Floating ground on camper with inverter

[suncamper9101]

I am setting up a 12V solar system for my small fiberglass trailer camper and I have some questions for the experts here.

System Details
The battery system is 2x 6V golf cart batteries in series. The solar panel is 2 x 100Watt in parallel (each panel is fused) connected to a pwm charge controller. Eventually I might get a MPPT controller and connect the panels in series. 10AWG wire is used in the run between the batteries, the charge controller and panels.

- A shunt connected to two digital current meters that track total power will be used to keep track of total battery charge and discharge to prevent excess discharging of the batteries
- An inverter will be used to run a $60 mini refrigerator. Inverter is a tripplite PINV1500. A relay connected to a refrigerator temperature sensor will be used to cut power to the inverter when cooling is not required to eliminate power consumption from the inverter during idle. A manual override will be used to allow occasional charging of laptops and use of a very small instapot.

- wiring from battery to inverter will be 2/0 wire
- Other loads on the battery will all be DC - lights, vent fan and usb chargers
- Trailer will never be connected to AC power at campsites. Only time AC will be used is at home via an extension cord to get the refrigerator cooled before the trip starts. This will be done by unplugging from the inverter and connecting to the extension cord.
- Fuses will series circuit breakers and battery post mounted fuses from Blue Sea
- Two 150A Busses from Blue Sea will be used as +ve and -ve bus.
- Inverter, fuse boxes, charge controller, all circuit breakers will be mounted on a sheet of plywood which would then be mounted to the fiberglass

I have decided to wire the system as a floating ground because of the shunts. I didn't choose to ground to the trailer chassis because that provides an additional path for current back to the battery via the trailer chassis potentially causing the shunt readings to be wrong.

Because of the floating ground, the battery I plan to fuse both ends of the battery. I found a similar setup on this thread (https://www.solarpaneltalk.com/forum...-and-grounding) and Sunking advised using 2 fuses at both battery terminals for inverter and charge controller.

My initial wiring plan was this:
a) Battery +ve => 150A fuse on terminal => +v bus
b) Battery -ve => 150A fuse on terminal => shunt => -ve bus
c) +ve bus => 30A circuit breaker => Charge controller (CC) +ve
d) -ve bus => CC -ve
e) +ve bus => inverter +ve
f) -ve bus => inverter -ve
g) +ve bus => fuse box => various DC runs (lights, fans etc.)
h) -ve bus => fuse box => various DC runs (lights, fans etc. )

Questions:
1) If i put a 150A fuse between the two 6V batteries can I eliminate the need for the 150A fuses at the battery terminals (a & b above)
2) Sunking advised in the linked post on having the CC coming to the fuse on the battery. Do I need to bring my CC connection to the battery or can i leave it as is (c & d above). I can change it if required, just need to return the single fuse holders and get double fuse holders and possibly a second shunt.
3) I would like to replace one of the 150A terminal fuses with a Blue Sea 150A circuit breaker to allow me to manually disconnect the battery. This would mean a 2-3 foot run of wire to the 150A circuit breaker which will be located at the entry point inside the RV. Is this OK? I could use a battery disconnect switch if the answer is no.

4) My inverter has a ground connection, however as stated above I was planning to use a floating ground so connecting ground connection to the trailer chassis will defeat the floating ground. Also the ground connector in the inverter is connected to the -ve terminal as well as the neutral of the two AC outlets in the front of the inverter. So looks like even without the ground connection, the inverter will be grounded to the -ve side of the battery. Will there be a risk of shock without the ground connection? Inverter doesn't have GFCI outlets, should I connect GFCI outlets to the inverter outlets?

Thank you for reading through the long post. Looking forward to your comments.

[Asterix]

First of all, fuses are there to protect over current discharging of something.
Questions:

1) If i put a 150A fuse between the two 6V batteries can I eliminate the need for the 150A fuses at the battery terminals (a & b above)

I can see your line of thinking here, however fusing on 2 lines is a waste of time, you may as well just add a fuse into either the positive or negative side. Given these lines are floating.

2) Sunking advised in the linked post on having the CC coming to the fuse on the battery. Do I need to bring my CC connection to the battery or can i leave it as is (c & d above). I can change it if required, just need to return the single fuse holders and get double fuse holders and possibly a second shunt.

A charge controller is there to make sure that the battery receives the correct Voltage and charging current. A fuse is there for protection, Putting a fuse in between the battery and CC is fruitless unless you are protecting the CC from sudden battery current drains and you would hope the CC would use its foldback current limiting under that type of failure. This is another reason for buying a decent CC. Just make sure the fuse on the Battery goes to any external circuitry.

3) I would like to replace one of the 150A terminal fuses with a Blue Sea 150A circuit breaker to allow me to manually disconnect the battery. This would mean a 2-3 foot run of wire to the 150A circuit breaker which will be located at the entry point inside the RV. Is this OK? I could use a battery disconnect switch if the answer is no.

A circuit breaker is the best thing to have anyhow, as they will trip out faster than a fuse blowing. Even 10 foot of wire would make no difference, as long as the wire is the correct size.

4) My inverter has a ground connection, however as stated above I was planning to use a floating ground so connecting ground connection to the trailer chassis will defeat the floating ground. Also the ground connector in the inverter is connected to the -ve terminal as well as the neutral of the two AC outlets in the front of the inverter. So looks like even without the ground connection, the inverter will be grounded to the -ve side of the battery. Will there be a risk of shock without the ground connection? Inverter doesn't have GUCCI outlets, should I connect GFCI outlets to the inverter outlets?

Thank you for reading through the long post. Looking forward to your comments.

Just mount it on insulators, then the whole thing is floating. Just make sure nothing can short the case to ground. I don't see why you should get a shock, unless you do something silly like grabbing hold of the inverter outputs.

[Mike90250]

> First of all, fuses are there to protect over current discharging of something.

NO Fuses (and circuit breakers) are to protect the wiring from melting and starting a fire. It is very easy to put a 10A fuse on a battery and use a 5A light bulb and run the battery totally flat to 0V. Fuse does nothing until it's current rating is exceeded


> , Putting a fuse in between the battery and CC is fruitless

Not sure why you say that. You put a fuse ( or circuit breaker) to protect against over-current. It's very
possible for a charge controller to "go bad" and short between + & - Which if un protected, will start a fire.

I use a circuit breaker, so I can reboot the controller easily when needed.


> A circuit breaker is the best thing to have anyhow, as they will trip out faster than a fuse blowing

Oh boy. You just engaged the BS Detector. Once is a mistake. 2 times in the same post, I'm calling you on it.
Breakers and fuses both come in a wide variety for disconnect speeds. There are slow blow fuses, and fast trip beakers. There are even some fast blow fuses that will go before FET's fry, but they cost more than the FET
Time delay breakers are often used on motor circuits, to allow the motor to spin up instead of tripping off line.

Now, I'm cranky Asterix, because I have to review your postings carefully for dangerous suggestions

[Asterix]

> First of all, fuses are there to protect over current discharging of something.

NO Fuses (and circuit breakers) are to protect the wiring from melting and starting a fire. It is very easy to put a 10A fuse on a battery and use a 5A light bulb and run the battery totally flat to 0V. Fuse does nothing until it's current rating is exceeded

Fuses are NOT there to protect the wiring, A fuse is to protect the circuit, if you have wiring that is not rated properly then you had better find someone that knows what they are doing.

> , Putting a fuse in between the battery and CC is fruitless

Not sure why you say that. You put a fuse ( or circuit breaker) to protect against over-current. It's very
possible for a charge controller to "go bad" and short between + & - Which if un protected, will start a fire.

If you are connecting a fuse between the CC and the battery, you are achieving nothing at all if the CC was to go up in smoke.

[/QUOTE]

I use a circuit breaker, so I can reboot the controller easily when needed.


> A circuit breaker is the best thing to have anyhow, as they will trip out faster than a fuse blowing

Oh boy. You just engaged the BS Detector. Once is a mistake. 2 times in the same post, I'm calling you on it.
Breakers and fuses both come in a wide variety for disconnect speeds. There are slow blow fuses, and fast trip beakers. There are even some fast blow fuses that will go before FET's fry, but they cost more than the FET
Time delay breakers are often used on motor circuits, to allow the motor to spin up instead of tripping off line.

Now, I'm cranky Asterix, because I have to review your postings carefully for dangerous suggestions

You stay cranky and read your own post for BS

A fuse is always going to be slower than a trip, particularly as you are not taking into account the type of circuit that has been described. You certainly would not use a fast blow in this system and an anti surge fuse would be no good.
Why bother trying to go off on one about relative speeds of trips to fuses, as the bog standard trips that are purchased are good enough for this task.

[SunEagle]

Fuses are NOT there to protect the wiring, A fuse is to protect the circuit, if you have wiring that is not rated properly then you had better find someone that knows what they are doing.


If you are connecting a fuse between the CC and the battery, you are achieving nothing at all if the CC was to go up in smoke.

You stay cranky and read your own post for BS

A fuse is always going to be slower than a trip, particularly as you are not taking into account the type of circuit that has been described. You certainly would not use a fast blow in this system and an anti surge fuse would be no good.
Why bother trying to go off on one about relative speeds of trips to fuses, as the bog standard trips that are purchased are good enough for this task.


[/QUOTE]

Before you continue with your banter I am going to warn you that your statements are not true and you are at a point of a very long vacation.

Over current devices (fuses and circuit breakers) are there to first protect the wire downstream of it and also to disconnect a shorted load. While that may be defined as the "circuit" that term does not provide clarity of what a fuse is protecting.

Please try to understand that a lot of inexperienced people like to perform DIY systems and have no idea about protection from burned up wires or equipment.

[Asterix]

You stay cranky and read your own post for BS

A fuse is always going to be slower than a trip, particularly as you are not taking into account the type of circuit that has been described. You certainly would not use a fast blow in this system and an anti surge fuse would be no good.
Why bother trying to go off on one about relative speeds of trips to fuses, as the bog standard trips that are purchased are good enough for this task.

Before you continue with your banter I am going to warn you that your statements are not true and you are at a point of a very long vacation.

Over current devices (fuses and circuit breakers) are there to first protect the wire downstream of it and also to disconnect a shorted load. While that may be defined as the "circuit" that term does not provide clarity of what a fuse is protecting.

Please try to understand that a lot of inexperienced people like to perform DIY systems and have no idea about protection from burned up wires or equipment.

Understood and I should have qualified the circuit as the whole system, rather than how it appears to have been taken.