Reply
 
Thread Tools Display Modes
 
Old 04-28-2016, 08:59 AM   #21
Guru
 
City: Seaford Va on Poquoson River, VA
Country: United States
Vessel Name: Old Glory
Vessel Model: 1970 Egg Harbor 37 extended salon model
Join Date: Jan 2016
Posts: 1,304
Quote:
Originally Posted by FF View Post
It would be a real feat to lose only 3% at that current level. The main culprits are the wire size, the quality of the crimp and it's connection to the wire, and the quality of the connection to the battery posts.


And dont forget the class T fuse that should be in the circuit.

I went with a semiconductor fuse for my 3000 watt inverter as it was cheaper than class T.

Fuses Unlimited Semiconductor Fuse - 300 Volts

I don't think any such power supply fuse can actually save any inverter, the fuse is only for the wires. Inverter cascade failure of the mosfets happens just too fast.
__________________
Advertisement

sdowney717 is offline   Reply With Quote
Old 04-29-2016, 08:27 AM   #22
Guru
 
mbevins's Avatar
 
City: Windsor
Country: Canada
Vessel Name: Keeper IV
Vessel Model: 44 Viking ACMY
Join Date: Nov 2013
Posts: 1,305
I don't think any such power supply fuse can actually save any inverter, the fuse is only for the wires. Inverter cascade failure of the mosfets happens just too fast.[/QUOTE]

That is true. I went the same route as you.
__________________

__________________
"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

mbevins is offline   Reply With Quote
Old 04-29-2016, 11:54 AM   #23
Guru
 
Xsbank's Avatar
 
City: Pender Harbour, BC
Country: Canada
Vessel Name: Gwaii Haanas
Vessel Model: Vancouver Shipyards Custom Aluminum 52
Join Date: Sep 2013
Posts: 2,447
Blue Sea has an ampacity calculator/app. Put in your parameters and it tells you the required cable size.
__________________
Don't believe everything that you think.
Xsbank is offline   Reply With Quote
Old 04-29-2016, 02:53 PM   #24
Guru
 
City: kemah
Country: USA
Join Date: May 2015
Posts: 997
In case there are some thinking a semiconductor fuse is made from semiconductors...

Introduction to Semiconductor Fuses | PowerGuru - Power Electronics Information Portal
what_barnacles is offline   Reply With Quote
Old 04-29-2016, 04:07 PM   #25
Guru
 
City: Seaford Va on Poquoson River, VA
Country: United States
Vessel Name: Old Glory
Vessel Model: 1970 Egg Harbor 37 extended salon model
Join Date: Jan 2016
Posts: 1,304
A semiconductor fuse might protect a semiconductor, like a mosfet, if each individual mosfet had its own individual semiconductor fuse. In an inverter exists multiple banks of mosfets. In mine I have 8 banks and in each bank 4 mosfets. A timer chip turns banks on and off using a mosfet driver. But I really doubt even an individual fuse can protect any mosfet unless the fuse is way underrated compared to mosfet capability, and designers will run these mosfets right close to the max power edge.

So since each mosfet is maybe rated 90 amps max, when too much demand or heat or age on the mosfet or age on capacitors, or the mosfet drivers shorts out, then the mosfet fails to turn off. Then all sorts of bad things happen, like this is an internal short. Mosfet is not designed to stay on flowing huge amps, but still the supply semiconductor fuse is 350 amps so it just wont blow. Then one mosfet goes, it brings down the others, then the bank is in a continual conduction phase, wont turn off, so they get so hot they burn. This can destroy all the other mosfet banks, yet the main power supply fuse never blows.

You want a quick fuse, cause you don't want to overload the inverter power wire in a short for a long time, whats the point, the wire will just get hot waiting for the fuse to open, meanwhile the inverter might even start a fire. Although if your there you will just smell a lot of nasty electrical smoke. I had an inverter burn, and it kept conducting current till I turned off the battery switch. The amp draw through a few burned mosfets, was not enough amp flow to blow the inverter fuse. The fuse is just in case the supply wire shorts together.

Most fuses blow with much higher amps than what is their rating, and they blow slow. So for inverter, you want that super fast fuse. A slow fuse is just bad idea there.

A starter motor you want a regular, not a super fast fuse. If you put a super fast fuse on a engine starter, a good chance it will blow open since the instantaneous amp flow is going to be very high.

I do not have any breaker-fuses on any engine starters, but I read ABYC is now recommending them.
sdowney717 is offline   Reply With Quote
Old 04-29-2016, 06:00 PM   #26
Guru
 
City: kemah
Country: USA
Join Date: May 2015
Posts: 997
A fuse technically isn't designed to protect the MOSFETs/scr's/diodes etc. Its job is to keep the wires from catching on fire when load faults.
while a semiconductor fuse is fast its not fast enough by itself. Generally when they talk about protecting they mean it will blow at a current level the device can withstand for the time it takes the fuse to blow. In order for that to happen there has to be done filters in the circuit to slow down the rise time of the current

Designed properly the semiconductor fuse can protect a multibank inverter but it had to have been designed accordingly.
what_barnacles is offline   Reply With Quote
Old 04-29-2016, 10:00 PM   #27
Guru
 
City: Seaford Va on Poquoson River, VA
Country: United States
Vessel Name: Old Glory
Vessel Model: 1970 Egg Harbor 37 extended salon model
Join Date: Jan 2016
Posts: 1,304
A good inverter has a load detection circuit and shuts itself down on overloads, so then self protects.

Thing is all electronics eventually seem to fail and self destruct regardless of the kind intentions of their circuit designers.

Today even with the intense circuit complexity, I think they like them to eventually fail so the customer comes back to get another, 'newer and improved' design. Keeps the business going.
sdowney717 is offline   Reply With Quote
Old 04-30-2016, 10:31 AM   #28
Senior Member
 
City: Madisonville
Country: USA
Vessel Name: Nirvana
Vessel Model: 41' Litton
Join Date: Feb 2011
Posts: 142
Since my original post went from cable size to MOSFETs and inverters, let me throw another fly into the ointment. Now that I have my new bank setup I will need to reprogram the settings in the inverter. I intend to set the cutoff at about 60% rather than 50% of discharge. By reducing the depth of charge the new batteries should last longer. This is done on the MV system by setting the cutoff voltage for the bank. A 12v setting is suppose to be around 55%. Is there a formula the calculate the voltage for exactly 60%?
__________________
41' Litton
Dixie Life is offline   Reply With Quote
Old 04-30-2016, 10:38 AM   #29
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,903
Quote:
Originally Posted by Dixie Life View Post
Since my original post went from cable size to MOSFETs and inverters, let me throw another fly into the ointment. Now that I have my new bank setup I will need to reprogram the settings in the inverter. I intend to set the cutoff at about 60% rather than 50% of discharge. By reducing the depth of charge the new batteries should last longer. This is done on the MV system by setting the cutoff voltage for the bank. A 12v setting is suppose to be around 55%. Is there a formula the calculate the voltage for exactly 60%?
Trouble with using voltage as an indicator of state of charge is it cannot be under load and should be at rest for a period of time.

I'd leave it as an emergency cutoff, raising it may give you a false cutoff need.

Use a better indicator of status than an inverter voltage cutoff....even guessing based on time and averaging loads is probably as accurate if you try a little.
__________________

psneeld is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 11:42 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012