busbar - cell connectors

[Bernd]

I the meantime I´ve received 32x 280Ah EVE cells, but missed to order enough busbars for 8s4p :-(

Does someone have a suggestion on where to buy high quality cell connectors?

I learned not to use pure copper and will stay at the stuts which are very nice compared to screws.

Can someone help my out on where to buy (and not to wait 8 weeks on delivery from china ...) 

[Franco De Mei]

https://www.ebay.com/itm/Copper-Braid-Flexible-Busbar-60-68mm-cc-6mm-holes/233341038193?hash=item365435ae71:g:P1gAAOSwmUBbzeoY

[Franco De Mei]

https://www.ebay.com/itm/2012-2017-Toyota-Prius-C-Battery-Bus-Bars-New-18-pieces-in-set-with-nuts/254623766516?hash=item3b48c257f4:g:EGoAAOSwrkJe2msX

[Dacian Todea]

Yes that flexible braid busbar is how all should be made as that is the proper way to connect cells and not solid bus bars like in the last link.

I will say this represent examples of the best and worse version of bus bars :) 

On Friday, March 5, 2021 at 11:42:00 AM UTC-6 Franco De Mei wrote:

https://www.ebay.com/itm/2012-2017-Toyota-Prius-C-Battery-Bus-Bars-New-18-pieces-in-set-with-nuts/254623766516?hash=item3b48c257f4:g:EGoAAOSwrkJe2msX

[Peter Kuczynski]

I have to say, I enjoyed hammering out my copper bus bars from 1/2 inch copper pipe, it was fun.

[Machiru]

Hello, just ordered my SBMS0 etc. for a marine installation using Listen cells, I am UK based, Liverpool.  I will be picking the collective brain quite a bit I suspect over the coming weeks.

The supplier did not send any busbars so I will be making my own I guess. Cells will be compressed and located inside the cabin however dissimilar metal corrosion is always a concern in the marine environment. I am hoping to find tinned copper flat bar to minimise copper oxidation but may need to use bare copper depending on what I can source. I will therefore have Aluminium battery posts, stainless studs or screws and copper bus bars, should I be looking for a different approach or is there a conductive grease or paste anyone can recommend to minimise potential corrosion/ resistance.

Thanks Jon

[Dacian Todea]

Jon,

Corrosion and humidity will sure be a problem and that includes the SBMS and DSSR20 not just the battery. They will need to be installed in a sealed box as they are designed for indoor use non condensing humidity.

Somoane mentioned this nce flexible busbars but it seems they are no longer available  https://www.ebay.com/itm/Hardware-fo-4s-green-cells-Copper-Braid-Flexible-Busbar-/233367418486  but there should be other similar options and you sure do not want just simple coper even if not used in your conditions.

[David Jones]

Dacian,

 So if I put Noalx on the alum battery terminals or solder tin the copper busbars would that take care of battery corrosion concern ?

 I have a few feet of scrap 1 inch copper tubing that would be a shame to waste.

[Dacian Todea]

Tinned copper will be OK as long as that is uniform else there may not be much contact surface ho you will have high contact resistance.

You will also want the busbars to be at least semiflexible so they should have a bent in the middle to allow for the small contraction and expansion.

Something like in this photo  https://www.alibaba.com/product-detail/Battery-Bus-Bar-Connections_60643646427.html  as they do know what they are doing.

[Machiru]

Thanks Dacian, I guess for SBMS and DSSR20 I can use IP 66 enclosures in a creative way to counter  condensation problems.

I have found copperbraid.co.uk who supply tinned copper braid by the metre in various sizes. I will check if they supply tinned copper ends that I could use. Quick question on braid sizing, obviously lengths are very short however do I need to size the braid to be able to handle max system current? (There will be many daft questions). My design isn't anywhere near finalised I have 8 272Ah cells which will be either 2p4s 12v, 544Ah  or 8s 24v, 272Ah. Largest load will be a Victron multiplus 3000 therefore 250 A or 125 amp but with possible peak surge of 500A or 250A. 

The solid busbars normally supplied with batteries look to me approx 25mm x2.5mm to 35mm x2.5mm ( 65 -90 mmsq), the flexible braid is getting pretty big 40mm x3.5mm for 70mmsq equivalent.

Any thoughts much appreciated. Jon

[Dacian Todea]

Jon,

The peak current is irrelevant as is usually less than a second at least for Victron it can not be more than that above 3000VA based on spec.

So max continuous current will not be that high and so busbars only need to handle 125A no matter if you go with 12V or 24V as with 12V you have current shared over multiple busbars.

Thus about 25mm2 will be more than decent for the busbar or 35mm2 if you want overkill.

[Machiru]

Great news. Thanks again Dacian, your customer service was one of the reasons I chose to go Electrodacus, thanks for the forum also which is a great resource. 

Dealing with water tank problems today, looking forward to the electrical installation there should be a good deal less fibreglass itch involved. Jon

[Casey]

I am looking at upgrading or replacing my current battery bank with a 8s4p setup to support larger loads, and am (perhaps irrationally) concerned that the busbars included with the batteries may not be sufficient for the series links when charging or load is at sufficient current.  I suppose I won't really know if there's a problem until I have things all set up and run a large test load, and then could measure temperatures with a laser thermometer.

Curious if anyone has run into similar issues, and what you did about them if so.  For reference my target bank will be between 800 and 1120Ah, supporting a maximum load of 750A (realistically, will be less than that, but that's the upper limit I'm planning to support and I want the system to be able to manage it without issue).  I will have two Victron Quattro 5000s as well as some 24V and 12V (through a converter) loads.  I'm currently using 200Ah CALB cells which have busbars that seem fairly substantial to me, but I was considering aluminum-sided 200-280Ah cells, as they are smaller and lighter weight per Ah.  However, the busbars they appear to come with are a lot smaller than the CALB ones, hence my concern.  Creating custom copper busbars seems impossible to do without large tools (like a drill press) that I don't own and don't have space for, and would be difficult to do with precision.

I will have to consider trying to find some braided copper busbars of an appropriate length after reading this thread.  Aside from eBay, does anyone know of a supplier of these that is based in North America?

Regarding overcurrent on the Victron - they are actually fairly tolerant.  I thought that my Multiplus 3000 would go into overlead at 2400W, but it didn't until exceeding 3000W.  I ran 3300W through mine for about a minute when testing - the overload light blinked but it kept running.  If I recall correctly, they will tolerate at least some degree of overcurrent for up to 2 minutes, though I read that they will derate if the temperature is too high.

[David Jones]

So couldn't one make braided copper busbars pretty easily from components from Amazon like this and this ?

[Dacian Todea]

Casey,

The 750A is also the limit the SBMS0 can measure and if you want to be around that you will need 1000 or 1200A current shunts.

And yes 750A will be a bit much for a 800Ah battery as I will say is preferable that max discharge rate is not higher than around 0.6C continues so with a 1120Ah that means around 670A so likely OK.

Now this say 600 to 700A continuous current will be split in 4 as you will have 4 parallel cells so each busbar will need to be able to handle around 150A.

The Victron is 3000VA so should be 3000W if you have resistive loads and I assume it will handle 3500W for a minute or two but above that I think is just a second or so if you are close to 6000VA and it will stop in likely ms if above 6000VA

David,

Yes you should be able to make your own bus bars that way.

[michael clark]

Good morning Dacian,

Could 2 2P8S batteries of 272Ah Lishen cells be parallel together to make a 1088Ah battery? for a larger storage capacity? the SBMS0 would be monitoring each 2P8S battery so there would be 2 SBMS0's.

or would it be better to do a 4P8S with only 1  SBMS0? the battery would then have 1088Ah potential capacity and the likely maximum draw would be (8000watt LowFrequency Split Phase Inverter =24voltx333.33 amps) at this time. so maybe only 333 amp max discharge from the 4P8S Lishen battery constructed of 272Ah Lishen Aluminum cased prismatic cells. but then I would need to get 1000 or 1200A shunts for it to function/monitor correctly?

then the discharge  C rate would be 333/1088  =  0.31  (correct? )

good or bad?

not sure if I would get up to 8000 watts discharge though.

thanks in advance for your suggestions/advice!

Michael

[Dacian Todea]

Michael,

No you can not parallel Lithium batteries you will will need to build a single 8S4P (4P8S means the same thing as there is only one option possible but 8S4P is the most used notation as number of cells in series is more important than how many cells are in parallel).

If your max load will be 8000W from the AC side and that inverter is 85% efficient then on the DC side it will require 8000W/0.85 = 9411W so 9411W/24V = 392A still not much and maybe a 600A shunt will be OK unless you are thinking to increase consumption in the future to more than 8000W

Is important what the max continues power is and not the peak power for a few seconds as that will not count. If you say have just 4000W max continuous load (for many minutes consecutively) and then peaks up to 8000W for a few seconds then a 500A current shunt will be more than enough.

Also with a 8000W peak inverter you likely can get away with just a 8S2P battery but it depends on what is your exact application as you may not have enough storage energy if you use that for many hours continues. 

[michael clark]

hello Dacian,

ok, thanks for the information.

I thought I had read someplace that you can not parallel lithium batteries>>>ok. i had to revisit that. as lots of mis-information on the DIYsolarforum.

the second plan was to put 4 cells in parallel, then put each of those in series. the word police on the DIYsolarforum claimed it would be written as 4P8S. but I can easily enough write it as 8S4P if that is the more correct notation.

I know several times you had written to put them in parallel 1st as they will act as 1 when in parallel. (the individual 3.2V 272Ah Lishen cells). 

the continuous discharge is the reason I was wanting to have the larger capacity battery to the 24-volt battery. I am not likely not have high amp discharge most of the time but want more reserve for the cloudy days and snow days.

thanks, 

I understand a little better all the time. when I can add more panels with more DSSR20's I will but the weather has slowed things a bit. more snow coming for a couple more days plus we had strong wind, snow, ice, and rain the last 2 days here.

again thank you.

Michael

[Dacian Todea]

Michael,

The only reason someone will claim it is written as 4P8S is if he thinks that there are two options when there is just one correct option. The way it is written is less important as long as pack is connected correctly.

An example of company that sells huge volume of custom made batteries for hobby remote control toys https://hobbyking.com/en_us/zippy-compact-8400mah-4s2p-30c-lifepo4-pack-w-xt90.html  if you look you will see that the notation an all their batteries is correct 4S2P in that example and you can be sure they have groups of two cells in parallel and then 4 of those groups in series in that battery.

Same a Tesla Model S pack will be called a 6S74P and of course it is made as groups of 74 cells in parallel and 6 of those connected in series https://evshop.eu/en/batteries/56-5300wh-tesla-module-6s74p.html

[michael clark]

Good morning Dacian,

is this ok? sorry for the rather crude graph paper sketch.

 thanks for all you do

Michael

[Dacian Todea]

Michael,

Yes the connections are electrically correct.  It will depend on what sort of max current you expect to use in your application. If your max power is 3000 to 3500W continues this should work but if you need more then it will be best for cells to be oriented in a different direction and connected as you have connected the cell 4 to cell 5 as then current from one cell to another will be done through 4 buss bars instead of just one and also you can connect the positive and negative to 4 terminals instead of just one.

[Dacian Todea]

I'm not referring at the fact that battery is folded in two it can even be folded in 4 depending on what space you have for the battery.

So Imagine the first 4 cells group (cell1) rotated by +90 degree and cells 5 to 8 (cell2) rotated by -90 degree then you have 4 connection for battery negative and there are 4 busbars connecting cell1  to cell2

Those cells are 72mm x 174mm so the way you have oriented them a group of 4 parallel cells will be 288mm long while if you orient then rotated at 90 degree they will be just 174mm thus you will have a shorter battery.

Each cell is 5.3kg so if you want to be able to compress them and also have the ability to move then you will need to compress groups of 4 parallel cell basically creating a large probably 25kg cell of 1088Ah

[Casey]

How would that be done?  By beating the lugs until flat with the braided copper inside with a sledgehammer and anvil?

[Casey]

I have 8s so 750A / 8 = ~94A, so let's a 100A busbar rating should be the minimum.  Can the amperage capacity of a busbar be determined from it's dimensions?  I'm planning on using EVE 280Ah cells (same as Bernd), which come with non-flexible solid busbars (not sure how many, and not sure of the bolt size):

"You will also want the busbars to be at least semiflexible so they should have a bent in the middle to allow for the small contraction and expansion"

I didn't realize that this was an issue, but it explains why the CALB busbars have a bunch of layers and bend in the middle.  I wonder how the quality of the EVE cells compares to what I'm used to, but I digress...  Do you reckon the busbars included with the above cells should just be avoided altogether?  I've been keeping my battery cells enclosed in an insulated box - if they might expand/contract then I'm concerned about the box maybe being a problem as it might not let them expand enough or might break apart in time.  Is this expansion/contraction enough to really worry about?

Bernd, since you have these cells already, can you tell me what the bolt hole diameter is?

[Casey]

Is the expansion/contraction based on temperature, state of charge, or other factors?

[Dacian Todea]

Casey,

If you need 750A then the busbar needs to handle that 750A and having 8s will not help with anything unless you mean 8p so maybe 8s8p

Expansion contraction is both based on temperature but also based on SOC (the cell dimensions will slightly change with SOC).

[Casey]

Apologies, I misread "Now this say 600 to 700A continuous current will be split in 4 as you will have 4 parallel cells so each busbar will need to be able to handle around 150A."

So each busbar between series needs to be able to handle 750A, unless there are multiple busbars between each series.  I don't know how to be sure, but those little ones that come with the EVE batteries don't look like they'll be sufficient.

How much expansion/contraction is there to worry about?  I'm wondering how others have designed battery boxes to contain and maybe insulate all their cells if the size of the cells is somewhat variable...

[Dacian Todea]

If you have a 8s4p then each buss bar will need to be able to handle 150A if total battery current will be 600A

If you only have a 8s1p then each buss bar will need to handle the full current say 600A but of course there are more limitations here as a single 280Ah battery will not be capable of 600A anyway so is not just a buss bar problem but also the cell and cell terminal that are not capable of that.

Well I do not have those type of cells but here is how my battery is connected 8s10p to deal with expansion/contraction. Notice the compression plates and the 8 threaded rods with the red compression spring to maintain pressure.  I do not need insulation as my battery is inside the house where is always at ideal operating temperature.

[Bernd]

Regarding the busbars....

Does someone follow "the offgrid garage" on youtube and check Andy´s yesterdays video on busbars topic

https://www.facebook.com/PowerPaul-Australia-103561108175556

PowerPaul seems to have quite nice busbars, but these are not flexible and Andy seems to know, the cell compressing if not needed.

I´m still searching for my perfect busbars ....

[Casey]

Wow, that's an intense-lookig setup Dacian.  Are those pouch cells?  I haven't seen those for sale but heard about them in some video a while ago - I'm open to otther possibilities for battery cells than what I had planned...

Are the compression plates a custom design?  This looks like a great way to manage it, but seems like a daunting task to take on.

[Demosthien]

I would think you could just use a standard crimping method for the size of the cable itself (irrespective of braiding). I mean, regular stranded cable has many strands which you bunch together then slam a ferrule over the end by application of brute force (which causes some kind of cold welding effect IIRC). Really the braided cable is just more of the same but instead of a rubber/PVC/whatever covering holding the strands together it is braided. So, it shouldn't really make for a different crimping method.

Another method (but much less mechanically sound) could be to sandwich the braid between two copper bars, then drill a hole through the whole shebang. Use the hole for the terminal post and the pressure from the terminal bolt would hold it all together... But, as I said earlier, I am pretty sure this would *not* be a sound method of securing the braid and (depending on the type of cell) would also risk stripping the terminal thread or piercing the cell.

You could also buy them pre-made, I don't know prices but I found a place in the UK that makes them for industrial applications. I was actually going to be contacting them just to find out what they'd cost to have 20 or so made.

[David Jones]

I don't know why you couldn't use a standard crimper. I use this . A little trial and error my be needed to match terminal lug AWG size to busbar width

[Dacian Todea]

Bernd,

There are some bad busbar solutions outhere as they try to keep the cost low and maybe some of the sellers do not even have the knowledge of what a good busbar should look like.

Casey,

Yes those are 20Ah A123 System cells I got over 3 years ago and it is my main house battery around 180Ah 24V. There is to much work so I will not recommend such small cells especially for larger packs.

Demosthien,

Yes in fact if you look at my battery photo you notice the two halves of the battery are connected with two 8AWG (8.29mm^2) silicone wires (I think 1650 strands super flexible) as that is more than enough for may max load of around 90A

 

David,

Yes a crimper can be used and flexible cables to make your own busbars. It may be a bit more expensive but fairly good quality if crimping is done properly.