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BMW 5 Series Battery Pack – Reconfiguring The Modules & Wiring

Mounting Board
Mounting Board

Now the cell modules have been removed from their original home, it’s time to get them repurposed! A custom mounting board has been constructed from timber, and the modules mounted on them. To say this assembly is heavy would be an understatement – it’s barely a two-man lift!
As assembled in the car, the pack as 96S1P, with every cell in series. As we need a low voltage bus, the modules have been reconfigured for 4S4P, in total this makes 4S24P with all 6 modules bussed together. As the cell interconnects are laser welded, some ingenuity was required here.
It turned out the best method (and the safest, to avoid any swarf shorting out cells!), was to use a grinder to cut off the top of the loop on the aluminium interconnects, separating them.

Battery Bus Links
Battery Bus Links

12 5-way bus bars have been installed on the board, and 25mm² cable links them together. To get the angry pixies from the cell modules, 8mm² flexible silicone cable has been used, 4 links to a bus bar. This setup should provide more than enough current capacity.

Cell Connections
Cell Connections

Here can be seen the cell interconnects – and the grinder cuts to separate them where required to break the module up into 4S strings. As the interconnects are Aluminium, special solder was required to get the copper cables soldered down, in my case I used Alusol 45D solder, which contains a very active flux capable of stripping the oxide from the Aluminium.

Batteries Wired
Batteries Wired

Finally, here is the new pack, all connected together. All that needs to be done now is the balance wiring loom, which will allow the BMS to sense each cell voltage individually, and connection of the BMS, Coloumeter & fuses, this will all be covered in a future post!

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nb Tanya Louise Heating Upgrades – The Pumps

 

Pierburg WUP1
Pierburg WUP1

With some recent upgrades to the boat’s heating system, the hot water circulation pumps we’ve been using are becoming far too small for the job. After the original Johnson Marine circulation pump died of old age (the brushes wore down so far the springs ate the commutator) some time ago, it was replaced with a Pierburg WUP1 circulation pump from a BMW. (As we’re moored next to a BMW garage, these are easily obtainable & much cheaper than the marine pumps).

WUP1 Cutaway
WUP1 Cutaway

These are also brushless, where as the standard Johnson ones are brushed PM motors – the result here is a much longer working life, due to fewer moving parts.

The rated flow & pressure on these pumps is pretty pathetic, at 13L/min at 0.1bar head pressure. As the boat’s heating system is plumbed in 15mm pipe instead of 22mm this low pressure doesn’t translate to a decent flow rate. Turns out it’s pretty difficult to shove lots of water through ~110ft of 15mm pipe ;). Oddly enough, the very low flow rate of the system was never a problem for the “high output” back boiler on the stove – I suspect the “high output” specification is a bit optimistic.
This issue was recently made worse with the addition of a Webasto Thermo Top C 5kW diesel-fired water heater, which does have it’s own circulation pump but the system flow rate was still far too low to allow the heater to operate properly. The result was a rapidly cycling heater as it couldn’t dump the generated hot water into the rest of the system fast enough.

The easiest solution to the problem here is a larger pump with a higher head pressure capability. (The more difficult route would be completely re-piping the system in 22mm to lower the flow resistance). Luckily Pierburg produce a few pumps in the range that would fit the job.

Pierburg CWA-50
Pierburg CWA-50

Here’s the next size up from the original WUP1 pump, the CWA50. These are rated at a much more sensible 25L/min at 0.6bar head pressure. It’s physically a bit larger, but the connector sizes are the same, which makes the install onto the existing hoses easier. (For those that are interested, the hose connectors used on BMW vehicles for the cooling system components are NormaQuick PS3 type. These snap into place with an O-Ring & are retained by a spring clip).
The CWA50 draws considerably more power than the WUP1 (4.5A vs 1.5A), and are controllable with a PWM signal on the connector, but I haven’t used this feature. The PWM pin is simply tied to the positive supply to keep the pump running at maximum speed.

Once this pump was installed the head pressure immediately increased on the gauge from the 1 bar static pressure to 1.5 bar, indicating the pump is running at about it’s highest efficiency point. The higher water flow has so far kept the Webasto happy, there will be more to come with further improvements!

CWA-50 Pump Teardown

CWA50 Cutaway
CWA50 Cutaway

Above is a cutaway drawing of the new pump. These have a drilling through the shaft allows water to pass from the high pressure outlet fitting, through the internals of the pump & returns through the shaft to the inlet. This keeps the bearings cool & lubricated. The control & power drive circuitry for the 3-phase brushless motor is attached to the back & uses the water flowing through the rotor chamber as a heatsink. Overall these are very well made pumps.

Impeller
Impeller

Here’s the impeller of the pump, which is very small considering the amount of power this unit has. The return port for the lubricating water can be seen in the centre of the impeller face.

3-Phase Driver
3-Phase Driver

Inside the back of the pump is the control module. The main microcontroller is hiding under the plastic frame which holds the large power chokes & the main filter electrolytic.