Global Sources
EE Times-India
Stay in touch with EE Times India
EE Times-India > Power/Alternative Energy
Power/Alternative Energy  

Battery management for car start-stop systems

Posted: 20 Aug 2015     Print Version  Bookmark and Share

Keywords:start-stop  fuel consumption  Battery  SoC 

Some futurists state that in 50 years our grandchildren will be driving autonomous electric vehicles that they summon up from the cloud on demand. Gasoline will be a historical curiosity, and Middle East will be known primarily for its solar power.

These days, though, gasoline is still King of The Hill, and the United States' Department of Transport has been slowly turning the screws on vehicle fuel economy ever since the first CAFE regulations passed Congress in 1975 following the Arab Oil Embargo.

There are a couple of well-recognised ways to reduce fuel consumption – make smaller or less powerful vehicles. But [American] buyers love their trucks, SUVs and V8 power.

The quest for reduced fuel consumption, while still catering to consumer preferences, has led to the introduction of several new technologies. One of them is the "start-stop" (or stop-start – we'll leave that discussion to the "chicken or the egg" folks) system; it automatically shuts down and restarts the engine to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions.

This is most advantageous if you a spend significant amount of time waiting at traffic lights or frequently get stuck in traffic jams. This feature is present in hybrid electric vehicles, but has also appeared in otherwise conventionally-powered vehicles, so-called "micro" hybrids. For such vehicles, fuel economy gains from this technology are typically in the range of 5 to 10%.

Turning off the engine at a stop light. What could possibly go wrong?

Predicting battery failure
Battery failure is the single biggest cause of vehicle breakdown, accounting for 52% of failures in one study of 1.95 million vehicles less than 6 years old; in another study, failure rates ranged from 1000ppm to over 10000ppm for batteries older than 3 years. Battery failure is exacerbated by operating conditions that don't allow the battery to fully charge, such as driving short distances using heavy accessory power. Excessive heat is another contributing factor.

Battery death can occur without warning especially if you inhabit the USA's Desert Southwest – both [EDN editor] Steve Taranovich and I live in the Phoenix, AZ, area. I once drove 40 miles, turned off the engine for a moment outside a restaurant, and had to be pushed to the nearest parking space. Lucky I wasn't on te intersate highway during rush hour.

To forestall this possibility, it's critical to have precise knowledge of the current state of the battery to disengage the start-stop system if there's a possibility that the vehicle may not start following a deliberate shutdown, as well as alert the driver of impending battery failure.

It might seem reasonable that a measurement of minimum battery voltage during crank would give a good indication of impending doom, but this is not the case: Figure 1 shows a comparison of cranking voltages of a battery that was subject to accelerated ageing. In week 13, a week before eventual failure, both the worst-case droop voltages are essentially the same as a cranking sample from week 9, so a more sophisticated approach is needed.

Figure 1: Comparison of cranking voltages of battery with accelerated ageing (source: Ryan J. Grube).

1 • 2 • 3 Next Page Last Page

Comment on "Battery management for car start-sto..."
*  You can enter [0] more charecters.
*Verify code:


Visit Asia Webinars to learn about the latest in technology and get practical design tips.


Go to top             Connect on Facebook      Follow us on Twitter      Follow us on Orkut

Back to Top