Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake

Hi guys. Okay, I think you answered this once before but I can't find the answer and a friend of mine swears this is possible, but I don't. So I'm hoping you can settle this argument before he inadvertently blows himself up, or perhaps sets himself on fire. Either way, if I'm right, things won't end well for him. Anyhow, here's his argument. Since you can apparently take two hot 120v lines on normal house power (I'm quoting him as I don't really know myself) and blend them together and run the negative side out using one neutral line to create 240v (which doesn't make sense to me as they're parallel and not in series, but then again this is AC, so I don't know) he claims that if you plug into two separate plugs on the same inverter you can create more or less the same thing by using the same side on both plugs as the hot, and the opposite side as the neutral. From what little I understand of inverters, it's not only not possible, but it'll earn you a trip to the hospital. Is he completely insane, or is he onto something? I'm guessing he's completely insane thinking this, but since I can't find any information to know for certain one way or the other I'm coming to you guys before he goes and blows himself up. And if you answered this already, I apologize. My google mojo has been sucking of late.

bill von novak

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

Since you can apparently take two hot 120v lines on normal house power (I'm quoting him as I don't really know myself) and blend them together and run the negative side out using one neutral line to create 240v (which doesn't make sense to me as they're parallel and not in series, but then again this is AC, so I don't know) he claims that if you plug into two separate plugs on the same inverter you can create more or less the same thing by using the same side on both plugs as the hot, and the opposite side as the neutral.

That will just give him 120 volts on both. If he tries to go hot to hot he will get zero volts.

From what little I understand of inverters, it's not only not possible, but it'll earn you a trip to the hospital.

Probably not. Doing what he suggests likely won't do anything at all. (However, ignorance of basic electrical design leaves him open to a great many ways to hurt himself, which would be the risk.)

Steven Lake

Re: Help! Friend thinks you can get 240v off 120v inverter!

Okay, that makes me feel better. So he does qualify in the "idiot" category. I kinda figured it wouldn't work, but I felt it safer to ask just to be totally sure. Now with that said, how in the blazes do they get 240v off of mains power on one circuit, but 120v on another? Our old house had 120v, 240v, and 480v connections, and all off the same breaker box. It never made sense to me how that was even possible.

Cariboocoot

Re: Help! Friend thinks you can get 240v off 120v inverter!

Boy is he ever confused.

Split-phase 240 VAC has neutral center and 120 VAC between it and either 'hot' leg.

An inverter that puts out 120 VAC puts out 120 VAC and no combination of its output wires (hot, neutral, and ground) will produce 240 VAC.

You want 240 VAC from a 120 VAC inverter you use an autotransformer.

bill von novak

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

Now with that said, how in the blazes do they get 240v off of mains power on one circuit, but 120v on another?

By using an "intermediate" voltage (neutral.)

Think about it this way. Let's say you had a +12V, ground, and -12V supply driving your off-grid home. Anyone connecting a load between +12 and ground will see 12 volts. Anyone connecting a load between ground and -12 volts will ALSO see 12 volts. However, if someone connected to +12 and -12 volts, they'd see 24 volts.

H2SO4_guy

Re: Help! Friend thinks you can get 240v off 120v inverter!

If he does that, he will likely get an exciting light show, but quite brief. POP! Then the magic smoke will likely be let out of the devices. I use an Outback PSX-240 transformer that will get 240 VAC from a 110 VAC inverter. I can run it off of an 1100 watt Exeltech (In 12 volt or 48 volt version) and run the minisplit for AC, or I can run it on the Outback inverter. Any of them work just fine, but they are all pure sine wave inverters, not modified sine (or square) wave inverters. It makes a big difference.

Good luck and let us know how it worked out.

ggunn

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

Hi guys. Okay, I think you answered this once before but I can't find the answer and a friend of mine swears this is possible, but I don't. So I'm hoping you can settle this argument before he inadvertently blows himself up, or perhaps sets himself on fire. Either way, if I'm right, things won't end well for him. Anyhow, here's his argument. Since you can apparently take two hot 120v lines on normal house power (I'm quoting him as I don't really know myself) and blend them together and run the negative side out using one neutral line to create 240v (which doesn't make sense to me as they're parallel and not in series, but then again this is AC, so I don't know) he claims that if you plug into two separate plugs on the same inverter you can create more or less the same thing by using the same side on both plugs as the hot, and the opposite side as the neutral. From what little I understand of inverters, it's not only not possible, but it'll earn you a trip to the hospital. Is he completely insane, or is he onto something? I'm guessing he's completely insane thinking this, but since I can't find any information to know for certain one way or the other I'm coming to you guys before he goes and blows himself up. And if you answered this already, I apologize. My google mojo has been sucking of late.

Your friend should not be playing around with electricity. What he is suggesting is not in and of itself dangerous as long as he isn't working hot, just ineffective. However, as others have said, his ignorance of things electric make him very likely to hurt himself if he keeps messing around with dangerous things he does not understand. I wouldn't even know where to start if I were to try to explain what's wrong with what he is saying.

Here's hoping he was just speaking hypothetically.

mike95490

Re: Help! Friend thinks you can get 240v off 120v inverter!

This sounds like a fun show to watch Attachment not found.

Steven Lake

Re: Help! Friend thinks you can get 240v off 120v inverter!

Okay, I told him, but he still doesn't believe me. However he wisely agreed not to attempt it. ^_^;;

Cariboocoot

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

Okay, I told him, but he still doesn't believe me. However he wisely agreed not to attempt it. ^_^;;

Good.

I wonder if he came across one of those 'balanced' outlets where the two hots are each on a separate line? With one of those you'd find 240 VAC between the 'upper' and 'lower' hot leads and 120 VAC between either hot and either neutral (both common). Some places use such outlets, and in other jurisdictions they're not allowed.

BTW, 240 VAC on its own doesn't have or require a neutral line.

bill von novak

Re: Help! Friend thinks you can get 240v off 120v inverter!

Cariboocoot wrote: »

I wonder if he came across one of those 'balanced' outlets where the two hots are each on a separate line? With one of those you'd find 240 VAC between the 'upper' and 'lower' hot leads and 120 VAC between either hot and either neutral (both common). Some places use such outlets, and in other jurisdictions they're not allowed.

There is a company called "quick 220" that sells 110-220 volt converters; they are just two plugs that go to one 240VAC outlet. You hunt around for two outlets that are on different sides of the breaker panel, plug them in and you have 220 volts. (Often used for EV chargers.) He may have seen one of these and thought "I can do this with an inverter!"

solar_dave

Re: Help! Friend thinks you can get 240v off 120v inverter!

bill von novak wrote: »

There is a company called "quick 220" that sells 110-220 volt converters; they are just two plugs that go to one 240VAC outlet. You hunt around for two outlets that are on different sides of the breaker panel, plug them in and you have 220 volts. (Often used for EV chargers.) He may have seen one of these and thought "I can do this with an inverter!"

YEah the EV charger crows does this quite often.

Steven Lake

Re: Help! Friend thinks you can get 240v off 120v inverter!

Huh, that's entirely possible. Given what you said about the EV chargers, that's likely where he got the idea. Now, as a small aside, since we're on the topic of 110-220 (or 120-240v depending on where you are) I've got a cool little plug that I take with me camping that converts the 220 outlets they use for the big campers and motor homes and knocks the 220v 15amp line down to 110v 30 amps. What's funny is I use that little converter for one thing only. Running a fan in my tent at night.

solarvic

Re: Help! Friend thinks you can get 240v off 120v inverter!

Coot, Is that why an electric waterheater only has 2 hot leads and a bare ground wire? I was wondering why they do not have a neutral.



BTW, 240 VAC on its own doesn't have or require a neutral.

Cariboocoot

Re: Help! Friend thinks you can get 240v off 120v inverter!

solarvic wrote: »

Coot, Is that why an electric waterheater only has 2 hot leads and a bare ground wire? I was wondering why they do not have a neutral.

Yes. 240 VAC runs "hot to hot" and a neutral line is not involved. People get confused because 240 VAC outlets for stoves, dryers, et cetera will include a neutral connection. This is to supply 120 VAC to whatever is plugged in there to run low Voltage components like oven lights and controls.

In Europe (and elsewhere) the standard is 230 VAC 50 Hz and has no neutral. Some say it is better than the North American 240 VAC 60 Hz split-phase standard, some say it is worse. It's a matter of which way you want your house fire to start: arcing connections or over-current on the wires?

bill von novak

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

I've got a cool little plug that I take with me camping that converts the 220 outlets they use for the big campers and motor homes and knocks the 220v 15amp line down to 110v 30 amps. What's funny is I use that little converter for one thing only. Running a fan in my tent at night.

Note - if it's a cool LITTLE plug then it's probably just a diode. So instead of getting 240 volts 100% of the time, you get 240 volts 50% of the time, and that usually averages to 120 volts. It works for most incandescent bulbs, heating appliances (old toasters) and universal motor devices like fans, but will cause problems for anything with a transformer or anything expecting to see a max of 120 volts AC.

Steven Lake

Re: Help! Friend thinks you can get 240v off 120v inverter!

No, it's actually 240 to 120v. I've tested it already. And I call it "little" but it's actually just as big as a standard 240v plug. I guess the "little" is more an expression of generality than an actual description of size.

niel

Re: Help! Friend thinks you can get 240v off 120v inverter!

bill is referring to a diode voltage doubler and i doubt you will get 1/2 current from this for power status quo. if it's more sizable it may be just a 2:1 transformer, but i'm unclear on its physical size. a 2:1 transformer will work in reverse too. even transformers will have some losses so it won't be power in = power out so the current will be less here also.

Ken Marsh

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

I've got a cool little plug that I take with me camping that converts the 220 outlets they use for the big campers and motor homes and knocks the 220v 15amp line down to 110v 30 amps. What's funny is I use that little converter for one thing only. Running a fan in my tent at night.

Bet what they are doing is taking one of the lines and connect it through to the 120 volt plug.
This will not double your current.

bill von novak

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

No, it's actually 240 to 120v. I've tested it already.

Now switch your meter to DC and see if you measure an 80 volt offset from the diode.

These "travel converters" are pretty common and are by far the cheapest way to get "120" volts from 240 volts. If you look at it with a scope it's half of a 240 volt sine wave. To get an actual 120 volts (i.e. a sine wave at 120 volts instead of 240 volts) you need a transformer, and those are a lot bigger and heavier. For more info here's a post from Electric Vehicle Discussion Board that describes them:
===========
Hi Folk's, those foriegn converters that cut the voltage in half are just a diode, take it apart and see, just knocks the bottom part of the sine wave off. Best regards,mark

---

Original Message

---

From: [hidden email] on behalf of EVDL Administrator
Sent: Fri 4/13/2012 12:50 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Buying an EV on the cheap to pour $ into a J1772 ability...

On 12 Apr 2012 at 16:58, EV Convert wrote:

> I can buy a wall wart size, 240VAC to 120VAC, 2000w(that's what it
> says!), voltage reducer for $20 to run the heaters. For inductive loads
> and loads with electronics, the converters are generally bigger and
> have a capacity of 50-85w. Price range: $20-50. These are travel units
> for reducing overseas voltages.

Virtually all travel converters are light duty devices, not intended for
continous use. In most cases their instructions have fine (or not-so-fine)
print defining their duty cycle. Usually it's on the order of 5-10 minutes
on, 20-30 minutes off.

I have found them to be pretty unreliable, too. I had one fail in the
middle of an overseas work assignment. Another (personal) unit abruptly
decided to reduce its output to the point where it was nearly unusable.

I doubt that travel converters will be suitable for any EV application.
================================

Steven Lake

Re: Help! Friend thinks you can get 240v off 120v inverter!

http://www.walmart.com/ip/Road-Power-15-30-Amp-RV-Power-Adapter/16817350

This is the one I was talking about. It plugs into a 240v connector at the campgrounds and converts it down to 120v for use in your tent, camper, etc. It's a handy little thing to have and has already paid for itself many times over.

jcheil

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

http://www.walmart.com/ip/Road-Power-15-30-Amp-RV-Power-Adapter/16817350

This is the one I was talking about. It plugs into a 240v connector at the campgrounds and converts it down to 120v for use in your tent, camper, etc. It's a handy little thing to have and has already paid for itself many times over.

That doesn't "convert" power. It simply takes one leg of the 240 and the neutral and gives you 120v via the NEMA 15 plug. The same way your house panel does it to give you 120v. And you will only be able to get 1/2 the current from it (15amps).

Cariboocoot

Re: Help! Friend thinks you can get 240v off 120v inverter!

Yes, note that it says it has a "30 Amp male end" and a "15 Amp female end"; there's no transformer inside this giving you 2X the current at 1/2 the Voltage. But it does have an LED to let you know it's active.

BB.

Re: Help! Friend thinks you can get 240v off 120v inverter!

Be very careful with these types of adapters... From what I can see, there is no fuse/breaker inside the plug assembly. This will give you 30 amps of 120 VAC rated current to the 15 amp receptacle--A very good way to light a camp fire if there is a short on your 120 VAC appliance.

I don't see how these are "UL Legal" to sell. The retailers (and mfg. if US based) are taking on some big liability issues.

-Bill

Cariboocoot

Re: Help! Friend thinks you can get 240v off 120v inverter!

It may have a non-replaceable fusable link inside it. Of course they wouldn't want to give you details like that.

bill von novak

Re: Help! Friend thinks you can get 240v off 120v inverter!

Steven Lake wrote: »

This is the one I was talking about. It plugs into a 240v connector at the campgrounds and converts it down to 120v for use in your tent, camper, etc.

I don't think it does that. From the picture, that converts an ANSI TT-30R outlet (125 volts 30 amps) to a NEMA 5-15R outlet (125 volts 15 amps.) The TT-30R does not have 240 volts available.

Here's a link to the description of that sort of outlet:

http://www.myrv.us/electric/Pg/30amp_Service.htm

From the above link: "Due to the appearance of the TT-30 plug, many people assume that it is to be wired for 240-volt, but this is a 120-volt device."

inetdog

Re: Help! Friend thinks you can get 240v off 120v inverter!

I just noticed in my local hardware store and even smaller adapter (less than 1/2" thick") that let you plug a 30A RV cord into a standard 15A (not even 20A) duplex receptacle.
Not as dangerous, but probably blows a lot of breakers.
Well, maybe dangerous in that a 15A receptacle can be wired into a 20A circuit as long as there are at least two receptacles on the circuit. So there is a window of overload possible.

jcheil

Re: Help! Friend thinks you can get 240v off 120v inverter!

inetdog wrote: »

I just noticed in my local hardware store and even smaller adapter (less than 1/2" thick") that let you plug a 30A RV cord into a standard 15A (not even 20A) duplex receptacle.
Not as dangerous, but probably blows a lot of breakers.
Well, maybe dangerous in that a 15A receptacle can be wired into a 20A circuit as long as there are at least two receptacles on the circuit. So there is a window of overload possible.

Yeah, my ex's ex used one of them in their old house, and got tired of the breaker tripping so the idiot put a 30a breaker in place of the 15a breaker in the house panel.
Doing a remodel years later (after he was an ex) I opened that wall and the insulation had melted off the wires to that outlet nearly all the way back to the house panel!

ggunn

Re: Help! Friend thinks you can get 240v off 120v inverter!

jcheil wrote: »

That doesn't "convert" power. It simply takes one leg of the 240 and the neutral and gives you 120v via the NEMA 15 plug. The same way your house panel does it to give you 120v. And you will only be able to get 1/2 the current from it (15amps).

It seems to me that it would give you the same amount of current. The same current at half the voltage is half the power, which seems reasonable to me.

Cariboocoot

Re: Help! Friend thinks you can get 240v off 120v inverter!

If you have a 240 VAC 30 Amp outlet and use one leg to ground to get 120 VAC the current rating is still 30 Amps. The trouble is as Bill pointed out; if it changes to a standard outlet you have that 30 Amp current potential on connectors and wiring meant for only 15 Amps. That is why there should be over-current protection built in to such an adapter. The same applies if you switch from the HD 30 Amp 120 VAC outlet depicted to the 15 Amp standard.

If you divide out a 240 VAC 30 Amp line properly to 120 VAC (as I've just explained to my neighbour who is doing this in an outbuilding) you would get four 15 Amp 120 VAC lines because you are dividing both the Voltage and current: 7200 Watts is 30 Amps @ 240 VAC or 15 Amps * 4 @ 120 VAC, each with its own 15 Amp breaker.

techntrek

Re: Help! Friend thinks you can get 240v off 120v inverter!

Camper expert here. Cariboocoot got it. As already mentioned it just taps one of the legs on the 240 volt outlet to get 120 volts. The safety issue is the 50 amps available on each leg is also available on the 30 amp outlet (usually the "hockey pucks" or "dog bones" go from 50 amp 240 to 30 amp 120, never heard of one that has a 15 amp 120 outlet on it... but you could use a 30 amp 120 to 15 amp 120 "hockey puck" on top of it to do it). There is a 30 amp breaker in the camper so the only potential problem is a short in the line between the power pole and the camper.