I have commented on this topic nearly a dozen times. I am a power electronic engineer who has worked on systems up to 12MW in size and currents up to 6300A. So I easily understand this kind of application. It is very evident that someone inexperienced has decided on this configuration without consulting the connector company on how to derate the pin current and how to implement this reliability. And then there is marketing specmanship that you find in the connector datasheets themselves.
I would have selected an Anderson connector or something similar. Paralleling DC power pins is a dangerous thing to do, especially in light of the complex physics. If they are Hell bent on sticking with this configuration on the GPUs, they should be using interleaved PWM switching stages, with one power stage used per pin. This allows the PWM controller to force each pin to draw a balanced load and not rely on uncontrolled path resistances. These resistances are for example: connector pins, wire crimp, and wire - on both ends of the cabling system. So the imbalance can occur at the GPU side and the PSU side.
The 9A current derating quoted in the article seems high. When I looked at the Minifit application notes for similar parts, I saw that it showed a derating to 5A (or was it 5.5A?) for a 16 way housing. That is 8 pins bringing power into the GPU, and 8 pins taking power out (return). So for the current coming into the GPU I get:
I (total) = 8 pins x 5.5A per pin = 44A
I would expect the voltage to droop badly with this much loading on the PSU and cabling so for a 600W load the voltage could easily be around 11.75V or even lower. The GPU will pull what it needs regardless. So 600W / 11.75V = 51A.
Connector systems are all about power dissipation, cooling, and material heat capability. Most UL approved nylon housings are 94V0 which will tend to not flame up and self extinguish when the heat is stopped. This nylon is usually rated for 105 Deg C at the housing.
The connector industry is not very transparent on what assumptions they used for the datasheet, and where the alligators exist in the usage. So for the datasheet info they will take a brand new pin and socket, crimp on a freshly stripped wire, and plug the entire assembly together and make measurements. The connector system is almost never this pristine the rest of its existence. Was the PSU or interface cabling made in Asia and sent by boat? It will suffer from humidity and corrosion. This is a double hit if it was shipped in the summertime. Accelerated failure modes due to higher heat.
And the datasheets are expecting decent wire cooling to draw heat away from the connector housing, i.e., no "pretty" nylon shroud covering the wiring to allow for reasonable convection cooling of the wire. The wire is expected to act as a heatsink for the connector pins and sockets.
Here are some suggestions to help people with this issue - but this is offered as unpaid assistance. In some states they say "buyer beware". But these should help:
1. Do not use cabling that has a wiring loom wrapped around it, which acts as to reduce and constrict the airflow. The datasheets are expecting decent wire cooling to draw heat away from the connector housing, i.e., no "pretty" nylon shroud covering the wiring to allow for reasonable convection cooling of the wire. If this loom exists, remove it and allow the wire insulation to convection cool better. The wiring looms should require yet another current derating if you want to use them.
2. The wire is expected to act as a heatsink for the connector pins and sockets. Again this is simple physics. The pin and socket contact points are tiny and much smaller than the wire cross-sectional area. For this reason, suppliers should find a way to use larger wire than is presently being used.
3. Since the pin and socket contact points have gone through oxidation and corrosion before you even install them, you should plug and unplug them several time to knock this oxidation off. Don't get excessive with it because you don't want to create fretting failure by scrapping off too much tin plating. About 3-5 time is great. Make sure the last pass is seated well.
4. You want to get the heat out of the cabling ends. So mount a fast fan by the GPU connector, as well as at the PSU connector. The imbalance can occur at both ends!
I hope these suggestions help people while the industry addresses these shortcomings.
Facebook
Twitter
Instagram