real current needs calculation

[Jambonjoebob]

Hi!

I want to upgrade my solar system and before I do I want to calculate my real current needs. For most of my equipments (fridge, lights, etc.) I'm ok, but there is something I'm not sure of. My television has an input current at 110v and obviously a different output current at another voltage. I don't remember the real numbers and I'm not at my cabin right now. Witch one should I use to calculate AMPS for my amp hour total calculation (the input current or the output current?). When I turn the TV on, the Inverter meter shows under 50W but doesn't show the real number when it's under 50w. Let's say I'm doing a test and plug few things until it goes to 100W and then I turn on the tv. Let's say it goes to 120W, tv consomption should be 20W. Is it 20 W at 120 volts or at 24 volts (I have an inverter for my 24 volts battery kit). It's a 5:1 difference...

Thanks!

[SunEagle]

Well 20W at 120v is only about 0.2 amps which is pretty low. 20w at 24V is less than 1 amp so still pretty low.

Have you tried a Kill A Watt meter yet. That will provide you the watts and amps at the input voltage which should be around 115V AC.

[checkthisout]

Hi!

I want to upgrade my solar system and before I do I want to calculate my real current needs. For most of my equipments (fridge, lights, etc.) I'm ok, but there is something I'm not sure of. My television has an input current at 110v and obviously a different output current at another voltage. I don't remember the real numbers and I'm not at my cabin right now. Witch one should I use to calculate AMPS for my amp hour total calculation (the input current or the output current?). When I turn the TV on, the Inverter meter shows under 50W but doesn't show the real number when it's under 50w. Let's say I'm doing a test and plug few things until it goes to 100W and then I turn on the tv. Let's say it goes to 120W, tv consomption should be 20W. Is it 20 W at 120 volts or at 24 volts (I have an inverter for my 24 volts battery kit). It's a 5:1 difference...

Thanks!

You are confused. Wattage is Wattage regardless of voltage. Wattage is calculated by multiplying volts and amps.

Are you trying to figure out how many amps it's going to draw from the battery?

1 amp @ 24 Volts is 24 watts. Your tv is drawing less than 1 amp from your batteries.

[Jambonjoebob]

I have two questions.

#1-

I guess I'm not clear enough. I'll illustrate my question with an example from an other transformer I have with me right now. If you look at the image, input is 100-120 v AC with 0,7 amps. It's 70-84 w. Output is 12V DC 2A (24 w). There's a loss of around 50 W (Heat I guess). Let's say I use it on my system. What is drawn from the batteries? I have 4 x 6V batteries 430 ah connected to 120v inverter.

Few options: (not taking into consideration the lost during voltage conversions)

1 - input current : 0,7 A (don't think so)
2 - output current : 2 A (don't think so)
3 - input power (70-84 W) / 24 V = around 3 to 3-5 Amps (My guess)
4 - output power (24 w) / 24 V = 1 amp (Would love that but I don't think so!)

#2 -

If the inverter meter shows 120 W (for example), it's 120 W at 120 V. So it should also be 120 W taken from the batteries. 120 W / 24 V = 5 Amp. am I right?

Picture for question #1.

IMG_3625 Medium.jpeg

Thanks for your answers.

[checkthisout]

I have two questions.

#1-

I guess I'm not clear enough. I'll illustrate my question with an example from an other transformer I have with me right now. If you look at the image, input is 100-120 v AC with 0,7 amps. It's 70-84 w. Output is 12V DC 2A (24 w). There's a loss of around 50 W (Heat I guess). Let's say I use it on my system. What is drawn from the batteries? I have 4 x 6V batteries 430 ah connected to 120v inverter.

Few options: (not taking into consideration the lost during voltage conversions)

1 - input current : 0,7 A (don't think so)
2 - output current : 2 A (don't think so)
3 - input power (70-84 W) / 24 V = around 3 to 3-5 Amps (My guess)
4 - output power (24 w) / 24 V = 1 amp (Would love that but I don't think so!)

The best answer was given by someone else earlier. You need to measure the actual wattage draw at the input side with a kill-a-watt meter or a Fluke or whatever. There is no set universal standard there in regards to what those numbers mean or whether they even bother making them correct.

If the inverter meter shows 120 W (for example), it's 120 W at 120 V. So it should also be 120 W taken from the batteries. 120 W / 24 V = 5 Amp. am I right?

Picture for question #1.

IMG_3625 Medium.jpeg

Thanks for your answers.

In theory but you're asking a specific question about your specific inverter and it's efficiency without telling us the make and model of inverter. There is no rule and efficiency varies widely across makes and models and at differing power ouput levels.

Your inverter probably consumes 50 watts at idle so a 10 watt load is drawing 60 watts from the batteries. If your owners manual doesn't provide any efficiency data then the only way to measure the amps on the input side and see.

[checkthisout]

I think after re-reading and reading some more and re-interpreting your question.

In your picture shown above, I would use the output numbers (24 watts) for my calculation.

*USUALLY* The 70 watts indicated on the input side takes into account the in-rush current when the device is plugged-in/turned on. It's not indicating what the constant current draw of the device actually is.

So in your above example, the device it's powering (say a laptop or TV) is 24 watts and will draw 24 watts if hooked directly to a 12V DC power source (like a battery) and probably have an in-rush current when first powered up of like 60 watts for a split second.

[Jambonjoebob]

I didn't know the existence of a kill-a-watt meter. I'm ordering one right now and I'll confirm the real drawing. By the way, inverter is a tundra s2524 with a 99% efficiency.

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