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Author Topic: 24VDC generator UPDATE:  (Read 8450 times)
gr8njt
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« on: January 23, 2007, 05:51:36 PM »

I have decided to use a DC (24V) generator VS AC in my conversion.

My research pointed the fact that DC generors are much more efficient than AC generators.
There is MINIMAL wasted energy everytime the DC generator is running because all the amps are directed to the house batteries for storage and the inverter produces the AC power needed in the coach from that stored energy.
They are apparently more preferred by the marine industry.

Additionally, when on the road, the 270 amp Bus alternator can fully charge the 24 volt house batteries.

My search took me to the G24/175 made by Ample Power.
This DC generator (G24/175) is an ideal partner(sold separately) to the Trace SW4024 (4000 watts Sine wave),
and produces 5000 watts of DC charge to keep up with the SW4024 inverter demand.

Does anybody have personal experience with DC generating in general?
Any other options on DC generators?
« Last Edit: January 26, 2007, 04:38:39 PM by gr8njt » Logged

****1982 MCI-9 Crusader-II Bus Conversion****
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« Reply #1 on: January 23, 2007, 06:01:50 PM »

To my knowledge, DC generators have not been manufactured in many many years. All the DC components on any vehicle for the past 30-40 years have been alternators instead of generators. The alternator is an AC device that internally rectifies the AC produced to DC.
Richard
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gr8njt
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« Reply #2 on: January 23, 2007, 06:46:09 PM »

To my knowledge, DC generators have not been manufactured in many many years. All the DC components on any vehicle for the past 30-40 years have been alternators instead of generators. The alternator is an AC device that internally rectifies the AC produced to DC. Richard

Ample Power presently makes 24Volt DC gensets (up to 175 amps DC) to charge any House battery bank. They also make enclosures (optional) for quiet operation. Click the underlined link for more details of this product and scroll all the way down to the bottom of the page.

I do understand that the bus (or any vehicle in the past 30-40 years) uses an alternator to charge the bus battery bank when on the road.
However, when properly equipped with an "Isolator" between the bus battery and the house battery, the bus alternator can charge both battery banks simultaneously when the bus engine is running.  When the bus engine is turned off, the "Isolator" automatically separates the bus battery bank from the house battery bank so that the bus battery bank does NOT get depleted during dry camping.  At this point, both banks are fully charged.

Like I mentioned earlier, the DC genset sends ALL of the amps generated to the house batteries. In comparison, AC gensets have minimal DC amp charging (although some use inefficient inverters/chargers for more amps to the battery) and it would take hours to fully charge a HUGE house battery bank while running the AC genset at optimum rpm.

The DC genset is very efficient and dependable in the Marine industry. Has anyone used this system in a Bus Conversion?
Any info will be appreciated.
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« Reply #3 on: January 23, 2007, 06:52:51 PM »

gr - Bill Glenn has been toying with the same idea - you might contact him from the board profiles and see if he has can be of any help - handle is "homegrown diesel" - HTH
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« Reply #4 on: January 23, 2007, 07:15:55 PM »

How do they cool the unit pictured?  Looks like a marine unit.    Do they have a "stationary" radiator package that could be supplied?  How much will that add to the cost of the unit? 
I have one of those tiny Kubotas, but it has a belt driven water pump where that spigot is located on the pictured engine.   
I can attest that the little Kubota twin will run on diesel fumes.   It'll also crank in 10* weather without aids.
Also add that they are noisy unless very well isolated. 
Interesting angle!
BTW, the Chinese are producing Kubota "style" engines that are to be avoided at all cost....be sure that you're buying a genuine Kubota.   
You could buy a Kubota industrial engine and attach it to a 24V bus belt driven alternator and have a similar item...output would be DC of whatever size alternator you buy.   
Unlike the critical speed governing of 120 VAC generation units, the engine RPM could be anywhere within reason using an automotive or bus alternator. 
JR 


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JR Lynch , Charlotte, NC
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DrivingMissLazy
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« Reply #5 on: January 23, 2007, 08:21:36 PM »

Did you read the AD? It specifically states that they use AC alternators.
Richard


To my knowledge, DC generators have not been manufactured in many many years. All the DC components on any vehicle for the past 30-40 years have been alternators instead of generators. The alternator is an AC device that internally rectifies the AC produced to DC. Richard

Ample Power presently makes 24Volt DC gensets (up to 175 amps DC) to charge any House battery bank. They also make enclosures (optional) for quiet operation. Click the underlined link for more details of this product and scroll all the way down to the bottom of the page.

I do understand that the bus (or any vehicle in the past 30-40 years) uses an alternator to charge the bus battery bank when on the road.
However, when properly equipped with an "Isolator" between the bus battery and the house battery, the bus alternator can charge both battery banks simultaneously when the bus engine is running.  When the bus engine is turned off, the "Isolator" automatically separates the bus battery bank from the house battery bank so that the bus battery bank does NOT get depleted during dry camping.  At this point, both banks are fully charged.

Like I mentioned earlier, the DC genset sends ALL of the amps generated to the house batteries. In comparison, AC gensets have minimal DC amp charging (although some use inefficient inverters/chargers for more amps to the battery) and it would take hours to fully charge a HUGE house battery bank while running the AC genset at optimum rpm.

The DC genset is very efficient and dependable in the Marine industry. Has anyone used this system in a Bus Conversion?
Any info will be appreciated.
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captain ron
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« Reply #6 on: January 23, 2007, 08:31:42 PM »

Did you read the AD? It specifically states that they use AC alternators.
Richard

Hate to bust your bubble or start a fight but Qoute from web site"Charging batteries from an alternator is much more efficient than going through an AC generator and a battery charger. That's why we use Kubota diesels to drive large frame DC alternators ...to charge batteries fast and full."
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DavidInWilmNC
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« Reply #7 on: January 23, 2007, 08:49:02 PM »

I'm all for a big inverter to run an A/C or whatever when the bus is running.  Is 33 amps going to be enough AC power?  That's what a 4000 watt inverter produces.  There's also no redundancy in that system.  With an AC genset, you have power if there's a problem with the inverter.  If the genset has issues, the inverter can provide limited power (no A/C, though) for a while, depending on your battery bank.  I'm sure the system you propose will work, but it sure seems like a round-about way to get AC power.

David
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gr8njt
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« Reply #8 on: January 23, 2007, 09:31:28 PM »

JR, I do not know how these Kubota units cool. Thanks for the info as I may end up fabricating my own hybrid system using a small diesel engine running a large (maybe 270 amps) 24VDC alternator used in trucks or buses. I'm still in the research stage of the project.

Did you read the AD? It specifically states that they use AC alternators. Richard
Richard, Yes, I've read it very closely and the AD states that they use DC alternators with their Kubota engines.

David, I pondered that angle for a while.  And yes, if the inverter fails, there'll be no AC power in a single inverter set-up. I already have a small Xantrex 24 volt modified Sine inverter/charger which will be a back-up to a larger pure sine 4k inverter/charger. Or if finances is not too much of an issue, I may stack two (2) 4k inverters together.  Also, in this system, a huge battery bank is an integral part to factor in.
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****1982 MCI-9 Crusader-II Bus Conversion****
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« Reply #9 on: January 23, 2007, 10:39:07 PM »

If you're talking about efficiency, producing 120v through an inverter is about as inefficient as it gets.  First you have a 12v (or 24v) alternator to produce electricity.  There is efficiency loss in that since you are only using one side of the sine wave on a 3 phase alternator to produce the DC voltage.  Then there is the loss through the electrical cables to the batteries (why do you think we use AC current all over? Because it was discovered very early on in electrical development that DC current does not travel well for any kind of distance over wires).  Then there is another efficiency loss at the batteries.  Then another efficiency loss again with the battery cables going to the inverter.  Then the inverter has efficiency loss also.  If you take 10% loss for the Alternator, 5% for the battery cables, 10% loss for the batteries, 10% loss at the inverter, you're at only 65% efficient.  Now compare that to a straight generator that is usually around 93% efficient producing the power once, then transmitting it directly to your sources.

I also have an inverter/charger.  The charging side can be adjusted up to 130 amps and is a three stage adjustable to your type of battery you are using.  Personally, I like to think of the inverter as 120v power for intermittent use-like for the coffee maker, toaster oven, microwave, powering low draw stereo and TV, refrigerator, etc.  If you want to power the air conditioner, run the 120v generator.

That 1 cylinder Kubota is aimed at blow boaters that don't have enough accessories to warrant a normal generator, but need some sort of stand by power so they don't have to be running the main propulsion engine just to charge the batteries.  Believe me when I say your electrical requirements on the bus (especially if you have 2 or 3 air conditioners, electric heat, electric water heaters,etc) are way above what that little Diesel powered 12 charger is capable of producing.  That Kubota engine is probably only about 8hp, compared to the 18hp on a 10kw gen like I have.  If you have a question about using a new idea, just look at what everyone else is using and ask them why they are using the systems that way.  It'll save you alot of grief down the road.  Good Luck, TomC
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« Reply #10 on: January 23, 2007, 10:44:23 PM »

Boy you take the fun out of every thing Angry ....
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gr8njt
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« Reply #11 on: January 24, 2007, 04:45:26 AM »

If you're talking about efficiency, producing 120v through an inverter is about as inefficient as it gets.  First you have a 12v (or 24v) alternator to produce electricity. There is efficiency loss in that since you are only using one side of the sine wave on a 3 phase alternator to produce the DC voltage.   I also have an inverter/charger.  The charging side can be adjusted up to 130 amps and is a three stage adjustable to your type of battery you are using.  Personally, I like to think of the inverter as 120v power for intermittent use-like for the coffee maker, toaster oven, microwave, powering low draw stereo and TV, refrigerator, etc.  If you want to power the air conditioner, run the 120v generator.
Good Luck, TomC
All points well taken. Thank you.
Since we are talking about charging a battery bank using DC genset, please explain the highlighted statements further though. I thought all along that modern bus/automotive  alternators produce DC amps directly to the battery. Your statement above indicates that DC amperes are being produced from one side of the sinewave on a 3-phase alternator. If I am confused,  please explain as my research says otherwise.

Or if anyone can school me on automotive DC charging.  My goal is to charge a big house battery bank in the least amount of time,  least use of fuel and without the use of the grid.
« Last Edit: January 24, 2007, 04:51:37 AM 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
DavidInWilmNC
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« Reply #12 on: January 24, 2007, 05:12:57 AM »

I thought all along that modern bus/automotive  alternators produce DC amps directly to the battery

Alternators produce alternating (AC) current.  The AC is rectified by the diodes in the alternator to produce the DC used for charging and the vehicle's elec. system.

David
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« Reply #13 on: January 24, 2007, 05:24:39 AM »

My answer would be to use an automotive type alternator with a three stage regulator on the alternator. To obtain the best efficiency, you need to know the maximum current that your battery bank can use and then size the alternator and engine to get peak efficiency at that current. The last 10% of battery charge takes time and can't be avoided regardless of the system used.

 BTW: an automotive alternator is three phase AC into a full wave three phase bridge rectifier. This uses both halves of the sine wave from all three phases with minimal ripple.
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gr8njt
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« Reply #14 on: January 24, 2007, 07:31:31 AM »

My answer would be to use an automotive type alternator with a three stage regulator on the alternator. To obtain the best efficiency, you need to know the maximum current that your battery bank can use and then size the alternator and engine to get peak efficiency at that current. The last 10% of battery charge takes time and can't be avoided regardless of the system used.

 BTW: an automotive alternator is three phase AC into a full wave three phase bridge rectifier. This uses both halves of the sine wave from all three phases with minimal ripple.
Thank you Stan for a very informative post.
Please help me with this math:
I would like to use a Xantrex SW4024 (or any efficient 4kw inverter/charger) from a bank of four 200Ah 12V AGM batteries.
If the batteries were wired in series to produce 24 volts, I should have a 400Ah. Correct?
Using the SW4024 at maximum AC use of 4kw, the inverter will draw about 35 amps (110v) AC = 175 amps (24v) DC. Right?
If I find a 200 amp 24V automotive alternator, would this be sufficient to charge this bank of 400Ah without discharging it beyond 50%?
Do you think I need a larger battery bank? Do you suggest a more powerfull alternator for quicker bulk charging?

FWIW, my coach & H2O heating will eventually be the "Pro-heat" system.  The electric system I have in place now will be the "on grid" back-up system for some redundancy.
« Last Edit: January 24, 2007, 07:34:24 AM 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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