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UPS system Answered

hello every one recently i found a 12v 9000mah battery in my stuff and decided to make sth with it and found out that a UPS system can be good. I want to make a system that can give me power for a short time while I am outdoors so the low amper wont be a problem but I want to make the system with lower cost and better quality so I found out that I had to choose an inverter(12 to 220) which I think a 100w one would work. But my problem is choosing the inverter these are my choices based on my research:

An inverter starter kit---------the cheapest

An inverter module(ones without box and fan which are small too)

Inverters that are used in cars(ones with a box and fan)----------the most expensive


Jack A Lopez

8 days ago

You have listed three objects, what you call your, "choices based on my research:"

An inverter starter kit---------the cheapest

An inverter module(ones without box and fan which are small too)

Inverters that are used in cars(ones with a box and fan)----------the most expensive

So why not buy all three? And you can do the testing, for to discover how well these work, with whatever load you want to try energizing.

I mean, it is difficult for the persons reading this forum to like, peer into a crystal ball, and prognosticate the future success (or failure), of the things you are building.

This task is made more difficult by the fact that your researched "choices" do not point to anything specific. Supposing you did find these objects for sale somewhere, on the internet, is there a reason why you have only described them vaguely, rather than just copying and pasting the links into your topic?

Also, did I mention some kinds of loads work better than others, when powered by an inverter?

Loads that just produce heat (e.g. soldering iron) or light (e.g. compact fluorescent bulb) usually work well with inverter produced AC power.

Audio equipment, like music players, or sound recorders, often do NOT work well with inverter produced power, because the inverter produces a lot of low frequency noise, e.g. 60 Hz plus harmonics of that (i.e. 120, 180, 240Hz, etc) and this noise finds its way into the audio of the music being played, or sound being recorded, and so forth.

Electronic guyJack A Lopez

Answer 7 days ago

Well buying all three items is expensive and I'd rather choose based on researxh but according to all of the current answers I think the low price starter kit inverter shouldnt be choosed. Now lets discuss the other two choices.

Jack A LopezElectronic guy

Answer 6 days ago

Ah! So there is a budget.

Because I was also going to suggest you get a car to go with that inverter of the kind , "that are used in cars..."

;-) Ha!

I dunno. Maybe the cheapest one is the best one?

Maybe there are also constraints about the physical size of the thing?

Especially if you plan on carrying this thing around in a backpack? Or a briefcase? A lunch box?

Actually, I think the weak link in this chain is the battery. You said it had capacity of 9000 mA*h = 9.0 A*h.

I can picture this thing supplying 1 ampere, for maybe 9 hours.

But I am not so sure about 10 amperes, for 0.9 hours (54 minutes), especially if it is a lead acid battery.

Maybe instead of a car, you could get a motorcycle?

It seems like it would be convenient to have something with an engine and a generator on it, for to recharge this battery, or to help push current though the inverter that goes with it.

Electronic guyJack A Lopez

Answer 5 days ago

Well I have a car and i can use it to recharge the battery but there is two problems if you want to charge this battery on car battery:
1-the standard voltage is 14.4 for charging
2-1 amp is the standard current
3-the car battery is like that!


6 days ago

Had another thought....
With a 9AH battery and assuming it is not a deep cycle type, you 4 hours of 100W inverter use.
And that is by neglecting all losses and assuming the battery provides the full 9AH before it reaches the cut off voltage for the inverter.
Realistically you are looking at around 2.5 to 3.5 hours depending on the battery type and efficiency of the inverter.
You have to keep in mind that normal batteries should not depleted below around 10.5V.
And even the deep cycle types struggle to provide a good lifespan if they are costantly drained below their limits.

Just to give you and idea:
In my old camping setup I had two deep cycle batteries with 40AH each.
Back then I thought that is plenty for a long weekend away from civilisation.
Since then I realised I neither really need a TV and DVD player, nor all sorts of stuff running on 240V just because it is convinient no to buy dedicated 12V replacements.
I still have the 250W inverter somewhere but no real use for it anymore.
And no, the all up 80AH are still not enough for my needs, but then again I rarely have the time to enjoy the great outdoors these days :(

Jack A Lopez

6 days ago

By the way, there are a few existing 'ibles documenting vaugely this kind of project, consisting of a battery in a box, sometimes with an inverter too, and perhaps you can find some inspiration by looking at these. I am not sure what are the best words to capture this idea, but I tried a Let's makesearch for,

"battery box with inverter"

And also,

"portable power"


10 days ago

My first question would be why you would need an inverter to begin with.
100W is not really something big for mains voltage.
It might be cheaper and way more efficient to aim for suitable 12V appliances instead.
And not everything actually works with a inverter of the dirt cheap kind.

Jack A LopezDownunder35m

Answer 9 days ago

I recall, a few years ago, examining one of these dirt cheap, less than 100 watt, power inverters, and discovering that it did not actually produce AC, but rather DC at around 150 volts.

The funny thing is, some loads might not care, in particular things like switching power converters, like for a phone charger, whose first stage is just a rectifier circuit, to convert the mains voltage to DC, at the peak mains voltage; i.e. the RMS voltage (110 or 220) multiplied by 2^(1/2) ~= 1.4142.

Downunder35mJack A Lopez

Answer 8 days ago

I know what you mean, I had a transmitter like that too.
Labeled "Purse Sine Wave" and just 150W.
First disappointment came with the arrival as then I could read the fineprint stating the 150W are peak power at 2% duty cycle.
No clue how to get a 2% duty cycle for any device but I guess it was meant for sending morse code with a 150W flood light.
100% duty was possible at 60W ROFL
But no matter the load, it made using things like a FM radio, CB radio or the good old Nokia 6130 pretty much useless.
Ha no proper test equippment at home back then and was not allowed to use the company stuff for private purposes, so took it to friend for examination.
Here is the list of highlights we found quickly:
The powder coated metal enclosure was just plastic with the weight coming from two rusty metal bars slotted into the housing.
No fuse, no thermistor no nothing in terms of inpur OR output protection.
The circuit board was a mess with extreme thin copper traces that were fully covered by solder to make up for the missing copper.
A bit further down the track we also discovered that the power handling was entirely done through PWM frequency control.
And it made no sense how it operated.
Under full 150W it started as square wave with about 60kHz but within seconds dropped to 20kHz and then up to over 180kHz.
The later repeated itself until the load was reduced.
And with just around 50W the frequency was all over the place, like a manually controlled petrol generator that has a blocked air filter - going up and down all the time.
For the output was another PWM circuit, rectifier first (what a waste).
Here we ended up with anything from 42 to 72Hz and again as a square wave but not as the advertised sine wave.

By the way: I noticed that some switchmode power supplies now struggle with inverters the produce a too high frequency and hand it over by interference.
Where I come from it is now recommended to buy properly rated devices for the use with an inverter.
If not rated then you should not use it as it might interfer with the inverter or the inverter interfers with the device.
A lot of this has to do with peak power usage.
If you take a modern smartphone charger with 20W as an example:
It only checks if the input voltage is present but not if the current is sufficient.
When you then connect a dead empty phone and the charger jumps to full power the inverter is slightly behind to provide the power required.
(If the inverter is quite small, like for camping use of the essentials).
As a result the charger jumps back to a lower charging current because it just won't get the juice required.
But then the inverter is back on full power, which is no longer needed.
"Oh, I can charge with full power , so lets do it!"
Inverter goes back to a lower mode and the charger fails again.
This toggling can cause overheating a failure if there no suffient protections included.
An inverter rated switchmode supply will always increase the output power slowly or have a suitable capacitor built in to deal with the inrush current until the inverter keeps up.
Had a small LCD TV that struggled like this.
Backlight comes on, TV goes off in an endless circle.
Only ended after I added a supercap on the 5V rail and some beefy electrolytes on the other voltage lines.

Damn, sometimes I really miss the good old tinker days where you still tried to figure out how everything works in detail.
Explains why a good inventor needs a sponsor or lucrative patents - he has no time for a real world job LOL

Electronic guyDownunder35m

Answer 9 days ago

I just want to make portable power supply and not a UPS because certainly, 100w is very low for a ups system according to this explanation which one do you recommend