Help needed - 48VDC system (Skoolie)

[John Frum]

The “conversion penalty” at 48v will be quite a bit lower than 15%. For a Victron unit, I can tell you it will be 8% or less.

Victrons are top shelf and have demonstrated ~90% efficiency.
Anyone want to test their mpp 48 volt all in one unit?

 

[Hedges]

To put a number on that, a 6 kW Sunny Island burns 25W under no load, 4W if snoozing and occasionally powering up AC to see if anything was turned on. That's 600 Wh/day, or 96 Wh/day. (OK, so I burn 2.4 kWh/day; big deal! I can afford it! That's just two panels.) Efficiency ranges from about 91% to 96% depending on load.

 

[snoobler]

The “conversion penalty” at 48v will be quite a bit lower than 15%. For a Victron unit, I can tell you it will be 8% or less.

Nope. Depends on load.

from:

https://www.victronenergy.com/upload/documents/Output-rating-operating-temperature-and-efficiency.pdf

My 48V 5K unit spends the majority of its hours with a 72-76W load (overnight lights, floating RV batteries). At this level, I'm lucky to get 85% efficient. When you factor in the 30W consumption of the unit itself, my efficiency is about 65%.

 

[berksrunner]

Nope. Depends on load.

from:

https://www.victronenergy.com/upload/documents/Output-rating-operating-temperature-and-efficiency.pdf

View attachment 25025

My 48V 5K unit spends the majority of its hours with a 72-76W load (overnight lights, floating RV batteries). At this level, I'm lucky to get 85% efficient. When you factor in the 30W consumption of the unit itself, my efficiency is about 65%.

I've calculated my 24V Multiplus to be 90% using real-world numbers. A 48V Quattro (no 48V Multiplus) will be even more efficient.

 

[Hedges]

View attachment 25025

If I didn't know any better, I'd almost suspect that data table was dry-labbed.



I asked the question, "Is power dissipation the result of 11W consumed by circuits and I^2R loss of transistors & transformer windings?"
After subtracting 11W from each value, I took square root and then ratio of the result to output power. Result was 0.00707xx across the board.

Might even be measured ... instantaneously. But with copper TCR 0.4%/degree, if given time to heat up the figures probably change.

 

[snoobler]

I've calculated my 24V Multiplus to be 90% using real-world numbers. A 48V Quattro (no 48V Multiplus) will be even more efficient.

I'm speaking specifically about my 48V 5K Quattro. I literally have a 65% efficiency at < 75W draw using real world numbers logged in VRM with my CCGX.

The Quattro and Multiplus are almost identical. The Quattro has a second AC input.

As of this exact moment while powering my absorption fridge, lights and float chargers, I'm consuming 405W DC to get 360W AC.

That's 88.9%.

 

[snoobler]

Another up-to-the-second snapshot... 107W DC to produce 71W AC: 66.4%

 

[snoobler]

And... for the last 30 days... logged every 5 minutes. You can see when we visited.

 

[Opusdei]

And... for the last 30 days... logged every 5 minutes. You can see when we visited.

View attachment 25034

Inverter inefficiency due to 11W idle power consumption seems to be critical especially at low power consumption condition.

 

[Opusdei]

I'm wondering if there is AC mismatching inefficiency between the AC generated and AC delivered. I mean, AC transfer inefficiency between inverter and load, due to pure sine wave, impedance mismatch, phase distortion, etc.

 

[Hedges]

Inverter inefficiency due to 11W idle power consumption seems to be critical especially at low power consumption condition.

Insignificant, at least for a non-mobile system.
With my 5.5 hours average sun, takes me 48W of PV panel, a $17 investment, to cover that.
(simple numbers, before I correct for SCC inefficiency and PTC vs. STC, but other guys pay half what I did for my panels.)

Overall efficiency including loads throughout the day drive array size.

 

[Hedges]

I'm wondering if there is AC mismatching inefficiency between the AC generated and AC delivered. I mean, AC transfer inefficiency between inverter and load, due to pure sine wave, impedance mismatch, phase distortion, etc.

That could be more important, if a load shoves power back into the AC line out of phase. Big question is, what does the inverter do with it? Put back in capacitors, or dissipate?

I believe my "buzz box" arc welder limits short-circuit current (and no-load current) by inductance. "Somebody" could measure current/voltage with a scope to see how much reactive power, and compare battery current to real AC power.

 

[snoobler]

Inverter inefficiency due to 11W idle power consumption seems to be critical especially at low power consumption condition.

worse when the idle consumption is 30W, which is decent for a 4kW unit.

 

[creeky]

Look at what JiPe did and copy. That's a sweet system. Nice to see the Victron crowd here. Look. I've helped people build off grid and bus systems for the past 3 years. Done quite a few. Many dozen. Had all kinds of hassles, headaches and heart breaks. Victron is the cats meow right now. The few extra dollars pay off again and again. Imagine. I diagnosed a guy's (emailed me from north of 60) system problem with his Victron solar controller history. That easy. Now. Its minimum 1200 to go visit one way.
DC is a mugs game. The conversion losses of AC are so low. And, as pointed out, the money you will save on appliances and fixtures will pay you back for the inverter many times over. Not to mention the safety. AFCI, GFI, etc. Really. You're that knowledgeable about electricity you're going to engineer your own safety equipment?
Enjoy the build. Its going to be a blast.

 

[45North]

Forget it!
There are too many moving parts and not enough hours in the day.
I'd advise you to keep it simple and stick to conventional power. Do not go down this rabbit hole!

 

[MadElectrician]

Where did you get the notion that there is any upside to a low voltage DC system? You know, Tesla and Edison famously had this debate over 100 years ago and Tesla and AC power won. Switch to 120v as fast as possible and just use regular plug in chargers for your gadgets. They even have receptacles with USB ports now. If you absolutely must not use an invertor for your gadgets, there are step down DC transformers you can buy and you can tap off before the invertor. Or, a separate battery. But a low voltage DC setup will require huge wire and the appliances are way more expensive.

 

[Opusdei]

I'm not arguing the benefit of a higher voltage DC system. As far as AC power is concerned, I understand there is a clear advantage of the availability of 120 volt AC power for other uses. Inverter and a shore power charger would cost as much as you want. Not as efficient though because you are converting from DC to AC and then back to DC. Battle between Tesla and Edison is about power transmission, not power conversion and a lot changed in 100 years.

 

[MadElectrician]

I'm not arguing the benefit of a higher voltage DC system. As far as AC power is concerned, I understand there is a clear advantage of the availability of 120 volt AC power for other uses. Inverter and a shore power charger would cost as much as you want. Not as efficient though because you are converting from DC to AC and then back to DC. Battle between Tesla and Edison is about power transmission, not power conversion and a lot changed in 100 years.

Look at the list of things he is trying to run. The only DC appliances I have seen are limited selection and insanely expensive. Is there even such thing as a DC clothes dryer? The loads and wire requirements for this stuff would be crazy. One could just buy ordinary 120V appliances at the big box store, and purchase an entire 800W solar system for less than DC appliances would cost. The problems and drawbacks of using DC outweigh any efficiency difference by light years.

 

[John Frum]

Look at the list of things he is trying to run. The only DC appliances I have seen are limited selection and insanely expensive. Is there even such thing as a DC clothes dryer? The loads and wire requirements for this stuff would be crazy. One could just buy ordinary 120V appliances at the big box store, and purchase an entire 800W solar system for less than DC appliances would cost. The problems and drawbacks of using DC outweigh any efficiency difference by light years.

DC cloths dryer.
That's a good one!

 

[Opusdei]

@Tecchie said he found "Clothes washer/dryer combo unit (found some, yes expensive, but wash/dry in a single unit)" Then, who's arguing here ^^;