I'm a little rusty on making 110/120V systems work for gear like the S9's or Avalon 841's. They both have the ability or firmware to be underclocked to work but it's a stress on the system. Here is a thread from a while back that goes over the considerations, and has links to how people have made it work. https://bitcointalk.org/index.php?topic=2799754.0
Personally though I suggest you put in 220/240 V circuits for your miners. It's not difficult and would be offset by the cost of an additional PSU. Considering you said your power cost is low and not based on consumption, you can get a more powerful machine that is less efficient - which will help your earnings.
I linked another thread to review as I'm not sure where you are planning to place this machine but there are plenty of factors to consider before investing in gear. Good luck.
Topics for you to review:
First time/Small miner reference for getting started.
Current List of Competitive Hardware - July 2019
https://bitcointalk.org/index.php?topic=2799754.0
Thank you - I will check out that thread on the older ones and making them work on 120V! [Edit - funny, that is one of the first ones I searched for and read yesterday. Personally though I suggest you put in 220/240 V circuits for your miners. It's not difficult and would be offset by the cost of an additional PSU. Considering you said your power cost is low and not based on consumption, you can get a more powerful machine that is less efficient - which will help your earnings.
I linked another thread to review as I'm not sure where you are planning to place this machine but there are plenty of factors to consider before investing in gear. Good luck.
Topics for you to review:
First time/Small miner reference for getting started.
Current List of Competitive Hardware - July 2019
https://bitcointalk.org/index.php?topic=2799754.0
] I would love to change to 220V but, I cannot. Building wiring is fixed and it is not my role to tell them what they can or cannot change. Basically the space is an unused storage garage/shed. I have had to let my GPU rigs run warm this year, last year I shut down half of them to keep stable temps under 80 deg F.I am thinking it is best to just wait until I can order from Bitmain - I didn't realize they are still making S9 for example, and better than ever (16 TH on 1280 watts? that is even better, almost fits on a 15 AMP circuit as-is!)... and $350, same price as the used ones from Alibaba!
The only things GPUs having going for them is they didn't lose as much value as ASICs from two years ago would have - BUT, there is MUCH more dollar value tied up in them. So to me, even if new S9s only earn half as much in 6-9 months from now as they do today, they will still have covered themselves (something it will take another two years+ for my GPUs to do), and any extra funds I get back from selling my GPUs, I can just invest directly in bitcoin.