Range extender for a stock Bosch e-bike

[the_wr]

Hello community,

Sharing my project should somebody find this useful. I could not find any info here on using any custom batteries with stock Bosch motors (apart few posts stating that Bosch motors only work with stock batteries and it's not worth the hassle in general). However I was able to find some posts on German forums and armed with Google Translate I was able to understand that it's possible to trick the system by connecting extra battery in parallel to the stock battery.

I wanted to have a EU-legal e-bike without spending two extra grand on spare batteries, since my requirements are 100+ km horizontal, 2+ km vertical distance while towing a child trailer.

Hard requirements:
- Don't ruin the bike
- Don't ruin the warranty

I picked Canyon Pathlite:ON 7 as a vehicle with a good price/value ratio and started experimenting. It also had a power socked that allows charging the bike without removing the battery. My crazy idea was to use this socket to access the power line of the battery, thus not making any irreversible changes to the bike.

I also had two 48 V 16 Ah batteries as leftovers from my previous projects, so preferably I'd like to reuse them and not buy anything else. Obviously this ruled out parallel connection since the bike runs on 36 volts, so the voltage converter was necessary. Fortunately a decent converter is an order of magnitude cheaper than two batteries, so that was the way.

Step 1: Figure out whether power connector can be used to access the power line.



Looks good!
Less temporary solution:











Great success!
A bunch of lightbulbs drawing power from the bike's stock battery!

Thermal glue to the rescue to turn all this shit and sticks into a makeshift plug:



I bought a 800W DC-DC Converter from Aliexpress (the bike's motor is 250W, so 800 "chinese" watts should be enough, right) for 40 bucks.
The converted (surprisingly!) turned out to be an adjustable CC/CV power supply (i.e. a proper lithium battery charger!), so I thought the following:

- Set the output voltage to 37 V (mid of the "36V" battery voltage range);
- Set the output current to maximum possible.

That way,
- the stock battery would always stay at 50%;
- the converter and the "extender" battery would kick in as soon as the voltage of the main battery drops due to load from the motor;
- the converter would provide maximum current to keep the voltage of the stock battery intact, effectively rerouting *all* load from the stock battery to the "extender" battery.

That way,
- the stock battery would stay effectively unused as long as "extender" battery provides power to the converter;
- the bike would first drain the "extender" battery to zero; having two of them I would easily swap out the emptied one and replace with a fresh one on the go;
- I would never have to recharge the stock battery, or even remove it from the bike;
- the stock battery would always stay at the most comfortable charge level;
- due to no effective usage, the stock battery lifespan would be only limited by aging, and not the cycles (=> live much longer);
- I would still have the "safety buffer" by the (lower half of) the stock battery when I drain both extender batteries during a trip.

Here's the intended layout I had in mind:



To be continued. In the next post: Not everything went as planned. Bosch is still shit.

 

[calab]

I had great hopes that something would come of your endeavours for the proprietary battery situ but I agree Bosch is still shit.
Back when BionX was still around, it did not take much to fool its electronics, but as technology advances so do the component lockdowns. Tool pack batteries now, will brick themselves on purpose if something their electronics doesnt deem right.

So if I have this correctly, your just using a generic battery to top up your stock battery. If thats the case its better then fuckinnothing.

Hello community,

Sharing my project should somebody find this useful. I could not find any info here on using any custom batteries with stock Bosch motors (apart few posts stating that Bosch motors only work with stock batteries and it's not worth the hassle in general). However I was able to find some posts on German forums and armed with Google Translate I was able to understand that it's possible to trick the system by connecting extra battery in parallel to the stock battery.

...........

To be continued. In the next post: Not everything went as planned. Bosch is still shit.

 

[the_wr]

Not only to top up the stock battery, but also redirect the load from the stock battery to the extender battery.

Anyways upon further testing, I discovered some interesting behavior of Bosch electronics:

- When I connect my extender to the charging port of the the bike that is turned on, the current doesn't start flowing from the extender to the stock battery instantly, but it takes about 2 seconds instead. That made me assume that either: a) there is no direct connection from the charging port to the battery (some electronics in between maybe?); or b) the battery doesn't enable the "charging" mode instantly when higher external voltage appears. But that doesn't hurt much, just an observation.

- The bike doesn't turn on if there's any load on the charging port. It just doesn't. The power on button does nothing. Short circuit protection maybe? I don't know.

- The bike doesn't turn on if there's external voltage on the charging port. Therefore I can't connect the output of my DC converter directly to the charging port, I need a switch of a breaker in between.

- As soon as the current that flows into the stock battery exceeds about 4.2 amps, the bike turns off. Battery protection?
This only counts the current that flows _into_ the stock battery, though, i.e. the difference between what the extender produces and the motor consumes.

- During the heaviest usage scenario (max assistance level, steel hill), max current that I observed from the extender was about 16 amps. At 37 V it means the motor consumes about 600 watts. Even though it's labeled 250 W.

- When the stock battery and the extender output have exactly the same voltage -- 37 V in my case -- the current from the extender to the battery is zero in idle mode, as expected. My setup assumes all load gets handled by the extender battery. However, after some driving, there's a small current from the extender into the stock battery that persists after I stop. It starts at about 2 amps and slowly degrades over time. This probably means not all the load gets handled by the extender, but the small part of it goes into the stock battery as well. This may happen due to the voltage loss in long wires between the extender and the stock battery, so it can't exactly match and compensate the voltage drop the stock battery would be having under load.
This doesn't hurt much as well (as long as this idle current doesn't exceed 4.2 amps that would shut down the bike), but the max I've seen was about 2 amps. The stock battery still bears only the minimal load, and those small discharge-charge cycles are happening at exactly 50% soc, so no significant wear expected.

- DC efficiency, as measured by two identical and calibrated wattmeters before and after the DC converter, is about 97.5%. Impressive! The huge heatsink it comes with will likely stay cold

Therefore, my setup looks like this:

Extender battery -> Breaker -> DC-DC Converter -> Switch -> Bike charging port.

Developer build and first test drives:







To be continued. In the next episode: Unexpected problems. Bosch is still shit.

 

[the_wr]

Update a year later:

The main problem I've been facing so far with this setup is that Bosch electronics throws error 505 once every ~2 kilometers. The bike shuts down until I turn it off and disconnect my extender. This is annoying, but manageable -- I have to flip the breaker, turn off the bike, wait 2 seconds, then flip the breaker back. Sometimes it can be done even on the go without stopping. Not very convenient when going uphill though.
I haven't figured out the exact behavior that triggers this error, and I haven't found a way to fix it either, so I lived with it for about a year.

As a next step, I felt adventurous again and decided to overcome this error by remodeling the setup and feed the bike battery directly, so the bike would not feel any intrusion at all; my goal would be to connect to the cells bypassing all bike electronics, so the bike would just think it has an endless battery and that's it.

Obviously that would not work if the battery actually calculates spent energy rather than monitors cell voltage, but fortunately that's not the case; bosch electronics looks monstrous and overengineered but luckily it's not that smart.

I also had to drop my initial requirement to "not ruin the warranty" -- I don't think I could do a battery surgery without leaving the traces

To be continued soon with pics of the battery vivisection and direct cell access.

 

[leffex]

Update a year later:

The main problem I've been facing so far with this setup is that Bosch electronics throws error 505 once every ~2 kilometers...

As a next step, I felt adventurous again and decided to overcome this error by remodeling the setup and feed the bike battery directly, so the bike would not feel any intrusion at all; my goal would be to connect to the cells bypassing all bike electronics, so the bike would just think it has an endless battery and that's it.

Obviously that would not work if the battery actually calculates spent energy rather than monitors cell voltage, but fortunately that's not the case; bosch electronics looks monstrous and overengineered but luckily it's not that smart.
...

Yes, I think it calculates somehow.

I have a customer that has connected another Bosch battery to his bike and his Intuvia display shows an extra icon of a battery.

I don't know if you have connected your battery directly to the positive and negative of the charge port and or if not that causes any error. Important here is that you connect with the same voltage. Even Bosch has extender and it specifies this.

 

[marka-ee]

I'm thinking of getting a bike with the Bosch CX gen 4 motor. Does anyone know if the Bosch gen4 electronics will error out if I parallel a battery directly to the cells of the stock battery? If Bosch is tracking Whr usage and not just voltage, I fear it would error out, perhaps even permanently.