12v or 24v ?

[Whats-n-Watts]

Hello all I have a max load of 210 watts that will be consuming about 700 to 800 watts per 24 hours. Seems like I saw a rule of thumb something like 12v for up to 1,200w , 24v for up to 3,000 watt then above that 48v. However it didn't state what those watts represent. PV watt? Inverter watt? Daily consumption wattts?

I plan to set up two 305 watt panels for the job. Parallel will give me 19.72 ISC and 39.42 voc. I have three 30 amp mppt scc's and will be running the system on a 600 watt continuous inverter.
The PV wire will be around 50 feet. Any reason to lean one way or the other between 12 and 24v?
Also how does the mentioned rule of thumb work if that was even correct information?
Thanks for any and all input!

 

[ryankshaw]

If your inverter puts out a max of 600w then you only need 12v. Actually, if you already have your inverter, then it's decided for you: Use whatever voltage that inverter is (I'm guessing it's 12v if it's 600w)

also, you are confusing "watts" with "watt hours". watts is a measure of power at a specific moment in time. "watt hours" is a measurement of energy storage. so when you say your "max load of 210 watts will consume 700 to 800 watts per 24 hours". what you mean is that it will consume 700 to 800 watt hours per day.

 

[time2roll]

Max load of 210 watts would put me in a 12v set-up unless there was a special situation such as an existing available 24v charging source.

 

[Whats-n-Watts]

If your inverter puts out a max of 600w then you only need 12v. Actually, if you already have your inverter, then it's decided for you: Use whatever voltage that inverter is (I'm guessing it's 12v if it's 600w)

also, you are confusing "watts" with "watt hours". watts is a measure of power at a specific moment in time. "watt hours" is a measurement of energy storage. so when you say your "max load of 210 watts will consume 700 to 800 watts per 24 hours". what you mean is that it will consume 700 to 800 watt hours per day.

No confusion on my end. 200 watt max load about 4 hours a day. Is that not 4hs x 200w = 800wh?

I haven't selected 12v or 24v at this time just the brand. The idle draw was lower for the 12v than the 24v and since it was that small of a system I thought I would ask if it really matters or not. I will be only using this after dark for a couple lights, tv, dvd player and phone charger.

 

[chrisski]

If you use a phone charger, then you get fast charging with 24 volts USB-C or QC 3.0 with something like this socket charger.

At your low inverter wattage, really depends on the DC loads. 12 volt accessories are easier to come by, but some 24 volt accessories will give you more power.

In my RV, there's plenty of 12 volt accessories: lights, fridge, carbon monoxide detectors, propane heater fan among others.

 

[Steve_S]

Clarification:
We generally recommend that people not exceed 250A draw from a battery system, because things can get whacky fast afterwards. As such, you will see the limits as stated. 12V X 250A = 3000W, 24V X 250A = 6000W, 48V X 250A = 12000W
3000W ÷ 120VAC = 120V/25A or 240VAC/12.5A
6000W ÷ 120VAC = 120V/50A or 240VAC/25A
12000W ÷ 120VAC = 120V/100A or 240VAC/50A
! - NOT corrected for losses & inefficiencies.

The SCC sets to the Battery Voltage. Most can do 12/24/48 Volt, this is why the Batteries must be ON when the Solar Controller is turned on so it senses the voltage to set itself to. Note that value gear & cheapo SCC,s may be limited to one or two voltages and may require manual settings. Solar Panel Voltage is converted to what the batteries need via the SCC. For instance, a 200VDC Solar Array can & will charge 12/24/48V batteries through a solar controller as long it supports that voltage / amperage.

Solar Panel array configuration is dependent on the Solar Controller Limitations.

 

[Whats-n-Watts]

If you use a phone charger, then you get fast charging with 24 volts USB-C or QC 3.0 with something like this socket charger.

At your low inverter wattage, really depends on the DC loads. 12 volt accessories are easier to come by, but some 24 volt accessories will give you more power.

In my RV, there's plenty of 12 volt accessories: lights, fridge, carbon monoxide detectors, propane heater fan among others.

I use the charger that came with the phone. Watts are watts and my max load will be 200w and I am going to power it with a 600w continuous inverter. That max load won't ever happen. That would include every light in our 500 sqft house. 99 percent of the time it will be around 140w.

Tv, vcr, dvd @ 50w
2 lamps @ 10w combined
2 led clocks @ 3w combined
Occasionally heat pad & 50w
2 phone chargers @ 9w combined

So you can see a 600w with 1200 peak is overkill regardless of inverter volts 12 or 24 so it's looking like it really doesn't matter. I only use 800 watts per night for this battery which will be large enough for a good 5 nights back up.

 

[Whats-n-Watts]

Clarification:
We generally recommend that people not exceed 250A draw from a battery system, because things can get whacky fast afterwards. As such, you will see the limits as stated. 12V X 250A = 3000W, 24V X 250A = 6000W, 48V X 250A = 12000W
3000W ÷ 120VAC = 120V/25A or 240VAC/12.5A
6000W ÷ 120VAC = 120V/50A or 240VAC/25A
12000W ÷ 120VAC = 120V/100A or 240VAC/50A
! - NOT corrected for losses & inefficiencies.

The SCC sets to the Battery Voltage. Most can do 12/24/48 Volt, this is why the Batteries must be ON when the Solar Controller is turned on so it senses the voltage to set itself to. Note that value gear & cheapo SCC,s may be limited to one or two voltages and may require manual settings. Solar Panel Voltage is converted to what the batteries need via the SCC. For instance, a 200VDC Solar Array can & will charge 12/24/48V batteries through a solar controller as long it supports that voltage / amperage.

Solar Panel array configuration is dependent on the Solar Controller Limitations.

Thank you that's very helpful to know as I have some other mini systems to set up. One being 5,000w inverter and the other a 3,000 watt inverter.

 

[chrisski]

What is your total idle draw?

For me 90% of the time I use the DC items. That’s when I like to shut the inverter off and save 500 Wh a day by shutting it off and just using DC.

 

[Whats-n-Watts]

What is your total idle draw?

For me 90% of the time I use the DC items. That’s when I like to shit the inverter off and save 500 Wh a day by shutting it off and just using DC.

I don't know how else to explain it. The maximum watts drawn at any given time is 200 watts but will be 140 watts unless I turn every light in my house on at which point will be 200 watts. The inverter will stay on 24 hours a day but will only have a load 4 hours of that 24 and that is at night. It powers my lights so it must stay on. From what I can tell is the only significant difference in 12v or 24v is the size of PV input for an appropriate amp scc.
My 30amp is rated for max voc at 50v and 420w max input on 12v and 840w max input for 24v. I see no real benefit between battery volts outside of that. I will have to return 800 watts back to bank and have the entire day to do so but plan to put the maximum I can safely put in as far as pv goes. I have thirty new 305w panels so needless to say that is the least of my concern.
Idle draw for that small of an inverter in the brand I am looking at is only 6 watts. I couldn't care less about that as I am going have days worth of backup and pv will more than make up for the daytime idle currently as well as any other losses.

 

[Reed Cole]

I don't know how else to explain it. The maximum watts drawn at any given time is 200 watts but will be 140 watts unless I turn every light in my house on at which point will be 200 watts. The inverter will stay on 24 hours a day but will only have a load 4 hours of that 24 and that is at night. It powers my lights so it must stay on. From what I can tell is the only significant difference in 12v or 24v is the size of PV input for an appropriate amp scc.
My 30amp is rated for max voc at 50v and 420w max input on 12v and 840w max input for 24v. I see no real benefit between battery volts outside of that. I will have to return 800 watts back to bank and have the entire day to do so but plan to put the maximum I can safely put in as far as pv goes. I have thirty new 305w panels so needless to say that is the least of my concern.

Inverters consume watts when running, which is what they seem to be concerned about, but I can't imagine that a 600w inverter would draw more than 5 watts or so at idle. So maybe another 120 watt hours a day, though definitely figure out how much the inverter actually uses at idle. Typically the spec sheet for an inverter will list idle consumption, but you'll probably need to set it up and measure to be sure.

 

[Whats-n-Watts]

Inverters consume watts when running, which is what they seem to be concerned about, but I can't imagine that a 600w inverter would draw more than 5 watts or so at idle. So maybe another 120 watt hours a day, though definitely figure out how much the inverter actually uses at idle. Typically the spec sheet for an inverter will list idle consumption, but you'll probably need to set it up and measure to be sure.

With a load of 200w on an inverter with a continuous load rating of 600w I highly doubt what the inverter uses will matter at all. I will have days of bank and more pv than required so idle isn't an issue either. All use will be during dark hours and the bank will have all day with a 6 to 10w per hour idle draw. With 610 watt of pv aka 488 watts x 4 being 1,920 watts and only needing to replenish 800 watts idle is pretty irrelevant in this set up unless it is crappy weather for days at the time wich is next to never. Few days tops. The reason I was thinking of going 12v is because the 24v same brand says a slightly higher idle draw but not significant. Outside of a solar panel, ssc and a usb port tied to a phone this is about the smallest system in the forum lol

 

[Whats-n-Watts]

Clarification:
We generally recommend that people not exceed 250A draw from a battery system, because things can get whacky fast afterwards. As such, you will see the limits as stated. 12V X 250A = 3000W, 24V X 250A = 6000W, 48V X 250A = 12000W
3000W ÷ 120VAC = 120V/25A or 240VAC/12.5A
6000W ÷ 120VAC = 120V/50A or 240VAC/25A
12000W ÷ 120VAC = 120V/100A or 240VAC/50A
! - NOT corrected for losses & inefficiencies.

The SCC sets to the Battery Voltage. Most can do 12/24/48 Volt, this is why the Batteries must be ON when the Solar Controller is turned on so it senses the voltage to set itself to. Note that value gear & cheapo SCC,s may be limited to one or two voltages and may require manual settings. Solar Panel Voltage is converted to what the batteries need via the SCC. For instance, a 200VDC Solar Array can & will charge 12/24/48V batteries through a solar controller as long it supports that voltage / amperage.

Solar Panel array configuration is dependent on the Solar Controller Limitations.

I understand the controllers in full it was the battery voltage vs inverter watts I was wondering about. I have a new 4,000 watt 120v inverter that is 12v.
If 12v x 250a = 3000 watts then how is one supposed to use the inverter? So it's useless? Now I'm not understanding that at all.

 

[wopachop]

I will be only using this after dark for a couple lights, tv, dvd player and phone charger.

Sounds like a cool spot. Sure down the road you wont want a fridge or AC/heat?

When you look at your example of a 4000w inverter at 12v you can see why going to 24v or higher helps with wire size.
If you have a blank slate and no current 12v items i would go 24v and something closer to 2000w inverter.
Ive had a 12v bank and 1000w inverter for a couple years. Its kind of limiting at times. Moving to 24v eventually.

 

[rodrick]

That’s when I like to shit the inverter off

Is that the next level when pissing off just doesn’t cut it?

 

[Whats-n-Watts]

Sounds like a cool spot. Sure down the road you wont want a fridge or AC/heat?

When you look at your example of a 4000w inverter at 12v you can see why going to 24v or higher helps with wire size.
If you have a blank slate and no current 12v items i would go 24v and something closer to 2000w inverter.
Ive had a 12v bank and 1000w inverter for a couple years. Its kind of limiting at times. Moving to 24v eventually.

The 4000w 12v was purchased for one job and that's a completely separate system for water heating. It was new and cheap. Ebay $140 to the door. It's a modified sine so perfect for resistive loads.

The system in question as to go 12v or 24v is for the above mentioned task only. I'm not a person that puts all his eggs in one basket.

Never the less does the v (x) watt apply or doesn't it with any amp? If so 12v is deemed to low for the 4,000 watt continuous, 5,000 for up 5 minutes and a 10,000 peak so I can't understand why it exists if it doesn't comply with 12v x 250A rule.

 

[Pi Curio]

Lot's of good information here.

In regards to OP, for such a small load and required capacity, I'd go with a 12V.

One of the benefits is that you can get away with using an MRBF fuse instead of a Class T fuse for the battery which is a decent saving. It is very compact and practical too.

By staying at 12V for such a small power requirement, you can build the top-of-the-line system for a fairly reasonable price.

Interestingly enough, I've built something similar that could give you an idea or two, here's the link: https://diysolarforum.com/threads/daxos-dynamics-the-build-the-journey-and-whatnot.74114/

I hope it helps a bit.


Obviously, once you start getting over 1000W AC, it would probably be a good idea to go with a 24V build. Having a small independent system for essentials that take very little power to run and another for heavier loads is a good route to take.

 

[Whats-n-Watts]

Lot's of good information here.

In regards to OP, for such a small load and required capacity, I'd go with a 12V.

One of the benefits is that you can get away with using an MRBF fuse instead of a Class T fuse for the battery which is a decent saving. It is very compact and practical too.

By staying at 12V for such a small power requirement, you can build the top-of-the-line system for a fairly reasonable price.

Interestingly enough, I've built something similar that could give you an idea or two, here's the link: https://diysolarforum.com/threads/daxos-dynamics-the-build-the-journey-and-whatnot.74114/

I hope it helps a bit.


Obviously, once you start getting over 1000W AC, it would probably be a good idea to go with a 24V build. Having a small independent system for essentials that take very little power to run and another for heavier loads is a good route to take.

Thank you and that does help. I've divided my needs up to use mini systems and individual banks rather than one big system. I will be using a total of 5 inverters but only the smallest will be powered all day why the rest are off. My wife and I are pretty routine with electricity use so their isn't any variance except using less. Also should my bank go dry for this system it's no big deal. My freezers and one mini-fridge are on a collective system of their own (In a shed). Well pump has its own and so forth. The refrigerator inside has it's own. Heat and air has its own combined system. The kitchen outlets have it's own system for coffee maker and microwave use.
Other than water heating, refrigeration, well pump, washer/dryer, heating or air conditioning we only consume 2,050 watts per day.
I went decided to go all individual components to keep failures as inexpensive as possible to repair/ replace. That will allow me to keep spares in stock at the cost of one AIO that would handle the entire load. Just made more sense for us to do that. We stay outside and or gone from home daily from 6 a.m. until around 5 in the winter and outdoors even later in the summer with the longer sunlight hours.
For 3 months I have documented every single watt of electricity to find any anomaly and there are none other than temperature control. That of course is never set in stone. As far as the rest its in stone. Banks will carry 5 days using 100% capacity so any variance is covered anyway. So no concern there. I have thirty 305w Hyundai panels so I can install more than required so low solar days will be covered even at 25% output. In other words my array is not strapped to a AIO units specs.
In other words I don't multiply 244w out of a 305w panel by 4hrs. Nope. 1000w array might do it on a sunny day but on a heavy cloud day that a nope. So I do this 1000w ÷ 244w = 4 * 244w panels for me. One could say just get a bigger bank? Why? Panels are cheaper and last longer. I drive one truck every day but I have 4. I always have a back up with everything. I got caught with my pants down at 18 years old and vowed that wouldn't ever happen again. So far it hasn't and I am now 52.
Something I have learned being in this group is solar needs are individual in every way. No one size or method is practical for all. I like that.
I have a dissociative disorder so anyone in here could be reading a post an alter creates besides myself.
Having this demands redundancy in most aspects of life. So my thought process has to take that into consideration.
Thank you for your input it was very helpful.

 

[740GLE]

Id go with A 24v victron Phoenix inverter.

Victron Energy Phoenix 800VA 24-Volt 120V AC Pure Sine Wave Inverter https://a.co/d/5XrWIjU

 

[Whats-n-Watts]

Id go with A 24v victron Phoenix inverter.

Victron Energy Phoenix 800VA 24-Volt 120V AC Pure Sine Wave Inverter https://a.co/d/5XrWIjU

It's a no surge 140-210 watt draw so that's way over kill. I can get a reliable power 600 for about $98 and it's even overkill for this small load. The 800 watts mentioned are total 24 hour consumption.