Tag: 221-2411

Wago Inline splicing connector with lever
https://www.wago.com/global/installation-terminal-blocks-and-connectors/inline-splicing-connector-with-lever/p/221-2411

Building a battery case for an 16s Eve LF280K configuration

The other day, I realised that I never wrote about the case build of our 16s 48V batteries, as I did for the 8s case and the 4s case. So, here it is – and I am actually describing 2 revisions as we made some adjustments.

First, the total weight of the cells alone would be roughly 16 * 5.3kg ~ 85kg. This is way beyond what a single person can – or at least should – lift. So, I deciced to split the battery into 2 separate cell blocks of 8 cells each (similar as I did split the 8s battery in the Toyota HiAce). With this approach, I would be able to:

  • reuse the 8s design (including the RAKO boxes)
  • be able to move or lift half a battery (which weighs roughly 53kg)

This battery has a nominal capacity of 3.2V * 16 * 280Ah = 14'336Wh and can be charged or discharge with up to 140A ^= 7'168W. We currently have 2 of these batteries running on our 3-phase setup with 3 * Victron MultiPlus-II 48/5000/70-50.

So essentially, I built 2 8s batteries with a connection cable between cells 8 and 9. The main negative and the BMS would be in one box and the main positive with the DC breakers would be in the other box. To avoid confusion, in this setup I went for coloured Anderson SB175 housings, with

  • Red
    2 * 35mm2 H07RN-F cable main positive
  • Grey
    2 * 35mm2 H07RN-F cable main negative
  • Blue
    Interconnecting both blocks
    2 * 35mm2 H07RN-F cable connecting from cell 9 positive to cell 8 negative

In all cases

16s Battery Connectors

To connect the cells to the BMS balancer cables I extended the balancer cables with 2.5mm2 wire via WAGO 221-2411 inline splicing connectors. I then measured the increased resistance of the additional cable length and adjusted the values in the BMS configuration for cells 1 to 9.

With these inline connectors I am now able to disconnect the blocks from each other so I can move them around independently, if needed.

On the BMS, I connected a USB RS-485 TTL adapater with a USB extension cable which leads to one of the USB ports of the Victron Cerbo GX. With the help of dbus-serialbattery and BatteryAggregator I can control the DVCC settings in Venus OS.

The rest of the build is, as I already mentioned, pretty much like the 8s build.

Revision 1

Here are some images of the completed build of revision 1.

16s Battery top view
16s Battery Block 1 main negative with BMS
16s Battery Block 2 main positive with DC breaker

Revision 2

These are the changes I am currently making for the next revision:

  • add additional connectors for the balancer cables to further facilitate the disconnection of both blocks;
  • use 16mm2 M6 Klauke DIN46235 compression cable lugs for the connection of the main negative (cell 16) to the B- of the BMS (only relevant to the older JK-BMS), to be able to disconnect and potentionally replace the BMS;
  • use a WAGO 35mm2 DIN rail connector in the main negative block on cell 1/9 for the outgoing cable;
  • use cable glands on the external connections;
    (this allows for easy disconnection and re-building the block as an 8s battery);
  • use ratchet straps for compressing and mounting the cells to enable easier maintainability of the cells;
  • use Anderson PowerPole PP180 connectors instead of SB175, so I can use mounting plates for the PP180 and do not have dangling cables on the outside of the case
    (these connectors are expensive and increase the price of the overall build by roughly 60GBP).

Building a battery case for a 4s Eve LF280K configuration

Based on our Eve 8s design, I made a sketch for a 4s 12.8V battery, which I could later connect to a Victron MultiPlus Compact 12/1600/70-16:

Wooden case for the 4s Eve LF280K battery

Again, this battery has a wooden inner case and sits inside a utz 400mm x 300mm x 325mm RAKO container.

There are a few differences however:

  1. There is no space for fuses inside the container
    (so it is more like a traditional battery);
  2. all bus bars are “bent” and not straight
    (we need three 35mm2 pairs, so six cables altogether);
  3. main positive and main negative are on the opposite sides of the cells;
  4. I use a JK-BMS B2A8s20P without soldered cables but with dual M6 threads
    (so I can use 35mm2 cables all the way).
utz RAKO 400mm x 300mm x 325mm container with wooden frame

To cut the plywood in an efficient way, I used a web site called cutlistoptimizer which gave me this result:

Cutting suggestion by https://cutlistoptimizer.com/

For this build, I planed all the boards after cutting, before putting in the cells. With this, I hoped to minimise the chance of any particles on the board damaging the cell insulation.

And for the small board at the short side of the case, I did also use 20mm plywood, but planed it several times until it I could just slide it in.

This is how the wooden case looks with the cells and insulation boards (shown in red):

Top view: battery cells with depicted insulation boards (shown in red)

Note: when using a JK-BMS I found it important to have the main negative connection point on the upper left (or lower right). Only with this orientation it was (relatively) easy to connect the cell to the BMS.

BMS connected to cells

It needed some fiddling to get the main negative cable pair to the BMS and the main positive cable pair out of the frame, as we can see from the image above.

The connection to the individual cells are fed through WAGO 221-2411 2 conductor inline splicing connectors. The holes into the top board were done with a forstner bit and a jigsaw. This version of the BMS can be fixed with four screws to the board (so no need for wire straps as with the 24s version).

Again, instead of a display I just used the pluggable power button that is connected to the display port of the BMS to power on and off the device.

In the end, I added Anderson SB175 connectors and 1383 (2AWG) contacts to both pairs and connected them to the inverter.

Battery connected to inverter

Some more details

  • All 35mm2 cables are Eland H07RN-F flexible rubber cable;
  • compression cable lugs are Klauke M6 35mm2 DIN46235;
  • cell contacts were secured with M6 serrated washers and M6 16mm steel bolts;
  • BMS threads B- and P- were secured with M6 lock nuts to M6 16mm steel bolts (with the bolt upside down);
  • cell wires from the BMS were fitted with uninsulated ferrules;
  • cell wires on the positive cell poles were fitted with ring lugs and a 2.5mm2 hookup wire;
  • I added handles to the SB175 connectors to facilitate disconnecting the cable pairs;
  • I added dust covers to the SB175 connectors;
  • all compression cable lugs and the SB175 were crimped with a Hilti NUN54-22;
  • all cable lug connections and Sb175 were heat shrinked;
  • I added 2*35mm2 cable pairs with SB175 connectors to the inverter by replacing the existing 35mm2 welding cable with M8 lugs (you still need M8 lugs on the inverter positive and negative terminals).

Things to improve next time

  • Mount the SB175 connectors to the outside of the container
    With this the lid can be closed and the cables and BMS are better protected against pulling;
  • add 3A inline fuses to the cell wires;
  • use 45° angled cable lugs for main positive and main negative to make it easier to get the wires routed outside the container;
  • feed an additional wire pair for the voltage sensor from the main positive outside the container to be able to connect it to the inverter (but I am not too sure about this, as I think the voltage drop on the 2*35mm2 connection is neglectable – it might better to add a temperatur sensor to the main positive):
  • maybe add protective wire sleeves to the SB175 connectors (but they are quite expensive):
  • add a Victron MK-3 USB-C interface with RJ-45 cable into the case (to be able to restrict AC power on the inverter).

What did it cost?

Cost calculation for the 4s battery including case and inverter

Summary

This case is not as complete as the 8s version – due to its form factor. Neither the inverter has an RCBO nor the battery has a DC MCB. This has to be added separately (incurring additional cost and space). As written above, the 4s version is more like a traditional battery. However, the form factor is quite compelling; 3.5kWh in 400mm x 300mm x 325mm case. Especially in combination with the compact edition of the Victron MultiPlus. And the cost (as always without labour) is very reasonable, as well.

The inverter delivers 1200W constant power – in my opinion, enough for a small and mobile electricity build. Runnig a Krups Inissia Nespresso machine is not a problem, and boiling water with our 1000W immersion heater neither. Worst case, you could also run a 300W infrared panel heater for more than 11 hours.

One drawback of the inverter is probably the relatively small charger. With 70A at 12V it can only charge the battery with around 840W. This is certainly not the problem of the battery which would support charging up to 1344W.