Auxiliary battery problem with Hymotion

[roperld]

You might want to read about some problems I and another local Hymotion owner have had with the Hymotion interaction with the Prius auxiliary battery. Hymotion has been informed of the problem; we are waiting for a fix.

Dave Roper

[TheForce]

I replaced my AUX battery with an Optima yellow top a few months ago. I did it myself and I had no problems installing it. Not a lot of room to do it but it can be done without moving the Hymotion battery. Just a few days ago I accidentally left the interior lights on and my battery dropped down to about 9v. After jump starting the car and let it charge its now sitting between 11.5v-12v. I haven't had any issues with the brake lights running down the battery. I have had the flashing LED twice now which I think its tied to the AUX voltage or some kind of communication error with the car.

[ibcs]

I had to replace my aux battery after the installation. It was probably a little weak, since my kids left the back light on several times. I have not had any trouble after changing the battery. I had Toyota dealer replace mine.

[glaf8421]

How about running the car without the sysem on for a couple a days a week? This will charge the 12 volt battery too.

Grant
Miami

[roperld]

Here is a hypothesis of what may be happening with regard to the auxiliary-battery problem with a plug-In Prius:

Hypothesis:
In EV mode the hybrid system, after using the auxiliary battery to start the system, does not charge the auxiliary battery from the system battery in order to reserve the system battery energy for motion. Instead, it uses the DC-to-DC converter to provide 14 volts for the dash, etc. Out of EV mode the DC-to-DC converter does charge the auxiliary battery. Thus, a plug-in Prius does not charge the auxiliary battery as much as a Prius without the possibility of EV mode. So, a weak battery in cold weather might not get charged enough to keep it above the voltage level needed to start the plug-in system, or even enough to start or keep running the hybrid system.

If this hypothesis is correct, a plug-in system probably could solve the problem by using a AC-to-DC converter off of the plug to charge the auxiliary battery while the plug-in battery is being charged. I have not had the problem, even in cold weather, since I installed a separate plug out the trunk lid connected to a trickle charger that is connected to the auxiliary battery.

I got this idea because the auxiliary battery ran down on my electric pickup, which I detected because I had a device connected directly to it. However, the pickup still ran because the battery is vestigial and no longer is needed to start and run the electric motive system.


Dave Roper

[hobbit]

Why would the stock DC/DC converter simply cease producing its
14V just because the Hymotion system is online in tandem with
the big battery? If the car's DC/DC stops making its output,
the car's pretty good about sensing that and throwing a DTC,
regardless of what the source of its 200V comes from.
.
_H*

[gkalkas]

Originally Posted by ibcs

I had to replace my aux battery after the installation. It was probably a little weak, since my kids left the back light on several times. I have not had any trouble after changing the battery. I had Toyota dealer replace mine.

Ibcs, just curious. How much did the dealer charge for the new battery/instalation? My '05 isn't getting any younger, but have had no trouble with the Hymotion system, since Jan 8 when installed.

I did let it run down last year while away for 2 weeks. (left the keyless entry on).

[TheForce]

During these colder days I have seen my 12v battery sit around 11-11.5v before starting the car. I have not had a problem the the Hymotion since I have been leaving it turned off during start up.

[Lithium]

I have the Hymotion upgrade and have not had any issues yet with flashing error codes or a low aux. battery. I leave the HyMotion enabled all the time. I don't believe that EV mode is preventing the DC-DC converter from charging the 12V battery. With Hymotion enabled and the car on (press brake pedal + press power button), the 12V battery voltage is consistently around 13.9V regardless of the EV state. If I power up the car without enabling the hybrid system (press power button WITHOUT pressing brake pedal), the battery sits at around 11.5-11.7V. The higher voltage seen with Hymotion and EV enabled tells me that the 12 DC-DC converter is pushing energy into the 12V battery.

Now, after having said all this, there is some doubt in my mind that the dealer connected the EV wire correctly when my Hymotion was installed. See my other thread on this:

http://priuschat.com/forums/prius-mo...ecm-whats.html

I do, however, see the EV status change quite often the scangauge when Hymotion is turned on.

[boxer93]

Lithium,
If the EV wire was not connected you would never see EV mode on the SGII. Since you do see it I believe it's connected. Don't forget when the Traction battery temp drops below 0C EV will not engage. for the last month I've probably see EV mode 20% of the time. No EV definitely impacts MPG more than just the cold temps and normal L5 function.
Chris