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Forum Index : Electronics : Fuse size
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Wombat Regular Member  Joined: 27/05/2011 Location: AustraliaPosts: 72 |
Hi all. Purchased a 3000W inverter/charger for my 24v battery bank and was hoping someone could tell me what size fuse I should use on the battery side. The spec sheet doesn't tell me the max current draw for AC or DC. Thanks in advance, Russ  |
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yahoo2 Guru  Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
hi wombat, I use a fuse made by littelfuse called a Mega slo-blo 32V bolt down fuse. The size and speed of the fuse will depend on what you are trying to do with it. I would guess a 3000W inverter should be capable of 6000W surge for a few seconds up to 30 seconds depending on the inverter. The fuse should be large enough to handle this load. That's roughly 250 Amps depending on the dc voltage.edit(dont take my word for this, find out what your inverter is actually rated at surge, the info must be somewhere) A 175 Amp Mega will handle 300A for about 30 seconds so that is around the ballpark. A 250 Amp Mega will handle 400A for between 100 and 1000 seconds. This range of fuses blow instantly at 2000 amps, if your battery bank is capable of punching out this sort of grunt and you only want protection for a dead short a 500 amp fuse would work, its a bit risky though, cos perfect shorts are pretty rare. Hope this helps yahoo PS these are not suitable for a 48 volt battery bank, 60 volts will arc across the fuse terminals like a welder and possibly start a fire, just thought I would mention it, I wouldn't like to see anyone reading this to get caught 
I'm confused, no wait... maybe I'm not... |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Wombat I use a 200 amp breaker used for electric winches rated for 12 / 24 volts as it is re settable and has a surge time I tested to be five seconds, I run a 24 volt 5000 watt inverter of it I also use a 16 amp AC circuit breaker on the output to save overloads on the AC side. All the best Bob Foolin Around |
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| Wombat Regular Member Joined: 27/05/2011 Location: AustraliaPosts: 72 |
Giday Yahoo2. Thanks for the link. Gives me a starting point. The inverter will supply a max of 9000W for 10 secs and will easily start a 1HP motor. The battery bank is 720AH/10HR AGM's (6 x ALCO AC12-240). If 6000w = 250A (or there bouts), then 9000W = 375A. How does a 400A fast blow sound? I would rather this fuse to go first before the inverter needs to shut down. And use 150A slow blow between each pair of battery for short circuit protection. How's my logic so far? 
I'm trying to get some sort of balance between battery capacity, current drawn, and panel size with the battery's welfare being first priority, and current drawn being the last variable. Really, I expect to draw only 2Kw max at any one time (except for the odd surge) so as to use 70% of the inverters output and not overload it. As for panels, I'm thinking of 180W per battery for starters. As I don't currently have that many, I may have to reduce the battery bank or the current draw from the inverter to suit. I only have 3 x 170W @ 24V and 1 x 190W @ 24V. The odd panels are a neucense, needing 2 controllers. Yes, I'm rambling on a bit, but I figure all things must be considered to juggle a happy medium. Thankx again, Russ P.S. Does anyone have/know of any of these panels? - SL190CE-27P & SST170-72M. 1 more off each would be great. |
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| Wombat Regular Member Joined: 27/05/2011 Location: AustraliaPosts: 72 |
Opps! Max current draw on the AC side is 9000W for 10sec! You goose! HA! 
Hello Bob. Nice to catch up with you again. Your help with my battery's earlier has been very successful with all battery's are now happily "holding hands"
A AC beaker/fuse sounds like common output and will probably go with 2 x 8A, 3 x 6A, or 1 x 8A & 2 x 6A breakers so I can turn off the "less necessary" circuits to suit... and add an Earth Leakage Breaker for good measure. From curiosity, how many watts @ 240VAC can you pull from your inverter before the 200A @ 12VDC trips? It looks like I may have to experiment with the DC fuse/breaker to find out what size would suit the inverter best. Should start with one of those breakers first I think... with a larger fast blow fuse in series... Hmmm... going to need a big shunt as well! Hahaha... Thinking out loud now!
All sound nice and safely... :P] Russ |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Most of the inverters I have worked on have internal fuses and circuit breakers, I would be comfortable if the internal breakers are only tripping a few times a year. Breakers have a limited lifespan with DC, eventually they will stop working or stick shut, an external breaker that trips just before the internal ones go is a good idea, far cheaper to replace. cheap high amp fast blow fuses can be unpredictable, I have melted a perfectly good sidchrome spanner and not blown a 400 Amp fuse (lifetime warranty didn't cover that )
If you cant find anything you like locally companies like midnite solar or outback power make some good stuff. Quality inverters don't tend to go with a bang, they die slowly with constant abuse. Donate the old 9 inch angle grinder to someone and buy a good 5 inch, fit a big accumulator to the water pump so it is not starting every 10 seconds and keep the inverter cool and it will be with you for a long time. I'm confused, no wait... maybe I'm not... |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Russ, If your panels have the same size and number cells the difference between a 170 and a 190 is just the grade that the cells are sorted into at the factory, if you are not wiring them in series and using a fancy high volt mppt controller and only have one 190 that means you will only lose a few watts, hardly worth the effort, just bolt them together fit a PWM controller and go. If you are using less than 2Kw per day, this time of year, the panels will spend some of the afternoon sitting idle anyway. If you need more power in the long term you could generate and use 6 - 9 Kw /day with that sized battery bank. Getting multiple controllers to work together is a headache. The low price of panels has got me thinking that a single controller could handle 60 or 80 amps with an additional array of panels on a dump load to provide the extra kick for bulk charge. yahoo [quote=]Just had a look at the panel specs 54 cell 6" polys and 72 cell 5" mono's that's not a good match, nuenergy still stock the qixin 27P. Failing that any 54 cell 6 inch poly panel between 185 and 205 watts will go very close to the operating volts of your 190w panel[/quote] I'm confused, no wait... maybe I'm not... |
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| Wombat Regular Member Joined: 27/05/2011 Location: AustraliaPosts: 72 |
Thanks Yahoo2 Yes, these panels are a bad match... I think I'll mount the single 190W on top of the Disco 2, with a little extra center panel bracing to prevent a fracture. I really want more of the 170Wers. I will talk to some mates in the game. They will know more than me for sure. 3 would be just right. Looking, looking... Have acquired a bunch of various fuses from old 3 phase sprung circuit breakers. I'm sure these will do, being not cheap junk and all. 
Still to chase a DC breaker of decent size. And a RCD, 20A one I think for 3000W. Will let you know how I go, thanks again, Russ |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
If you have second hand gear to select parts from, some circuit breakers make good switches. I have some info (that I cant find) on how to disable the breaker mechanism it is either bend or remove a little piece inside, memory is not the best at the moment. Anyway, point I was going to make was, in some lines of circuit breakers they are identical internally from the lowest amp rating to the highest. So if you come across some larger cased breakers that can be opened up it is worth a punt )I have been gritting my teeth and hanging back on buying some panels for 18 months now, hoping to find some locally . The big killer for me is freight and insurance I am looking at about $60 per panel from the Eastern states, it adds up pretty quick. I am thinking of buying a panel from Low energy developments in Melbourne to check it out. At $220 for a 190 watt panel I don't expect much, never know, I might be pleasantly surprised. 
yahoo I'm confused, no wait... maybe I'm not... |
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| Wombat Regular Member Joined: 27/05/2011 Location: AustraliaPosts: 72 |
Hey Yahoo2. Just read your reply.. been a bit busy lately. Those panels your looking at are interesting. Will have to take a closer look for myself, time permitting. I can't use the ANL or Mega fuses as there 32V and I'm running 24V. My boost charging is @ 30V max and inverter high voltage is 32V cutout. To close for comfort with no margin for error. I'm using 160A fork lift fuses for each pair for batterys (3 off). These are heavy duty and rated at 82V I think (or something up there). Good for short circuit protection on each set. 50mm flex is used to hook the batterys together in a balanced fashion so each set has the same length of cable. From this theres a 200A T class fuse which I think should be around 350A, through a 100A shunt (the only one I had on hand), that will be changed to a 300A shortly. Then 70mm flex to the inverter. So far, so good. I really should have a switch between to battery and inverter like you suggest and fortunately have a 100A 3 phase switch on hand. I'll hook the phases together so I'll have a 300A switch and only use it when no current is being drawn. I don't think it would last long otherwise. For the 240V input I'm using lightning protectors (voltage & current) with a 16A breaker wired with 6mm cable. They say the unit can draw up to 30A! The output has a 30mA 62A RCD with a 16A & 6A breakers also wired with 6mm cable. Being able to pull 9000W for 10 sec, that's 75A! Well!... now I have to get the Dingo controller to read a 300A shunt, and another for a DC-DC converter! Fun, fun, fun!!! Russ.
P.S. Having 3 sets of 2 x 12v AGM's, would a 24V Infinitum desulfator on each set be going overboard? I already have 2 x 24V and 2 x 12V units. Thanks. P.S.S Those panels are just down the road from me. I think I'll drop in for a visit! |
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