Battery - Extender

As a commuter, you want to get from A to B quickly, which means you are unlikely to fall back on assistance levels 1 or 2 unless your daily range is over 50 km and you have no charging facilities at work. And not everyone wants or can afford an ST7 with a 1440 Wh battery.

With a new, blue BQ983 battery, around 50 - 60 km are possible with an 'all-in', moderate altitude profile and average system weight.

Longer ranges are certainly achievable, but only if you ride with level 2 or 1 and a reduced setting of the pedal sensor (torque sensor). In practice, up to 120 km are then possible, although the 180 km advertised by Stromer are difficult to achieve, but not impossible.

Unfortunately, Stromer has not provided for the use of additional batteries. This is technically feasible and would probably also have a market. The only alternative is to install an additional battery (extender) using the DIY method.

Pros & Cons

In addition to the gain in range, there is also a gain on the economic side. By distributing the discharge currents or charging currents (especially during recuperation) over more cell strings, the cells are subjected to less stress. This has a noticeable effect on the service life of both batteries and therefore on your wallet in the long term.

The end result with my ST3

As the extender cannot be integrated into the Stromer electronics (CAN bus connection not possible), the only option is manual operation of the battery, i.e. charging and connection to the Stromer 48 V system is done manually. In principle, there are no problems with this, but there are a few things to bear in mind.

• Before the additional battery is connected, both batteries should be at the same charge level. Ideally, this should be 100%. If this is not observed, very high equalizing currents may flow. In this case, the overload protection of the power battery is triggered (error E21000D) and the battery is switched off. Depending on the manufacturer of the extender, the BMS protection circuit also triggers and switches off the battery. My extender also has a 20 A fuse installed in the supply line to the Stormer.
• After driving or during breaks, the extender must be disconnected to avoid triggering the Stromer protective shutdown of the battery (error E210110)
• The errors mentioned can be cleared by restarting the Stromer. The extender must always be disconnected before this.

The solution shown is an 'in-frame' variant, i.e. the cable routing to the extender runs inside the frame. As my ST3 Sport M did not allow installation in the frame triangle, I had to switch to the luggage rack. With the Racktime Snap-it adapter and a mounting plate, I was able to find a mobile solution for the extender. I realized the 48 V connection of the extender with a Y-SAE splitter between the battery and the controller in the bottom bracket shell, so that a dismantling would be possible. The in-frame version requires two holes, one above the existing feed-through for the rear light in the bottom bracket shell and one in the rear mudguard.

Costs and range

In addition to my Snap-it/Racktime variant, there are also other solutions on the net:
kawajan74 | JM1374 / JM1374 - 2 | cookiemonster