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Open Roads Forum  >  Tech Issues

 > Measuring MPPT gains

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Salvo

California

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Posted: 08/03/11 03:27pm Link  |  Print  |  Notify Moderator

I added a switch to my solar so that I can either charge directly into the battery (bypassing the charge controller) or charge via controller.

Setup:
Kyrocera 130W panel (flat) (Vmp = 17.6V, Imp = 7.39 A)
Blue Sky 2512iX
Battery: 2 x GC
Load: the battery was loaded with -4A (total bat current = 4A discharge)
Panel temp: 49 C
Ambient temp: 22 C
Time: 2 pm
Location: Santa Barbara, Ca

1. With MPPT controller:

Panel output voltage: 14.79V
Controller output voltage: 12.85V
Controller output current: 8.00A

2. Panel connected directly to battery:

Panel output voltage: 12.85V
Panel output current: 7.80A

MPPT gain: 0.2A / 7.80A = 2.6%

Sal

smkettner

Southern California

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Posted: 08/03/11 03:39pm Link  |  Print  |  Notify Moderator

Much less than most controllers claim. Although the 14.79 panel voltage seems low. Much lower than the Vmp.
Is this in perfect conditions? How about a test when battery is at 12.0/12.2


2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675 watts solar
Send a PM if I missed something

jauguston

Bellingham, WA

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Posted: 08/03/11 04:00pm Link  |  Print  |  Notify Moderator

The SB 2000i I used before I added panels and went to the 3024 gave me amps in and amps out readings and it was generally about a 15% gain. Surely worth the cost. The SB 2000i is gathering dust hanging in my shop(-:

Jim


2005 Coachman Sportscoach Elite 402 40'
350hp Cat C-7 w/MP-8
7500w Onan quiet diesel generator
6-Kyocera 130w solar panels SB3024i MPPT controller
Pressure Pro TPMS
1987 Suzuki Samurai tintop Toad w/VW 1.6 turbo diesel power


Salvo

California

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Posted: 08/03/11 04:35pm Link  |  Print  |  Notify Moderator

I believe the 2000i is a first generation MPPT controller. It requires adjusting pots to estimate Vmp. It is not efficient. However, I believe the 2512i maximum power point algorithm is similar to the 3024.

Have you verified your 15% gain accuracy using another amp meter? I think 15% is quite high. What are your measurements?

Sal

jauguston wrote:

The SB 2000i I used before I added panels and went to the 3024 gave me amps in and amps out readings and it was generally about a 15% gain. Surely worth the cost. The SB 2000i is gathering dust hanging in my shop(-:

Jim


Salvo

California

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Posted: 08/03/11 04:47pm Link  |  Print  |  Notify Moderator

I'm also surprised to see a lower Vmp. Right after controller turn-on, I can see the panel voltage moving around as the controller searches for the max power point. I believe it's functioning correctly.

I'll discharge the battery tonight and see if the efficiency improves.

Sal

smkettner wrote:

Much less than most controllers claim. Although the 14.79 panel voltage seems low. Much lower than the Vmp.
Is this in perfect conditions? How about a test when battery is at 12.0/12.2


shepcal

Oakhurst,California

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Posted: 08/03/11 05:03pm Link  |  Print  |  Notify Moderator

Bing! watching this post

KendallP

Southern Oregon

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Posted: 08/03/11 05:04pm Link  |  Print  |  Notify Moderator

Thanks for the real-world measurements, Sal.

Was it a foggy SB day?

Was the panel angled?

I would think 2:00 PDT in SB should yield you near peak voltage, eh?


Cheers,
Kendall

1986 Winnebago Chieftain 22RC
Our Camper (Don't laugh...
Unlike our credit cards... she's paid for)


SCVJeff

Santa Clarita, CA.

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Posted: 08/03/11 05:32pm Link  |  Print  |  Notify Moderator

shepcal wrote:

Bing! watching this post
Me too

Salvo: I can't quote numbers, but I have a switch that lets me look at the panels direct vs. controller output and I remember it's a much larger gain than that. It also depends on the SOC of the battery. It would be interesting to see those numbers at the same time of day and conditions with different SOC's. The closer to 100% SOC, the lower the MPPT gains (they say). Having the RV parked off-site doesn't allow me to do much empirical testing, so I'm watchin' yours..


Jeff - WA6EQU
'06 Itasca Meridian 34H, CAT C7/350


KendallP

Southern Oregon

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Posted: 08/03/11 06:33pm Link  |  Print  |  Notify Moderator

SCVJeff wrote:

It would be interesting to see those numbers at the same time of day and conditions with different SOC's. The closer to 100% SOC, the lower the MPPT gains (they say).

That would definitely be interesting.

AFAIK an MPPT controller still uses MOSFET switching on the output side like a PWM controller does in order to limit charging voltage. If the batteries are full enough that panel capacity is exceeding the charge rate, then yes... there should be less of an "MPPT gain" because some of the panel power is no longer being utilized.

If I'm wrong, I'm sure Sal will let me know it.



KD4UPL

Swoope, VA

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Posted: 08/03/11 07:19pm Link  |  Print  |  Notify Moderator

You evaluated your system under the exact conditions that produce a minimal MPPT gain: a hot panel and a full battery. The gain experienced with an MPPT controller is due to the difference in the battery voltage and the panel's Vmp. This is typically about a 5 volt difference (12.5v battery, 17.5v panel). Your battery was nearly full and thus the voltage was higher. Your solar panel was quite warm (49 c) and so it's voltage was lower. If you try this same experiment with a battery that is discharged to maybe 12.2 and a panel that is closer to 25 c you will see a much larger voltage difference and thus more possible gain thru the controller.
I am surprised your Vmp was only 14.79. I don't have the temperature coefficient specs for that panel handy but I don't think it should be that low at that temperature. You may need to check your array wiring for a bad connection or excessive voltage drop due to too small of wire.
For 14,79 volts and 8 amps, even going only 20 feet with #8 wire you still have .25 volts of drop. What size wire are you using?

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