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Really dificult question

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large_ghostman

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Ok normally I give all the info I can when asking a question, but as this relates to a certain project I cant say much! But I do need some advice, so if you can help without asking me too many (read any) questions, then great. If you cant help with limited info then thats ok I would rather not cheat and just try things out.

So the question.

I have any Voltage I like DC or AC upto around 70V to play with, the source is capable on its OWN of providing around 3A. I need 12-15V at around 10-12A. What is the best topology.

I have a BLDC dev board that takes 30V 2.5A supply and runs a 14V 10A motor, so from this I am assuming a few things. Not much to go on I know and I apologize, but much m,ore info and I cross from guidence into help and thats cheating. So if its possible to only offer a topology to use I would be grateful, I have been thinking about model train point 'motors' the solenoid ones that use a cap bank to fire a succession of points.

The dev board is H bridged but that may or may not matter (I dont need a H bridge), What is being fed the output dosnt matter but it might run at a frequency of 10KHz ish.

Thanks
LG
 
70v x 3A = 210W
15v x 12A = 180W
180/210 = 85% efficiency
That needs a good switching type supply.

30v x 2.5A = 75W
14v x 10A =140W
140/75 = 186% efficiency
Something is not right here. The over-unit guys would be delighted with this.

JimB
 
motor board.JPG
70v x 3A = 210W
15v x 12A = 180W
180/210 = 85% efficiency
That needs a good switching type supply.

30v x 2.5A = 75W
14v x 10A =140W
140/75 = 186% efficiency
Something is not right here. The over-unit guys would be delighted with this.

JimB
Your right! Give me a couple of hours so I can go dig the board back out and I will post a pic. I didnt run the numbers so there is two options.

1) Silicon Labs now own the HOLY GRAIL of all our power needs.

2) I have read a label wrong somewhere OR made some other mistake!!:confused:

Who would of thought Silicon Labs would come up with that!!!:joyful::joyful: (Well its better than option 2!)

EDIT

There is a pic of the board on my desktop!! So here it is :oops:.

my only defense is I gave the numbers from memory and before my glasses! I was sure it was 14V. At least I got the 4 right :D, I better check the PSU that powers it!! In the unlikely event I *may* have been myopically challenged when I read it the first time
 
The board isnt being used, so I could drop to 10A and 12V. I related it to the board for other reasons, but clearly I messed that up!
 
Ok something very wrong! here is the psu for the board, note the board isnt relevant to what i want to do as such. So I will ignore the board for now, but when I get a chance I am going to see whats going on with the board, I havnt ever measured it I took the labels at there word. Maybe its a max rating but I would expect it to say that??

psu.JPG


EDIT NVM I spotted the label! Didnt notice the input ;), and the output being related to the 100V input. I assume the output at my voltage is 24V and 10A.

The board isnt being used and I wasnt paying attention, sorry the board is a complete red herring and I am a myopic idiot!!

Best solution to the above pics is a marker pen on certain bits and declare silicon Labs geniuses!! Everyone agree? So Over unity does indeed exist and the photoshopped pics I do later will prove it :D
 
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The output is fixed at 12VDC @ 5A for any AC input of between 100VAC and 240VAC.
Then that makes no sense!

You can see the board, the board output is 24V 10A the way it would make sense is if the 12V 5A was related to the 100V input. Now I am going to have to waste time measuring it lol or it will drive me mad!
 
The output is fixed at 12VDC @ 5A for any AC input of between 100VAC and 240VAC.

Then that makes no sense!

You can see the board, the board output is 24V 10A the way it would make sense is if the 12V 5A was related to the 100V input. Now I am going to have to waste time measuring it lol or it will drive me mad!


Hi LG,

Taking the picture of the PSU in isolation and forgetting the apparent anomaly for the moment, tronitech is right. That power supply has a 12V 5A output regardless of the input voltage. The label is confusing, but that is nothing new. The lower information is for UL registration and would not necessarily make sense from an electrical theory point of view. That is certainly an off-line switch mode power supply typical of laptop PSUs. Its maximum output power is 12V * 5A= 60W and, assuming a typical conversion deficiency of 80%, would give a maximum input power of (100/80) * 60W= 75W.

In terms of the system a few measurements should sort the situation.

spec
 
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It needs UL and Japanese labels. Some areas of Japan has 100 V mains.

So 12*5 = 60 VA

It's 105 VA at 100V. So, you have a 60/105*100 or a 57% efficient power supply.

The supply can deliver 5A at 12 V. There will be a plot of efficiency vs load.

Efficiency at the max designed output is a good spec to start with. The no load Wattage would be another good spec to publish.
 
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It needs UL and Japanese labels. Some ares of Japan has 100 V mains.

So 12*5 = 60 VA

It's 105 VA at 100V. So, you have a 60/105*100 or a 57% efficient power supply.

Not necessarily true. The input voltage and current stated on labels are not necessarily concurrent and are not intended to be used to calculate efficiency. They are normally worst case values or other criteria.

There are a million and one things that would affect the instantaneous efficiency of a power supply of any type.
 
Not necessarily true. The input voltage and current stated on labels are not necessarily concurrent and are not intended to be used to calculate efficiency. They are normally worst case values or other criteria.

There are a million and one things that would affect the instantaneous efficiency of a power supply of any type.

Didn't I just say that:

The supply can deliver 5A at 12 V. There will be a plot of efficiency vs load. (means efficiency is all over the map)

Efficiency at the max designed output ( other criteria). is a good spec to start with. The no load Wattage ( other criteria) would be another good spec to publish .

Must be a full moon. Mom goes "I'm not eating..." and I missed the "until you make me dinner".

And your vitamins will cost you $5.25 for ninety 500 mg tablets at buy one get one free. No, she'd rather hear $10.49 for 90 tablets and buy one get one free. Then there's You'll get 180 tablets for $10.49 USD, The proverbial 6 in one and a half-dozen in the other.

The bigger problem is it's not worth arguing over.

Earlier we talked about something else she wanted if the price-coupon <=$9.00. It ended up being $10.00 and she said when I got home, she wanted it because \she din;t have any more.

Go figure?
 
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And CUI (The manufacturer of LG's supply) says: https://www.cui.com/catalog/resource/efficiency-standards-for-external-power-supplies.pdf

CUI said:
he internationally approved test method for determining efficiency has been published by the IEC as AS/NZS 4665
Part 1 and Part 2. The approach taken to establish an efficiency level is to measure the input and output power at 4
defined points: 25%, 50%, 75% and 100% of rated power output
. Data for all 4 points are separately reported as well
as an arithmetic average active efficiency across all 4 points
.
 
From my Philosophy class:

Proof that God exists.
If the grass is green then God exists.
The grass is green.
God exists. Q.E.D.
I have read a couple of philosophy books, also the Bible and Koran- they are way above my simple brain :happy:
 
I have read a couple of philosophy books, also the Bible and Koran- they are way above my simple brain :happy:
Do they mention switch mode psu's by any chance?
 
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