The QuinLED-Dig-Octa system has a feature called “QPowerPost” or “QPP” for short. QPowerPost allows a stack of a brainboards and powerboards to share power through their brass stand-offs. This means that brainboards will automatically receive power from connected powerboards.
The way the system works is that powerboards are only able to output power and brainboards can only receive power*. All power conversion is done on the brainboards and a stack can consist of multiple types of powerboards each running their own voltage (5v, 12v and 24v is supported). All connected brainboards will automatically use the highest voltage available and switch without interruption to another source if a brainboard (or power supply) is turned off.
*There might be versions in the future that work differently
The QPowerPost feature consists of 4x M2.5 GND brass posts on the outside of the brainboard and 1x M2.5 VCC brass post in the middle of the board. Partly this is done to minimize the risk of something short circuiting with the VCC post but even if this happens built in protection circuits will make sure nothing disastrous can happen.
[diagram of post locations]
*Powerboards have separate M3 posts which are used for mounting and stacking
Both the powerboards and the brainboards protection circuits in place to make sure it’s safe. Each side has diodes directing power flow and also have a PTC (auto resettable fuse) in place to make sure that only a limited amount of power can flow. This means that in a case that a short happens it automatically interrupts the flow of power until the short is removed.
Voltage drop and protections
Because of the above mentioned protection circuits there will always be a voltage drop present over the QPowerPost bus. The DC-DC circuit on the brainboards has been designed the handle this and should function properly in proving 5.12v for the brainboard even if voltage coming in is as low as 3v!
Stack Power limits
Because of the protection circuits in place there is also a limit to how many brainboards you can stack in a single stack. Powerboards have a limit of providing up 1500mA through the QPowerPost system. Brainboards have a limit of 1000mA coming in.
*Running multiple powerboards may but will not always raise this limit
Typically a brainboard will use a maximum of 5v 500mA when both Ethernet and a relay is enabled, because of this the following maximums are advised:
- Recommended a maximum of 3 brainboards in a stack
- Recommended a maximum of 6 brainboards in a stack
- Recommended a maximum of 12 brainboards in a stack (although this might become quite tall….)