12v battery/ 12./24v MPPT ~ 24v PV Panel

[Old___Slow]

This question troubles the Old and Slow mind. I have a 24v/120w Cynergy PV panel. I would like to use it for duel purpose. For my 24v e/scooter and my 12v RV, not at the same time. The MPPT states (15a 12v/24v), hook battery first, then panel/then load. What will happen with use for the 12v Is it mix and match? Just a novice. Like one fine fellow said, who am I, where am I and why am I here?



Floyd

[JiminDenver]

BFL13 wrote:
You might be there already for leaving it flat. You can test that on the ground while it is still a portable.

On the many half sunny days we get, where it is cloudy morning and clears up by noon or VV, you can still get lots of AH in the half day by pointing the panel.

The very day I would nail down the panel flat on the roof we would get one of those half days, and I would be up there with a crowbar so I could point the panel again like before 🙂

Considering every day we were up there is was sunny early and socked in by noon......

Even then I bet flat will be enough...for now.

[HiTech]

Exactly. PWM charges at pretty close to Isc for most panels most of the time, especially panels where the Vmpp is above the Vbattery. So watts from the panel are way down when using a 24v nominal panel against a 12 v battery. But it works fine if within the capability of the controller. The Voc will just be high when switching PWM pulses on and off.

Jim

[westend]

Old & Slow wrote:
I may have missed it somewhere reading through this thread. Blame it to being O&S.

Anyone have hands on, charging 12v batts, using MPPT or PWM controllars with 24v panel?

I will try soon but would like someone to perhaps chime in and say, yes, NO problems.

Yes, I have a 24v nominal panel charging 12v batteries. My solar controller is a Morningstar Sunsaver MPPT-15. It works well.

My understanding is that using a PMW controller with the 24v panels will result in less charge to your batteries than using an MPPT controller.

[BFL13]

You might be there already for leaving it flat. You can test that on the ground while it is still a portable.

On the many half sunny days we get, where it is cloudy morning and clears up by noon or VV, you can still get lots of AH in the half day by pointing the panel.

The very day I would nail down the panel flat on the roof we would get one of those half days, and I would be up there with a crowbar so I could point the panel again like before 🙂

[JiminDenver]

Don
True and if I were a big power user I would have noticed.

BFL

That was in absorb mode after I did the coffee pot test and it didn't last long as I had only taken the battery down to 13.4v to get the system out of float for the test. Sky conditions were not perfect either as I was working between cloud banks.

I would be more concerned about getting every last drop of power from the system except it is so over sized for our needs that it doesn't really matter. If I ever find a way to use that kind of power I'll buy a second Eco-worthy and run the 220w panel too.

[BFL13]

230/130 x 8.2 = 14.5a for PWM at "12v" Isc. What were the circumstances for that 13a?

[pianotuna]

Hi JiminDenver,

13 vs 16 = a 19% loss.

[Old___Slow]

Tuna,

One fine fellow said, "Any 'lectrican that has not made a few wires smoke, hasn't been at it long"

[JiminDenver]

I just spent 6 days charging my 12v battery with a 24v (mid to high 30's) panel and a MPPT charger. Works great!

For me there wasn't a huge difference in PWM and MPPT output. 13a max PWM and 16a max MPPT. The 3 amps would have mattered if actually drained the battery enough to stay in bulk long but really the system was in float most of the time.

[pianotuna]

Hi,

I use MPPT and the input voltage to the controller is 33.

With 24 volts, MPPT would be more desireable than PWM. However, some PWM controllers may not be damaged by 24 volts input. Others may let out the magic blue smoke. Read the manual carefully.

A 24 volt panel with PWM will "waste" a lot of watts. The approximate loss amounts to over 25% of the harvest.

Old & Slow wrote:
I may have missed it somewhere reading through this thread. Blame it to being O&S.

Anyone have hands on, charging 12v batts, using MPPT or PWM controllars with 24v panel?

I will try soon but would like someone to perhaps chime in and say, yes, NO problems.

[HiTech]

I have done it with PWM. It all depends on your controller. Some controllers recommend against it, others like it just fine.

Many people do this with MPPT.

Jim

[Old___Slow]

I may have missed it somewhere reading through this thread. Blame it to being O&S.

Anyone have hands on, charging 12v batts, using MPPT or PWM controllars with 24v panel?

I will try soon but would like someone to perhaps chime in and say, yes, NO problems.

[pianotuna]

Hi KJ,

I believe Blue Sky for the 3024di says 98% @ 17 volts and 96% @ 30 volts input. I agree that line losses can be significant. My RV came with a #10 prewire. To use it with low losses I chose to go series parallel for the Unisolar panels (system voltage @ 33). That gave me a line loss of under 1%. (dual #12 from panels to combiner box, #10 to the controller, #8 from controller to battery banks).

I believe I'd choose the new Rogue 3048, when the time to add panels comes around. I can't justify it yet, as I keep failing to run out of power. *grin*

I do wish Marc had chosen to do a 6048 Rogue. If he had, I might have "started over" and would aim at 1200 watts of solar.

I'm currently sending 170 watts (13v, 13a) to the battery banks from 256 watts of flat installed panels at 10:30 a.m. local time. I've deliberately forced equalization mode as my house keeper is running an 1100 watt vacuum cleaner. I'll be doing about 45 minutes of driving so that should pump about 15 amp-hours back into the bank.

[KJINTF]

PT

I do not believe I said all Blue Sky controllers were cheap - what I said is that the one I had the misfortune of looking at had a "JUNK" MPPT tracking system with a user adjustable pot nothing more - to me that's cheap junk

A bit of a correction / explanation is needed for your earlier statement
"The higher the input voltage the more of the energy will be wasted as heat inside the controller--so it still behooves one to use lower voltages unless you wish to save on the cost of #4 wire to the controller from the roof."

The losses in a properly designed buck conversion stage is negligible at best with higher voltages, the advantages far out way any potential loss. Smaller more flexible wire, lower cost wires, easier to hide out of sight, far less line losses, P=I(squared)*R half the current 4x less line loss. Lijne losses at high current say 30 amp array current even with 4 awg wire can be 3 to 4% if running long lines - a proper buck conversion stage might have 1% loss difference between the input voltage range