BMW i3, SimpBMS, Victron Multiplus 48v 5000 build


New member
Feb 10, 2021
My attempt to build a powerwall.

I will try and give as much relevant information that i can here.
I originally wanted to go for the Commercial Tesla Powerwall, but it can not be obtained in my country (Denmark). So i went for plan B.

I have an existing solar installation (multiple actually) Theoretical capacatiy at around 15 kwh mark, actual seems to be about 13kwh, I have a Growatt battery already, but it is under powered and has too little capacity.
So time to build my own.

I like everybody else wanted Tesla batteries, but they are quite expensive these days running at around 1200eur each. In the hunt i fell over SimpBMS, that supported Leaf and BMW i3 batteries. Both reasonable available. Originally wanted the leaf because of capacity, but found that the BMW was easier to locate and have shipped (Damn you Corona). Normally i would have driven to any place within about 1.000km to get the battery, but i cant.
Found BMW i3 battery on ebay, 3500 eur + shipping of about 400 eur.
In one of the SimpBMS threads i noticed another Dane (Lykke), he gave me some advice and one was to contact egomotor in Lithuania. They offered a 60ah pack for 3000 eur and 200 eur shipping. On Lykkes recommendation i also got the power cable from battery towards car (Great advice) for another 50 eur (i think it was).
The adventure was on.

Lykke gave me much advice and even managed to arrange that i could see his actual install, this helped immensely. He warned that the big parts may seem expensive, but many of the other components will end up costing quite a bit of money. He ended up being very correct.

Main purchase list:
BMW i3 60ah battery, if you can go for the 90ah one, seems like better bang for the buck.
Victron Multiplus II 48/5000
Victron DC-DC 48-12v
Victron Color GX (Thanks for selling me yours Lykke)
Victron Smart shunt 500a (may be to small i will learn soon)

Other than that there was things like:
Large diameter cable 35mm2 (from batterypack to inverter)
Minor diameter cable 25mm2 (internal in battery pack). Lykke said he used 16mm2, but my brain liked the 25mm2 better. No good reason....
8x Fuses (Lykke had 60a 58v fuses after each battery in the pack, so i followed), we both went for the MID, but it feels flimsy. May change this some day.
Busbar (Lykke said this was an expensive and a bit elusive part he was right. Ended up with copperbar that i milled myself, se more later).
Link connectors 35mm2 and 50mmw (bought 25mm2 but they didnt work well, se more later).
Connector rings 25mm2 and 35mm2 to connect individual batteries to busbar and to connect bmw control box to busbar. And for me also the smart shunt.
SERIOUS cable cutter (bought large single hand and a large dual hand)
SERIOUS cable clamper (dual hand se more later).
Combined DC fuse/breaker between batterypack and Victron multiplus. Expensive, again Lykke warned me.
Cable heatshrink 25mm2, 35mm2, 50mm2.
Protective cable shroud (approx 20mm2 i think)
Plexiglass (75cmx50cm, 5mm think) to build busbar "container", more later.

And then loads of bits and bobs, plus tools of a more generic term. I will do my best to illustrate, and remove as much as possible of my failures, so i dont confuse you too much. Ie. i severily over bought link connectors in 25mm2 that it is silly, and ran out of 35mm2.

I will try and add as much photos as i can without bombing the board completely.

One final note, my initial route was to look at the battery in its original configuration at 300v+ DC, and then have a Growatt inverter working against it.
Carel strongly recommended that i did NOT do so. Reason is that 300v dc is more serious than 300v ac. I personally still feel that it is the right way to go, but could not find enough documentation to prove it. I do believe that work is in progress enlighten the area.

Oh and i'm not an electrician, just a software geek that likes gizmoes.
Also i live in a country with strict regulations on electricity, so i will need to use an inverter that is on the "safe" list etc. Finally I will need to employ an electrician to verify and connect my setup to the Mains.


New member
Feb 10, 2021
Another little challenge, is that i need the powerwall to be grid connected, and therefore need a smartmeter to control flow.
When i started the EM24 seemed the only one available, which sucked because i allready have the SM630 for the Growatt.

I found a thread working on adding the SM630 into the open source part of Victrons software. and before i knew it they had completed the change. I have added it to my Color GX, it is not super clear where their software parts go "upload to your device".... ehm the inverter, the color gx the smart shunt, the SM630. Luckily some of the screenshots lead me to going for ssh access to the color gx, and that seems to be the right way to do it. I haven'nt tested it yet but will as soon as i get a few issues with can fixed. The can pinout in the SimpBMS for the i3 is not great, and i didnt quite get photos in the right angles of Lykkes setup. Im currently trying to measure out if i connected it correctly.

I have sourced most of my parts on, since they seem to be the ones that can help, after breexit has made close to worthless for smaller items.

I will add photos and steps over the next couple of days


Well-known member
Aug 23, 2017
Sounds like a well planned out system hard to go wrong with a EV battery. there a few here most have used either 48v or 60v dc. Hope to see photos soon.
later floyd


Sep 26, 2017
Your going to need to reconfigure the packs to 48v - you cannot use them with Victron gear at 300v ?


New member
Feb 10, 2021
So time to add some more information. (I'm struggeling with time on work, actually building it, and documenting it at the same time :)

Box arrived from EgoMotor, it about the size of a queen size mattress. approx 120cm wide and 180cm high. All in a nice wooden box. Unfortunately it took nearly three weeks because DHL managed to misplace the battery, somewhere between sweden and denmark.
Super nicely packed, with a loot of screws.


The battery has a lid that is hled in place by a large number og hex bolts (think it was 25size.

You will see the 8 batteries inside, they are held in place by m6 nuts on bolts that are welded to the battery tray.
I recommend using a 10mm top, a long extender and a rachet to get them loose. They can be a bit fidgety to get out.
Each battery has a major battery cable going to next battery, easy to get of with your hand. It also has two small connectors pointing to the center of the battery tray:

The two smaller handles CAN and temperature + balancing wires. .They can be disconnected by hand.


The control cables are held in place with a rather annoying grommet:

I lifted out the batteries in a pattern going from top to bottom and put each set of 4 on a roller. (visible in the bottom of the picture.

The individual battery is quite heavy, so expect to wrestle it a bit to get it out.

At the bottom there is a slightly different power connector, just unscrew it we will look at it later. The aim is to pretty much clear the tray so we can mount as easily as possible.

Below the 8 batteries, there is a heating element:

I will remove this since i dont need to worry about heating/cooling. I wont be able to draw enough current to affect the batteries.
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New member
Feb 10, 2021
Having removed all 8 batteries the tray is fairly manageable.

I removed the heating/cooling element, disconnected tube/connectors, and also a few electrical connectors (orange), they seem to control the heater. It includes a temp sensor that i deemed not relevant, so it went too.


Having been quite inspired by Lykke, i decided that a wall mount was the way to go. I spend a long time debating with my self if i should mount the tray directly to the wall or have a wooden plate between. (My wall is quite uneven). I ended up mounting it directly to the brick wall. I bought some heavy duty wall mounts at Biltema (common in the nordic region) They were essentially expansion bolts. I decided that it would be ok if not all holes would hit a brick. Those would not be used. I was very focused on the top ones, they are my main bolts. I put some wood beneath to even it out and mounted the tray to the wall.


Mounting can be done by a single person, but i recommend being two. I tend to do my things on my own (engine changes, gearbox changes etc).
The bolts i believe are m10x40mm, sot they are not going anywhere.
REMEMBER take care of mounting busbar BEFORE mounting it to the wall.
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New member
Feb 10, 2021
So next step was to build a busbar (power distributor plate). I would have prefered to buy one, but Lykke warned me that there were few products and they were quite expensive.
The need for the busbar arises, because we need to configure batteries in parallel rather than serial as it came from BMW.
We need to busbars, one for positive cables and one for negative cables.
One of the reason that it is hard to find commercial products is that i would need to be 9 pin or more. Most seems to stop at 6.
So i decided that i would build my own. Quite a bit of tinkering went on and i arrived at a copper bar, with plexiglass as insulating layer. Aluminium is not conductive, but i would prefer to have an additonal layer, and choose plexiglas, since it was available in (you guessed it) Biltema.
I bought the copperplate from a local metal shop (they have a parts bin, that tends to be cheap). I ended going a biiiit overboard. I bought 7 kg of copper :). In essence i ended up buying enough for 3-4 battery packs.
I overengineered and oversized it .. a lot. I made them 10mm thick, and 50mm wide, and approx 320mm long. In retrospect it could be somewhat thinner. maybe 5-6mm would do. Look at the busbars at the contactor in the battery and you will see why. They are more like 4mm wide. (picture will follow somewhere below.

I drilled out two mounting holes(10mm) at the outer edges of the busbar, and then made eight holes(8mm threaded) of tp one of the sides. And finally one single 8mm threaded to the opposite side of the eight. Reason: one to go out of the battery and eight to go in. I used the cable connectors to determine how far in i could put them and how far i should space them out.

Mounting is a 8x50mm bolt going through the back of the batterypack, through THREE layers of plexiglass.

Idea is: initial layer is insulating, second layer holds mounting bolts for the actual busbar, third layer holds it all together and gives needed stability. The second plate has drilled out holes to acommodate the two bolts facing the busbar.

I then didnt have a nice spacer so i used an oversize bolt,. and then a 8mm bolt to provide a mounting surface to the busbar.
Of course you need two, one for positive and one for negative:


The busbar is somewhat inspired from the one that Lykke purchased.


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New member
Feb 10, 2021
I had removed the entire heating element including the shroud going out of the battery. I decided that it would be more "correct" to add it back in, so the heater element had to be split. There are two lines going into a connector that can be split from the housing, result:


The keen eye will spot that one of the bolt holes looks different.... broken bolt, i drilled it out afterwards and remounted the shroud to the battery tray.


Active member
Oct 21, 2017

can wire connecto tor SIMPbms J5 connector = 10 pole Molex minifit series
from BMW battery take the can cable that connects the modules bms slaves, CSC's, cut cable at the blue connector
disregard the blue cable.
2x white red = pos out 5V on pin 5
2x white brown = gnd on pin 10
2x yellow brown = CAN H on pin 4
2x yellow red = CAN L on pin 9

If your SIMPboard has a can termination resistor use it, else crimp a 120 Ohm between CANL and CANH
use a blue termination plug in second canbus port if using Victron GX device,
Both ends of the can bus need to be terminated with a 120 Ohm resistor.

Please make sure to check if GND or POS have been connected correct,
a wrong connection will blow up all your bms-slave boards....
and absolutely do not think these will run on 12Vdc


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New member
Feb 10, 2021
So time for an update. Can see i forgot a few things about the disassembly. the right tools helps. I use an electric impact gun(wheel lug nut thingy), combined with a 10mm top.

That makes it a dream to pull of all the bolts. The (outerskin) bolts also offer the option of af hex t30. But since we need a 10mm top to get the batteries out... For this we also need the extender, since the batterys are about 15-20cm heigh. Remark the converter from normal "umbraco" to ½inch top. They are brilliant to adapt the tooling.

Next step Rewiring the battery. This very easy but also tricky.
In theory we cut the connectors, splice a fuse and extended wire into them and connect them to the busbar.

However as always, the devil is in the detail. Again i was super lucky that Lykke offered me to watch his setup, and thereby learn from him. So basic things like where to cut the cable to ease cable management, cable draw ideas etc helped alot. Funny enough... i still did it my way :) (Sorry couldnt help myself.)
Lykkes design on the cabling is better than mine, it sits prettier and flows nicer. So you may want to think this part over.
Lykke also mentioned a detail i wouldnt have though about, cable length. It seems it is recommended that all cables have equal length to ensure same resistance in cables. Since Lykke disregarded it on his second battery, i decided to go the same way. Cabling would just be to messy. And at least in theory it should get balanced while running anyways.

So as not to forget tooling:

This is what i used, wisegrip, an 8mm wrench?, a sharp knife, a serious cable cutter, a automotive solder machine., normal cable cutter, voltmeter, the mounting clap device thingy, and a metal tube cutter. You may also want to get a metal hack saw, depending on if you will remove anoying edge on a single battery. (top left).


Lykke used 16mm2 but i fell in love with 25mm2. (i'm not a certified electrician).

Red 25mm2 cable about 15-20m depending
Black 25mm2 cable about 15-20m depending
9x Midi fuse+box (decided to go for 58v 60 amp, may that should actually be smaller). The midi fuses are tiny physically, more later. Got a spare..
16x cable connector clamps 30mm2 (buy 20 so you have something to screw up). And yes 30mm2. Cables from batteries are larger than ours.

Pr battery:
For the red cable(pos) we need 2x25mm2 / 8mm hole connectors and one 25mm2x10mm connector. Maybe 3 x 8mm would do. I overengineered it i think.
For the black cable(neg) we need 1x25mm2 / 10mmhole or...
So for ease, we need 4 pr battery or a total of 24pcs of 25mm2 / 8mm hole. Buy 30 or more. You will screw up some of them.

We need a shit load of heat shrink material. It needs to fit at least the 25mm2. And a bunch of electrical tape. If you can i would get them in red+black.
Also i would recommend that you get some electrical tubing just big enough for the cable to fit. Cables will be "cutting corners".

So that sort of sets the shopping list. I went completely overboard and bought 50m cable... that was overkill. The battery part of the battery box is about 130cm heigh and about 80 in total (dont forget 4x2). Each battery is about 15cm deep x30 heigh x 35cm wide. So worst case i would say about 2m-2,5m cable length for each of the 8 batteries, but if you run "logical" lengths some will be considerably shorter.
The cable connectors cobber tube to connect two cables are a bit of a mess. They need to fit the 30mm2 from the battery side and our 25mm2. I put the battery cable directly in, and folded the connecting battery, to ensure sound connection.


New member
Feb 10, 2021
Actual mounting:
When in series, there is a short cable jumping between each battery, and an odd extender at the bottom of the battery. It allows BMW to use the same batteries anywhere by just adding the extender.
We need to cut this cable, i measured it out so the cable connector would sit at the cable holder:

You can sort of use the barcode sticker as a navigation tool:

Just leave a few mm after the sticker and it should be fine (he said not having closed his battery pack yet). This is the negative lead (measure to make sure, trust no one).
The negative cable is to run to the busbar without fuse, i only fused positive cables. Measure out, dont forget corners take up distance, and that some will need to cross the battery box to reach busbar.

The connector clamp i learned can be set to connector size (i actually broke the first one, because i thougt is was one size fits all.... it is not).

Push it up and select the size needed. Then you wont break the tips like i did.
Remember to put on the heatshrink material. I put it on the battery connector, then clamped the cable connector on to the cable ends. The extending cable will need to be folded otherwise the material thickness will be problematic. BMW uses some aluminium type material and i use copper, i believe that explains the different thickness's.
Use the soldergun to heatshrink .. the heatshrink material in place.
For god measure i use electrical tape too, old habbit i guess. I also put it on the final end of the cable to ensure no sparks (both pos and neg):

I then added electrical tubing to protect the cable especially from the corners of each battery :


I dont like the sharp edges. The battery is fixed to the wall, but still.
Speaking of sharp corners on the picture with my finger you can just see the edge that on the top left battery is a bit "un-cool". You may want to get rid of it when it is NOT in the box.

On the other end we put a connector to be connected to the busbar:

Sorry for red cable, no pictures of black cable avail.

The positive is a bit more work. The cable is fused to the battery, and we use a cable connector and heatshrink to connect it to a fairly short length of red cable.

Maybe about 40m of length.


I used a bottle of antifreeze to support the cable. If you are a one man band like me, this will end up being a problem. Keeping cable in position and clamping it with both hands.

This new length of cable goes to the midi fuse box:


The Midi fuse is quite flimsy. I dont understand how come i need high end cable and then a small ass wusy fuse out of approx 1mm think connection points.
You can see that i choose to add washers on the outside, this is because i bought too many 10mm connectors, think it may still be "icky" with 8mm. So buy a bunch of washers.(at least 5mm hole)

Again i like electrical tape:

I want a fuse as close to the connector as i can get it, without problems with closing or twisting the cable. I decided that the fuse should be just after the cable has bend around the battery it is connected to:


And of course a bolt/cable connector at the end, heatshring and electrical tape.

Lykke warned me about one thing.... your arms are going to hurt.... he was right. there are many many heavy compressions and cuts to make.... tender muscles = found.


New member
Feb 10, 2021
Ok, so i mounted all but the two top batteries, and created all the cables as described. Reason: better access to the busbars.

Lykke and i mounted it around the same way, he used nice commercial grade items, i went diy. This may be the reason why he's cables mounted nicer than mine.
Getting the right mounting flow (what batteries at what time ... i cant say, struggled a bit with this part, so had to re pull the wires a few times. Still think it was smart not doing the two top ones incl mounting until last.
Problem is that you will have positive on one side of the batterypack and negative on the other. That means we need to pull some quite lengthy cables to some of the batteries. This is of course especially bad for the two bottom ones, furthest away from the relevant busbar. I pulled the two bottom once's along the bottom of the pack. Lykke pulled all over the top of the pack.

Before mounting the cables, disconnect negative plug from batteries for safety.

Mounting is quite basic, draw cables as protected as possible, bottom onces should be closes to bottom of batterypack.

Also we will need (i did) to remove a small plastic bracket on most of the batteries:

You should end up with 8 batteri's with each their connection to the negative bus bar and positive busbar.

I have negative on right and positive on left. Think that Lykke has it reversed of me. For me the cables from the top box could then be used. (More later).

We now have the batteries mounted in the tray and connected to the busbars.


New member
Feb 10, 2021
We are now getting to the point where i start to struggle, the visible evidence from Lykkes install and the online documentation, is not super clear from here on in.
Things from here on down are subject to change for now:

Initially we need to sort out the remaining internals of the battery. We need to use the original contactor/fuse box.(top of the batterypack) We remove the BMW battery ecu, it bolts of easily.

There are a few torx bolts, think it was t25. Also there are three connectors, they have en simple slide mechanism to extract the cable, if you are using force to get them out... you are doing it wrong.

There is a basic plastic lid on top of the box behind, that can be opened by fingers or a screwdriver.

After the lid is off this will greet you:


A quick description, be aware that this may be inverted, since cables coming out of box can be "twisted" at Victron.
Negative contactor:


Positive contactor:



These three components are controlled by SimpBMS to ensure safe operations. This means that if overvolt/overtemp is detected it will stop power to contactors, and they will close the connections on both cables.
Lykke has operated out the computer components beneath since they are not needed. I haven't ... yet...

I have disconnected most of the auxillary power (control of heat/cool element etc cal).


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New member
Feb 10, 2021
Since we are nearing the point where i am at, i will skip a bit, as not to post uncertain data.

We need to connect the databus back to the batteries, and prepare them to be connected to SimpBMS. Lykke has choosen a very clever way, he has desolded the connectors from the battery ecu, soldered them to prototype boards (one for CAN bus, and one for Contactors/precharge). It is the white plug and the blue plug.
I personally cant get my self to butcher the ecu (yet), and also dont like the thought of cutting of the other end of the connector and soldering it all together directly. Currenctly im on a stick in prototype board, since i have/had some issues getting it all to work.


New member
Feb 10, 2021
So it is Vitron time now. There are two components, again inspired by Lykkes setup:

Victron Multiplus II 48/5000, most others use the quad. but it is not whitelisted in Denmark, and i cant use it. Multplus is whitelisted, but maxes out at 5000w.

We also have a dc-dc converter from Victron, the Orion-Tr DC-DC 48->12 110w
This provides us power to run several components, the Victron Color GX (Thanks to Lykke for selling his surplus to me). It will also power SimpBMS, and maybe a relay (To be determined).

So as mentioned we have a Victron ColorGX (could be any GX device as i understand it).

Then i have the Victron SmartShunt, i choose the small one, it is rated at 500amp...
I'm currently not 100% sure that this component is actually needed, or if i can rely on either the Multiplus or SimpBMS/Can.
Important note, the Smartshunt needs the same current level as power supply as it measures, otherwise it will show power supply voltage. I tried with 12v because the manual for smartshunt didnt lead me to think of it as anything but power supply. But it seems to link in to the power in the measuring cables.

Finally i have a large DC breaker/fuse as again... recommended by Lykke. It is expensive, hope that other solution can be source. I ordered some chinese DC breakers but kind of lost trust in the. The breakerbox is expensive in my world, and it is hard to get fuses at the level we are looking. And it was only avail in UK = import fees to get it into EU... yay....

I also ordered the BMW powercable with my battery, to ease connection to the battery box:

The plugs make it very easy to plug and unplug it. Not really relevant with the breaker...but hey.
Will update with pictures, dont have them on computer currently. More to follow.