[LithiumaniacsEVRacing]

I am looking for input from all on this issue. Most pouch cells are designed with one tab copper (negative) and the other aluminum (positive). I have read there are issues when connecting aluminum to copper, so what about using copper blocks for the copper tabs and aluminum blocks for the aluminum tabs?

[etischer]

At some point, copper needs to connect to aluminum if you're going to connect cells in series. I would use tin plated aluminum blocks. That seems to be the standard for electrical connectors that are compatible with both aluminum and copper wire.

[LithiumaniacsEVRacing]

Yes, you have a very good point, but we have 10 cells in parallel all using blocks to connect. 9 blocks of aluminum would sure save some weight.

Tin plated aluminum sounds interesting.

Originally Posted by etischer

At some point, copper needs to connect to aluminum if you're going to connect cells in series. I would use tin plated aluminum blocks. That seems to be the standard for electrical connectors that are compatible with both aluminum and copper wire.

[LithiumaniacsEVRacing]

Found this info researching copper to aluminum connections:

The answer is that as the metal wires heat and cool, they expand and contract. Copper and aluminum expand and contract at different rates, so when you put them together under 1 termination point (as in a wire nut), it tends to loosen that splice up over time. This is where potential problems can occur. So one of the biggest differences about the AlumiConn is in its unique patented design. Using an AlumiConn connector keeps the dissimilar wires separated, but connected through a tin-plated aluminum block inside the connector. The tin-plating of the internal aluminum block, along with a secure mechanical connection, provides a much cooler, safer splice – completely and permanently repairing the problem.

[LithiumaniacsEVRacing]

One way to secure the connection might be to use a lock washer on your bolt connecting the tabs, when the expansion and contraction happens this will maintain a tight fit.

Originally Posted by LithiumaniacsEVRacing

Found this info researching copper to aluminum connections:

The answer is that as the metal wires heat and cool, they expand and contract. Copper and aluminum expand and contract at different rates, so when you put them together under 1 termination point (as in a wire nut), it tends to loosen that splice up over time. This is where potential problems can occur. So one of the biggest differences about the AlumiConn is in its unique patented design. Using an AlumiConn connector keeps the dissimilar wires separated, but connected through a tin-plated aluminum block inside the connector. The tin-plating of the internal aluminum block, along with a secure mechanical connection, provides a much cooler, safer splice – completely and permanently repairing the problem.

[LithiumaniacsEVRacing]

Another issue that I keep reading is the amount of current aluminum can carry compared to copper is much different. It seems the blocks would need to be much larger if I went with aluminum.

Originally Posted by etischer

At some point, copper needs to connect to aluminum if you're going to connect cells in series. I would use tin plated aluminum blocks. That seems to be the standard for electrical connectors that are compatible with both aluminum and copper wire.

[steven4601]

The amount of current you can pass through a conductor depends also how long you wish to do that at which duty-cycle. Drag strip duty cycle is small and the duration is also.

Even though im about a megawatt short of what you are doing, I calculated the energy dissipated in my cell interconnects. I chose 100 seconds max for full power and used that as my thermal time limit for the interconnects to heat up a certain amount of Fahrenheit/Kelvins. This output from the calculation allowed me to use very thin copper interconnects. 0.5mm thick strips of 20mm wide @ 100Amp per cell. Length doesn't matter as volume & powerloss goes up linear with length.

[rwaudio]

Originally Posted by LithiumaniacsEVRacing

Another issue that I keep reading is the amount of current aluminum can carry compared to copper is much different. It seems the blocks would need to be much larger if I went with aluminum.

Don't get too caught up in this, since one of your cell tabs is already a thin aluminium strip. There are plenty of online calculators that will give you a voltage drop for a certain cross section at a given current. You can compare copper to aluminium easily.

One thing that I have learned from my connection method is that I have slightly higher than expected/wanted connection resistance due to the simple quantity of connections in series.

Using my method you would have the tab of the 1st cell connected to a block, connected to the tab of the 2nd cell, connected to a block, connected to the 3rd cell etc. Cell one and Cell ten would be many connections apart (I only have a 3P set up and at 1000A I can measure a small voltage difference between the cell one tab and cell three tab)

In short if you can devise a method where tab one, two....ten are all connected to a single electrical point then I think you would have lower loses and less sag in the pack.

I have my pack apart anyway for capacity measurements I'll be putting it back together a different way to avoid/reduce this problem.

[EVfun]

Originally Posted by rwaudio

Don't get too caught up in this, since one of your cell tabs is already a thin aluminium strip. There are plenty of online calculators that will give you a voltage drop for a certain cross section at a given current. You can compare copper to aluminium easily.

I just wanted to point out that not all aluminum is equal. The conductivity of aluminum alloys varies widely from that of electrical grade aluminum. 6061 has about 70% of the conductivity of pure aluminum, 5052 only about 60% of the conductivity of pure aluminum, and 7075 only about 50% of the conductivity of pure aluminum. It isn't hard to get electrical grade copper but more difficult to get electrical grade aluminum. I think all the 1xxx series alloys are pretty close to the conductivity of pure aluminum. They are often harder to find.

[LithiumaniacsEVRacing]

I have found two grades of aluminum in bus bars that are very conductive:

Grade 6101
Grade 1350

It seems the 1350 is more conductive, anyone know the difference in these two alloys?

Originally Posted by EVfun

I just wanted to point out that not all aluminum is equal. The conductivity of aluminum alloys varies widely from that of electrical grade aluminum. 6061 has about 70% of the conductivity of pure aluminum, 5052 only about 60% of the conductivity of pure aluminum, and 7075 only about 50% of the conductivity of pure aluminum. It isn't hard to get electrical grade copper but more difficult to get electrical grade aluminum. I think all the 1xxx series alloys are pretty close to the conductivity of pure aluminum. They are often harder to find.