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Old 10-06-2015, 03:24 PM   #1
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32" TV, 300W inverter- not working?

Long story shortest, I bought/came into possession of a 300 watt modified sine wave inverter. I used it last night to run my CPAP machine and it did that well.

Today at lunch, I thought I'd hook it up to my TV and Roku and we'd watch some TV. The Roku is tiny and powered up just fine. However, the TV would go into standby mode and when it went to actually click on, it would just go black.

Is this a product of the inverter being too small? (The back of it says for TVs up to 27".) Or is the problem that it is a modified sine wave inverter (vs pure sine wave)?

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Old 10-06-2015, 06:27 PM   #2
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My guess is the modified sine wave. They make for some really "dirty" AC. Some appliances do ok with them, some don't. 300W should be enough power for the TV, but that is probably "peak". The rating and the modified wave may be a bit too much to handle...
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Old 10-06-2015, 07:12 PM   #3
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for sure the inverter is not producing enough power for the TV

Harbor Freight sells a 750 watt continuous for $42


the modified sine wave should only be a problem for motors which perform best with a full sine wave...
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Old 10-06-2015, 09:15 PM   #4
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Most motors typically do fine on modified sine waves. (They can often run a bit warmer.) More complex circuits with internal power supplies (like TV's, Stereos and SOME PC's are the ones that have problems.

Inductive loads and not much of a challenge, and in fact, a modified sine wave inverter is more efficient in those applications.

Fact sheet: Pure sine wave VS modified sine wave | eBay
"Only basic products such as normal lights bulbs and induction or shunt motors can safely be run on a modified sine wave."
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Old 10-06-2015, 09:57 PM   #5
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as always you can find stuff on the internet to support most anything...

I contend that electronic products, that typically run off 5 to 18 VDC ( check the output VDC of that transformer you plug into your wall socket for the output voltage) get that voltage off rectifier circuits that convert any type of AC into DC... modified or pure sine waves make no difference, and electronic items like TV's and radios and even laptops do not care how the DC is being made.

Power drills and saws and other VAC powered motors will not get full power from a modified sine wave inverter which is the reason that they run warmer, and at reduced output power, but they will run.

Modified Sine Wave Inverter

Quote:
Devices That Will Typically Work Fine with a Modified Sine Wave Inverter

The list of electronics that usually work just fine with a modified sine wave is far too long to get into here. Suffice it to say that if it doesnít use an AC motor, and it isnít a delicate piece of medical equipment, youíre probably going to be in the clear.

It is worth mentioning that if the device that you want to power uses a rectifier to change the AC into DC, itís extremely unlikely that youíll have any issues. That means your laptop is going to be fine, although you might be better off (from an efficiency standpoint) getting a 12v adapter and not going through the inverter at all.
The point is that the OP has too small of an inverter for his usage. No matter what inverter type he may purchase, he needs something that can supply more watts, not that he has the wrong kind of inverter for his application of powering a TV.
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Old 10-06-2015, 10:30 PM   #6
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I have seen quite a few complaints about cheap inverters not being able to supply their rated output. If you can attach a total of about 250 watts of lighting load (example: two 100 watt and one 60 watt bulbs in table lamps, drop lights, etc.) you can confirm if the inverter is in fact putting out enough by comparing the brightness on inverter vs. being plugged into a wall outlet.

Make sure that you are supplying a full 12 volts minimum at input to the inveretr when it is under load. You must use a voltmeter for this.
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Old 10-07-2015, 09:20 AM   #7
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Quote:
Originally Posted by rsdata View Post
as always you can find stuff on the internet to support most anything...
I referenced that one since it was easy and reputable. However you can also do a search and find several white papers from .edu etc. sites giving you the same info. I assume you would trust them?

My other options were to cite from authority. (I am an EE), or explain the theory in more detail. (I will do that)

Quote:
I contend that electronic products, that typically run off 5 to 18 VDC ( check the output VDC of that transformer you plug into your wall socket for the output voltage) get that voltage off rectifier circuits that convert any type of AC into DC... modified or pure sine waves make no difference, and electronic items like TV's and radios and even laptops do not care how the DC is being made.
When designing front end power supplies and filtering, most all consumer electronics assume a 110/120 RMS 60hz Sign wave supply. These front end capacitance and inductance values are NOT specifically designed for simple or complex square waves. Those type of waves not only create multiple harmonics, but harmonics well up into the RF range which can hinder performance in many other internal circuits beyond the power supply. That is why I stated that the lack of sine wave is likely the problem.

Purely inductive devices like most motors, don't care, as long as the supply is near 60hz/ 110 V. AND.. as a matter of fact in combination with a modified sign wave are MORE efficient. (It takes much less overhead to develop a modified sign wave, and the inductive load filters out much of the "dirt" and the motor doesn't care about harmonics.) Note: There are some non-purely inductive motors that also don't like modified waves.

Quote:
The point is that the OP has too small of an inverter for his usage. No matter what inverter type he may purchase, he needs something that can supply more watts, not that he has the wrong kind of inverter for his application of powering a TV.
Actually probably NOT. His inverter states it will run up to a 27" TV. If it truly is a 300W unit that it claims to be, it is most certainly talking about a CRT TV. (typical use in the 150W area) The original poster did not have a CRT, TV, so assuming LED or LCD, its demand is 60 to 75W max. So, we are not asking much of the inverter power wise. Even if his inverters rating is only 150W capable, it should have no problem with the LCD/LED TV.

It is far more likely the issue is the modified sign wave. But note, I said: "The rating AND the modified wave may be a bit too much to handle...

Back to the "citing from authority" I have designed many power supplies and other circuits and stand by the above.

Hope that helps..
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Old 10-07-2015, 02:45 PM   #8
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Quote:
Originally Posted by ependydad View Post
Long story shortest, I bought/came into possession of a 300 watt modified sine wave inverter. I used it last night to run my CPAP machine and it did that well.

Today at lunch, I thought I'd hook it up to my TV and Roku and we'd watch some TV. The Roku is tiny and powered up just fine. However, the TV would go into standby mode and when it went to actually click on, it would just go black.

Is this a product of the inverter being too small? (The back of it says for TVs up to 27".) Or is the problem that it is a modified sine wave inverter (vs pure sine wave)?

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My guess would be your tv needs a full sign wave inverter. Without getting into a discussion about electronics I have read on more than one occasion about others having problems with different manufactures not working on a modified sign wave. One members tv in bedroom worked fine but the LR one, a different make, wouldn't run. Bought a full wave inverter and had no problems with anything after.

I have a 750 watt HF inverter I keep in my truck and it is fine for what I use it for such as charging my boats 12 volt battery for trolling motor. For the trailer I invested in this full sign wave inverter. Only a 1000 watts but that is all I really need.

http://www.amazon.com/dp/B000WGNNUQ

I love the remote control feature!

Jim
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Old 10-08-2015, 08:40 AM   #9
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Here is a couple ideas. Is your TV LED? Did you check the watts for what it is supposed to need (Tag on back)? Did you try switching inputs on the remote? It could be running fine. The screen will be blank on HDMI input,etc,
Unless you run straight from the battery with the right size cable any inverter will choke and not deliver the rated output if you exceed what the wire can handle.
Good luck!
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Old 10-08-2015, 08:53 AM   #10
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Quote:
Originally Posted by Grn_Mtns View Post
Here is a couple ideas. Is your TV LED? Did you check the watts for what it is supposed to need (Tag on back)? Did you try switching inputs on the remote? It could be running fine. The screen will be blank on HDMI input,etc,
Unless you run straight from the battery with the right size cable any inverter will choke and not deliver the rated output if you exceed what the wire can handle.
Good luck!

Thanks Green Mountains... It was definitely a case of it going off vs. being on the wrong inputs. It works well when on shore power. It was this random "hey, I have an inverter and time to kill while my wife buys groceries" time on the cheapo inverter.

I think ultimately what I'm going to do is buy a bigger PSW inverter and install it- solving either/both problems. I just don't know when- I really just don't boondocks all that much.
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