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Auxiliary battery problem with Hymotion

Discussion in 'Prius PHEV Plug-In Modifications' started by roperld, Dec 21, 2008.

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  1. roperld

    roperld New Member

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    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
  2. TheForce

    TheForce Ron Paul 2012

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    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.
  3. ibcs

    ibcs New Member

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    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.
  4. glaf8421

    glaf8421 New Member

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    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
  5. roperld

    roperld New Member

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    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
  6. hobbit

    hobbit Senior Member

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    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*
  7. gkalkas

    gkalkas New Member

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    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). :(
  8. TheForce

    TheForce Ron Paul 2012

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    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.
  9. Lithium

    Lithium HyMotioned Member

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    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-modifications/57364-hymotion-white-wire-ecm-whats.html

    I do, however, see the EV status change quite often the scangauge when Hymotion is turned on.
  10. boxer93

    boxer93 Psyched for PHEV

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    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
  11. ibcs

    ibcs New Member

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    The cost for replacement from the dealer was $223 installed.
  12. chogan2

    chogan2 Senior Member

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    Dave,

    Thank you for this post and posting you referenced at the start of the thread.

    We have the Hymotion pack installed. Following your lead, I've just installed an automatic-cutoff trickle charger on the auxiliary battery on my wife's 2005 Prius.

    Once the temperatures dropped here (Virginia), we had several instances where we had to reboot the car several times to get it to start. Finally, we got the red triangle, and were unable either to start or to turn off the car. At that point, I read your post, then measured the auxiliary battery voltage. It was under 9 volts.

    Is there a definitive answer on whether you do or do not have to move the Hymotion pack in order to change the auxiliary battery? Your dealer said so, but maybe that was more a matter of convenience than necessity? Has anybody else with an L5 put in a new auxiliary battery without moving the L5 pack?

    I'm in no hurry to pay Toyota $250 to replace my battery. The current one appears to be holding a charge OK, and if I have to replace it, the consensus seems to be that the "yellow top" battery is more durable. So I'd probably put one of those in when the current one dies. But I really don't feel like monkeying with the L5 pack at all. If I have to move it to replace the auxiliary battery, I'm taking it back to the dealer who installed the L5. But if I can get it in without moving the L5 pack, I'll put in a "yellow top" myself when the current one dies.
  13. ibcs

    ibcs New Member

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    Had a great conversation with the senior tech at Hymotion, Mr. Strong, concerning the battery voltage and red triangle problem. The Hymotion BMS system requires a higher voltage than the Prius to start. They are sending me a voltage regulator circuit to put between the Hymotion harness. With the modification you will be able to start the Prius with a low voltage situation without showing the red triangle caused by the Hymotion BMS. The best part is they are shipping it to me free of charge. I will report back on how the installation proceeds with pictures and feedback.

    ---Kent
  14. TheForce

    TheForce Ron Paul 2012

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    I installed an Optima yellow top battery a few months ago with no real problem. Its a tight space with the L5 in there but its still doable.
  15. drees

    drees Senior Member

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    Sounds like the proper solution to the problem untli they can fix their system to run on lower voltages. They should probably start fitting this as standard.
  16. chogan2

    chogan2 Senior Member

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    Just want to say thank you both (IBCS and The Force). I suspect that Hymotion didn't quite count on a bunch of old, marginally-performing auxiliary batteries. One could solve the problem either with a voltage-stabilization circuit or by keeping the aux battery voltage up. I already have the trickle-charger installed, so I'm just going with keeping the aux battery voltage up. I'm going to replace the OEM battery at my leisure and keep on with the trickle-charging during the Hymotion charge.
  17. ibcs

    ibcs New Member

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    Just to let you know, I replaced the battery on Oct. 27th so it is hardly marginally-performing. The reality is that the draw in extremely cold weather causes the voltage to drop below the Hymotion threshold. I will post pictures once I get the fix from Hymotion.

    ---Kent
  18. chogan2

    chogan2 Senior Member

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    Kent, thank you for the clarification.

    I am surprised at how many issues there have been with the Hymotion conversions, given that they road-tested a bunch of them prior to sale. For example, the Fairfax County VA government got one back around January 2007. I'd have thought they'd have thoroughly debugged the product by this point. Off the top of my head, I count:

    1) Several people could not get a full charge in hot weather. (I was one, and Hymotion replaced my pack. My impression is that the fan did not run during charge on my first pack).

    2) I and at least one other Priuschatter broke off the ground prong from the Guest socket in the bumper. (And for the time being, both of us are charging the car with this slightly unsafe condition.)

    3) The auxiliary battery drains as the Hymotion battery charges, causing problems for those with marginal auxiliary batteries. (Trickle charger fixed that for me.)

    4) The Hymotion pack draws enough current so that, in very cold weather, it drops the aux battery voltage below what is required for proper startup, even for a fresh auxiliary battery. (Requires voltage regulator fix from Hymotion.)

    5) Some people have sporadic failure-to-communicate errors between pack and car (13 flashes of the switch LED), which again seems related to auxiliary battery voltage drop at Hymotion startup. (Workaround is to start the car with the Hymotion battery off.)

    Nothing fatal, but cumulatively kind of annoying.
  19. ibcs

    ibcs New Member

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    Hymotion sent the L5 Booster to me about two weeks ago. The device plugs between the existing harness and can be installed a few minutes. Of course, I spent about 15 minutes making sure I was following each step. The hardest point was determining the pin to press down to unplug the existing harness. So far, everything has been working great. I have not had really cold weather since the installation which is when I would get the red triangle. I have attached pictures for everyone to see.

    Attached Files:

  20. drees

    drees Senior Member

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    Nice to see that it's an easy fix!
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