I installed a 20A controller and LCD from Sierra ebike (formerly velomobileshop). I will add commentary to the pictures, but here are a few things to note. First, the positives:
1) The bike runs like a scalded cat! The 48v battery with the 20A controller on the smaller wheels (and lighter frame) feels like it pulls stronger than my 36V 25A fat bike. I also hit a throttle-only speed of around 26mph. My son took it for a test drive and said "holy crap what did you do to this bike?!" after he rode it. :)
2) The install was fairly straightforward and can likely be done by anyone that's even marginally handy
Here are a couple of challenges and/or things you should know:
1) The LCD cable doesn't reach if you run it through the guides. It reaches to program it and even ride with it running in the wrong location, but it needs a 14" or so extension. Kyle Chittock at Sierra is aware of this. If you want to do this upgrade, talk with him about getting a cable as well (I'm not sure they're on his site still)
2) The LCD settings need to change. I posted a picture of the stock Fold X settings and what the generic LCD ships with. You're also going to want to set the bike for a 22" or 24" wheel because the generic controller doesn't have 23" as an option. With the 22" I got 24mph reading, and with the 24" setting I got a 26mph reading. Your choice in which way to go.
3) The PAS cable on the Sondors controller is a few inches longer than on the generic controller. This makes it tricky to connect, but it can be done. You just have to run the PAS wire into the frame, grab it from inside the frame (the hard part), and plug it in. It reaches fine once connected and the controller is inserted.
4) I'm still not sure a 25A controller will fit due to the depth of the tube. I show some additional measurements in the pictures. Also, we don't know what kind of fuse the Fold battery has since it's not accessible from the outside. My guess is 20A, which would make running at 25A quite risky.
That's it for now. Check the pictures for more info. Click images to enlarge.
I recommend coffee and a bowl to hold screws and nuts
This is inside the frame with the controller removed. You can't tell easily in the picture, but that V down in the frame is how far you can go with any aftermarket controller
This is the depth of frame where the controller goes. You would have 5 7/8 inches from the bottom of the frame to the mounting plate
Just shows the measuring device (I used a level) up against the bottom of the frame
20A controller is the same physical size as the stock 15A controller. However, the power wires run out the other side. This does not cause ANY issues with installation
Top end of the stock (left) and 20A (right) controllers. You need to do a plate/mount transplant from the stock to the upgrade.
Just the inside of the stock controller with the power wires running out the opposite end.
Here is the stock mounting bracket lined up on the new controller. It's a perfect fit. I will pirate the rubber grommet from the stock mount as well
The mounting plate transplanted onto the new 20A controller,. You can see I made small cuts on the grommet to get the wires out so I can re-use it.
New controller mounted and ready to go. You can see that the power wires on the new controller reach just fine.
Issue #1. The PAS cable on the stock controller is a few inches longer than on the 20A upgrade. This made mounting a bit of a pain, but it DOES reach.
If you look into the frame you can see the PAS cable connected. The "pain" is getting your hand in there to do it since the PAS cable on the bike only reaches that point and it's hard to reach
The PAS connection
All buttoned up. You can see that I have not tucked the wires up into the frame yet. Also, it's easier to do this with the bike folded and the battery/controller compartments pointing UP for easy access
Aftermarket LCD works, although at this point it's not been calibrated yet
Issue #2. The LCD cable will not reach the controller if you run it correctly. It's around 14" short. You will need an extension cable. Kyle at Sierra is working on a solution.
However, I was still able to ride it with the LCD cable run like this. Not pretty, but it works in a pinch. I might also cap the connector, coil up the LCD cable and ride without it for a bit.