I have a project that requires me to be able to read the Li-ion charge level while the PiP is charging. I've got a OBD-II ScanTool arriving this week; but I'm not sure if I can get any information off the OBD-II interface while the car is charging? Is there any information readable from the OBD-II while the PiP is off? If not; is there another safe sensor point I could read this data from?
In addition to what John posted: You can use a ScanGaugeII or other similar device (Torque App on Android with a bluetooth ODB-II reader/sender) to read SOC (state of charge), battery pack voltage, Amps in/out of the battery, and host of other charging/battery related values. However, you can only read this information while the car is on. Once the car is off, the ECU goes to sleep and whatever OBD-II tool you are using loses communication with the car.
Sorry; I should have been more clear. I need an automated way to read the charge level. Ugh...that's what I was afraid of. And no way to leave the car on while charging obviously. I guess if the button press John mentioned allows me to get a quick ODB-II read...I could have a robot in the car push the button every 5 minutes or something. Wearing out my power button sounds like an expensive issue though ;-) Maybe I'll have to find someplace I can wire in a sensor. If it helps; the project is to build a computer into my open source charging station to allow me to set the max charge level to say 95% before it cuts off. This will save me a LOT of gas each month, as I live on the top of a hill. Currently I'm burning about 1 gallon of gas every 150 miles on the warm up the engine does when it is fully charged and going down the hill (no place to put the energy). Living on top of a hill | PriusChat
How about measuring the current that the PiP is charging at. Once it nears its maximum SoC, it starts to slow down considerably. If you log the data (or if someone who has logged the data shares it, Priuskitty comes to mind), I'm sure you'll be able to at least "ball park" a current vs SoC range. EDIT: Here's some data Priuskitty posted.. on 120V, looks like it dropped down to 5A for a bit before it cut off Attention Kill A Watt Nerds | PriusChat
You may want to consider sihfting into neutral when going down the hill to prevent the ICE from starting.
I've been doing this some -- and it does seem to work. There are two problems though: 1) It uses up more brakes down the big hill -- which is the big opportunity for regen braking -- so will probably be more expensive than using the gas in brake repairs. 2) Having difficulty with the WAF (Wife Acceptance Factor). She wants it to be easier than switching into N and back and forth to D on the hill in traffic (it's stops every block for 6 blocks on the hill).
Yes, if you watch the charging current (or kw) you will see if drop about in half for the last 15 minutes. Depending on your total estimated EV range, this is about 0.8 to 1.0 miles before full...maybe about 93% full plus or minus a percent or two. If you want to be at 95% you could just wait until this event happens, then wait ~1-2 minutes more Mike
Seems awfully complicated when you could just as easily plug into a timer switch and set it for 2 hours or whatever it takes to get 95%. You're going to lose regen opportunity in neutral, not to mention increased brake pad wear and you risk engine damage if you go too fast.
Doesn't really work when the car begins it's charge at a random state of charge. I really have no idea how long each charge will take. I guess I could try to guess based on the SOC reading...I may experiment with this to see how accurate I could be. The trick is that I really want no less or no more than the optimal amount (95% .... Possibly more after testing of hill charge).
Maybe a low cost solution would just be some sort of alarm that goes off when the amps drop...and I could run down and unplug. Hmm...
As soon as you plug in the car, the screen will tell you approximate kwh and charge time. You can adjust the timer accordingly.
The time to finish recharging is very inaccurate. It will say 20 or 30 min left and then in 5 min it is done. It is giving a very conservative estimate...probably considering the worst case amount of heat and that the charger will have to allow a very small current intermittently or something. Mike
I've thought about automating this as an upgrade to the openevse project. Current sensor plus some software to read it and and a timer function to turn off charging. Might be useful for hilltop PIP's or better yet as a built in option to short charge for the onboard charger timer system. SoC can't be read while charging for any battery because you're really just seeing the charger voltage and current output. The PIP BMS turns the charger off periodically to check the batteries actual voltage. Somewhere on this site is a pretty good discussion of this topic including some links to tech documents on the difficulties of accurately reading SoC. This in addition to the links posted above.
This was exactly what I was thinking. I haven't started buying parts for my own openevse yet, but was planning on doing so soon. This feature (partial charge) would be an important one to build into my system. Building it into an openevse is probably the most cost effective approach as well. I'm going to dig for that "difficulties of accurately reading SoC" discussion. It's too bad the J1772 standard didn't include some pins to send back the SoC whenever the cars periodically check. It seems like all cars must do this; and it would be useful information to have at the charge point for a variety of purposes. I'm also considering replacing the LCD board with a Raspberry Pi so that I could have an internet enabled openevse; but I'm not sure if this is going to be overly ambitious. The $25 Raspberry Pi model A supports i2c and costs about the same as the LCD parts; I believe. I don't need a screen on my openevse box, but would like to be able to monitor from an iPhone or computer.
Once you figure that out, let me know where I should send my OpenEVSE to so you can upgrade mine as well .. logging and internet access (to control on/off and notifications) would be awesome
