Counting Ah vs Wh

A project log for Battery Desulfator Kit, TESLA 12V compatible

This is a fast, heavy-duty Pulse Engine derived from my Commercial grade desulfator. Up to 80% battery yields overnight.

mosaicmercmosaicmerc 08/09/2017 at 23:040 Comments

Something to remember when rating batteries of any kind.

What matters is Watt hours or Kilo Watt Hours as per your utility meter.

A lot of batteries are rated in Amp hours though and that's a bit misleading.

When rating a lead acid battery, it is discharged to 10.5V and the Ah discharged at a C/20 rate is the standard 'rating'. So a 100Ah battery will discharge 100Ah at a 5A rate for about 20 hours.

Faster discharging brings in the Peukert factor into significant play and this has to do with electrochemical and energy losses due to chemical changes inside the battery and heating.

Now "counting" Ah is a common thing done on installations that hope to monitor charge efficiencies and battery performance. Charge Ah in vs discharge Ah out.  Discharge: Charge ratios of 80% eff. is a number experienced with lead acid batteries.

HOWEVER,  with pulse charging things will change. Efficiency can go DOWN at high pulse levels.  heating losses I*I*R become significant. Since pulse charging requires a significantly higher supply voltage, you must consider Wh and not Ah as a measure.

I recently processed a Caterpillar diesel SLI battery. It was showing around 40Ah discharge BUT only with 27Ah charged.  Well...the supply V I use is 36V, so we're actually looking at 36V * 27Ah =  972 Wh inputted vs an average 12.1V x 40Ah = 484 Wh discharged. Which ballparks to a 50% charge efficiency.

Seems about right since the 200A battery clamps get a bit hot during the pulsing (100's of Amps) , with ONLY 2.5 mΩ loss at the battery clamps causing the heating.

There's a bit of mild heating in the 12AWG x 8 cabling as well but some of that is conducted from the terminals. The cabling adds about 8mΩ to the loss.

Well, with a charge eff. of 50% , why do charging with this system you might ask?

Well here's why:

You are dynamically stress testing each battery well beyond it's service environment to be able to qualify the battery as suitable for service and not about to die off unexpectedly from borderline internals. No regular charger does i am sure we can all attest to.

This is necessary when bringing back borderline or dead batteries. You need to know they will stand up.

No 'battery vitamin' or chemical additive will inform you of this NEED to KNOW info.