amberwolf wrote:Looks like it only does up to 60V full charge, and 35A discharge rates.
Yeah. I really was hoping we'd be able to pull of the standard unit to work with up to 72V batteries OK but in the end the component selection for the mosfets for charge (p-channel) and discharge control made this difficult. Our main target for this is for bike shops that deal with ebikes where 99% of what they encounter are 36V / 48V / 52V batteries and where a 10-20A characterization is more than sufficient.
I wonder what it would take to up the discharge rate to something useful for large / high-current packs?
Basically if you don't _need_ the test to terminate the discharge and start the charge cycle automatically, and are fine running it just as a discharge test until the BMS trips, then you can skip the Grinspector base station completely. Take an existing V2 CA device, load on the Grinspector firmware, and hook it up inline with your battery using a shunt and load that is appropriate for your discharge currents. You'll get to use the software that makes the discharge plots and will be able to test batteries right up to the full 150V rating of the CA device and at whatever current you want. If you did want the automatic charging functionality on higher power and voltage packs, then you could take the CA's throttle output signal and have it turn a relay board on and off as shown in this image here, basically replicating the base station functionality with appropriately rated parts:
Matador wrote:AND !!!! Calculate DC internal resistance.
Now that's very interesting.... DCIR measurement can be complex too. Hence i'm intrigued how they do it.
Can you measure DC-IR in function of State of Charge and get a cruve of the DC-IR evolution through whole the discharge cycle ??? (DCIR on y-axis versus SOC on x-axis) ?
Basically in the initial implementation we have it so that IF you run two more more discharges at different current levels, then the software will compare the terminal voltages between the two plots at a handful of SOC levels and compute an average/effective DC internal resistance value. However, for that to work it means that the user needs a load bank that lets them switch the discharge current and do two or more discharge tests.
We'll be modifying the software fairly soon so that it has an option to do a periodic pause during the discharge cycling to get an internal resistance value on just a single discharge test at a fixed current. This is what we've been doing during the QC of our LiGo battery modules, and it allows for some pretty nice graphs of the DCIR versus the SOC level. Here is a recent test on a pack that failed QC. We have it so that every 0.1 Ah the discharge current stops, the voltage is measured at 0 amps, and compared to the voltage when current was flowing.
Since we're communicating directly with the BMS in this case we can see all the individual cell voltages and do a cell by cell resistance comparison. In this case, cell #10 (purple) has a much higher resistance than the others, averaging 40.7 mOhm compared to ~35mOhm, and you can see that during the discharge this was reflected in a lower voltage too since there is more terminal voltage drop. So the Grinspector software will be doing something similar, but it would just be at the pack level voltage and resistance, not the cell level.
Currently recovering from the Suntrip race on a back to back tandem solar powered row/cycle trike
. 550 watt solar roof, dual Grin All Axle hub motors, dual Phaserunner controllers, 12 LiGo batteries, and a whole wack of gear.
Now back in Vancouver with my Big Dummy Frame (yes This One
, thanks ES!) with Grin all-axle front hub, Phaserunner controller, and 52V 19Ah Cellman triangle pack
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