Tristar 45 (non MPPT) charger

rabbit_39 · June 2011

Hi, I have a quick question on this charge controller. It says max Voc of 125V. Does that mean if I want to charge a 12V battery bank I can input 125Voc from my solar array? Or is that just Voc for a 48VDC system array?

Thank you

Joe_B · June 2011

Re: Tristar 45 (non MPPT) charger

The Voc rating of a charge controller is the maximum voltage from the array you can apply to the input. Remember to calculate the Voc of the array at the lowest temperature you will ever see. The Voc of the PV goes up as the temperature falls.

BB. · June 2011

Re: Tristar 45 (non MPPT) charger

For a Non MPPT charge controller, the Voc is the maximum open circuit (no load) solar array voltage... Typically, the maximum voltage is obtained in very cold/sunny weather.

There is almost a 2:1 range for solar panels between Vmp-hot (under load, hot) and Voc-cold (no load, -40C/F weather).

So, if you are on the Canadian tundra with charging a 48 volt battery bank at 60 volts--You would be looking at Voc-cold of ~120 VDC (when the controller "turns off" the current flow as the battery approaches full charge).

So--yes, a PWM 48 volt charge controller would need to be rated for such a high voltage for general use.

Of course, if the install is in Hawaii where it is only 70-80F 365 days a year--then a lesser rated PWM controller could be used just fine.

-Bill

rabbit_39 · June 2011

Re: Tristar 45 (non MPPT) charger

But if I want to charge 12VDC battery bank, the Voc of the array coming into this charger shouldn't be more than 14.5V x 2 = 29V? Or can it be 125VDC then the Tristar 45 will reduce the input voltage to 14.5? I thought non MPPT can only "pass through" the input voltage.

I guess I'm still going back and forth because as I mock up different designs, the amperage goes up and down drastically (of course) as I change the array voltage to a much higher one. Especially when I'm charging 12VDC or 24VDC banks. For example, with 8 x 80Wp panels that are 22Voc and 17.2 Vmp with 5.18Imp, I am looking at 40+ amps if I wire them in parallel to charge a 12V battery bank. Hence I'm looking at the Tristar 45.

But if I get an MPPT, like the 15A one, I can use 3 in series and 3 in parallel to use 9 panels, but only use 15.6 amp into the charger. Oh wait...but then the charging is only at 15 amps x 14.5V = around 200 watts...ooooo I see....I'm losing lots of wats. I probably should be using 48VDC battery bank so I can use up all 720 Wp when charging, ie 15 amps x 58V.

Am I getting this right?

Slappy · June 2011

Re: Tristar 45 (non MPPT) charger

this is a PWM controller. read this link.......> http://www.morningstarcorp.com/en/support/item.cfm?ItemId=192 this link was taken from the "tech specs from morning star for this controller that you are referring to" only a MPPT can pass a higher voltage array to a lower voltage battery bank......somebody please correct me if im am wrong?

Cariboocoot · June 2011

Re: Tristar 45 (non MPPT) charger

Slappy wrote: »

this is a PWM controller. read this link.......> http://www.morningstarcorp.com/en/support/item.cfm?ItemId=192 this link was taken from the "tech specs from morning star for this controller that you are referring to" only a MPPT can pass a higher voltage array to a lower voltage battery bank......somebody please correct me if im am wrong?

Clarification: Only an MPPT type controller can pass a higher Voltage array to a lower Voltage battery bank - and make use of all the available power.

You can connect a 24 Volt panel to a 12 Volt battery through a PWM controller. But basically you lose half the power, so your 200 Watt panel becomes a 100 Watt panel.

And no, that is not a precise description of what will happen - but it's good enough for government work so don't quibble.

mike95490 · June 2011

Re: Tristar 45 (non MPPT) charger

What happens is a PWM controller (those are all controllers that are not labeled MPPT) simply connects the PV to the battery. The battery pulls the PV array down to it's (battery) voltage and the power between the arrays design Max Power Voltage, and the batterys present voltage, is simply lost.

MPPT works like a "DC transformer" and converts the high voltage (PV array) power, to battery voltage power, with only a few % internal loss.

Tristar 45 (non MPPT) charger

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