I’m currently designing a 3d printed frame for a Framework 13 mainboard (7840U), to turn it into a displayless ‘computing slab’ build that can be taken with on the go.
Think the shape / form factor of the CJ64 (Project CJ64 is Done! Machined Aluminum Enclosure), with further tweaks, and containing the 61Wh battery.
I’ve got some questions about the battery, including whether to mount it above or below the mainboard.
Is it better to mount the battery above the mainboard with some space between the two? I’m guessing this is the case due to the air flow requirement from the bottom of the mainboard, but just looking for some confirmation here. I’m guessing mounting the battery below the mainboard would require a rethink of how the air is directed through the device.
Should I have a 3d printed layer separating the mainboard from the battery, and put some heat reflective foil on the side facing the mainboard? Or is it better to just leave it open in-between? I’m concerned about the thermal impact from the mainboard + SSD’s on the battery. Is there an ideal amount of space to leave between the two?
I’ve looked at other handheld mainboard + battery form factors, and they seem to keep everything on a single layer - the Steam Deck, ROG Ally, and other handhelds all have the battery and mainboards next to each other instead of stacking them.
Is this just a convention to keep things simple and devices thinner, or is there some sort of travel requirement related to computer equipment with batteries going through airport scanners to make it clear what’s inside the device that I’m not aware of?
I’ve had a look at TSA / IATA rules, but couldn’t find anything related to hardware design.
The intent would be to make something travel safe as well, so getting this right is also a priority.
Due to the battery connection length, and based on some rough information provided here about the battery connector part (Connectors for battery extension cable - #6 by nrp), the simplest way to connect the battery to the mainboard when stacked is probably to extend the 10 battery wires by cutting and soldering additional lengths on. Do I just need to use shielded silicon wire of matching gauges to what is currently used? The battery uses a combination of 24AWG and 28AWG I think.
I’ve done soldering before but not with the wires on a lithium battery. Want to be as careful as possible here. There will be no courting of spicy pillows.
To avoid the potential of thermal runaway you shouldn’t stack the battery with the motherboard at all. I went into detail on this in my last Patreon video but this is why I didn’t include a battery in my CJ64 design, why I’m not stacking the battery in my handheld console design, and one reason why all portable electronic devices don’t stack a lithium ion battery over heat generating components ever. There are safety standards that govern how far individual Li-ion calls have to be separated from each other and how far cells have to be from other internal components, to include how much shielding is required based on generated heat and cell capacity. The FW mainboard generates a lot of heat and while the chances of thermal runaway are small in regular usage, the additional heat that’s generated while the battery is plugged in and charging, and the system is in use and under load can cause the battery to get too hot and possibly catch fire or explode. It’s a admittedly small chance but it’s not zero. I blew up a gaming laptop once just by stacking 2 li-ion batteries ontop of each other. If you do decide to do it, I’d place the battery below the mainboard, as it’s cooler and heat rises, and use a flexible ceramic heat shield material like Zircoflex between the two and leave enough space between for airflow.
So, it would be actually be better to place the battery below the motherboard, if it were to be placed back to back? I have been experimenting with a stacked battery layout as well (with my own plans for a portable console) and have placed it on top, used only for a few hours. I made my own 3D printed PETG spacers which are designed to screw in with the mounting holes, and shaped so that they fit around the soldered components. The spacers are flat at the top and elevate the battery some 2-3 mm above the fan. Someone else made a mini tablet case which also requires stacking the battery, essentially having it sandwiched between the motherboard and the screen. But you have more experience in making custom enclosures for the mainboard so I trust your judgment. I have a 11th Gen Intel board and it does get warm to the touch. To me, avoiding battery overheating is much more important than having the power button more accessible. It does make another thing easier, too- making a fixture to hold the battery in place with the built-in screws.
Unfortunately since the mainboard isn’t a short, square-ish shape like the one in the Steam Deck or ROG Ally we have to get more clever with handheld designs. Screens that include standard HDMI and USB-C inputs tend to have their own controller board too, and their main ICs also get very warm. My 10" portable monitor uses the metal back panel as a heat spreader for its board. So going for a Steam Deck style design you may also have to keep an eye out on heat generated from there as well.