bikey Posted June 27, 2023 Share Posted June 27, 2023 Hi all fitting a 2000watt inverter to a 250amp lithium battery, what size inline fuse should be fitted in the positive line thank you Link to comment Share on other sites More sharing options...
Brian Kirby Posted June 27, 2023 Share Posted June 27, 2023 Sorry to be picky, but which "positive" line are you referring to? The (presumed) 230V output line from the inverter, or the 12V feed line from the battery to power the inverter? As a general rule, the fuse is there to protect the wiring "downstream" from the fuse, and the size of fuse required required for safety relates to the maximum current that wires of that gauge can handle without overheating. The starting point in both cases should be the gauge of wire required to safely conduct the current involved, and then select the fuse rating to ensure the fuse "pops" before the wiring overheats. But, you also need to take account of the input current required to run the inverter, so that it can deliver its full potential, and the maximum safe continual discharge rate from the battery to ensure the battery is not damaged by being discharged at too high a rate. Aren't there instructions with both battery and inverter, that specify recommended wiring gauges and safe discharge rates? I think more detail is required. The potential risks in getting either wrong are 1; fire - if the wiring overheats, and 2; damage to the battery - if it is discharged too fast. Link to comment Share on other sites More sharing options...
mtravel Posted June 27, 2023 Share Posted June 27, 2023 I'm not a guru but it will depend on wire size from batteries to the equipment. On the internet there are size to rate tables. Link to comment Share on other sites More sharing options...
Dave S Posted June 28, 2023 Share Posted June 28, 2023 A 2,000 Watt inverter could easily draw 200 Amps from your battery so you probably need a 250A fuse and fuseholder. Link to comment Share on other sites More sharing options...
Keithl Posted June 28, 2023 Share Posted June 28, 2023 Bikey, What is the maximum permitted current draw from your Lithium battery? As Dave S has said above your inverter can draw in excess of 200 Amps so is 1C (ie Current = Capacity) permitted? Link to comment Share on other sites More sharing options...
MikeF Posted June 28, 2023 Share Posted June 28, 2023 Consider the cable , since the current may approach 200 amps, at least 35mm2 cable is needed. The volt drop between battery and inverter needs to be as low as practical, there will be slight drops in fuses and cable terminations but the majority will be in the cable. For a one meter length 35mm2 cable will drop 0.23 volts, 50mm2 will drop 0.16 volts and for 70mm2 the drop is 0.12 volts . If the inverter is within 2 metres of the battery and the inverter maximum is rarely used, the 35mm2 should be OK. For a greater distance or use at maximum power, consider the more heavy duty cable. Automotive or marine grade cable is suitable, as is welding cable ( more flexible). Use quality cable terminations made with professional crimp tools. I suggest a 200 amp fuse as it's unlikely the battery BMS can reliably supply more. If you have loads requiring high start up currents, example, air conditioning, perhaps 250 amp fuse with 50mm2 cable/70mm2 cable. The fuse position and type is important, idealy it should be fitted as close as practical to the battery positive post and be a type that can withstand the extremely high currents a lithium battery can deliver under failure conditions. It's estimated, and tests have shown, this could be in the region of 7000 amps. The fuse must be designed to tollerate this, otherwise, even if the fuse fails as designed at say 200 amps, the battery ability to deliver very high current, allows energy to 'jump the gap', ( just like arc welding ), and destroy/ melt/ set on fire the rest of the 12 volt system. The common 'Mega' fuse only has a withstand current of 2000 amps so is not suitable. For a 12v system MRBF fuses are acceptable ( withstand 10000 amps), class T or HRC industrial fuses, ( withstand 20000 amps or higher. For each type of fuse a quality fuse holder is needed. https://www.12voltplanet.co.uk/bussman-class-t-fuses.html https://rjsmarine.co.uk/product/mrbf-terminal-fuse/ https://www.mobilecentre.co.uk/blue-sea-5191 The Blue Sea holder, usefully, can be mounted directly on the battery post. Going somewhat beyond the current post, to meet UK regulations regarding permanent install of inverters, suitable protection against electric shock must be installed. This requires the inverter to be a type that has, or can be configured, a neutral to protective earth bond. A double pole RCD needs to be installed between inverter and any cables to outlets /appliances. Mike Link to comment Share on other sites More sharing options...
bikey Posted June 28, 2023 Author Share Posted June 28, 2023 Hi thanks to all for your help and advice especially Mike for his very in-depth and informative reply, the cable being used is 35mm sq and will fit a200amp fuse. the inverter was given to me by a friend who only bought it 6 months ago but has decided to sell his van due to the high cost of sites now and the insistence of many sites to now pre book , not how he wants to camp. I only want to use the inverter for low voltage items chargers etc so I believe this set up will be suitable Link to comment Share on other sites More sharing options...
Dave S Posted June 29, 2023 Share Posted June 29, 2023 16 hours ago, bikey said: I only want to use the inverter for low voltage items chargers etc so I believe this set up will be suitable It would probably be a lot easier to find chargers that work of 12 volts. Link to comment Share on other sites More sharing options...
MikeF Posted June 29, 2023 Share Posted June 29, 2023 If you are only intending to use very low power appliances you do not need a high power Inverter and associated costs for cable and fuses. Either obtain 12v based converters for phone and computer charging, or fit a pure sinewave low power inverter of say 300 watts. Running a 2000 watt inverter for low power appliances is inefficient , and there is a possible constant overhead power requirement of upto about 30 to 40 watts, 3 amps per hour, even with the inverters switched on with no load. Its not stated what type of inverter, but unless pure sine wave, may damage some types of low power appliance chargers. Note, even if you decide not to install the inverter, a specialist fuse, as I discussed, should still be fitted to the lithium battery. The fuse should be rated for the current expected and cables in the system. Mike Link to comment Share on other sites More sharing options...
bikey Posted June 29, 2023 Author Share Posted June 29, 2023 Hi the inverter is a pure sine wave 2000 watt as I said was given to free gratis I have already got several metres of red 35mm sq cable and 3 fuse holders so only cost is the actual fuse, wife has a 750 watt hairdryer so may use it for that. Mike what fuse rating would you suggest in the battery cable which is also 35mm sq thanks Brian Link to comment Share on other sites More sharing options...
Brian Kirby Posted June 29, 2023 Share Posted June 29, 2023 But, how do you re-charge your lithium battery? Your 230V usage seems generally quite light, yet you have a 250Ah battery + 2kW inverter, which is substantially larger than average, suggesting heavy 12V consumption, albeit possibly over extended periods of time. If you only intend to to use the inverter for phone and computer charging, with an occasional short burst of 750W hair drying, the proposed set-up does look excessive. If, as seems the case, you mainly use your van "off grid", you will be mostly reliant on the alternator to simultaneously re-charge both lithium (leisure), and lead acid (assumed) starter batteries. Do you have a solar panel? If not, and you don't spend at least some time on EHU, can your alternator cope with re-charging a heavily discharged lithium battery. Equally, can your on-board battery charger cope with that load if/when you plug in to 230V mains power? Re the solar panel, will it put sufficient charge back into the lithium to enable either the alternator, or the on-board charger, to bridge the gap? Apologies again, but you do have to put back what you take out, and my (very limited! 🙂) understanding is that just as lithium batteries can deliver relatively heavy supply loads, they also demand relatively heavy charging loads - that may not have been contemplated when either the alternator, or the on-board charger, were specified/installed. Ditto the installed wiring between alternator, charger, and lithium battery. Link to comment Share on other sites More sharing options...
bikey Posted June 29, 2023 Author Share Posted June 29, 2023 Hi Brian I have 2 x 100 solar panels and when I purchased the battery I also purchased a 20amp lithium charger from the same company who hard wired the charger to the battery , the reason I bought a250 amp battery the cost differential between 150 and 250 was not that high most of my usage is at non hook up sites C&C temporary holiday sites we have just returned from 10 days at a THS in Southport electric hookup £5 day so £50 saved there, very pleased with the lithium battery and the capacity gives me no concerns with regards to how I will charge it. regards Brian Link to comment Share on other sites More sharing options...
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