PCIE-riser cards

Why do you need a PCIE-riser card? The answer is in order to connect the GPUs to the motherboard. Imagine that in the mining motherboard of “Asrock H81 Pro BTC”, there is one slot for PCIE X16 and five slots for PCIE X1. As the GPUs only come with PCIE X16 sizes, you will need an adaptor to convert the PCIE X16 to the PCIE X1 of the motherboard.

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Most modern DDR3 and DDR4 motherboards, which offer PCIE 2nd _{generation X1}

slots, have a bandwidth of 500 MB/s [16]. In the 1st _{of generation of PCIE X1, the}

speed was 250 MB/s. However, apparently, the GPU mining application doesn’t saturate the whole bandwidth of the PCIE X1 slot, unlike a 3D game that may require a higher transfer rate19_.

There are many different types of PCIE-riser cards on the market, but in my opinion, the PCIE-raiser card of X1 to X16, which can be connected through a USB3 cable and powered board is the best and cheapest. It is usually priced around $10 and can be found easily in any electronic online shops. I usually get mine from Amazon through link below [17].

Here is another example of these PCIE-riser cards from a company called “mintcell” which are available on Amazon.com at this link.

19 _{Unfortunately, I have not found any particular software or tool to measure the PCIE-usage bandwidth to} demonstrate here. I can only report on my personal experience.

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The PCIE X1 card does not fix to the motherboard firmly and therefore when you work with a compact system, it may get lose or fall out of the socket. To prevent this, I usually fix them firmly with a hot glue once I have set up the system. This is not a very good solution if you decide that you want to remove them later on, as you may damage the slot. So, you should use just a little glue to keep the PCIE- riser card in place. Be verycareful not to damage your motherboard.

Figure 29 - Asrock Z97 Anniversary edition, 3 PCIE X1-riser cards being glued with hot glue gun.

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After introduction of M.2 expansion slots and being a norm to implement it on every motherboard, companies have started to make relative accessories and possible adaptors. Related to the GPU mining rig is PCI Express 4X Female to NGFF M.2 M Key Male Adapter converter card that comes with power cable. This expansion card is being used to connect an extra GPU through M.2 expansion slot. So, a normal USB3 PCIE riser card is installed on the expansion card. As a result, a motherboard with 6 available PCIE slots can connect one or two more GPUs through M.2 port.

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5.3.2. Remote control

The main problem with un-attended and remotely supervised GPU mining rig is the difficulty of restarting the system physically when system is frozen or crashed, as system becomes unresponsive and most of the time the resetting the system through software is not possible. However, there are few options available for such a problem, one of the is SSRv1 device, which is remotely controlled re-setter that can be connected to eight mining rigs at the same time and control the reset and power switch of the motherboard of the mining rig by wire. So, it can automatically reset frozen and crashed rigs. This device is available to buy on simplemining.net.

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5.3.3. Cooling fans

Why do you need additional cooling fans? The reason is because the GPU itself does not deliver fresh air into the chassis. Usually a computer case is equipped with fans that bring fresh air into the system or exhaust the warm air to the outside. What about a mining rig? If you decide to have a maximum of 2 or 3 GPUs and you have placed in them in a typical full-tower ATX case, you require a very good air flow to keep them cool.

General information on computer-cooling fans is given in Chapter 2. Here I make a choice between the thousands of options that are out there, based on the following:

1. Fan noise, 2. Fan price, 3. Fan air flow, 4. Fan controllability

In my own builds, I go for affordable PWM fans which also have decent air flows. My recommended fan choices are:

ARCTIC F12 PWM PST- Standard Low Noise. They have a maximum airflow of 74 CFM (126 m³/h) and can be purchased for €5.99 [18]. These fans are very quiet and their price is almost half of that of the nearest competitor. In addition, being a PWM fan, it can be controlled much more easily by the motherboard. Also, the other unique characteristic is that they can be bonded together with a PST (PWM- Sharing Technology), so you wouldn’t need many fan headers on the motherboard or an external fan controller. However, strangely, Arctic recently lowered the airflow of its F12 fans to 53 CFM (90.1 m3_{/h), see their website.}

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Each GPU usually requires two 120-mm-case fans for additional airflow in a mining-rig chassis.

What about your open-air chassis? If your rig has more than 2 GPUs, for instance 5 GPUs, and you have a custom-made chassis, you will require a higher airflow, which is hard to obtain with the computer-case fan. You need an airflow of 120– 150 CFM per GPU to keep them sufficiently cool and under control.

My first choice is the 150-mm 220 V (or 110 V in USA) low-noise duct fan. I recommend these fans because:

1. Duct axial fans have less noise than the blow-type fans; the hub and shroud of the fan help the airflow pass more quietly.

2. 150 mm is the best size, as it has big enough blades for a decent airflow and also you can purchase 150-mm-diameter air ducts to route the air into and out of the system. In a closed-air system, or a computer-case type GPU mining rig, without air ducting, the airflow cannot be guided actively into and out of the system, as the system sucks in the air of the room and dumps the hot exhaust into the same atmosphere. But, with an air duct, you can bring fresh air from outside, insert a dust or humidity absorber on the way and then exhaust the warm air out of the room, or you can reuse the warm air for general purpose heating.

3. As I have already said, it is relatively cheap. I have purchased them for less than €20 [19] which is comparable to the price of a 120-mm-PWM fan! Each of these 150-mm fans has a maximum airflow of 257 CFM, but the actual airflow varies from manufacturer to manufacturer and you will need to study the product details before you purchase them. Always look for airflow and noise! The noise should not be more 40–45 dB (A) (3m).

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So, for a five-GPUs system, you require ten PWM 120-mm-computer fans or three 150-mm-duct fans.

If you don’t care about noise, and your cooling fans are being controlled by direct 12-V current or a fan controller that supply 12 volts, you should choose a high- RPM high-airflow fan. A good example is the Delta AFB1212VHE (link is here! And

here!). A brushless 12-V fan with a current of 0.9 amps and a speed of 4000 RPM, should be able to deliver a maximum airflow of 129.9 CFM, which is almost twice that of the Arctic F12, with a noise level is 48 dB20_.

If you are looking for higher airflow and the noise of the fan is not important and you have a fan controller which is able to supply a 12-V, 4-A current to a fan header, you should go for a higher-grade PWM fan, such as Delta TFC1212DE- SP07. This can rotate at speeds of up to 5200 RPM and supply an airflow of 250 CFM with a current of 3.9 A. Here is the purchase link.

20 _{Warning: do not connect these high-power fans to the motherboard fan headers, as the high wattage of the fan} may damage the fan connectors.

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What are the other options? You can always go for a simple blower axial-style fans, but I’m not keen on these. They are however easier to place next to the rig, and they work well when the room has an exhaust fan or ventilation, as a blow- style fan just blows the hot air away from the system into the surrounding environment. However, you can’t do anything about filtering the air. Furthermore, you don’t want to spend a lot on cooling units that have a low efficiency and consume a lot of power. Always look at the price, airflow and power consumption. The fan below from “Trotec” or similar types seem to be good options if you want to use this type of fan [19].

Table 1 - This table shows the specification of high-airflow Delta fans. For more information, please visit delta- fan.com at this link! Pay attention to the CFM/Power columns, the higher numbers are better. The lower CFM fans have almost twice the efficiency than very high CFM fans.

Fan Part # Size Voltage Range Voltage Current (A) Power(Watts) Max RPM Noise Airflow (CFM) CFM/Watt

PFR1212DHE 120x120x38 8.0~13.2 12V 3.7 44.4 7400 68.5 254 5.73 PFB1212UHE 120x120x38 8.0~13.2 12V 4 48 5500 66.5 253 5.27 AFB1212GHE-C 120x120x38 6.0~13.8 12V 2.45 29.4 5200 62 241 8.20 PFR1212UHE 120x120x38 8.0~13.2 12V 2.7 32.4 6600 65.5 229 7.06 PFB1212GHE 120x120x38 8.0~13.2 12V 2.7 32.4 4800 64 218 6.72 AFB1212EHE-C 120x120x38 6.0~13.8 12V 1.8 21.6 4600 58.5 213 9.84 QFR1212GHEXUM 120x120x38 8 ~ 13.2 12V 1.8 21.6 6000 64 210 9.74 AFB1212EHF 120x120x32 6.0~12.6 12V 1.85 22.2 4800 59 199 8.95 AFB1212SHE-C 120x120x38 6.0~13.8 12V 1.25 15 4100 55.5 190 12.70 FFB1212EHE 120x120x38 7.0~13.2 12V 2 24 4000 59 190 7.92 THB1212B-AXHF 120x120x25 7.0~15.0 12V 1.6 19.2 5300 59 184 9.59 PFB1212EHE 120x120x38 8.0~13.2 12V 1.6 19.2 4000 59 181 9.44 FFB1212SHE 120x120x38 7.0~13.2 12V 1.5 18 3600 56.5 171 9.50 AFB1212SHE 120x120x38 4.0~13.2 12V 1.05 12.6 3700 53 152 12.05 FFB1212VHE 120x120x38 7.0~13.2 12V 1 12 3200 53 152 12.65

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As explained at the end of Chapter 2, the recommended fan type for a GPU mining-rig is an airflow-optimized fan, not a static-pressure-optimized fan. In a open-air chassis style, there is no restriction or obstacles such as a radiator or dust filter in the way of the stream of air. The purpose of an external fan on a GPU mining rig is to exhaust the warm air of the GPUs out of the system. So, the main feature of an efficient axial fan is to bring a high airflow the system.

Always look at the fan efficiency. Do the calculation for yourself, as follows: The efficiency (Eff) of a simple fan of a GPU mining rig is given by the formula: Eff = maximum airflow rate (CFM)/ (maximum power of fan in W)

Accordingly, the points below should be considered:

1. The maximum airflow rate of a fan should be more than 70 CFM. 2. The maximum power of a fan is with the voltage (12 V) multiplied by

the maximum current (A).

3. An efficiency (Eff) of more than 12 is acceptable.

Why is fan efficiency so important? Imagine this scenario: your AMD Radeon RX 470 consumes around ~120 watthours, and suppose that you need an extra air stream of 150 CFM to maintain the recommended airflow to a GPU. While this airflow can be delivered with an efficient 120-mm fan such as “Delta FFB1212VHE”, this extra airflow requires 12 watts of energy, which is 10% of the total GPU consumption. consequently, considering the cost of power, the efficiency of the fan is important. Note that some AC fans have terrible airflow efficiencies. So, you should give careful consideration to the choice of fans. The efficiency (Eff) of the ARCTIC F12 PWM PST is given by:

Eff = 53 / (0.24 x 12) = 18.75

where 53 is the maximum flowrate (CFM)21_{, 0.24 is the current (A) and 12 is the}

voltage.

Another competitor is the “Noctua NF-S12B [20] redux-1200 PWM” which is currently priced at ~€12–14 on Amazon. Noctua is a computer hardware manufacturer of CPU coolers and computer fans for primarily the enthusiast market [21]. Noctua has many different designs and types of fans, but other the

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important of the cooling system is: its costs, most of Noctua fans are expensive and are targeted for premium and enthusiastic customers.

So, let’s calculate the efficiency (Eff) of the Noctua NF-S12B fan:

Eff = 59 / 0.9 = 65, where 59 is the maximum flowrate (CFM) and 0.9 is the power.

5.3.4. The complete HVAC

_system

As I said in the previous section, you can’t get away with just a few simple blowers or a couple of exhaust-duct fans. You will require a complete operative HVAC system in your mining farm. Ventilation and air conditioning are important matters that need to be taken into account in the design of a building or room for a GPU mining farm. I don’t intend to get into this. Suffice it to say that before you decide to carry on with your GPU mining-rig plans, you will need to think ahead, and in doing this, you should take account of the following:

1. How big is your mining farm? Typically, you will require about 5 square-meters for each mining rig with 6 GPUs. For horizontal ventilation, a rectangular-shaped room would be better with a length/width ratio greater than 2. For vertical ventilation, the room should be high enough to allow the heat to be collected and vented

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to the outside. So, four 6-GPU miners will need a 20-square-meter room, preferably ~6.5 m by ~3 m.

2. You require at least 100 CFM of extra airflow for each GPU than is provided by the GPU fans themselves (I recommended a total of about 720 CFM for a 6-GPU mining rig above). So, for four 6-GPU miners (i.e. with a total of 24 GPUs), you will require a ventilation of 24 x 100 CFM, i.e. 2400 CFM. You may think this is overkill, but definitely you will need it on hot summer days. If you don’t spend money on good ventilation, you will pay later by reducing the life of the components or lowering the performance of the GPUs.

3. You will need to filter out the dust before it reaches the mining farm. Also, the fresh air may be humid, in which case, you will need to deal with both dust and humidity. Think carefully about the choice of location.

4. What’s your plan for the generated heat? In the previous four-miner- example case, you would have been generating about 4000 watts of heat. You can reuse and circulate it in the building or just dump it outside.

A simple schematic of a ventilation system for a mining farm is givenin Chapter 4 (where a more than five 6-GPU mining rig is available) consists of:

1. An air inlet.

2. An air box, air-inlet filter, or inline filter (different names for the same component).

3. A duct fan.

4. Duct and air channels. 5. A blower, axial fan. 6. An exhaust air collector. 7. An air outlet with exhaust fan.

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But you will need to remember that expenditure on a ventilation system should not exceed the suggested budget of 5%–10% of the total cost of the mining rig.