Charging at the top of a hill

Ok, the first experimental data is in. Last night the battery was at 61%, this morning it was 100%, but it still gave me a warning that the charger had disconnected before charging could complete. Also, it dropped to 99% while I was sitting in the driveway, so I think it was on the low end of 100% (like 99.5%). It made it all the way all the way down the hill without the engine turning on. I did have the heat turned on, so that would have helped. The battery was down to 55% at the end of the drive. Ambient temp was 45F.

I also captured data from the drive with the HybridAssistant app. That shows a starting state of charge (SOC) of 81.18% and a ending SOC of 51.37%. SOC maxed out at 82.8% at the bottom of the hill. You can see from the graphs that there were a couple times in the drive where the engine almost kicked on because the battery couldn't soak up charge fast enough: the first time at the bottom of the hill, and the second time where I had to slow down suddenly for some construction workers. The drive is in two parts, so two graphs, one mostly downhill and the other the mostly uphill return trip.

More data coming this afternoon, as I've got another 1.75hr charge scheduled to finish at 1pm.

 

This is a cool idea. I might be able to set up a single raspi within the house but close enough to the car to get a bluetooth connection. I could also have it turn off the the charger through it's web interface, with no extra hardware needed. I don't think the OBD adapter works when the car is powered off though, so that'd be a killer (I'll go check).

It's about 3/4 mile long, dirt road, moderately steep. I typically drive it at 20 to 25 mph, much faster and I might end up in a ditch. There's really no where to burn off charge by goosing it. I typically regen 3 to 4% of the battery going down and consume 8 to 10% of the battery on the way up.

 

Well, it appears I was at least partially wrong. I can connect to the OBD adapter with the car off. I'm not sure how to get the battery % or state of charge though. HybridAssistant connects to the adapter but says "waiting for car" and shows very little data. I can also connect with the OBDLink app, but that doesn't show any battery data either. It's possible that OBD adapter simply can't access the data with the car off. Anyone know a PID code for battery charge info?

 

Right, it wouldn't be an ideal solution to intentionally burn off charge. However, if you're about to go down a hill then the car has a bunch of gravitational potential energy that has to be converted to something. Ideally it would be converted to battery charge, but if the battery is already full then you've got to pick a less ideal option. 1. Go down in neutral and convert the energy to heat in the brakes. 2. Let the engine turn on and use that as a brake. 3. Convert it all to kinetic energy (minus air drag) and try to stay on the road at 100mph. 4. Hit a tree 5. Intentionally bleed off some energy in advance. 6. ...

 

Second charge is complete, but I haven't driven it yet. It charged up to 90% (from 55). SOC is 76%. Charger recorded 2.40 kWh of energy use.

So, 35% charge this time, 39% last time. That's maybe more variability then I was expecting, but not too bad. I don't have the pre-charge SOC or kWh used for the first charge, so I don't know if there is similar variability there yet. I'll try to keep a closer eye on those in the future.

 

Correct!

 

ooo... just thought of another workaround (#6): The L2 charger's web interface reports the current charge rate in amps. The car automatically reduces the charge rate as the battery fills up. I could write a script to monitor the charge rate and turn off the charger when it reaches some low value (like 3 amps).