22 thoughts on “Intelligent Battery Charging

    1. Laptop batteries have inside a BMS (Battery Management System) . It charges, monitors AND makes the batteries charged equally. As I am everyday dealing with those (and other) batteries, I can tell, for sure, that the real problem is the bad quality of the cells used , even with high quality laptops. Also, BMS’s have a built-in “time-and-number-of-charges” counter that tells You that “battery is bad” (programmed obsolescence” , as we know It.

  1. “I’ve always wondered why most laptops don’t have this already built into them. ”

    have you seen the price of a laptop battery, now look who sells them … and add the two together

    This is a handy little gadget, especially if your into robots or rc

  2. Are you sure that this is included in most modern laptop batteries? I had a laptop that had a perfectly good battery, used it daily, then I left it plugged in for about a month and the battery was shot, it lasted about 20 minutes, down from about 1.5 hours.

  3. yes, a similar circuit is in all modern laptops. The key killer of laptop batteries is the heat associated with being always plugged in and running. If your going to leave it plugged in, charge the battery about half way and then take it out.

  4. What I really want in my laptop is a smart charging circuit that doesn’t just stop charging but makes sure that the battery is more than 50% discharged before allowing charging to begin again. Laptops may have a cutoff on their chargers but dispite what the manufacturers may say, the batteries are still being used while the laptop is plugged in. This kills the batteries fast if the laptops are left plugged in after their batteries are fully charged. I was just saying that a more intelligent approach to this is needed in most laptops. I’ve seen IBM laptops that at least beep once the battery is fully charged. This circuit will not help with that though. I was making a general statement about other areas that need improvement.

  5. In fact, not only do modern laptops have smart chargers, but the batteries themselves are smart. At the very least, the batteries relay thermal info. Many can even give voltage, discharge rate, and even stuff like model number, etc… I still wonder if some companies use this info to force batteries into an expected lifetime. I’ve had several old laptops. Some batteries still work after many years, while others seem to crap out way to quick.

  6. This design is alright for charging a 12V lead acid battery only. Doing a simple float charge design like this one could take a long time depending on the capacity of the battery, however it is fairly cheap.

    A faster charger version would charge to about 14.5-14.7V, and then switch to a float charge of about 13.8V once the current reaches a certain low threshold. There’s tons of designs like this, just go look online. Fairly simple and cheap.

    Other chemistry types require very different charge profiles. Most laptop batteries(lithium ion) for example, require a constant current constant voltage charge profile, and has to be sensed with fair precision. Overcharging can destroy the battery as well as be dangerous.

    Someone needs to look into Nickle Iron batteries again… Edison did them back in the day, and they are very interesting…

  7. @cidtrips: It’s not just the heat.

    While perusing the Pandora gp32x.com forums, I saw a chart showing cycle dropoff at various voltages. Charging to about 4.175v-4.2v gives a steady decline, which should give around 1000 cycles. Most laptops charge just beyond that, to ~4.25v cutting potential cycles from 1000+ to maybe ~200-300.

    Heat makes it worse. I’ve seen batteries from older Acer laptops die in mere months.

  8. Lithium Ion batteries have a limited life – no matter how well you look after them they degrade over time. Older laptops used NiMH (or even NiCd) cells which had different failure modes.

    All by-the-by – looks like a useful circuit for keeping Pb cells in good condition. We had a load of cheap UPS systems at work that regularly killed their cells. We’ve replaced them all now with a big (and expensive) one that “guarantees” a 10 year life on the cells. We’ll see what happens in a few years time…

  9. “Doing a simple float charge design like this one could take a long time ”
    Tell me about it, my god damn 1500VA ups keeps charging for more than 24 hours after the batteries got sucked down.

    I built one charger circuit once but it depends on battery type what you need.

    Thats true that the constant charging kills laptop batteries faster but if you don’t use a lithium battery for years that will die anyways.

    I have an 5 years old asus notebook with the battery so fucked up in it dies in 2 mins. Certain OSes like NetBSD bitching about it(there are 30sec freezdowns on the console). The average lappy batterys die in 2 years if you actively use your laptop eg. you have it always online, when u travel in sleep mode.

  10. Would this device be useful for a DIY wind turbine to help keep the battery from overcharging? If not, will someone point me in the direction of something that would?

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