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Topic: Not too interesting electrical stuff: Combined currents for the air (Read 8 times) previous topic - next topic
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Not too interesting electrical stuff: Combined currents for the air
Yahoo Message Number: 100115
Hello all on-board techies:
 I'm still in the (never ending) planning stage.  I would like to see if either of these setups would work.  The goal is to run the rooftop A/C in the absence of shore power.

Rooftop A/C = 13,000 btu.  Max draw = 1,250w at coldest setting.
Battery bank (bbank) = 500AH Inverter = Modified sine wave, 4000w surge, 2000w rated On board AC/DC generator: DC 12V mode:  Max output 90amp AC mode:  Max ouput: 1,100w
 Setup #1:  Generator in DC 12V mode, connected directly to the bbank.  The A/C will start/run off the inverter.  My calculation tells me that this should work for at least 5 hrs before the bbank gets down to 50% charged.  I'm assuming that the generator will actually output 2/3 of its max.  I'm also assuming that the A/C compressor is on all the time (unlikely, but possible in very hot weather.)
 Setup #2:  Generator in AC mode.  I don't even know if this is possible.  Can I "somehow" combine A/C output of the generator with the output of the inverter?

Sam
Re: Not too interesting electrical stuff: Combined currents for the
Reply #1 –
Yahoo Message Number: 100116
I can't give a definitive answer, but I can offer a couple of observations that may help.

1. I've run my air conditioner, which is comparable to yours, from my 520 Ah battery bank a couple of times using a proSINE 2.0 2,000W inverter. As I recall, it took about twenty minutes to bring the battery bank down from a full charge to 50%.

2. To combine a generator's AC output with that of an inverter, you'd have to have perfect synchronization--not only both devices putting out 60 Hz, but no phase shift between the two. No gasoline-powered AC generator is stable enough to do that.

Honda pulls off that trick with a pair of specially designed gensets such as the EU2000i model, because they actually generate DC and convert it to AC with inverters on the generators. They can't synchronize the gensets, but they can sync the two inverters by slaving one to the other. But syncing even a Honda generator with a standalone inverter from a different manufacturer... well, I don't think it's possible, unless you're savvy enough to design circuitry that can slave one inverter to another. I know I'm not.
 Your best bet is scheme #1: pump DC into the battery bank to partially replenish the DC that the inverter is pulling out. I wouldn't venture to predict exactly how long you could run that way, but five hours sounds pretty optimistic based on my experience.
 One other factor to consider: most inverter/chargers such as the proSINE 2.0 can either charge or invert, but can't do both at the same time. To implement your first scheme, which requires simultaneous charging and inverting, you'd have to use a separate inverter and charger.

Andy Baird http://www.andybaird.com/travels/
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Not too interesting electrical stuff: Combined currents for the
Reply #2 –
Yahoo Message Number: 100118
Quote
"To implement your first scheme..."

Andy Baird
Andy

Okay, I'll play the part of the fall guy here...

I get the impression someone is trying to reinvent the wheel!

Steve S.
Lazy Bones & Jiggs
Steve S.
Lazy Bones & Cedar
2004 30'IB (Island Bed)
Yesterday is History, Tomorrow is a Mystery
Live for the day!
Re: Not too interesting electrical stuff: Combined currents for the
Reply #3 –
Yahoo Message Number: 100127
Quote
1. I've run my air conditioner, which is comparable to yours, from my 520 Ah battery bank a couple of times using a proSINE 2.0 2,000W inverter. As I recall, it took about twenty minutes to bring the battery bank down from a full charge to 50%.
That's strange. 1,250w is 104amp.  At 90% efficiency for the inverter, the actual current is 116amp.  You should be able to run at least 2 hrs before getting down to 50%.

Quote
One other factor to consider: most inverter/chargers such as the proSINE 2.0 can either charge or invert, but can't do both at the same time. To implement your first scheme, which requires simultaneous charging and inverting, you'd have to use a separate inverter and charger.
I plan to get a 2000/4000 inverter.  I don't need a charger.  The generator is capable of supplying 90amp in DC mode.

Sam
Re: Not too interesting electrical stuff: Combined currents for the
Reply #4 –
Yahoo Message Number: 100128
Sam, a compressor is a tough load for a modified-sine-wave source. Inefficiency is high, as is heat dissipated from phase mismatch. Your efficiency could run as low as 50% depending on ugliness of waveform, which means you will need that much more inverter to do the job. Also, bear in mind batteries are rated to deliver charge at about 20A. Much higher current flows greatly reduce the total charge available. Note that a true sine wave source - such as an AC generator, will deliver the power with much higher efficiency. You could also get a real sine wave inverter, but those also have lower native efficiency, maybe 80% max.

Steve
2004 FL
2013 Honda Fit
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #5 –
Yahoo Message Number: 100132
Quote
Also, bear in mind batteries are rated to deliver charge at about 20A. >Much higher current flows greatly reduce the total charge available.
This didn't sound right at the late hour I penned it - luckily I reread it this AM, so here's the correction:
 Batteries are rated to deliver their rated charge when discharged at a 20-hr rate. They will deliver much less when the rate is accelerated.
 E.g., a 200 A-hr battery will deliver 10 Amps for 20 hrs. At a 100 Amp rate, it will last Steve
2004 FL
2013 Honda Fit
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #6 –
Yahoo Message Number: 100133
Quote
> > Batteries are rated to deliver their rated charge when discharged at a 20-hr rate. They will deliver much less when the rate is accelerated.
 > E.g., a 200 A-hr battery will deliver 10 Amps for 20 hrs. At a 100 Amp rate, it will last
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #7 –
Yahoo Message Number: 100135
My take on the 2000w honda generater is it will not run your rooftop AC unit. I have a 1 year old unit I bought brand new from Camping World. It runs tools and 500w halogen lites fine, but will not run my 2 gallon Sears air compresser. Stalls real bad while trying to build up psi
Re: Not too interesting electrical stuff: Combined currents for the
Reply #8 –
Yahoo Message Number: 100137
Quote
Setup #2:  Generator in AC mode.  I don't even know if this is possible.  Can I "somehow" combine A/C output of the generator with the output of the inverter?
NO! Not good! Very very bad!
 You can't combine different alternating current sources like that. Even if both were clean sine waves (and they aren't) the inevitable phase difference would at best be very inefficient, never get you near 110 volts, and kill your AC compressor motor. At worst it would lead to a spectacular Hollywood-action-movie equipment failure!  If you do decide to try this, park in front of a fire station and make sure you take video and post the results to YouTube.
 The only way to do this is to create all the alternating current from one source. If you're running your generator anyway, why not simply run the AC off a more powerful generator and be done with it?
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #9 –
Yahoo Message Number: 100138
I don't want to get the EU3000is because of it's bulkiness (it's not $$), but if the 2000i is uncapable of starting the A/C, I won't have much choice.


 Get 2 Honda 2000's with the parallel kit.  They don't take up any more room than a Honda 3000 and are easier to cart around than the almost 150# 3000.
We have 2 Hondas and they run our 15K BTU A/C just fine.

Linda Hylton http://map.datastormusers.com/user1.cfm?user=1167 http://earl-linda.blogspot.com/
Linda Hylton
Re: Not too interesting electrical stuff: Combined currents for the
Reply #10 –
Yahoo Message Number: 100139
"That's strange. 1,250w is 104amp. At 90% efficiency for the inverter, the actual current is 116amp. You should be able to run at least 2 hrs before getting down to 50%."
 Batteries are not linear. Drawing a huge amount of current--especially from a deep-discharge battery, which unlike a starting battery, is specifically NOT optimized for that kind of use--changes the rules drastically. Draw a trickle, and a battery will last longer than its rating. Draw a flood, and its usable output drops well below its rating. So, by the way, does its overall lifespan (charge/discharge cycles).
 "I don't need a charger. The generator is capable of supplying 90amp in DC mode."
 With what kind of regulation? A good charger has three stages: bulk, taper and float. It puts in the maximum amount of power the battery can safely handle at any given point on its charge curve. That way you get the fastest allowable charging *and* the longest possible battery lifespan. Now, maybe your generator has three-stage charging, but my guess is that it doesn't. It probably just puts out 90 amps all the time, regardless of whether the battery is fully discharged... or 90% charged and boiling like a teakettle. This is really, really bad for the battery.
 Let me put it this way. You're proposing to brutalize your batteries by regularly draining them at a rate they weren't designed for... and/or brutalize them by charging with a brute-force DC source. If you do this, your five batteries won't last long. You've already caused one or more batteries to die prematurely by draining them to 20% of capacity, instead of staying well above 50% as manufacturers recommend. Now you want to beat *five* batteries to death. This just doesn't make economic sense.
 Why don't you simply trade for a larger generator--one that can run your air conditioner all by itself--instead of trying to do it with a Rube Goldberg scheme that ensures your batteries will die premature deaths? It's gotta be cheaper to buy an adequate generator and do this the right way than to keep burning out sets of five batteries. :-)

Andy Baird http://www.andybaird.com/travels/
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #11 –
Yahoo Message Number: 100140
"I don't want to get the EU3000is because of it's bulkiness... but if the 2000i is uncapable of starting the A/C, I won't have much choice."
 I've seen a number of posts here and elsewhere over the years, and the consensus is that the EU200i is marginal with the air conditioners in our rigs. A couple of people have been able to start and run the A/C, but many have not. So if you're going to buy a Honda generator, the safe way to go is the EU3000i... or take Linda's suggestion and buy a pair of EU2000is with the synchronizer box.
 But those aren't the only alternatives. Why not install a 4,000W Onan generator--the same one Lazy Daze uses--in the generator compartment provided by Lazy Daze? (I assume your '82 has one; my '85 did.) Co-moderator Tessa Hill bought a 1992 LD that came without a generator, and was able to retrofit a 4kW generator to it without too much trouble. Search out her posts on the subject for the details.
 With a built-in generator, you don't have to store and carry a heavy, bulky unit; don't have to worry about it being stolen; don't have to worry about providing a safe (vented to the exterior) place to carry your gas can... and you don't have to go outside in the rain or darkness and yank a rope every time you want power. Push a button on the wall, and the generator fires up. Now, *that's* the way to do it! :-)

Andy Baird http://www.andybaird.com/travels/
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #12 –
Yahoo Message Number: 100151
Quote
 
 Batteries are rated to deliver their rated charge when discharged at a 20-hr rate. They will deliver much less when the rate is accelerated.
 E.g., a 200 A-hr battery will deliver 10 Amps for 20 hrs. At a 100 Amp rate, it will last Steve, that's much better! ;-)
 Anyway, I just completed a test of the AC/DC generator that arrived yesterday.  It was not satisfactory.  In DC primary mode, the generator could only deliver 30 amps (at 13.5V) even though it's connected to 60% charged 300AH battery.  That's only 1/3 of the claimed output.  Oh well, now I have an emergency generator at home.
 Time to stop playing.  Will a Honda EU2000i run a 13,000btu A/C?  I know its rated 1,600w is more than enough once the A/C has started.  I'm concerned about the starting draw.  I don't want to get the EU3000is because of it's bulkiness (it's not $$), but if the 2000i is uncapable of starting the A/C, I won't have much choice.

Sam
Sam, if the generator has a voltage-regulated output - almost certainly the case - it cannot force the battery to take more current than the battery will accept at that voltage. The generator is probably rated for its current at 12V dc. Once the voltage starts creeping up on the battery, the voltage from the charge source needs to be raised to keep the same charge current flowing.
 This is what the more sophisticated multi-stage chargers will do. First stage is current regulated with a max voltage limit of 14.5V or so. This is what a generator is missing. This is also what most alternators are missing - and why it can take many hours of driving to fully recharge batteries even with a 150+ Amp alternator.
 You can get 2 EU2000's with a sync cable to double the output, and they may be easier to store. However, if I may ask, where are you planning to use your LD where you will be boondocking and need to use the air conditioner? If humidity is low, a roof swamp cooler, a source of water to refill the tank, and a good battery bank with solar recharging will keep in comfy inside all day and into the night, indefinitely. This is what we do when a fan alone won't cut it. We've kept our LD oem cooler maintained and up to snuff for just this reason. Frankly, though, if we need to stay inside all the time to stay cool, we head for cooler climes or home.

Steve

I did once see a couple camped in Death Valley, towing a medium size low trailer containing a huge battery bank, a big inverter, and a large array of solar panels that could be aimed. I would guess their setup could support an air conditioner.
2004 FL
2013 Honda Fit
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #13 –
Yahoo Message Number: 100155
Quote from: Andy Baird"

But those aren't the only alternatives. Why not install a 4,000W Onan generator--the same one Lazy Daze uses--in the generator compartment provided by Lazy Daze? (I assume your '82 has one; my '85 did.)

My '84 doesn't. I couldn't install one if I wanted to.
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #14 –
Yahoo Message Number: 100158
"My '84 doesn't [have a generator compartment]."
 Ah, then 1985 must have been the first year for that option. I didn't realize that. Well, that blows my idea of installing a generator in Sam's '82 out of the water--too bad.

Andy Baird http://www.andybaird.com/travels/
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #15 –
Yahoo Message Number: 100159
Quote
Sam, if the generator has a voltage-regulated output - almost certainly the case - it cannot force the battery to take more current than the battery will accept at that voltage. The generator is probably rated for its current at 12V dc. Once the voltage starts creeping up on the battery, the voltage from the charge source needs to be raised to keep the same charge current flowing.
Steve, it's a Subaru Ultimite generator http://www.drive.subaru.com/01_04_Winter/Ultimite.htm It's supposed to be somewhat sophisticated, but so far it has not delivered yet.  The owner's manual is not very detailed, but did say that it would pump out up to 90amp and gradually step down as the battery gets closer to full.  This morning I hooked it up to a bank of 3 brand new batteries (which I discharged the night before down to 12.2V).  So I know, together the batteries can accept more than 30 amp.  I was expecting to see at least 50.  Still it's much better than my current 6amp charger, and I can run it without shore power.  The main reason I bought it is to charge the coach batteries while on the road.

Quote
This is what the more sophisticated multi-stage chargers will do. First stage is current regulated with a max voltage limit of 14.5V or so. This is what a generator is missing.
May be you're right.  I'm still searching for detailed technical specification on this generator.  There must be a way to pump more amp, I think, or Subaru wouldn't dare making such a lofty claim.

Quote
where are you planning to use your LD where you will be boondocking and need to use the air conditioner?
I am sort of a vagabonder even before I bought the LD.  When bored, I just jump in the van and take off for weeks.  Of course, sleeping in the van is a lot less comfortable, and cold sandwiches are no match to hot food, however simple.  A few years ago, I took a month long trip from Houston to the Artic Circle and back with my kids.  It was fun.  Now the kids are grown up and no longer interested.  I might do it again soon in the LD.  I don't really need the A/C, but since the generator is handy, I thought why not give it a try.

Quote
If humidity is low, a roof swamp cooler, a source of water to refill the tank, and a good battery bank with solar recharging will keep in comfy inside all day and into the night, indefinitely.
The swamp cooler was no longer there when I bought it.  Which is quite understandable as we live in extra high humidity Houston.

Quote
Frankly, though, if we need to stay inside all the time to stay cool, we head for cooler climes or home.
I agree, that's what the engine and the wheels are for!

Quote
I did once see a couple camped in Death Valley, towing a medium size low trailer containing a huge battery bank, a big inverter, and a large array of solar panels that could be aimed. I would guess their setup could support an air conditioner.
Oh yeah.  I hope I will never get to that point.  I just love the tinyness of the 22' LD.  It's so great to be able to go/park just about everywhere.  I hope I will never tow.  My dream LD is the 26.5 rear bath because of the additional room, but each time I squeeze my 22 footer into a tight spot, I have second thought.

Sam
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #16 –
Yahoo Message Number: 100160
Ciao didn't have a "generator compartment" either, did she?
 But the RV shop was able to knock out the front compartment, fabricate a metal frame, and install a micro-quiet 4000 under the passenger side dinette on our Mid-Bath.

There's more info
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #17 –
Yahoo Message Number: 100161
Quote
Ah, then 1985 must have been the first year for that option. I didn't realize that. Well, that blows my idea of installing a generator in Sam's '82 out of the water--too bad.
Yes, I think 85 was the first year for the generator.  Anyway, I'm almost done building a big sturdy storage box for my batteries.  It has more than enough room left for a small permanent generator.  But for now I'll just use my tiny Utimite to recharge the batteries when necessary.

Sam
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #18 –
Yahoo Message Number: 100162
"My '84 doesn't [have a generator compartment]."

Sure it does. Generators where optional on all LDs in 1984 (even if Ed said 'you don't need it').
In the Front Lounge models, LD mounted the optional generator where the driver's side exterior storage bin is now located.
This positions the generator close to the coach battery, the electrical panel and converter.

Larry

-
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #19 –
Yahoo Message Number: 100163
Quote from: teresadhill"

 Thanks Tessa.  I think the wiring is doable.  What concern me most is tapping into the gas tank.  But that's just talk, I don't plan to install one permanently.

Sam

Ciao didn't have a "generator compartment" either, did she?
 But the RV shop was able to knock out the front compartment, fabricate a metal frame, and install a micro-quiet 4000 under the passenger side dinette on our Mid-Bath.
 There's more info in the LINKS > Improvements > Exterior > Generator
 if you're interested. There were no "pre-wires" for generator as I'd hoped, but they were able to run them.

Tessa
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #20 –
Yahoo Message Number: 100164
Quote
Sure it does. Generators where optional on all LDs in 1984 (even if Ed said 'you don't need it').
In the Front Lounge models, LD mounted the optional generator where the driver's side exterior storage bin is now located.
Larry, but that storage bin is long 10" high on my 82 front lounge.

Sam
Re: Not too interesting electrical stuff: Combined currents for the
Reply #21 –
Yahoo Message Number: 100165
Quote
NO! Not good! Very very bad!
Thanks, I realize that's not something to try by an amateur tinkerer.

Quote
If you do decide to try this, park in front of a fire station and make sure you take video and post the results to YouTube.
Better than that, I will email you ahead of time so you can come and witness "the event of the year!", ok?  ;-)

Sam
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #22 –
Yahoo Message Number: 100166
Quote from: mynetsig

Correction:  Should read: Larry, but that storage bin is only 10" high on my 82 front lounge.

 Sure it does. Generators where optional on all LDs in 1984 (even if Ed said 'you don't need it').
In the Front Lounge models, LD mounted the optional generator where the driver's side exterior storage bin is now located.

Larry, but that storage bin is long 10" high on my 82 front lounge.

Sam
Re: Not too interesting electrical stuff: Combined currents ...oops
Reply #23 –
Yahoo Message Number: 100167
Quote
My take on the 2000w honda generater is it will not run your rooftop AC unit. I have a 1 year old unit I bought brand new from Camping World. It runs tools and 500w halogen lites fine, but will not run my 2 gallon Sears air compresser. Stalls real bad while trying to build up psi in the storage tank. Good Luck Sam. John O in the ol 85.
Thanks John.  I wish all electrical equiqments have built-in slow start operation mode and eliminate the pesky sky high starting current

Sam
Re: Not too interesting electrical stuff: Combined currents for the
Reply #24 –
Yahoo Message Number: 100168
Quote
Batteries are not linear. Drawing a huge amount of current--especially from a deep-discharge battery,
Yes, I understand the non-linear characteristic of batteries.  But your particular case still keeps me wondering.  You were discharging at a 20% rate.  High, but not high enough for that stiff penalty.  At that discharge rate, I would not expect to lose more than 50%.

Quote
Let me put it this way. You're proposing to brutalize your batteries by regularly draining them at a rate they weren't designed for... and/or brutalize them by charging with a brute-force DC source.
I'm still in the "R&D" stage, so destroying a few things will be ok.  Just kidding.

Sam