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Author Topic: Drawing power directly form the generator or Alternator  (Read 2963 times)
goodnews
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« on: February 20, 2013, 12:04:53 PM »

I am trying to determine if it is possible to draw power directly from my generator or alternator to provide 110 volt AC without going through the batteries by using an inverter on an isolated circuit.
 
I want to operate coach air conditioning and other 110 volt appliances without drawing from the batteries and I have been told that this is possible. If anyone is doing this and is willing to share how you are doing it I would appreciate hearing from you.

I have PD 4104-5030 which is a 1960 model.[ GM. I have removed the factory air conditioning and am experimenting with ways to replace it with on the road Air Conditioning. Either my roof air or another type of built in system.

What would be the minimum size inverter needed to do this job? How should it be wired in?

Thanks,

Clifford Neal
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« Reply #1 on: February 20, 2013, 12:13:09 PM »

You will need to have some sort of battery bank..   

If you run the Delco 50 DN @ 27.5 volts you can get 7400 watts out of it..   

Do your calcs based off the 7400 watts.   The road A/C motors will eat alot of the wattage.

I run the 450 amp Niehoff with a custom Balmar regulator.
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« Reply #2 on: February 20, 2013, 02:22:58 PM »

goodnews, from your question, I think you've got this a little confused.

The batteries are in the circuit all the time, you hook your inverter up and carry on. The regulator for the alternator takes care of everything, the batteries won't be harmed in a properly sized system.

For your loading considerations, in rough terms, using a good quality pure sine wave inverter, running two roof airs via the proposed system is pretty much equal to the electrical load that the original coach HVAC fans put on the alternator.

So the alternator won't know the difference.

happy coaching!
buswarrior
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« Reply #3 on: February 20, 2013, 02:36:59 PM »

Are you saying that I do not need to add a larger battery bank? That is what I am attempting to eliminate. I do not need to have a large reservoir for use when the bus is not running. I can use either shore power or my generator when the bus engine is not running. I understand what you are saying but had gotten the idea that in slow, start and stop traffic, I would draw from the batteries and pull them down dangerously with the standard two battery bank that is in my bus. Someone told me that I could isolate a circuit directly from the alternator and bypass the batteries altogether. Is this not the case?

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buswarrior
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« Reply #4 on: February 20, 2013, 02:48:39 PM »

As noted, there will be no difference to the coach stock electrical system if you use an inverter and a couple of roof airs or the coach stock HVAC.

Same loads, same conditions as the manufacturer built it to.

How big/small are the two batteries you are using for the system now?

happy coaching!
buswarrior
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Sam 4106
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« Reply #5 on: February 20, 2013, 06:09:59 PM »

Some of you are assuming that a 4104 has a 24 volt electrical system. Unless the bus has been substantially altered to 24 volts, it is 12 volts.

Before you can know if you can run an A/C with your bus charging system you need to determine if you still have the 12 VDC original generator which was positive ground. It's unlikely you can find a positive ground inverter. If your bus has been switched to negative ground you will have a chance to run 1 A/C if you have a large enough battery bank, an adequate inverter, and large enough cables from batteries to inverter if you have a 225 amp alternator. A 120 VAC A/C that draws 15 running amps will require at least 180 12 VDC amps to run. Maybe higher, depending on the efficiency of the inverter. So forget running 2 A/Cs. tell us what alternator you have, the size of your batteries, the size of the inverter, and the running amps of your A/C and we can give you some better answers.

Good Luck, Sam
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« Reply #6 on: February 20, 2013, 08:38:37 PM »

You are correct that my 4104 is 12 volts with positive ground. My 110 volt Ac circuits have been isolated to negative ground however. I will have to check to see the battery sizing tomorrow and get back to you. I honestly do not know if the bus has an alternator or a generator. I do not know how to distinguish between the two. I also do not know exactly what the output of the power supply is from the alternator/generator. Do I have to use a voltage and amperage meter to determine this or is there another way to do it?

The bus has always used two 8D batteries till recently. I changed to smaller size because of the weight of the 8D's. Actually, I think the smaller batteries I have provide higher amps than the 8D's did but I will check that tomorrow and get back to you guys.

I do appreciate your help.

Clifford Neal
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Len Silva
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« Reply #7 on: February 21, 2013, 05:32:30 AM »

If you bus is still positive ground, it most likely has the generator and carbon pile regulator, both can be problematic and hard to find.

In addition, even with a big 50DN alternator at twelve volts, you will not have enough charging at idle speeds to maintain the air conditioner load with substantial batteries.  That is not the case with a 24 volt bus.  Two 8-D's should be OK and be sure to raise the idle speed (with the hand throttle) if you are going to be stopped for any length of time.
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« Reply #8 on: February 21, 2013, 06:56:30 AM »

If you have the engine space to bolt in an Auragen system, it's a no brainer from there.

There's a complete one on ebay right now  http://tinyurl.com/bjkqb9r

These things are basically a gigantic alternator-kind-of-thing with a built in inverter that puts out 120 volts AC (sine wave) up to 5KW.

But you gotta have three things- engine space, bucks, and a little bit o' crazy (which we already have if we own busses..!)
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« Reply #9 on: February 21, 2013, 07:51:06 AM »

Your going to spend Big money to get it done and even more to maintain. History proven by time here.  My question is why not just spend it once on a good used gen set?  The end total cost and more flexible and economical use would be worth it.  Many --Including myself-- have been where you are in your thought process..Just look at my off wall bus building--don't guess I will never learn. 1  ea 15000 roof top is going to take a min 18 amps @ 120v clean to start and 14 amp @ no less than 110V 60h to run: or basically you risk destroying unit.  Then your out-- All your supply work plus AC unit. I fried 2ea AC units in past.   FWIW  In the final big picture----We are busnuts That's why we do it our way anyway.   Best of luck.   Bob
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« Reply #10 on: February 21, 2013, 07:59:42 AM »

Wanted to add I know of couple that have been succesful(sp) here but have extensive batt banks and or inverter AC systems. Big bucks compared to simple 7.5 KW gen set. Just wanted to acknowledge it is being done and do respect those who are doing it. It is not cost effective for my lifestyle.   Bob
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« Reply #11 on: February 21, 2013, 08:16:16 AM »

Running a 12v inverter, about a 2,800 watt is the largest made. 24v can get 4,000 watt or higher and can stack them. I would run at least a 270amp alternator (at 14.1 volts that makes 3800 watts). Then you should run through a bank of batteries-like at least 2 8D deep cycles to buffer the idle and full speed to the inverter. Without a deep cycle battery there would be too much voltage drop and peaks that would take out the inverter in a very short time.

I have a 2,500 MSW inverter, but just use it for short term, or low watt usage. Like TV, Stereo, microwave, toaster oven, bathroom heater, primary electric water heater, etc. If I use any of my three roof tops, they are not wired through the inverter. Hence, either the power pole or generator. Good Luck, TomC
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« Reply #12 on: February 21, 2013, 01:01:56 PM »

Oops.

Absolutely correct, I did not consider the coach was a 4104.

The 4104 air conditioning compressor was powered by a separate engine all together, however, the coach electrical system still had to run the big fans, so that part is quite strong. But, the positive ground makes some more trouble for off the shelf inverters.

In your case, running a separate generator for the air conditioning going down the road would be an easy choice to make.

There would be no need for a big battery bank if contemplating using a big inverter to run some AC going down the road. The chassis batteries would be just fine. That's all the coach had in revenue service?

happy coaching!
buswarrior

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« Reply #13 on: February 21, 2013, 04:08:15 PM »

Hi Clifford,

I emailed Dave Shiney at Northern Arizona Wind and Sun to see if there is a positive ground inverter available. Neither Magnum nor Outback has one and I suspect no other company does either. You could change your bus to negative ground and install a 50DN alternator. But, with that cost and the cost of an inverter, battery cables, fuse and holder and other associated expenses, I think you will be better off using a diesel generator to power your A/C, as buswarrior suggested. I know that's not what you wanted to hear, but that's the best advise I can give. Sorry!

Good luck, Sam
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« Reply #14 on: February 21, 2013, 04:55:51 PM »

Thanks again guys. I am not sure I am understanding all the information I am getting here however.  Buswarrior seems to be telling me that I can run the roof air, ( I only use one unit going down the road in the front half of the bus. The rear of my bus is closed off by a door) in the way I thought possible but the use of terms seems to confuse me and others who are writing as well.

Let me see if I can be very clear in what I am talking about. Forget that I have a genset in the bus. I am trying to set up not to use it. I want to use the power created by the alternator on the 671 diesel power plant. The fact that the bus has positive ground should be overcome by simply reversing the wires when connecting to the inverter and insulating the inverter from the chassis of the bus. This creates an isolated circuit to be used with the air conditioner and whatever else I might want to connect to it. I have already accomplished the with small wattage inverters for running microwave, refrigerator, Television and computers. They work fine and have for several years with no difficulty whatsoever. So this is what gave me the idea to do the same with the roof air by using a larger inverter. My concern was whether I would need to have a larger capacity battery bank.

If I understand Buswarrior, this is not a concern as the coach is already set up to produce more power than I need after removing the large 12 volt fan that ran the factory air, which has been removed.

I hope this makes it very clear what I am proposing. If this works, I find it hard to believe that there are not many 4104 owners already doing this.

Does this change the advice anyone is providing? Not being an electrician, I may be completely off base and I hope someone can clearly tell me that it will or will not work without me going to the trouble and expense to try it.

Thanks,

Clifford Neal
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Sam 4106
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« Reply #15 on: February 21, 2013, 07:04:03 PM »

OK

I'll try once more. What size batteries do yo have? How many 120 VAC running amps does the A/C you intend to run draw,and how many amps do any other 120 VAC loads use at the same time as the A/C? Then add up all the 12 VDC amps that will be used (lights, radio, etc). How large is the inverter you intend to use and its efficiency rating? How many amps does your generator put out? You can determine the generator output by taking the bus to a battery store with a large enough load tester and have them keep adding load until the DC ammeter stops rising. If you give us all those numbers someone can tell you if your idea will work.

Good luck, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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« Reply #16 on: February 21, 2013, 07:43:00 PM »

If you have the engine space to bolt in an Auragen system, it's a no brainer from there.

There's a complete one on ebay right now  http://tinyurl.com/bjkqb9r

These things are basically a gigantic alternator-kind-of-thing with a built in inverter that puts out 120 volts AC (sine wave) up to 5KW.

But you gotta have three things- engine space, bucks, and a little bit o' crazy (which we already have if we own busses..!)


That's really cool! It's like an inverter, fed from the engine driven alternator, that doesn't need(?) a battery bank. The magic must be in their electronic box.
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« Reply #17 on: February 22, 2013, 05:50:26 AM »

The original 4104 blower motor was rated at 3/4 horsepower and only pulled around 50 amps at high speed.  The total DC load at full air conditioning was about 60 amps including the defrost blowers.   A 2800 watt inverter is going to pull over 200 amps at load.

The point is, that while the 4104 was originally designed to operate the air conditioner from the bus system, it is no where near the capacity we consider normal today.

I will echo the others here; use a generator.  It is far less expensive than trying to run air conditioning from the bus.  In hot Florida like climate, you will need more than one roof air to keep up with the sun on the windshield.  In addition, the 4104 is under powered to begin with, you will be better off not using the engine for those loads.

None of this would apply to a larger, 24 volt bus.
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« Reply #18 on: February 22, 2013, 06:49:22 AM »

I hear a determined busnut typing...

goodnews, I think a good quality inverter running a single AC is within reach, and you have a good idea what it will take to overcome the positive ground issue.

As for the math, the battery bank will take care of start currents, that's their job.

The running current will be somewhere 11-12 amps on a typical roof air, which you multiply by 10 to get the amps needed at 12 volts for the inverter. So, for this conversation, we go big and say 120 amps.

Then you have to add the efficiency loss of the inverter you choose, which even if it was a crappy 80% unit, would be another 24 amps or so in inverter waste. This number goes down if you select a better inverter. There are lots to choose from on the internet. It requires careful inspection of the technical specifics, and at what amperage the efficiency was measured. Inverters are not consistently efficient across their operating range. Once the selection process has been narrowed down, a call to the manufacturer to clarify would be time well spent.

So, your question for the AC issue is whether the charging system in your 4104 can reliably produce a continuous 145 amps, just for the AC install, or a bit less, depending on your exact numbers?

And, before we're done, you need more than that to run the rest of the loads and to charge the batteries.

If the batteries are only used to start the bus and support the chassis while underway, they won't need much charging. If those batteries get used while camping, without a charger on them, they will need more charging while underway.

Lots of variables, but let's keep working the numbers!

happy coaching!
buswarrior

 

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« Reply #19 on: February 22, 2013, 08:08:34 AM »

Running off an inverter, a rough rule of thumb is to take the running amps of the 120vac and multiply it by 11 to include efficiency losses. Hence a 15 amp 120vac running load, like an A/C would be drawing 165 amps/hour from the batteries. So to run an A/C all night on batteries for 8 hours (if the compressor is running continuously-like in over 100 degree weather in summer [it will stay over 100 at night in the desert]), you would draw 1320 amp/hours. An 8D Lifeline AGM battery has 255 amp/hours and then you don't want to run it down past 50%-for a usable 130 amp/hours. Round figures, you'd need 10-8D batteries-or 1650lbs worth of batteries! In this case-just run the generator.

I have 2 Lifeline AGM 8D batteries (that I just bought-the old ones went almost 7 years) for 255 amp/hours usable at 50% discharge. My refrigerator draws 5 amps, but runs about 50% of the time-so that's 2.5 amp/hours. Then at night, I generally pull around 20 amps of lighting for 6 hours-another 120amps. Basically, when dry camping, my 2-8D's will get me through the night comfortably running lights, TV. Then in the morning, fire up the generator to warm up the two water heaters, brew coffee, run the bathroom heater, charge the batteries for two hours. Good Luck, TomC
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« Reply #20 on: February 22, 2013, 08:21:31 AM »

I use an inverter to run my roof-top on the road, and I'd be perfectly comfortable with just my two 8D start batteries if need be, but as noted you have to be careful of the charging steady state output capacity of your alternator/charging system, and you have to be real careful not to run the AC from the batteries if the engine is off.  In my case, I have a 24 volt system with the 50DN, so I have a different situation than you do.

Brian
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« Reply #21 on: February 22, 2013, 08:25:12 AM »

Inverters are rated Example  :4000=surge but are only continous 3200  watts Less 20% efficiency or about 25 amps start up and 18 running at max battery/alt performance. would prob pull batteries below starting capacity with engine off in less than 1/2 hr. Don't know about idle or slow traffic. If your is same post that was on other board and you have a 15000 roof top your power load should be up toward the 18 amp start up and 14 amp running. The older your units get; normally power demands go up. Not trying to talk you out of it!!!! Just be aware. A Harborfreight unit is not going to do it. Read the actuall output continous of whatever you buy.  Do math gen set fuel vs cost of all the inverters etc and possible damage to AC.  If your not the same guy that posted over at BNO sorry about confusion. Do experiment!::: but at least little sign of trouble have a back up plan. If you take nothing else from these comments have a backup as not to ruin your trip and bussin experience.   Bob
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« Reply #22 on: February 22, 2013, 10:14:48 AM »

You're already running a fairly low power engine to start with.  Power from an engine driven alternator/generator is not free.  The more amps you demand from the alternator the more power it uses from the engine.  You probably need all the power the engine can provide when going up a grade.

The cost of an inverter can probably pay for about 500 hours worth of fuel for a generator if you already have a generator.

You can certainly do what you want, you have to decide if the cost and loss of engine power is worth it.
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« Reply #23 on: February 24, 2013, 08:23:52 AM »

Yes, the loads on the engine to run the AC exist...

In my younger days, I experimented extensively, the customers on the coach being unwitting guinea pigs..

Numerous times, numerous hills, tried turning the AC on and off during the climb.

Auto and manual transmissions. 6V92 and 8V71.

Steady state, settled into the climb, full power, mid revs, engine working flat out with all it had.

Felt no difference, no change in speed, no change in engine note, switch on or off...

I was quite discouraged at the time, after having read how much HP the AC is supposed to consume.

So much for gaining an edge...

Sometimes I miss those days.

But I expect my customers like that the AC stays on now...

happy coaching!
buswarrior
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« Reply #24 on: February 24, 2013, 08:34:15 AM »

I think your experience might have been different with a 6-71 NA.
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« Reply #25 on: February 24, 2013, 08:37:59 AM »

Full power is full power.

The 4104 and the MCI's I fooled with aren't that far apart in power to weight ratio in stock trim.

happy coaching!
buswarrior

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« Reply #26 on: February 24, 2013, 05:32:47 PM »

On our 4104, we ran the generator when we needed AC. We installed a small inverter to run small items. Because of limited space for more batteries and being a 12 volt system, this was the simplest setup. If the two 8d's got too low to start coach (rarely), we would start generator to recharge batteries. It would take a long time to recover savings from adding a large inverter, more batteries, and bigger alternator. Running ac's off engine instead of generator. Engine mileage would drop some, maybe close to generator consumption. I would go to the house battery/inverter setup on a 40footer with 24 volt system, maybe depending on how much it is actually used.You could use the generator to charge the house batteries while it is running to take load off of coach engine....many possibilities. Anymore, many owners aren't going to put the miles on a conversion like they did 5 or more years ago, when diesel was $2 a gallon. 
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« Reply #27 on: February 25, 2013, 07:40:14 PM »

I just seem to have lost a post. Will try again. I really appreciate all the help. I have had to miss the conversation for a couple of days but wanted to let you know that all the information has been wonderful and I am still trying to look at all options.

Which brings me to ask if any of you 3104 owners have mounted a regular automotive air compressor on your 671 inline engine? I have a a unit the I am thinking of mounting on the engine and running freon lines to the cooling coil in the cabin for down the road air but do not see a good place to mount it on the engine.

If any of yiou have done this and could share some information and perhaps a photo of the install, I would greatly appreciate it. The unit I am talking about is belt driven.

Thank you again,

Clifford Neal
Pd 4104-5020
East texas
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