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 view16s Battery Block 1 main negative with BMS16s 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).
Now, that we got our Toyota HiAce we thought it might be a good idea to add more power to the vehicle: in form of an 8s EVE LF280K LiFePO4 battery and a Victron MultiPlus Compact 24/1600/40-16 inverter/charger. In the following, we describe our setup and the reason why we built it like this.
The Requirements
The sustained output power of the inverter must be over 1'200W.
Charging via AC via EVSE or generator must be possible.
Charging via alternator must be possible (but is not the norm).
Charging of 60% of the battery (from 20% – 80%) via AC should take less than 180min.
The installation should use the minimum amount of space possible.
We should be able to use our existing Eve LF280K cells, thus limiting the overall current to 140A.
As the vehicle will not have a diesel heater, it should be possible to run a 150W infrared heater for at least 3 * (4+2)h = 18h (^= 2'700Wh).
In addition, the battery should be able to run a refrigerator with an average power consumption of 50W for at least 72h ^= 3'600Wh (next to other power consumption).
Design Considerations
With a maximum current of 140A and a cable run length of 1.5m, we should plan with a cross section of at least 35mm2.
Basically, with Eve LF280K cells we have three choices regarding the battery size:
1* 4s (“12V”) Configuration 4 * 3.2V * 280Ah = 3'584Wh This would lead to a required nominal AC charge power of at least 716.8W/h and a charge current of at least 56A/h.
2* 4s (“12V”) Configuration 2* 4 * 3.2V * 280Ah = 7'168Wh This would lead to a required nominal AC charge power of at least 1'433.6W/h and a charge current of at least 112A/h.
1* 8s (“24V”) Configuration 8 * 3.2V * 280Ah = 7'168Wh This would lead to a required nominal AC charge power of at least 1'433.6W/h and a charge current of at least 56A/h.
The Victron MultiPlus Compact xx/1600VA inverter/charger provides enough sustained power output (while being smaller than the non-Compact edition). Depending on the voltage of the battery, this will slightly impact the amount of charge current.
To charge the battery via the alternator we would need a DC/DC converter that depends on the battery configuration as well (either 12-12 or 12-24). So, let’s have a look at the battery first.
1* 4s (“12V”) Configuration
The smallest, lightest and cheapest configuration. But capacity requirements regarding the fridge are only fulfilled, if there are no other loads. In addition, the discharge current is relatively high (scratching the maximum discharge rate of 0.5C).
2* 4s (“12V”) Configuration
More complex setup, as each battery needs a separate BMS, which leads to the need of an aggregator for both batteries to correctly report SoC and calculate CCL and DCL. In addition, more cabling and fusing is required (and probably to a large bus bar). Comes with the advantage of having a redundant battery in case a single battery fails. Most expensive configuration.
1* 8s (“24V”) Configuration
Custom battery build needed, as there is not enough space for a typical 2 * 4 cells setup behind he seats. But, only a single BMS and thus less wiring is needed. Comes with a slight disadvantage of not having native 12V from the battery. This is actually not an isse, as all our DC devices also accept 24V. Cells can better balance voltage differences across a single 8s bank.
The Setup
In the end, I decided for the 8s configuration, due to less complexity. Splitting the 8s configuration across two cell blocks seemed to be an acceptable compromise.
As a regular MultiPlus 24/1600/40-16 would not fulfill my AC charge requirements, I had to decide to either add a second MultiPlus or to add a dedicated charger. I opted for a Phoenix Smart IP43 Charger 24/25 instead of a second MultiPlus. The MultiPlus in parallel would always consume 10W though most of the time I would not need the output power. Whereas, the Phoenix would only need power, when connected to AC. And reconfiguring the MultiPlus every time I charge was not an option for me. And yes, I lose redundancy – but also save some money (Phoenix is much cheaper). So, in the end the nominal charge power is 40A + 25A = 65A, which lets me charge at 1'560W reaching 60% within 165min.
The HiAce comes with a 70A alternator, so I chose a Orion-Tr Smart 12/24-15 DC-DC Charger. With this charger, I could run the engine in standby and still have the car heater running. And this is probably the predominant use case (if charging via alternator at all).
For the DC bus bar I went for a Victron Lynx Distributor, so I could use and install MEGA fuses. Having a 1’000A bus bar seems certainly overkill, but a separate bus bar and fuse box that accepts 35mm2 cable and MEGA fuses would be not be much smaller.
I changed the existing AC inlet of the HiAce to Neutrik PowerCON True1 TOP (congrats to the marketing department, I am still amazed how this name rolls of the tongue) and installed 2 Siemens compact 16A CRCBOs (external AC in, internal AC out). I am aware that theoretically I could support more than 16A on the internal AC out (via PowerAssist). If ever needed, I can replace the RCBO with a 20A version.
I added a VE.Bus Smart Dongle to the MultiPlus and opted against a complete (Raspberry-based) GX installation. The reason, I keep a USBMK3 with me anyway (in case I need to reconfigure the MultiPlus) and still have (Bluetooth) access to the most important settings and information of the MultiPlus. With the GX, I would to be running a WiFi hotspot (and consuming more energy as well). The disadvanage of not being able to use DVCC with information from the BMS is clear to me and accepted.
I selected a B2A8S20P JK-BMS that has an integrated 2A balancer and an RS485, CAN and heat port. In case, I ever add a GX device, I am still able to connect them and use DVCC.
The Specs
Nominal power (“capacity”) 8 * 3.2V * 280Ah = 7'168Wh
Maximum discharge power 1’600VA (1'280W, capped by the inverter) with a maximum current of 80A/63A/55A (at 2.5V/3.2V/3.65V)
Maximum AC charge power 1'560W
AC Charging from 20% – 80% in 165min
Maximum DC charge power 360W
MultiPlus self-power consumption 10W
The Build
As mentioned before, due to space constraints I had to split the battery in 2 parts (with each having 4 cells). Instead of using utz RAKO boxes I used 12mm (sanded) plywood which I did not screw together but tied down with a banding/tensioning tool and a ratchet strap. With this setup, I can easily access und disassemble the cells if needed, while still having a sturdy case. Both cell blocks are connected with a (blue) Anderson SB175 connector.
The BMS itself is mounted to the side of one of the cases (I took extra care to use short screws, in order not to drill into the cell casing). I used M6 Weidmüller 35mm2 90° angled compression cable lug to get the wire away from the BMS and into the bus bar. All other compression cable lugs are DIN 46235 from Klauke (M6 35mm2 on the cells, and M8 16mm2/35mm2 on the bus bar).
The AC and DC wires are all Eland H07RN-F (except for the last two points):
Charger to bus bar, battery to bus bar: 35mm2
Cell block to cell block: 2 * 35mm2
Alternator to DC-DC converter, DC-DC converter to bus bar: 16mm2
External AC in to RCBO, RCBO to inverter/charger (both directions), RCBO to internal AC out: 3G2.5mm2
For the connection of the Inverter/charger to the bus bar, I used the Victron installed 25mm2 welding cables.
Images
The installation is barely visible behind the seatsView from the back with preliminary wiringConnection of cell blocks with SB175 connectors, cell block 2 and DC-DC converterLynx Distributor with cell block 1Inverter/charger with space for second charger and cell block 2 (left)
Note: the Phoenix charger is not visible on the images, as I am still waiting for it to be delivered.
Charging via EVSE
Conclusion
We now have more than 7'000Wh of additional energy without losing any storage space for roughly 2'850 CHF/2’500 GBP (parts without labour). We can survive an extended weekend of 72h without recharging while still being able to enjoy amenities as using a coffee machine, heating and refrigerator. In case of longer periods of usage, we can recharge at any EVSE, or via shore power. And in emergencies, we can also charge via our Honda EU10i or via the alternator of the vehicle.
The battery is placed directly over the engine which helps in cold weather conditions to easily warm up the batteries to a chargeable level.
Out of the box the MultiPlus comes preconfigured with a pair of 1m35mm2 (2AWG) welding cables (and as a side note: with unusually thin M8 cable lugs).
When connected to a 12V battery based on 4s Eve LF280K cells, the maximum current drawn can go beyond the recommended 0.5C rating – especially when the cell voltage decrease under the nominal 3.2V or the total cable length is longer than 1m. Using a larger inverter or smaller cells will make things even worse.
And when we look at Victron’s Recommended battery cables document, we see that they are recommending 50mm2 for currents up to 150A anyway (for cable lengths of up to 5m).
For a 1m cable the theoretical voltage drop is within their recommended range of 0.259V. But they explicity state that resistance leading to additional voltage drop due to contacts is not calculated into the recommended cables size.
Already a cable size of 2m will lead to over 3% and 0.3V voltage drop when the cell voltage is only 4* 2.6V = 10.4V (and by default raise a “Low Voltage Alarm” on the MultiPlus). And even a cell voltage of 4* 2.75V = 11V is close to 3% and over the recommended threshold (of course, calculation is based on full inverter load of 1600VA). Besides Victron explicitly recommends a voltage drop of under 2.5% in their Wiring Unlimited document.
So why is Victron fitting the inverters with only 35mm2 cables? Especially since they are using welding cables that are only rated up to 60°C. I do not know.
But I do know, how I can fit an additional 35mm2 pair into the inverter and minimise a potential heating problem.
Adding a second pair makes particular sense at least in my case, as I am using a JK-BMS and Eve cells that both come with two M6 terminals per connection point. So running two cable pairs to battery and BMS saves me from using a bulkier and stiffer 70mm2 cable that I would have to split at the BMS and main positive cell anyway. And with that, I can still use the Anderson SB175 connectors with regular housing and 1383 wire contacts and without having to resort to 2/0 housings and 1328G1 wire contacts.
The inverter comes with 30mm holes in the front panel where the supplied cable is fitted with an M25x15mm cable gland (side note: why are they using IP68 glands when the whole inverter is only rated at IP21). Eland H07RN-F 35mm2 cable has a diameter of 14.6mm, so actually two of these cables do not fit through the holes at once.
But as the cable lugs are actually that long that they stick out of the chassis the required diameter is 2* 12.5mm = 25mm which is just the size of the hole. When wrapped in heat shrink we need some more space. And certainly we want a little bit of head room, so the cables do not scratch against the metal when moving.
So, the M25 holes had to be enlarged slightly to make space for the double cable lugs as seen on the picture below. I used a Hilti GDG 6-A22 grinder for this. I covered the inverter to prevent metal splices and dust getting inside (board, circuity) of it. And I added extra insulation around the cable lugs to prevent them cutting into the metal.
Bottom side of MultiPlus with enlarged holes and extra cable insulation
Mounting the cables to the connection points is done with two Klauke M8 35mm2 DIN 46235 compression cable lugs (back to back).
Note: the compression cable lugs from Weidmüller will not fit, as their connection plate is too long.
Instead of the factory supplied washers, spring locks and nuts, I use M8 serrated washers and lock nuts. As the negative connection point (which is directly under the 250A MEGA fuse) is around 2mm higher than with only one cable lug, I added an additional (copper) washer under the fuse terminal to make more space.
I could cover the original bolts with insulation tape to prevent accidental contact with the chassis when squeezed (but this is something that could have happened even before).
Victron MultiPlus Compact 12/1600/70-16 with dual 35mm2 battery cables
Now we have a 2* 35mm2 = 70mm2 connection to our battery as seen below.
2* 35mm2 connection between battery and inverter
So the voltage drop over the whole cable (1.5m from invert to battery with 70mm2) should be around 114mV:
Voltage drop at different cell voltages
So as it seems, the main difference between the larger and the smaller cable is the power loss (17.22W vs 34.44W at full power or 15W vs 30W at 0.5C). So all in all we save nearly 0.84% battery capacity per cycle with the thicker cables (which is 5000Wh over the whole cell life) – probably less than we spend on the cables and lugs, the labour and the time to do the calculation and writing up the article …
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.
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):
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.
In one of our previous articles, we stated that, due to power, weight and size, we would rather go for a 24V 8s (280Ah) battery configuration instead of 48V 16s.
However, there are relatively few battery cases for 8s battery packs that fit our Eve LF280K cells. And they are pricey! So, instead of spending a 500+ USD per case, I was thinking to repeat what others have done before me: build a case myself. And certainly, I took inspiration from variousothers and commercialkits.
So first, here are my requirements:
Case must fit 8 EVE LF280K cells including all electronics and cabling such as BMS, MCB, GX.
Battery must be pluggable to the inverter via Anderson SB 175 connector. Check: why not use Amphenol sockets/plugs?
Case must not absorp moisture/liquids that would build up from below.
Case must have no external display or buttons (i.e. solid walls).
Cells must be insulated against each other.
Cells must be fixed to the case so the do not fly around when the box is moved.
Battery status should be readable from the box itself (optional).
The case should be usable independant of any BMS.
Battery is meant to be used 1:1 with a single inverter.
Battery must have an integrated MCB that can also act as a mains switch.
Basic considerations
Zerobrain – LiFePO4 – ALLES und noch viel mehr über Lithium Akkus
Of course, there are more questions to be answered. And I took a lot of inspiration and advice from the discussion above and came to these conclusions:
Fire resistance The cells should not involve themselves in a “chain reaction” if a cell becomes faulty. The critical temperature of the cells starts at around 90°C. If something is really getting sideways, the resin board will not withstand any of that at all. But as the battery case will be contained either within an aluminium container or directly inside in an aluminium box, I will take that as a mitigation (only the brave).
Moving and lifting the cells should have a weight of roughly 8* 5.5kg = 44kg; the 20mm resin board weight roughly 3.34kg (13.67kg/m2); BMS, MCB, cables, lugs etc might add another 3kg; the Rako(R) box has a weight of 2.35kg; resulting in a total weight of 52.69kg – which certainly is over the official limit of 32.5kg to be lifted by a single person – but still doable if one has to. For moving the battery box around I have a trolley where the RAKO box just fits on.
Compression Initially I thought, I would *have* to compress. But according to the above video, it seems the is only needed (or recommended) during the initial charging of the cells (to minimise gas bubble inside the cells). And from then on, it is not *required* for a safe operation of the battery, but instead might contribute to an extended cell life – how much? we do not know. So, I will probably only slightly compress the cells by placing them firmly into the frame inside the box.
Layout
So, I started with some sketches in FreeCAD and came up with the follwoing layout.
It should be possible to fit 8 EVE LF280K batteries in a 600mm x 400mm x 325mm RAKO box and still have space for the electronic components. Inside the plastic box there is a wooden structure, so the weight of the batteries is better balanced (the plastic floor might like this).
Batteries will be insulated against each other and fitted with sponge strip. Internal cabling will be fed through the lid where the BMS is mounted on. Cables to the outside (VE.Bus, 2*35mm2 DC, 2* 3-core AC) will be fed through the side wall.
Empty utz RAKO box 600mm x 400mm x 325mmBox with batteries and electronic components on topView of frame with cells inside box
BMS Cabling
I am going to use a 150A JK-BMS for the battery which comes with 2 pairs of 7 AWG wiring (approx. 10.5mm2 per wire). As I am going to have a mximum current of 150A (at 20V; or 117A at 25.6V) this will result in a voltage drop between 0.1% and 0.2% on the BMS cable. For the rest of the cable to the battery I will use a 50mm2 that results in an additional max 1% of voltage drop. The actual connection to the batter will be done via an Anderson SB 175 connector.
The individual BMS cell wires will be fed through a WAGO TOPJOB S 3-conductor through terminal block (with a separate fuse) (or I use a WAGO 2-conductor fuse terminal block – don’t know yet). With this I can easily connect and disconnect the individual wires from/to the cells. And with the 3-conductor terminal block if needed, I can later add an additional balancer to the system without having to rewire the cells either.
The cells will be wired in a regular 8s cconfiguration to the BMS. Both voltage sensors will be placed in the middle of the batteries.
Bus bars
My Eve LF280K cells have 2 M6 thread for each pole. The bus bars that came with the cells (cross section is 2mm * 20mm) were not flexible and only suitable for connecting the poles on the long sides. However, with my 8s configuration, I need 4 connections on the short side and 3 connections on the long side of the cells.
So, I created my own bus bars with the help of 2* 35mm2 DIN46235 M6 cable lugs per connection.
Dimensions: short side 30mm + 29mm; long side 30mm + 80mm (cutting at 30mm for the cable lugs to be crimped).
The Build
So, I with this information I started the actual build. And certainly I made some adjustments to the layout. This is what it looks like:
Case with all the cells on one side
As you can see, I moved the batteries to one side. With that I have more space on one end to install a MCB and leave room for cables.
Updated drawing with cells on one sideWago fused terminal blocks for connecting the indivisual cell wires
Connection of the BMS to the cellsCase with cells covered
The BMS rests on a board that can be fixed to the side walls. I intentionally left some space between both boards to have room for the temperature sensors. On the right hand side, we see the BMS wires connected to the terminals. With this it is easy to see which cable goes where. I could have cut the BMS wires. Maybe I will do this later.
As the DC cables were quite stiff, I used a screw to support a 90° angle on the cable going out of the box. The screws are fitted with electrical insulation wire. Let’s see how long this holds up.
Victron MultiPlus-II 24/3000/70-32 with Neutrik connectors
The inverter now has Neutrik panel connectors. I used a 24mm and 29mm hole saw for this. With this I do not have AC cables hanging out of the inverter. The connectors are rated for 16A (VDE) or 20A (UL). I set the maximum current on the inverter settings (as the inverter supports up to 32A which is beyond the capabilities of the socket).
Of course, the DC cable is still present. Maybe I can install a socket for that as well.
Inverter with battery
Above you see the “final” case. The battery is connected via Anderson SB 175 to the inverter. The battery cables fits into the case when not in use.
Not seen on the picture. The inverter has been fitted with a Siemens 16A RCBO for AC out. And inside the case is a non-polarised Thomzn 125A DC MCB.
The BMS charge and discharge current is set to 125A (though the inverter only supports up to 70A, and in reality only seldomly charge with more than 63A).
The Specs
With this inverter/battery duo, I have a system with a nominal power of 7168Wh that can deliver 2400W of constant power (below the 0.5C rating of 140A). Down to a cell voltage of 3V I can make use of the full power (then running at 125A). As the current minimum cell voltage is configured to 2.55V I always have a minimum power of 2550VA (or 2040W). But in reality I have never seen all the cells at the minimum voltage at the same time.
The case weighs around 51+kg and the inverter is around 20kg.
The maximum charge current of 70A @24V result in a maximum charge power of 1680W. So theoretically it takes slightly over 4h to fully charge the battery. In reality we can expect the battery to be charged around 20% per hour. A real life test shows that within 3h we can charge from 20% to 85%.
The Aftermath
What went well, what went wrong? Here are some of my thoughts:
The case looks and feels solid when lifted. So I really think the weight will not by a problem, though the RAKO box is not certified for that weight. I think, I could have used even thinner plywood and that would have saved some additional space.
Moving the cells to the right made more space on the other side, so I was able to fit the DC cable with the Anderson plug into the case as well (in addition to a MCB).
Creating the bus bars was relatively easy. The cable is still quite stiff. And the longer bus bars bend over the edges. That is why I had to add an extra piece of board to the sides.
The JK BMS wires are very fine strained and hard to get into the lugs (it literally took me over an hour to connect the 4 wires).
The addition to the fused terminal blocks makes the cabling much cleaner. But the WAGO terminals are not cheap.
Unfortunately, with my JK BMS the cables are soldered to the BMS and cannot be replaced. I think 2* 7 AWG is relatively small/thin. I would have preferred 2* 35mm2 (as for the bus bars). With the new JK BMS model there is the option to connect my own cable to the BMS.
This version of the BMS comes with a power button, making it much easier to turn it on than before. No need for a DC power source with higher voltage than the cells.
Fitting the cells into the case (with some compression) was easier than I thought. I used some insulation board between the rubber and the board to push it between the frame and the cells.
I actually do not use the RS485 option for this standalone installation. The BMS seems to take care of the the charge and discharge currents. And if I have really have to know the SOC, I connect via bluetooth to the BMS directly. And I only use the VE.BUS connection with the VictronConnect App when I want to change or limit the AC input current. For this I use the VE.BUS bluetooth dongle.
Having the Neutrik connectors makes it much easier to disconnect the inverter when moving.
Regarding the Neutrik panels on the inverter. I could not fit them in the holes where the AC wirng would normally go through, as the cable clamps were in the way. So I had to use the space between the ventilation slots. It is quite fiddly to get them screwed onto the cover. I used a 24mm and 29mm hole saw with M3 x 20mm hex bolts and M3 hex nuts for it.
The integrated RCBO saves me from having a separate elecitrical panel.
Maybe I change the DC connectors to Amphenol sockets as the SB175 is quite bulky. (update on this: probably not; they are quite expensive and only have 50+ connection cycles guaranteed; plus, it is not specified if they can be switched under load)
The cost
Here is a rough estimate of the accrued cost for this build:
Estimate for the material used for this build
If I only count the cost for the case (excluding cells, inverter, BMS) I come up with approx. 400CHF/450USD/350GBP/400EUR. So it seems, that I could have bought a prebuilt case for nearly the same amount of money, right? True. But … with this case, I have the exact dimensions that I want and with much less weight. And with the exact components I want. Plus, I can repair (if needed) everything by myself, as I completely know how it was built.
Let’s see what I will change on the next case I build.
Updates
Here are some hints and thoughts that arose after I wrote the article.
Getting the cells into place I used a 12mm marina plywood with an extra sheet of insulation board, so the board could “slide” (be pushed) between the frame and the cell. I used a planer with a depth of 0.5mm to cut away just as much so I could just firmly squeeze it in.
Frame and any wooden part in general It is a good idea to grind the surface of the wood facing the cells to remove any pieces sticking out that could damage the very thin insulation of the cells.
Insulation boards At first, I cut the insulation boards from a 250mm x 500mm board. I found it the easiest way to use a drawing pin to mark the cut and then bend it bothways. But this means we have to do 5 cuts for getting 3 boards – that takes time. So, I now have precut 170mm x 200mm insulation board with rounded corners. Much easier to handle.
Fixing the M6 bolts to the contacts I used an insulated torque ratchet wrench (4Nm) to tighten the bolts to the contact.
For the cable lugs I used Klauke M6 35mm and 16mm DIN 46235 cable compression lugs.
For the cell voltage sense cable I used 2.5mm wires (I know, 1.5mm would have been more than enough, but it was the only wire size I had). The JK-BMS supplied voltage sense cables were fitted with uninsulated ferrules, so they would fit into the WAGO 2002-1681 terminal fuse blocks.
Regarding cost The other day, I saw Pylon US3000 3.55kWh Lithium Battery being sold at CCL Components for 860.06GBP (excl. VAT). This includes a 19″ rack metal case, a BMS, connectivity and the cells and equates to roughly 269 GBP/kWh. Quite a bargain! Why making your own battery (case) any more?
I will replace the 24s BMS with an 8s version so I can use 35mm2 cable all along. Plus, I will use two pairs of 35mm2 cables from the inverter to the battery. That also means, I will have 2 separate 63A DC MCBs instead of a single 125A MCB.
Cutting the plywood
I found web site that offers help in cutting rectangles in a more efficient way that I could come up with: Cut list optimiser. The board for the case could be cut like in the image shown below.
The Caravan we got last year did not come with an inverter, so getting coffee in the morning or running a microwave was only possible when our main generator was running. And the installed battery for 12V support had a rather small capacity. This was clear to us from the beginning, as we eventually wanted to connect the Caravan to our EVE 280Ah cells.
But since we got our Starlink internet and our router did not seem to run easily on DC power, we needed -in addition to the temporary morning AC coffee spike – a more permanent AC solution.
Of course, first I updated the firmware of the inverter and configured it work with the battery:
Setting the AC input to 16A
Setting the battery type to LiFePO4
Setting the charge current to 70A (which is over the recommend amount of 50A, but see below for details)
As I did not want to connect a Cerbo GX to the system, I just used the VictronConnect App. Maybe I add a VE.Bus Smart dongle later on, or I connect some GX nevertheless. Who knows … Until now, it needs a wired connection to the inverter to see its status.
After powering on the generator, I confirmed everything was roughly working as expected. During the first run, the SOC was shown as 100% though the BMS of the battery internal saw it differently. In addition, the reported Amps and temperature were seen differently, as well. So, even that I set the inverter over the recommended maximum of 50A for the battery, the actual charge power was never much higher than the actual maximum).
This is what the inverter saw (100% SOC, 14.05V DC cell voltage, charging at 64A):
MultiPlus charging the Liontron battery via the generator
And this is, what the Liontron BMS reported (76% SOC, 13.8V DC cell voltage, charging at 55.5A):
The SOC as seen by the Liontron battery BMS
In the end, the BMS stopped charging when it thought its batteries were full. And the inverter did not complain. However, I noticed that the cells were really not in balance (with a delta of 200mV between the lowest and highest voltage).
Discharging was ok, as well. However, I soon realised that the 100A discharge current could not be achived in my setup. The inverter tried to draw power and the BMS cut off with a “Discharge over-current” (OCD). SO, still no coffee via our Nespresso machine (and no microwave either, for that matter).
So, what is the take away of all this?
It works and now, I can run the Internet all day.
All in all, it is a relatively simple and quick setup.
The Liontron battery does somehow not live up to its specs (and yes, I know the battery could be a size bigger for what I want to achieve; but I did not want to buy an additional battery for this temporary solution).
It is way cheaper and more flexible than to buy this “off the shelf”.
Maybe, I add a Victron SmartShunt to get a more accurate SOC reporting (as I do not see any other way to integrate the BMS with the inverter).
Charging of the battery is quite fast when running the generator.
Living in the north of the northern Highland comes with its own kind of specific “challenges” (as one would euphemistally phrase in today’s project world).
One of it would be that most delivery is only to “Mainland UK” which is sort of extends only to south of Inverness (which is only somehow understandable when one looks far back at the “Caledonian orogeny“). Anyway.
But even worse: Along with that delivery restriction comes the fact that there are also only very little shops with proper (or professional) selection of material up here. And this is also quite logical in itself. What could be sold in a shop, if nothing can be delivered to it?
This seems to have led to a “What we don’t have, you don’t need” attitude (no offence) and a supply:demand ratio that equates to higher sales prices.
So why am I writing this? I was looking for high current DC connectors for the battery systems I am making, I was looking to buy the Anderson Power Product SB 175 Connector. But the trusted (or only) electrician shop up here (CEF, a nationwide chain of 390 shops across UK) does not stock them, so I would have to resort to Mouser Electronics or Digi-Key Electronics for online ordering. There prices are about the same around 20 GBP per connector, which is not spent easily and about twice as much as other resellers or distributors charge (according to the Anderson web site).
In Switzerland I saw Distrelec selling compatible connectors under its house brand “RND Connect” for a converted price of 15 GBP (depending on the current exchange rate). This is not much of a saving taking into consideration that these are only rated for 175A instead of 280A.
And then there are numerous sellers on Aliexpress where we do not know beforehand what we actually get – but at a much lower price point.
So I went shopping to see the quality of the different manufacturers. My criteria for ordering were availability, low shipping cost and good reviews.
A selection of Anderson SB175 clones
I also ordered a shop with pre-manufactured cables and one with handles (where the price difference is even bigger).
I post an update when the items arrived and I had time to test them. So then we will see if these connectors can compete and are really compatible.
Our Journey to Scotland 