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Advice on cable and fuse sizing for battery rack

My guess is Victron recommendation of 400A fuse, the fuses need to be sized for surge rating of the Multiplus. Those Multiplus units have great surge ratings.

Small spikes of 400a will fry a 200/300a fuse, especially a super fast blow class T. The 4/0 cables can handle small surges as it takes a bit longer for the heat to build up. Breakers are also similar in they take longer to “act”.
 
740GLE said:
Small spikes of 400a will fry a 200/300a fuse, especially a super fast blow class T. The 4/0 cables can handle small surges as it takes a bit longer for the heat to build up. Breakers are also similar in they take longer to “act”.
Click to expand...

According to my wife a class t can take 200% current for ~30 seconds.
I guess the Quattro could flirt with that.

The manual calls for 2x 50mm2 and a single 400 amp fuse.
Those 2 criteria are at odds.
Should be 2x 50mm2 with 2x 250 amp fuses.

page 9 of https://www.victronenergy.com/uploa...V-(firmware-xxxx4xx)-EN-NL-FR-DE-ES-SE-IT.pdf
 
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All depends on the clearing time of each. Fuses usually have a minimum melt point where irreversible damage is starting to happen. Breakers typically don’t have that same gray area.
 
John Frum said:
According to my wife a class t can take 200% current for ~30 seconds.
I guess the Quattro could flirt with that.

The manual calls for 2x 50mm2 and a single 400 amp fuse.
Those 2 criteria are at odds.
Should be 2x 50mm2 with 2x 250 amp fuses.

page 9 of https://www.victronenergy.com/uploa...V-(firmware-xxxx4xx)-EN-NL-FR-DE-ES-SE-IT.pdf
Click to expand...
2x50mm^2 is similar to 2x1awg which is just above 3/0, that’s why many people just round up to 4/0.

My guess 4/0 isn’t compatible with the terminal blocks of the Victron unit but can be used for bus bar to battery wiring.
 
740GLE said:
2x50mm^2 is similar to 2x1awg which is just above 3/0, that’s why many people just round up to 4/0.

My guess 4/0 isn’t compatible with the terminal blocks of the Victron unit but can be used for bus bar to battery wiring.
Click to expand...
Are you assuming the busbar to battery wiring comes off the backplane?
 
I used 300a fuses on that build. Yes, it's less than what Victron asks for, but my logic is a 300a can support over 100% load on a 300a fuse (300*51.2 = 15.3kw) and I'd rather have a fuse blow than a FET board. In my testing, the MEGAs can handle a brief 400a surge without blowing.

4/0 fits no problem on these inverters, both on the terminals and through the grommets. My kits also are provided with 4/0 cable as well.
 
John Frum said:
Are you assuming the busbar to battery wiring comes off the backplane?
Click to expand...
7F35FFEE-9179-4DC7-B850-179E2099B4DF.png

Sure looks like two terminal inputs for the DC, probably why the manual states 2x conductors can be used for DC.

Does that mean only 1 4/0 can’t work? I’d say as long as it’s a quality lug and has proper area of contact it’ll work plenty fine.
 
John Frum said:
Not until you write one.

No but the I'm big fan of the feeder/branch design pattern.
A fused busbar makes that really elegant.
Also the fused busbar approach means less joinery which means less resistance which means a more efficient system.
My philosophy is best described by Antoine de Saint-Exupéry as "A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away."

The power_ins are are what the batteries terminate on .
The distributor is what the loads and charge sources terminate on.
If you don't want to use a power in that is fine then you will need to fuse each each load or charge source.
45 service amps / .8 fuse headroom = 56.25 fault amps.
By the standard calculation your 50 amp MCBs are to small to go between the MPPTs and the positive busbar.

Nice.

Because only mega fuses fit in the lynx distributor.
If you don't want to do structured wiring that is fine.

That will be the choke point unless you use the lynx system.
Click to expand...

Thanks John, been getting a bit overwhelmed trying to take it all in. In the last few days I've learned that DC breakers are polarised, or non polarised, and nasty things can happen when you get it wrong with polarised breakers, so I'm revisiting the breaker/isolator plans. I've ordered 250a and 400a t class fuses and holders.

You say the Victron Smart Shunt 500 will be a choke point, I don't understand why this is, its rated at 500 amps, but the data sheet doesn't say whether that is peak or constant. My inverter, which is 8000w would be at most around 160 - 210 amps constant, depending on battery voltage and efficiency. Threads I've read have said that the Smart Shunt 500 is perfectly up to this. Could you explain why it would be a choke point please?
 
Ron-ski said:
Could you explain why it would be a choke point please?
Click to expand...
Because it will go between the power-in and the distributor.
I think your are going to have to use 4/0 wire for joinery.
Its the joinery that is the choke point.
 
I was considering using 60 or 70mm cable 1/0 is 53.5, 4/0 is 107 mm2. But double up on the main runs - the Quattro is designed to have two battery cables connected, so the run from battery busbar to shunt could also be doubled up, so long as lengths are exactly the same.

I was considering mounting the shunt either directly to the busbar, or using 40 x 8 tinned copper bar, then the two cables directly to a Lynx power in using the end connections, then straight out the other side for the inverter, with the SCC connected to the Lynx power in, which can be fused.

Of course it does beg the question of whether two stacked connections would be OK, I think I read somewhere that it was.

Of course using the complete Lynx system would look better, but it is three times the money, but I may just go with that, it would be cleaner.

Victron do a SmartShunt 500, 1000 and 2000, only the 2000 has two connecting terminal each end at the top, all are M10. But, I have just noticed that the 1000 and 2000 have M10 side mounted terminals as well.
 
Just to update this thread.

I ordered new breakers and fuse holders from ZJ Beny, they have several different websites, I found the downloads didn't work on the solar website, but you can find them on the main website. Ordering which was via Alibaba was a little different, but all worked very well. I paid on the 31 October, and received the items today. I was kept constantly updated via WhatsApp, so all was very easy, there was only one slight bit of confusion, and that was I couldn't work out how to pay - for some reason she hadn't raised an invoice, once that was done it appeared on Alibaba and I could easily pay.

The breakers are no polarity or bi-directional, so perfect for solar battery storage systems, and SolarEdge suggest to use their products in one of their documents, so hopefully that's a good sign.

I ended up going with 160A breaker for each battery shelf, and 250A for the whole rack - I figured that due to the time it takes a breaker to trip it would be fine for momentary peaks - the maximum continuous current fromt the inverter would be about 160A. 63A breakers for the charge controllers, and 32A for the solar combiners, and individual fuse holders for each string of panels.

I ordered the Lynx Shunt VE in the end, just to make things tidier really.

Main cable run I've order 120mm cable for busbar to shunt, runs from battery to busbar are 70mm, and there will be two runs (2 x positive, 2 x negative) from the Lynx Power in to the inverter, both in 70mm. MPPT to Lynx Power in will be 35mm cable. Cables are 0361TQ which is double insulated.

I have on order 250A T Class for each battery, and 400A for the whole rack.

Cable size conversion:

4/0 is 107 mm2 - Available cable size 120mm2
1/0 is 53.5mm2 - Available cable size 70mm2
006 is 13.3 mm2 - Available cable size 16mm2
010 is 5.26mm2 - Available cable size 6mm2

PS Next items to buy are the cable lugs, I've found these which look substantial.
 
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I went with 70mm cable from batteries to rack busbar. 120mm from battery rack busbar to Lynx shunt. Then 2 x 70mm from Lynx Distribution to the inverter. MPPT to Lynx Distribution is 35mm
 
Nice setup and planning.
I am looking at the zj Beny DC cb as well. I'm in the buying stuff phase.. Just wondering what the cable input are on the zj Beny cb's are? Bolt on connection? What size bolts / lugs?
Cheers
 
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