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Please confirm that my wiring on left for my bank works.
Trying to work out if my green, orange and blue lines (and single red and black lines) match what the manual suggests. The series and midpoints links don’t allow connecting midway on cable, so I placed on one side. For red and black, use same terminals as inverter.
1, 2 and 3 (blue) are the 3 battery balancers.
I have studied this and it seems correct to me.
EDIT:
I should add that, in this configuration with mid point inter links between banks (the vertical black wires in the Victron drawing), you need to follow the theme and have the positive and negative wires coming from the end of each bank of equal length. Have these wires meet at a common point like a bus bar.
Basically follow the Victron diagram for the end connections each of equal length.
Taking positive from one bank and negative from the other is perfect when you do not have mid point links.
Thank you.
The mid point links x 3 are all of equal length and gauge (same gauge as series links).
The two parallel links joining the positive and negative sides of each bank are the same length and the same gauge as the rest of the link described above.
To confirm, the midpoint links are the same length as one another, the series links all the same length as one another and the two parallel links (one + and one -) are the same length as one another. All of these are the same gauge.
Even the two links into the Inverter are the same length (though I believe this is not necessary).
HOWEVER, there is no bus bar. I would have to cut each of the parallel links midway and introduce a busbar on each side to meet this requirement, right? Then my black and red links in my diagram on the left (of identical length) would need to connect to the bus bars?
What would happen if I did not do this and wired the battery balancers into the positive from one bank and negative from the other?
Hi @warwick
Yes, you could cut the dotted connections and connect halfway, or have equal length cables from both banks to the next connection point (positive to the fuse, negative to shunt or directly to inverter)
For safety, if using double cables, please also add the dotted connections to prevent big currents if one of the cables has a problem.
Most inverters have dual battery connections so you can use two 'thinner' cables instead of one big one.
Hey Daniel
Thank you for the reply.
Below is a representation of the system is it is right now (before we connect the battery balancers). The green midpoint links have been added in to make the bank ready for the balancers.:
Hi @warwick
Nothing wrong with that (without the green connections), but under load (charging / discharging) there will be a voltage shift between the two banks, due to the way it is wired.
This is no problem, but if you want to connect balancers, the batteries need to be at the same level.
The top bank will be at a higher level than the bottom one wile charging, the bottom one at a higher level when discharging.
This is due to the longer positive / negative cables.
(I'm sorry I don't know how to explain this better, but with the green connections in place, without proper wiring to pos / neg connections of the banks, things will go wrong)
Ok, but what if I make the black and red connections to be battery balancers the same length? I have actually already cut an connected those two cables to the battery balancers, and they are the same length to the millimetre.
Hi @warwick
It's not the connections to the battery balancers that are the problem.
It's the main wiring from battery to the next point. this has to be the same length on both positive and negative connections, as per the Victron diagram on the right in your original post.
Where do you have the battery fuses connected?
Balancers are mounted and ready to be wired. I just need to understand what must be done to ensure the batteries are "at the same level".
I am ready to introduce bus bars at whatever point you suggest. Do I understand that this should be exactly midway along the dashed parallel links - ie. I must cut those cables midway and introduce busbars? And then when I add MPPTs, they connect to same busbars?
There is a single 125A Mega Fuse on the positive battery lead:
Hi @warwick
It's very simple: if one of the positive posts has a longer wire = more resistance, it will be at a different voltage than the other.
The same goes for the Negative post.
if you then connect the interconnect cables, you'll introduce a lot of problems.
call it a busbar, call it a connection point, just make sure the wiring to both banks is exactly the same from a point where they come together.
If you're not sure, please get an electrician / installer involved.
This is like a dark science to any installer or electrician I have consulted. I've been told, 'It doesn't matter', 'You don't need those balancers'.
I've done Victron training myself, and I do not think it is as simple as referring it to an electrician (who mostly have no clue about DC) or an installer (who, in my experience are drowning in the complexity of the Victron product environment and the fuzziness of electrickery).
Ps. When you say positive posts, you mean these two, right?
I assume the same applies to the opposite negative posts because they add up for resistance of the entire charging circuit?
Also, please note that I updated the above post at the same time as you replied.
Hi @warwick
Nothing black magic about voltages, just draw a diagram and see for yourself:
for ease of explaining, 1 v voltage drop over the longer connections, and you have a 1v voltage difference between the two strings.
Use the green wires and forget the blue connections, and your done:
Hi Daniel
I have done the following:
I've put batteries 1 & 4 in each bank right next to one another so the cable runs to the bus bars are short. I've added busbars. I've moved the inverter to connect from the busbar instead of the battery.
All four of the dashed cables to the bus bars are the same length as one another. All the yellow serial links are the same length as one another.
If you may, please confirm:
1. this is the same as your diagram above;
2. the balancer wiring is right: Do I need to cut the midpoint links halfway and put the balancer wires at the middle of the midpoint links?
Warwick
Hi @warwick
Why are you complicating things so much by not taking the system negative from the most right side batteries?
Because of the spacing I have to work with - batteries are to the right of the equipment because of gassing if they were below:
Everything is on the left side - want to reduce the amount of cable.
Ps. I know this is messy. I am making progress every week to getting it cleaned up. When I started it was just the batteries and the MultiPlus II.
It now has 12 panels and 2 x 150/35 and bus bars:
Balancers and midpoint links removed for now until I know how best to wire them.
See at: https://vrm.victronenergy.com/installation/34733
Hey @Daniël Boekel (Victron Energy Staff) does that answer your question.
Let's assume I am happy that the battery wiring is all OK, I just want to know about the optimal midpoint configuration.
Should I cut the current midpoint cables at their centre point for the wires from the battery balancers to join or can they just go to the terminal on one side?
