Power Inverter Fuses

[Grt118fr14]

I've bought a modified sine wave 500w - continuous / 1000w - peak inverter. It is for 12v use and has two 30amp removable blade fuses on the outside in plastic housings, easily accessible unlike some models where they can be soldered or housed internally. I've searched the Internet and can't find out what I want to know which is: does this mean it's effectively a 60amp fuse or is it perhaps two separate circuits each with 30amp protection?

As its a 500w inverter with 12v power supply the amps could be around 41 at full power using P=IV

I'm hoping it's not a case of the answer being so basic that that's why there's no info on this but I am totally new to inverters and understanding anything electrical.

I'm planning on using a 240v tyre inflator with the inverter which draws 360watts at 1.5amps and is fitted with a 5amp fuse on the 3 pin plug.
I'm assuming from that the much higher rated 30amp fuses are for the inverters dc side of things and as they are the same type as car blade fuses which works off dc that kind of confirmed that to me?

I may as well also ask while I'm here, if my car battery is a 68amp 12v (I'm aware it has a much higher cold cranking rating of nearly 700amps but dont think you use that figure?) and my alternator is 140amp which do you use in working out the maximum inverter you could run off your car system? Obviously there's a difference of 816watts for battery or 1680 watts for alternator and does it work like that as in a direct translation of volts x amps = watts which equals max watt of inverter you can use with that battery?

If I've made errors in my working could someone please advise where I'm going wrong as would be good to know this info before looking at bigger inverters and choosing out cables and in line fuses and all that side of things.

Thanks.

 

[Geoff1946]

I very much doubt that your fuses will be in parallel. That's just not done. They will be feeding two circuits which compliment each other to perform the inverter function.

Volts X Amps = Watts is valid for DC, but everything you do has losses. There are resistive losses in every connection, every length of cable, fuse, or connector. Inverter efficiency will be quoted for your device, but will vary with load. Also the battery voltage will drop quite quickly under heavy load. Every fraction of a volt lost to circuit resistance is significant when you only have 12 volts to start with.

Battery AH rating of a battery will be at a specified load which is likely much lower than your invertor will draw.

I f you want to run a tyre inflator from a car battery by far the best thing to do is buy a 12volt inflator.

Your car alternator will only produce its rated output when the engine is running at speed. I wouldn't have thought you would normally use it to feed an inverter.

 

[Grt118fr14]

I very much doubt that your fuses will be in parallel. That's just not done. They will be feeding two circuits which compliment each other to perform the inverter function.

Volts X Amps = Watts is valid for DC, but everything you do has losses. There are resistive losses in every connection, every length of cable, fuse, or connector. Inverter efficiency will be quoted for your device, but will vary with load. Also the battery voltage will drop quite quickly under heavy load. Every fraction of a volt lost to circuit resistance is significant when you only have 12 volts to start with.

Battery AH rating of a battery will be at a specified load which is likely much lower than your invertor will draw.

I f you want to run a tyre inflator from a car battery by far the best thing to do is buy a 12volt inflator.

Your car alternator will only produce its rated output when the engine is running at speed. I wouldn't have thought you would normally use it to feed an inverter.

Thanks for quick response!

Okay that makes sense to me now, I did use the setup with inflator plugged into inverter connected to car battery (running) yesterday and it worked fine so no fuses were blown and no damage done. I did take it to be the case the manufacturer- Streetwize would have spec'd the inverter appropriately but was just curious as to why multiple fuses rather than just one but if there's multiple circuits that makes sense I guess, I'll need to see if there's any information on how that actually works to help me understand it though unless its just a case of each circuit supplies say 20 amps each to make up the maximum of 40amps for 500 watts output obviously not taking into account the peak power of 1000w which i assume happens for such a brief period the effect on the fuse is negligible. Also the manual states the inverter operates at 90% efficiency so I thought that meant it takes more draw to provide output power? 500 watts at 90% efficiency being equal to 555 watts equaling 46amps? Or taking my current example 360watts becoming 400w equaling 33amps. I had watched a video where they warned some inverters are supplied from manufacturer with incorrectly matched fuses but taking your point about losses I'm sure that's all factored in and I know you're advised to choose an inverter with 20%-30% more than you think you'll need but I didn't think the manufacturer would supply a fuse 20%-30% less than rated performance but that's why I was asking for info as I think I've been thinking along the wrong lines as they've effectively used a 60amp fuse?

I take the point about using the 12v cigarette lighter style inflator. I'd chosen the 240v 3 pin plug model as I'll mainly use the inflator at home and had read that the 240v model has a dual piston and would probably outlast the other 12v style with only a single piston so that's why I then bought the inverter incase I ever had to use the inflator when away from home and if not near a power outlet. I guess I've maybe overthought that all of that though as I have breakdown cover and unlikely to be in an emergency situation where a tyre only needs a top up of air so inverter is probably reasonably redundant for my needs, just a nice to have.