Shunt Sizing

[Ninjakitty]

Hi, my inverter/charger calls for a 300 amp anl fuse and 4/0 wire between batteries and inverter/charger. This is directly from the manufacturer. Would my shunt also need to be 300 amps? Thanks!

[Iceni John]

Shunt for what? An ammeter or a remote meter? What make of inverter is it?

John

[Ninjakitty]

A shunt for a battery meter off the negative terminal. The inverter is an Aims 3000 watt (120 volt) inverter/charger with auto transfer switch. I have the remote panel for the inverter as well.

[Ninjakitty]

I had picked this up awhile ago. Saw that the shunt was 100 amps. Wasn't sure if that was enough for the application. It would go between my battery and the negative busbar I plan on using for all my negatives.

[JDOnTheGo]

Originally Posted by Ninjakitty

Would my shunt also need to be 300 amps? Thanks!

Originally Posted by Ninjakitty

The inverter is an Aims 3000 watt...

You need a shunt that is rated for the maximum current flow that will be passing thru it (either into or out of the battery bank). Assuming you have a 12VDC battery bank, you're inverter will likely be the big ticket item at a maximum of something around 250 amps. Therefore; a 100 amp shunt would be too small. They key is making sure battery monitor can be configured for the size of shunt that you install (100mV vs 500mV).

[Ninjakitty]

Thank you. That makes sense to me. I guess I will be looking for a different sized shunt and monitor.

[JDOnTheGo]

Originally Posted by Ninjakitty

Thank you. That makes sense to me. I guess I will be looking for a different sized shunt and monitor.

If you are going to do that....

Might I suggest a "good" battery monitor?? They really do pay for themselves (good information that allows you to properly care for your battery bank). A TriMetric (from Bogart Engineering) or even a Victron BMV-700 are good options.

[Ninjakitty]

Thanks. I was just looking at the Victron

[Iceni John]

Just be aware that all aH-in/aH-out counters such as the Trimetrics have an intrinsic inaccuracy that will get worse with time. Blame Mr. Peukert for that one. Battery SoC meters such as the SmartGauge, and to a lesser extent the NASA ones, overcome this limitation because they operate on a completely different basis, using algorithms derived from voltage under load. (This doesn't mean that you can just connect your $20 multimeter to a battery and call it good!).

Another effective way to know the true health of any FLA battery is to measure its SG using a good hydrometer. pH never lies!

John

[Ninjakitty]

I'll be using AGM batteries

[Ninjakitty]

Originally Posted by Iceni John

Just be aware that all aH-in/aH-out counters such as the Trimetrics have an intrinsic inaccuracy that will get worse with time.

How much time are we talking? 1 year, 5 years?

[JDOnTheGo]

Originally Posted by Ninjakitty

How much time are we talking? 1 year, 5 years?

It's not that sort of time thing. It's that little variables add up. In a very crude/imprecise way... Say that you are pumping 10 amps into your battery for charging. The whole 10 amps does not actually end up in the battery (and able to be used). Maybe only 9.9 amps gets there. If that happens every day for 100 days, the monitor will be reporting far more "available power/capacity" that actually exists.

That's why the Trimetric has so many configuration options. With some time/attention, you can tuned it to be pretty accurate. All battery monitors have this issue - the better ones let you tune them. As Steve often says, the absolute best indication of state of charge is an hydrometer. The problem is, not many of us want to crawl under/into the bus, remove 50 battery caps, test 50 cells, etc... just to get an idea of SOC.

[aaronsb]

The managin alloy that makes up the resistor on a shunt is temperature sensitive. If you have a shunt there are different ratings for continuous load vs. partial load, and you'll need to size it (and position it) accordingly so heat can be shed from it. Remember it's a calculated resistive load, so it will generate some amount of heat. A shunt should come with a spec sheet that describes its installation parameters.

[2martins]

Originally Posted by Ninjakitty

Hi, my inverter/charger calls for a 300 amp anl fuse and 4/0 wire between batteries and inverter/charger. This is directly from the manufacturer. Would my shunt also need to be 300 amps? Thanks!

I am looking at this inverter as well. It does say to use 4/0 wire which seems like overkill and I can't find a 4/0 FUSE to attach to it. I was considering using 2/0 wire but can't find a fuse designed for more than 0 gauge.

I won't have solar nor be full time, so do I really need to pay so much attention to my SOC? I will need something to charge/maintain the batteries. Doesn't the inverter do that? Do I really need to make sure the battery cables are all the exact same length and rotate the batteries due to weird charging/usage effects? I have 4 × Duracell 6 volt 220 amp hr FLA batteries all the same date 6/18. Is it really a problem to add two more later from a different batch? I have read a lot of conflicting things and I don't know enough to be able to evaluate what is true and or meaningful for my situation. Perhaps some of these things do make a difference, but for non FT use it doesn't matter enough to justify the extra work and or equipment to maximize the life/efficiency or whatever of the batteries?
Also, I live where it is COLD at night. There are only a few nights per year in the summer when it is above 50 degrees. It's normally in the 10s-40s overnight, which means the batteries are going to be much less efficient. So my son wants to store them inside and vent them to the outside. Apparently if they are in a "sealed box" this is ok, but what does that mean exactly? Should the box be made of metal in case of explosion? How far away from the fuel tank or anything else should it be? He is thinking right behind the driver near the electrical panel to minimize the battery cable runs.

[Ninjakitty]

I don't really have any answers to your questions. Perhaps if you list them numerically, the folks with more expertise than me will share their thoughts.

[2martins]

I'm going to post on the thread of the guy who offers electrical question help.

Originally Posted by Ninjakitty

I don't really have any answers to your questions. Perhaps if you list them numerically, the folks with more expertise than me will share their thoughts.

[Iceni John]

Originally Posted by 2martins

I am looking at this inverter as well. It does say to use 4/0 wire which seems like overkill and I can't find a 4/0 FUSE to attach to it. I was considering using 2/0 wire but can't find a fuse designed for more than 0 gauge.

I use 4/0 almost exclusively for all the house batteries' cabling, including from the main DC busbar that combines both my house battery banks and sends power to my Magnum MS 2000 inverter and DC load center. I use an ANL 250 amp fuse (cheap, five for less than $10) for the inverter, with ANL fuse holders from VTE. Don't scrimp on the high-current cables - just use the good stuff and be done with it!

John

[2martins]

We got 4/0 wire for the batteries themselves, but not from the inverter to the fuse out. Does that make sense? My son is actually the one doing this. He knows more about it than I do, but I doubt he knows enough because he's 18. There just only so much experience one can have at 18!! He has read up some on RV wiring, he's an engineering student, he has some experience wiring small projects with way less power, and he's smart. But I'm paranoid and I don't know enough to double check him which makes me uncomfortable.

Originally Posted by Iceni John

I use 4/0 almost exclusively for all the house batteries' cabling, including from the main DC busbar that combines both my house battery banks and sends power to my Magnum MS 2000 inverter and DC load center. I use an ANL 250 amp fuse (cheap, five for less than $10) for the inverter, with ANL fuse holders from VTE. Don't scrimp on the high-current cables - just use the good stuff and be done with it!

John

[Ninjakitty]

This screenshot is directly from Aims, about the fuses. Aims calls for 4/0 from battery to inverter, on both sides of the fuse.

[Iceni John]

[QUOTE=2martins;274918]I won't have solar nor be full time, so do I really need to pay so much attention to my SOC? Yes. If you don't, you'll end up trashing your expensive batteries. Your choice. I will need something to charge/maintain the batteries. Doesn't the inverter do that? Yes, but only if it has a built-in charger; not all inverters do. Most good inverters' chargers have decent 3-stage chargers with a good PF. Just make sure that it is programmable to whatever batteries you use. A typical RV converter is NOT a good charger! Do I really need to make sure the battery cables are all the exact same length Yes. and rotate the batteries due to weird charging/usage effects? If your batteries are correctly wired they will charge evenly. Rotating the batteries because of charging imbalance is not solving the underlying issue of uneven charging that will kill the batteries. I have 4 × Duracell 6 volt 220 amp hr FLA batteries all the same date 6/18. Is it really a problem to add two more later from a different batch? Yes! Don't do that.I have read a lot of conflicting things and I don't know enough to be able to evaluate what is true and or meaningful for my situation. Perhaps some of these things do make a difference, but for non FT use it doesn't matter enough to justify the extra work and or equipment to maximize the life/efficiency or whatever of the batteries? Who cares if it's for FT use or not? It needs to be done right, regardless of use.

Also, I live where it is COLD at night. There are only a few nights per year in the summer when it is above 50 degrees. It's normally in the 10s-40s overnight, which means the batteries are going to be much less efficient. So my son wants to store them inside and vent them to the outside. Apparently if they are in a "sealed box" this is ok, but what does that mean exactly? All FLA batteries produce hydrogen and sulphuric acid fumes when being charged. They should not be inside any living area, and they must be vented to prevent hydrogen buildup. Should the box be made of metal in case of explosion? If you're already thinking of the likelihood of explosions, perhaps you need to rethink your plans! How far away from the fuel tank or anything else should it be? Batteries should be close to the inverter to keep the high-current cable as short as possible, but they must be in a separate compartment so the acid fumes don't damage the electronics. Distance from a diesel fuel tank is irrelevant. He is thinking right behind the driver near the electrical panel to minimize the battery cable. What electrical panel? The bus's original junction box, or the house electrical panel? Put the batteries under the floor to keep the CoG as low as possible, put them inside an insulated box if it's that cold, and vent them. Put the inverter no more than a few feet from them in a separate area. Who cares how long the AC cables are - it doesn't much matter. [/QUOTE]

I suggest reading all the collective wisdom and experience on the Northern Arizona Wind & Sun forum, and read what SmartGauge has to say about wiring batteries: http://www.smartgauge.co.uk/batt_con.html

John