Power meter for charging your EUC

[Mantraguy]

I admit, I'm a bit of a tech geek, and like to know that my chargers are working properly, the batteries are taking the correct charge, and the BMS is doing its job in balancing cells and decreasing current towards the end of the charge cycle. I also like to look at actual capacity used during a ride and compare energy usage of my fast rides with slower rides.

I used to use a Charge Doctor but they've been unavailable for a while, and limit out at 100v. So when my Sherman finally arrived, I wanted a way to see how much energy I was 'actually' using (or, specifically, putting back into the battery). The Charge Doctor won't work with the larger 100.8V Sherman battery, so I ordered a few parts and made my own. This is what I came up with:

You can't see the GX16-5 ports in the photo, but it connects to the output of your charger at one end, and to the EUC (Sherman, in my case) at the other end. It simply measures the DC voltage, current, and energy (in watt-hours or amp-hours) that has gone from the charger to the EUC during charging. This makes it much more accurate than the smart-meter option (plugging your charger into the AC smart meter), as there's no 'guessing' at efficiencies etc - it's measuring exactly the power being transferred to the EUC from the charger (it takes almost no power to run itself). At any given time, I can see the output voltage, current and power, so it's easy to see that the power is dropping down to just a few watts at the end of the balancing phase. The chargers these days have green lights that indicate some seemingly random point in time when the power has decreased to a pre-set level, but the EUC is still balancing for some time after that light has changed from red to green. With this, I know exactly when all charging / balancing has completed and I can unplug everything.

It's also a great way to track, long-term, any decrease in the capacity of your battery, or see if there's a problem with the BMS and that it isn't properly balancing the cell groups (which would be obvious if the current did not gradually decrease down towards zero before shutting off). An added bonus is that the recorded time and energy (Wh or Ah) is stored in memory when you unplug it, so that data is not lost in case of power outage etc. When the charge resumes, the data updates from the last position. You can reset this the next time you charge simply by holding the one button (MENU) on the device.

I bought the tester as a stand-alone unit, and wired it up with 5-pin GX16 input and output ports with the proper pinout {1-2 (+) and 3-4 (-)} for the Sherman. It displays 3 digits of voltage and current, so under 100V it will show 1/10V resolution (but only 1V resolution after 100V is reached). This controller will handle up to 10A, but others are available if you want to charge at over 10A (up to 50A - can't see that happening any time soon)! My wiring is a little messier than I'd hoped (ran out of the right size of heat-shrink) but it's all encased in a plastic box with grommets on the input/output wires so nothing gets pulled etc. The voltage and current can be calibrated / adjusted with internal potentiometers, in case you actually have a way of accurately measuring these values. It seems to be pretty accurate out of the box, as it's within 0.5% of all of my other DMMs.

Just thought I'd post here in case anyone else was interested in making one of these. Or, if there's any interest, I'd be happy to build one for you.

 

[Chriull]

28 minutes ago, Mantraguy said:

The chargers these days have green lights that indicate some seemingly random point in time when the power has decreased to a pre-set level

Normally it's an (adjustable) charging current threshold. As Li Ion full charge is "defined/specified" by such a charging current threshold. Manufacturers datasheets for the normally used 18650/21700 cells specify about 50-60 mA (per paralleled cell)

28 minutes ago, Mantraguy said:

but the EUC is still balancing for some time after that light has changed from red to green.

Is minimal balancing and more bothering of the cells.

The bleeding redistors (try to) keep the weakest cells from reaching the single cell overvoltage cut off limit so all cells can charge to (almost) 4.2V. Then after charging - connector unplugged - the bleeding resistors discharge such weaker, now a bit overcharged cells (if they exist) downto 4.19V again.

And voila, cells are balanced without the trickle charge, which li ion cells do not like at all.

[Mantraguy]

I think I've seen 70 watts or so when the light is green, so that would be in keeping with ~70mA x 10P = 0.7A (or 70 watts at ~100V). Next charge cycle I'll try to keep an eye on the current reading when the charger light turns from red to green; I'm sure it's in that general range somewhere. 

I should also mention that the meter also has an input for a thermocouple (temperature probe); the temperature in 'C displays on the bottom left of the display ("--" in the image) when the thermocouple is connected. I didn't find anything even remotely warm while charging, other than the charger of course, so I left the thermocouple disconnected.

[Robert Rijkers]

can't you just turn on the euc world app during charging... it connects even when you just plug in the euc charger without even turning on the euc , at least on my KS S18

[Mantraguy]

I know on my Tesla that when you turn it on (plugged in or not) it balances, and if on a stand, spins up so that's no good. Unless the EUC is on, the app won't show anything since it has no way of connecting to the wheel. With the Sherman, you can turn it on (and therefore get the app connected to the wheel) but I don't believe it shows charge capacity etc. Even with the smart plug, I think the current (and therefore power) going into the wheel is an estimate based on estimated charge efficiency. I know that the energy numbers (Wh) I got from the smart plug (and EUC World) are all over the map - this seems much more accurate. I like to use these numbers to determine my overall usage (Wh/km) for different types of rides, and with the app, those figures were very different than what I get now.