Inverter cabling question

[Helmsman]

Source of the post I think part of the reason for the rules, is the tremendous amount of amps that can be run thru the wires in a short. Depending on the fusing there could be a fire before the fuse goes.

The other, in my fuzzy understanding is they want all the short energy going thru a short direct path directly to ground. If it runs thru a buss, all the wire sizes change to smaller.

I wrestled with this recently with a new charger install and a bow thruster battery bank to get charged....it took a lot of reading and phone calls to get it right. It seems that just when you think you got it figured, someone comes along with another perspective. Even the engineers have some disagreement.

I think Neil that once you get the cable sizes right you will be on the right track. Myself I was one volt low and changed out the cable sizes and got to where the isolator would work.

I think you are right. Now I have to figure out if all cables would need to be larger within the various circuits. The circuit for the inverter will be ok, once I add the 3/0 to the circuit from the isolator.

I will add 2/0 to the two engine circuits. The engine feeds from the isolator are Currently 4 gauge (OEM). That is on a sixteen to eighteen foot circuit. That cable feeds to the battery shutoff switch. There is also the feed from the 60 amp Charles Charger to the circuit.

[Helmsman]

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Interesting. This must be a newer change to the ABYC rules. My Heart Interface inverter does not have that as a requirement. I don't see it on the Mastervolt inverters either but do see it on the Xantrex. It's interesting that on the Magnum inverters the requirement is just for a 8AWG ground, except on boats where it must be "one size smaller than the DC feed". There also appears to be a (rather new?) ABYC requirement that the case cannot be connected to the negative supply side... I wonder why that is? (considering all the other things that ARE like that including starters and alternators).

Like I said earlier, there's nothing "wrong" with it being larger, but I didn't think there was a requirement for it to be that large.

On your boat, Is there also a connection from the negative terminal on the inverter battery back to the engine or some other "negative buss"?

No there isn’t a connection to a negative buss. Just the case ground. So it is a self contained unit as it shows in the drawing.

Well, that could be an issue then, to your charging circuit. That means your charging circuit has to go from the engine, to the negative buss, then to the case ground on the inverter then back to the inverter battery via the negative cable. That's a circuitous path, when it should be direct from the negative buss (which essentially should be the engine) to the inverter battery negative post. This will be complicated if there is ANY current draw from the inverter, where all bets would be off on how much voltage drop would be on the negative cable from the inverter battery to the inverter. Any voltage drop on that portion of the circuit would impact the charging capability from either alternator.

I am not sure what you are trying to teach me. Just not that good with understanding current flows.

The path is exactly the same as the drawing I attached. The path for the charge is from the alternator, to the isolator. Then from the isolator to the positive battery switch on the inverter circuit. From there, to the positive on the battery bank. The current from the isolator would charge the battery bank at that point, If the battery bank does need a charge. Then the current would pass through the negative cable back to the inverter.

That seems like the same way the isolators would charge the engines and the house bank. Their circuits have a component that is alt to iso to battery and then to the circuit which incorporates a neutral yellow cable right? Any excess current goes through those neutral connections and then off the boat when connected to shore power. When it isn’t connected, it is a closed loop circuit.

The inverter circuit also has an AC component to it. So the flow of electricity is from the DC positive into the inverter, then converted to AC then to the circuits and back to the inverter. Then back to DC to the batteries. The case ground is not part of the circuit. It is designed to handle a short.

Here is the manual. Pages 20, 21, and 22 show wiring diagrams.
https://www.manualslib.com/manual/62897 ... =17#manual

One of them has 24 volt set up and shows a negative connection back to a buss bar. My scenario is the 12 volt split buss set up that does not show a negative connection back to a buss bar or an engine connection. I will call them in the morning to ask them about whether it should and it is a typo or whether it should have one with a charge coming from an isolator.

[Helmsman]

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Interesting. This must be a newer change to the ABYC rules. My Heart Interface inverter does not have that as a requirement. I don't see it on the Mastervolt inverters either but do see it on the Xantrex. It's interesting that on the Magnum inverters the requirement is just for a 8AWG ground, except on boats where it must be "one size smaller than the DC feed". There also appears to be a (rather new?) ABYC requirement that the case cannot be connected to the negative supply side... I wonder why that is? (considering all the other things that ARE like that including starters and alternators).

Like I said earlier, there's nothing "wrong" with it being larger, but I didn't think there was a requirement for it to be that large.

On your boat, Is there also a connection from the negative terminal on the inverter battery back to the engine or some other "negative buss"?

No there isn’t a connection to a negative buss. Just the case ground. So it is a self contained unit as it shows in the drawing.

Well, that could be an issue then, to your charging circuit. That means your charging circuit has to go from the engine, to the negative buss, then to the case ground on the inverter then back to the inverter battery via the negative cable. That's a circuitous path, when it should be direct from the negative buss (which essentially should be the engine) to the inverter battery negative post. This will be complicated if there is ANY current draw from the inverter, where all bets would be off on how much voltage drop would be on the negative cable from the inverter battery to the inverter. Any voltage drop on that portion of the circuit would impact the charging capability from either alternator.

EDIT: Actually, rethinking this, it could even be a bigger issue. Since there appears to be an ABYC requirement that says " the case cannot be connected to the negative supply side", there might be NO legitimate negative connection between your charging sources (engines) and the inverter battery bank. Is this accomplished some other way?

Regarding your initial post, see my previous post for further info. Regarding your edit, there is no legitimate connection from the negative post on the battery back to the engine. The drawings don’t show one either other than the 24 volt set up I mentioned in the previous post. I will call the tech back in the morning to determine if their should be. If there shouldn’t be, then I will ask how the current flows with a charge from the isolator attached to the positive at the battery shutoff switch.

By the way, I really appreciate your help, Bud’s, and the others who are helping me with this.

[km1125]

Note that in my last couple posts I'm just talking about the NEGATIVE path, not the positive circuit path. There needs to be a "return" circuit corresponding to any positive (forward) circuit. If you lose just a volt on the return path, it's just as detrimental as if you had lost in in the forward path.

[Helmsman]

Source of the post Note that in my last couple posts I'm just talking about the NEGATIVE path, not the positive circuit path. There needs to be a "return" circuit corresponding to any positive (forward) circuit. If you lose just a volt on the return path, it's just as detrimental as if you had lost in in the forward path.

I understand. If the inverter only had the battery and inverter charger in the circuit, it would not need a negative feed back to the engine. Since it has a charge coming from the alternator, it would make sense that it would need a negative cable back to the engine. I will ask the tech in the morning. If so, then the only question will be cable size, which will be the same size as the one from the alternator I suppose. If not, I will see if he can explain why not. Will get back with you when I get information back from him.

I guess the other question is where to connect it. Perhaps another battery buss, or directly to the engine?

[km1125]

OK, so doing a little digging around, there was an update to the ABYC rules that addressed that "safety ground" wire from the case of an inverter or battery charger to the boat's negative buss (or an engine ground block, which should be the same potential). It's still hard to wrap my head around the failure modes that cause a need for that, but that's a different subject.

NOW- ALL THE BELOW IS POSTED WITH THE CAVEAT THAT THIS IS BASED ON A MISSING CONNECTION. IF THAT IS THERE SOMEWHERE, THEN WE CAN 'SCRUB' THIS POST!

For your boat, I updated that diagram to what I think you're describing. This might make it easier to see what I'm talking about. This also explains the weird voltage you read (the 15VDC) and how that's possible. If you look at the simplified diagram below, I think it has all the key components. I think you said your isolator #4 connection goes to the inverter DC switch instead of the battery post, but that's a moot difference for this discussion.

If you look at the diagram, find the purple arrow. There SHOULD NOT be a connection between those two yellow lines at the case, although they should be at the same potential. The safety ground goes to the case, which (according to the ABYC rules) should NOT BE connected to the negative battery input on the inverter. The negative input on the inverter is connected to the inverter battery bank negative, so the inverter gets power. However, there is no connection from the inverter battery negative back to the engine grounds or the negative posts for batteries 1, 2, or 3. Therefore, there is no "reference" of "zero volts" at the negative post on the inverter battery. While you can measure a voltage at any of the batteries, that measurement can be different depending on which battery or what source you use as the negative connection for the meter. NO CURRENT can actually flow from the alternators through the isolator and over to the inverter battery, unless there is SOME OTHER CONNECTION that is not shown in the diagram that connects the negative of the inverter battery back to either the engine blocks or the negatives of batteries 1,2, or 3.

Ironically, since there that connection doesn't exist, your "safety ground" is essentially useless, as no current can possibly flow there and get back to the inverter battery bank. EDIT: as I went to post this, I saw you had posted some additional info. The answer on the location, is that it needs to tie to the negatives on the other batteries, or the engine blocks... if you have a "negative buss bar" that would be a good place. The size would be "bigger is better", but it would also need to be at least as big as your "safety ground wire", as it would now be part of that circuit.

Inverter-wiring-customized.jpg

[Helmsman]

Source of the post OK, so doing a little digging around, there was an update to the ABYC rules that addressed that "safety ground" wire from the case of an inverter or battery charger to the boat's negative buss (or an engine ground block, which should be the same potential). It's still hard to wrap my head around the failure modes that cause a need for that, but that's a different subject.

NOW- ALL THE BELOW IS POSTED WITH THE CAVEAT THAT THIS IS BASED ON A MISSING CONNECTION. IF THAT IS THERE SOMEWHERE, THEN WE CAN 'SCRUB' THIS POST!

For your boat, I updated that diagram to what I think you're describing. This might make it easier to see what I'm talking about. This also explains the weird voltage you read (the 15VDC) and how that's possible. If you look at the simplified diagram below, I think it has all the key components. I think you said your isolator #4 connection goes to the inverter DC switch instead of the battery post, but that's a moot difference for this discussion.

If you look at the diagram, find the purple arrow. There SHOULD NOT be a connection between those two yellow lines at the case, although they should be at the same potential. The safety ground goes to the case, which (according to the ABYC rules) should NOT BE connected to the negative battery input on the inverter. The negative input on the inverter is connected to the inverter battery bank negative, so the inverter gets power. However, there is no connection from the inverter battery negative back to the engine grounds or the negative posts for batteries 1, 2, or 3. Therefore, there is no "reference" of "zero volts" at the negative post on the inverter battery. While you can measure a voltage at any of the batteries, that measurement can be different depending on which battery or what source you use as the negative connection for the meter. NO CURRENT can actually flow from the alternators through the isolator and over to the inverter battery, unless there is SOME OTHER CONNECTION that is not shown in the diagram that connects the negative of the inverter battery back to either the engine blocks or the negatives of batteries 1,2, or 3.

Ironically, since there that connection doesn't exist, your "safety ground" is essentially useless, as no current can possibly flow there and get back to the inverter battery bank. EDIT: as I went to post this, I saw you had posted some additional info. The answer on the location, is that it needs to tie to the negatives on the other batteries, or the engine blocks... if you have a "negative buss bar" that would be a good place. The size would be "bigger is better", but it would also need to be at least as big as your "safety ground wire", as it would now be part of that circuit.

Inverter-wiring-customized.jpg

Thank you. In my set up, the negative from the battery connects to the negative terminal on the inverter just like the positive from the battery connects to the positive terminal. It does not connect to the case ground.

If I read your post correctly, I should look for the buss bar that the engine start battery negative already attaches to. That should not be a problem as long as it doesn’t materially change the “doubled” length of the isolator to inverter cable.

Would it make any difference if I connected the new negative cable which goes back to the buss bar to the negative post on the inverter (where the negative cable from the battery is connected to) as opposed to the battery negative post? It is closer to the buss bar. If not I can just directly connect it to the negative post on the battery and run it to the buss bar there. Just trying to look at all options since it is tight in there.

[Helmsman]

Source of the post OK, so doing a little digging around, there was an update to the ABYC rules that addressed that "safety ground" wire from the case of an inverter or battery charger to the boat's negative buss (or an engine ground block, which should be the same potential). It's still hard to wrap my head around the failure modes that cause a need for that, but that's a different subject.

NOW- ALL THE BELOW IS POSTED WITH THE CAVEAT THAT THIS IS BASED ON A MISSING CONNECTION. IF THAT IS THERE SOMEWHERE, THEN WE CAN 'SCRUB' THIS POST!

For your boat, I updated that diagram to what I think you're describing. This might make it easier to see what I'm talking about. This also explains the weird voltage you read (the 15VDC) and how that's possible. If you look at the simplified diagram below, I think it has all the key components. I think you said your isolator #4 connection goes to the inverter DC switch instead of the battery post, but that's a moot difference for this discussion.

If you look at the diagram, find the purple arrow. There SHOULD NOT be a connection between those two yellow lines at the case, although they should be at the same potential. The safety ground goes to the case, which (according to the ABYC rules) should NOT BE connected to the negative battery input on the inverter. The negative input on the inverter is connected to the inverter battery bank negative, so the inverter gets power. However, there is no connection from the inverter battery negative back to the engine grounds or the negative posts for batteries 1, 2, or 3. Therefore, there is no "reference" of "zero volts" at the negative post on the inverter battery. While you can measure a voltage at any of the batteries, that measurement can be different depending on which battery or what source you use as the negative connection for the meter. NO CURRENT can actually flow from the alternators through the isolator and over to the inverter battery, unless there is SOME OTHER CONNECTION that is not shown in the diagram that connects the negative of the inverter battery back to either the engine blocks or the negatives of batteries 1,2, or 3.

Ironically, since there that connection doesn't exist, your "safety ground" is essentially useless, as no current can possibly flow there and get back to the inverter battery bank. EDIT: as I went to post this, I saw you had posted some additional info. The answer on the location, is that it needs to tie to the negatives on the other batteries, or the engine blocks... if you have a "negative buss bar" that would be a good place. The size would be "bigger is better", but it would also need to be at least as big as your "safety ground wire", as it would now be part of that circuit.

Inverter-wiring-customized.jpg

Well, you were absolutely right in regards to the negative feed from the battery to a buss bar! I spoke with Protech, and he stated that even though their manual doesn’t show the negative, when you add a power source to the system (positive feed) the current has to have somewhere to go to complete the circuit. So a negative feed is required.

We have an issue here with timely and competent electrical help. The fellow I used is supposedly the best on the lake, not cheap and recommended by many. Last year I found the eng 1 and bat 4 connected the wrong way, after experiencing a battery drain to almost dead level. I switched those after a day of tracing wires. Now, with your help, I find that I don’t even have a completed circuit. I also didn’t get the right gauge wire on the circuit either.

If you and others hadn’t joined in to help me, I would have never figured this out. So, I truly appreciate the help on this.

[km1125]

I understand that your inverter battery negative connects to the inverter negative input (and how I drew the diagram), but what I was referring to is the ABYC reg that says the inverter case cannot connect to the inverter negative input (a manufacturer requirement). I still don't understand why this is, as it would eliminate the need for one of the "safety grounds" if the case was already bonded, just like your starters and alternators. But that's just just a reg issue.

Ideally, you'd want that negative tie-in to be as close to the battery as possible, but there may be reasons to actually prefer somewhere else. It could be after a shunt if you have (or plan to have) one of those on your inverter battery, as then the shunt could track anything going in or out of your battery, whether the supply or load was from the engine or the inverter. If you move the negative tie-in closer to the inverter then the voltage drop between the battery negative and that point will be "subtracted" from the battery voltage when the alternators are charging the battery. If the inverter is not running, then there will be very minimal voltage drop and it won't make any practical difference. The more the inverter is loaded, the more difference it will make.

You could calculate worst-case by taking the maximum amp load (~180A at 2kW), which for a 2/0 wire at 6 ft would be about 0.143V. I would consider this an "insignificant difference" as it would only be when the inverter was at full load and that you'd probably see more variation in the supply voltage than that small voltage.

Now, here's an interesting thing to ponder. If you took both the negative tie-in line and the charge line from the Proiso isolator and connected them closer to the inverter than right at the battery, that voltage drop calculation would double (again, this is only when the inverter is at full load and using those assumptions (2kW, 2/0 wire and 6 ft length)). This would actually cause the inverter to draw a larger percentage of its supply current from the running engines rather than the battery, which means the battery charge would last longer and you wouldn't have to recharge the battery as much after the inverter was done. This is using voltage drop in your favor to help limit or redirect current flows.

EDIT:... we must have the same "time cycle" brains.... I see you did another post as I was creating this one.

[bud37]

As this thread started , I was going to ask you to make a rough schematic drawing of what you have down there. Still may be a good idea, even for yourself to consult later.

All batteries, banks whatever have to be grounded back to their source , which in this case in is the engines, which should be tied together as well. Routing can be eased with the use of the appropriate sized buss bars and cables to minimize clutter.

Km....I will try to find the technical explanation for the case ground instruction being an alternate route in case of internal short, than the circuit ground. I understand it , just no good at explaining it properly, I initially thought the same as you.....