Updated 7 Dec--Not that this is picking a fight or anything :)I went with the story that you should have a big inverter for the big things and a small inverter for the small things for a few years, but then decided it was a scam. Now just have a big inverter for everything. That's after some "quality time" with my Trimetric over the years.For example, you can run the TV/DVD on a 300w or 3000w inverter, but you can't make popcorn for the movie with the 300w job. The Xantrex-made 3000w MSW inverter now fitted, pulls 0.5 amp in standby ( which is peanuts to me, but never mind that). I don't know how much more it pulls in amps to run a TV/DVD than a 300w inverter would, but let's say it is twice as much. Might even be the same as that 0.5 although that is bogus, since it is now a question of inverter efficiency curves when under load that counts which has nothing to do with their respective stand-by draws. Anyway let's go with 0.5 vs 0.25 to get started.So there you are after supper with DW watching a movie (10 amps say) and the furnace is on (7 amps say) and one light on (3 amps say)So there you are with 20 amps draw for a two- hour movie, never mind the furnace going on and off)So the difference is 20.5a vs 20.25a for two hours, or 41 AH vs 40.5 AH in the same time with the small inverter. This is a joke, right?Ok so after the movie, you turn off the inverter with its remote on/off switch so now there is no inverter draw at all, no matter how big or small the inverter is.Which is why after smartening up :) I no longer have two inverters, just one big one that does everything from charging phones to running a MW.

12thgenusa wrote:Welcome to the other side.Ok, so I am slow. I should get some points for getting there eventually. No? Oh well. :)

Who told you to put in two inverters in the fist place?

valhalla360 wrote:Who told you to put in two inverters in the fist place?That would be telling. So it would be wrong to say it was smk, who also told me a while ago it was ok to combine my 20 amp Vector with my then new 35 amp Vector and get 55 amps into the battery bank, which actually worked. Life has not been the same since!

valhalla360 wrote:Who told you to put in two inverters in the fist place?Many folks who are considered as "wise" on this and other RV forums HAVE mentioned the idea of a large and a small inverter..It has a lot to do with how much no load standby current draw an inverter has..One would think that a smaller inverter should have a much lower no load draw..BUT in reality the difference between a 300W and a 2000W inverter no load draw is not much more than a few Milliamps..I run ONE 1250W inverter to run my home fridge plus it can be used for a TV/DVD or what ever other 120V devices I wish to run..Works for me..

The Big and Small Inverter Scam UPDATE-Tested. | Good Sam Community

94 Replies

westend
Explorer
Dec 09, 2015
pnichols wrote:
westend wrote:
A user may get off with never a shock but it is one of the worst electrical connections possible.

You realize of course that tens of thousands of wells and water tanks all over the U.S. have 240V AC submerged pumps in them with the short pigtails from their pump motors connected via an UNDERWATER CONNECTION to the 10-4 power cable coming down to them. Ultra scary to me ... but done every day by the "professionals" and in complete agreement with the electrical codes. :h
Actually, I have a well that is wired similarly. How this relates to a "suicide cord" in an RV is beyond me.

You could get past using that cord by buying a transfer switch or using the shore power cord plugged into the inverter. I'm not here to tell you what to do, proceed at your own risk.
Salvo
Explorer
Dec 09, 2015
Probably more like 2.5A savings for a movie. The media player may have a 1/4A reduction when connected to battery.

That savings is 8 to 9% of my total usage over 24 hours. So it is significant.

I gather you don't use led lights. From your OP, that saving is insignificant to you.

BFL13 wrote:
So you save 1 amp (1.5 vs 2.5) so that's 2 AH less for a two hour movie.
wa8yxm
Explorer III
Dec 09, 2015
pnichols wrote:
pianotuna wrote:
Another issues is that folks with large inverters tend to run all the outlets.

FWIW, I made a male-to-male-plug cord

Also known as a Suicide cord, Please replace one of the ends with an outlet matching the plug on your RV and go that way instead.. please.. Much safer.
BFL13
Explorer II
Dec 09, 2015
I doubt the inverters come with adjustable high voltage shut down settings. I bet Mex knows of a gizmo you could put on the wires to the battery that would make the inverter "see" a lower voltage than the battery is really at. The gizmo would have to pass through really high amps though.
ewarnerusa
Nomad
Dec 09, 2015
My own troubleshooting has led me to "B" being the most likely answer. The big inverter doesn't like it when charging is occurring at 14.7ish volts or higher and gives a fault. Small inverter does not. Big inverter works fine once solar panels are disconnected and battery voltage falls back down to below 14.7ish volts and I cycle power to it.

Both inverters share a 0 gauge wiring connection to the batteries, no socket connections are used and inverters are located right next to each other. Voltage readings have been taken all over the place, including at the battery posts and at the large inverter DC input terminals.

Can a high voltage disconnect setpoint be adjusted?
BFL13
Explorer II
Dec 09, 2015
ewarnerusa wrote:
Both my inverters are bargain models. The big one faults out around 14.7 V even though the rating is up to 15V. The small one does fine at the high voltages. I'm just getting the performance I paid for with the big one and exceeding expectations with the small one.

If the big inverter is wired up close to the batts it will have less voltage drop than the small inverter in the Winegard socket.

If both have the same 15v inverter shut down setting, then when the batts are at 14.8, the small inverter might be "seeing" 15v and shut down while the big inverter might be seeing 14.9 and still be running.

In the case where the big inverter is shutting down at 14.7 when it should be 15, there might be "other reasons"
A. bad wiring connection so high voltage drop
B. badly built so the 15 really is set at 14.7
C. some mix-up in how the "14.7" value was measured--where and with what.
SoundGuy
Explorer
Dec 09, 2015
BFL13 wrote:
I agree that Phil should have kept his secret to himself. However Phil is not a newbie so he is safe and will not leave anything for a stranger to learn about the hard way.

As I was reading "Phil's secret" I kept thinking "Great, now someone with limited electrical knowledge will copy this idea not realizing that he's energizing his rig's entire 120 vac system, which in turn means that the male plug on the end of any main service cable that's hard wired into the rig will also be hot." :E As "captain of the RV" that may not be an issue for Phil but it sure can be dangerous for others who may not consider all the implications in using a suicide plug or adapter. I too have various personalized adapters intended for my own use but I sure wouldn't post details on a public forum. :R Hopefully any newbies or those with limited electrical knowledge following this thread will take note. ;)
ewarnerusa
Nomad
Dec 09, 2015
Both my inverters are bargain models. The big one faults out around 14.7 V even though the rating is up to 15V. The small one does fine at the high voltages. I'm just getting the performance I paid for with the big one and exceeding expectations with the small one.
Almot
Explorer III
Dec 09, 2015
ewarnerusa wrote:
Based on the info in this thread, it seems like my only reason to keep using the small one would be because the big one doesn't play well with the high charging voltage that my solar charge controller can provide.

High charging voltage of controller affects any inverter the same way. Or is there a tendency for small inverters to have higher shut-off voltage than big ones?
JiminDenver
Explorer II
Dec 09, 2015
Not all big inverters are so efficient. My PowerJack was a pig in stand by or running the TV/sat. There was a considerable savings using the 150w MSW inverter especially over night. Then again as mentioned, it meant minutes to the solar system.

Don't most inverters have their idle draw and efficiency in their specs?

Until we got the satellite we didn't need a inverter for TV/DVD. We used a Toshiba 15 inch TV/DVD combo that uses a 120v brick that puts out 12v or a 12v cord I made myself. It's rated for 65w, I can test that with the killawatt at 120v, see how many amps the 150w MSW inverter pulls running it vs running it direct on 12v. (this weekend)

Now this may not be all microwaves but when ours is just on, it pulls power charging something up. I found that out when we plugged the shore cord into a 500w inverter to run the TV and charge phones. I turned on the breaker to the microwave and set the clock only to have the power go out a few minutes later. Turned the breaker to the MW back off and reset the inverter and it never went out again. Now we don't have the microwave breaker on unless it's in use even with the big bank, etc.