Battery charging/alternators tech info

vyv_cox

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About a month or so ago somebody posted a link to an excellent site that gave impartial advice about the need for alternator controllers, amongst lots of other electrical information. The part I remember was pointing out that alternators built within the past few years did not need a controller as their characteristics were aimed at yachts, rather than automotive. However, this was just one of a long list of answers to common questions.

I was certain I had saved the link but now, when I have promised to send it to someone else, I find I didn't /forums/images/graemlins/blush.gif Can anyone point me to the link, please?
 

Plevier

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That is a very interesting website and lots of good information and sense about charging.
However Chris Gibson's explanation of Peukert's equation is rather novel to say the least.

Peukert's equation does empirically quantify the fact that a battery can deliver less capacity (Ah) at high rates than low rates. However Gibson takes that further and says

1. Firstly, there is the problem of a certain Mr Peukert (see Peukert's Equation). Peukert's equation quantifies how heavier discharges actually remove more power from the batteries than a simple "Amps X Time" calculation would show. What this means for the amp hours counter is that, assuming the example given above worked, then doubling the discharge current would give erroneous results.
For instance, discharging at 20 amps for one hour from a 100Ahr battery, the amp hours counter would have accumulated -20Ahrs. However, according to Peukert's equation the true figure would be much higher. Around 30 amps with a typical Peukert's exponent for a deep cycle battery. So now, after one hour of dishcharge at 20 amps, the amp hours counter reads -20Ahrs but in actual fact the battery is at -30Ahrs. When the charger is switched on (the same 10 amp charger as before), after 2 hours the amp hour counter will have accumulated 20 amps total charge so will be reading 0Ahrs, indicating that the batteries are full. In actual fact the batteries are at minus 10Ahrs.

This is an "unusual" interpretation. The Peukert effect is normally taken to be due to short term effects inside the battery such as electrolyte diffusion. The higher rate doesn't "remove more power from the battery." If you let the battery stand after the high rate discharge, it will recover and then be able to deliver the rest of its capacity. Specific gravity measurements will also show this.

Taking Gibson's argument to its extreme, if you ran the battery at its max cranking amps for the rated 20 or 30 seconds down to 1.6V or 1.5V per cell, it would then need a full capacity recharge. This just doesn't happen. For a rough example, take a 60Ah battery and assume cranking at a typical 500A. 30 secs is 4Ah, it doesn't need 60Ah to recharge it.

For a more authoritative treatment see http://www.ee.ncue.edu.tw/note/data/o/21/91.pdf and particularly p356.

Gibson's interpretation of Peukert to me destroys his case against normal battery condition monitors (Ah counters) and he is very coy about how his SmartGauge works, just talking about special algorithms. The fact is that the SmartGauge's only input appears to be battery voltage, which is not generally accepted as a satisfactory basis for capacity measurement.

I'd be interested in a proper explanation, without which I'd back the Ah meter against the SmartGauge.

Has anyone here tried the SmartGauge and found it good or bad?

Mike /forums/images/graemlins/confused.gif
 

John100156

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Willow3 - I accept your point. I suppose energy cannot be destroyed and therefore if only 20AH has been removed from the battery the balance must still be there in one form or another (chemical energy) and the battery should recover. Thanks for the info, will read through it tomorrow.....
 
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