I've got a few old Antminer S7's that I made some water cooling blocks for and I wanted to test overclocking and changing the voltage. I don't want to do anything stupid so I wanted to ask you guys about what the best practices are for tuning frequency and voltage. I know the S7's aren't profitable and what not, but this is more for proof of concept for other ASICs. Are there any pitfalls or common mistakes people make? Can I just choose any frequency in increments and then observe chip temperatures? Any advice?

It's cheap but the power efficiency is everything long term and better for density. Electrical infrastructure is a bottleneck.  My rx 470s and 1070s outperform this substantially. Plus this is terrible for home mining if it sounds anything like my S9s. A GPU is made to be quiet. It is also nice that if I ever want to resell my cards I can get a little money. I can see how this can seem like a good idea but my Bitmain stuff needs constant attention. My GPU stuff I sometimes forget about because of the stability and ability to stay cleaner. I haven't bought GPU in over a year but I remember seeing mining specific cards in bulk for 200 each. Rx 470s. Prices are relatively close.

With a 150 KVA transformer you can technically squeeze 416 amps out of it on each line. That is called your full load amps. But as you get closer to 100% capacity the thing is going to get super hot and you start to lose a bit of efficiency, depending on the transformer.

Now, if you are in USA you will wire your receptacles line-to-line, 2 hot wires of 120v. So the formula is:

Amps = Watts / (Sqrt(3) * Power factor * Volts)

So if your first plug uses line A and line B then each line will be loaded with 7.44 amps. You get this by 1455w/(110v * 94%) for each line. If you add a second machine on to line A and line C, then line A now has 12.9 amps and lines B and C have 7.4 amps. Your load total is the number of amps that is the largest of the three.

Math answer DO NOT DO THIS: If you perfectly balanced your phases and loaded your transformer to 100% you could technically have about 96 machines but your transformer is going to be super hot and angry. I definitely would not recommend to EVER load to 100%.

For me, 58-60 machines would be a sweet spot for a 150 KVA transformer. 50%-60% load is efficient and a safe area to be in. Rule of thumb, 80% should be your max.

So each 2 pole breaker is 2 machines.

As for PDU's I can't recommend anything since it really depends what you want the PDU to do. You will have a lot of empty plugs since PDU's usually don't have 1400w+ machines loaded onto it in a data center. You can run directly to outlets if you want cost-effective. Make sure to use the correct rated outlet for your voltage.

I feel your pain man. The solution I came up with for surge protection is to use a whole house surge protector. There are different models depending on if you are using 3 phase or single phase. Here is an example:

https://www.homedepot.com/b/Electrical-Power-Distribution-Whole-House-Surge-Protectors/N-5yc1vZbm05

Another option is to use tripplite Euro-50. It works with 50 and 60 Hz, but it only works for like 10 amps or something so you can probably get away with 2 miners for each unit:

https://www.tripplite.com/isobar-4-outlet-200-240v-surge-protector-2m-cord-680-joules~EURO4

As for amps, just use a clamp ammeter on the line. It is pretty consistent if you can keep your temps regulated and your miners clean.

https://www.kleintools.com/catalog/clamp-meters/digital-clamp-meter-acdc-auto-ranging

Thanks man. Yeah, I tried flashing the firmware and that didn't work so clearly the board broke. I just wanted to make sure that I can prevent it in the future. 

Great review. What is the average and max CFM of the 841 if you don't mind me asking.

Okay, that makes sense. Do you know specifically what can cause it? Chips too hot? I also didn't have that machine on a surge protector, but the PSU is fine so I'm curious if that caused it.

Hello everyone, I just diagnosed an Antminer S9 of mine and it has something called "Chain Scission of chips". I couldn't find a lot of information on what causes that to happen. I have a couple other machines and I want to make sure they don't end up with the same problem.

Hey everyone. Wanted to reach out to see what you guys think about using 277v for mining. I currently am using a step-down transformer to 240v, but I wanted to build out a little section for testing some machines at 277v. I know HP makes some power supplies for 277v and I am going to give those a shot with some breakout boards, but I wanted to see if anyone has had any success with other power supplies.

IBM 2880 Bladecenter
I have seen a discussion from 2015 here that talks about different power supplies that run at 277v and on that list is the IBM 2880. Link: https://bitcointalk.org/index.php?topic=1206101.0

I bought a couple of them and tried it on 277v for about an hour and it ran great. I was curious if anyone has tried it long term. Also, why does this power supply work for 277v compared to other power supplies rated for 240v?

Bitmain APW3++ or Avalonminer Sorcerer PSU
Has anyone tried these power supplies with 277v? The sorcerer says it is rated for up to 264v so I am curious if either of these will run at 277v long term. Anyone had any success?

Anyone know of other PSU's that work at 277v safely?

Wanted to see if these are still available. Probably would need a bunch. 

This is what I was looking for. I guess I thought you had to use PDU's for some reason. I think I got caught up reading too many datacenter posts about 3-phase density.

Do I need to worry about setting up a system wide surge protection then?

I'm having a terrible time understanding how to distribute power to a bunch of miners. I have a few hundred Antminer S9 to put in my warehouse. It has 480v 3-phase power so I have a few transformers to bring in the 208v 3-phase power. The question is, what is the best way to power a whole bunch of miners? If I use 3 phase PDU's they are crazy expensive and the biggest 208v PDU I can find is 17.3KVA, so about 12 Antminer S9. Basically, each 70 inch shelf is going to need like 6 of these massive PDU's that cost 1000s of dollars each and are around 80 inches long! The female ports alone are $300! How do large-scale operations deal with this? I feel like a giant power bar is unnecessary since each Antminer uses a pretty set load.

I have been scratching my head for a while over this so if anyone has some insight I would really appreciate it.