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    EEVblog #1047 – Solar Roadways FINALLY BUSTED! Colas Wattway

    Dave finally puts an end to the idea of Solar Roadways. We have the test ...

    • Mastew

      Hey David great blog… But it seems you screw it up on your last post, the video isn’t there lol

      Regards from Argentina

      • Tyler

        Dave — Why aren’t rechargable batteries at 1.5V like standard alkaline’s? And for the for the purposes of using them in equipment can this difference in voltage ever be a bad thing? (Such as in a Nintendo Wii controller..I feel like I have noticed some funny business before, but generally it works just fine)

        • @ Tyler
          The chemistry of the cell determines the open terminal voltage and the discharge curve, so it’s essentially impossible to make a 1.5V NiMH or NiCd cell.
          A well designed piece of equipment should be able to handle both Alkaline and NiMH/NiCd, as the end voltage is not too dissimilar at around the 0.9-1V mark. Alkaline still has usable energy down to around 0.8V, so really well designed equipment that wants to get the most battery life will have a setting to switch between Alkaline and rechargable.

    • Timothy Tee

      You did not tell us whether the Varta batteries can fully charged up in 15 minutes.

      Nice video. Keep up the good work.

      • Haven’t done any actual capacity tests on these yet, sorry, as that requires a bit of work and I’m a tad lazy ;->

        • Will

          There is no way they’ll charge up to the 2.1Ah on the side of the battery. 15min at 7.6A will charge the battery with 1.9Ah,but there is no way you’ll get 100% charge efficiency at 4C- even though you can get 100% charge efficiency at certain temps and state of charge with NiMH batteries. It would be interesting to see how (in)efficient the charging is at 4C.


    • peet

      thanks dave for publishing your videos!
      i really enjoy watching your EE lessons!

      i’m looking forward to an informative future 🙂


    • Dave,

      You should have a peek over at the RC electric helicopter / airplane side of life.

      We’ve got these Lithium Polymer batteries that are 3.3Ah at 22.2 volts, capable of sustained 30C discharge rates! (Yea 2Kw for 2 minutes!)

      Here’s one:


      Some manufacturers are claiming 5C charge rates, but finding a charger that can actually perform a 5C rate is near impossible 🙂

      Oh, and back to the topic, these batteries are charged during the first part of the cycle at a constant current. Once a target voltage is reached (4.2v per cell) the charger switches over to a constant voltage charge scheme.

      The biggest problem is newbies with GOOD NiMH chargers figure they can use them to charge their LiPo batteries. Unfortunately, these lipo batteries never display a negative delta voltage and the charger never shuts off!!!

      The batteries will exhibit a positive delta temp, unfortunately that change in temp is associated with a massive and complete discharge, emitting quantities of smoke and flame. :-0

      Many a hobbyist have lost vehicles and work shops from charging on the wrong setting while attending to other details!

      If your bored, Youtube for “Trex 500” You’ll find things like this: 🙂


    • I did a review of a intelligent battery charger just a week ago ( http://aonomus.wordpress.com/2009/10/02/review-of-the-gt-power-a8-battery-charger/ ), and at least for NiCd, I have a chart of the charging curve that helps illustrate what is going on during NiCd charging (http://i139.photobucket.com/albums/q297/aonomus/GT%20Power%20A8/NiCd_charge.jpg ). (Note that the temperature is a little funny because I had just done a 3C discharge on the pack and it was still warm.)

      Mainly the charger shuts off after detecting the -dV/dt following the peak voltage.

      I’d be interested to see what you think about the various lithium battery chemistries including LiFePO4 and LiPo. The RC world probably is the most demanding on batteries because of size/energy density, and sustained discharge rate (many larger 5Ah packs that are happy at the 30C discharge rate).

      @ James:
      LiPo batteries and Li-ion both have that positive deltaT at the end of their charge cycle, and the energy required to liberate oxygen and fuel a further exothermic reaction is relatively low, hence why alot of lithium batteries can get really hot, and then burst into flame. On the bright side LiFePO4 batteries need much more heat and energy to liberate oxygen and start said runaway reaction (to the point where if the battery is going to explode, everything else around it has already caught on fire).

      • Daniel Meinzer

        Battery charging is often overlooked, it seems. Working on various research projects, I’ve heard a many stories of lithium-ion batteries exploding from improper charging. From just last week, here’s a picture of one that was left charging overnight in our lab when the charger failed (or wrong setting, don’t know the whole story). We’re lucky it didn’t catch fire to anything and burn the whole building down. Our normal procedure is to do all li-ion charge testing in ammo boxes, with someone always present.


        • Now that’s NASTY!

        • Standard policy for charging LiPo’s is to use one of these: http://hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4134

          They are fiberglass bags with enough space at the top to vent the flammable gasses, while at the same time preventing any flame from actually reaching the battery causing a instant explosion…

          People use ammo cans, soup cans, other containers filled with sand, etc. No matter what, do not confine your batteries!

          • KTP

            If Dave has the knowledge, a discussion of the different Lion battery types and how to charge them would be a great blog entry.

            There are “safer” types such as LiFePO which will not blow up, but they have downsides…tricky charging with the need to balance each cell by draining it after charging. Also they do not have nearly the energy density of the LiPo batteries like those used in RC craft.

            I purchased some Sony LiMg rechargables that are supposed to be similar to the LiFe, but haven’t had the chance to research how to charge them. They are currently at 3.8V per cell.

    • Walter

      I have had a version of this charger, sold by Energizer, for two years (or so). I use the batteries mostly with small speed lights (flash strobes) and have noticed that the batteries last for about 18 months in this environment. For me that would mean a set of four would last for 15-20 charges.

      Another thing I’ve noticed is that right after the charge light goes off the batteries are very hot. Too hot to hold comfortably, but not so hot as to cause an actual burn.

      At $10/set for the batteries, I don’t mind the reduced life span in exchange for the fast charge. The 15 minute claim definitely seems to be accurate.

    • Dan W

      Hi Dave,

      In both videos you noted that charging at 4C would not get 1000 charge cycles on a battery. What is the relationship between charge rate in C and battery life? At what rate to we start eating into the life of the battery?

    • Hi Dave,

      I built a universal battery charger (smart) with a PIC I’d like to show in my blog (in spanish)

      Currently charge lead acid batteries), NiMH, NiCd, Li-Ion battery and Lipo (Lithium Polymer)


      • Ivan

        Se ve bien, para que la resistencia de alta potencia?

        Looks good, what’s that current sensing resistor for?

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