There is voltage drop in every conductor, and there will be more drop in the long (10 foot) connection between modules than in the shorter connection, but since it is a series connection between pairs of modules that won't matter to the balance between modules - the current goes through each of them, and that's the important part.
Posts by brian_
1 - 9 of 39 Posts
So it's a 10S6P module, assembled from 1S2P sections with 8 Ah cells. Then you're putting those modules in parallel pairs, which makes no sense to me... but that's not what you're asking about.
The parallel connections are done by bus plates. Because there is one pair of threaded sockets for each pair of 8 Ah cells, in the 6P modules the plates have three rows of holes (at the ends) and six rows of holes (3 for positive one cell group plus 3 for negative of the next cell group); to reconfigure these modules to 5S12P you would replace those plates with plates twice as long (six rows of holes at the ends and 12 rows of holes for the other plates). With 5S12P modules you would then connect all modules in series for the same 30S12P overall pack. This would simplify the BMS substantially, but if the seller doesn't offer different sizes of bus plates (they don't appear to) you would need to custom-build the longer plates.
As you get the modules from Battery Hookup them, each module is wired the way the Orion diagram suggests - that's good. What you are proposing to do is connect each module in parallel with another module, which is not suggested by the diagram.
Yes, that avoids any balance issues between modules and cuts the BMS complexity in half.
The "side view" bit doesn't apply any more.
That's 6P, and that's what he already has. To configure his battery as desired, without parallel modules, he needs 12P.
Interesting things about that busbar:
- I didn't see it when I looked, but I didn't check all of the categories
- checking all BatteryHookup products, there are only 4P and 6P intermediate plates and 6P end plates (mis-labeled as 3P)... no end plates for 4P, no plates for larger numbers of cells in parallel
- the construction is bizarre: as seen in any of the photos of these modules there is a notch in the plate exposing a copper section where the BMS tap is attached; this description suggests and the photos confirm that it is a copper plate with a steel plate over top, with the steel acting essentially as a big common washer
- the steel-on-copper construction is only for the intermediate connections, while the end cells are terminated with copper plates that extend to the module terminals (no steel)
Yes, that would work (after disassembling the module and re-orienting the cells into 12P groups, of course), but the extra electrical connections would be undesirable.
With 100 amp-hour combined cell group capacity, 1000 amps (10 kW/kWh, or "10 C" discharge rate) even momentarily would be aggressive for any EV cell, and especially for these cells which are intended for backup power applications. Even 400 amps is 4 C, which is much too high for a battery without any cooling at all.
For an illustration of reasonable rates:
The Nissan Leaf has cells intended for EV use, but no active cooling. All variants have fundamentally the same motor, but the peak power allowed depends on the battery:
- 24 kWh battery: 80 kW maximum, 3.3 kW/kWh
- 30 kWh battery: 80 kW maximum, 2.7 kW/kWh
- 40 kWh battery: 110 kW maximum, 2.8 kW/kWh
- 62 kWh battery: 160 kW maximum, 2.6 kW/kWh
10C (now that you know what "C" means, including that it makes no sense dimensionally) is wildly inappropriate, and 3C is optimistic by comparison with well-designed production EVs... so why would 5C be appropriate without liquid cooling? The module cases are plastic, so air cooling will be very ineffective.
An interesting spec. No reasonable person would claim that an 8 Ah cell can handle 200 A continuous and 400 A intermittently; those are the specs from the retailer (Battery Hookup) and are given by various retailers, but the cell manufacturer isn't even known, and I really doubt that they would claim those rates if you could find them (the images of these cells that I have seen have labels without any indication of the manufacturer).
Apparently these "SPIM08HP" cells are widely used for DIY e-bikes. If getting incredible discharge rates was just a matter of buying hobby-grade cells, all the EV manufacturers would use them... but of course they don't. I don't have any reason to believe that there's anything wrong with the cells, but I also don't have any reason to believe that they can perform any better than production EV cells... so my guess (and it's just a guess) is that it might be reasonable to plan on 3C peak without active cooling, and much less continuous.
1 - 9 of 39 Posts
