Watt to Ah

[Bowdrie]

Originally Posted by boatpoker

Its even more disrespectful to refer to a Scotsman as an Englishman

Yes, and the Scots drink whisky, mere mortals drink whiskey.

[ErnestV]

Originally Posted by Xavierp

400Ah is 1/2 of my 800Ah battery bank

let's say the appliance is on all day. How long would it take to empty the bank?
2 hours or 2 days?

Given that lead acids should not be depleted below 50% your device would suck your bank empty in 24hrs.

[catalystcat]

That's a nice video, Gord. I would recommend people might want to view a couple of his earlier videos, as he references them a couple of times in this one.


While many here may know about vector algebra in power systems, a couple of intro item that might help people pick up his points in the video. This may be a bit basic for some others. My apologies.


a. All of this math and discussion is the AC extension of the power calculations people have been discussing. It is a way to deal with the issue that AC systems use sinusoidal signals that are not necessarily in phase and include non-linear aspects like inductance and capacitance.

In this area,
V=IR becomes E= IZ,

where E and I have amplitude, frequency (sometimes omitted) and phase and Z is the complex impedance (real part and reactive part)

b. the "j" is the square root of negative one. (in some nomenclatures, an "i" is used.) That is a way to represent the components as vectors to let you visualize/do vector calculations. (Kinda like AWA and AWS wrt TWA and TWS). You can see this when he does the multiplication of the conjugates (with the j's in them).

In the video he shows the vectors visually when he draws the triangle. One leg is the real power and one leg is the imaginary (old terminology that he slips into) portion.


c. He uses Vrms and Irms. The RMS power is a form of averaging the power of a sinusoidal signal; this more accurately represents the power being delivered, rather than just using the amplitude. This helps make the math a lot more tractable. There is a lot more to this; but, this should be good to get started.





OTHER WAYS TO THINK ABOUT IT

It may be helpful to some to think of reactive power as a mathematical representation that includes the component of power in an AC system that doesn't get "delivered". Not being delivered doesn't mean it can't have huge effects. It is usually due to capacitive or inductive components in a power system (e.g. long transmission lines are inductive).



Another way to look at it is it takes into account any phase shift between the V and A components (in an AC system with capacitive or inductive aspects or when two sources are not synched). Maybe think of it as a bunch of people pushing back and forth on an oar. When people are not in synch it is less efficient and when some are pushing while others are pulling, you can really see how there are problems.

This is a nice tutorial on high level aspects - https://www.electronics-tutorials.ws...-circuits.html



While reactive power is sometimes thought of as a problem/inefficiency, reactive power can have huge effects.
This becomes a big deal in power grids where multiple sources feed the grid and long transmission lines impose delays/inductance. https://clouglobal.com/the-hidden-fo...t-on-the-grid/

Here is an interesting story about it crashing power for 50 million people: https://practical.engineering/blog/2...-2003-blackout

[RaymondR]

Deliberately introduced to make induction motors and generators work??

[RaymondR]

Very interesting article titled "The Formula 1 Power Unit" in the May 2024 edition of Silicon Chip, an Australian electronics magazine, which details what the formula 1 power train builders are doing to reduce losses and exploit every source of power in the latest F1 vehicles. Which technology is also beginning to appear in consumer electric vehicles.

The parts I thought particularly impressive was what they are developing with induction motors to minimise power losses and the connection of a motor generator to the shaft of the turbocharger to both generate electrical power rather than just waste gate the excess exhaust heat energy to prevent over-boost.

[catalystcat]

In response to you question, "Yes." I did a lot of nonlinear control systems for various motor systems before grad school. We rarely ever simplified to pf. We did full reactive models of power systems.

[IOM]

Originally Posted by Baronkrak

Do you have practical experience with power factor?

I know a few brilliant minds in the field of electronics and high power AC, and they respectfully ask to be directed to where they can learn about pf in pure DC, the likes of which only a battery can supply....yes, we have split those hairs as well.
And please don't say Google it. That implies you don't know either.

[ekelly36]

very informative post and there is a lot of knowledge here from all of you fine folks, but I have one question. From as far as I have researched, and please correct me if I'm wrong..... AC is more efficient that DC... Why would anyone even want to keep DC devices on a boat if they get much more efficiency from just having a large inverter and using AC devices and equipment. Wouldn't it be more beneficial to just completely convert all boat systems to AC power? I think I read somewhere that most new boats are primarily AC now and DC systems are being ditched.

Example- If I install an aircon that runs on AC power that uses a quarter of the power as a DC unit, why would I not want that? Or am I missing something.

example 2- if said aircon is advertised as using 20 amps (just an example) and I have an 800Ah bank of LifePo, in a perfect scenario if I'm only drawing 20 amps from the aircon, wouldn't it be able to run for 40 hours? I'm not speaking about the recharging or anything else. Just capacity vs draw for an aircon running on AC power. OR does that 20amps that are advertised need to be converted to watts then factored as WH vs Capacity of 9600 since its Ah*V.... 800Ah*12v=9600.

It seems to me that the math of an appliance that uses 20 amps per hour is the same whether its converted or not, so just using the unconverted Ah vs Ah Battery bank capacity is the same....

20amps - 240 watts x 40 hours = 800Amps or 9600Watts.

In a perfect world that is, without other things consuming power and any kind of inverter losses.

[GordMay]

Originally Posted by ekelly36

... but I have one question. From as far as I have researched, and please correct me if I'm wrong..... AC is more efficient that DC... Why would anyone even want to keep DC devices on a boat if they get much more efficiency from just having a large inverter and using AC devices and equipment. Wouldn't it be more beneficial to just completely convert all boat systems to AC power? I think I read somewhere that most new boats are primarily AC now and DC systems are being ditched...

No - or at least, not necessarily.
The differences between Alternating [AC] and Direct [DC] current are many; and it would be difficult to pronounce one, as more efficient, than the other, across the board.

Direct current is used in essentially all consumer electronics, since transistors [essential to all modern electronics] rely on it to operate.
Devices that use DC current include LED lights, cell phones, laptops, TVs, microwave ovens, variable speed motors, and much more.

Many DC Powered Devices are Intrinsically Efficient
LED lights are a great example of an efficient DC powered device; they use 75% less energy, than AC-powered incandescent lighting.
DC HVAC motors operate at least 50% more efficiently, than AC motors, so this switch alone saves a significant amount of energy.

A study [1], featured on ScienceDirect, highlights how distributing DC electricity has been proven as an effective way to reduce electrical consumption, in commercial buildings, through the reduction of power conversions, and facilitation of a transition to efficient DC appliances.
In the study, they also show that residential buildings experienced savings of up to 25%, when solar PV was distributed to all home appliances, and when battery storage, for excess solar energy, was considered [solar power provides DC power, and batteries store DC power].
These results are promising, but the best way for buildings to receive DC power, is for power grids to supply it. This will happen when a technological solution is devised, that will replace the need for [or decrease the cost of] expensive rectifier stations, in HVDC transmission systems.


[1] “How much electricity can we save by using direct current circuits in homes? Understanding the potential for electricity savings and assessing feasibility of a transition towards DC powered buildings” ~ by Brock Glasgo et al
➥ https://www.sciencedirect.com/scienc...06261916309771

“... Results show site energy savings between 9% and 20% when solar PV is distributed to all home appliances. When battery storage for excess solar energy is considered, these savings increase to 14–25%. At present DC equipment prices, converting all equipment to DC causes levelized annual costs of electricity to homeowners to roughly double. However, by converting only homes’ air conditioning condensing units to DC, the costs of direct-DC are greatly reduced and home site energy savings of 7–16% are generated ...”

[boatpoker]

Originally Posted by Bowdrie

Yes, and the Scots drink whisky, mere mortals drink whiskey.

Aye ! We walk among ye.

[JustMurph]

Originally Posted by ekelly36

very informative post and there is a lot of knowledge here from all of you fine folks, but I have one question. From as far as I have researched, and please correct me if I'm wrong..... AC is more efficient that DC...

The short answer is that on boats, we store our power in DC, therefore if we use it in DC it minimises the number of conversions we need to do, all of which will have losses. Most inverters run at efficiencies in the 90-95% range, so straight up, you're losing 5-10% in creating that AC power. AC devices aren't intrinsically more efficient than DC.

As an example, I have an electric dive compressor. The flow conversions from the battery -> inverter -> VFD (variable frequency drive) -> motor, go like this:
27VDC -> 24VAC -> 240VAC -> 240VDC -> XXX VAC. Each of those steps has inefficiencies. The end result is that my 2.2kW motor requires a 3.3kW draw at the battery.

On the other hand if I used a DC motor, I'd probably lose 5% in a motor controller and that would be it.

[boatpoker]

I don't want to spend hours on here tonight refuting uninformed posts so I'll give it to you bite size and I suggest you look up the conversion method for calculating AC amps to DC amps or vice versa on your own. You can also look up the formulas and do the calculations your self. You should also lear the difference between amps and am hours.

There are many free AC to DC (and DC to AC) calculators on line ... like the one in the photo below.

I'll give you the facts to chew on ...

- Running a 230VAC appliance that requires 15amps AC will draw about 20X those amps (317.4amps) DC from a battery.

- Running a 120VAC appliance that requires 15amps AC will draw about 10X those amps (165.6amps) DC from a battery.