Big Inverter + Batteries and the Air Conditioner

[eXodus]

Hey guys,
so got yesterday the news that the replacement of my coach A/C would cost about $1050    Won't spend this much money in old Technics

I've got a very good working roof A/C which I would like to run instead. My Idea:

-2500 or 3000w Inverter
- Two or more Trojan T-105
suggestions ?

So I want to run the roof A/C during drive, so I have to get the power through the alternator, how do I know which alternator is on my engine ? (not really easy to get there) What is the biggest single alternator for a 454 ? Could I replace my failed Coach AC compressor with a second alternator ?

My A/C has a 15a breaker and needs about 11-13A at running. This should be around 1500w continous.
Why I don't run the generator ? It's loud and I don't wanna waste fuel, and for the Future I would like to go dry camping and boon-docking and then I would like to add some solar-panels.

Thanks in advance

Sebastian

[pvoth1111]

I would just run a genny to run the roof A/C.....the grand to fix your dash? A/C is probably mostly labor.....its not rocket science per say....getting enough battery and inverter to run that A/C may cost  a thousand by itself....you can have more than one alternator on your engine...MPG maybe affected....what's wrong  with the dash A/C....compressor, Freon, all doable by you.

[eXodus]

it's about cost effectiveness, 

about 600 are only parts. (compressor, hoses, dryer, expansion valve)  I could do it myself, so I would still spend $600 on something which I use only 3-6 hours every two weeks.

I was searching around and saw Inverters with a good modified sinus for under $200 and I would get two Trojans for another $200.

This system I could use for weeks and not only hours.

Then I would still have $600 left for a decent solar-panel system which should be enough for around 400w of panels and a charger.

Dash A/C also affects MPG, a compressor sucks about 5 hp from your engine.

Or should I get one high output alternator ?

I would go for the local junk jard for alternators.

[M & J]

There are many more factors to be considered beyond the running wattage of the rooftop. Compressor startup current is much higher - at least 50%, efficiency of the inverter, reserve capacity of the batteries. Plus the alternator(s) will rob horsepower especially under load. Capacity VS. load VS. charging rate.
Many including self runs the rooftop while under way and I cant think of a single person who doesnt use the genny.
Search the forum for solar. There are a number of threads on calculating loads, charge rates, etc. You need to think through this much deeper.

[Oz]

Correct.  For solar info, just look at the top of this board,  the pinned topic - >   Everything Solar

Also, there's at least one topic on higher output alternators & adding an alternator.

http://www.classicwinnebagos.com/forum/index.php/topic,3448.msg8360.html#msg8360

http://www.classicwinnebagos.com/forum/index.php/topic,1213.msg1242.html#msg1242

The message search is your fastest way to find a lot of great info here.

[eXodus]

There are many more factors to be considered beyond the running wattage of the rooftop. Compressor startup current is much higher - at least 50%, efficiency of the inverter, reserve capacity of the batteries. Plus the alternator(s) will rob horsepower especially under load. Capacity VS. load VS. charging rate.
Many including self runs the rooftop while under way and I cant think of a single person who doesnt use the genny.
Search the forum for solar. There are a number of threads on calculating loads, charge rates, etc. You need to think through this much deeper.

Really everyone uses the Generator ?

That's why I was interested in a 3000w inverter. Or bigger.

But i did understand now that this gonna get a longer project than just ordering two batteries and a inverter

[Oz]

The roof a/c is the primary reason for using a generator.   Those bad boys need a lot of power to run and if you're running other things as well...  If you read phred's poop sheets on solar & batteries, iin order to be genny-free, he had a bank of six or more gel batteries, if I remember correctly. 

Make no mistake, if you want to be able to be able to live off-grid for weeks at a time, you're going to need to use your generator and the dollar investment may be more than you anticipated.  But... do your homework thoroughly, read the info here and in the resources about it, and do it right the first time.  You'll be very pleased with what the think tank will help you accomplish.

[ClydesdaleKevin]

You'd need one heck of a secondary alternator which will sap your horsepower running a rooftop AC unit just as much as running dash AC.  You'll also need a bigger battery bank than just 2 Trojan batteries...more like 6.  And your inverter would also have to be a big one, like a 5000 peak, 3000 continuous. 

You are MUCH better off just running your generator and the rooftop air.  Its what we do, and we've been fulltiming it for years now.  You won't notice much fuel usage.  If all you are running off the genny is the rooftop AC (we unplug our converter when driving with the genny running), you MIGHT go through a 1/2 gallon an hour with the AC on high on a super hot day.  That is about what our Onan Emerald 3 6.5K uses if all it has to run is the rooftop air. 

If your genny seems too loud for you while driving, you can always improve its muffler system.  We can't hear ours at all over the engine and highway noise while driving.

Kev

[eXodus]

Hey thanks Kevin,
I've got a 4K Emerald Plus. Just ordered a new control board, maybe it get's less noisy if it's running well

Why do I need 3000w continous ? My rooftop hast max 1500w continous. My Refrigerator should run off LP (not yet but will get there). So my additional usage should be minimal.

I don't watch TV or have any big electronic gadgets which are sucking a lot of energy. All I got is running of 12V direct.

1500W / 12V = 125A + losses in the inverter, probably around 150A.
So if I change my alternator (165A) against a 250A version, there should be a little bit of reserve left.

Or I kick out my A/C compressor and mount a second 150-165A I could only use this alternator to charge only the AUX batteries. I'm just brainstorming here and thankful for you input. Appropriate it.

[M & J]

As I explained before - the compressor start up current will be at least 50% higher. You cannot use running wattage as your factor for how large anything needs to be. You have to factor in efficiency plus parasitic losses in the charging/load/capacity.

[yvan]

How long does it take a standard alternator to recharge the house battery? I have a Sleep Apnea machine that I run off an inverter and in 2 days my house battery is too weak to run it. I have a generator built in, but don't want to have that running all night, so in the morning I start up the old 440 and let it run 10 mins, is that enough? I like the idea of running a second house battery and a larger inverter to fire up the micro wave occasionally, as far as AC goes, at 60mph with all the windows open it says comfortable, and when parked if it's that hot I will gladly fire up the Onan and let it cool us down..

[eXodus]

Depends how big you batteries are: Simple mathematics

135 or 165 Alternator - at idle charging about 80-100A PER HOUR. So if you got a 100ah batterie which is empty you have to wait ? Probably ONE hour.  But nothing is perfect - most likely it's longer, two hours if really empty.  10mins are nothing.
You will kill your engine and your batteries with this over time. Get a solar-system to recharge your batteries over the day so you can run your inverter at night.

Or take a scenic ride for two hours every two days 

[DaveVA78Chieftain]

Some rules of thumb

   
• You should not discharge a battery lower than 50% capacity.  To do that repeatably will drastically reduce the life of the battery.  (e.g  100AH is 50% of a 200AH battery bank; basically 2 group 27 batteries)
• A battery should not be charged at rate greater than 25% of it's total AH capacity. (e.g. 25% of 200AH battery bank is 50 amps max charging rate)
• An automotive alternator is based on a voltage controlled regulator design. This design has a high initial charge current and tapers off to a low amp rate fairly quickly.  While this is ideal for a chassis battery designed for short bursts of high current (engine start) it is not ideal for house deep cycle style battery (slow steady AH drain).  House battery needs a 3 stage charger for rapid recharging where the bulk stage recovers around 80% of battery capacity at a high amperage rate.  The automotive alternator rate of charge (amp rate) drops off such that it takes many hours to fully recover a deep cycle battery.  While this is no big deal when driving many miles from point A to B it normally a issue in an engine idle situation.
• Most automotive alternators are not designed for extended periods of high amperage output.  They will overheat if operated at their max rate for extended periods.

Dave

[ClydesdaleKevin]

What Dave said ^^^^^. 

Kev

[kattkisson]

One other thing that no one has addressed is that you would have to be running wires as big as plumbing pipes as the size is current (Amps) dependent not voltage dependent. 

[eXodus]

@Kattkisson,

I know about wires, electrical engineer. And I don't understand why people in mobile environments are using such unpractical cables.
You can run several separate wires for high current.

They are cheaper and can be overloaded more easily because of the better surface to square ratio. With more wires it is much more easy to get rid of the heat.

Instead of getting one 200A cable get three 80A for the same price. Easier to install, but ! you have to get for each cable a separate fuse/breaker.

[kattkisson]

sorry if I stepped on a nerve. Multi-conductor low voltage feeds really fall victim to resistance balance issues. Have fun.

[eXodus]

I know about this phenomena. Shouldn't be a problem in AWG 1 or 0 zero or even bigger cables.
If the length is the same (+- 1 inch) there is no big issue. If one wire has a lower resistance then the other it gets warmer- resistance increases and the current goes to the other cables.
We are speaking about 10-15feet not hundreds of yards.


You are right I've we had much smaller cables,  like a 12 or 18 gauge, here you've got a significant drop over a couple of feet. But if something happens, like I suggested , there should be fuses for each and every cable.

[Rickf1985]

Not trying to be smart but if you are an electrical engineer then shouldn't you already know the answers to the questions you are asking here? I am not an engineer so I may be off base here. Hm? If so correct me, I have been known to be wrong a time or two......... or three. W%

[pvoth1111]

I'm glad in don't insure or sleep in some peoples rigs.....

[eXodus]

Not trying to be smart but if you are an electrical engineer then shouldn't you already know the answers to the questions you are asking here? I am not an engineer so I may be off base here. Hm? If so correct me, I have been known to be wrong a time or two......... or three. W%

Basic Electronic Knowledge has nothing to do with devices and batteries, there are all forms of specialists out there. My major is data communication. I could wire a network, but no idea about how dimension a inverter.
And I was asking for suggestions for inverters and batteries. There are millions out there, can't research everyone.

[Oz]

You're in luck.  Here's a topic which discusses inverter needs, batteries, and solar combos:

http://www.classicwinnebagos.com/forum/index.php/topic,4160.msg12088.html#msg12088

In addition, since you are an engineer, Collyn Rivers, from Australia, published some excellent info in his books on boondocking in the outback, thoroughly covering self-contained systems.  It should suit your needs quite well.

http://www.caravanandmotorhomebooks.com/books/solar_really_works.htm

[circleD]

Those Australians know a thing about boondocking.

[DonD]

http://kingtecsolar.com/

[eXodus]

Thanks for the links


Just checked my alternator and it states 105 amps ! ... not really much. But I should get a 250A alternator at the same position. For $300...
I have to get my generator working then we go from there.