AC Inverter/DC Power consumption?

[OldFrog75]

1. Assuming a boat has an inverter but not a dedicated starter battery, when the inverter is "on" does it draw power uniformly from all the batteries in the bank simultaneously regardless of how the battery selector (1, 2, both, off) is set or can one choose which battery to power the inverter?

2. Is the battery test gauge on the DC panel a reliable indicator for how many amp hours a battery has left before it needs to be charged?

[Zil]

1 all of this depends how you have things wired.
2 gauge is just an estimate, accuracy depends on how you have it programed.

[Target9000]

Originally Posted by OldFrog75

1. Assuming a boat has an inverter but not a dedicated starter battery, when the inverter is "on" does it draw power uniformly from all the batteries in the bank simultaneously regardless of how the battery selector (1, 2, both, off) is set or can one choose which battery to power the inverter?

2. Is the battery test gauge on the DC panel a reliable indicator for how many amp hours a battery has left before it needs to be charged?

1) An inverter can be thought of as a LOAD. Anything that draws power and uses it can be considered a LOAD. It really doesn't matter if it is an inverter, a radio, some lights, etc, they all do the same thing. They draw power from the batteries. So in the interest of simplifying your question, I suggest you think in these more general terms. You also bring the battery selector into your question. Why? The selector is "usually" there to select which bank of batteries will be used to feed the loads. If it is selecting a certain bank, you can usually assume that the bank it targets will be feeding the loads. So why bring it into the question? Are you confused about the wiring of it? You need to separate these things out and understand the building blocks instead of conflating things into a single unanswerable question. Lets look at a simple and more approachable questions that might get some meaningful and easy to understand answers:

Do the loads on my battery bank draw uniformly from all batteries in that bank?

This depends on how the batteries are wired. There is much information on this in several other threads that explain the optimal ways to wire batteries so that they will have a uniform state of charge. I suggest you make up a diagram which shows how your wiring is setup and include what type of batteries are in use and where the switches are. You may also want to see this:
http://www.smartgauge.co.uk/batt_con.html


Does my battery selector switch work as intended, isolating or combining the battery banks I select?

Please see above. Show us what is in YOUR boat so we can help answer.

How much power will my inverter draw?

What model inverter? What will it be powering?

Does my DC panel gauge (voltage gauge) give me an accurate picture of the number of amps left in my battery bank? Does it give me an accurate picture of the state of charge?

It can be used as a very very rough guess. There are more accurate ways to determine the state of charge (SOC). The most accurate way is probably to measure specific gravity of the batteries which involves opening each battery and using a gauge to determine its SOC, but this is a big pain. Use of a smart battery meter can help to give you a better educated guess than just a voltage alone. You might want to check out these this article:
Installing A Battery Monitor Photo Gallery by Compass Marine at pbase.com

[OldFrog75]

Originally Posted by Target9000

1) The selector is "usually" there to select which bank of batteries will be used to feed the loads. If it is selecting a certain bank, you can usually assume that the bank it targets will be feeding the loads. Are you confused about the wiring of it?

Do the loads on my battery bank draw uniformly from all batteries in that bank?

This depends on how the batteries are wired.

Does my battery selector switch work as intended, isolating or combining the battery banks I select?

Show us what is in YOUR boat so we can help answer.

Thanks for the post.

Would that I could show you my boat, but I'm a club sailor and sail on a lot of different boats rather than my own. Some have dedicated starter batteries and inverters; many do not.

I've read articles about how inverters work and how to compute how much power they are drawing out of the batteries but I've never used one. The one time I tried to switch on an inverter to use a microwave oven and activate some AC outlets I couldn't get it to work. (BTW there were 8 people on that boat, most with a lot more experience than I and no one could figure it out. Maybe it was us - maybe it was faulty wiring or a bad inverter.)

Just curious about how they are "generally" wired and if it is safe to assume they draw power from the specific battery indicated by the battery selector switch like the rest of the house power.

[Stu Jackson]

Originally Posted by OldFrog75

Just curious about how they are "generally" wired and if it is safe to assume they draw power from the specific battery indicated by the battery selector switch like the rest of the house power.

Inverters come in three varieties:

1. Standalone - plugged into a cigarette lighter plug (usually used for low loads)

2. Wired in - generally connected to the house bank for power because the wiring from the batteries to the inverter have to be very large to handle the load. These can be of two types: a) standalone where you plug the loads into the receptacles on the inverter itself with extension cords; b) wired into the boat's A.C. system which requires a special switch that will never allow shorepower and the inverter to be on at the same time. Some of the newer inverters have this ATS switch (automatic transfer switch) built in.

3. Combined inverter chargers - these are pretty big blocks of equipment wired into the boat's A.C. system and has BIG wires to the house bank with a built in ATS.

In no case I have seen do these ever run through the 1-2-B switch. That switch is used to determine which battery bank is used for D.C. loads on the boat, like the engine starter and the house D.C. distribution panel.

How you use them is determined by what kind of inverter is installed.

Hope this helps.

http://www.westmarine.com/webapp/wcs...r#.UggjKT_pz-I

[OldFrog75]

Originally Posted by Stu Jackson

In no case I have seen do these ever run through the 1-2-B switch. That switch is used to determine which battery bank is used for D.C. loads on the boat, like the engine starter and the house D.C. distribution panel.

How you use them is determined by what kind of inverter is installed.

Hope this helps.

The West Advisor: Selecting an Inverter

So they a) draw power from a specific battery/bank they are hard-wired to or b) draw power from all the batteries (other than a dedicated starter battery) simultaneously?

[Zil]

The inverter draws power from the battery bank to which it is connected. If the inverter connects through the 12B switch then the switch selects the bank. It is all boat (system) specific.

[rw58ph]

Also keep in mind that 1 amp AC 120 volts equals 10 amps DC 12 volts. So AC electic items can draw down a battery bank in a hurry. Most boats with inverter have two sets a battery banks, house and start, and the invert is only connected to the house.

I still use the volts as a indicator as to amps left. A battery should not be drawn down below 50% or 12.4 volts.