Nowadays when we assemble a mining farm which contains several video cards, we use x1-x16 PCI-E USB 3.0 risers. They allow connecting several graphics cards to the motherboard at the same time (usually from 4 to 6). Due to the popularity and high demand, there are several variations presented on the market today, and since people are prone to saving, users increasingly run against poor quality products.
Risers are not exactly those tools that you can save on, since a relatively small price difference will seriously affect the quality and productivity of your future farm.
How to choose a riser for a graphics card (Riser GPU)
Today we will discuss what to choose and which problems you can face trying to save on risers PCI-E > USB 3.0. First of all, thanks to risers it is possible to place video cards far from the motherboard which guarantees better cooling. They consist of several elements: a board with a lot for video cards, USB 3.0 cable, and also an adapter for power supply (optionally) (Molex for SATA power, SATA power for Molex, PCI-E power for SATA power etc.). If it’s colors we are talking about, it can surely be said that the quality of the black and blue boards leaves the green ones behind. We recommend you to avoid the green color risers.
Most often it’s the board itself that has issues, though those cases are not that frequent. The most widespread “disease” of the cheap risers is bad soldering. That is why be sure to double-check all connections and soldering quality. It is better to do this before you run of the rack, so that nothing burns out suddenly.
Check the soldering quality on the voltage controller, since if it is not connected properly, everything may seem to work fine, but the graphics cards will not work. We had lots of risers with unsuitable LDO voltage regulators soldered to PCB.
Always check the markings, and be sure that they are with 3.3V output. If there is a 5V marking, which means you need to convert this voltage to 3.3V, otherwise these graphics cards will not function properly.
Check the board for solder leakage, especially in the power supply area. We saw the risers, where this issue led to the Molex adapter short circuit. At best, such short circuit will trigger a built-in power supply protection, and it will not turn on. At worst, something will burn.
A smaller size board that is connected to PCI-E slot on the motherboard, usually does not cause any problems. If something is not working, just check USB-adapter soldering. We have encountered the problems of this kind only on the green boards so far, and all of them were connected either with saving on solder, or with poor quality plugs. Usually, you can cope with these problems at home, meaning you can modernize the things you have. In fact there is nothing else here that can break or stop functioning. You can re-test the connections with a voltmeter before the rack is assembled.
We have tried many USB 3.0 cables that were used together with PCI-E > USB 3.0 riser boards, and they never posed any difficulties. And you will hardly experience any issues either. These cables are used only for data transfer – no power is supplied through them. Though they are called USB 3.0, and we really use USB 3.0 cables, the risers themselves do not support USB connection. These cables are used due to their good conductivity and protection, to transfer data from the motherboard to the graphics card. You will not be able to connect the video card to the USB slot through these risers.
Don’t even try, since the graphics cards just will not work.
Some PCI-E > USB 3.0 riser boards also have other power ports, and that is why some additional cables often come with the device. Most modern power supplies are equipped with SATA power connectors, and the number of Molex plugs grows smaller. We recommend you to use standard 4-pin Molex connectors, even if the adapters would be required for this. Just do not connect more than 2 risers to one pathway. There were cases where theoretically the supposed connectivity would be enough, but the plastic plugs still got heated and melted, and that led to poor connection.
Checking out the PCI Express 1x 16x riser types available on the market
Later on we will use a simplified riser classification method based on their textolite color. In fact, changes may occur within one color “at work”, or the risers with textolite of different colors may be completely identical at the technical level.
Black full profile risers
PCE164P-N003 VER006 board marking
Stabilizer from Diodes or from Fortune Semiconductor
The classic rectangular board, which has been produced for 3 years. Thick protective Velcro. Manual sliding lock. Auxiliary power is connected via the 4pin IDE connector directly from the power supply, or via the complete 4pin IDE “female” -> 15pin Sata “male” connector. Modern power supplies are equipped with both these options. But you need to pay more attention to the cable thickness and marking. Cheap power supplies with SATA line often use 20AWG cable (American wire gauge where the less the number, the thicker the wire), and not 18AWG, therefore I would not recommend connecting more than 2 risers using one such cable.
The USB cable is crossed.
Blue full profile risers
VER 4.0 board marking
The complete analogy of the “black” ones described above with the stabilizer of different manufacturer, the layout of the board is the same. The protective Velcro from the other side of the board is thinner and softer. It sticks to the board better and does not unglue if touched accidentally. No lock.
The USB cable is crossed.
Light blue full profile risers
PCE164P-N003 VER005S board marking
Stabilizer G1084-33 from (Manufacturer is unknown to the author. Should anyone identify the one, please write in the comments!)
Almost the complete analogy of the “black” and “blue” described above with the stabilizer from another manufacturer, the layout of the board is a little bit different, but these differences are not used. Protective Velcro from the other side of the board is the same as the “blue” USB-risers have. The lock is manual and sliding.
The USB cable is crossed.
Light blue full profile risers with auxiliary power 6pin
PCE164P-N003 VER006С board marking
DC-DC converter from Fitipower and stabilizer G1084-33 from (Manufacturer is unknown to the author. Should anyone identify the one, please write in the comments!)
Our friends from China tried their best here to get 3.3v which are necessary for the graphics card. We have a voltage of 12v from the 6pin connector, that gets to the FR9888 converter (load of up to 3.5A, which is more than enough), and it gives 5v output exactly due to the strapping applied. And these 5v in turn go to the stabilizer G1084-33, which turns them into 3.3v.
It is not quite clear yet why do that instead of using just one DC-DC converter. Perhaps they just used what they had to get the intermediate 5v for the future unknown purposes. You may share your ideas in the comments.
Particularly this riser doesn’t need 5v/3.3v voltage from the power supply, since it has everything necessary onboard to get such voltage. Accordingly, it can easily be used in server power supplies.
However, I don’t think that the increasing of nods on the riser adds up to its stability. Quite the contrary, there are more possibilities of breakdowns.
The board is from the same “manufacturer” that produces the “blue” risers described above. There are slight differences about the wiring. The protective Velcro from the other side of the board is the same as the “blue” and “light blue” USB-risers have. The lock is semi-automatic and clamping. These risers are supposed to be used with server power supplies, but there is a Sata15pin – PCI-E 6pin connector included, to connect to conventional power supplies. It should be used with caution, and the causes will be described in the given material later.
The USB cable is crossed.
Blue full profile risers with DC_DC converter and 2 types of auxiliary power 6pin/Sata15pin
EP105 VER 1.0 board marking
Full DC-DC 3A voltage converter MP2307DN from MonolithicPower. Known, reliable and cold. The power of this converter is more than enough. It works in conjunction with the throttle.
Auxiliary power can be connected via 6pin GPU connector, as well as via 2x Sata 15pin connectors. Thus, it is suitable for both server and conventional power supplies. If you run the thing using one Sata15pin, this may cause the connector burnout, since it is supposed to work on 12v line with 4.5A only. Both types of auxiliary power are connected in parallel, there is an opportunity to connect directly to all connectors from the power supply if you wish. It won’t get any worse.
For this particular riser to work, there’s no need to have 5v/3.3v on the power supply, since voltage 3.3v is available right from the converter. The minimum nodes you have, the more reliable it is. Nowadays I consider this riser to be the most optimal solution, but not the cheapest one though.
The USB cable is crossed.
Green full profile risers
Stabilizer from AMS
It is a more compact, “aerodynamic” board. Auxiliary power is provided via the 4pin Floppy connector. There are 1 or 2 such connectors on modern power supplies, which is definitely not enough to power all risers of an average farm. Adapters from IDE 4pin to 4pin Floppy may be parts of some power supply kits, but this is more the exception than the rule. There is an adapter for 15pin Sata provided with the riser. You will find more details about this adapter in the text below in a separate paragraph. The lock is semi-automatic and clamping.
The USB cable is crossed
But the most important thing is that these risers are dangerous for use exactly because of the 4pin Floppy connector. The fact is that its design load is around ~40W for 5v and 12v together. As we know, the graphics card consumes up to 75W from the slot, and if it’s about the USB-riser it can consume even more because of the losses on stabilizer. As a result, we have a real chance to get a fused connector, and sometimes even a spontaneous combustion. But if you modify this riser, it can be used. When we talk about the modification, we mean that we have to unsolder this connector, and install a full-fledged 4pin IDE connector as it is on full profile risers.
There are 3 stages of such riser modification in the photo above:
- Removal of the connector plastic part
- Removal of the excessive contacts length and subsequent tinning,
- Wire soldering with insulation directly.
Why do we need USB 3.0 risers for mining?
In these risers, a USB 3.0 cable serves as a pathway (the data line for exchanging data). It only connects 9 contacts from each side of the riser.
Such things as USB-interface speeds, full-duplex and the rest do not work here, and nothing is “improved” here compared to conventional stubby risers. The hashrate also does not increase. This is just a “ribbon” that works by analogy of a flexible in-line ribbon in classic risers. USB3.0 is used here just because it has 9 contacts, and those 9 contacts are enough for mining, provided the external power is supplied to the graphics card.
A USB 3.0 connector of A type is used on both sides of the cable:
Contacts from 1 to 4 are connected directly to each other at both ends, and from 5 to 9 they are already “in position 69”.
This is due to the small board layout peculiarities, that is plugged into the PCI-E connector of the motherboard. The general crossing rule is as follows:
1 -> 1
2 -> 2
3 -> 3
4 -> 4
5 -> 8
6 -> 9
7 -> 7
8 -> 5
9 -> 6
That is why if anyone would like to buy a longer cable for their risers, they should be ready it’s not going to work, because this wire can be crimped directly. Either way you have to open this wire and change the places of the wires for the contacts 5/8 and 6/9.
Why is it better not to use complete adapters for auxiliary power of risers?
Firstly, it is because of the wire cross-section, secondarily, it is because of the connectors crimping quality (see pictures below):
According to a “good” Chinese tradition, 18AWG is written on the wire (strands diameter is 1,024mm), and it will be great if in reality it is 20AWG (0,812mm). Those risers that I tested had 23AWG (0.573mm), and it’s 2 times less than promised. You can see the comparison of complete adapters in the photo. Those that come with the black full profile riser and those come with the green low profile riser.
In reality, it is enough to power a graphics card via PCI-E connector, since the conductors on the boards, video cards and also acknowledged and tested through years stubby risers are even smaller. But it is another thing that is important here: the wire diameter is different depending on the riser. And it is only up to the seller with what adapter he is going to complement the device. And sometimes even the seller himself doesn’t know everything about the complete set, since it was taken from another Chinese guy and he just believed in 18AWG on the coverage. It is also possible that once you get the wire of such cross-section that will overheat and even burn out under full load.
On top of that, there is a problem in Sata 15pin connector that is used. On the 12v line it is rated at 4.5A, that is 54 watts, and a graphics card consumes up to 75 watts from the slot. It is also known that there were cases where it wasn’t limited by 75 watts for some AMD graphics cards. But this relates to those connectors officially produced by Molex. We do not know which load is possible for the official “Chinese” versions: it can be more, but it can be less as well. Therefore we can use such kind of adapter only with those cards that consume no more than 50 watts from the slot. But it is better not to use them at all.
That is why I recommend connecting the auxiliary power to the riser directly from the power supply, bypassing these adapters. If you have a riser with 4pin Floppy connector, which means you need to solder directly to the connector, or at least simply strip the wires to check the cross section. It is necessary to check all 4 cables, since I have seen cables where those of yellow color had real 18AWG, and all the rest did not. Be ready for surprises, since the Chinese like tricks like those.
If you still need to connect riser power to Sata, just go ahead and replace the adapters with those of a good quality, there are 4pin IDE -> 15pin Sata on real 18AWG, and I have them in place.
Why do we need a stabilizer on the riser board and how safe is it?
Considering the fact, that USB cable has only 9 wires, there is no sufficient place there for providing power of 3.3v for the riser (a graphics card consumes not only 12v, but also 3.3 in small amount), and the Chinese engineering mastermind guessed to get these 3.3v on the riser directly by converting 5v voltage through the stabilizer. As a result, we have an additional node in the design. Whether it’s reliable or not, I just cannot tell. But I can tell exactly that if the stabilizer will not make it, the current can either just stop flowing (a graphics card will not start), or the stabilizer will be broken and all 5v instead of the expected 3.3v will flow to the graphics card. What is going to happen with this graphics card after that I just cannot tell, because I have never conducted such tests before.
Most of the stabilizers used on risers had an upper input voltage range from 12v to 18v, and some miners use it. They provide not 5v, but 12v to the riser. The same 3.3v are obtained at the output of the stabilizer. However, when in this mode, the stabilizer starts to work to its limit and it becomes very hot. The chance of its breakdown/death is increasing. In this case, the video card will get 12v instead of 5v expected, and it will probably just stop functioning.