Ohmmu Battery Update and Inverter Question

Discussion in 'Gen 3 Prius Accessories and Modifications' started by Hybrid Hound, Jul 29, 2021.

  1. Hybrid Hound

    Hybrid Hound Junior Member

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    It has been about 3 months since I installed the Ohmmu Lithium battery. So far it seems to be doing just fine. I have connected my Renogy 1000/2000 Pure Sine Inverter and tested it out in case we need to run the car as an emergency generator. I have the #2 gauge cables and the Anderson connector so I just open the little port in the rear of the hatch area above the battery and plug in as needed. Hence my question...Would it be possible to have connected a Lithium power pack with a built-in inverter and have it be the battery for the Prius AND also be ready anytime you needed 120 volts for AC power? Could the 12 volt charging system in the car be connected to the charging input on the power pack? How many amps are involved when the 12 volt battery is being topped up by the HV battery? A bit too late for me since I have already bought my battery and inverter, but was wondering IF this would have worked? A 1000 watt output power pack is about the same price as my battery and inverter was. Any thought as to whether this would damage the car or the power pack?
     
  2. black_jmyntrn

    black_jmyntrn Active Member

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    Honestly, you should get 0 gauge, I haven't figured it out yet if it's the PIP and the BMS but running my induction stove or air fryer off my 2000W inverter would trip breaker or appliance would turn on and off on all sizes I went through until the 0 was added.
    Custom Battery and Inverter Cables for the Win! - black_jmyntrn

    I say all that to answer your question, in theory, it would work. I've learned on this Prius journey thought, things you'd think would work on say a nonhybrid car and operate efficiently don't apply to the Prius. Trial and error have been my best tool.

    Do you know the weight difference between the two? What would you accomplish that would be better than your current setup? Personally, I like your setup better, this way if one goes out you can replace it while having the other. When you start combining things into one unit, if a fuse blows or other, all is down and not just the one. How many AH is your battery? Did you know on those power packs, they say do not leave in a hot car on the manuals?
     
  3. Hybrid Hound

    Hybrid Hound Junior Member

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    Very valid points, thank you. Like having a TV and DVD combo...if one dies...bury the whole thing! The Ohmmu battery is 45 AH. The inverter seems to really do it's job well. I read many posts on here before deciding that 1000 watt was all that I could safely use for an inverter. I also went down to a 60 amp inline fuse...just in case. I could just barely work the #2 cable in...0 must have been a bear! As far as weight, the battery is about 17 pounds and the inverter around 7. So, likely the combo power station would be heavier. And, here in SW Fl the heat in the back of the hatch area can be quite toasty. Thanks for the voice of reason. And...if someone swiped the power pack...it would be a bigger loss, not to mention being stranded!!
     
  4. PriusCamper

    PriusCamper Senior Member

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    It should be fine, but the safest way to do it would be to have a battery management (BMS) to ensure your secondary 12v is well cared for and never gets too much charge. I suspect that's already built into your Ohmmu, so I'd get clear on how well that system works and how you could improve it.
     
  5. black_jmyntrn

    black_jmyntrn Active Member

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    You know, I've read a lot on here about inverters and batteries that in my experience are false statements.
    I replaced my main 12v with an 85AH battery and added another to the opposite side, each running a 2000W Pure Since Inverter. I only had issues using the included cables with the inverter and every time after going thicker wire until 0 gauge left me with no issues.
     
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  6. Grit

    Grit Senior Member

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    tint the hatch window so no one will see and less heat build up. I took asrdogman’s advice and did the self tint kit, looks & working great soo far. We re in the 105 to 110F heat all summer long.
     
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  7. PriusCamper

    PriusCamper Senior Member

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    Please let us know what kind of 12v 85AH battery fits in a Prius... Are they expensive?
     
  8. black_jmyntrn

    black_jmyntrn Active Member

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  9. black_jmyntrn

    black_jmyntrn Active Member

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  10. ASRDogman

    ASRDogman Senior Member

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    Did you watch the video of how to clean the rear window with the defogger?
    Little bit of a pain, but will worth it! Mine still looks factory!


     
  11. Primefan

    Primefan Junior Member

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    This question fascinates me. @Hybrid Hound have you learned anything more?
     
  12. ChapmanF

    ChapmanF Senior Member

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    Huh ... if the shortened amazon link worked right, that says it's a BCI group size 24. Very common, had in truck and in GF's sailboat years ago, but I could swear the Gen 3 Prius OEM S46B24R is smaller.

    Oh wait, I've got an old one right here! So it's 23.5 by 12.5 cm by 20 cm high (22.5 to the post tops).

    BCI group 24 dimensions given here are 11.13" 6.60" 9.25" LxWxH (28.3 by 16.8 cm by 23.5 including the posts).

    The VMax one appears to be a little smaller than a true group 24 (it lists 10.2"L*6.6"W*8.3"H, or 25.9 by 16.8 cm by 21 cm high; I wonder if they're including the posts).

    So it's maybe about 2.5 cm longer than the OEM, 4.3 cm wider, and either a little taller or a little shorter, depending on whether they include the posts in their 8.3" height spec). I guess that still fits in the OEM hold-down without mods?

    The height is kind of a critical dimension for me, 'cause of this DIN rail stuff that still has to fit under the deck piece.

    [​IMG]
     
  13. Primefan

    Primefan Junior Member

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    @ChapmanF (or anyone else) could you comment on one of @Hybrid Hound original questions below? With this modification: Let’s assume @Hybrid Hound keeps the lithium Ohmmu battery installed in his Prius but then attaches to the Ohmmu 2 AWG cables that then connect to a DC input on on a lithium portable power unit (or simply attaches to another Ohmmu battery). If the portable power unit was rated for perhaps a maximum of 50 amps/600 watt DC input (or higher) would the depleted portable power unit (or depleted Ohmmu) safely charge at anything like 600 watts while the Prius is running?

    Oh, and I should add connecting the second Ohmmu/portable for the purpose of quick charging to use the battery elsewhere. Not a permanent installation like @black_jmyntrn.

    The obvious way people deal with this is to connect an inverter to the installed Ohmmu and then charge the portable station from the inverter. But is there a way to avoid the DC to AC to DC losses and connect directly?

    Hybrid Hound wrote: “Could the 12 volt charging system in the car be connected to the charging input on the power pack? How many amps are involved when the 12 volt battery is being topped up by the HV battery?”
     
    #13 Primefan, Aug 13, 2021
    Last edited: Aug 13, 2021
  14. ChapmanF

    ChapmanF Senior Member

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    Maybe this last one is the best one to take a swing at.

    A Gen 3 has no direct control over how many amps go into the 12 volt battery. It does not have anything like the Gen 4 battery state sensor assembly. It doesn't even have the Gen 1 and 2 direct at-battery voltage measurement. (The Gen 3 converter still has the voltage-sense input, but it is only wired as far as the front fusebox, so that's the voltage it measures.) Edit: Gen 3 does have a temperature sensor in the air above the 12 volt battery. I left that out before.

    The Gen 3 DC/DC converter puts some volts on a bus that the whole car's 12-volt stuff runs from, and the 12 volt battery is also across that bus, and whatever happens, happens ... up to the converter's rated output of 120 amps, which has to include what everything else in the car is using.

    The power management control ECU does command small adjustments to the DC/DC converter output voltage, up to around 14.8 or down sometimes as far as 13.6 while driving. The adjustments seem to suggest the ECU has some rudimentary idea of how fully charged the 12 volt battery is. Maybe it gets that idea right during power-on, when it sees what the battery's voltage is at that moment and how far it dips before the converter comes online. Not much detail in the manuals. Clearly, once the converter is online and all kinds of car loads are drawing power, without something like Gen 4's state sensor, the ECU doesn't have any good ongoing sense of the 12 volt battery's charge. My best guess is it grabs a snapshot at power-on time of how much charging it thinks the battery needs, and makes its converter voltage adjustments while driving according to some fixed scheme based on that.

    Naturally, the battery will accept a bunch more amps when the converter is supplying 14.8 than it will when the converter supplies 13.6, and a bunch more amps when it's hungry than when it's near full charge.

    As far as I know, that's about all that can be said for Gen 3's charging strategy.
     
    #14 ChapmanF, Aug 13, 2021
    Last edited: Aug 13, 2021
  15. Primefan

    Primefan Junior Member

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    @ChapmanF Any thoughts about what happens if a Prius Prime has an installed Ohmmu (like @Mark in NY ) and one directly runs the shortest possible 2 AWG cables to another, and depleted, Ohmmu. What might be the overall speed of charge? What are the hazards?
     
  16. ChapmanF

    ChapmanF Senior Member

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    I don't think I know enough about the characteristics of the Ohmmu product to take a swing at that one. If they wanted to pay someone to study it and make that analysis ... they probably wouldn't ask me, they'd look for someone more routinely involved in that kind of work.
     
  17. Primefan

    Primefan Junior Member

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    @ChapmanF How about the same question just using the OEM battery to another depleted OEM battery. Can we predict what happens when you connect the cables directly and leave the Prius on?
     
  18. Primefan

    Primefan Junior Member

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    @ChapmanF How about the same question just using the OEM battery to another depleted OEM battery. Can we predict what happens when you connect the cables directly and leave the Prius on?
     
  19. ChapmanF

    ChapmanF Senior Member

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    Car doesn't know the difference. It puts somewhere between 13.6 and 14.8 volts onto the 12 volt bus, and each battery will do whatever it does with that. Up to the converter's rated maximum of 120 amps, which has to include what everything else in the car is using.
     
  20. Primefan

    Primefan Junior Member

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    Thanks ChapmanF. If the additional battery charges at 10 amps I might as well just use the cigarette lighter. But if it charges at 50 amps we start approach the wattage sometimes used by AC chargers in portable battery stations. If an additional lead acid battery is at 50% discharge can we predict the amperage which will flow to the depleted battery when the Prius is turned on - or is that too complicated?

    Surely someone has tried this?

    Actually @black_jmyntrn I think you might know the answer to this. Do you let the second battery get depleted and then recharge - or is the Prius always in ready mode when you run anything off of your second battery?
     
    #19 Primefan, Aug 13, 2021
    Last edited: Aug 13, 2021
  21. ChapmanF

    ChapmanF Senior Member

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    Grab a lead-acid battery of the kind you're interested in and hook it to a 5-amp, 10-amp, 20-amp, 50-amp charger and plot the charging current v. terminal voltage at different levels of discharge. You might be able to get such data from the battery manufacturer, or from somewhere like Battery University, for some battery of comparable capacity and construction.

    Using the plot, predict what current it would be accepting when the car supplies 14.8 volts, and what current it would be accepting when the car supplies 13.6 volts, and you will have the ballpark.
     
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