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Author Topic: 24VDC generator UPDATE:  (Read 8834 times)
Jerry32
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« Reply #15 on: January 24, 2007, 07:53:30 AM »

Then you caould do aircraft AC and have lighter wieght components using 400 cycle three phase.
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DrivingMissLazy
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« Reply #16 on: January 24, 2007, 08:00:39 AM »

I have been told that all automotive type alternators are high frequency in the 4-6,000 Hz. range. That is why they can output full capacity over a very wide rpm range and are of course much smaller than a 60 Hz. alternator. Also, the higher frequency gives a much lower AC ripple on the DC output. And they are three phase full wave rectifiers for minimum ripple.
Richard
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« Reply #17 on: January 24, 2007, 08:26:09 AM »

All DC generating on todays cars and trucks are done with alternators.  They are all 3 phase (120 degrees apart) so that even when you install the three diodes (diodes are electronic devices that go inline that allows electricity to only flow one direction-hence no more alternating current, just direct current) the electrical flow will be smooth (rather than single phase that would make for flashing lights).

Now for your 4kw inverter.  I think you're looking at the mathematical requirements backwards.  With 4kw, from the 24v power source you will need about 185 amps of battery power (figuring 90% efficient on the inverter).  With any battery bank, to get maximum battery life you don't want to run the batteries down more than 50%.  So now your advertised 400 amp hour battery bank is only 200 amp hours.  That means at full power on the inverter you have about 65 minutes of electricity.  Even if your average electrical requirements are only averages 1200 watts per hour for 24 hours, you would need a battery bank (again figuring 50% discharge only) of 14 AGM batteries.  Or if you use the AGM 8D batteries like I have, they are rated at 255 amp hours.  Again at 1200 watts per hour for 24 hours, you would need 10 8D's at 155lb apiece, or 1550lb of batteries.  That's about 3 times what my 10kw generator weighs.  My personal usage and my VERY strong suggestion- use a Diesel gen and the inverter for additional standby power.  If you do any kind of boon docking, you'll be the happiest.

The only propane on my bus is the stove and furnace.  My reefer and freezer are Norcold compressor type 12v/120v, 2-10gal elec water heaters piped from one into the next with the final water heater wired through the inverter, electric heat in the bathroom, 3-roof air conditioners with heat strips, microwave, TV, Stereo, etc.  I have just 2 8D AGM's.  When boon docking I just run the gen in the morning for coffee and to get the water heated (we take morning showers) and to charge the batteries.  Run it again at dinner if needed to float the batteries again.  The trick is to have a generator that is extremely quiet.  My could be quieter.  It is actually noisier inside than outside-which doesn't bother me since I'm more concerned with my neighbors.  Please reconsider your electrical methodology!

Richard-car alternators frequency is whatever rpm they are running at.  With a bus and the 50DN, my gear drive is 2.75 to one.  So at 2100rpm the alternator is running at 5775rpm. That translates into 192 cycles per second (or for 3 phase 576 cycles per second total-compared to 60 cycles per second for household electricity).  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
gr8njt
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« Reply #18 on: January 24, 2007, 09:24:28 AM »

Thank you for everyones input. All suggestions/opinions are greatly appreciated.
Like I said earlier, I'm still in the research phase so the more informative data that comes by,
the better for my project analysis at the end of each day.
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Stan
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« Reply #19 on: January 24, 2007, 09:48:01 AM »

Richard: I think automotive alterantors are 12 pole so that gets them up to 6 khz at 5000 RPM. Sometime back someone did all the calculations to figure out the number of pulses related to speed when hooking up a tachometer to the alternator.
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DrivingMissLazy
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« Reply #20 on: January 24, 2007, 11:15:53 AM »

Richard-car alternators frequency is whatever rpm they are running at.  With a bus and the 50DN, my gear drive is 2.75 to one.  So at 2100rpm the alternator is running at 5775rpm. That translates into 192 cycles per second (or for 3 phase 576 cycles per second total-compared to 60 cycles per second for household electricity).  Good Luck, TomC

Tom, alternator frequency output is determined by rpm and number of poles in the alternator.  A household 1800 rpm alternator has four electrical poles, a 3600 rpm alternator has two poles, each delivering 60 hertz at rated RPM.

The formula for finding hertz is: rpm times number of poles divided by 120. For example  an 1800 rpm, four pole alternator will generate 60 hertz.  1800 X 4/120=60. Single or three phase has absolutely nothing to do with it. Since you do not define the number of poles in your example, it is impossible to determine the output frequency.

Using your example of 5775 rpm, a 12 pole alternator would produce 5,575 hertz, single or three phase depending on how the alternator is wound. Automotive alternators are all wound for three phase output. The frequency would vary as the rpm varies.
Richard
 PA Stan and I both believe the standard number of poles for automotive alternators is 12.
« Last Edit: January 24, 2007, 11:18:23 AM by DrivingMissLazy » Logged

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« Reply #21 on: January 26, 2007, 04:23:32 PM »

When I first proposed the idea that I can built my own RV, my entire family almost chocked laughing.
When I tell other people I am building my 2nd RV using a "Greyhound type" bus, they look at me like I am high on something.

I know this topic is almost taboo here, but as usual I  am always trying to think outside the box so I  took the plunge and purchased  this complete brand new Kubota water-cooled diesel engine to spin a 24 volt high amp automotive alternator. This will be the start of this project. As soon as the engine gets delivered, I will start designing and fabricating "isolator" motor mounts,  a slide-out,  adjustable alternator mount and a "quiet" box.

I am presently watching a 24volt 105 amp single wire alternator on ebay going for $50 and see how lucky I am.
I am still on the hunt for an elusive higher amp 24V alternator close to 175-200 amp range. If somebody knows a source of one,  I would appreciate if you direct me to it.




« Last Edit: January 26, 2007, 04:35:01 PM by gr8njt » Logged

****1982 MCI-9 Crusader-II Bus Conversion****
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« Reply #22 on: January 26, 2007, 05:45:00 PM »

gr8njt: A single wire alternator has an internal voltage regulator and you will not be able to set it at the voltage you need for your particular type of battery. You need an alternator that uses an external regulator so that you can use a muti stage charging voltage.

Any of the places mentioned on the board that dismantle buses will have belt driven 50 DN alternators that are 270 amps at 28 volts.
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gr8njt
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« Reply #23 on: January 26, 2007, 06:01:31 PM »

gr8njt: A single wire alternator has an internal voltage regulator and you will not be able to set it at the voltage you need for your particular type of battery. You need an alternator that uses an external regulator so that you can use a muti stage charging voltage.
Any of the places mentioned on the board that dismantle buses will have belt driven 50 DN alternators that are 270 amps at 28 volts.
As usual, you come up with very helpful info Stan. Thanks. I will surely look for a used 50DN alternator at Camp Luke.
I am also looking at DEKA UNIGY non-spillable Industrial 12 volt batteries rated at 150 amps each.
What do you think of them?
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****1982 MCI-9 Crusader-II Bus Conversion****
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Stan
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« Reply #24 on: January 27, 2007, 07:06:08 AM »

gr8njt: I don't know anything about those particular batteries.

It sounds like you are starting a project that requires a lot of mechanical end electrical engineering knowledge, which you may or may not have. If this is just a fun project where capital cost, operating cost, size, weight  and maintenance are not a factor, then have fun, but don't do anything that will get you hurt.

If you are trying to build a fuel efficient, cost effective system then here are a couple of pointers for you to start with.

1. The engine speed will be determined by the point where the horsepower curve crosses the torque curve.

2. The rear main bearing on an automotive type engine is not designed for side loading. This means that you have to have a coupling of the flywheel to a driveshaft or flexible coupling to a jack shaft that hold the belt pulley. The engine manufacturer may have a bell housing and outout shaft for this purpose. This will be quite a large pulley with at least four V-belt grooves and the diameter will be deternined by the size of the pulley on the alternator, to get optimun efficiency out of the alternator.

3. Just designing the pulley diameters and belts is a speciality in itself. The size of the jack shaft and its supporting bearings are critical to not having a catastrophic failure. The major power transmission companies have a lot of help on this point.

4. Your maximum electrical load will be handled by a combination of alternator capacity and size of battery bank. These have to be calculated to get the most hours of use with the fewest number of hours of generator time wjile balancing the cost and weight of batteries to the cost of running the generator.
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TomC
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« Reply #25 on: January 27, 2007, 08:01:32 AM »

GR8NJT- Since it seems you've decided to go this route of making your own low volt system, I'd like to make some suggestions.  First- buy all equipment that is readily available on the road-or in another words, don't buy off beat stuff that is only made in one part of the country (like those Deka Batteries).  If you want AGM batteries that are spill proof, etc (personally have 2-8D Lifeline AGM's and love them), stick with AGM batteries that are made in normal automotive sizes (like 8D, 4D, 31, 6v golf cart) so you can easily replace them anywhere in the country, and if need be can replace them with wet leaded batteries, since AGM's and wet batteries can be charged the same. 
Delco is making some really nice alternators.  Some are brushless, and will operate at higher temps (because of the higher under hood temps now).  The DN50 is really the ultimate alternator (mine is gear driven for no belts-as a matter of fact, I have NO belts at all on my engine), but it requires a pressured oil hook up since it is cooled by oil (sealed, brushless, cooled and lubricated by pressured oil) and I think it would be too hard to adapt to a small Kubota.  There are air cooled replacement alternators for the 50DN that would be more suitable.
On the Kubota engine.  Any of the Kubota engines are just about as close to 100% reliable as you can get with an engine.  But- I would stay away from both the 1 and 2 cylinder because of vibration.  Kubota makes a mini series that has a 3 cylinder that would be very smooth and long lasting.  Running at about 2400rpm, (1800rpm is actually too slow for the small Diesels-as we will find out when Tier 4 emissions are attempted.  You'll see the small Diesels sped up to the 2500-3000rpm range to get into their power curve that will clean up the exhaust), and could run two, three, four smaller alternators.  The alternators that are run on trucks can be bought for about $250 new!  Then if one goes out, can get it at any truck parts place.  Good Luck, TomC
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DrivingMissLazy
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« Reply #26 on: January 27, 2007, 08:09:43 AM »

Further to what Stan says, coupling the alternator to the engine in line will create a very long unit. Torsional rigidity is very necessary in this type construction. I manufactured a lot of units coupled end to end and to attain the necessary rigidity, I would typically weld together two six inch sections of "C" channel angle iron or whatever width channel required for the base required. Sometimes three channels were required, based on the mounting hole dimensions of the motor and alternator. Cross pieces on the bottom of the base were then welded on to attach the vibration isolation pads to. It was generally a very heavy piece of machinery and typically not suited for installation in a coach.
The units I manufactured were typically an electric motor driving an AC alternator to provide clean power for a computer system. Anywhere from 5kva to several hundred kva.
A good rule of thumb to use when manufacturing engine driven gensets is to use two hp per kw. In other words if you want to generate 10kw of power an 18-20 hp engine should be selected. This will keep the engine at about 80% load when the alternator is producing 10 kw and you never want to run the engine at full rated hp continuously.

Richard
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« Reply #27 on: January 27, 2007, 01:51:37 PM »

A good rule of thumb to use when manufacturing engine driven gensets is to use two hp per kw. In other words if you want to generate 10kw of power an 18-20 hp engine should be selected. This will keep the engine at about 80% load when the alternator is producing 10 kw and you never want to run the engine at full rated hp continuously.

Richard

That translates to 14-15 hp for a 270 amp 50DN @ 28v.

Len
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« Reply #28 on: January 27, 2007, 04:06:34 PM »

I would like to see the drive end of the engine that you have ordered. Also, are you open to any suggestions as to how to accomplish what you want to do?
Richard
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« Reply #29 on: January 27, 2007, 04:43:56 PM »

I would like to see the drive end of the engine that you have ordered. Also, are you open to any suggestions as to how to accomplish what you want to do? Richard

I have reassesed my position on the use of 50DN 270 amp bus alternator.
I am seriously and patiently looking for 175 amp 24 volt automotive alternator to match a 3kw-4KW sine-wave inverter/charger.

Installation of "Proheat" for radiant heating and water heating is in the works sometime before next winter. This makes my present electrical water/heat as "back-up" systems and for campground convenience.

Therefore my goal on this project is:
To fabricate the fastest charging time on a 300-400Ah battery bank from the smallest possible water-cooled diesel engine which I just purchased. This alternator should be able to keep-up with a 3kw-4kw inverter use. I do not intend to "fulltime" or dry-camp for extended periods of time. A weekend is the MOST I would dry camp. I use my bus basically from home to campground and would like to be self sufficient for 24-36 hours MAX when resting at a Walmart and/or rest area. One reason for my choice of a 24 volt system is to have the charging done on both the bus and house 24 volt banks at the same time WHILE the bus is running. This gives me a full house charge to use before I run the small Kubota.

Richard, I am always open to suggestions on any of my projects.  Here's a pic the drive end of the genset and a few wiring diagrams that I may need I obtained from my research. Thank you.
« Last Edit: January 27, 2007, 04:50:33 PM by gr8njt » Logged

****1982 MCI-9 Crusader-II Bus Conversion****
R&M 102 C-3 style Front & Rear cap with louver kit
smooth side kit, dash-board kit, one piece siding
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