Power in = Power out

**Sunking** · 05-19-2015, 04:37 PM

Originally posted by mj52

Hi,

Does an MPPT CC knock the V down which in turn kicks the A up?

One 100W panel Vmp =18.9V and Imp = 5.29A

Does the MPPT knock the V down to 12V which kicks the A up to 8.33A?

Yes minus conversion losses of about 2 to 5% if it is a real MPPT controller.

PWM controllers are series voltage regulators. Current In = Current Out.

MPPT Controllers are DC Power Converters. They act kind of like an AC Transformer. Output Current = Panel Wattage / Battery Voltage

You want your charge current top be between C/8 and C/12. 33 amps on a 300 AH battery is roughly C/10, or the perfect charge current. If that makes you unconformable throw away a panel or two.

However none of that means you have enough panel wattage or batteries. Your system panel wattage and batteries are sized correctly for each other. You batteries can supply up to 1 Kwh per day. But no one knows if you use that much or more, or if your location can even generate that much power year round.

Lastly it is plain silly to have your panels in parallel with a MPPT charger. You loose the benefits of high voltage and simple series circuit

**Wy_White_Wolf** · 05-19-2015, 04:40 PM

Originally posted by mj52

hi,

does an mppt cc knock the v down which in turn kicks the a up? that's the idea

one 100w panel vmp =18.9v and imp = 5.29a

does the mppt knock the v down to 12v which kicks the a up to 8.33a? close, actuall charging voltage will be a litte different depending on the SOC of the batteries. Usually somewhere between about 12.5v and the kick off point of the charge controller

the reason i ask is i don't want to overcharge my wet cell batteries

4 100w panels in parallel produce vmp of 18.9v and an imp of 21.16a (4 x 5.29a= 21.16a) or 400w question: With an mppt controller why do you have the panels parralleled? In series the higher voltage would mean less line loss and/or smaller wires could be used. Also 4 panels should have a combiner box with each panel fused. In series that wouldn't be used.

if the cc knocks the v down to 12v would the a be kicked up to 33.3a? To make 400w see above. 14.5v would also be 27.5amps

the bank consists of 2 150ah in parallel or a 300ah 12v battery. 33.3 amps into a 300ah battery band is about as close to ideal as you can get. I don't see you worry. Charge rate should be between c/8 and c/12 with c/10 being ideal. That would be 37.5 and 25 amps. Both the 33.3 and 27.5 split that c?10 pretty good.

i thought i was starting to get a toe hold but maybe i'm not.

Thanks, mike

www

**Bucho** · 05-19-2015, 07:23 PM

Originally posted by mj52

Does an MPPT CC knock the V down which in turn kicks the A up?

Thing is MPPT quickly looses that advantage after your battery bank's 80% full.

You know how you're battery bank's typically supposed to only get down to 80%.....so.....yeah.....

**mj52** · 05-19-2015, 07:33 PM

Thank you both, WWW and SK,

What are the benefits of serial connections regarding the 4 100W panels. Other than lighter guage wire?

4 panels wired in SERIES...... ea 5.29A @ 18.9V = 5.29A @ 75.6V = 400W
4 panels wired in PARALLEL.. ea 5.29A @ 18.9V = 21.2A @ 18.9V = 400W

Physically the only difference would be SERIES would have no 2 to 1 couplers (parallel uses 4) and 20' less 10 AWG PV wire.

I built this as 2 groups of 2 panels. Each "Group" weighs 38 lbs and is 48" x 48". Making it much easier for one guy to move around.

So each "Group" carries 10.6A @ 18.9V over it's own 10' span of #10 AWG PV wire. Even the 10' length of PV wire is there to give me a little wiggle room. I hate Banjo Strings.

I only describe my setup in case you want to visualize what I've done and why i used 4 - 2 to 1s and 20' extra PV wire.

It's all plug and play so I could certainly wire my panels in SERIES.

Could you explain the benefit to SERIES because I don't get it yet.

Respectfully, Mike

**sensij** · 05-19-2015, 07:45 PM

Wiring those panels in parallel without fuses is a safety risk. Fuses would be another source of efficiency loss, if you were using them as you should.

**Sunking** · 05-20-2015, 12:22 AM

Originally posted by mj52

Thank you both, WWW and SK,

What are the benefits of serial connections regarding the 4 100W panels. Other than lighter guage wire?

1. No combiners
2. No fuses.
3. Higher Efficiency
4. Much smaller wiring and less of it like 75% less.
5. Saves Big Buck$

Need any more reasons?

**mj52** · 05-20-2015, 08:34 AM

SK,

Very well said.

No combiners.... I like that
No fuses..... I really like that
Much smaller wire....I understand that
Much less wire.... I think you're referring to lbs/ft run

Much more efficient...... I'm stumped so I went back to a water system analogy.

A bucket of water thrown on a dirty car just gets things wet. Little V but Big A
Same water through a garden hose nozzle. Big V and Little A
Garden hose is more efficient

Within this system where is this added efficiency most effective, manufacturing (panels), transmission (wiring), modification (CC), storage (battery)? I imagine scale is also a factor.

But if all I have to do is rewire 4 panels and see a measurable gain, this is something I can do.

Thanks, Mike

**Bucho** · 05-20-2015, 10:02 AM

Originally posted by mj52

SK,
But if all I have to do is rewire 4 panels and see a measurable gain, this is something I can do.

Having a higher voltage lower amperage let's you reduce voltage drop.

Here's a voltage drop calculator so you can see what I'm talking about: http://www.calculator.net/voltage-dr...21.16&x=56&y=7

So right now 12v-14.4v at 4 x your Imp gives you a power loss over 10ft of 10AWG do to voltage drop of 3.5%-2.92%

If you wired things in series 4 x vmp at your Imp gives you a voltage drop of 0.15%

So there is a gain but when you look at the size of your system *shrug* it's not a big gain in terms of watts.

**Sunking** · 05-20-2015, 10:26 AM

Originally posted by mj52

Much more efficient...... I'm stumped so I went back to a water system analogy.

A bucket of water thrown on a dirty car just gets things wet. Little V but Big A
Same water through a garden hose nozzle. Big V and Little A
Garden hose is more efficient

Water analogy is not going to work, because it does not account for spilled water. It assumes every drop of water makes it to its destination. It assumes if you poor 100 gallons in, you get 100 gallons out. It does not know you only get 95 gallons at the other end.

Why do you think utilities use up to 1.5 million volts to transport power? For a utility 4160 volts is about as low of a voltage they use for secondary distribution in a local neighborhood. Next step up for a slightly longer length is 13.2 Kv

**mj52** · 05-20-2015, 11:27 AM

Bucho and SK,

Thanks,

I'll check out that calculator and I will wire the panels in SERIES. Every little drop helps.

**Sunking** · 05-20-2015, 12:21 PM

Originally posted by mj52

Bucho and SK,

You are welcome.

One last Sanity Check before you pull the trigger. Look at your controller specifications. Check maximum Voc input voltage. Then check your panels Voc at 25 degrees C.

Add you 4 panels Voc up. Example if your panels Voc is 22 volts 4 in series = 4 x 22 = 88 volts. Multiply that voltage by 1.25 x 88 = 110 volts. Now look at the controllers Voc. It would have to be 110 Voc or higher.

Last check your controller conversion efficiency graph or table if they publish it. Example it may say for a 12 volt battery panel Vmp range is 36 to 50 volts for 97% conversion efficiency. You have to way that against your wire length power losses. At 110 volts efficiency of the controller may drop to 95% down from 97. If you are 100 feet away you can take that extra 2% loss in the converter once you add 100 feet is smaller wire at higher voltage. If your panels are real close it maybe better to run a lower voltage on the panels.

You gotta work the numbers to find the right fit.

**inetdog** · 05-20-2015, 08:51 PM

Originally posted by Sunking

You gotta work the numbers to find the right fit.

+1
You either work the numbers or they work you!

**mj52** · 05-20-2015, 09:16 PM

Originally posted by Sunking

You are welcome.

One last Sanity Check before you pull the trigger. Look at your controller specifications. Check maximum Voc input voltage. Then check your panels Voc at 25 degrees C.

Add you 4 panels Voc up. Example if your panels Voc is 22 volts 4 in series = 4 x 22 = 88 volts. Multiply that voltage by 1.25 x 88 = 110 volts. Now look at the controllers Voc. It would have to be 110 Voc or higher.

Last check your controller conversion efficiency graph or table if they publish it. Example it may say for a 12 volt battery panel Vmp range is 36 to 50 volts for 97% conversion efficiency. You have to way that against your wire length power losses. At 110 volts efficiency of the controller may drop to 95% down from 97. If you are 100 feet away you can take that extra 2% loss in the converter once you add 100 feet is smaller wire at higher voltage. If your panels are real close it maybe better to run a lower voltage on the panels.

You gotta work the numbers to find the right fit.

I was doing good till the last paragraph "Last check you controller..............." Thats when I made the same face my dogs do when I ask them where my keys are.

The max Voc of the Tracer 40A MPPT is 100Vdc
The 4 100W panels make 110 Volts

So I flunked that test.

THIS is my only hope.

"If your panels are real close it may be better to run a lower voltage on the panels."

My panels will be set up within an arm's length of the CC and battery bank and if needed could even be rested against the wagon carrying everything. If I laid a 4 x 8 sheet of plywood on the ground my entire set-up, battery cart, panels and cooler would fit with room to spare.

So maybe a lower voltage would be best for this situation.

Thanks, Mike

**Sunking** · 05-20-2015, 10:28 PM

Originally posted by mj52

I was doing good till the last paragraph "Last check you controller..............." Thats when I made the same face my dogs do when I ask them where my keys are.

The max Voc of the Tracer 40A MPPT is 100Vdc
The 4 100W panels make 110 Volts

So I flunked that test.

No Sir you did not fail the test. You passed. The results means you wire them 2 x 2. 2 in series, in parallel with 2 in series. Still do not need fuses, still get the higher voltage benefit, just not as much. That is all it means. You did good and what you are suppose to do.

If you had connected the 4 panels in series and connected to the panels you would have failed the test. Your score would be reported by the smoke coming out of the Controller. Then you know you failed to do your homework.

Power in = Power out

Power in = Power out

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