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Inverter Installation ?'s


alan0043

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Hi Everyone,

 

I need to install an inverter in my truck. I have a Cobra CPI 1550. It is 1500 watt continuous and 3000 watt peak. Here are some of my questions. What would be the best wire to use ? What size wire ? Welding wire ? What size fuse do you use ? Where do you locate the fuse ? To you ground the inverter to the truck ? I understand that there is negative cable that goes to the inverter but there is also a smaller wire on the inverter. I assume that the inverter is wired to the starting batteries. If you could re-do the install of your inverter. What would you change ? I am looking for the best way. Have I missed anything ?

 

Thank you for all help,

Al

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Al,

 

I have a Xantrex Freedom HF 1800. Wires to battery were 3/0 AWG (red and black battery cable) for less than six foot run to batteries. Can't remember for sure but think it was 250 amp DC fuse on positive cable to battery located right next to battery. I also used a 6 AWG wire from the grounding lug to ground to my cab and chassis. Al, if you want to PM me an email address, I would be happy to send some pics. My inverter is in the drivers storage compartment on a plywood board.

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A disclaimer: If you cannot use the wire size specified in the following table, don't blame me for any fires!

I have performed 4 inverter installs and several converter installs. I am always amazed at how large the cable must be and how little room the mfg's give you to put the cables on the inverter. A firefighter friend once told me that he has responded to a lot of truck fires parked in someone's driveway caused by inverters. My theory is simple. Just apply the formula: Power = Voltage x Current. If the Power (load) remains constant and the battery voltage starts dropping, the current must rise. Therefore, the size of the cable is important and more important is that the protecting fuse must not be larger than the cable can handle.

  • The Cobra starts off saying use the biggest wire available and later in the installation is says to use #4 at a distance of no more than 1.5 meters between the battery and inverter. Like that is possible! :rolleyes: Read on.

http://www.solar-win...-DC-cables.html

The above site will let you input your installation specs and give you an answer to wire size.

 

Cobra does not specify that the length of the run must include the positive cable and the negative cable. You will get voltage drop on both runs. Xantrex does. Some DC wire size tables do. The x2 length of cable will give you a headache when you put the numbers in the table to calculate wire size.

 

At peak of 3000 watts, you will draw 250 amps @12 VDC. Assuming an approximate run length of 1 meter (2 meters total), with 2% acceptable loss (drop to 11.8 volts), the wire size is 3/0 (.4096" diameter). The shorter the cable run the better. For example, if you change the run length to 2.5 meters, the size becomes 4/0 (.46 inch diameter). Change it to 2.6 meters and there is no wire large enough.

 

Now comes the kicker: The terminals on the Cobra are not big enough to handle the cable you need to run it more than about .5 meters. I put a Cobra in my 5th wheel on the storage side of the battery compartment and the cables are longer than .5 meters. Even if you use the "continuous output of 1500 watts", a 2 meter cable length @ 125 amps is 1 AWG which has a diameter of .2893 inches. As I can remember, I could barely get 4 AWG (.2043" diameter) in my Cobra.

 

So, what do you do? The only thing that comes to mind is to measure the Cobra terminals and get the largest size wire that will fit into those holes. The wire diameter is available on the internet. https://en.wikipedia.org/wiki/American_wire_gauge Then, FUSE the cable at the cable's maximum rating, not the inverter's maximum surge.

 

Put the fuse as near the source battery as possible and definately before the wire passes through or over any body, chassis or frame component. Just for reference, the highest DC amp setting on my Lincoln welder is 150 amps and it will make some huge sparks :o

 

Heavy duty grommets are a must. Where possible, get some rubber tape (not vinyl) and protect the wires any where they might rub metal. Putting the cable in conduit or covering it completely will cause it to retain heat. Don't get too protective.

 

The DC cable should be multi-strand insulated copper with insulation rating of 90c (per Cobra installation manual). Another CYA. They know this wire is going to get hot. Xantrex says 75c minimum.

 

Ground: Remember, you are grounding more than the negative side of the battery. The chassis ground will also ground the AC side of the install to the vehicle. To be safe, you should put a GFCI on any outlet wired to or plugged into the inverter.

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Al,

 

I have a Xantrex Freedom HF 1800. Wires to battery were 3/0 AWG (red and black battery cable) for less than six foot run to batteries. Can't remember for sure but think it was 250 amp DC fuse on positive cable to battery located right next to battery. I also used a 6 AWG wire from the grounding lug to ground to my cab and chassis. Al, if you want to PM me an email address, I would be happy to send some pics. My inverter is in the drivers storage compartment on a plywood board.

 

Carl, P/M has been sent. Al

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Al,

 

I have a Xantrex Freedom HF 1800. Wires to battery were 3/0 AWG (red and black battery cable) for less than six foot run to batteries. Can't remember for sure but think it was 250 amp DC fuse on positive cable to battery located right next to battery. I also used a 6 AWG wire from the grounding lug to ground to my cab and chassis. Al, if you want to PM me an email address, I would be happy to send some pics. My inverter is in the drivers storage compartment on a plywood board.

im also running the same Inverter/charger... and mines also in the drivers side storage on a plywood board. though im running 4/0 Marine wire and i got a resetable breaker within 18" of the batteries. i have Both negative and positive to the batteries on opposite ends of the bank. i tend to overbuild everything.

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im also running the same Inverter/charger... and mines also in the drivers side storage on a plywood board. though im running 4/0 Marine wire and i got a resetable breaker within 18" of the batteries. i have Both negative and positive to the batteries on opposite ends of the bank. i tend to overbuild everything.

That is not overbuilt. It is built right. You are over on the 4/0 but other than that it is not overbuilt. :)

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Ground: Remember, you are grounding more than the negative side of the battery. The chassis ground will also ground the AC side of the install to the vehicle. To be safe, you should put a GFCI on any outlet wired to or plugged into the inverter.

I've written about this several times in the past, as well as explaining the risks and why the the GFCI is necessary in a presentation at the 2014 ECR. Also, it is OK to tie the grounding terminal of the inverter to the truck/car frame as long as the inverter is NOT internally bonded so that the designated neutral on the 110 outlet is tied to the grounding terminal (called bonding). If the inverter is internally bonded and the bond cannot be removed I will be glad to once again step through the safest install process and why it is necessary. In any event the GFCI is a must do addition for maximum safety should a fault ever occur on the 110 side.

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Randy,

 

I'll take a refresher. Here is what my Xantrex installation manual says. I have a grounding wire from the grounding lug to my frame and cab. I think I'm ok from what you wrote.

"The AC source feeding the Freedom HF must have the neutral conductor bonded to ground. When the inverter passes shore power through, it will lift the bonding relay on the output and will rely on the input being bonded in order to ensure that the power delivered to a sub panel is properly bonded. See AC Output Neutral Bonding on page 19 for more information on bonding relay operation."

 

I usually plug my shore power into either 110 on the pedestal if available or an outside plug on my trailer. Are these sources neutral bonded?

Here is a PDF of manual for my model if you need more info.

http://www.xantrex.com/documents/Inverter-Chargers/Freedom-HF/Freedom%20HF%201000-1800%20Install%20Guide%20(975-0395-01-01_Rev-A).pdf

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That is not overbuilt. It is built right. You are over on the 4/0 but other than that it is not overbuilt. :)

i also hang my extra rear lighting and accessories off that 4/0 wire. its still overkill BUT i dont like fires....

 

and my inverter ISNT bonded to the frame of the truck (AFTER reading the post from RandyA a while back

about inverters).

 

i also have a 30amp surge suppressor wired between the shore power and the Freedom HF 1800.

 

the Freedom HF 1800 also has builtin GFCI built in but since i hardwired everything i wired a GFCI so it covers

all the outlets in the truck. (hardwiring appears to bypass the Builtin GFCI outlets).

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I've written about this several times in the past, as well as explaining the risks and why the the GFCI is necessary in a presentation at the 2014 ECR. Also, it is OK to tie the grounding terminal of the inverter to the truck/car frame as long as the inverter is NOT internally bonded so that the designated neutral on the 110 outlet is tied to the grounding terminal (called bonding). If the inverter is internally bonded and the bond cannot be removed I will be glad to once again step through the safest install process and why it is necessary. In any event the GFCI is a must do addition for maximum safety should a fault ever occur on the 110 side.

 

Randy,

 

I am glad that you has seen this thread and made some comments. I remember your presentation at the 2014 ECR. That is the reason why I am re-doing my inverter installation over. I had a feeling that it was not quit right. The wire or leads from the batteries needs to be a larger gage wire. The old fuse was 100amp at 32 volts. From some of my research and with the help from Carl (SuiteSuccess) the fuse should be 250amp. There also was no GFCI. I have a few questions. How do you know if your inverter is bonded ? What would be the best fuse to use ? And where can I get this fuse at ? More question could follow later. I am going to a welding supply house to get my wire. I will get the largest gage wire that can fit into the Cobra inverter.

 

Thank you for your help,

Al

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Carl, it appears that your Xantrex unit was designed to provide the necessary isolation between the designated neutral on the inverter and the grounding lug to the frame.

 

Thanks for finding and posting the link to the previous discussion. I had lost it and going back has saved a considerable amount of re-writing. I hope anyone that is interested in this topic will go to the link and digest the discussion.

 

The bottom line for all of this is an RV (or HDT) does not have a true connection to earth ground unless it is plugged into a properly wired shore power outlet. A RV should have no connection between the neutral wire and the grounding wire anywhere in the RV while a brick and mortar residential electrical service will have a connection between neutral and grounding ONLY at the Service Entrance Panel. In essence, the RV is treated like an appliance plugged into a power outlet.

 

An inverter mounted in a vehicle will not have a true neutral tied to earth ground - the neutral is designated on the same longer slot (silver screw) that we find on residential duplex outlets. The other slot is the designated hot wire (gold screw, shorter slot) and the grounding wire is bare, green or yellow-green. In a previous posting Mark called the grounding wire a safety wire - even though the NEC does not identify the grounding wire as a safety wire, I personally liked his designation as it made it clearer as to the purpose of the grounding wire.

 

Most off-the-shelf inverters were designed to be installed in a vehicle that does not also have a shore power connection with isolated ground. Therefore, the unit should be bonded and grounded to the vehicle frame. Whatever device is plugged directly into the inverter outlet is typically isolated. This is considered safe and complies with NEC 250.34 on Portable and Vehicle Mounted Generators (generators = inverters too). Unfortunately, this rule does not address vehicles that have both inverter/generators and shore power connections so we need to go to NEC 551.20 for rules on Combination Electrical Systems. There we find that such a vehicle should not have any current carrying conductor attached to the vehicle frame. This negates the requirements of NEC 250.34 on bonding meaning that a bonded inverter will defeat the intended isolation requirement specified by the NEC. Fortunately (for Carl) his Xantrax unit addresses this with switching of the bond depending on the external power source.

 

So, let's return to the off-the-shelf inverter that one might purchase at a truck stop, off eBay, at Harbor Freight, Amazon, etc. These inverters are typically modified sine wave (stepped square wave) and will have an internal bond between the designated neutral (long slot) and the grounding or safety wire that attaches to the frame. They are typically OK for most everything except ceiling fans, electric clocks and some microwaves. BTW, I have a 1500 watt unit of this type in my HDT that runs the refrigerator and a 3,000 watt unit in my fiver. Both are mounted so that they are insulated from the vehicle frame and have a GFCI immediately after the inverter outlet that goes to the transfer switch.

 

Remember, we are talking about RV's with shared electrical systems now - not vehicles that have ONLY an inverter and no connection to shore power. The added breaker box in the RV or HDT should have two buss bars. One will be for for neutral or ground wires (usually white) and a second for grounding wires (usually bare copper, green or yellow green insulation). The ground or neutral wires will NOT attach to the vehicle frame - the buss bar must be insulated from the breaker box. The grounding wires attach to a buss bar that is connected to the metal breaker box and the vehicle frame.

 

If you connect a multimeter capable of measuring AC voltage in the 120 volt range to the outlet of an inverter you should measure 110 volts (give or take depending on battery voltage) between the two blade slots on the outlet. With the inverter on if you measure the same voltage between the shorter blade slot (gold screw) and the grounding hole (green screw) on the outlet you have a safety issue as this indicates that the designated neutral will be bonded to the vehicle frame and will also defeat the isolation between current carrying conductors and the grounding wire as required by the NEC. If this is true you should isolate the inverter from the vehicle frame. You see, since the inverter is not connected to true earth ground this will also put the vehicle frame and all attached metal at a floating 60 volt potential. Just insulating these inverters will not provide the needed protection. If a short circuit should occur between a current carrying conductor and the vehicle frame a circuit breaker or fuse will not open, once again putting the metal of the vehicle at a 60 volt potential. To protect against this type of fault you should have a GFCI immediately after the inverter output and before your transfer switch. Since the grounding or safety wire of a bonded inverter, even with frame isolation and a GFCI, is at a 60 volt potential I eliminate the safety or grounding wire between the inverter and GFCI. The grounding terminal of the GFCI (green screw) is then attached to the ground in the breaker box (NOT grounding) or the vehicle frame. This will put you in the safer zone and preserve NEC requirements for shared power systems.

 

Clear as mud - right?

 

Oh, almost forgot, someone wanted to know where to get power fuses for the input to inverters. Keep in mind that this will be a disaster fuse. Amazon has the fuse here. Shop around for a holder and fuse at places that install big car sound systems. Also eBay, Grainger and electrical supply sites like Moser, Parts Express, Jamco, etc. Jack should have some more sources to share. I've made all of my fuse holders.

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Okay Randy, sorry to be so dense but just to be sure I understand. If I plug my shore power extension for my truck into a 110 outlet on my trailer (not the pedestal) the earth ground bond from the pedestal should still be present?

YES. If the trailer is wired properly (no bond between the safety wire and neutral) and the pedestal is wired properly with the bond occurring at the service entrance panel and your truck does not have a bond between the safety wire and neutral all will be good. The thrust of the all the technical rambling is the why and how to avoid unknowingly creating a bond along the chain of vehicles because a bond anywhere along the line bonds both the trailer and truck and - a situation we do not want.

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YES. If the trailer is wired properly (no bond between the safety wire and neutral) and the pedestal is wired properly with the bond occurring at the service entrance panel and your truck does not have a bond between the safety wire and neutral all will be good. The thrust of the all the technical rambling is the why and how to avoid unknowingly creating a bond along the chain of vehicles because a bond anywhere along the line bonds both the trailer and truck and - a situation we do not want.

Thanks so much Randy. You are such an asset to this forum.

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Al,

 

Found a link to previous thread where Randy discusses in depth.

 

http://www.rvnetwork.com/index.php?showtopic=106689&hl=randya#entry641121

 

Carl,

 

"Thank You" for posting the link to the previous thread. I will have some reading to do. Now to find that fuse that I need. I do have a Blue Sea fuse holder that was hooked up to the inverter with the wrong size fuse.

 

Al

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Yes Jay, thanks for the link (I did not have it). All of what I am going to say is in the Resource Guide but home grown wiring add-ons for our trucks really take abuse from road grit, salt, water, etc. Marine grade wire and connectors are worth every penny in extra cost when you consider the down time and aggravation of chasing down corroded wiring and connectors. The insulation on marine grade wire is also more resistant to UV, ozone and oil when compared to a spool of automotive wire you might pick up at Advance Auto, Walmart or similar.

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Yes Jay, thanks for the link (I did not have it). All of what I am going to say is in the Resource Guide but home grown wiring add-ons for our trucks really take abuse from road grit, salt, water, etc. Marine grade wire and connectors are worth every penny in extra cost when you consider the down time and aggravation of chasing down corroded wiring and connectors. The insulation on marine grade wire is also more resistant to UV, ozone and oil when compared to a spool of automotive wire you might pick up at Advance Auto, Walmart or similar.

This is why I only use marine grade, fully tinned wire, and only use premium stainless steel hardware on my truck. Some systems have been onboard for 800,000 miles plus. The only failure that I can remember to date is the cheap battery switch, which literally broke a terminal. Other than that, it's bulletproof. I prefer to only do projects once..

 

Jay

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