Wh ( watthour) standard growing in popularity

Did you noticed that on more and more battery powered products, like the laptop, drill, media player etc, the battery have his energy unit expressen in Wh instead of Ah.

Since the Ah old standard can't now apply on every battery to indcate their energy they have because it doesn't take account of the voltages, it appear that the¸Wh is growing in popularity.

Since the most common battery voltages in the past decades was 6V and 12V, the Ah was the right unit to evaluate their energy, but today, with all new battery chemistry and voltages, the Ah just can't give us enough information.

Wh = Voltage nominal x Amperehour.

Just lok under your laptop computer on the battery, you will probably see the Wh number indication..

I'm very happy with that because that mean battery will have now one more step to better be comprehended by people!

I often heard people that for exemple , bought makita 14.4V 3Ah battery trying to convince me that it have more energy than the 36V 2.2Ah from bosh.... ... because they are convinced tha it's the ah that is the more important...

All them might now better understand with these easy to understand Wh units...

Doc

I've also been happy to see this trend.

It's also been interesting to see laptop voltages rise over time. My first super ghetto $5 IBM 386 laptop used a 7.2V NiCd pack, it had about 20mins of battery life. My first early used pentium laptop used 9.6v of NiMh, it had maybe 30mins of battery life. My first toshiba used 11.1v of lithium ion, and had about 2hrs of battery life. My netbook also uses 11.1v of lithium ion, and now my new ASUS laptop uses 14.8v of lithium polymer, both of these get 6+hrs of battery life! Voltages climb, current needs drop, and batteries keep getting lighter and more compact. It's a good thing.

For sure it's better but I think it is also a little misleading (maybe splitting hairs a bit here) as it is seems to be the norm for the Whrs be just the nominal voltage time the Ah, but as we all know that is not the case. The real Whrs at various discharge rates would be a useful figure I reckon and give users a better idea of the actual energy they'll get from a pack. That would be useful to see how high C cells stack up against low C cells when the discharge rate becomes a bit higher.

When it comes to state of charge calculation,it's still better to measure Ah instead of Wh. Because it's one errorprone measurement less and therefor more accurate.

If you ask a quote for battery packs, you sometimes get the price in $/Ah or $/Wh. I agree to cell_man/Paul that in this case the Ah price is more relevant.

-Olaf

This is a trend in laptops for the simple reason that the airlines are banning cells over a certain WH capacity in some countries...

olaf-lampe said:

When it comes to state of charge calculation,it's still better to measure Ah instead of Wh. Because it's one errorprone measurement less and therefor more accurate.

-Olaf

Click to expand...

I would correct that,

As we know a full battery have a voltage higher at the begining and a lower voltage at the end.

that mean that the first Ah draw is at higher voltage

and.. the last Ah is at the lower voltage

so... The first Ah draw mean more energy!!

Let say you have a 36V Lithium battery of 10Ah ( the classic one...)

at 1C discharge rate the voltage of the first Ah draw will be around 40V
and.. at the end of discharge the last Ah will be between 32 to 30V ( let say 31v)

that mean the first Ah will represent MORE energy ( 1Ah x 40V = 40Wh)

and.. the last Ah will represent less energy: ( 1Ah x 31V = 31Wh)

so.. the first 5Ah of the battery will represent less energy as well and the last 5Ah of it will represent less energy...

My understanding is that if you draw 50% of Ah, THAT DOES NOT correspond to 50% DOD !

But.. if you calculate using the Wh, ( A TRUE ENERGY UNIT) the 36V 10Ah ( 360Wh) battery will probably reach 180Wh (50%)SOC at around 4Ah draw....

Since the last 6Ah are at lower voltage, it's equivalent to 4Ah at higher voltage..

If you plot a discharge graph using a CBA II load discharger, you will see that at 50% of the Wh that does not correspond to 50% of the Ah..

so using Ah to see SOC is not the most acurate way.

it's the Wh that is the best.

Doc

Doc

liveforphysics said:

I've also been happy to see this trend.

It's also been interesting to see laptop voltages rise over time. My first super ghetto $5 IBM 386 laptop used a 7.2V NiCd pack, it had about 20mins of battery life. My first early used pentium laptop used 9.6v of NiMh, it had maybe 30mins of battery life. My first toshiba used 11.1v of lithium ion, and had about 2hrs of battery life. My netbook also uses 11.1v of lithium ion, and now my new ASUS laptop uses 14.8v of lithium polymer, both of these get 6+hrs of battery life! Voltages climb, current needs drop, and batteries keep getting lighter and more compact. It's a good thing.

Click to expand...

The first Wh units i saw was writen on a laptop battery... now i se more and more cordless powertools showing this unit. like the dewalt 18V 1.1Ah nano new model..

BTW.. I think that if its a recent ASUS laptop you have it might include the new 2.9Ah Panasonic 18650 cells :wink:

My mini MSI wind notebook dont have them.. .. But...it WILL

It would be great to find a document about the SOC energy calculation for laptop battery!.. I am curious to see wich algorithm and parameters they use..

Doc

Doctorbass said:

It would be great to find a document about the SOC energy calculation for laptop battery!.. I am curious to see wich algorithm and parameters they use..

Doc

Click to expand...

Doc, there are some great documents on the Texas Instruments web site about their Impedance Track Gas Gauges and the algorithms they use to calculate all sorts of stuff; SOC, impedance, etc. The data sheets have some info but it's the Technical Reference Manuals and gas gauge white papers that have all the really good stuff. Most of the documents are listed near the bottom of the pages for each of the chips.

Try the bq20z40-R1/bq20z45-R1, bq20z60-R1/bq20z65-R1, and bq78PL114/bq76PL102 chips as these are their latest and will have the newest algorithms.

Or this one:
"Theory and Implementation of Impedance Track Battery Fuel-Gauging Algorithm in bq20zXX Product Family", document number SLUA364B. Had to reread something today for a project so it was easy to post it here.

Doctorbass said:

...
so using Ah to see SOC is not the most acurate way.

it's the Wh that is the best.

Doc

Doc

Click to expand...

I agree with you that its not a linear function, but if you only measure Ah's charged it's the best practical way.
AD-Conversion is not very exact ( you can not rely on the lowest 3 bits of a 10bit ADC ). Multiplication of two AD-values( A*V) make it even worse.
-Olaf

olaf-lampe said:

Doctorbass said:

...
so using Ah to see SOC is not the most acurate way.

it's the Wh that is the best.

Doc

Doc

Click to expand...

I agree with you that its not a linear function, but if you only measure Ah's charged it's the best practical way.
AD-Conversion is not very exact ( you can not rely on the lowest 3 bits of a 10bit ADC ). Multiplication of two AD-values( A*V) make it even worse.
-Olaf

Click to expand...

The cycle Analyst is doing that multiplication without any acuracy problem...

I've always relied on the Wh instead of the Ah to calculate the precise 50% battery energy for liong ebike ride and it was just perfect.

If 10 bits is not enough let's try 12 bits...

Anyway.. The cycle analyst just do the job with a watthour unit.

Doc

If Ah is not used anymore, I guess they'll also have to use a different unit for max discharge rate since its based on Ah (i.e. 25c = 25 x Ah). Just stating that value in amps would be good.

So a 22.2V 5Ah 25c Lipo pack would be 22.2V, 111Wh, 125A max pack.

I like that, it would eliminate the noob confusion between A and Ah. But them again it might introduce a new one... i.e. "my motor is labeled as 500 watts but my battery only says 200Wh..."

Well, that one is at least quite easy to explain to them--if they use full 500 watt power constantly then they can only do it for half an hour.

I much prefer wh. My Ping v3 "48V20aH" produces at least 1100wh. My rate is watts and my consumption is in wh/mile. Watts count up linearly to maximum and I know what I need to do to get where I am going. The wh/mile "rate" (instantaneous product of watts divided by speed) is not shown on the CA though - this would be helpful as well as an individually resetable (reset without resetting the rest of the statistics) or fixed/adjustable period (i.e. the wh/mile for the last minute or two minutes or the last mile or two) moving average of the wh/mile.

It is laundry night so I may get back to working on the Android dashboard application for my Archos 5IT (now with Donut - Android version 1.6). Now I have something I think I need that my CA combined with Google Maps/Trip does not provide...