superdiy Posted October 28, 2016 Share Posted October 28, 2016 13 hours ago, AndewJ said: I use a 100A fuse on my 250A bank since the Axpert only draws 93A. You get some nice blade fuses at the audio installation places for about R50. The fuse holder cost about R200. Rockford Forcegate makes one with a built in Ampere meter as well. A 100A fuse will maybe just cut it, but under extended full load conditions and higher ambient temperatures it might blow. Rule of thumb is to use a fuse rated at 25% higher than the required current, so in your case you should actually use a 115A (or 125A standard) fuse to prevent nuisance blowing. Do not use fuses intended for car audio for 48v systems. Automotive and car audio fuses are usually rated for 32V or less and is not designed to work at higher voltages. Any fuse has a voltage rating as well and if it is used at a voltage higher than what it is rated for, it might not be able to isolate the circuit as intended in case of a fault condition. Quote Link to comment Share on other sites More sharing options...
___ Posted October 28, 2016 Share Posted October 28, 2016 4 hours ago, superdiy said: Any fuse has a voltage rating as well and if it is used at a voltage higher than what it is rated for, it might not be able to isolate the circuit as intended in case of a fault condition Amen. I think we discussed this before, but you must imagine what it looks like in slow motion when a fuse blows. Perhaps a bit like when a bridge collapses: It's not like the whole bridge is just gone in an instant, instead cracks appear first, then a part right in the middle falls away, and then the rest comes tumbling after with the gap progressively widening. Same with a fuse: When it burns through the gap is very small initially, small enough that the voltage can jump across and ionize the air. As long as the current keeps flowing the fuse wire will keep melting and the gap will become bigger until it is too wide for the voltage to jump across. Unless the design gap isn't big enough and the gap never becomes big enough, leaving you with a nice hot electrical fire. Those Mersen fuse holders are very nice though. I have one of those too. superdiy 1 Quote Link to comment Share on other sites More sharing options...
superdiy Posted October 28, 2016 Share Posted October 28, 2016 9 minutes ago, plonkster said: you must imagine what it looks like in slow motion when a fuse blows. Perhaps a bit like when a bridge collapses: It's not like the whole bridge is just gone in an instant, instead cracks appear first, then a part right in the middle falls away, and then the rest comes tumbling after with the gap progressively widening. Same with a fuse: When it burns through the gap is very small initially, small enough that the voltage can jump across and ionize the air. As long as the current keeps flowing the fuse wire will keep melting and the gap will become bigger until it is too wide for the voltage to jump across. Unless the design gap isn't big enough and the gap never becomes big enough, leaving you with a nice hot electrical fire. As I was reading this I could "see" the collapsing bridge and the melting fuse in slow motion. It was like reading a good book. viper_za, Chris Hobson and ___ 3 Quote Link to comment Share on other sites More sharing options...
___ Posted October 28, 2016 Share Posted October 28, 2016 Come to think of it... when you strike up an arc with a welding machine that's precisely what you're doing, widening the gap to get a nice hot flame, but not so much that you lose the flame. With fuses, we'd like to lose the flame thank you very much :-P superdiy 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted October 28, 2016 Share Posted October 28, 2016 Just for clarity for future readers of this very informative thread on fuses It must not be forgotten that the fuse is there to protect the wire. So it is of no use having a 250a fuse on a wire that can only handle a max of 100amps. Quote Link to comment Share on other sites More sharing options...
Chris-R Posted October 28, 2016 Share Posted October 28, 2016 Anybody up for grabbing 8 x 180ah Monbat AGM batteries. Price very negotiable. Brand new !! Quote Link to comment Share on other sites More sharing options...
Guest Posted October 28, 2016 Share Posted October 28, 2016 Also put them under Classifieds on the forum: http://powerforum.co.za/forum/27-classifieds/ Quote Link to comment Share on other sites More sharing options...
Chris-R Posted October 28, 2016 Share Posted October 28, 2016 Thanks TTT. Must get used to the forum facilities. I am trying to sell these batteries and want to replace them with a set of 24 x Raylite 2v 560AH batteries. Thinking to use the Energy Pro Active battery equaliser system on them and then I hope I will be sorted. What is your opinion on this? I can't afford to make a second mistake and need to start putting all of this together now. - Thanks Quote Link to comment Share on other sites More sharing options...
Guest Posted October 28, 2016 Share Posted October 28, 2016 @Chris Rossouw for me to give any suggestion, I would first want to know the load you need powered, and for how long, from batteries. To run a household off batteries, you need a lot of batteries, a LOT. But, if you can adjust the load that must run on the batteries, then you may not have to sell what you have and use them to their full capabilities. Like in my case, my T105RE's should last me 10 years on 20% DOD ... and if there are infrequent power failures, I will happily run them to 50% DOD at times. Quote Link to comment Share on other sites More sharing options...
AndewJ Posted October 28, 2016 Share Posted October 28, 2016 12 hours ago, superdiy said: A 100A fuse will maybe just cut it, but under extended full load conditions and higher ambient temperatures it might blow. Rule of thumb is to use a fuse rated at 25% higher than the required current, so in your case you should actually use a 115A (or 125A standard) fuse to prevent nuisance blowing. Do not use fuses intended for car audio for 48v systems. Automotive and car audio fuses are usually rated for 32V or less and is not designed to work at higher voltages. Any fuse has a voltage rating as well and if it is used at a voltage higher than what it is rated for, it might not be able to isolate the circuit as intended in case of a fault condition. The next size up is 150A which I think is too much. The inverter shouldn't draw more than 93A constantly and I haven't yet had any problems with the current fuse. The way I understand it, is that DC rated fuses are not entirely limited by voltage. it is basically just another conductor but with limited ampere ratings.The voltage rating only plays a role after the fuse has blown. I guess these ANL fuses are big enough to quench the arc well enough in case of fault. Quote Link to comment Share on other sites More sharing options...
Chris-R Posted October 28, 2016 Share Posted October 28, 2016 5 hours ago, The Terrible Triplett said: @Chris Rossouw for me to give any suggestion, I would first want to know the load you need powered, and for how long, from batteries. To run a household off batteries, you need a lot of batteries, a LOT. But, if you can adjust the load that must run on the batteries, then you may not have to sell what you have and use them to their full capabilities. Like in my case, my T105RE's should last me 10 years on 20% DOD ... and if there are infrequent power failures, I will happily run them to 50% DOD at times. Hi TTT, I was wondering tonight whether I should not install the inverter & panels, run it for a month generating during the day and using the grid at night time. Connecting the genie with a switchover switch when the grid goes down. This way I would generate data of exactly what I use per day from the grid and I would be able to calculate fairly accurately what size of battery bank I would need. Could you agree with this idea? A battery bank is expensive and I might have made a mistake already, no use doing it again! Quote Link to comment Share on other sites More sharing options...
Guest Posted October 29, 2016 Share Posted October 29, 2016 Hi Chris, we all made mistakes and those who have not made any, should add the word 'yet' at the end. So having made a few myself, some quite spectacular, and having gotten pretty excited to change things in a hurry, I offer the following take. Don't spend more money bar a BMV right now and battery balancers soon. Get everything set up. Then see what your load is doing. Then sort the load with facts to not use batteries where possible - batteries are for power failures coupled with using them the rest of the time for the best possible ROI. You can with the batteries you have, power selected important circuits during power failures with ease, but as an EXAMPLE, like I always hint, not a kitchen. It is a want, not a need. Others may disagree but consider that if you have Eskom to use that for the kitchen for it tends to be used at night, after work, and therefor relies on batteries, drawing huge currents. Geyser and pumps and other loads daytime are obviously generating huge savings with no need for batteries. Lights should be off grid to use some of the batteries capacity to offset something against their cost, and so forth. There are a host of other ideas between us all that you can do, if you are technically minded you do it yourself, to improve what you have already bought. Set yourself a goal of say 30 days to see what your system does, then, with new facts and ideas, make the call on how to improve, then decide on the batteries. Quote Link to comment Share on other sites More sharing options...
Chris-R Posted November 1, 2016 Share Posted November 1, 2016 Hi TTT, I was away for 4 days and only saw your post toady. Thanks for confirming my way of thinking. It is exactly what I am going to do, except that I think I will not connect the batteries as yet, for in case I need to change them, they will still be unused. They are fully charged and have a shelf live of up to 6 months. Many thanks Quote Link to comment Share on other sites More sharing options...
Guest Posted November 1, 2016 Share Posted November 1, 2016 3 minutes ago, Chris Rossouw said: I think I will not connect the batteries as yet, for in case I need to change them, they will still be unused That is one option. OR install them, after having asking your supplier if and how you need to "break / settle" them in, that once you do sell them in a short period of time, they are checked and ready to roll. Also eliminates the potential issue that one may accidentally need to be replaced under warranty. Quote Link to comment Share on other sites More sharing options...
Chris-R Posted November 1, 2016 Share Posted November 1, 2016 Well thought , thanks Quote Link to comment Share on other sites More sharing options...
zathras Posted July 22, 2020 Share Posted July 22, 2020 Hi all. Need some advice on a battery fuse disconnect. Resurrecting an old thread. I have a small backup system: 200ah LiFePo4 battery, 850VA inverter/charger, charges at max 13A. A Victron mega-fuse holder on the positive wire, with 100A fuse. Even with the inverter switched off, and bypass switch off, its still drawing down the battery. Been looking at a few different options as a disconnect on the negative wire and would like your suggestions: https://4x4direct.co.za/battery-accessories/6802-isolator-switch-heavy-duty-marine.html https://4x4direct.co.za/circuit-breakers/5891-circuit-breaker-60a.html https://www.sonopsolar.co.za/product/battery-fuse-disconnect-1-pole-160a/ Is the last one complete overkill? Very costly once you add the 100A fuse and shipping. Quote Link to comment Share on other sites More sharing options...
Johan Kotze Posted February 10, 2022 Share Posted February 10, 2022 Hi, I noticed that this is an old thread but maybe some can help me. I bought a used mecer 5kva inverter, recently served by Mustek, with 4 x 100AH batteries. Must there be a fuse per battery installed Quote Link to comment Share on other sites More sharing options...
Coulomb Posted February 10, 2022 Share Posted February 10, 2022 2 hours ago, Johan Kotze said: Must there be a fuse per battery installed All 4 battery modules will likely be in series, assuming it's a 48 V inverter. In that case, a single fuse will suffice. Local regulations may require a fuse at the positive and negative ends; I have such with my system. But you won't need 4-5 fuses. Of course, battery fuses have to be DC rated; AC fuses won't clear a fault. I had a fault recently that blew one of my 100 A battery fuses. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.