Upgrading the bitmain t21: switching from 3 boards to 2

The bitmain t21 is kind of an odd miner since it uses a 3 phase power supply, which can be a hassle. You can make some changes with four different mods. 1) Grab the 240 volt model F power supply from bitmain or find it at a local dealer. 2) Get some bus bars that are compatible. 3) Pick up the epic controller. 4) Remove the middle board and add a spacer in its place. I used wood covered in aluminum tape.

spacer two boards in 3 builds as I turned 2 t21s three phase  3 board   into 3 t21s 2 board edit 1 phase is you look closely you can see one unit has poor performance a the steep down clock the tuner had to crank up the volts to get an okay percent for some chips so one machine does not want to down clock a lot. this was a 66 down clock so 2 boards is about 44 hash rate.  this is pretty much as low as you can down clock with the tuner and you can see one of the three builds does not like the low numbers on a few chips.

spacer next clock is 99 not 66 so 2 boards give  66 hash rate. the weaker unit does better at the 240mhz 99th down clock if you look at the weaker unit it uses less volts at a higher clock! and that weak chip on clock 160mhz is doing better with less volts on the 240 MHz (99th)  downclock you can see the tune numbers below

spacer first clock was 66th or 160 MHZ second clock was 99th or 240 MHZ third clock is 120th now on the third clock of 120th or 290mhz still a down clock you can see that the weaker unit is now catching up to the other miners. also this down clock is giving close to the stock 19 watts a th that the t21s will do in a cool room. also note fans are not set high in fact one unit uses only 2 fans and is fine with that if you look closely one board does have weak chips if I let the tune go on voltage will increase trying to get that chip closer to 85-95%

spacer. this will be set to 150th so 2 boards will do 100th if you look here you see one unit actually is better than spec of 19 watts a th it is at 17.9 the other 2 are close to 19 watts a th

spacer this will be set to 180 th so 2 boards will do 120th. this would be just a tad lower than the 190th stock setting

spacer I will try this at 210 th not sure I can do this with all three units due to noise and cooling as these are in my garage.

Why did I do all this well first off the bitmain gear is over driven and too dense so it breaks like mad. I would love to do a good long test of these this summer but my summer power rates are goning to go from 15 cents a th to 29 cents a th on may 1. I think I will have my guy in Iowa take these for the summer. around may 1. but for anyone that can run a few miners 2 t21s 2 s21s 2 s21 pros 2 s21 xps going from 2 units with 3 boards to 3 units with 2 boards will likely make for more durable gear.

need 1 correction the 1st 2nd post where you say: Removing the 3rd leg turns it into single-phase, not 2-phase. Yes it becomes 2 hot legs and if used, a neutral but is still called single-phase because power is only pulled from the single set of (2) hot legs.

thank you I will fix that. I like the results so far. I would likely keep the troubled unit in my house and send the other 2 to the host in Iowa .

Out of curiosity, does the 3-phase PSU use 4 wires (3 hot + ground) or 5 wires (3 hot + neutral + ground)? I'd hope it is 4 -wire as there should be no need for a neutral connection.

Let me look at the wire that came with it. found one of the wires on each end there are 5 wires.