jason compo Posted April 29 Share Posted April 29 Hi all I have an axpert 7.2kw inverter connected to 6 x US 2000 polylithium batteries The fuse inbetween the inverter and the batteries has blown.. which size fuse should I put in its place Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted April 29 Share Posted April 29 2 minutes ago, jason compo said: Hi all I have an axpert 7.2kw inverter connected to 6 x US 2000 polylithium batteries The fuse inbetween the inverter and the batteries has blown.. which size fuse should I put in its place What size fuse did you have in? Quote Link to comment Share on other sites More sharing options...
jason compo Posted April 29 Author Share Posted April 29 I do not remember as it was over a year ago Quote Link to comment Share on other sites More sharing options...
Vaal Posted April 30 Share Posted April 30 I might be wrong but this looks quite a bit like a hot connection which caused the temperature to rise and that influenced the fuse rating. What is the size of your cable and how long is it? You can see that on the cable or even on the lug if it is thd correct size lugs used. The fuse size is decided by the cable size. I suggest that you get a decent double pole dc rated fuse isolator (Keto or the like), shorten the cable to get rid of the burnt part or replace the cables, crimp the lugs decently (or get someone to do it) and the tighten the lugs to the correct specs. Quote Link to comment Share on other sites More sharing options...
jason compo Posted April 30 Author Share Posted April 30 All i want to know is the fuse size Quote Link to comment Share on other sites More sharing options...
JaseZA Posted April 30 Share Posted April 30 Inverter states DC Input of 48V and 164.8A. This is the max continuous value. Pylontech US2000B batteries have a continuous output of 25A (so 150A for 6) and a peak of 100A (600A for 6). I would size the fuse to protect the inverter as the batteries should protect themselves by shutting off at the BMS. So 165A fuse.As a logic check, 165A at 48V gives 7920W which is just slight higher than the max continuous output of your inverter. You might not be able to get exactly a 165A fuse so I would go to the next closest larger size. Quote Link to comment Share on other sites More sharing options...
jason compo Posted April 30 Author Share Posted April 30 Thank you, so much. For your help and knowledge on the subject JaseZA 1 Quote Link to comment Share on other sites More sharing options...
Mauritius B Posted April 30 Share Posted April 30 You should find 180amp DC on aliexpress easily. Quote Link to comment Share on other sites More sharing options...
TaliaB Posted April 30 Share Posted April 30 1 hour ago, jason compo said: All i want to know is the fuse size The Axpert MAX 7200-48-230 has a surge rating of 15000va or 12kw so i would suggest you upgrade the fuse to 250A to accomodate the surge value of the inverter and the battery surge rating of 600A. Also as @Vaalsuggested 50mm² battery cable as short as possible. Quote Link to comment Share on other sites More sharing options...
Mauritius B Posted April 30 Share Posted April 30 54 minutes ago, TaliaB said: The Axpert MAX 7200-48-230 has a surge rating of 15000va or 12kw so i would suggest you upgrade the fuse to 250A to accomodate the surge value of the inverter and the battery surge rating of 600A. Also as @Vaalsuggested 50mm² battery cable as short as possible. I would never protect any equipment at surge values cause you are allowing it to work at 12kw continuosly or use 250amp continuosly. Surge operation is limited in time to avoid damage to the equipment. Protection should be designed at nominal working values. Agree with the wires. I would never bolt such kind of fuses or connections to any wooden thing... Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted April 30 Share Posted April 30 (edited) 15 minutes ago, Mauritius B said: I would never protect any equipment at surge values cause you are allowing it to work at 12kw continuosly or use 250amp continuosly. Surge operation is limited in time to avoid damage to the equipment. Luckily inverters cannot work at stated surge level for more than seconds. As stated we rate the fuse for normal load operation. Edited April 30 by Scorp007 Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted April 30 Share Posted April 30 (edited) 1 hour ago, TaliaB said: The Axpert MAX 7200-48-230 has a surge rating of 15000va or 12kw so i would suggest you upgrade the fuse to 250A to accomodate the surge value of the inverter and the battery surge rating of 600A. Also as @Vaalsuggested 50mm² battery cable as short as possible. Inverter can only supply 250A for seconds. No need to rate the fuse that high. I agree with @Vaal that fuse burnt due to hot connection and not the type of fuse holder used. Due to the high current on the battery side of systems it's a good thing to check those connections say every 6/12 months. Edited April 30 by Scorp007 Quote Link to comment Share on other sites More sharing options...
TaliaB Posted April 30 Share Posted April 30 Fuses aren't sized for the inverter. The inverter will have its own internal fuse. But obviously if you undersize your fuse, you are going to be replacing a lot of fuses. If you think the fuse is protecting the inverter you are deluding yourself. As a rule of thumb, the fuse size should be 125% to 175% of the inverter continues operating current. So 165A in this case: 165 x 125%=206A or 165 x 175% = 288A so in this instance i will use a 250A fuse as previously suggested. Bobster. 1 Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted April 30 Share Posted April 30 51 minutes ago, TaliaB said: Fuses aren't sized for the inverter. The inverter will have its own internal fuse. But obviously if you undersize your fuse, you are going to be replacing a lot of fuses. If you think the fuse is protecting the inverter you are deluding yourself. As a rule of thumb, the fuse size should be 125% to 175% of the inverter continues operating current. So 165A in this case: 165 x 125%=206A or 165 x 175% = 288A so in this instance i will use a 250A fuse as previously suggested. You are spot on with your selection. I would just rather change a 200A external fuse than rely on the last line of defence being the internal fuse. The 200A fuse would need some time to blow I guess being within the 25% extra amps over inverter rating. Blowing the inverter fuse means you could be without the inverter for weeks if the "normal" user. Just as I would not rely on my BMS to cut out if it has a overcurrent setting. I would rather blow the external fuse. We see many posts where too many rely on the last line of defence with sad endings. TaliaB 1 Quote Link to comment Share on other sites More sharing options...
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