How to calculate current draw from a step up transformer

[JRH]

It was helpful had you understood the BASIC GCSE level physics!!

Read this - the BBC have written a page especially for you!!

http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/keeping_things_moving/transformers/revision/4/

P=IV is all that needed to be said...

 

4 is not the correct answer. It's not that simple. Not helpful.

 

I never said 4!!

Did you get your English A-level from the same place as your Physics A-level?? Cuz clearly your can't read or do physics haha

if you read back [mention]Joeman[/mention] I said 4. P=IV and IV= 4 in roman numerals. need to study Latin next

[Guest]

It was helpful had you understood the BASIC GCSE level physics!!

Read this - the BBC have written a page especially for you!!

http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/keeping_things_moving/transformers/revision/4/

P=IV is all that needed to be said...

 

4 is not the correct answer. It's not that simple. Not helpful.

 

I never said 4!!

Did you get your English A-level from the same place as your Physics A-level?? Cuz clearly your can't read or do physics haha

 

You said P=IV was all that was needed. In this case that gives 4 amps. But it'll draw more than 4 amps won't it.

[Guest]

Well thanks JRH for the correct answer.

Joeman and Mr Fro, trolling and pretending to know it all yet again, yet still coming up with the wrong answer

Thread done.

[JRH]

P=IV

IV=4

[Westbeef]

I couldn't have even began to attempt this, but I'm mechanical so that's my excuse

 

When i was doing my ONC many years ago we had to do electrical and mechanical engineering.

I got higher marks in the first year mechanical exams than the electrical (and i am supposed to be an electrical engineer)

 

I couldn't have even began to attempt this, but I'm mechanical so that's my excuse

 

Bollocks Beefy, this is year 1 stuff!

 

I know I know , my ONC was also Elec/Mech but that was 5 years ago now, and I've not touched it since . If I refreshed myself on the topic I might pick it up again, but it's all foreign to me again.

[Mr Fro]

Well thanks JRH for the correct answer.

Joeman and Mr Fro, trolling and pretending to know it all yet again, yet still coming up with the wrong answer

Thread done.

If you stomp all over someone else with your "knowledge" but then ask a very noddy question that should easily be within the scope of your apparent qualifications then you should expect a bit of a ribbing old son.

Oh, and I do know this stuff because I've just done it at uni - did quite well in fact:

I can dig out my A-level certs too if that'd make you feel better.

[Joeman]

P=IV

IV=4

 

Baloo can barely deal with the decimal system let alone Roman numerals!

[Guest]

Well thanks JRH for the correct answer.

Joeman and Mr Fro, trolling and pretending to know it all yet again, yet still coming up with the wrong answer

Thread done.

If you stomp all over someone else with your "knowledge" but then ask a very noddy question that should easily be within the scope of your apparent qualifications then you should expect a bit of a ribbing old son.

Oh, and I do know this stuff because I've just done it at uni - did quite well in fact:

IMAG0722.jpg

I can dig out my A-level certs too if that'd make you feel better.

 

If it's such a noddy question, please give me the EXACT answer of how many amps this charger will draw from the 12v battery.

I got a B in A level Physics about 25 years ago and haven't used it since BTW This is why I ask an expert and don't claim to know it all myself.

25 years ago, you were 9 years old, so I'd expect your memory to be a bit better than mine.

[Mr Fro]

If it's such a noddy question, please give me the EXACT answer of how many amps this charger will draw from the 12v battery.

 

[Westbeef]

Well thanks JRH for the correct answer.

Joeman and Mr Fro, trolling and pretending to know it all yet again, yet still coming up with the wrong answer

Thread done.

If you stomp all over someone else with your "knowledge" but then ask a very noddy question that should easily be within the scope of your apparent qualifications then you should expect a bit of a ribbing old son.

Oh, and I do know this stuff because I've just done it at uni - did quite well in fact:

IMAG0722.jpg

I can dig out my A-level certs too if that'd make you feel better.

 

Swot!

Well done mate, good effort that .

[Guest]

But how do I calculate how much current the battery charger will be drawing from the 12v battery?

 

Without knowing the efficiency of the unit, how long is a piece of string.

ball park figure depending on efficiency say 5 Amps best guess.

 

If it's such a noddy question, please give me the EXACT answer of how many amps this charger will draw from the 12v battery.

 

 

What? Just a laughing smiley?

Are you telling me that with your A level physics, you can't tell me the efficiency of the unit, and give me a formula that takes that efficiency into account, and allows me to calculate the exact draw?

I thought you said this was "very noddy" level 1 stuff?

Bear in mind what JRH has told us about step up transformers, AC and DC current. The formula you give me has to work for DC.

[RantMachine]

OOH

OOH

I missed my chance in the other thread because boring Hoggs McModface locked the thread before I clicked submit:

I argue on the internet ALL THE TIME

[Westbeef]

The real question is, how much current will leak from this transformer when nothing plugged in to the output?

[Guest]

The real question is, how much current will leak from this transformer when nothing plugged in to the output?

 

Now, I said we weren't getting into that one, when not in use I will unplug it

[Mr Fro]

What? Just a laughing smiley?

Are you telling me that with your A level physics, you can't tell me the efficiency of the unit, and give me a formula that takes that efficiency into account, and allows me to calculate the exact draw?

I thought you said this was noddy level 1 stuff?

 

Sorry, I thought you were on a wind up!

From your original figures, the efficiency would be 100% (obvs).

Wind back a couple of pages to the equation Joeman and JRH gave and stick eta in there, rearrange and insert the actual input/output values. That will allow you to calculate the efficiency of the unit.

You can then account for the characteristics of the components pre and post the unit and calculate the absolute current draw. This value will only be applicable for a specific environment so if you change temperature for example, the calculated value will change a bit.

I reckon it'll be between 4 and 5 though. You like 5 so we'll go with that.

[Guest]

What? Just a laughing smiley?

Are you telling me that with your A level physics, you can't tell me the efficiency of the unit, and give me a formula that takes that efficiency into account, and allows me to calculate the exact draw?

I thought you said this was noddy level 1 stuff?

 

Sorry, I thought you were on a wind up!

From your original figures, the efficiency would be 100% (obvs).

Wind back a couple of pages to the equation Joeman and JRH gave and stick eta in there, rearrange and insert the actual input/output values. That will allow you to calculate the efficiency of the unit.

You can then account for the characteristics of the components pre and post the unit and calculate the absolute current draw. This value will only be applicable for a specific environment so if you change temperature for example, the calculated value will change a bit.

I reckon it'll be between 4 and 5 though. You like 5 so we'll go with that.

 

Thank you for that. I don't have the knowledge to say whether it's right or wrong, I'll leave that to JRH, but thanks for a sensible answer to the question asked.

Seems like there are all sorts of variables though, components, input values which I don't have and can't find (or I wouldn't have needed to ask the question because the manufacturer would already have told me the answer), environmental variables like temperature.

I guess "noddy" is relative depending on your knowledge, but it doesn't seem all that noddy to me, and I had no idea when I asked the question whether the efficiency would result in 4,5,6,7 amps. I had no idea how efficient these units were and I couldn't find the answer from the manufacturer, hence asking for help.

Edited July 13, 2017 by Anonymous

[RantMachine]

I guess "noddy" is relative depending on your knowledge, but it doesn't seem all that noddy to me.

You're not alone - I just turn on the spot and walk out when people talk about electrical stuff

[Guest]

Anyway, we don't really know exactly, but everyone thinks it's not sigificantly more than the 4 amps a simple calculation would give you. Thanks those that helped.

5 amps allows me to estimate how long a 95AH leisure battery would last and how many charges I could run off it.

 

Thread done.

[Joeman]

So what fuse are you putting in....

[JRH]

6 inch nail works for me

[Hoggs]

[ boring_modding ] Well that was predictable. Everyone play nice or there will be no afternoon break cookies for you all. [/ boring_modding]

carry on

[JRH]

Can i have fruit scones with currents in please.

[Mr Fro]

Anyway, we don't really know exactly, but everyone thinks it's not sigificantly more than the 4 amps a simple calculation would give you. Thanks those that helped.

5 amps allows me to estimate how long a 95AH leisure battery would last and how many charges I could run off it.

 

Yeah, assuming 5A will probably give you a reasonable safety margin. You won't really know the draw until you get a unit and measure it.

[Glorian]

OOH

OOH

I missed my chance in the other thread because boring Hoggs McModface locked the thread before I clicked submit:

I argue on the internet ALL THE TIME

 

NO MAY MAYS