Norcold DC 558 power requirements

[7Gentex]

As there are many engineering types (EE or not) on here that understand this stuff WAY better than I:

ETI factory setup:

With a Norcold DC 558 compressor fridge, which claims 3.2 amps draw when running, will 2 190 watt solar panels and 2 lithium 100 amp/hr batteries keep up with the fridge power demands?

If not, in general for how long will it?

I know there are lots of variables, but...............

Central Texas location based.


I'll be on hookups or gen power about 2/3rds of the time due to the need for A/C in Texas , but was wondering how far behind the 8 ball I would be with no hookups for the above.

[richm]

Originally Posted by 7Gentex

As there are many engineering types (EE or not) on here that understand this stuff WAY better than I:

ETI factory setup:

With a Norcold DC 558 compressor fridge, which claims 3.2 amps draw when running, will 2 190 watt solar panels and 2 lithium 100 amp/hr batteries keep up with the fridge power demands?

If not, in general for how long will it?

I know there are lots of variables, but...............

Central Texas location based.


I'll be on hookups or gen power about 2/3rds of the time due to the need for A/C in Texas , but was wondering how far behind the 8 ball I would be with no hookups for the above.

The average peak sun hours for central texas is 5hrs.
280W/13.5V * 5h = 103Ah produced per day

So, on average, you'd get 103 amp hours produced by 280 W of solar panels into a 13.5V lithium battery.

The energy consumed by the fridge is:

3.2A * 24h = 77Ah consumed per day

The fridge probably draws 3.2A continuously only when the temperatures are very high. When temperatures are high, there is likely more than the average 5h of peak sun equivalent. So, given the best case of clear skies, solar may be enough to power the fridge.

On the other hand, there are probably worst case scenarios, such as overcast days in summer that may not fully recharge batteries on a given day.

In winter, let's say you heat the trailer, in which case, the fridge would still consume a moderate amount of energy. In winter, the solar panels would produce much less energy even when skies are clear. So winter may be a worst case scenario.

Winter or Summer, overcast skies for a full day would be a problem.

There are always more details to discuss, such as efficiency of the solar controller, etc. But overall, I'd say the solar panels are the issue, not the batteries, and it'd be wise to have another power source on cloudy days.

[John in Santa Cruz]

I can run a Dometic CX3 75RZ, whihc has similar amp requirements, off the dual diesel batteries on my truck with a 100W solar panel for weeks with central west coast partial sun.

the fridge/cooler draws the full power less than 50% of the time under typical conditions, much of the time mine averages 1-2 amp*hours per hour (its drawing 0 to 5 amps, so my amp*hours/hour is effectively the average current it uses). thats 24-48 amp*hours/day. the diesel truck batteries aren't deep discharge, they are starting batteries, group 65, I'd estimate they are 60 or 80 amp*hour batteries each, with two in parallel.

I also ran without solar when I was in the shade for several days, as long as I drove the truck a few miles each day, everything was copacetic.

obviously, if you fill your fridge with warm stuff, its going to run on high til it gets it cold, but that generally doesn't take that long.

[John in Santa Cruz]

pssst? 2 x 190W is 380 W not 280 W :-p

[7Gentex]

Originally Posted by richm

The average peak sun hours for central texas is 5hrs.


280W/13.5V * 5h = 103Ah produced per day

So, on average, you'd get 103 amp hours produced by 280 W of solar panels into a 13.5V lithium battery.

The energy consumed by the fridge is:

3.2A * 24h = 77Ah consumed per day

The two calcs above are where it gets a bit fuzzy for me.


1. The 190 watt panels are rated at 20.4 volts and "Open Circuit" @ 24.09 volts. So wouldn't a 190 watt panel @ 20.4 volts produce 9.3 amps (at 100% in full sun)? ETI's RV Batteries and solar video seems to tend that way (go to about 14:50 in the video) Bottom left side of whiteboard.

https://youtu.be/VCHSlAEoa7k

So, if I use 9.3 amps times 5 hours average I'd get 46.5 amp hours per panel per 24 hour period.

When the solar controller is taking the 20.4 volts from the panel, and converting it to say 14 volts or so for the lithium battery, is there an amperage change / loss (ignoring solar controller efficiency)?

2. Compressor fridge usage of 3.2 amps is not 100% of the time. Let's use a 65% (?) average for such.

So, 3.2 x .65 x 24 = 49.92 amp/Hr usage per 24 hour period.

Seems like one panel ought to almost keep up with the fridge?

[John in Santa Cruz]

Originally Posted by 7Gentex

The two calcs above are where it gets a bit fuzzy for me.


1. The 190 watt panels are rated at 20.4 volts and "Open Circuit" @ 24.09 volts. So wouldn't a 190 watt panel @ 20.4 volts produce 9.3 amps (at 100% in full sun)? ETI's RV Batteries and solar video seems to tend that way (go to about 14:50 in the video) Bottom left side of whiteboard.

https://youtu.be/VCHSlAEoa7k

So, if I use 9.3 amps times 5 hours average I'd get 46.5 amp hours per panel per 24 hour period.

When the solar controller is taking the 20.4 volts from the panel, and converting it to say 14 volts or so for the lithium battery, is there an amperage change / loss (ignoring solar controller efficiency)? ...

with a solar controlller, you get the approximately the same wattage at the lower charging voltage.

I find my 100 watt panel[*] will output about 6-7 amps at 13.8V or whatever charging voltage during the bulk charge phase into a lead acid when its in direct sunlight and aimed approximately in the right direction. a panel thats flat on the roof will not be as efficient as one tilted and aimed more or less at the sun.

the big mistake in those preceeding calculations was that 190+190 == 380, not 280, so they left 100 watts off the table.

[*] this is a 100W Renogy Solar Suitcase, NOT the panels on the roof on my Escape, which are the older 160W ones... those I've just really not paid that much attention to, most mornings the batteries are fully charged before I am even up and around after a late night of Astronomy, but I'm not (yet) running a compressor fridge in my trailer.

[richm]

Originally Posted by John in Santa Cruz

the big mistake in those preceeding calculations was that 190+190 == 380, not 280, so they left 100 watts off the table.

Hey John, Thanks for catching that mistake.

[7Gentex]

Originally Posted by John in Santa Cruz

I can run a Dometic CX3 75RZ, whihc has similar amp requirements, off the dual diesel batteries on my truck with a 100W solar panel for weeks with central west coast partial sun.

the fridge/cooler draws the full power less than 50% of the time under typical conditions, much of the time mine averages 1-2 amp*hours per hour (its drawing 0 to 5 amps, so my amp*hours/hour is effectively the average current it uses). thats 24-48 amp*hours/day. the diesel truck batteries aren't deep discharge, they are starting batteries, group 65, I'd estimate they are 60 or 80 amp*hour batteries each, with two in parallel.

I also ran without solar when I was in the shade for several days, as long as I drove the truck a few miles each day, everything was copacetic.

obviously, if you fill your fridge with warm stuff, its going to run on high til it gets it cold, but that generally doesn't take that long.

Thanks - good info.

[richm]

Originally Posted by 7Gentex

The two calcs above are where it gets a bit fuzzy for me.

1. The 190 watt panels are rated at 20.4 volts and "Open Circuit" @ 24.09 volts. So wouldn't a 190 watt panel @ 20.4 volts produce 9.3 amps (at 100% in full sun)? ETI's RV Batteries and solar video seems to tend that way (go to about 14:50 in the video) Bottom left side of whiteboard.

https://youtu.be/VCHSlAEoa7k

So, if I use 9.3 amps times 5 hours average I'd get 46.5 amp hours per panel per 24 hour period.

When the solar controller is taking the 20.4 volts from the panel, and converting it to say 14 volts or so for the lithium battery, is there an amperage change / loss (ignoring solar controller efficiency)?

At the open circuit voltage, the current is zero. As soon as you draw current from the panel, the voltage will decrease significantly.

The open circuit voltage (Voc) is important because it needs to be less than the maximum input voltage of the solar controller, otherwise it will fry the controller. For example, a Victron 100|30 has a 100V maximum input and 30A maximum output. For a Victron 100|30 the Voc needs to be less than 100V to prevent damage to the controller.

With a MPPT solar controller, the panels will run at the Maximum Power voltage (Vmp), and the controller converts the output to the lower battery voltage with a higher output current, while preserving most of the power. There is a few percent loss for the conversion process.

A 190W panel with a MPPT controller will produce approx. 190W at the battery voltage. At a battery voltage of 13.5V (middle of the discharge curve) that would be 190W/13.5V=14A.

PWM solar controllers are different. They are only efficient when the panel's Vmp is closely matched to the battery voltage.

[7Gentex]

Originally Posted by richm

At the open circuit voltage, the current is zero. As soon as you draw current from the panel, the voltage will decrease significantly.

The open circuit voltage (Voc) is important because it needs to be less than the maximum input voltage of the solar controller, otherwise it will fry the controller. For example, a Victron 100|30 has a 100V maximum input and 30A maximum output. For a Victron 100|30 the Voc needs to be less than 100V to prevent damage to the controller.

With a MPPT solar controller, the panels will run at the Maximum Power voltage (Vmp), and the controller converts the output to the lower battery voltage with a higher output current, while preserving most of the power. There is a few percent loss for the conversion process.

A 190W panel with a MPPT controller will produce approx. 190W at the battery voltage. At a battery voltage of 13.5V (middle of the discharge curve) that would be 190W/13.5V=14A.

PWM solar controllers are different. They are only efficient when the panel's Vmp is closely matched to the battery voltage.

But, it's Friday.

So, what are you trying to get at here............?

I'm not following....can you boil that down a bit?

"Open circuit voltage" for the 190 watt panels from ETI are 24.09 volts.

ETI supplied controller (as stated "Factory" in the original post) is not MPPT. Not completely sure which GoPower model it is but likely this one and it appears the max input voltage is 28 volts for this model:

https://gpelectric.com/products/30-a...ler-bluetooth/

You state a MPPT controller will produce "X", then state a PWM controller are "different", and only "efficient" when the panel Vmp is closely matched to the battery voltage. Um.......OK......and..?

The main questions: Will the 2 factory installed 190 watt panels and 2 100 amp/hour lithium batteries be sufficient to run the fridge under "average" circumstances and for how long? How many amp hours can the 190 watt panels produce.

[richm]

Originally Posted by 7Gentex

The main questions: Will the 2 factory installed 190 watt panels and 2 100 amp/hour lithium batteries be sufficient to run the fridge under "average" circumstances and for how long? How many amp hours can the 190 watt panels produce.

The specs list the max power current (Imp) is 9.3A. Since the GP-PWM-30-UL is a PWM controller, it's probably in the 70 to 80% efficiency range.

2*190W *80% / 13.5V = 28A
28A * 5h (average peak sun in texas) = 140Ah generated per day

The Norcold DC 558 draws a maximum of 3.2 amps.
3.2A * 24h = 77Ah maximum consumed per day

It'll draw a fraction of that once the fridge has cooled down to a stable temperature.

So yea, you've got enough solar to run the fridge and charge the batteries on an average day.

[WanderBred]

We're picking up our 5.0 on the 27th, I have a compressor fridge, and two solar panels and two lithium batteries.

[7Gentex]

Originally Posted by richm

The specs list the max power current (Imp) is 9.3A. Since the GP-PWM-30-UL is a PWM controller, it's probably in the 70 to 80% efficiency range.

2*190W *80% / 13.5V = 28A
28A * 5h (average peak sun in texas) = 140Ah generated per day

The Norcold DC 558 draws a maximum of 3.2 amps.
3.2A * 24h = 77Ah maximum consumed per day

It'll draw a fraction of that once the fridge has cooled down to a stable temperature.

So yea, you've got enough solar to run the fridge and charge the batteries on an average day.

Thank you for the explanation in a format that I can follow.

[7Gentex]

Originally Posted by WanderBred

We're picking up our 5.0 on the 27th, I have a compressor fridge, and two solar panels and two lithium batteries.

I'd be interested in following how that combo works out for you.