Rant on terminology...

[Cal]

Son's '69 Charger.




After reading this thread, I've erred on units of measurements. I've been using AH which is not correct. "H" stands for Henry and is a unit of inductance. I've noticed some use "S" for seconds. That's incorrect. "S" stands for Siemens.

BTW, I have no problems using Ah, as opposed to Wh when dealing with batteries.

 

[HRTKD]

Son's '69 Charger.
View attachment 74641

View attachment 74642

After reading this thread, I've erred on units of measurements. I've been using AH which is not correct. "H" stands for Henry and is a unit of inductance. I've noticed some use "S" for seconds. That's incorrect. "S" stands for Siemens.

BTW, I have no problems using Ah, as opposed to Wh when dealing with batteries.

I can feel the rumble of that engine from here! Sweet looking ride.

When are you going to change your signature line from "AH" to "Ah"? LOL!

 

[upnorthandpersonal]

BTW, I have no problems using Ah, as opposed to Wh when dealing with batteries.

Depends on the situation. As long as you compare Ah between batteries of the same nominal voltage and this is clear in the discussion, it's fine. Sadly, we've seen times, and times, and times again that people see Ah as an absolute value to compare all batteries, and people don't want to get e.g., a 24V 75Ah pack because a 12V 100Ah battery has more Ah.

 

[Cal]

But Ah is more accurate. Wh is dependent on the voltage of the battery. Depending of the charge, voltage is not a constant. However when using Wh, voltage is assumed to be a constant. That's an error. There's no inherent error when using Ah. It is exact.

 

[sunshine_eggo]

But Ah is more accurate. Wh is dependent on the voltage of the battery. Depending of the charge, voltage is not a constant. However when using Wh, voltage is assumed to be a constant. That's an error. There's no inherent error when using Ah. It is exact.

By your own logic, on lead-acid Ah is just as inaccurate as it's only valid for a given current. Lotsa lead acid still in use.

Ah tells you NOTHING about the amount of energy in a battery... unless you multiply it by its NOMINAL (not constant) voltage.

 

[Cal]

By your own logic, on lead-acid Ah is just as inaccurate as it's only valid for a given current. Lotsa lead acid still in use.

Ah tells you NOTHING about the amount of energy in a battery... unless you multiply it by its NOMINAL (not constant) voltage.

Due to Pleukert constant Wh is just as inaccurate, even for LiFePO4.

I don't care about battery energy. It means nothing to me. I deal in amps. Watching a movie in my RV consumes 3.5A. The microwave consumes 155A. Solar outputs 5A. My battery has 180 Ah.

You have major errors when using Wh with LAB. There's a huge voltage discrepancy when charging at 14.7V and discharging at 12.8V. Do you shut your eyes to that?

 

[sunshine_eggo]

Due to Pleukert constant Wh is just as inaccurate, even for LiFePO4.

I don't care about battery energy. It means nothing to me. I deal in amps. Watching a movie in my RV consumes 3.5A. The microwave consumes 155A. Solar outputs 5A. My battery has 180 Ah.

You have major errors when using Wh with LAB. There's a huge voltage discrepancy when charging at 14.7V and discharging at 12.8V. Do you shut your eyes to that?

What you're missing is that I'm not saying one is more accurate than the other, I'm saying your claim of Ah being more accurate is just wrong. The singular advantage of Wh is it actually equates to energy regardless of voltage. It is also vastly superior for planning purposes across multiple applications. Are you going to take your electric bill and convert it to Ah to determine your offset? No. You're going to deal in Wh/kWh.

Even before selecting a battery voltage, one can compute their needed solar and needed battery storage purely based on Wh.

 

[Cal]

I'm saying your claim of Ah being more accurate is just wrong.

Say what? I just gave you an example when charging a LAB at 14.7V and discharging it at 12.7 V produces enormous errors. This error is not present when dealing with Ah.

 

[upnorthandpersonal]

This error is not present when dealing with Ah.

As long as you stay within the same battery nominal voltage. That's why Ah is great when measuring capacity of a single battery versus e.g. its nameplate capacity since voltage and loses don't matter - I've shown that here:

However as soon as you start comparing different chemistry and different nominal voltages, Ah on its own says nothing.

 

[curiouscarbon]

Joule Heating is the Bastard Middleperson

 

[John Frum]

However when using Wh, voltage is assumed to be a constant.

Is...
3.2 volts * $_amp_hour_rating = $n watt hours
...not accurate for a typical LFP cell?

 

[Cal]

However as soon as you start comparing different chemistry and different nominal voltages, Ah on its own says nothing.

Why would Ah says nothing when comparing 12V vs 24V batteries? Perhaps to some who don't know Watts law. Is that the reason to use Wh? In order to compare different systems?

Would you rely on a Coulomb counter or a Watts counter?

 

[Cal]

Is...
3.2 volts * $_amp_hour_rating = $n watt hours
...not accurate for a typical LFP cell?

IR losses make it inaccurate.

 

[upnorthandpersonal]

Is that the reason to use Wh? In order to compare different systems?

Yes. To compare energy stored in different systems. Using a Wh number means you can compare apples (48V LiFePO4 or whatever) to oranges (12V AGM or whatever) directly and objectively. When you discuss these two systems and use Ah rating, it doesn't convey anything - and we know this since tons of people are not clear on the fact that a 100Ah 12V system has less energy stored than a 50Ah 48V system.

 

[upnorthandpersonal]

Would you rely on a Coulomb counter or a Watts counter?

See the video I posted: for e.g. a capacity test compared to it's nameplate capacity, Ah. In order to compare energy stored between two systems in a discussion on a variety of batteries, Wh.

 

[wattmatters]

Here's an entertaining guide to the Ah v Wh thing, with real batteries as examples. 40-odd minutes.

 

[Bob B]

I think think both positions of the AH VS WH discussion have their merits .... WH is definitely better for comparing systems with different voltages .... but, for me, it is what your mind has gotten used to recognizing.
For instance, if you grow up your whole life thinking in Deg F and then have to start thinking in terms of Deg C.

Once you get used to thinking one way, it is hard to think the other way.

 

[Supervstech]

Son's '69 Charger.
View attachment 74641

View attachment 74642

After reading this thread, I've erred on units of measurements. I've been using AH which is not correct. "H" stands for Henry and is a unit of inductance. I've noticed some use "S" for seconds. That's incorrect. "S" stands for Siemens.

BTW, I have no problems using Ah, as opposed to Wh when dealing with batteries.

THAT is a sweet ride!

My 72 super bee 383 is in FAR sadder shape…

 

[nicorellius]

I went on a rant about this too on this board a few weeks or months back.

Makes me nerd mad.

Nerd mad. That's priceless

 

[Isaac-1]

To halfway get back on topic, the ones that get me are the incorrect terms thrown around regarding generator and inverter: Solar Generator, Inverter, Inverter Generator, etc:

Inverter - A device that electrconically converts DC to AC, and can be a part of a combination unit that also includes a charger and a transfer switch.

Inverter Generator, a typically gasoline though there are some diesel models generator that uses an alternator to generate power that is then rectified to higher voltage DC, and then converted to AC using electronics similar to an inverter mentioned above.

Solar Generator - A marketing term typically used to describe an undersized solar panel mated to a small battery bank with an inverter.