MPPT controller - voltage sensing without separate wires?

"but you want to stay inside the 45amps limit.

Not really
You want to stay within the WATT limit on th einput side for the operational voltage 12, 24, 36, or 48"

Argggh! But you said if you go close to the 45 the controller will heat up and you want to stay well below that limit. Now you don't care if you go over the 45?

I meant just use bigger panels at the same Voc to get more wattage as one choice.

mena661 wrote:

BFL13 wrote:
I have got myself all confused again. :(

What question are you trying to ask here? :@

I am trying to figure out how you can stay inside the 45a limit, the 150 Voc limit, and double the array wattage all at the same time by going from 12v to 24v batteries.

I haven't got a grasp on the ratio of controller size in amps and its Voc input limit if there is one, that the clever design allows all this, or if you hit one limit "too early" or what.

Don't controllers also have a wattage limit rating? ISTR some do.

BFL13 wrote:
150 Voc limit using panels with 35v Vmp and 42v Voc means 150/42 = 3 panels in series is the limit?

So to double the array wattage to 1200w and stay inside the 150 Voc you need to double the length and width of the three panels, because you can't use six of those others in series, but that doubles the amps, but you want to stay inside the 45amps limit

Or run another three-panel string in parallel but that doubles the amps, but you want to stay inside the 45amps limit.

I have got myself all confused again. :( They said 600w and 45a was the limit.

You just run series parallel if you hit max volts. 2 strings in parallel. Each string is 3 in series.

Jim

150 Voc limit using panels with 35v Vmp and 42v Voc means 150/42 = 3 panels in series is the limit?

Correct

So to double the array wattage to 1200w and stay inside the 150 Voc you need to double the length and width of the three panels, because you can't use six of those others in series

Not sure how you would increase the size of the panels..........???

Or run another three-panel string in parallel but that doubles the amps,

Now you have GOT IT
A series parallel combination of the panels to create the needed watts within the voltage limits. I do the very same thing with my four 20 Voc panels to increase the voltage thus reduce the current from the array to the controller

Volts times amps = Watts / raise either V or A and the watts increase

but you want to stay inside the 45amps limit.

Not really
You want to stay within the WATT limit on th einput side for the operational voltage 12, 24, 36, or 48

I have got myself all confused again.
It's all Good no worries

BFL13 wrote:
I have got myself all confused again. :(

What question are you trying to ask here? :@

150 Voc limit using panels with 35v Vmp and 42v Voc means 150/42 = 3 panels in series is the limit?

So to double the array wattage to 1200w and stay inside the 150 Voc you need to double the length and width of the three panels, because you can't use six of those others in series, but that doubles the amps, but you want to stay inside the 45amps limit

Or run another three-panel string in parallel but that doubles the amps, but you want to stay inside the 45amps limit.

I have got myself all confused again. :( They said 600w and 45a was the limit.

Listen to KJ! :)

Lost and now FOUND a good thing

Only thing most is not all of use will never use the 24, 36 or 48 volt battery bank. We are stuck with the traditional 12 Volt systems found in automobiles and our series parallel combination of 6 VDC batteries to make up the needed 12 VDC

"I am still stuck here. You jacked up the size of the array so it has more total Voc? so how can that 150v input limit still work?"

The size of the array has very little if any to do with it's Voc - remember earlier I could have several different 600 watt arrays all with different Voc values. Take a look at the manufacturers specification sheets for operation at 12 VDC and then at 24 VDC you will notice the array wattage doubles, Twice the operating voltage you need twice the wattage on the input to still obtain the rated output current of 45 amps. The max input before destruction is still valid and a specification that should be noted before purchase of the controller

I might have just seen it there for a minute!

I am using the same size battery bank in each case, but you are increasing it each time so it can still take the same amps at the higher voltage.

When you say 24v bank, you just forgot to say you need more batteries :) to keep accepting that 45amps. No, you said never mind battery acceptance rates, you are powering loads.

"..... everything is the same except the battery voltage is 48 as compared to 12 allowing the array max power (45 amp controller) to be (45 amps X 48 Volts = 2,160 watts) with the same max inout voltage limitation of 150 VDC – the controller will then be able to put 45 amps (it's 45 amp rating) into the 48 volt battery bank."

I am still stuck here. You jacked up the size of the array so it has more total Voc? so how can that 150v input limit still work?

" A 45 amp controller could have up to a (45amps X 24 volts = 1080 watt array) and then supply 45 amps to the 24 volt battery. "

But the 24v "battery" is half the AH of the 12v battery as when you have two 12s in series vs parallel, so it can only take half the amps.
which is where I got lost, but now I am found. :) You just need to double the number of 100AH batteries :)

You are making it harder than it really is
Input watts need to increase to keep output current the same as the battery bank increases in voltage. The increased battery bank voltage offers many many great advantages over our simple high current low voltage 12 volt systems.

Output current stays the same
45 amps into 12,24,36 or 48 volt battery banks
To make that happen you will need to increase the input side watts example for a (45 amp controller)
45 amps into a 12 v battery = Input side 600 watts
45 amps into a 24 volt battery = Input side 1,200 watts
45 amps into a 48 volt battery = Input side 2,400 watts

all the same percentanges hold true for 12 volt systems - 24 volt system double everything - 48 volt system 4 x everything, nothing magic or special here at all

Think WATTS

I remember many years ago at my office we had a UPS power system with a 48 VDC battery bank made up of over 60 each 2 Volt cells - I believe it was a 10KW sine wave inverter. Try that at 12 volt operation the wires would need to be 5" or more in diameter ..................

Sorry just noticed your last question the Voltage sense wire
It is needed no matter what voltage you are operating at if the system is large enough - Marc did a nice post outling the need for the sence lines at the different operating voltages