expect with cron not as manually - ssh

Question

backup.sh has :
#!/bin/bash
expect backup.exp
tr -d '\15\32' < backup.templog > backup.log
backup.exp has next content:
#!/usr/bin/expect -f
puts "----------------- [exec date +%Y.%m.%d\ %H:%M:%S] ------ exp start -----\n"
spawn ssh root#someIP2
expect "# "
send "su - postgres\r"
expect "\$ "
send "ls -lh db.dump.gz\r"
send exit\r
send exit\r
interact
when I run manually like next:
bash backup.sh >> backup.templog 2>&1
I get next, which I like:
spawn ssh root#someIP
Linux db01 3.2.0-4-amd64 #1 SMP Debian 3.2.68-1+deb7u1 x86_64
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Wed Sep 2 11:06:02 2015 from someIP2
root#db01:~# su - postgres
postgres#db01:~$ ls -lh /var/lib/postgresql/db.dump.gz
-rw-r--r-- 1 postgres postgres 218M Sep 2 10:39 /var/lib/postgresql/db.dump.gz
postgres#db01:~$ exit
logout
root#db01:~# exit
logout
Connection to someIP2 closed.
but with cron (has a line):
* * * * * bash backup.sh >> backup.templog 2>&1
I get only next:
spawn ssh root#someIP2
Linux db01 3.2.0-4-amd64 #1 SMP Debian 3.2.68-1+deb7u1 x86_64
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Wed Sep 2 11:04:13 2015 from someIP1
root#db01:~# su - postgres
postgres#db01:~$
Can I get the same with cron and manually?