Ok here's a question about surviving cranks and inline fuses

falconey · 07-14-2004, 11:37 AM

How would an inline fuse effect surviving cranks. I was playing around with my voltmeter and somehow blew(I know how) the fuse coming from the battery to the inverter. Well I was using a 20A fuse. I only had a 30a fuse handy and didn't realize I still had the inverter on since the fuse was bad. Well I put the 30a fuse in and since the inverter was still on the carputer powered up. So I go into the car without thinking to start it up and get reading on my volts at idle. I hear a slight beep(the normal one I get from the inverter when it reboots my computer from the voltage drop), but there was no reboot. I tried it again. Still no reboot. I still got the slight beep, but no reboot. Now like I've said in previous post I'm a real world guy. I lot of my experience is from trial and error and although I know a fuse should be rated at the max current going through I don't understand this. The two fuses on the inverter are 20a so I'm thinking(guessing) that if I go with a 40a fuse I won't even get the slight beep I was getting before. Anyone know if this is true or if the inline fuse has any effect whatsoever on surviving cranks.

mp3z24 · 07-14-2004, 12:16 PM

number 1. only use fuses of the same rating. they are there for a reason.
number 2. the fuse should have nothing to do with the voltage loss when cranking.

put a 20A back in there, and try it out again. if you are upping the fuse rating, you are running the risk of pulling more current than the manufacturer designed the circuit for.

i dont know what caused the fuse to pop in the first place, but when you put the 30A in after that, the same event may have occured, and since you allowed more current to pass to the equipment, something may have been damaged. like i said, put in a replacement 20A and try your system how it was running before.

~mike

Bobby Digital · 07-14-2004, 12:32 PM

Quote: Originally Posted by mp3z24

if you are upping the fuse rating, you are running the risk of pulling more current than the manufacturer designed the circuit for.

He is the manufacturer... it's a wire going from his battery to his inverter, there's not really much of a circuit there to design.

falconey · 07-14-2004, 01:12 PM

Quote: Originally Posted by mp3z24

number 1. only use fuses of the same rating. they are there for a reason.
number 2. the fuse should have nothing to do with the voltage loss when cranking.

put a 20A back in there, and try it out again. if you are upping the fuse rating, you are running the risk of pulling more current than the manufacturer designed the circuit for.

i dont know what caused the fuse to pop in the first place, but when you put the 30A in after that, the same event may have occured, and since you allowed more current to pass to the equipment, something may have been damaged. like i said, put in a replacement 20A and try your system how it was running before.

~mike

Yeah Bobby D hit it on the nail; I think you're confused on what I was saying. I hardwired my inverter myself. The inverter itself has two 20a fuses, one for each outlet(I haven't touched these). When I hardwired, I fused the line as a precautionary measure. I(being a dumbazz and not reading instructions) incorrectly used the voltmeter and it blew my inline fuse. That's when I threw in the 30A fuse. I think this has been my issue all along because this was the original fuse I had in place when I was surviving crank in the beginning(I didn't ever put 2 and 2 together). Now I am surviving crank. Went to lunch and tried it a bunch of times and it was working flawlessly. I think that 20A inline fuse was preventing the nescisary current flow I needed to survive crank. It even stopped giving me the beep noise. Man I'm happier than hell and I also found out I can swap my P.O.S. autozone battery for a optima red top and only have the pay the difference($50). I still wouldn't mind hearing more opinions on if this could be the reason or if somehow my voltage magically stop dropping. I checked voltage with the car off and it's 12.65V and at idle with nothing on 14.14V. So like I said I don't think voltage drops were even my issue outside of the fact that it was dropping low enough and the fuse restricted enough current that it didn't allow me to survive crank.

waltsongs · 07-14-2004, 02:58 PM

Sounds plausible to me. I have seen slow blow fuzes glow when they are in a circuit that is drawing close to their rated current. It may have been a bad/cheap fuze with a few hundred milliohms resistance as well. Have you tried another 20 AMP fuze? The previous posts cautioning you about oversizing the fuze are correct. If you overload your Inverter, somthing in it may pop instead of the fuze and this might cause damage to what ever your Inverter is powering at the time.

Walt
http://www.safossils.com/mp3car.html
http://www.safossils.com/waltsongs

Bravellir · 07-14-2004, 05:44 PM

If you do not have nothing between the 30A fuse and the 20A from the inverter ( like the pic ) the only thing that occurs to me is that you had a faulty 20A fuse on the battery side before.

But, I do have a very similar setup 40A fuse battery side ( like this http://www.cartft.com/shop/catalog/il/19 ) and a 25A inline on the inverter side. The behaviour is the same. Beep but no reboot.
Latter I installed a 30A relay close to the inverter witch is used ( controlled by an itps ) as main power cut-off. Still works flawless ( if you exclude the problem I’m having with the inverter overheating and shutting off. It's kind of hot around here

)
I did measure the voltage at the inverter and I got 9.9v while cranking. Maybe you could test this by measuring at the battery fuse and at the inverter fuse while cranking to check if a 20A fuse can cause the voltage to drop.

falconey · 07-14-2004, 07:07 PM

Quote: Originally Posted by Bravellir

If you do not have nothing between the 30A fuse and the 20A from the inverter ( like the pic ) the only thing that occurs to me is that you had a faulty 20A fuse on the battery side before.

But, I do have a very similar setup 40A fuse battery side ( like this http://www.cartft.com/shop/catalog/il/19 ) and a 25A inline on the inverter side. The behaviour is the same. Beep but no reboot.
Latter I installed a 30A relay close to the inverter witch is used ( controlled by an itps ) as main power cut-off. Still works flawless ( if you exclude the problem I’m having with the inverter overheating and shutting off. It's kind of hot around here

)
I did measure the voltage at the inverter and I got 9.9v while cranking. Maybe you could test this by measuring at the battery fuse and at the inverter fuse while cranking to check if a 20A fuse can cause the voltage to drop.

Good point I may try that out just in case it can help someone else.