Fuse sizing for inverter

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Tim, you might want to consider installing a high current 4 position battery switch on the house bank effectively dividing it in half. You can run it in the all position but if you ever have a problem with one of the batteries you can isolate one half of the system. This is what I am doing on my Gulfstar's new house bank.
Bill
 
Simply disconnect the problem battery (bank) with a couple turns of a wrench and you save the cost of additional wiring, ends, switch, chances for loose comnnections and corrosion.

Battery setups are rarely install and forget...they probably need more attention than any other system on the boat except crew.
 
The revised drawing will still not measure properly ,

I believe it needs to connect to the OTHER SIDE of the shunt , in order to go THRU the shunt, and create a reading.
 
The shunt is wired wrong in the above picture/ diagram.
Bill
 
Maybe I'd run the ground from the terminal block to the engine, but it looks like it's correctly wired with all load negs downstream from the shunt. What's wrong with it?
 
I was concerned about the engine ground lead depending on the amperage the starting battery draws. It's okay my mistake Al.
Bill
 
but it looks like it's correctly wired with all load negs downstream from th\e shunt. What's wrong with it?

I believe it needs to connect to the OTHER SIDE of the shunt , in order to go THRU the shunt, and create a reading.
 
OK, thanks guys, I've been off the grid for the last couple of days.

I believe the monitor is correctly wired. All loads are connected to the load side of the shunt. As shown on the diagram there are two cables connected to the load side of the shunt. One goes to the engine block and the other to a bus bar. The inverter and battery charger are connected to the bus bar and all other loads go through the engine block. But again both of these are connected to the Load side of the shunt.

I think Larry is correct. The inverter's positive lead should be connected to the battery farthest away from the battery whose negative lead is connected to the shunt thereby using the entire bank.

At least I think this is all correct. I like the idea of connecting the cable from the engine block directly to the shut and then connecting the lighter loads (inverter and batt charger) to a bus bar. This way the starting loads don't go through the 150 amp rated bus bar but rather through the higher rated 500 amp shunt.

Am I completely off base????
 
This way the starting loads don't go through the 150 amp rated bus bar but rather through the higher rated 500 amp shunt.

The starter loads should NEVER be run thru a shunt.
1. too small a load over time,

2. a shunt is basically a measured resistance,

A FUSE is a measured resistance .

Just do what 100% of the boats do and forget about measuring start amperage on the OC.

A volt meter across the operating starter is a great troubleshooting tool tho.
 
That's why 1000 amp shunts are manufactured so the entire vessel including start and engine loads can be used.
Bill
 
FF said:
This way the starting loads don't go through the 150 amp rated bus bar but rather through the higher rated 500 amp shunt.

The starter loads should NEVER be run thru a shunt.
1. too small a load over time,

2. a shunt is basically a measured resistance,

A FUSE is a measured resistance .

Just do what 100% of the boats do and forget about measuring start amperage on the OC.


Timjet is correct. FF is pretty much wrong on on all counts.

It is just fine to run starter loads through a shunt provided the shunt is rated to carry the current. A shunt is a measured resistance, but so small of a resistance that an engine starter will never see it. A 500 amp, 50mv shunt like most all of these monitors use only cause a 50mv drop with 500 amps of current. If you are starting from this house bank, and don't run the start current through the shunt, you have lost accurate measurement of the battery bank. I've started my 135 Lehmans through a 500 amp shunt for almost 13 years with no ill effects. Mater of fact, I've installed many, many shunts in starter circuits (properly sized) and have NEVER seen a shunt failure.

A fuse IS NOT a measured resistance. It is a fusable link.

100% of boats DON'T forget about measuring start current. I've seen many that do, including mine. Generally, if they have a separate start battery it doesn't get measured, but if they are started from the house, and they have a properly wired battery monitor installed, they do.
Click to expand...
 
Generally, if they have a separate start battery it doesn't get measured, but if they are started from the house, and they have a properly wired battery monitor installed, they do.

To what purpose?

With a dedicated start batt , only in an emergency would a boost from the house be required .

A few seconds of cranking is hardly going to change the house recharge requirement.

So why bother?
 
Billylll said:
That's not a breaker/ fuse I would use it won't handle high inrush currents.
Bill
Click to expand...

They are used quite often for just that. Most inverters have control circuits. You wouldn't be switching it on and off with a load. What is not good is to have an inverter connected to the DC battery bank without a switch to shut it down if it starts smoking or other silliness. Much quicker to toggle a switch than find your tools or fuse puller...

Bill Too:)
 
bglad wrote: What is not good is to have an inverter connected to the DC battery bank without a switch to shut it down if it starts smoking or other silliness. Much quicker to toggle a switch than find your tools or fuse puller...(endsnip)

Exactly correct. As I mentioned before, I've installed dozens of inverter / chargers, mostly 2000 to 3000 watt. I always install the proper size fuse and wiring, based on the Inverter manufacturer's recommendations, and always install a dedicated switch just for the inverter where you can switch it off without interupting the house circuits. I also only use the class T fuses because of the high current capacities of the battery banks normally associated with inverters, and the chance of an inverter failing with a direct short. An inverter is the only high current device that I've ever seen fail that way (direct short) and I've seen it happen twice.
 
Brent Hodges said:
bglad wrote: What is not good is to have an inverter connected to the DC battery bank without a switch to shut it down if it starts smoking or other silliness. Much quicker to toggle a switch than find your tools or fuse puller...(endsnip)

Exactly correct. As I mentioned before, I've installed dozens of inverter / chargers, mostly 2000 to 3000 watt. I always install the proper size fuse and wiring, based on the Inverter manufacturer's recommendations, and always install a dedicated switch just for the inverter where you can switch it off without interupting the house circuits. I also only use the class T fuses because of the high current capacities of the battery banks normally associated with inverters, and the chance of an inverter failing with a direct short. An inverter is the only high current device that I've ever seen fail that way (direct short) and I've seen it happen twice.
Click to expand...

what in the inverter direct shorted?
and did the manufacturer suggested fuse work?
 
I have no idea exactly what direct shorted, but they blew the Class T 300 amp fuses both times. One inverter was replaced under warranty. The other was out of warranty and was replaced with a new, different brand of inverter/charger.
Not sure what you mean my suggested "fuse work". They were properly fused in both cases, and the fuses did their jobs.
 
So why recommend additionl switching..which the manufacturers don't always recommend when the class "T" fuses did their jobs?
 
psneeld wrote: So why recommend additionl switching..which the manufacturers don't always recommend when the class "T" fuses did their jobs? (endsnip)

Well, this has been explained several times, but the switch is to isolate the inverter incase of a fault, or just for maintenance / testing. If you don't want to pony up the extra $25 on a $2,000 job to make it a better, safer installation, don't. I'll continue to do things right.................

Good grief, this thread is getting ridiculous. I think I'm done.
 
It is a good idea to have a "lock out" on the inverter because even with 120 volt power off the inverter can still be making it. There should be a warning in the AC panel that such a situation exists. It can kill you.
 
Brent Hodges said:
psneeld wrote: So why recommend additionl switching..which the manufacturers don't always recommend when the class "T" fuses did their jobs? (endsnip)

Well, this has been explained several times, but the switch is to isolate the inverter incase of a fault, or just for maintenance / testing. If you don't want to pony up the extra $25 on a $2,000 job to make it a better, safer installation, don't. I'll continue to do things right.................

Good grief, this thread is getting ridiculous. I think I'm done.
Click to expand...

What's ridiculous is not answering a simple question...

IF the fuses did what they were supposed to....then why the extra switch when not called for by the manufacturer?

Not hard to understand or explain.

And yes I'm probably as good with hooking up equipment as you are and just as safe.

I'm not an electrical engineer or inverter manufacturer so there might be something I am missing...it's not a trick question or trying to bait you into something...I'm just curious what I am missing....

If not..then "right way" is only a matter of opinion.
 
I am not sure who's high current inverter's battery switch costs $25.00? I like the BlueSea gray high current battery switch to shut down the inverter's DC feed as well as installing the properly sized Class T fuse in the 12VDC feed to the inverter. I want to install a 1, 2 on and off switch so I can effectively shut down the inverter when needed, use all 4 batteries in the house bank to feed the inverter, or charge off the inverters charger or split half of either bank if needed to feed or charge.
Bill
 
After all this discussion, I'm still curious as to why a simple stand alone 12V starting circuit is felt by some to need "protection" beyond good wiring and logical cable runs. :confused:

It seems I'm not alone.
 
Last edited:
sunchaser said:
After all this discussion, I'm still curious as to why a simple stand alone 12V starting circuit is felt by some to need "protection" beyond good wiring and logical cable runs. :confused:

It seems I'm not alone.
Click to expand...

:thumb: even ABYC agrees if done correctly...
 
psneeld said:
In electronics and electrical engineering, a fuse (from the French fuser, Italian fuso, "spindle"[1]) is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection...........

Fuse (electrical) - Wikipedia, the free encyclopedia
Click to expand...

Wikipedia is a source for school children to find information without doing actual research themselves. It is not a reliable source for technical information.

While a fuse does have some electrical resistance, it so small that it is not generally considered when designing an electrical circuit. The resistance of the circuit conductors is likely to be far greater than the resistance of the fuse. Professionals in the trades do not refer to or think of fuses as "resistors".

Also, a "fuse" does not necessarily open ("blow") on excess current. If you use a hair drier for a heat gun, you may overheat it and blow the "thermal fuse" (activated by excessive heat). These are also sometimes found in transformers and small motors.

A fuse (fusible link) may also be used to hold mechanical devices in a certain position and release them at a set temperature. Fire doors are an example.
 
psneeld said:
What's ridiculous is not answering a simple question...

IF the fuses did what they were supposed to....then why the extra switch when not called for by the manufacturer?
Click to expand...

An appliance such as an inverter needs a positive means of being disconnected for the safety of anyone working on it (and possibly for convenience). While removing the fuse is a positive means of disconnecting the appliance, it's often not the most convenient or fast way of doing so.

In my case, removing the fuse means getting out the tool box, removing four screws to swing out the electrical panel, removing the plastic cover over the fuse, then finding the correct socket and handle to loosen the nuts holding the fuse in place. The option is to reach down and turn a knob on a switch.

BTW: An inverter, even one with a remote power switch will still draw a small standby current when connected to the battery. A switch in the DC circuit will eliminate this standby current when turned off.
 
rwidman said:
Wikipedia is a source for school children to find information without doing actual research themselves. It is not a reliable source for technical information.
Click to expand...

Yeah, but it is a lot easier to post a link from Wikpedia than scanning those 50 year old EE text books on my shelf.
 
sunchaser said:
Yeah, but it is a lot easier to post a link from Wikpedia than scanning those 50 year old EE text books on my shelf.
Click to expand...
I used that stuff for many years on a daily basis. Of course I updated it when necessary.
 
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