Claculating fuse size

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pyxismx

Registered:1513601208
Posts: 6

Posted 1513601962	Reply with quote #1

Hi experts I just had a new system installed, unfortunately the company that made the installation did a somewhat poor job..... They installed MPP solar copy inverters, a "no name" brand.....and there is no fuses between the batteries and the inverters, they claim that its not nessesary, and the the inverters are already fused....I would feel more comfortable with a fuse between the batteries and the inverter, but how do I calculate the fuse size? I am guessing it relates to the inverters 2kv x 1.25, and the 24 volts from the batteries making it a 100 amp fuse, sounds a bit high to me, or am I on the right track???? the installer used caliper 0 or 1 for the batteries and the connection to the inverter, can I even get DC fuses for that cable size?? thanks guys Klaus

Rick H Parker

Registered:1489180564
Posts: 790

Posted 1513625487	Reply with quote #2

and the the inverters are already fused....I would feel more comfortable with a fuse between the batteries and the inverter, There already is a fuse between the batteries and the inverter, it is located at the input of the inverter. If you install a second fuse, it is just more things that can go wrong. If you have a reason to think the cables might short out, which should not be an issue at all, correct the issue not do a band-aid fix with a second fuse. __________________ Rick H Parker Kansas, USA Electronics Engineering Technologist

pyxismx

Registered:1513601208
Posts: 6

Posted 1513642449	Reply with quote #3

I am not sure there is a fuse in the inverter, its a no brand Chinese copy inverter, put against my wishes. so how would I know the fuse is there? In fact the manual of the original MPP solar recommends a fuse...... best Klaus

Rick H Parker

Registered:1489180564
Posts: 790

Posted 1513671295	Reply with quote #4

Original MPPT ... You mean not the one you have now? Never see a inverter without a brand. I have see lots of generics labeled with different brand names. __________________ Rick H Parker Kansas, USA Electronics Engineering Technologist

pyxismx

Registered:1513601208
Posts: 6

Posted 1513689889	Reply with quote #5

Hi Rick It is a copy of a MPP solar product, its confirmed by MPP solar, it looks excatly like a MPP solar inverter, but I have sendt pictures to MPP solar, and their reply is " 100% not our product". so there is (as I see it) no way to know if the inverter is actually fused, I dont see a fuse anywhere, and am guessing that if there is a fuse, I should be able to replace it if it blows.... I have no confidence in the product, and am struggling with the company that put them to change them to the MPP solar product mentioned in the contract, but it seems to be a loosing battle, I am 100% off grid, and cant afford to buy 2 new inverters at the moment, so I have to run with what I have, I would feel better if they where fused. I live in a tropical fores and although the room where the batteries and inverters are located has been sealed with net, you never know what kind of wildlife could make their way in there, and thats the reason for my question about fuse size... best Klaus

stmbtwle

Registered:1388591029
Posts: 2,860

Posted 1513690775 · Edited	Reply with quote #6

Doesn't it have a manual? (Might be one online). Without a manual, the only way you'll know for sure is to disconnect it, let it sit for a while to discharge the capacitors, then remove the cover and look. If you're feeling nervous about it (and I can understand) put a fuse on it, right next to the batteries. I think your calculation of fuse size is about right. My inverter has internal fuses, but the manual still recommends an external one between it and the batteries. This protects the wiring and batteries as much as the inverter. __________________ Solar is like the wind. It may be free, but putting it to work isn't! Willie, Tampa Bay

pyxismx

Registered:1513601208
Posts: 6

Posted 1513696593	Reply with quote #7

there is a manual, but is just a modified copy of the manual for the original product, and has no instructions to calculate fuse size....

Rick H Parker

Registered:1489180564
Posts: 790

Posted 1513717366 · Edited	Reply with quote #8

Got it ... you have good reasons not to trust anything the installer said. I am guessing it relates to the inverters 2kv x 1.25, and the 24 volts from the batteries making it a 100 amp fuse, sounds a bit high to me, or am I on the right track???? Do you mean 2KW (2 Kilowatts of power) not 2KV (2 kilovolts of force) or 2kVA ( 2 KiloVoltAmps) Which is pretty much the same as 2KW. 2KW x 1.25 = 2.5Kw I = P/V = 2500W/24V = 104.167 W/V = 104.167 Amps. A 100A fuse will be good to about 2400 watts @ 24V. What is the lowest voltage you allow the battery to go to? __________________ Rick H Parker Kansas, USA Electronics Engineering Technologist

pyxismx

Registered:1513601208
Posts: 6

Posted 1513718838	Reply with quote #9

Rick.. Thanks for your time, i am unsure if I can regulate the voltage, its a new system, and although I once finished my electrician education in Denmark, I am struggling to remember everything, i am unfortunately not eighteen anymore, and its more than 30 years since I finished... I have attached a photo of the label on the inverter, I am honestly confused..... once again, I really appreciate your help.. Best klaus Attached Images label.jpg (1.74 MB, 9 views)

Rick H Parker

Registered:1489180564
Posts: 790

Posted 1513726521 · Edited	Reply with quote #10

It is a It is a 1600 Watt hybrid inverter with a 60A charge controller and a 20A AC charger. This thing will work with a backup generator. Because DC is never out of phase use 1600 watts not 2000VA to calculate the DC current. 1600W/24V= 67 Amps. However if your going to add the fuse to protect the cables. A 100A fuse would be good for protecting a 1 or 0 AWG Copper cable and the inverter won't blow it. Place the 100A at the battery end of the cable. It is Copper cable not cheap Aluminum ... right? __________________ Rick H Parker Kansas, USA Electronics Engineering Technologist

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