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Old 09-07-2020, 05:50 PM   #1
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Inverter Powered by Engine?

Hello all,

Has anyone ever used a large inverter like this product along with a large alternator to provide 30A or 50A service from the idling motor of the tow vehicle?

Any advice would be welcome, thanks.
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Old 09-08-2020, 04:41 AM   #2
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Hello all,

Has anyone ever used a large inverter like this product along with a large alternator to provide 30A or 50A service from the idling motor of the tow vehicle?

Any advice would be welcome, thanks.
Welcome to the forums.


You'll need a lot more than 50 amp DC service to power that. About ten times more than that.
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Old 09-08-2020, 04:44 AM   #3
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That unit draws more than 4 amps (when it’s fan is on) with no load!
I believe that you will find that the draw on the 12 volt system will be enormous!
We’re you thinking of installing it on the tow vehicle and running 120 volt power back to the trailer?
I’d suggest that a generator is a far easier solution...
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Old 09-08-2020, 07:48 AM   #4
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I suppose I should have been more precise.

The tow vehicle has two 220A alternators for a total of 440A of DC current (nearly ten times 50A, actually)

I'm aware that a generator is a simple and typical solution, but I will only require this solution occasionally, so I was just asking if this method might be an option rather than hauling the weight and bulk of a generator around.
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Old 09-08-2020, 08:03 AM   #5
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So, if you have a trailer that requires 30A 120VAC, that is 3600 watts of power. To create that from a 100% efficient inverter will require 300 amps of 12VDC, so yes, you could do it.

If your trailer requires 50 amp service, that is 6000 watts of power and would require 500 amps of 12VDC so no, that won’t work.

But, you aren’t going to get the 300 amps out of your tv at idle so you will need some way to at least fast idle it while you are using it as a generator.
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Old 09-08-2020, 08:09 AM   #6
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Great, thank you for the informative answer!
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Old 09-08-2020, 09:28 AM   #7
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Hi

First up, a 220A alternator supplies 220A with the engine going full bore ( like a couple thousand RPM). Drop down to idle and you are down to (maybe) 1/3 of that.

Second, a 220A alternator will supply 220A for *short* periods of time. They are designed to quick charge batteries or run "rarely used" devices. Load them up at capacity for a long time ( .... who knows just how long that is) and you fry them. There are *lots* of posts on doing exactly this in a whole range of RV's. Best guess "long time" is > 20 minutes.

Next, An inverter pulls a big chunk of current when it starts up. If you take a look at the wire gauge and fuse ratings on a normal (say 2KW) inverter, they are way up there. They appear to want it set up for at least 3X what you normally would use.

At high current, an alternator or a battery (plus wiring ) is going to drop the voltage to the inverter. Best to figure that you have 10 to 11V into the device. Inverters running full load are rarely very efficient. If you are getting 80% efficiency, that's doing well. The net result of these two effects boosts the expected current by about 1.5X. If you *thought* you needed 500A, you really need closer to 750A.

The 50A service to your trailer is 50A at 240V (not 120). The equivalent at 120V would be 100A. So now double al the numbers ... you are up around 1500A. Your inverter would need to be a 240V unit (with a neutral lead). The standard plug and wiring in the trailer will only handle the full load current properly *if* you have 240V.

One could ponder *if* you really need 100A into a normal AS, that is a reasonable question. The answer is completely dependent on what you are doing in the trailer ....

Fun !!

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Old 09-08-2020, 09:33 AM   #8
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Hi

First up, a 220A alternator supplies 220A with the engine going full bore ( like a couple thousand RPM). Drop down to idle and you are down to (maybe) 1/3 of that.

Second, a 220A alternator will supply 220A for *short* periods of time. They are designed to quick charge batteries or run "rarely used" devices. Load them up at capacity for a long time ( .... who knows just how long that is) and you fry them. There are *lots* of posts on doing exactly this in a whole range of RV's. Best guess "long time" is > 20 minutes.

Next, An inverter pulls a big chunk of current when it starts up. If you take a look at the wire gauge and fuse ratings on a normal (say 2KW) inverter, they are way up there. They appear to want it set up for at least 3X what you normally would use.

At high current, an alternator or a battery (plus wiring ) is going to drop the voltage to the inverter. Best to figure that you have 10 to 11V into the device. Inverters running full load are rarely very efficient. If you are getting 80% efficiency, that's doing well. The net result of these two effects boosts the expected current by about 1.5X. If you *thought* you needed 500A, you really need closer to 750A.

The 50A service to your trailer is 50A at 240V (not 120). The equivalent at 120V would be 100A. So now double al the numbers ... you are up around 1500A. Your inverter would need to be a 240V unit (with a neutral lead). The standard plug and wiring in the trailer will only handle the full load current properly *if* you have 240V.

One could ponder *if* you really need 100A into a normal AS, that is a reasonable question. The answer is completely dependent on what you are doing in the trailer ....

Fun !!

Bob
Thanks so much, Bob. I totally spaced on the 30A and 50A being 240V, so you're right, this isn't going to work.

Appreciate it!
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Old 09-08-2020, 09:58 AM   #9
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The 30amp is 120v. The 50amp is two 50a/120v legs so,yeah I blew that calculation...
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Old 09-08-2020, 10:15 AM   #10
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Hmm, okay.

Well, running 30A of 120V on 440A (total) of alternators still seems feasible. Correct me if I'm wrong here, but, at the most, the trailer would be designed to draw no more than 80% of the full 3600 watts of 30A/120V per standard electrical overhead design, which equates to 2880 watts. This means that if I were to somehow max out the trailer's 30A electrical system (unlikely) I'd be pulling 240A of 12VDC, which would be just over half of my tow vehicle's generation capacity. This is a Ram 3500 with a high output diesel and running 'heavy duty' loads like this is not uncommon in the construction space.

I'd use 0/1 gauge cable to the inverter, and it's rated for up to a 10,000 watt peak, so the "burst" on startup should not be an issue.

What do the AS 'heavy hitters' (mainly the heat pump I guess) draw upon startup in amps AC, and how much do they draw afterward?
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Old 09-08-2020, 10:46 AM   #11
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Originally Posted by discodoc View Post
Hello all,

Has anyone ever used a large inverter like this product along with a large alternator to provide 30A or 50A service from the idling motor of the tow vehicle?

Any advice would be welcome, thanks.
Why idle a 18000$ engine when you can buy a 4000 watt gen for 275$?
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Old 09-08-2020, 11:14 AM   #12
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I suppose I should have been more precise.

The tow vehicle has two 220A alternators for a total of 440A of DC current (nearly ten times 50A, actually)

I'm aware that a generator is a simple and typical solution, but I will only require this solution occasionally, so I was just asking if this method might be an option rather than hauling the weight and bulk of a generator around.
As has been noted, it is all about watts. watts = amps x volts
5000w - 12V x 417A
Watts is the common denominator. Amps depends on Volts. Also, you have losses that occur in conversions, wire resistance, etc. Depending on the distance - it will take a 12v big wire to move 417 amps to convert it to 41.7 amps @ 120v
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Old 09-08-2020, 11:22 AM   #13
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Hmm, okay.

Well, running 30A of 120V on 440A (total) of alternators still seems feasible. Correct me if I'm wrong here, but, at the most, the trailer would be designed to draw no more than 80% of the full 3600 watts of 30A/120V per standard electrical overhead design, which equates to 2880 watts. This means that if I were to somehow max out the trailer's 30A electrical system (unlikely) I'd be pulling 240A of 12VDC, which would be just over half of my tow vehicle's generation capacity. This is a Ram 3500 with a high output diesel and running 'heavy duty' loads like this is not uncommon in the construction space.

I'd use 0/1 gauge cable to the inverter, and it's rated for up to a 10,000 watt peak, so the "burst" on startup should not be an issue.

What do the AS 'heavy hitters' (mainly the heat pump I guess) draw upon startup in amps AC, and how much do they draw afterward?
This is possible. I would check to make sure the wire gauge is large enough to provide minimal resistance in the distance to and from the inverter. 240A @ 12v is a lot and can generate some heat
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Old 09-08-2020, 11:27 AM   #14
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You asked: "What do the AS 'heavy hitters' (mainly the heat pump I guess) draw upon startup in amps AC, and how much do they draw afterward?"
Air conditioning - 1200 - 1400 watts (1300/12=108 amps, but will be closer to 120 amps via an inverter.

A welterweight appliance is the water heater, just keep that on propane, as well as the fridge. But my solar system will keep the batteries up and run the fridge, if I need to. I can actually run my a/c (3000w inverter with 340Ah of LFP), but I never do, it would require more panels than my roof will hold and more LFP than the budget allows.

Now if you only wanted to charge the AS batteries while driving I would suggest a DC/DC converter, say a 40 or 50 amps model. That requires running a #2-ish cabling between TV to AS and protected on both ends. An elegant way to do that.

If you want an incredible advice or an amazing system installed I would suggest contacting GMFL here on this forum. Or, go to airstream_nuts_and_bolts on Instagram. You can see his work there.

Fair Enough
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Old 09-08-2020, 11:28 AM   #15
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AIMS 3000/6000 on 30A flying cloud 27FB

I have a 2010 Nissan Armada with a 320 amp alternator and an AIMs 3000/6000 watt inverter. With that setup I could run most 120V appliances in my FC or run my AC with everything else possible turned off. In addition I now have a Victron Multiplus 3000 which allows me to run the AC and other 120V appliances. I still have the 2 original Lifeline AGM batteries and will eventually move to some sort of lithium.
The 320 amp alternator on the TV is supposed to provide a hot max amperage of 270 amps and a hot idle max of 220 amps.
I have only had the multiplus for one trip, but it is certainly helping split the load between my AIMS inverter and the Multiplus pulling power from the house batteries.
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Old 09-08-2020, 11:53 AM   #16
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I'm still trying to get my head around what you are trying to accomplish. Since you went along with some of the replies, I assume you literally want to power your 50A (actually100A) AS at its full potential from the tow vehicle? I would say that if you throw enough money at it it could be made to work.

Now if you only wanted to charge the AS batteries while driving I would suggest a DC/DC converter, say a 40 or 50 amps model.

If you want an incredible advice or an amazing system installed I would suggest contacting GMFL here on this forum. Or, go to airstream_nuts_and_bolts on Instagram. You can see his work there.

Fair Enough
Well, after realizing that the full 50A would require 240V, I've decided to scrap that idea.

Rather than purchase, haul, and fuel a generator that I may never use, why not simply use the massive "generator" and fuel tank I already have should the need arise? I'm just imagining some sort of fringe situation where I'm out of propane or something and need to heat for one more night.
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Old 09-08-2020, 11:54 AM   #17
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I have a 2010 Nissan Armada with a 320 amp alternator and an AIMs 3000/6000 watt inverter. With that setup I could run most 120V appliances in my FC or run my AC with everything else possible turned off. In addition I now have a Victron Multiplus 3000 which allows me to run the AC and other 120V appliances. I still have the 2 original Lifeline AGM batteries and will eventually move to some sort of lithium.
The 320 amp alternator on the TV is supposed to provide a hot max amperage of 270 amps and a hot idle max of 220 amps.
I have only had the multiplus for one trip, but it is certainly helping split the load between my AIMS inverter and the Multiplus pulling power from the house batteries.
This! Thanks so much for the message.
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Old 09-09-2020, 08:02 AM   #18
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Well, after realizing that the full 50A would require 240V, I've decided to scrap that idea.

Rather than purchase, haul, and fuel a generator that I may never use, why not simply use the massive "generator" and fuel tank I already have should the need arise? I'm just imagining some sort of fringe situation where I'm out of propane or something and need to heat for one more night.
Oh, I have considered an inverter (around 2000w PSW) in the TV that could run anything, singularly in the trailer. Even if only to charge the AS batteries via the converter. It can be close to the TV battery (less voltage drop) and run 120vac back to the trailer, where #10/2 would be enough. Or better yet, add a second TV battery (in parallel to what is there now) to run the inverter and use a Sterling current limiting voltage sensing relay (Pro Connect) between the two batteries. Very doable.
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Old 09-12-2020, 11:29 PM   #19
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Inverter Powered by Engine?

discodoc- I have installed a 1,000 watt pure sine inverter in my Tundra. This can be used to power the converter to recharge the lithium batteries if solar isn’t cooperating.



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Old 09-16-2020, 12:05 PM   #20
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. Now if you only wanted to charge the AS batteries while driving I would suggest a DC/DC converter, say a 40 or 50 amps model. That requires running a #2-ish cabling between TV to AS and protected on both ends. An elegant way to do that.

Fair Enough
That’s the way we decided to go but modified as follows: tow vehicle f150 has its own solar panel, lithium and dual (solar-alternator) charger. When airstream is shaded we leave f150 in the sun and when running errands or driving to trails the alternator helps solar. When back at the airstream, plug in tow vehicle battery via dc/dc converter and have option to bulk dump the charge to house lithium or run house directly from tow vehicle. If anyone is interested we posted the description on air forums.
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