Hi,Range extenders seem to be a hot topic nowadays and there are already some commercially available options (Levo Range Extender, Levorex, Trailwatts) to select from. However, IMO they are quite expensive. I did not want to pay ~500 EUR for a battery that I need only on those long, full-day rides a few times a summer. Hence, I decided to make one of my own. The technology is basically the same as with the commercial options, but I was able to even tune it with a bluetooth-equipped BMS.
I already wrote a longer how-to in a Finnish cycling discussion forum, but maybe it's good to share the basics here as well, because I bet there are some Doc Emmett Browns in this forum as well interested on the topic. Of course (and for a person, who believes that everyone is responsible of their own mistakes, this sounds stupid) I will not take any responsibility if you burn your bike, blow up your house or lose your eyesight when a cell explodes on your face or any such thing.
LONG STORY SHORT:
Stuff needed:
Tools needed:
- Case to put the battery in (I used a plastic tool pipe that I needed to form with a heat gun)
- Cells. I recommend to use only quality ones. I used 3350 Ah rated Sanyo 18650 cells ordered from Nkon.
- BMS. I used bluetooth-enabled "smart" BMS, ordered from GreenBikeKit
- "Ideal diodes". You need to have a way to avoid current flowing from one battery to another. There are few options for this, but ideal diodes are the best. I ordered that directly from the manufacturer re-voltage.eu
- All kinds of small stuff (nickel strips, battery holders, wire, shrink wrap, solder, glue, connectors....)
Steps:
- Quality soldering iron
- Hot air gun
- Drill
- Other basic tools
Cost:
- Work with the battery case. My plastic tool pipe did not fit L size Levo at first, so I used the heat gun to soften the plastic and then re-formed it to fit in. Reforming made it quite bumpy and lumpy, so I mixed some 2-component plastic/polymer padding, spread it and sanded down. Thats the reason, why you see in some photos that the pipe has white/grey-ish cast.
- Assemble the cells. Youtube is full of instructions for this. I made 10S2P, which means roughly 250 Wh. I did not have a spot welding machine, so I ended up soldering the cells together. Having a powerful soldering iron minimizes the time that you need to heat up the cell. Heat = not good. I did try make a spot-welder from car battery, solenoid and some copper nails, but after seeing the colour of lithium flame after puncturing one of the cells (luckily I ordered 21, i.e. one extra), I decided that heat or not, but I will solder them together
- Connect the BMS. BMSes differ a bit from each other, so I will not give instructions to this either - the basic principle is to have BMS connected to the both ends of the battery (full voltage) and then also to all the +'es in between the battery. This way BMS can monitor the charge, discharge and cell balance.
- Bluetooth and other battery connections. I plugged in the bluetooth and the app started to work right away. I was really surprised, asit was so easy. Then, I probably could have had just one set of leads for both charge and discharge, but ended having one for charging (inside the case, which is easy to open) and one outside the case for discharge, i.e. to attach to the bike. The BMS also had two temperature sensors: I put one between the cells and glued the other on top of the BMS heatsink. For charge and discharge connectors I used Amass XT60 that can easily handle the needed currents.
- Connections to the bike. Ok, this is important: you don't want the current to flow between the batteries but only from battery/-ies to the motor. In order to do that, I used "ideal diodes" and needed two of them. I'm not an electrical engineer, but I drew a simple diagram for this (check below). I made the connections so that it's not that easy to return the bike to the factory form (I have the diodes on top of the motor, no need to remove the crank to get to them), but you can do this also so that you put the diodes under the motor (like commercial options have) and then have an extra battery -> motor cable. This way you can quite easily take away this tune. In any case, I'm not worried on voiding the warranty on my bike - if the bike has worked already a year, why would it break down anymore at this point
- All done. I made a test ride and no smoke or flames and based on the iOS app also the extra battery got involved even though the batteries had different voltages to start with, so all good.
- Finalization and paint-up. Hey, one needs to have a name for this type of thing. I named this to "Olkiluoto 4". Olkiluoto 3 is a nuclear power plant here in Finland, which has gotten delayed for like a decade due to all kinds of problems during the building phase. It is to be started next year, but I already have Olkiluoto 4 up and running over here
--> ~210 EUR I also bought 2 Amps @ 42 V charger (25 EUR).
- Case ("free" as I had it laying in the carage)
- Cells (~90 EUR)
- BMS (35 EUR)
- Ideal diodes (63 EUR for two)
- Small things (15-20 EUR)
- iOS app (1 EUR)
Links:
Photos:
Tool pipe is taking its shape. It has already seen the heat gun as it fits the Levo frame. I needed to turn the CC coil show up-side down.
Cells are already soldered and BMS being soldered. Zip tie is keeping the BMS in place during this.
Wiring up the bike. Ideal diodes are under the shrink wraps. They fit well on top of the engine. I used 4 mm2 wires which probably were an overkill. I also secured the + wires with additional webbing in the places where it might get some friction and wore out the insulation.
A simple diagram for wiring up the diodes. "Lisäakku" = the extra battery. "Levon oma akku" = Levo's own battery. "Pyörän moottori" = the motor.
All secured inside shrink wrap, bluetooth on and battery being charged.
Ready for the test ride!
A view to the app. Olkiluoto 4 is powering my Levo.
All done and finalized - ready for the long rides!
Thanks for this.
Hello bronces
As far as I know they use a different voltage, the Levo is 36v and the Levo SL 48v ⚠
Thanks for the reply, the negatives on the diodes seem to be common on in and out as they are directly linked on the pcb. I'll get a picture at lunch time.
And the positives are connected as I have indicated in the image?
It is clear, the negative is not the problem.
They are 15amp ones from ebay! It does the problem with just the main battery in, as soon as you return the loom to original everything works fine
I use 2 ideal diodes of 50A each, because if on some occasion I do not have the extender, something more than 20A can pass through one of them and of course, it will not work.
Like this:
It is not my installation, I have used 12AWG but I think that 14AWG can be used judging by the diameter of the original cables.
Thanks 14 is more pliable than 12. Levo peaks around 700w according to BLEvo. That’s 20A for brief periods. I’m guessing that even that is a very choppy load due to pedal rotation, so the average amps over any period of time is way less.
To charge the main battery you have to disconnect it to connect the charger so once disconnected they cannot be seen in any way and that is why you can charge them both at the same time.
You disconnect the wiring of the bicycle to which "the box" is connected from the main battery as soon as you are going to charge the main battery, so both batteries are disconnected from each other at that moment.
Let's see... seriously?
Hi Joliver,
How do you connect the original main battery charger without disconnecting anything?
