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Author Topic: the real truth, the whole truth, and nothing but the truth about inverters...  (Read 9391 times)
circusboy90210
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« Reply #30 on: April 14, 2009, 03:59:59 PM »

Its amazing how many Douglas Adams readers there are here.  I wonder if there is a disproportional number of Douglas Adams fans among bus nuts or if there is a disproportional number of bus nuts among Douglas Adams readers.  Or maybe its just a sampling error to even out some infinite improbability somewhere else in the universe.
Jeremy, I think that is absolutely brilliant.  I hope the instructor saw the humor.    Okay, What CB completely failed to communicate was a question he has about using inverters to power the equipment in his Ice Cream truck. 

He asked this question in the chat room and was not satisfied with the answer.  So he is trying to ask it here to gather more opinions.    The considered opinion in the chat room was you can not take the cheapo inverters from J.C. Whitney and run the refrigerators/freezers/noisemakers etc.   At least not more than a few minutes. 

The inverter he purchased came with jumper cable connections and very light gauge wire.  We were worried about a fire as much as equipment failure.  As he alluded to in his post, Bus Warrior ( and several others ) suggested that he get a generator.  It was safer, easier and an quick  solution to his problem.  

However CB has talked to several drivers from other trucks who have stated that most of the trucks now use inverters instead of generators because of the noise.  So, if any of the real smart electrical guys want to guide CB thru the selection/installation  process of using inverters instead of a generator to power the equipment in his ice cream truck, make like a chicken on a june bug and jump on it.

I am sure CB would appreciate it.

Frank


Oh, and always remember to take your towel
ok I have several towels, I also am not panicking. the application is to run a 5.7 amp freezer possibly two I have a 2500-5000 watt inverter. I'm thinking of getting a cs130 170 amp alternator and installing a second external rectifier ina  box with a cooling fan with a deep cycle battery to hold the charge.(the external rectifier is after market)Amazingly enough I'm watching a mit professor talking about proportions in a physics lecture. hahaha talk about irony. I would like to run a second slightly larger freezer at 9 amps. I ran my smaller generator as a test yesterday and the 1800 watt genset was a epic FAIL. Now IT IS  necessary to get the 4k watt unit running again. I had the unit working last fall and have not ran it since the fuel tank melted and almost caught the whole unit on fire, fortunatly when it stopped running I went out to investigate and fuel was running all over the hot exhuast manifold and muffler(cherry red @ the time) but I think maybe it needs a new plug or something. Really not wanting to run generators as they are loud and offensive in this tree hugging city I live in, plus expense and something else to monitor all day long. so long and thanks for all the fish.
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NewbeeMC9
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« Reply #31 on: April 14, 2009, 04:05:40 PM »

Hey NewbeeC9 is that really your picture? Or is it your daughter? Either way I want a date!!!!! Smiley
Oh. It's Christina.
Too bad she's too fancy for me....

I bet u say that to all the boys Kiss        Grin
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« Reply #32 on: April 14, 2009, 04:23:52 PM »

Hey NewbeeC9 is that really your picture? Or is it your daughter? Either way I want a date!!!!! Smiley
Oh. It's Christina.
Too bad she's too fancy for me....

I bet u say that to all the boys Kiss        Grin

That's a little gay Wink
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Sean
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« Reply #33 on: April 14, 2009, 05:04:52 PM »

... the application is to run a 5.7 amp freezer possibly two I have a 2500-5000 watt inverter. ... I would like to run a second slightly larger freezer at 9 amps. ...


OK, so now I'm not sure if you want to run a 5.7 amp unit plus a 9 amp unit, two 5.7 amp units, or two 5.7 amp units plus a 9 amp unit.

In any case, I am assuming these are the steady-state, running currents (as opposed to inrush start-up current) for the units, and that's at 120 volts.

First off, to run compressors such as those in freezers efficiently, you need a "true" sine-wave inverter.  If you skimp on this and get an MSW unit, it (and the alternator, and the batteries, and the cables) will need to be at least 20% large, maybe more, the freezers will not run as cool, and you will likely burn the compressors out much sooner.

For the steady state running, you will need, for the following sizes:

One 5.7 amp freezer: 820 watts
Two 5.7 amp freezers: 1,640 watts
One 5.7 plus one 9: 2,120 watts
Two 5.7 plus one 9: 2,940 watts

If you get a sine-wave inverter with the correct capacity (as outlined above) for the steady load, you should be OK on starting current so long as the inverter's maximum rating (or surge rating) is at least double its continuous rating.

As a last comment, I suggest you actually measure the current draw of your freezers, rather than rely on specifications.  You may find that they actually draw more current under the circumstances in which they operate.  Remember that appliance ratings are established at a "standard" temperature (usually 70° ambient) and assume that installation instructions, including ventilation requirements and coil cleanliness, are followed to the letter.

If, in practice, it's more like 90° or 100° behind the freezer in the truck (or more), the ventilation around the condenser coils is poor, or the whole assembly is full of dust, you could find your equipment drawing a whole lot more current.  This might explain the failure of the generator to run it (although I suspect it has more to do with the genny's maximum surge output being in the ~2,000 watt range, and the start-up surge of the freezers to be more like 3,000 watts).

Hope this helps.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #34 on: April 14, 2009, 05:09:20 PM »

I bet u say that to all the boys Kiss        Grin

That was Meat Loaf, not Freddie Mercury

J
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circusboy90210
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« Reply #35 on: April 14, 2009, 05:20:01 PM »

... the application is to run a 5.7 amp freezer possibly two I have a 2500-5000 watt inverter. ... I would like to run a second slightly larger freezer at 9 amps. ...

yes this helps as one 1800 watt genset alone would not properly start up the compressor even over 4 hours and the  coil cooling fan was running at 1/3 the normal speed, no noticeable cooling on the gallon jug of water in the 4 hours.( maybe a few degrees but not enought to write home about)
OK, so now I'm not sure if you want to run a 5.7 amp unit plus a 9 amp unit, two 5.7 amp units, or two 5.7 amp units plus a 9 amp unit.

In any case, I am assuming these are the steady-state, running currents (as opposed to inrush start-up current) for the units, and that's at 120 volts.

First off, to run compressors such as those in freezers efficiently, you need a "true" sine-wave inverter.  If you skimp on this and get an MSW unit, it (and the alternator, and the batteries, and the cables) will need to be at least 20% large, maybe more, the freezers will not run as cool, and you will likely burn the compressors out much sooner.

For the steady state running, you will need, for the following sizes:

One 5.7 amp freezer: 820 watts
Two 5.7 amp freezers: 1,640 watts
One 5.7 plus one 9: 2,120 watts
Two 5.7 plus one 9: 2,940 watts

If you get a sine-wave inverter with the correct capacity (as outlined above) for the steady load, you should be OK on starting current so long as the inverter's maximum rating (or surge rating) is at least double its continuous rating.

As a last comment, I suggest you actually measure the current draw of your freezers, rather than rely on specifications.  You may find that they actually draw more current under the circumstances in which they operate.  Remember that appliance ratings are established at a "standard" temperature (usually 70° ambient) and assume that installation instructions, including ventilation requirements and coil cleanliness, are followed to the letter.

If, in practice, it's more like 90° or 100° behind the freezer in the truck (or more), the ventilation around the condenser coils is poor, or the whole assembly is full of dust, you could find your equipment drawing a whole lot more current.  This might explain the failure of the generator to run it (although I suspect it has more to do with the genny's maximum surge output being in the ~2,000 watt range, and the start-up surge of the freezers to be more like 3,000 watts).

Hope this helps.

-Sean
http://http://OurOdyssey.BlogSpot.com

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« Reply #36 on: April 14, 2009, 06:54:33 PM »

CB, you mentioned the idea of using a 170 amp alternator to keep the battery charged.  That would give a total of about 2000 watts maximum.  That also assumes the alternator is built for 100% duty cycle, many (most?) aren't.  Then there is the typical inverter efficiency of 85%-90%.  So that would further limit the useful power to about 1750 watts.  The battery could make up the difference for a little while, but unless you put in several large batteries, not for long enough.

So if you are looking at running it off of an alternator on the prime mover, it would just about have to be a 50DN.  And even then there is the factor of engine RPM.  An ice cream truck is going to spend a lot of its time idling.  At idle an alternator doesn't generate anywhere close to its rated output.

So if others are using inverters, I suspect they have some massive battery banks that they charge at night. And if you deep cylce them daily all Summer, you will probably need a whole new set each year.

All that said, the generator makes more sense and for a fraction of what you would spend on a big pure sine inverter and batteries, you could certainly get the genny running again and build a good sound box for it to reduce the noise factor.
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kyle4501
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« Reply #37 on: April 14, 2009, 07:22:27 PM »

If he would read a little, he would understand how underpowered his power supply to the inverter is for what he wants to run. . .

http://www.phrannie.org/invert.html

http://www.phrannie.org/battery.html

Or, maybe he is too busy listening to that mit lecture . . .  Shocked

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« Reply #38 on: April 14, 2009, 07:39:57 PM »

http://www.newegg.com/Product/Product.aspx?Item=N82E16882715001

Great little device for measuring how much power your appliances ACTUALLY use over time, over however long a period you choose to measure. Knowing that and the efficiency numbers of your inverter, you can do some battery life estimates and see if it works for you.

In the case of refrigerators and freezers, environmental temperature will still be a big factor in how much they run, of course.
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circusboy90210
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« Reply #39 on: April 14, 2009, 08:32:40 PM »

still thinking over all even with expenses ( this genset will not last more than a month or two 4k), I will have to get something else eventually . Almost any profitable ice cream truck in town here is inverter powered, multiple freezers. Nobody is out and running so I can't ask question about specifics yet. However in fuel alone the inverter will pay for itself not to mention good will from neighbors . The only ice cream trucks that run gensets are the ghetto cream trucks that make low sales, being as they all have low prices to sell to the food stamp crowd. I allready have good neighborhoods to run in where everybody allready knows me. Also I live in a Eco warrior community, if I run gensets for too long I will be labled a social pariah for not being green enough and loose my customer base.  so this will have to be a solution. from what I have found I can get a 170 amp cs 130 to run bolt in , I realize that I will have to run a couple of deep deep cycle batteries on a charger overnight but this is not a problem even if I have to run 3 or 4 of them. I have plenty of room to store them. I don't even have a problem with running two alternators if I can find brackets for doing so. What I do understand is that you can run smaller pulley's to accommodate lower idle speeds to maintain higher charging rates. I did read the two articles provided did find time to pull myself away from yet another MIT learning session. Seems like that's all I do now a day's even in my spare time.Really wanting to spend some time on deeper knowledge of developmental studies that I missed out out but I've allready progressed so far past these it's boring but necessary as to not muddy the waters in the future. I thank everyone involved in this for finally clearing the waters as far as this issue. It could have been so easy. maybe we should make a  FAQ for the different issues involved in many subjects to save the hearthache in the future.  Cry Grin Wink Cheesy Roll Eyes Cool Cool Cool
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« Reply #40 on: April 14, 2009, 08:46:36 PM »

.Really wanting to spend some time on deeper knowledge of developmental studies that I missed out out but I've allready progressed so far past these it's boring but necessary

I stand in awe, with my jaw agape in disbelief. Mitch
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« Reply #41 on: April 14, 2009, 08:55:59 PM »

Need the say more............M&C
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« Reply #42 on: April 14, 2009, 09:00:14 PM »

CB,

Please don't stop with the questions now.  Please don't. This so enlightening.

John
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« Reply #43 on: April 14, 2009, 09:09:41 PM »

You know, I was planning a NEV (neighboorhood electric vehicle) food cart to work my local farmers market in Granolaville. I was even going to put "solar panels" on the roof--a solar powered vehicle selling lettuce. That would work, eh?

Wasn't necessarilly going to hook-up the solar panels, but was going to most definetly have an invertor generator aboard.

Please don't tell anybody, some hippies have money and I need a retirement income Roll Eyes
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Sean
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« Reply #44 on: April 14, 2009, 10:06:16 PM »

CB, you mentioned the idea of using a 170 amp alternator to keep the battery charged.  That would give a total of about 2000 watts maximum.


Actually, a 170-amp alternator (12 volt, nominal) is good for about 2,350 watts peak.

Quote
  That also assumes the alternator is built for 100% duty cycle, many (most?) aren't.


True, and this is definitely a consideration when shopping for an alternator.  Also, the peak rating is only good at the specified RPM; since you will be driving at a variety of speeds and RPM's, you can not expect the peak output, even if continuously rated, at all times.

Quote
  Then there is the typical inverter efficiency of 85%-90%.  So that would further limit the useful power to about 1750 watts.  The battery could make up the difference for a little while, but unless you put in several large batteries, not for long enough.


My wattage estimates, above, included derating for inverter efficiency.  It should go without saying that the whole alternator/inverter concept requires a sizeable battery bank to carry over the periods when the engine is not running, or not running at peak RPM.  That being said, you should remember that freezers do not run 100% duty cycle, either.  So the batteries are charging when the compressor cycles off, and vice-versa.



Kyle,  while I admire Fred Tinseth and all he has done to post some of his wealth of experience on his web site, and I have recommended (and continue to recommend) both of these pages as good reading for anyone building RV electrical systems, they are not the be-all and end-all on the subject.

For one thing, the inverter discussion is now horribly out of date.  While much of what he has written deals with general principles and is still useful, virtually none of the models he discusses is still on the market, and improvements have been made across the boards.

The battery discussion, while interesting in its own right, is hardly relevant to the present problem, because the usage mode is so vastly different than RV deep-cycle applications.  This discussion, too, is also dated, and does not account for recent improvements in battery technology.

Lastly, I always caution folks to take the AC electrical portion of the discussion with a grain of salt, as Fred seems to be confused about some key concepts of grounding.

BTW, we Stanford alums have great respect for the MIT guys when it comes to technology -- nearly our equals  Smiley, and just down the street from Harvard, the "Stanford of the East"  -- but they don't know a damn thing about football.  FWIW.

-Sean
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« Last Edit: April 14, 2009, 10:11:53 PM by Sean » Logged

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