I’ve got some downtime waiting at the vet so I’ll expand a bit on my setup.
I’m repurposing an MPPT solar charge controller, it’s intended to take a PV array (solar panel) as input and it’s output is essentially a programmable CV/CV Li-ion charger.
I’m simply using another battery pack in place of the solar panel and using it as a DC to DC charger.
The particular ‘mppt’ model I’m using is step up only, not true MPPT, so you need a 10S to charge 10S-13S, etc, it won’t step down to charge a lower battery voltage. But it’s cheap, compact, and it works.
Wiring setup is simple:
10S5P Backpack Battery (w/ it’s own BMS and charge input) >> MPPT >> Charge cable to board.
This is my “Do Not Try This At Home” picture of my hastily thrown together test setup. I’m currently rebuilding it all with a 10S5P and enclosure.
I think you are on the right track. Steer clear of boost converter option 3. Mine worked for an hour and crapped out under 5A 42v. Option 1 may be your best bet. Keep in mind the amp output will be less than your input. It’s nice to have a voltage display that beeps at a set low voltage so you know when it’s time to disconnect.
And potting. Pot all your components with silicone or E6000. All those coils, capacitors, mosfets, make sure they are surrounded all around and at least some under what you can… Don’t miss one mosfet- especially if mounting all this to your board.
Your boost converter heatsink will need airflow, I wouldn’t enclose it- at least mount it with the heatsink outside something.
In the end, charging while riding is a dream. On my setup I feel like I cant go long before I’m hitting 50-60% charge. But, with 6S power tool batteries I can keep swapping and keep riding all day. At group rides I’ll end the days somewhere between 90-98% depending on how hard and fast we are going with just a few extra packs in my bag. Have fun, enjoy, good luck!
Just got back from a 22 mile test ride over 90 minutes. Based on the charger counter it added about 300Wh to my ride and I still had plenty of board juice left when I came back.
I have not caught fire yet.
@deckoz how retarded am I for trying this out without having a schematic for the MPPT or BMS? Hah
The TL;DR is I’m using a cheap MPPT solar charge controller + a battery in my backpack as a DC to DC CC/CV charger for a really lazy and simple mobile charger. So far it seems to work fine to charge-n-ride.
So that PV charge controller is feeding the battery directly? Or do you have a bms in there?
(like a D140) I’m guessing that you do have a BMS in there, so you have your range extended connected just like you would if you were using a regular charger to charge it?
Higher potential to go over voltage braking downhill on a full battery, but haven’t found it to be an issue so far.
@bsancken that’s correct. Backpack Battery has its own BMS. Output feeds into the input of the MPPT. That connects to the board through its charge port.
… Officer, please stand down those bomb disposal guys I’m just tweaking my charger
The more I see of these the more I think I need one, even before I got my first eboard I was emailing asking if there was a backpack or something I could use with it
I really like the idea and would like to build myself something like this. I just can’t stop thinking about what might happen if I were to go down at speed with a lithium pack in my backpack. Best case I land over a brick with my spine. Worst case, I land over a brick with my spine and then ignite. I guess proper padding would mitigate these issues. But it probably wouldn’t hurt to brainstorm some safety measures in addition to the technical side of things
I’ve had one of the secretaries at a building on my college campus want to call the police when she saw my board outside the room while I was in class, thought it was a bomb lol Though in all fairness, it was before I had a case for my lipos…
Haha awesome topic. I am for more then 6months working on this.
I hope to start selling a plug and play box in this and 3months.
I am very perfectionist in these things. That’s why it takes so long. Currently it is planned to offer two variants. a cheap one with a capacity of + -250wh. This will have locked charging voltage and current. And a more expensive one with a capacity off 450wh with adjustable current (0->5A) and voltage (0->70v). With the biggest one you can use it also like a small bench table power supply
