Fuse size question

[eric1514]

My RV currently has 2 grp24 deep cycle batteries, probably 85Ah each. I'm going to replace them with 4 GC2 batteries with a total Ah capacity of around 440. I am also going to install a stand alone 2000w PSW inverter. It will power only 1/2 of one dual outlet in the kitchen and only when I turn it on. No other additional loads are planned except a conversion to a compressor fridge maybe next year. I just want to be able to go a long time without worrying about capacity and this is more of a project than a necessity. I'm going to gather up all the positive and all the negative wires currently attached to the Grp24 batteries in their current location, attach them to large buss bars and send just 2 wires to the new location where the GC2 batteries will be. It's about a 5 ft run. No changes to the charging system are anticipated at this time. I know the 45 amp PD converter is undersized but it will do, for now.

I plan on installing a 300 amp fuse on the positive wire going to the inverter. The inverter will be in the compartment where the old batteries were and will be attached to the buss bar about a foot away. There'll be a shunt on the negative cable coming from the buss bar to the new batteries in that same compartment. There looks like there's a fuse on the positive wire coming from the present batteries now but it's old and I can't get any info off of it. I'm going to replace it, but my question is, what size?

TIA,
Eric

[booster]

The inverter should give you a recommended size for the inverter capacity, but you also will need to have big enough wiring to handle it. 3/0 or 4/0 for 300 amps, on both the positive and negative. A microwave at 700 watts will surge to maybe 150 amps from what we have seen on ours. If you are not going to have big loads you could probably use smaller DC wiring and lower fuse rating, but they have to match for safety.


If you are doing the outlet splitting routine, you have to very careful about neutral bonding issues, especially with a manual control inverter on a switch. There was just a long discussion on this forum about that that you probably would want to look through. IMO, an inverter with and automatic transfer switch and automatic neutral ground bonding would be the best solution, and then you could just wire the entire outlet to the inverter only and it would automatically power on shore power, if you have it, and inverter when you don't. Forgetting the inverter on would not matter at that point from a bonding standpoint so much safer.


Other option would be to permanently bond the inverter, but put it on a separate standalone automatic transfer switch.


We have the same 440ah in our Roadtrek 190, and to simplify I just did the inverter and charger upgrade together with a Magnum MS2000 and put the whole van on it. All outlets now auto switch from shore to inverter power safely and seamlessly. No added wiring to the outlet needed that way.

[eric1514]

Thanks Booster,

My needs as far as 120v is concerned can be handled with one outlet in the kitchen area. We're talking a cup of coffee in the morning with a Keurig, an espresso late afternoon with a Nespresso and maybe some MW popcorn at night. I do have a smaller 600w inverter factory installed with a transfer switch that powers the entertainment system. I don't need to supply the whole van with 120v when I'm not on shore power. Maybe I'm being shortsighted, but I can't see what else I need the power for.

I do see the problem with splitting the outlet now that you mention it. The way it is constructed, I can have separate hot and neutrals but the ground is common. I'll have to investigate that further. I could always run another outlet, but I'd rather not.

Any thoughts on what the fuse size should be on the main battery cables?

[booster]

Originally Posted by eric1514

Thanks Booster,

My needs as far as 120v is concerned can be handled with one outlet in the kitchen area. We're talking a cup of coffee in the morning with a Keurig, an espresso late afternoon with a Nespresso and maybe some MW popcorn at night. I do have a smaller 600w inverter factory installed with a transfer switch that powers the entertainment system. I don't need to supply the whole van with 120v when I'm not on shore power. Maybe I'm being shortsighted, but I can't see what else I need the power for.

I do see the problem with splitting the outlet now that you mention it. The way it is constructed, I can have separate hot and neutrals but the ground is common. I'll have to investigate that further. I could always run another outlet, but I'd rather not.

Any thoughts on what the fuse size should be on the main battery cables?

It all depends on the cable size what you fuse them at, unless there is lighter wiring someplace else which shouldn't be there.

[booster]

Be aware that if the inverter does not have an AC fuse or breaker for the output to the outlet that is suitable, you will also need to supply one as you will not be going through the AC fuse panel. Fusing on the DC side won't protect the AC side correctly.


The kitchen outlet may be 15 amp or 20 amp rated depending on the current wire size to it.

[eric1514]

Originally Posted by booster

Be aware that if the inverter does not have an AC fuse or breaker for the output to the outlet that is suitable, you will also need to supply one as you will not be going through the AC fuse panel. Fusing on the DC side won't protect the AC side correctly.


The kitchen outlet may be 15 amp or 20 amp rated depending on the current wire size to it.

The inverter has 4 15amp outlets on it's side. It is designed for you to plug in a 15 amp appliance. I would think that if I plugged a cord into one of the outlets and wired the other end to the back of an outlet, all would be OK.

[booster]

Originally Posted by eric1514

The inverter has 4 15amp outlets on it's side. It is designed for you to plug in a 15 amp appliance. I would think that if I plugged a cord into one of the outlets and wired the other end to the back of an outlet, all would be OK.

If you are going to use a cord, is it not going to be in the wall?


You could also just run the plug in cord and plug in a outlet strip mounted to the surface. That would also take care of all the isolation stuff. Are the outlets GFCI on the inverter?

[Nic7320]

If you only break the duplex (outlet one to outlet two) hot side strap, and wire both hot and neutral along with the ground from your inverter to one half the receptacle, you'll cross connect the two neutrals and share the neutral bonding that's already in your RV. Doing it this way is probably a good idea for such a large inverter. EDIT: but only if your rig provides a N-G bond when it is not on shore power or on the generator.

The other way is to break both straps on the receptacle and wire up hot and neutral, which keeps the inverter fully isolated from your main RV power system. Similarly, you can just use a plug strip which also keeps it isolated. In this isolated configuration, it no longer sees the N-G bonding on the main RV power system, so you should bond neutral to ground somewhere, preferably close to the inverter. And now, since it's an isolated secondary power source, you treat it like a different power system and you don't switch off the bonding when on shore power, as long as it stays isolated and there's only one bond on that isolated power string.

Most inverters connect their Electrical Safety Ground to the DC negative terminal which is already grounded at the battery or chassis, but connecting the inverter's ground to the receptacle ground shouldn't be a problem. More grounds usually mean more safety.

In our previous discussion, we (sort of) decided that small inverters with limited loads can get by without neutral to ground bonding or even a safety ground, simply because it's done so often, but technically it's a violation of electrical codes to let it float. It can be a problem if you connect equipment powered from one AC system to another (like a DVD player on one power source to your TV on a different AC source), or a computer on one AC source, and the monitor on another source, then the differences in ground potential can damage something.

The outlet strip is a good idea if it has a built-in circuit breaker. Not all do.

[eric1514]

Originally Posted by Nic7320

If you only break the duplex (outlet one to outlet two) hot side strap, and wire both hot and neutral along with the ground from your inverter to one half the receptacle, you'll cross connect the two neutrals and share the neutral bonding that's already in your RV. Doing it this way is probably a good idea for such a large inverter.

The other way is to break both straps on the receptacle and wire up hot and neutral, which keeps the inverter fully isolated from your main RV power system. Similarly, you can just use a plug strip which also keeps it isolated. In this isolated configuration, it no longer sees the N-G bonding on the main RV power system, so you should bond neutral to ground somewhere, preferably close to the inverter. And now, since it's an isolated secondary power source, you treat it like a different power system and you don't switch off the bonding when on shore power, as long as it stays isolated and there's only one bond on that isolated power string.

Most inverters connect their Electrical Safety Ground to the DC negative terminal which is already grounded at the battery or chassis, but connecting the inverter's ground to the receptacle ground shouldn't be a problem. More grounds usually mean more safety.

In our previous discussion, we (sort of) decided that small inverters with limited loads can get by without neutral to ground bonding or even a safety ground, simply because it's done so often, but technically it's a violation of electrical codes to let it float. It can be a problem if you connect equipment powered from one AC system to another (like a DVD player on one power source to your TV on a different AC source), or a computer on one AC source, and the monitor on another source, then the differences in ground potential can damage something.

The outlet strip is a good idea if it has a built-in circuit breaker. Not all do.

My original plan was to cut both straps on the outlet that is now only powered by shore power. I was going leave one side like it is and connect the other side to the new inverter. The problem I saw was that the ground terminal serves both outlets and can't easily be severed. I still like this idea for it's cleanliness and the fact I don't have to find a place for another outlet. You've introduced a new wrinkle by suggesting I cut only the hot strap. I assume the two neutrals will be connected as will the two grounds. All this is so far above my pay grade, that that scenario kinda scares me but you know more about this than I do so I trust your opinion.

I don't want to do the separate outlet or power strip because of space issues. I also have no idea how to do this as you suggest.

In this isolated configuration, it no longer sees the N-G bonding on the main RV power system, so you should bond neutral to ground somewhere, preferably close to the inverter.

Maybe you mean I should make one of those plugs like in the generator video from the other thread.

[Nic7320]

Multiple ground connections are not a problem. On any piece of equipment or rack full of equipment (like a stereo system), they may have any number of screws connecting the metal cases to the electrical ground, and every one of those screws are multiple grounds. The more, the better... usually. Ground loops in analog gear are sometimes a problem, but that doesn't apply here.

(some content edited)


But I'm also assuming here you have a straight inverter that's not doing anything other than making AC power, i.e. it's NOT a combo charger and inverter, where the AC wiring is sometimes an AC power source and sometimes an AC load. Those are a different issue entirely.

[eric1514]

Originally Posted by Nic7320

Multiple ground connections are not a problem. On any piece of equipment or rack full of equipment (like a stereo system), they may have any number of screws connecting the metal cases to the electrical ground, and every one of those screws are multiple grounds. The more, the better... usually. Ground loops in analog gear are sometimes a problem, but that doesn't apply here.

By connecting the two neutrals of your inverter and your outlet together, you no longer have an isolated inverter neutral, but that's why you no longer have to deal with N-G bonding, because.it now shares the N-G bond on your main AC power system.

But I'm also assuming here you have a straight inverter that's not doing anything other than making AC power, i.e. it's NOT a combo charger and inverter, where the AC wiring is sometimes an AC power source and sometimes an AC load. Those are a different issue entirely.

Thanks for your input. I'm learning, slowly, but I'm learning. This will be a straight inverter, no charger. It will be mounted to a piece of plywood in a location near the batteries and will be turned on and off with a remote on the wall. I plan on labeling the outlet sides and will use one side or the other depending. I will never have the inverter on if the shore power cable is attached.

[avanti]

Originally Posted by Nic7320

The more, the better... usually. Ground loops in analog gear are sometimes a problem, but that doesn't apply here.

This is incorrect. Ground loops can be a problem anywhere. They are not dangerous, but they generate electrical noise and are always to be avoided. A proper ground system in a vehicle will be configured as a tree of ground busses, with the vehicle chassis serving as the root of the tree. There should be one and only one path to ground from any point in the system.

[Nic7320]

One problem I see is when you run the inverter, but you're not plugged into shore power and not running your generator either, then your whole rig has no N-G bond. So you should put a N-G bond on your inverter and keep it isolated from the main AC neutral in your rig by breaking both duplex outlet straps.

[Nic7320]

Originally Posted by avanti

This is incorrect. Ground loops can be a problem anywhere. They are not dangerous, but they generate RF noise and are always to be avoided. A proper ground system in a vehicle will be configured as a tree of ground busses, with the vehicle chassis serving as the root of the tree. There should be one and only one path to ground from any point in the system.

Yes, you are correct. When we were wiring up a repeater system with analog audio circuits, we paid a lot of attention to ground loops to minimize hum and buzz. A microwave won't care.

With all the 20kHz-200kHz PWM noise in an inverter, this could potentially be a problem, but it's safer to have a known electrical ground from the inverter to the load. I wouldn't want to rely on the inverter's DC side to create a good enough ground for an AC outlet, because it's taking a much longer pathway.

[avanti]

Originally Posted by Nic7320

A microwave won't care.

That is true, but every A/V device in your van will.

[eric1514]

Originally Posted by Nic7320

One problem I see is when you run the inverter, but you're not plugged into shore power and not running your generator either, then your whole rig has no N-G bond. So you should put a N-G bond on your inverter and keep it isolated from the main AC neutral in your rig by breaking both duplex outlet straps.

How do I put a N-G bond on the inverter. Is this like building one of those plugs like in the generator video and plugging it into a spare receptacle on the inverter? The inverter will only be used when I’ m not plugged in or using the generator.

[Nic7320]

AFAIK, large inverters usually tie the safety ground to the battery/chassis ground, so there's some ground loops with any appliance that is screwed into the frame whether you want it or not. Also, your radio's antenna ground is tied to your vehicle chassis since it's a "vertical" antenna that needs a chassis counterpoise, and not a dipole of two elements.

I know it's not ideal, but those extra pathways are all over the place.

Even your doors have two ground paths from each hinge.

[Nic7320]

Originally Posted by eric1514

How do I put a N-G bond on the inverter. Is this like building one of those plugs like in the generator video and plugging it into a spare receptacle on the inverter? The inverter will only be used when I’ m not plugged in or using the generator.

Yes, you have multiple AC outlets on your inverter, so that's an easy way of bonding it right at the inverter. You can either buy a plug and wire the N to G, or find an old 3 wire appliance cord and connect the N to G with a crimp barrel. I'd recommend using a second barrel on the hot wire, just so the cut wire nub doesn't touch anything.

[Nic7320]

Originally Posted by avanti

That is true, but every A/V device in your van will.

When radios use chassis ground for signal returns, every RCA cable going to another unit creates another ground pathway somewhere. Hopefully these are routed and bundled together so the loop area created by the ground mesh is not picking up too much RFI.

Good grounding can be done with a mesh, since the inductance and resistance is less. An N x N mesh of any arbitrary size with the same size links has the same resistance across its diagonal as any single link.

But it's an interesting question, as to how far vehicle manufacturers control ground currents. Vehicles in the past relied on a lot of chassis connections, and the chassis itself is a mesh of welded steel parts with multiple pathways.

And I've found AV installers... their skill level can be anything from expert to trainee... to the occasional hack. YMMV.

[eric1514]

OK, so that settles it. I'm going to cut the straps on both the hot and neutral on the back of the outlet in the kitchen. I'm going to wire the inverter to one side and the other side will remain the same. The bare ground wires will be attached to the same ground lug on the outlet.

Back at the inverter, I will make a N-G bonding plug. I'll check first if that's necessary and later if it in fact works with my 3 light tester.

Fuse sizes, the original topic, yet to be determined.

Thanks, Booster and Nic7320 for your help and patience.