Efficiency of MX60 for 24v to 12v conversion

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Efficiency of MX60 for 24v to 12v conversion

Postby JPF on Tue Nov 29, 2005 11:49 am

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Postby Kent Osterberg on Wed Nov 30, 2005 4:03 am

The efficiency curves in the MX-60 manual suggest that the MX60 efficiency only drops about 1% if you wire the PV array in a 24-volt configuration rather than a 12-volt configuration. The improvement in wire losses between the PV array and the MX60 can easily make that up.

The system that you are proposing operates the MX-60 on the low end were it's effiency is the poorest. Still, the efficiency should be about 95% when in full sunlight.

For such a small system, the MX60 may not be the most economical choice. The price for a Sharp 123 is about the same as the price of a MX-60. Compare option A: two Sharp 123 modules and a MX60 and option B: three Sharp 123 modules and a brand X charge controller. Cost of the two options is similar but you'll get more charging current from option B.
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Postby JPF on Wed Nov 30, 2005 5:16 am

Thank you for the response.

Option A is actually two higher wattage panels such as the Sharp 208's which have a nominal voltage of 24 volts. So, from what I understand, I would need a charge controller like the MX60 to reduce that voltage to charge my 12 v battery setup. Given that I am trying to maximize wattage in a small space and that loss in efficiency is only 1% for voltage reduction it seems like this is the way to go.

Would wiring the two Sharp 208's together for 48 volts improve the performance of the mx60?

Thanks again
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Postby Kent Osterberg on Wed Nov 30, 2005 8:53 am

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Postby crewzer on Wed Nov 30, 2005 9:44 am

090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Postby crewzer on Sun Dec 04, 2005 2:17 pm

The new shunt arrived yesterday afternoon. So did the clouds, unfortunately. So, I installed the shunt and I'll try for some useful readings next Saturday.

In the meantime, here is some interesting data:

36 V array -> 12 V battery bank; numbers I recorded from my MX- and Mate display at ~Noon on November 25, 2005:

Vin 46.0 V
Iin 14.0 A

Vout 13.4 V
Iout 42.1 A

That's an indicated 644 W in and an indicated 564 W out, or 87.6% efficiency.

36 V array -> 24 V battery bank (temporarily rewired); numbers I recorded from my MX displays at ~Noon on December 3, 2005:

Vin 46 V
Iin 12.2 A

Vout 27.4 V
Iout 19.2 A

That's an indicated 561 W in and an indicated 526 W out, or 93.7% efficiency -- quite an improvement!
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Postby crewzer on Wed Dec 07, 2005 4:21 pm

Following up... I was able to make some quick recordings and measurements today @ ~12:40 EST on my system (nominally 36 V in and 12 V out) with the new PV array shunt installed. Here's the data and calculations:

Indicated (on MX display):

Vin 47 V
Iin 13.2 A

Vout 14.6V
Iout 37.5 A

That’s an indicated 620.4 W in and an indicated 547.5 W out, or 88.2% efficiency.

Measured:

Vin 47.3 V (DVM measured across the MX-60 PV input)
Iin 12.5 A (DVM measured 12.5 mV across the 100mV / 100 A shunt)

Vout 14.62V (DVM measured across the the MX-60 output)
Iout 37.3 A (Link 10 indicated 37.1 A, plus 0.2 A for Link 10 consumption)

That’s a calculated 591.25 W in and an calculated 545.33 W out, or 92.2% efficiency -- that would be better, then! :grin:

The local weather forecast for this Saturday looks promising... I'll try again.

HTH,
Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Postby crewzer on Sat Dec 10, 2005 10:03 am

Following up... I was able to make another set quick recordings and measurements today @ ~11:45 EST on my system (nominally 36 V in and 12 V out) with the new PV array shunt installed. Here's the data and calculations:

Indicated (on MX display):

Vin 48 V
Iin 13.0 A

Vout 13.8 V
Iout 39.6 A

That’s an indicated 624.0 W in and an indicated 546.5 W out, or 87.6% efficiency.

Measured:

Vin 48.4 V (DVM measured across the MX-60 PV input)
Iin 12.2 A (DVM measured 12.2 mV across the 100mV / 100 A shunt) -- cut & paste typo corrected -- thx, boB :oops:

Vout 13.8 (DVM measured across the the MX-60 output)
Iout 39.4 A (Link 10 indicated 39.2 A, plus 0.2 A for Link 10 consumption)

That’s a calculated 590.48 W in and an calculated 543.72 W out, or 92.1% efficiency -- that would be better, then! :cool:

It would seem that the "Amp in" calulation displayed on my MX' screen is consistently on the high side.

That's all, Folks!
Jim / crewzer :oops:
Last edited by crewzer on Sun Dec 11, 2005 2:43 am, edited 1 time in total.
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Postby nsingh on Sat Dec 10, 2005 11:27 am

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Postby crewzer on Sat Dec 10, 2005 1:44 pm

090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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