I am a bit confused on the topic of security and wire protection… a bit of help is really appreciated
I am trying to size and determine the types of fuses and switches between Pylontech and the Lynx Distributer. Setup is as follows:
- Pile of 3x US5000 wired with 2 pairs of Pylontech 25mm2 cables
- each positive cable a 125A Victron Mega fuse
- the 2 positives lead to a Victron DC-Switch wired through a 50mm2 to the Lynx Distributer with a 200A fuse
- the negative Pylontech wires go directly to the Lynx Distributer
Questions:
- Sometimes I read that a 2-pole DC-Switch should be used, a DC-Switch on the Positive is enough?
- Are the Mega Fuses on the positive wires enough protection? I hear they don’t protect enough against high shortcut currents… A class T should be used, or another type of protection…?
I was under the impression that the double Pylontech cables, the separate cable fuses, the DC-Switch and the 200A Lynx fuse, are a lot more protection than I see in a lot of other setups.
I would like to have a safe system, but not a overkill (all those elements are not cheap!)
My take on this is that paralleling Pylontech batteries using the short interconnect cables is not good because there is no protection if any one of the batteries develops a fault.
I imagine an (unlikely, but possible) scenario where the voltage of one of the batteries goes a few volts low. At this point there would be an unfused inrush of current from all the other parallel batteries. The 4AWG pylontech cables would not cope with this situation.
My installation takes each Pylontech battery +ve separately via a NH00 fused disconnect with an 80A fuse to a Lynx PowerIn. These fuses offer much better battery protection than MEGA fuses.
A pair of Pylontech cable is rateted with 100a with a 125a fuse in the user manual
The original 275A Victron DC switches runs hot at 60-80a continuous load. After making that observation, I removed the switches again. There are some discussions on the forum about DC switches that run hot.
Right now, I’m using one pair of cables for two US5000. When I expand the system, I’ll replace them with one pair of cables per US5000 battery, because i need more current than 100a from the battery stack.
Since the observation, I have been monitoring the temperature of the battery cables and the busbar.
I understand that you advise to wire each Pylontech with is own cable-set? What about all those daisy chained examples? You think it is a bad idea?
And I understand you use a knife fuse switch for each batterie? Regulation in France requires 1 main switch for all batteries. What’s your view in this?
I am in UK, so have designed my system around my understanding of UK regulations. I don’t know about French codes, but we all have the same desires - to avoid catastrophic events in our home energy systems.
I also have a fused disconnect on the +ve input to my MP2. I wonder if this would satisfy the French requirement to have one switch for all batteries?
Alternatively, the fused disconnect product link I sent has 3 circuits operated by one handle. Does this count as “One switch” for your three Pylons?
As I understand French regulation requires 1 movement to disconnect all batteries, positive and negative poles…
A 3 pole knife switch could cut the 3 positives, but what to do with the negatives..?
Or, joining positives and negatives in bus bars before the switch, which means that the cables are not separately protected and one very expensive and big switch due to high A-rating…
one movement, whole section isolated. Same counts for the solar panels. I have a 65A, 500VDC switch.
Yes, the device you mentioned is what i call a knife switch (holding the knife fuses). I found mainly 3 phase ones, but you can use 2 faces in a mono phase system, or use it on 2 or 3 positive wires. But… what to do with the negatives.. if it needs to be a single movement..
I’m suggesting you have both +ve and -ve wires running through a 2-pole fused disconnect between the inverter and the Lynx bus bars.
Edit: This in addition to having three knife fuses on the +ve only between your 3 batteries and the Lynx bus bars.
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
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I don’t mean to offend anyone, but it sounds to me like you might choose a battery manufacturer that allows for a remote emergency stop switch. The Pytes V5 is one such battery in your size range. A single press of an emergency stop (e-stop) switch and all batteries shutdown immediately. I don’t know if that would satisfy French regulations so you’ll want to check on that.
reducing Pylontech cables to 1 set →
resulting in 1 positive and 1 negative, which i can fuse and switch with a single action with a knife switch
disadvantage is that the one cable is limitid to 100A, but:
Charging: Solarsmart 100-250 has a max of 100A charging, MP2 can be configured limiting charging to 100A total.
Discharging: 100A = 4800W which is above the MP2 5000 capacity. And I dont intent pulling so much power from my (small) battery bank.
OR am I missing something by saying 100A is a high enough limit??
