Second system extension extension.

[nowty]

Jings, forgot about them! Cheers Nowty. I will sit down next couple of days and look at the links and purchase accordingly. Just goes to show, a little knowledge can be massively hazardous when remote planning! Thanks again!

If you've got the space though, another Keto unit would give you easy disconnection and consistency. And I'd be going up to at least 10mm or even 16mm cable for the Victron output.

Then you have the issue of the max current going into the Pylontech battery stack, from both the Goodwe and Victron as the 25mm cables on the Pylontechs get pretty warm over 100A and hot at about 120A.

[Andy]

Then you have the issue of the max current going into the Pylontech battery stack, from both the Goodwe and Victron as the 25mm cables on the Pylontechs get pretty warm over 100A and hot at about 120A.

Can you get a dc busbar and split the pylon tech into equal size stacks in parallel?

[nowty]

Then you have the issue of the max current going into the Pylontech battery stack, from both the Goodwe and Victron as the 25mm cables on the Pylontechs get pretty warm over 100A and hot at about 120A.

Can you get a dc busbar and split the pylon tech into equal size stacks in parallel?

Yes, that may well work, I have 3 roughly equal battery packs in parallel but you need to have each cable the same length back to the common points or else one pack gets used more than the other because of unequal voltage drops in the cables.

I know some folk connect them up at both ends back to a common point, to allow extra current flow, although I don't think that gives equal current flow from each battery even if you use same length cables as the outer batteries get used more than the ones in the middle of the stack.

[Stinsy]

The Pylontech manual suggests connecting both ends of the stack for 240A.

[nowty]

The Pylontech manual suggests connecting both ends of the stack for 240A.

Its a fudge but better than melting the cables or causing a fire, not sure whether I would risk 240A though. I use 50mm cables to my parallel batteries and things still get warm at my max charge rate of 166A when I am only running two of the three battery packs in parallel. In fact I upgraded the cable from 35mm to 50mm because I was not comfortable with the hot cable temperatures.

It might still in spec at 70 degrees but that is practically too hot to touch.

[Stinsy]

100A is a bit of a “natural limit”. Very tricky handling current levels in excess of that. High Voltage* battery packs are starting to become available that address this problem.

* Technically anything up to and including 120V DC is Extra Low Voltage (ELV), above 120V and not more than 1500V DC is Low Voltage (LV), and anything above 1500V DC is High Voltage (HV). The “High Voltage” battery packs tend to be in the 100-800V range so technically are Low Voltage. But it seems I’m fighting losing battles for correct terminology on a whole bunch of fronts.

[Joeboy]

We have been out for a lovely night with pals and are off on a boat trip tomorrow. Massive thanks to all you guys for weighing in with ideas and solutions. Please keep em coming! My phone is not displaying the images u guys are sending so i'll go back over it all when I get home.

I will also fully address the current flow on my return. All I can say at the moment is that the DC battery cables have never been warm to the touch and I went for max size on the original victron unit. I don't obsessively check them (regrets) but the times I do the system is normally peaking for that time of year and all is good.
Also I have had no need to check how well the bms controls flow from the main array depending on temperature induced by incoming from 2nd array as there has been no cable heat to worry me. I guess the time may come when the bms cuts back current in flowing from main array due to battery temp increasing from a well performing 60A second array? If this is the case it will send power from main array towards grid where it will be caught and diverted to HWT via Iboost?

Once again, thank you all. I ain't no natural sparky!

[Joeboy]

I think I will upgrade deck box, swap out Victron and limit it to 35A and then address fuses and cable sizes. We are heading into the time where 35A will not be happening anytime soon so step by step will work for me for change out. Also got to see my flow paths again and fix then in my head.
Keeping under SWMBO radar for costings also quite important.

[nowty]

Here you are Joeboy, this is the best way to connect up your Pylontechs for high current. I copied and edited it from the Victron website, sort of exactly as I explained but a picture paints a thousand words. And its better than the Pylontech fudge by simply connecting the stack at both ends with dual cables.

Note - The cables from each parallel stack back to the DC Distribution point should ideally be same spec and same lengths and preferably with a DC disconnector and more fuses from each stack to the DC Distribution point.

Thanks to Andy for the link he published on his other thread where I found the info, and to Andy, your going to need to do something similar with that Bigboy Victron if you are going to use Pylontech batteries with their 25mm cables.

[nowty]

And as an example, this is my positive DC Distribution point. I do have another negative one, just don't have a picture of it.

Note,
The black cable is actually a 70mm positive cable back to my Battery Inverter.
The thinner cable at the bottom of the picture is 25mm to my Victron charge controller and supplementary / emergency battery charger.
The other 3 red cables at the top are 50mm cables to each parallel battery.
And there is a small cable (with the green fuse) which goes to a DC Disconnector Contactor to take the Pylontechs out of circuit when they go over voltage.




EDIT - Now I have a picture of my negative DC Distribution point. I don't bother fusing that end but some people do both ends.