September 19, 20196 yr Hi all I'm getting different info all over. Regarding the fuse disconnect between the battery and inverter. To my understanding it is there to protect the cable, but in the event that the inverter (Quattro 10kVA) can surge to 20kVA - 400A and the battery can handle this, surely the fuse to use is 400A. If the battery (BYD 20KWh) can go max 280A, then a 250A fuse disconnect per inverter should suffice? One should the also limit current draw in the inverter? Am i correct on the above?
September 19, 20196 yr https://powerforum.co.za/topic/3230-fuse-and-quick-disconnect-between-pylontech-battery-and-inverter/#comment-49146 check the last posts
September 19, 20196 yr 5 hours ago, MrVolt said: then a 250A fuse disconnect per inverter should suffice? From the Manuel... 400A But I will use the 250Amp . (10000va / 48volt = 208.33Amp). I install 125Amp fuses as a rule on my 5kva Units.
September 19, 20196 yr May I ask, if the engineers who designed the equipment notes for a manual to use 400amps, why is that recommendation not followed, WITH the cable sizes? My 24v 3kva says 300amps 50mm2 cable, and that is what I did. Reason I ask also, IF there is a problem, warranty or a fire, and the fuse is not as per recommendation, could that cause a problem or not?
September 19, 20196 yr 41 minutes ago, The Terrible Triplett said: Reason I ask also, IF there is a problem, warranty or a fire, and the fuse is not as per recommendation, could that cause a problem or not? If there is a problem, the 250amp will fuse long before the 400amp do. So by installing fuses with lower ratings, youwill also lower the risk. Installing 500 or 600 amp fuses are asking for trouble. I don't understand the part about the cable size?
September 19, 20196 yr 1 hour ago, Jaco de Jongh said: So by installing fuses with lower ratings, youwill also lower the risk. That makes perfect sense. 1 hour ago, Jaco de Jongh said: I don't understand the part about the cable size? These as in the pic below: 1) Who follows them? 2) And who follows the recommended fuses sizes?
September 20, 20196 yr I fuse to the recommendation. Fuses blow through age as well. When a fuse blows, I go looking for a problem, I don't want to be guessing. Replacing a fuse 250Amp ( even if it is smaller) fuse back onto a fault, won't be a fun experience.
September 20, 20196 yr 2 hours ago, phil.g00 said: Fuses blow through age as well. And they age faster if they work too close to their limit. So I tend to agree. If it blows, it must be because something went wrong. It's job is to be the weakest link in the circuit, it should melt before anything else melts. It's perfectly okay for other things to get a little warmer than usual, what you want to do is keep it below fire-starting levels. A fuse doesn't blow the second you go over its rating. At that link @Dex_ posted someone helpfully posted a picture with the curves. It can take up to 3 hours for a fuse to blow when you exceed the limit by only a tiny amount. Same goes for breakers. The common C-curve breaker only trips instantaneously at 5 times its rating. It can take up to an hour to trip if you're only 10% over.
September 26, 20196 yr Author On 2019/09/19 at 9:40 PM, Jaco de Jongh said: From the Manuel... 400A But I will use the 250Amp . (10000va / 48volt = 208.33Amp). I install 125Amp fuses as a rule on my 5kva Units. Is the above table per inverter in a system. So in a three phase system each inverter has its own fuse disconnect? Again Victron has another view on this: Which is right then for SA? What would the size be if only one fuse disconnect is used then? Also most Lithium batteries does have on board disconnects, is it still necessary for fuse disconnects or can the Victron Mega fuses be used? they are much cheaper.
September 26, 20196 yr 1 hour ago, MrVolt said: So in a three phase system each inverter has its own fuse disconnect? Maybe this will explain it better. Its worth the time reading through it. I took a screenshot of an important part of this document as reference. https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems 1 hour ago, MrVolt said: Which is right then for SA? I would go for the middle option. If i need to isolate one unit, I can do it without affecting the others. and should there be any reason for panic, I can also isolate all of them simultaneously.
September 26, 20196 yr Author 1 hour ago, Jaco de Jongh said: I would go for the middle option. If i need to isolate one unit, I can do it without affecting the others. and should there be any reason for panic, I can also isolate all of them simultaneously. Any idea where one can source 250A single pole fuse disconnects?
September 26, 20196 yr 29 minutes ago, MrVolt said: Any idea where one can source 250A single pole fuse disconnects? That is a good point, No I dont, my brain is stuck on the equipment I normally use, and those are readily available. The double pole 250 Amp Holders are readily available as well, but at almost 2k per inverter. and then again, what do you do with the common Negative wire @ 3 times 250A? I am really uncertain right now, I need to go look what is available. If someone else has an idea, please jump in. There is a guy that recently brought in High Amperage double pole molded case DC breakers, Maybe his got something you can use to rather go for the Last option. His not keen on answering a phone so it might take some time to get hold of him.
September 26, 20196 yr Author 1 hour ago, Jaco de Jongh said: That is a good point, No I dont, my brain is stuck on the equipment I normally use, and those are readily available. The double pole 250 Amp Holders are readily available as well, but at almost 2k per inverter. and then again, what do you do with the common Negative wire @ 3 times 250A? I am really uncertain right now, I need to go look what is available. If someone else has an idea, please jump in. There is a guy that recently brought in High Amperage double pole molded case DC breakers, Maybe his got something you can use to rather go for the Last option. His not keen on answering a phone so it might take some time to get hold of him. Maybe a option is to use two 250A double poles disconnects, that way you can break three phases and one common neutral with the four poles?
September 26, 20196 yr 5 minutes ago, MrVolt said: that way you can break three phases and one common neutral with the four poles? I am worried about that common Negative. If you draw 100 Amps from the battery per inverter, the current in the Negative wire will be 300 Amps. Theoretically If you have a 250 Amp fuse on each positive wire, you will need a 750 Amp fuse on the Negative to balance it out.
September 26, 20196 yr Author 12 minutes ago, Jaco de Jongh said: I am worried about that common Negative. If you draw 100 Amps from the battery per inverter, the current in the Negative wire will be 300 Amps. Theoretically If you have a 250 Amp fuse on each positive wire, you will need a 750 Amp fuse on the Negative to balance it out. Yes I agree, I missed that. Another option is to use the mega fuse links from victron. But then there is no disconnect option. I did find a DC on/off switch but it's only rated at 200A/48V.
September 27, 20196 yr Author 12 hours ago, Jaco de Jongh said: I am worried about that common Negative. If you draw 100 Amps from the battery per inverter, the current in the Negative wire will be 300 Amps. Theoretically If you have a 250 Amp fuse on each positive wire, you will need a 750 Amp fuse on the Negative to balance it out. A possible solution is to use a 250A fuse disconnect for each of the BYD cabinets. In this system there are two cabinets of 4 cells each, so a 250A fuse will give 60A per cell. 250x48=12kW x2 = 24kW (thats the same as three 10kVA quattros.)
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