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Revisiting small 12v heater discussion

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by markabele, Jan 26, 2015.

  1. ChapmanF

    ChapmanF Senior Member

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    Honestly? Anywhere? Have they taken the manuals off of techinfo.toyota.com? ;)

    I don't own a PiP, so I've never had a reason to download the PiP manuals. I might not know if Toyota has changed the basic organization since my Gen 1, but assuming they haven't, there's a service manual split about half as specifications/diagnostics and half as repair procedures (for Gen 1 those are Volume 1 and Volume 2), an Electrical Wiring Diagram Manual (much more than just circuit drawings), a Body Repair Manual (for the kind of repairs you do with grinders and welders; all the body repairs you can do with wrenches and screwdrivers are in the regular service manual), and the New Car Features Manual, which is the book that explains how all the stuff in the car is supposed to work and why.

    So, using my Gen 1 as an example, the New Car Features Manual is the one that says there are electric elements and why. It gives the basic information on their wattage (2 ✕ 165 W in the heater core, all models, plus another 2 ✕ 165 W in the footwell duct except in southern US markets) and the basic information on when they turn ON. First, there is a signal "IDH" from the DC/DC converter that can always override and force them OFF if there isn't enough 12 V capacity (such as, you've got the headlights, rear defog, wipers, etc. all on at the same time). As long as they're not forced off that way, they come on whenever the coolant temp is below a threshold and:
    • you've selected defrost, and the ambient temp is below a threshhold, or
    • you've selected foot or foot/def, and the A/C amp has calculated max hot as its target air mix damper position.
    Those are the conditions for the elements in the heater core. The extra ones on the footwell duct also turn on in the second case, but not the first.

    To learn more specifics, the next stop is the diagnostics ("volume 1") manual, since a diagnostics manual would obviously have to explain some way to test them and make sure they're working. It gives a procedure for testing the HTR0 amplifier output, which should pull low if you have the temp dial to full warm, the fan to high, headlights and rear defog off, and 'foot' selected with coolant 60 C or below, or 'foot/def' selected with coolant 50 C or below.

    That doesn't mean those are the only conditions where HTR0 turns on ... remember the description in New Car Features says it's really whenever the coolant is cool, the amplifier is targeting max hot, and the DC/DC converter isn't asserting the IDH signal. What's in the diagnostics manual is a concrete way to test that it's working, so they give specific instructions that should always meet the conditions (headlights and rear defog off should make sure there's DC/DC capacity, temp dial to full warm should make sure the amplifier swings to max hot).

    Likewise, there's another diagnostics page for the HTR2 output, saying it should pull low in the same conditions as HTR0 except with the coolant threshold changed to 65 C for 'foot' or 60 C for 'foot/def', and also for straight 'def' if the coolant is 75 C or below.

    Putting this together with what New Car Features said, it stands to reason that HTR0 is controlling the foot duct elements, and HTR2 is controlling the ones built into the heater core. That matches the wiring diagram in New Car Features, but (in a very rare example of a Toyota manual mixup) it's backwards from the illustrations, and section headings, in the diagnostics volume. The Wiring Diagram Manual doesn't make a clear tiebreaker because it doesn't label which element is which. But it does have connector drawings, which look more like the pictures in New Car Features than the ones in the diagnostics volume. I can't overemphasize how few times I've found any sort of confusion like that in Toyota's manuals and had to sleuth it out; for the most part, they seem to really have it together and you can bank on the details in the manuals.

    Now, all of that just came from the Gen 1 manuals. As I said, I haven't looked in the PiP manuals, but anybody could who wanted to. From the parts diagrams, it looks like there is only one (big) electric element left, instead of the two with different rules used in the Gen 1. So somebody would have to look in the current manuals to find the rules for the PiP.

    -Chap
     
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  2. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I have not seen NCF for PiP. Can anyone with techinfo access share?
     
  3. retired4999

    retired4999 Prius driver since 2005

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    :cry:
     
  4. bisco

    bisco cookie crumbler

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    thanks chap, i suspect you might have to turn the heat on, for the elec. heaters to come on. otherwise, why would you want them on? of course, that would defeat the whole purpose of electric heat during ev only trips.
     
  5. ChapmanF

    ChapmanF Senior Member

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    The rules for when they come on I'm pretty sure will be in the manual ... without that we're just guessing.

    To satisfy my own curiosity re: my Gen 1, the clamp meter has now spoken and, at 13.8 volts, the elements in my Gen 1 draw 26 amps for whats built into the heater core, 13 amps each for the two in the footwell duct, 52 amps total, or about 718 watts of heat.

    From what's built into the heater core, I wouldn't be surprised if at least as much heat gets carried away by the coolant as by the airflow, at least when the coolant is cold, so it's probably halfway serving as an engine warmup aid.

    From what I see of the Gen 3 and PiP parts diagrams, the element-in-heater-core idea is done away with, and there's just one big separate element. But then, Gen 3 has the exhaust-to-coolant heat exchanger, which Gen 1 hasn't got.

    Also, for the historical record, the final word on the Gen 1 manual mixup is that the two drawings in Volume 1 that show the heater-core element and the footwell-duct elements show each with the correct connector, but the drawings got totally swapped, along with the section headings. The drawing showing the duct element is in the section whose heading suggests the duct, but the whole section's about the HTR2 signal (which controls the one in the core). The drawing showing the core is in the section that says it's about the core, but the section is about HTR0 (which controls the one in the duct). Ah well! :)

    -Chap
     
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  6. bisco

    bisco cookie crumbler

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    the owners manual? can't even find anything about an electric pre heater.
     
  7. ChapmanF

    ChapmanF Senior Member

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    The service manual(s).

    Something I keep thinking about is just to get a couple LEDs and tap them into my heater elements so I can see exactly when they're coming on ... maybe one on that IDH line too, so I can see when the converter is saying Uncle. Instead of finding places for them on the dash, I've considered just getting red ones and stuffing them up into the floor duct, so they'll indicate the elements are on by casting a ruddy glow just as if the elements really glowed red like a toaster. I bet that'll make the car feel warmer right away....

    After doing that to get a better sense of when they are on normally, if a person wanted them to be on at other times too, it would be pretty straightforward to wire up a little switch controlling the same relay(s). Probably best to build a little circuit to do that where (like the stock A/C amplifier) the IDH signal from the converter would be honored and suppress the heat.

    -Chap
     
  8. bisco

    bisco cookie crumbler

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    is it possible the u's. pip didn't get them?
     
  9. ChapmanF

    ChapmanF Senior Member

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    As a bystander posting in the PiP forum even though I haven't got a PiP, I'm figuring sooner or later someone in this forum is going to look that up in the manuals, or look up which fuses/relays are involved and walk out to their own PiP and check....

    -Chap
     
  10. bisco

    bisco cookie crumbler

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    chap, i appreciate your input. unfortunately, as the tech prius leaders, we're not that savvy a group. we have a lot of fun though.:cool:
     
  11. El Dobro

    El Dobro A Member

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    Check the fuse box listings in the owner's manual.
     
  12. retired4999

    retired4999 Prius driver since 2005

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    Who ever looks at a owners manual!!!!!?
     
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  13. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    :( I read every word. Then again, I'm a huge nerd and have no life, haha.
     
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  14. hill

    hill High Fiber Member

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    Want more heat than a chintzy 12v plug can provide? I'm not saying I'd ever approve of this . . . but . . .

    [​IMG]

    [​IMG]

    what with proper venting and all ... definitely not for me. Still, it's pretty clever, after you get past the creepy factor.
    :LOL:
    .
     
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  15. El Dobro

    El Dobro A Member

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    You can also keep the burgers warm, too.
     
  16. hill

    hill High Fiber Member

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    Yea !! Just make sure you carry a fire extinguisher . . . . . maybe a carbon monoxide alarm too.
    .
     
  17. -Rozi-

    -Rozi- Member

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    I thought the battery drop when ICE is running for heat was due to the ICE not being used as the only vehicle propulsion. As I understand this beast, the PiP continues to run mostly on battery until ICE warms up enough. If one uses ICE for cabin heat only, the ICE will shut off once engine coolant is warm => just before ICE would have started the full propulsion alone.

    My daily commute is all EV. However, I do use ICE to warm the cabin and I do notice EV range decreasing even when ICE is running. Only a bit slower.
     
  18. Michael33

    Michael33 Member

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    I'm fairly sure that I documented here my construction of a prototype battery-powered heating system for the PIP and Leaf. Try the search feature and search "heater in a box". Summary: given the poor quality of the 12 volt heaters out there, you really need to use an inverter and 120 volt ceramic heating elements. You can tap into the main 12 volt system somewhere the cabling is robust enough, but I avoided that can of worms altogether by using a deep cycle battery, in a battery case, with an 800 watt inverter and two 200 watt ceramic "personal heaters." These heaters, when placed at floor level in the driver's footwell, provided just enough heat, in a sort of 'bubble' around the legs, to increase comfort in sub-freezing temps. For real heat you'd need about 1000 watts' worth of ceramic heating elements, either from one heater or several small ones, placed to provide localized heat around the legs or upper body (I strongly recommend the former). You'd also need either a 100AH or better deep-cycle (AGM preferred) battery, plus a charger for recharging at home, or a charging system that used the car's electrical system to slowly recharge the battery when not in use. In that case the battery would act as a buffer to reduce the load on the car's electrical system at any one time.

    Ok, summary over. I won't necessarily be back to read replies, as I don't like this over-commercialized site.Have fun, but be safe. EDIT: here is a link to the earlier topic:
    Electric "Heater In a Box" System | PriusChat
     
  19. bisco

    bisco cookie crumbler

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    wow, talk about esp. were your ears ringing?:p