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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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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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Old 05-11-2016, 09:57 PM   #11
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Good luck and happy motoring!

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Old 05-12-2016, 02:28 AM   #12
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copy what a 18 wheeler has for inverter install. they are as close as you can get to a bus. all the engineering has been done for you.
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Old 05-12-2016, 03:55 AM   #13
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So, everyone so far has been right. I'm going through this exact thing at the moment. My 3kW invert is getting 4/0 (0000) welding cable on a 4 foot run from my battery box under the floor to the power center under a bench seat directly above it. I'm putting a 400A fuse right off the four 6V GC2 golf cart batteries in parallel pairs of series (2x2 for 12V). Xantrex recommends a DC circuit breaker as well. I'm not sure if I'm going to go that far yet.

Sterling Power (and maybe other companies, but I have a strong preference to their equipment) makes a series of things to help with charging your house batteries from your vehicle's alternator WAY better than just tying them together for a while or switching your inverter back and forth. They have basically three products. A battery to battery charger, an advanced alternator regulator, and an alternator to battery charger.

The battery to battery charger draws a small (relatively) current of about 60A from your starter batteries while they're being charged by the alternator. It's smart enough to never discharge the starter batteries and only do it when they're charging. This is , in my opinion, the worst way to go, but possibly the easiest. It just doesn't give you much power. 720W is the best you can reasonably hope for. You can tie multiples together, but that gets expensive.

The advanced alternator regulator is the middle option, in terms of personal preference for me. It draws the voltage down on your alternator a bit to make it produce higher current, basically simulating a large load. Alternators are real workhorses and can handle this just fine. Plus they include a temp sensor to prevent the alternator overheating. These can pull your alternator's max current rating (which in a bus is generally 120-280 amps) and top off your starters, then put the remaining current (probably 2/3rds of your capacity) into the house batteries. This really works well and is fairly cheap, but it is the hardest of all the methods. You have to disassemble your alternator to solder wires to the brushes, as a start.

The best option is probably the alternator to battery charger. This does the exact same thing as the advanced alternator regulator, but it does it all remotely. You run cables to it from the alternator lugs and both the starter and house batteries. It keeps everything charged and happy with minimal effort or required skill and only moderate cost.

And all three of these chargers do multi-stage charging, just like a charge wizard, MPPT solar controller, or any other high-end charging device. This keeps the batteries from cooking from too much power while charging them as quickly as possible.

Hope this helps.
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Old 05-12-2016, 11:32 AM   #14
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Quote:
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Xantrex recommends a DC circuit breaker as well. I'm not sure if I'm going to go that far yet.


Amazon.com: 200 AMP 12V DC CIRCUIT BREAKER REPLACE FUSE 200A 12VDC Scosche: Home Improvement

It's not hard to install


And all three of these chargers do multi-stage charging, just like a charge wizard, MPPT solar controller, or any other high-end charging device. This keeps the batteries from cooking from too much power while charging them as quickly as possible.

You're alternator already has a charge regulator installed for the load it senses. You'd need an advanced regulator if you were running a mobile crime scene lab with lots of electronics and communications on board. Only way you will cook your batteries is if your alternator goes bad. But that's why you have a charge guage in the dash!!

Hope this helps.
There is no need to spend more money on things you don't need. These alternators are set up for buses, not Civics.......
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Old 05-12-2016, 02:38 PM   #15
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wire recommendations

Adequate wire gauge is important as others already noted. Welding cable might be nice because its higher strand count makes it flexible and easy to work with, and has a durable rubbery jacket which adds to the flexibility. However, if you have screw-type lugs for termination, the finer strands can be a drawback. IMHO it'll be harder to secure and possibly more prone to working loose.

I'll take a moment to debunk one of the claims, though: skin effect. That's the phenomenon of electrical current traveling more on the "skin" of the conductor and less in the core. While it is a real thing, its effect is proportional to frequency. It doesn't exist for dc. Per the wikipedia Skin effect article, skin depth in copper at 60 Hz is about 8.5 mm. For most of us, working with either dc or 60 Hz ac, skin effect isn't a concern until the radius of a wire is greater than 8.5 mm. That's a diameter of 17 mm. The largest "gauged" cable, 4/0, has diameter about 11.6 mm and ampacity around 200 A depending on allowed temperature rise. By the way, even when skin effect is a concern, finer strands alone don't fix it. Each strand has to be electrically insulated as in Litz wire.

Anyway... choose your cable based on how much flexibility you need, what insulation characteristics you need, availability, terminations, and ampacity. Don't worry about skin effect.
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Old 05-12-2016, 03:45 PM   #16
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Ditto what FamWagon said about skin effect. In DC setups however the welding cable gives excellent flex and oil resistance.

On another "hint", twist the inverter input cables together and shrink-wrap them every few inches. At high loads these cables will radiate noise into nearby electronics. By twisting them together and holding them close to each other, you severely limit this problem where its easiest to cure - the initial point of radiation.
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Old 05-12-2016, 04:22 PM   #17
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Ditto what FamWagon said about skin effect. In DC setups however the welding cable gives excellent flex and oil resistance.

On another "hint", twist the inverter input cables together and shrink-wrap them every few inches. At high loads these cables will radiate noise into nearby electronics. By twisting them together and holding them close to each other, you severely limit this problem where its easiest to cure - the initial point of radiation.

Not sure I get this. Twist your input cables?? I only have 1. Or do you mean your battery connect and your ground?
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Old 05-12-2016, 05:06 PM   #18
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Yes, twist wires returning to the battery + and - terminals. Not too tight; it's heavy-gauge wire and we're not making a rope. Just a gentle twist, maybe one twist per several inches of length with something huge like 4/0.

It's recommended to run a ground return wire rather than simply grounding to the frame. Being able to reduce radiated interference by keeping the currents near each other is one reason. Here's another: somewhere, somehow, the frame/body has to connect back to the battery and the alternator. (Sorry, I'm thinking about start/chassis/coach battery again, but there's a similar frame-to-house battery connection too.) Who knows where their connection is? Who knows how good/clean it is, how many amps it's ready to carry, how much voltage drop across it, etc? Who does maintenance checks on it when they're looking at the other battery wiring? If the answer to the above is "uhhhh..." then that's a reason why high-power and noise-sensitive things should get their own return back to the battery.
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Old 05-12-2016, 05:09 PM   #19
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Yup, I was referring to the battery (input) cables. I should have been a bit more clear.

FWIW, both input cables, both positive and negative, should go all the way back to their respective battery terminals. No using a "local" or "frame" grounding point. Thats cheating.

Edit: FW and I cross-posted about the dedicated ground. Sick minds think alike!
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Old 05-12-2016, 05:17 PM   #20
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Yes, twist wires returning to the battery + and - terminals. Not too tight; it's heavy-gauge wire and we're not making a rope. Just a gentle twist, maybe one twist per several inches of length with something huge like 4/0.

It's recommended to run a ground return wire rather than simply grounding to the frame. Being able to reduce radiated interference by keeping the currents near each other is one reason. Here's another: somewhere, somehow, the frame/body has to connect back to the battery and the alternator. (Sorry, I'm thinking about start/chassis/coach battery again, but there's a similar frame-to-house battery connection too.) Who knows where their connection is? Who knows how good/clean it is, how many amps it's ready to carry, how much voltage drop across it, etc? Who does maintenance checks on it when they're looking at the other battery wiring? If the answer to the above is "uhhhh..." then that's a reason why high-power and noise-sensitive things should get their own return back to the battery.
Never heard of this, however I am not a DC engineer. I have 2/0 wire. Not going to get too many"twists" unless I braid them. How does that affect heat?? I don't braid my welding leads.......
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