System losses

[Bala]

Just want to try clarify system losses in my head for a stand alone system,

I have PWM controllers,

At times they will show AMPS of close to panel specs,

So is this what the panels are sending to the controller, and if there was an ammeter after the controller it would show that the batteries are not receiving all that the controllers are?

[Sunking]

Yeah that is the problem with PWM controllers they are linear series regulators where INPUT CURRENT = OUTPUT CURRENT which makes them at best 70% efficient. In reality only 50% at very best with very careful design and equipment selection. So when you use PWM controllers your system efficiency is less than 50% from cradle to grave. Which means for every watt hour you consume, your panels need to generate more than 2 watt hours.

[Bala]

You say that input current = output current,

but is it not really that output is 50% of input?,

so if my reg says 50amps i am only getting 25 at the battery,

thats what i am trying to get my head around, I accept that I have the losses, I am not disputing that, I am trying to understand what the meter on the controller tells me and what is getting to the battery.

[Sunking]

You say that input current = output current,

but is it not really that output is 50% of input?,

No this is where your understanding of electricity fails. If you have 50 amps input to a PWM controller is outputs 50 amps. That is what the formula INPUT CURRENT = OUTPUT CURRENT means. It is a TRUE statement of facts.

Now think about that a while. After you strain your brain read this

[Bala]

I am running a mechanical workshop on a remote island in the solomon sea, with all local island labour, trying to get parts organised that need to come via a couple of barges and air craft, i only have internet and skye, no land line phones, the gear is all very run down,

I have more than enough to strain my brain, I know I could read and work it out, i was hoping someone would just tell me

I will look at the link tonight, I really should concentrate on my job at the moment

cheers

[Sunking]

I have more than enough to strain my brain, I know I could read and work it out, i was hoping someone would just tell me

Bala the answer requires just as much reading and thought as me telling you right now. Difference is if you figure it out on your own you will understand and never forget. Here it is in math, figure it out .

PWM Controller

Controller input = 17 volts @ 5.88 amps = 100 watts
Controller output = 12 volts @ 5.88 amps = 70 watts

Same panel using a MPPT controller

Controller input = 17 volts @ 5.88 amps = 100 watts
Controller output = 12 volts @ 7.91 amps = 95 watts

Now figure out what happened.

[Bala]

I know I should be doing my work!!

this is where your understanding of electricity fails

this quote from you is the key and i dont dispute it,

i have always measured power in amps, so amps in = amps out to me would mean no loss, but it would appear that Watts are power and I dont know squat!.

To me it would appear that an MMPT is making power, as there are more amps going out than coming in, but i do know that we cant make electricity like that.

I will have to do some more research and increase my understanding of w,v, a

[Naptown]

Always think in WATTS
1Amp at 120V =120Watts
10Amp at 12V=120Watts

[Sunking]

i have always measured power in amps, so amps in = amps out to me would mean no loss, but it would appear that Watts are power and I dont know squat!

well that is far from the truth. I can generate 1000 amps and the power is 0.

When it comes to electric power it is expressed as Watts and/or Power

Watts = Voltage x Amps.

So if I have 1000 amps flowing and no voltage, I have no power, just amps. 1000 amps x 0 volts = 0 watts.

[Sunking]

To me it would appear that an MMPT is making power, as there are more amps going out than coming in, but i do know that we cant make electricity like that.

No it does make power, it just looses less power than PWM. Use this formula Power = Volts x Amps, then go back to the example and work the math out.

Controller input = 17 volts @ 5.88 amps = 100 watts
Controller output = 12 volts @ 7.91 amps = 95 watts

100 watts are going in, and 95 are coming out a loss of 5%

[Bala]

PWM Controller

Controller input = 17 volts @ 5.88 amps = 100 watts
Controller output = 12 volts @ 5.88 amps = 70 watts

Same panel using a MPPT controller

Controller input = 17 volts @ 5.88 amps = 100 watts
Controller output = 12 volts @ 7.91 amps = 95 watts

Ok, i still dont get it, remember I am a mechanic not an electrical engineer, everything is easy once you know how, and i have just come back to work after my two week break and as usual its all gone pear shaped, bla bla bla

lets pretend I look at my panel specs and it tells me that it is 5.88A 17V so i can work W = V x A so 17 x 5.88 = 100, I have a 100w panel. I go to my charge controller and the AMP reading is 5.88. , I can then use the battery voltage and W = V x A so 12 x 5.88 = 70, so i am only getting 70w to my battery, I get that, my mind still wants to look at the amps, but I must not and I must focus on the watts figure.

Hope I got that correct? To me it makes sense and i can see how PWM losses occur, I can work it out off the amp reading on the PWM controller and my known system voltage

Now if that is correct, what I now need to understand is where the 7.91 amps from the MPPT comes from,

I know the panel is W = V x A so 17 x 5.88 = 100, that is going to the controller, where do I find the 7.91A figure to use in the equation, W = V x A, or is it just a known fact that the MPPT is 95% efficient so we can do the equation by W / V = A so 95 / 12 = 7.91

did i get any where?

This is the edit, i have just gone back to Sunkings controller explanation page, now I am focussing on watts instead of amps i
spotted MPPT input power = output power

INPUT CURRENT does not = OUTPUT CURRENT, and INPUT POWER = OUTPUT POWER – CONVERSION LOSSES

So following on from above we have a known W output from the controller of 100W as we know that for MPPT W in = W out.


Now because the controller manual told us the unit is 95% efficient??, and we know W / V = A we can do the following,

100 / 12 = 8.33 x 95% = 7.91A to follow on 7.91 x 12 = 95W to the battery

It adds up but do I really get it?

[Sunking]

Bala what is getting by you is an MPPT controller is a Switch mode true DC - to - DC converter. You work with power and voltage, not amps directly.

Let's break it down with the 100 watt panel at the input 100 watts = 17 volts x 5.88 going into the controller. OK ?

Think of the inside the MPPT controller is like a transmission with a transfer gear ratio of torque. It takes that 100 watts on th einput, and changes it to match the battery voltage minus a small bit of power to do the work. So at the output is 95 watts @ 12 volts. That means the current = 95 watts / 12 volts = 7.91 amps

[Bala]

minus a small bit of power to do the work

All I believe I dont know is how you come up with the figure of 5watts being the small bit required to do the work,

thus reducing the out put form 100w to 95w

[Naptown]

All I believe I dont know is how you come up with the figure of 5watts being the small bit required to do the work,

thus reducing the out put form 100w to 95w

Conversion losses run abut 5% which is where the 5W comes from.

[Bala]

Conversion losses run abut 5% which is where the 5W comes from

.

thats what i said at the bottom of my other post,

So I do believe I now do get it?