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Old 05-10-2016, 09:43 PM   #1
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Inverter Connection To Battery

I am installing a 1000W Pure Sine Wave inverter in our shuttle bus conversion (Glaval Universal). The 12V DC input goes through a Blue Sea Systems switch that allows selection for house or chassis batteries. The inverter is mounted behind the driver seat (about 15 feet from the primary chassis battery). Everything I read states that the inverter should be connected directly to the battery. In my case, there is a power distribution panel over the driver seat that includes a direct feed from the battery. Can I connect the Blue Sea Systems switch to the the battery distribution point (on the power distribution panel) or do I need to run a direct feed to the battery? The switch only switches positive, so I plan to wire the inverter negative input to a common negative distribution that includes negative from the house and chassis batteries. Complicating the challenge is that my bus has two 12V chassis batteries. It is a 2002 Ford E450 7.3l diesel. If I need to connect the inverter switch directly to the battery - which battery? Thanks
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Old 05-10-2016, 10:23 PM   #2
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Most people connect the inverter to the house bank only and task the starting batteries only for starting. An inverter can suck a battery bank dry pretty quickly and you don't want to be stranded out in the boonies with a dead starting bank.

SOP for inverter-to-battery cabling is to use a large cable and keep the cable run as short as possible. Make sure your cable gauge and length are sized for the amperage your inverter will be drawing. I've seen conversions where the inverter was switched or run through a relay. Just be sure your switch/relay/cabling is rated for the amperage you plan to draw.
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Old 05-10-2016, 11:13 PM   #3
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What Roachy said is correct.
Don't use your chassis batteries to operate the inverter.
Don't try to get away with a 15 foot run from your house batteries to the inverter--the results will be piss poor at best.
Do locate the inverter as close as possible to the house battery bank and do run dedicated positive and negative cables of the appropriate size to the inverter. Arc welder cable works well for this because it has many fine strands of wire rather than a few heavy strands typical of most battery cables. The reason for this is that electrons actually travel on the outside of the wire strands and more fine strands makes it easier for the electrons to flow. A common "bar" as you suggested will add resistance to the system--which you don't want.

How do you plan to recharge the house batteries? What type of batteries do you plan to use for the house?

1000 amps won't go very far. What do you plan to operate with the inverter? Jack
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Old 05-11-2016, 12:29 AM   #4
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my math is bad but this is what i get.... crazy huge wires

if you put those values into a dc wire sizing calculator.

12v
1000w inverter

the amps would be 1000w/12v = 83a
5% loss
15 ft
works out to 000 AWG wire size.

the wires in your distribution panel would fry if you put that kind of load thru it.
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Old 05-11-2016, 02:09 AM   #5
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My plan is to keep the house batteries and the starting batteries separate by switching the inverter input. The inverter will use starting batteries when the engine is running and house batteries when parked (boon docking).

I have two 6V deep cycle batteries for the house batteries. These batteries will be recharged using a charger when connected to shore power or when using the generator.

My reason for this is to prevent the inverter from discharging the starting batteries when parked.

The inverter will be powering electronics only (TV, satellite dish, and laptop).

It sounds like there may be a flaw in my plan. ;-(
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Old 05-11-2016, 02:21 AM   #6
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You can use the alternator to charge your house batteries as long as you have a cut off in between start and house batteries. I would never run your inverter on the start batteries because they discharge too quickly. And if you run them down low enough, they never regain a full charge. You risk damaging the thinner plate in your start batteries that way. I was told a constant duty solenoid would work to seperate the two, but I am adding a 200 AMP DC breaker inline from start to coach that way I can isolate them, or if they get too much draw, the breaker flips, and they auto cut off.

As far as the wire from your batteries to your inverter, read the directions from your manufacturer. They are the ones who have designed and tested it.

Jack is right, welding leads are great for direct connect for your inverter to battery because of the thread count. My manual told me a minimum if 4awg I decided on 2awg for faster recharge when I am plugged into shore power. Mine is an inverter charger with a 50 amp charge regulator built in.
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Old 05-11-2016, 08:04 AM   #7
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i've only looked at inverters, so i dont have any personal knowledge or experience with them.

but i do know that its wrong to ever run an inverter off of a starting battery. your starting battery already has a load, and a charger (your alternator) set up to keep that battery topped up and at or near 100%.

running your inverter off of that will put an undo load on the battery, alternator, and will leave you stranded on the side of the road with a melted battery and a fried alternator. starting batteries are for starting. house batteries are for invertors. you can charge you house battery on with your alternator, but it wont keep up with the discharge of the inverter.
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Old 05-11-2016, 08:46 AM   #8
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Originally Posted by turf View Post
you can charge you house battery on with your alternator, but it wont keep up with the discharge of the inverter.

It all depends on what your load is while driving, If you have low power needs while driving it should be ok. Your alternator was designed to run all of your bus' accessories at the same time, meaning, lights, heater fans, radio, engine, if electronic, and charge the batteries. Many people don't use 1/3 of those at 1 time. So if you essentially only used say an A/C and your refrigerator while driving, your alternator should be ok to keep up with the charge.

If you have a kid on a laptop, one on a video game console, mom streaming movies on a tablet, headlights, strobe, heaters, A/C, fans and windshield wipers, and whatever else you can think of running at the same time, then of course no, you can't rely on the alternator to keep up with the power use level, unless you had a seperate or even a larger HO alternator.

Remember, an alternator has a charge regulator in it, it will only put out what is being used to stabilize the system.
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Old 05-11-2016, 08:55 AM   #9
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Originally Posted by AdventurousWanderers View Post
The inverter will use starting batteries when the engine is running
I wouldn't use your inverter on the start batteries ever. The lighter plates in a starter battery are not designed to support the load it draws. Think of it like this, if you take a shop vac hose for a 2 gallon shop vac and add it to a commercial vacuum on a ocean liner, what would happen to the hose? Some of the hose may flex back, but it will be weaker, repeated draw will decrease the integrity of the hose, same with the plates in a starter battery, until complete failure occurs.

Put your inverter on your deep cycle batteries only. Then if you want to charge as you run the bus, run a line from the start battery to the house battery with an inline interrupter. that way you can isolate them and not run down the start batteries while you are parked.
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Old 05-11-2016, 09:36 PM   #10
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Many, many thanks for the great insights, opinions, and advice.

I am going to use the inverter only with the two 6V deep cycle house batteries. We plan to workamp for three months at a time; therefore, the majority of our time will be spent connected to shore power. When traveling, we plan to rarely cover more than 200 miles per day. Therefore, I believe the house batteries will hold up while my wife watches a movie or works on her laptop while I drive.

If we are not connected to shore power at night, I can use the genie to recharge the house batteries.

As we get a few miles and several months under our belt, I may make some modifications; such as, using the engine alternator to charge the house batteries while driving.

We are six weeks out from hitting the road as full-timers. Can't wait for the adventure to begin.

Again, thank you for the great advice.
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