Research | Drive Unit Repairs

Bosch Research

Interesting discoveries, issues and false specifications

These are our own findings, we can't guarantee that everything is an unmodified OEM part

Bosch Powerpack temperature monitoring

The Powerpack Rack and frame version have only 1 single temperature sensor. The rack version has it 1/4 of the way into the pack, near the BMS. This one monitors about 8 cells fairly directly, white thermal compound ensures better contact.

On the Frame version it it on the outside, monitoring only 2 cells directly.

In any case, we've found packs with cells on the opposite side reaching over 90 degrees C during discharge at 10A. Especially older packs can have these issues.

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Bosch Powerpack 500 with 30Q cells

We've come across a couple of supposed 500Wh OEM batteries where the customer complains that their range is less than with other 500 packs. Inside we found this:

30Q cells with a max capacity of 430Wh. FAR from 500Wh.

30Q 18650 from samsung have 3Ah, there's 4 parallel cells making only 12Ah instead of 13.4Ah, which is written on the spec sticker.

Bosch Powerpack 300 with M29 cells

29M cells with a max capacity of 2.9Ah, making 11.6Ah. If you're shipping these batteries and need to file documentation with capacity for ADR, or for legal requirement with regards to battery sales and import, these pack can get you possibly into trouble.

Completely wrong capacity is marked. Also when taking batteries on planes this needs to be correct for liability.

On the Bosch tester it will show 300Wh, but the entire capacity can be used on the bike, so here you get more than what you paid for.

Bosch Powerpack rack (pre-2020) is far from rainproof

Sometimes the Bosch battery will flash LEDs 1-3-5 or error 201 - 202 - 602 -640 on the display, this means either the pack is out of temperature range, or the ISL chip, which also manages balancing at 20mA, has failed. If this chip fails, it can drain or unbalance the batterypack.

We get about 70 powerpacks per year with waterdamage, because they didn't use any rubber seals between the screw and the screwholes. This is a hazard, as the BMS can short circuit because of this. It is advised to remove the screws, put some silicone caulking in the hole and put the screws back.

Processor failed due to water

This can cause heat development, bypass the temperature protection or even short circuit

Corrosion spots

Screw holes without water seals, just bare plastic

Here you need to add silicone to increase waterproofing

Catastrophic water damage with fire as result

Water can come in through the torn indicator sticker, this thin membrane is the only thing keeping water out. If it is damaged it must be glued shut.

Water visible through the indicator sticker

Bosch Powerpack wire thickness

It seems that 3 of the 4 full current output wires run through the pack. They seem to be 1.5sq mm wires, a bit thin for the 12-16A current running through them at max assist. They could only heat up some cells, which could lead to unbalanced cells. Also the balance wires often get pinched, leading to smoke or damage. In the picture you see them run close to each other without being held in place. Sometimes the factory machine squishes them together over the cross shaped lid alignment pegs.

Bosch Powertube waterproofing

In our own tests we've determined that powertubes can withstand 10sec of submersion. The water comes in through the indicator LED sticker circuit.

Bosch Powerpack loose spotwelds

This is one of the more dangerous faults. Since Bosch uses only 2 welds per contact, there is a higher chance of disconnection.

This is particularly dangerous because it can disconnect the cell, and reconnect when the state of charge of the other cells is way higher or lower, causing very large unregulated, unmonitored currents to flow. The BMS has no control over this current, so even if it detects temperature rise it can't do anything.

Gen 2 motors

The gen2 Active Line, Active Plus, Performance line and CX are all identical inside. Same mechanical parts, only limited by the firmware. This is why we are comfortable doing the torque mods, making an active line feel like a CX.

They do have issues with water ingress. Bosch provides a felt ring to retrofit, but we've been packing the axle with extra grease or even filling the motor with oil to prevent waterdamage and increase cooling for higher power levels. The next picture shows rust from water ingress.

The freewheel can also break, causing the motor to spin in place but no assistance is applied:

Note the crack in the bottom half.

The gen 2 motor isn't very tightly wound, there is room for more power density:

Gen 3 motors

The gen3 Active Line and Active Plus are identical inside. Same mechanical parts, only limited by the firmware. Polymer gear. The Performance Line has a steel gear, but this makes the motor rotor the weakest link. Bikes with speed chip are at risk here. We can fix it, but it's not done by many other shops.

These motors also have a common failure mode with their power supply.

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