Confused about Wake Up and Start Up voltages.

[Wayfarere]

I was initially going to go put in a 24V system (MPPT, inverter & batt) in my ambulance conversion, but now I'm looking at 48V All In One systems. But I'm really stuck on the concepts of Wake Up voltages and Start Up voltages. In threads that reference these terms, the MPPT wake up voltage appears to be higher than the minimum voltage needed. I'm not even sure if this is an MPPT issue or AIO or even panels or all of the above.

I will have four 385W panels with Voc of 36.2V.

First, I was looking at the EG4 3KW, but now looking at a PowMr 5000W POW-LVM5K-48V-N SRNE rebadge with a 120-450V range. While I can theoretically hit the range with my panels in series, since my panels will be laying flat on the roof I worry that I have to wring every possible volt out of usable sunlight and I need to reconsider.

Can anyone point me in the right direction or enlighten me on this issue? Is wake up voltage the same thing as start up voltage? Does an MPPT's voltage range consider in a system's overall efficiency?

 

[DIYrich]

The startup voltage is the lowest voltage for the inverter to do anything with the power. It can be below the mppt operating range.

The panel operating voltage is what you care about. There is not many watts at Voc, so you can ignore it for startup purposes.

 

[sunshine_eggo]

I was initially going to go put in a 24V system (MPPT, inverter & batt) in my ambulance conversion, but now I'm looking at 48V All In One systems. But I'm really stuck on the concepts of Wake Up voltages and Start Up voltages. In threads that reference these terms, the MPPT wake up voltage appears to be higher than the minimum voltage needed. I'm not even sure if this is an MPPT issue or AIO or even panels or all of the above.

I will have four 385W panels with Voc of 36.2V.

First, I was looking at the EG4 3KW, but now looking at a PowMr 5000W POW-LVM5K-48V-N SRNE rebadge with a 120-450V range. While I can theoretically hit the range with my panels in series, since my panels will be laying flat on the roof I worry that I have to wring every possible volt out of usable sunlight and I need to reconsider.

Can anyone point me in the right direction or enlighten me on this issue? Is wake up voltage the same thing as start up voltage? Does an MPPT's voltage range consider in a system's overall efficiency?

Those definitions may vary.

If your array is going to be close to a value of concern, don't try it. Go bigger.

For that particular unit, your Vmp must be above 120V.

Note that light gives voltage. Intensity of light gives current, so flat panels on a roof will give you almost exactly the same voltage as panels perfectly tilted to the sun (ignoring some nuances).

 

[Mattb4]

Wake up voltage is the minimum Voc you will need from panels from your AIO to recognize and turn on. In order to provide charge current the voltage must stay above listed minimum PV operating voltage. Since the PowMr needs 150vDC your 4 panels in series in insufficient to operate. The PowMr (SRNE) are setup to be able to run without battery and use higher PV voltage to accomplish this.

 

[RCinFLA]

PV panels are illumination based current source clamped in maximum voltage by the inherent forward biased diode of each PV cell. Each cell also has some leakage current shunting some of the illumination generated current away.

Array will achieve Voc when illumination generated current exceeds panels' shunt leakage current. No external power can be extracted at this point. Voc will collapse again if SCC starts to draw current at this point, until illumination on panels increases,

Most SCC's turn on with initial loading based on pulling down PV array voltage to about 0.6 x measured initial Voc, after a minimum (and maximum) Voc requirement is met, then lighten load on PV array until Vmp is found. If greater than maximum Voc is detected the SCC will not attempt to start up which helps protect SCC from overvoltage PV input damage.

Most AIO's rely on battery power to provide their overhead power so when SCC first fires up in the morning you will likely still have discharge current from battery. If AIO has 60 watts of no load idle overhead power requirement you need at least 65 watts from PV to break even on battery.

SCC, when activated, adds 4-10 watts of overhead power consumption to AIO inverter.

If you allow battery to be totally depleted during the night you will need for PV to supply full inverter idle overhead power to begin charging and the battery must still be able to supply at least an initial inverter overhead power to get the process started. If you really deplete battery you can get into a situation where AIO cannot startup charging, and you will have to externally charge battery up enough to allow inverter to startup to charge battery.

 

[Wayfarere]

Wake up voltage is the minimum Voc you will need from panels from your AIO to recognize and turn on. In order to provide charge current the voltage must stay above listed minimum PV operating voltage. Since the PowMr needs 150vDC your 4 panels in series in insufficient to operate. The PowMr (SRNE) are setup to be able to run without battery and use higher PV voltage to accomplish this.

Thanks for the heads up. Made me look at my numbers again. The calculator I was using showed "temperature compensated voltage."

 

[Wayfarere]

Thanks for the help on this.

This is an important topic that with the rise of economical 48V AIOs gets easily overlooked by edge cases like mine where I am restricted to a small number of panels.

 

[Mattb4]

Thanks for the help on this.

This is an important topic that with the rise of economical 48V AIOs gets easily overlooked by edge cases like mine where I am restricted to a small number of panels.

It is becoming a bigger issue now that high wattage panels and high voltage AIO's are more common. Having a somewhat low Voc, but a lot of watts, it takes more of them than a person might think. Using only 100 watt panels I run 8 in series (176Voc) to get my voltage high enough. But that is only 800w that 2 larger panels might produce. 5 or 6 of them to get enough voltage means having a lot of real estate covered.