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  • #61
    Originally posted by Justin B. View Post
    I was poking around looking at different used/surplus batteries and came across listings for Tesla Model S battery modules, 24V, 250Ah. Since Li can be discharged a lot further than SLA/AGM would something like this be a good replacement for a 600 Ah AGM bank or could they be ran in parallel? Pricing was in the $1300 - $1400 neighborhood.
    Just google Tesla Powerwall

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    • #62
      Originally posted by nebster View Post
      No thermal mgmt needed for Tesla packs at fractional-C rates.
      Cheese and Rice what a load of BS. Get a clue, EV's run and charge at fractional C-Rates. Anyone with any kind of math skills like a 5th grader would know that is just plain ignorance, or a blatant lie. Which is it? Are you ignorant or a liar?

      For the rest of you who have at least a 5th grade education, take note. Tesla vehicle mileage is 300 to 400 miles. If the batteries were discharged at 1C would require you to go 300 to 400 mph. 1C is the 1-hour charge/discharge rate. Now Jethro you made it to 6th grade and should smell a idiot or liar. Those mileage are calculated at 50 to 60 mph. OK Jethro how many hours does it take to 300 miles at 50 mph?

      Did you come up with 6 hours? Well Jethro that is C/6 fractional C-Rate. Most off-grid systems can and will discharge a lot faster than that up to 1C in some applications.

      Jethro's, for the charge side of Tesla batteries depends on what class of charger you have. Level 3 is the fastest and you will never use one at your house unless you have $100,000 for one and even then you are talking a C/4 charge rate or about the upper limit of off-grid solar. Level 1 is your common house 120 volt 20 amp circuit and takes 12 to 17 hours aka C/12 to C/17 which is much SLOWER than any off-grid solar. The most common Charger in a house is Level 2 and is the exact same circuit your electric dryers uses of 240 volts @ 30 amps produces a C/8 charge which is where most solar systems fall into.

      So if someone tries to tell you EV batteries do not need the same protection because Solar Systems run at fractional C=Rate, tar and feather that Snake Oil salesman and run him out of town.

      -- question removed -- [COLOR=#FF0000]Moderator.[/COLOR]
      Last edited by Mike90250; 11-20-2018, 11:55 PM.
      MSEE, PE

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      • #63
        Let's stick with the facts and ignore the boorish behavior.

        Originally posted by Sunking View Post
        Get a clue, EV's run and charge at fractional C-Rates.
        They operate at an average C < 1.0, but peak C is what matters when we want to understand why there is active cooling (glycol loops) in the design, because heat production goes with the square of C.

        Tesla Model S charges at peak C of close to 1.4 in the lower portion of the charge envelope.

        Tesla Model S discharges at peak C of roughly 4.5 on hard accelerations. It will regularly be at C > 2.0 when driving casually around town.

        Someone charging at 0.5C produces 80 times less waste heat than the Model S flooring it off the line. At a more practical 0.25C to 0.4C for a house bank at scale, we're talking hundreds of times less heat.

        The Tesla cooling compressor doesn't even turn on until ~125F, a temperature the pack won't reach in casual driving on a moderate day.

        Finally, there are lots of people charging Tesla modules on their own at sub-C rates for ESS applications, and no one is really finding it necessary to hook up a pump and move coolant through the system. They just don't experience much ohmic heating.

        So if someone tries to tell you EV batteries do not need the same protection because Solar Systems run at fractional C=Rate, tar and feather that Snake Oil salesman and run him out of town.
        Don't conflate "protection" with "active cooling." Cobalt chemistry packs most definitely need monitoring and protection. What they do not need is what I've now written twice.

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        • #64
          Originally posted by nebster View Post
          ...............
          The Tesla cooling compressor doesn't even turn on until ~125F, a temperature the pack won't reach in casual driving on a moderate day........
          I can validate that statement regarding charging. When I charge my 90kWh at 48 Amps (12 kW) the compressor does not come on. When I charge at a supercharger at 88kW the compressor comes on. The supercharger rate is approximately 1C and the charge rate expressed in MPH is above 250.

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          • #65
            Originally posted by Ampster View Post
            I can validate that statement regarding charging. When I charge my 90kWh at 48 Amps (12 kW) the compressor does not come on. When I charge at a supercharger at 88kW the compressor comes on. The supercharger rate is approximately 1C and the charge rate expressed in MPH is above 250.
            Pardon my ignorance and confusion, but why is a charging rate expressed as a velocity ?

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            • #66
              Originally posted by J.P.M. View Post

              Pardon my ignorance and confusion, but why is a charging rate expressed as a velocity ?
              I was trying to relate to the Cheese and Rice explanation Sunking used earlier. Perhaps not a good idea to follow in his footsteps. (Insult intended)LOL

              KiloWatts are what matter to understand the issue and relate to C rates. But there is a big range of battery capacities among Teslas (40 to 100 kWhr) and it is important to take battery capacity into consideration when looking at charging rates.
              Last edited by Ampster; 11-21-2018, 12:50 PM.

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              • #67
                Originally posted by Ampster View Post

                I was trying to relate to the Cheese and Rice explanation Sunking used earlier. Perhaps not a good idea to follow in his footsteps. (Insult intended)LOL

                KiloWatts are what matter to understand the issue and relate to C rates.
                Perhaps only a good idea if the goal is to help perpetuate insults. Less so if the intended goal is real information exchange.

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                • #68
                  Originally posted by Ampster View Post
                  KiloWatts are what matter to understand the issue and relate to C rates. .
                  Wrong, dead arse wrong. C-Rates are about charge and discharge currents.

                  Amp Hours = Amps x Hours
                  Amps = Amp Hours / Hours
                  Hours = Amp Hours / Amps.

                  Wattage has nothing to do with it other than an end result. Here is IEEE, BCI, and ANSI definition of C-Rate anyone can look up as you have failed to do.

                  C-Rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of [B]100 Amps[/B].

                  Power has nothing to do with the calculation.

                  [B][I][U]So here a link for you[/U][/I][/B]
                  Last edited by Sunking; 11-21-2018, 01:24 PM.
                  MSEE, PE

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                  • #69
                    Yes, you are correct. I fall into the habit of using Watts because, as you say it is the end result of current times voltage.

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                    • #70
                      Originally posted by Ampster View Post
                      Yes, you are correct. I fall into the habit of using Watts because, as you say it is the end result of current times voltage.
                      OK think about that for a moment. Let's use a KISS example. I have a 12 volt battery that is discharge and I am using a 10 amp charger. Assuming the battery is at 50% SOC and I connect the charger, the voltage and current starts at 12.2 volts @ 10 amps = 122 watts. As we charge, the voltage goes up until we reach 14.8 volts @ 10 amps = 148 watts in say 10 hours. What was the constant? Hint it is not voltage or power. It took 100 Amp Hours to charge.

                      Kick it up to a 120 volt battery with a 10 amp charger. Same result, 100 amp hours but power and voltage are 10 times higher.

                      A very common mistake rookies and DIY's make is they fall for the BS claim Lithium Ion batteries are near 100% efficient with a range of 95 to 99% charge efficiency. The mistake is that is a Coulomb Efficiency, NOT ENERGY EFFICIENCY. Coulomb Efficiency is AMP HOURS, NOT Watt Hours. So what might you be missing leading you to the wrong conclusion? Think about it for a second.

                      Figured it out yet? Amp Hours go in (charge) at a HIGHER VOLTAGE than the Amp Hours going out (discharge) at a LOWER VOLTAGE. So for a LFP 4S we go inza at 14.4 jolts and goes outza at 12.8 jolts making energy efficiency 12.8/14.4 x 100 = 88%.
                      Last edited by Sunking; 11-21-2018, 02:35 PM.
                      MSEE, PE

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                      • #71
                        Yes, I understand that the voltage may vary significantly in that scenerio.. It is a bad habit I have working with low voltage Lithium which has a flatter charge curve. In a high voltage Lithium pack the voltage deltas would also be significant.

                        One could also point out that there aren't any shunts or clamps that measure Watts.

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                        • #72
                          Originally posted by J.P.M. View Post
                          Pardon my ignorance and confusion, but why is a charging rate expressed as a velocity ?
                          It's not. It is in miles per hour, but it is miles of RANGE added per hour of charging, not miles MOVED per hour of charging.

                          It's like hauling ten cubic yards of dirt with your truck per hour. Doesn't have anything to do with the speed of the dirt, just how much dirt you haul in that time.

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                          • #73
                            Originally posted by Ampster View Post
                            One could also point out that there aren't any shunts or clamps that measure Watts.
                            Do not be silly, every home in the USA that has electric power has power meters. Just about every Grid Tied Inverter has them. All it takes is a Shunt or Clamp-On Amp Meter and a Voltage Meter Kwh meters are utilities cash registers. Very simple devices.

                            MSEE, PE

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                            • #74
                              Originally posted by Sunking View Post
                              Do not be silly, every home in the USA that has electric power has power meters. Just about every Grid Tied Inverter has them. All it takes is a Shunt or Clamp-On Amp Meter and a Voltage Meter Kwh meters are utilities cash registers. Very simple devices.
                              Don't forget Power Factor. Bruce Roe

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                              • #75
                                Originally posted by Ampster View Post
                                It is a bad habit I have working with low voltage Lithium which has a flatter charge curve.
                                Hate to keep beating you up, but that is complete [COLOR=#B22222][B]nonsense.[/B][/COLOR]

                                The flattest Lithium Ion is LFP (LiFeP04), and in a 4S operation for 12 volts is 10 to 13.8 volts or a spread of 3.8 volts from 100% to 0% SOC. A 12 volt Pb FLA battery is 12.6 to 11.9 volts or a spread of 0.7 volts. Which is the Flatter Curve of the two? 0.7 volts or 3.8 volts? So how can you make that statement? It is complete nonsense.

                                Now you wanna talk about all the other Lithium batteries that have even Steeper curves. Pb batteries in my book from a charge curve POV is 542% flatter than LFP, and it only goes higher for all other lithium batteries. Pb batteries blow lithium out of the water with respect to discharge curves. It is no contest, Pb is far superior to any Lithium with respect to charge curves.

                                You need to reevaluate everything you think you know about lithium batteries, because from what you have expressed here so far is false, and leading you to the wrong conclusions.

                                FWIW commercial EV's do not use LFP batteries. Reason is because LFP Energy Density is not much better than Pb, and thus you could NOT get any meaningful range in an EV. They have to use much higher energy density cells which are much more volatile and prone to thermal runaway. Telsa uses the most unstable unsafe battery there is. It is the only way they can get the range, and requires extreme thermal management like liquid cooling and heater all of which use energy.
                                Last edited by Sunking; 11-21-2018, 05:22 PM.
                                MSEE, PE

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