I plugged in my Hymotion whiel the car was still on...

Well, your first mistake was listening to AC/DC in an electric car. Each side of the electronics system tends to cop an attitude, and they end up brawling.

Seriously though, I think the bar situation at this point is a coincidence. The pack should never have turned on when the car was on, just like the car won't turn on with the pack plugged in.

I'll assume you've fully charged the pack a time or two and have observed this problem each time. If so, I would say this is most likely an indicator that your pack is a bit imbalanced. It's pretty easy to fix if that's your problem. When the pack charges, if balance isn't achieved within a certain amount of time, the BMS gives up and stops charging. The fan shuts off when this happens, so it should be easy to tell. After the fan shuts off, let the pack rest for half an hour or so, unplug it, and plug it back in. Charging will resume and the balance should improve. You will likely need to repeat this operation many times to fully restore good balance--once or twice a day for a week or two should yield an easily noticeable difference. Keep doing it regularly until you stop seeing improvement. I have used this technique on a couple of packs successfully, and do it a couple times a week as part of my normal routine. Please report back and let us know if this works for you. It's possible there are other things going on, but this should be the first thing you try. Good luck, and rock on!

 

I'm very happy to hear that the technique worked for you! This probably means you have a cell group with a bit of a self-discharge issue. To keep balance as good as possible, keep doing this on a somewhat regular basis.

Yes, the cold makes it harder to tell how much the "margins" may be moving. Thanks for reporting back.

 

WB9K, Just noticed this year+ old thread. I haven't had any issues with my Hymotion, (knock on wood!) . Though, I used to average around 78 mpg. Now it's more like 73. Do you recommend this "top off" method for any Prius with Hymotion, even with no problems? I plug in at night, then unplug in the AM. Should I unplug in the AM, then replug once or twice a week? Maybe I can get back that lost 5 mpg?

 

WB9K,

I have been using your technique for a while now. I plug in around 11 pm, unplug around 6 AM for an hour or so, then plug in again for at least an hour. Some days, I may leave it plugged for several hours if I don't need to use the car. I still have very little to no Red Bars. If I don't need to use the car on a particular day, would it be a good idea to recharge several times in one day, one hour on, one hour off, repeated several times in one day? If I understood one of your earlier posts, if the battery is balanced, I should hear the fan still running when I go to disconnect the power. Right? I never hear it running when I disconnect, after the long charge, or the shorter recharge. Even with no Red Bars, I am still getting about 72 mpg, as long as I don't take any long mileage drives.

There have been just a few times that I have plugged in the car, and partially charged it, unplugging before it is fully charged. Of corse in this case, the fan is still running at disconnect. Would doing this partial charge compromise the battery in any way?

 

Sorry for the double-post. My response is below....

 

The battery's state of health (SOH) and balance should have no impact on your mileage while the pack is active. Unless you are fully depleting the pack, your mileage should only change with:

1) Driving conditions/style. Are you running heat/AC, accelerating the same all the time, that kind of stuff. A shift from 78 to 75 mpg would be easy to inflict with very subtle changes in driving patterns/habits.
2) SOH of OEM hybrid or 12Volt battery. It could be that one of these batteries is beginning to fail and not hold a charge properly, placing a bit of an additional burden on the Hymotion pack during regular operation. I have seen a whole host of bizarre behaviors from Prii with 12 Volt batteries that are dying.

Today, my recommended routine goes like this:

1) Plug in the Hymotion pack and allow to charge until is shuts itself off (fan stops running).
2) Unplug/replug the pack and monitor how long charging lasts (fan runs). If charging stops in under an hour, the pack can be presumed balanced. If it takes longer than that, unplug/replug until charging time falls to less than that. IME, a well-balanced, fully charged pack will shut off in 15 minutes or less.

Try these steps and see if the pack is really out of balance or not. If balance is OK, consider the earlier two points. If it's not, repeat the lower two steps until it is. I have doubts that the "red bars" and "mileage" situations are directly related.

Hope that helps.