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Adding 2nd Lithium pack in Parallel

Discussion in 'Gen 4 Prius Technical Discussion' started by Brandon Kennedy, Feb 28, 2022.

  1. Brandon Kennedy

    Brandon Kennedy Junior Member

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    As the title says, would it be possible to add a 2nd battery pack in parallel? Therefore the voltage of the pack etc would stay the same, and the only thing the computer would recognize different, is the voltage taking longer to go up or down, therefore the battery Gauge, power and everything else would stay the same.

    atleast that is how I would see it. Let me know if this could be done. I thought about making other packs, maybe out of lifepo4 instead of li-ion and make the voltage match closely. But, then I was thinking it might be better to buy a used pack out of a 2nd Prius that’s be wrecked etc. and just put it in parallel just for increased efficiency and lasting in ev mode.

    reasons I’d want to do this,
    increase regen time going down mountains
    Last longer in ev mode
    Potentially better mpg

    not really worried about gaining power. Thanks again.
     
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  2. alanclarkeau

    alanclarkeau Senior Member

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    Me - I'd steer very clear of something like this. I'd doubt that the electronics would like it at all - po$$ibly a cata$$trophic failure.

    I'd doubt you'd get enough extra mpg to make it worth it - extra weight.

    And whether the inverter would handle it - it monitors temperature, and if there has been a lot of activity, it has a breather for a while till temperatures settle. Having 2 batteries could possibly do this twice as much.

    Trade up to a PRIME maybe.
     
  3. Brandon Kennedy

    Brandon Kennedy Junior Member

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    well that’s no good lol. I’ve been thinking bout swapping over to Tesla, but figured I’d tinker n play with the Prius beforehand… but if the inverter wouldn’t be able to handle it etc… we’ll that’s sad lol.

    the electronics I wouldn’t think would see anything different. It’s just like with solar, add batteries in parallel, the voltage and charge controller etc are still the same, you’re just increasing capacity. So I guess the biggest thing would probably be the inverter handling the cooling etc…

    I actually just this morning, went an hour driving on ev mostly… forcing it to charge and discharge the battery over and over to warm up temps on purpose. The inverter didn’t seem fatigued during that situation. But it also wasn’t pulling twice the capacity either.
     
  4. sam spade 2

    sam spade 2 Senior Member

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    Of course it would "see" something different.
    Any battery pack has an internal resistance that varies as it charges and discharges.
    Having a second pack in parallel would certainly screw up the charging of the battery(s).
    Exactly how is just a wild guess.

    Given the cost and potential problems......certainly NOT a good idea.
    It has been discussed on here before I think.
     
  5. bisco

    bisco cookie crumbler

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    i don't see a problem, you should be able to find plenty of good advice and instructional videos on youtube
     
  6. sam spade 2

    sam spade 2 Senior Member

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    Of course you don't.
    But you aren't even close to being qualified to make that call.
     
  7. Rmay635703

    Rmay635703 Senior Member

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    Possible yes but very bad cost to benefit ratio

    Back in ye olde times folks would do this alongside trickery hardware/software to gain a small EV mode range.

    In this day and age not financially worth it, just get a prime if you want these effects on steroids

    All this said a small handful of $500 Gen 3 PRII with blown engines have been converted to BEV using OEM electronics and a Chevy Bolt or Volt battery
    Way down the rabbit hole of extreme effort and mods, documented mostly on the
    open inverter forums

    More fun to read about them to do unfortunately
     
  8. Brandon Kennedy

    Brandon Kennedy Junior Member

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    Welp. Was worth a try. Lithium has extremely low internal resistance so I wouldn’t be concerned with that. Even my pack with 137k miles still tests with 93% capacity, internal resistance is excellent, and voltages are extremely close, as in .01 and .02 volts difference, as would most of these lithium packs….
    I’m concerned that people are comparing these packs to the older style packs.
    So let’s put this in perspective with solar since I’m an owner of a solar company…

    your inverter would be the engine/transmission/magnet whatever u wanna call it, that is doing the charging and discharging of the battery pack…

    the bms is going to monitor those parameters, (voltage, high and low voltage, discharges, and charge current etc.)

    so in a solar setup, you would put two packs in parallel. So let’s say you have a 51.2v 100ah pack… put another one in, you still have 51.2v but now you’re at 200ah. The inverter doesn’t freak out, the charge controller doesn’t freak out etc. so therefore your engine, inverter, magnet, whatever isn’t going to freak out.
    The difference is, your solar will take longer to charge those packs up because now there is twice the capacity. So wouldn’t this therefore be the EXACT same scenario for the car?

    another example. Tesla. The only difference they do, is add more packs in parallel to increase from 60 to 80kwh pack or 100kwh pack… that’s it. So why would this not be the same situation?

    give me logical explained answers of why this wouldn’t work, instead of oh no it might freak out etc. I appreciate the input, but I need real input, real data of why you are 100% sure it wouldn’t work, because it doesn’t make sense to me why it wouldn’t. Granted no I don’t exactly want to blow anything up, but I don’t see why there would be anything that would cause that to happen.
    If you doubled the voltage by putting them in series sure, same thing would happen in a solar setup, it’ll blow up.

    I know this is a topic a lot of people don’t understand fully, but I still wanted to see if there might be a guru on here that may know for sure on this, or be able to capabily explain why not.
     
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  9. royrose

    royrose Senior Member

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    The point that you seem to be missing, that others have touched on, is that even if it would work the trade off isn't worth it. You would only occasionally go over the current capacity for capturing energy from regenerative braking. The rest of the time, the majority, you would have lower mpg because of the extra weight.

    Related to the above. Toyota limits charging of the hybrid battery to about 80% to prolong battery life. Would the system recognize the added capacity and charge up to 80% of that? I don't know, does anyone else know?
     
  10. bisco

    bisco cookie crumbler

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    don't give up so easily, you'll never accomplish anything!
     
  11. Brandon Kennedy

    Brandon Kennedy Junior Member

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    if it wouldn’t be worthwhile, then I’m sure Tesla or any other electric manufacturer wouldn’t add the extra batteries… same for the Prius prime, or anything else that involves electric. The added weight is negligible.
    As far as capacity. It’s basing it off of the voltage, as any other controller would do. As long as you get the voltage to match very closely with the pack that is in the car, you won’t have to add a bms etc to it. It’ll charge and discharge with the pack that’s hooked directly to the vehicle in the first place.
    Even if you’re off 5 volts (which you shouldn’t be, if anything you’d be off maybe a volt or two.) then you might charge the 2nd pack to 85% instead of 83%, or discharge to 25% and the other be 23 or 27, depending where you’re at on the closeness.

    but in reality you should be able to get them VERY close together without having them hooked into a seperate bms. I’d obviously keep a check on voltages every 10k etc and internal resistance… but so far these lithium packs are holding up very very nicely. As they should be, because their staying within a 20-80% range which is ideal for them.

    I guess there’s only one way to find out, and that’s do it, but it’s scary to do on a car that’s still worth a decent amount of money I suppose. It wouldn’t be bad to purchase a pack off eBay for 1k or so, and parallel it, but I’d had to go through the trouble and then it not work… but I honestly feel fairly confident with the knowledge I do know about batteries bms systems etc, and inverter/converter tech.
    I’m just more concerned with what Toyota may be hiding in their software to keep a possibility of this happening.
     
  12. royrose

    royrose Senior Member

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    Not a fair comparison IMO. Those are batteries that can be used to full capacity by plugging in. I continue to believe that your added battery wouldn't be of enough use to be worth it. Or maybe you could add an external charger while you are at it. Since I have been known to be wrong when I'm sure I'm right, I'd love for you to try it and report back. ;)
     
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  13. Brandon Kennedy

    Brandon Kennedy Junior Member

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    lol, and you all attack bisco. Alright then. Provide something valuable and I’ll take you more serious, other than false statements that aren’t even true ‍♂️‍♂️ Same lithium ion tech, etc… if you have nothing valuable to add then don’t.

    but if you do then by all means go ahead. I’ve gave reasons why it should work, which you Havnt been able to argue against, because I am right on that fact. But instead you’re thinking 50lbs is going to change your mpg… better not throw a suitcase for vacation in, it’ll ruin your mpg!!! Come on now ‍♂️ I can have a 150lb passenger get in and not notice any difference hardly, it doesn’t make a difference until you start getting toward to carrying capacity of the car, which I’ve exceeded before, and you do notice it significantly then.

    this is just an experimental idea, which, would potentially help the community if they wanted to do this in the future. Who knows maybe I’d be one of the first to try it on the 4th gen, but someone on here has to have reasons of why it wouldn’t work. And if you don’t, then it should work just like any other bms system, battery, etc…. No reason it shouldn’t… this being a hybrid forum, you shouldn’t be scared of the unknown just because it’s a HYBRID at the end of the day, it’s the same thing. You have a normal gas engine car on one side, you have a full electric car on the other, mended together… hence HYBRID…

    so, hang on a second, an electric vehicle is that much different? No ‍♂️‍♂️I’m not going to argue if you don’t have any understanding of the rest of the systems. The only thing I’m not understanding here is the Toyota software that may be implemented to impair this, or any special hardware that I’m not seeing. But from tear downs etc and the research I’ve done, and again my further knowledge in the solar industry, I don’t see why this wouldn’t work, unless there are thresholds that would prevent it from working.

    the only time I have ever had my car start the engine and turn the hybrid charging off is when going down a steep grade and that’s because the battery reaches the capacity the bms wants to kick off charging… same for when discharging… I can pull full power all day long until it hits the capacity the bms triggers for the engine to come on, and recharge the pack… so therefore, this inverter/charger isn’t near its limits… if there was more capacity I am to believe it is MORE than capable of doing so.

    do you have any relevant information on why the bms wouldn’t withstand the parallel capacity? Is there anything that states it can’t handle a paralleled pack?
     
  14. ColoradoBoo

    ColoradoBoo Senior Member

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    An interesting idea but you assume it's just adding another set of batteries but it's not. There's temperature sensors throughout the banks and a series of air vents with it's own cooling fan, controlled by an ECU so it would need some way to control the fan and to monitor the temperatures. (If I remember right, the cooling fan has six different speeds.) I haven't verified this, but I've heard if any of the cells are outside of specs, 0.3%, the ECU will throw a traction battery alarm.
     
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  15. Brandon Kennedy

    Brandon Kennedy Junior Member

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    Good info. Basically it would be just adding another pack in. You wouldn’t necessarily have to connect it to the bms that Is there, therefore the car wouldn’t recognize the new pack, and wouldn’t throw any faults unless it’s hooked to that. The only thing I’d plan on connecting is the positive and negative, AFTER I have balanced the new pack to the existing pack in the car, very closely, in voltage. The car would still sense the parameters from the main pack in the car… as far as temperature controls, could splice in a wire to the existing fan that is there, and the main power source and have it feed off that signal, or install a seperate temp probe and fan relay for the new pack. This would be the easier side of things to solve.
    To be honest I probably wouldn’t even make a container or anything for the new pack or any kind of permanent home, until I realize this will work without issue.
    I’ve also thought about doing a complete ev conversion on the Prius… but the only thing holding me back there is I won’t have the slew of information like Toyota provides on the display… nor will the display etc be nearly as neat… it would be more… well… diy material lol. I’m not an auto engineer or anything of that nature, or graphical person, and I want the car to still feel like a normal manufactured car. So the only thing I can really do to the Prius, Is this.
    Yes I could do a Prius prime, but then I’d want to add a 2nd prime pack to it etc… or even Tesla, who says I can’t fill the trunk area etc with more packs for more battery? It’s the same concept all around… just fun in tinkering, learning, and seeing what parameters we can cross or can’t cross. as bisco said, if you give up easily you won’t accomplish anything… and this has proven true in everything I have ever done. But it has also lead me to have the set of skills I have.
    I don’t mean to come off rude to those that think I have been, I just want true factual information. It won’t only help me and teach me more, but it will also make it to where in the future I can help others with the knowledge I’ve gained, pass it on, and also accomplish what goals I have set. thanks for your understanding
     
  16. sam spade 2

    sam spade 2 Senior Member

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    NO. The "intelligence" of the controller likely is VASTLY different.
    And the controllers are not "universal" but are designed as an integrated part of the whole system.......in both cases.
    So throwing in a second battery bank with "extremely low internal resistance" is almost guaranteed to throw the whole system for a loop.

    While I don't know for sure, a scant little bit of experience leads me to believe that the solar controller is more basic and "dumb" and probably would operate in a satisfactory fashion with a wide range of battery storage options. Not optimally maybe but OK.
    The system in a hybrid car almost certainly would NOT.
     
  17. Brandon Kennedy

    Brandon Kennedy Junior Member

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    i do agree that their made for each system. But I’m not attempting to throw something random into the mix. It would be the same pack, from a different car yes, but the same car lol of that makes sense. Same make and model but different car ‍♂️‍♂️‍♂️ I give up on trying to word that right but you know what I mean I hope haha.
    The packs were all built with the same quality, same manufacturer etc. and lithium, thankfully, doesn’t vary on internal resistance much at all, even when they get later in life. The internal resistance of my pack in my 137k mile car is still the same as when I bought it with 60k on it. So I’m not tooooooo worried about the IR varying, but more so if it’s going to play nicely. There is a reason Toyota made it as one member said a .3% difference would trigger a fault. This is because Toyota knows that lithium does not vary much in IR much. But again, the bms or anything that monitors anything on the 2nd pack WILL NOT be monitored. The thing is, the car should not notice the 2nd pack, and I’m trying to figure out why or what system, would even recognize the 2nd pack. Instead it should just recognize voltage is taking longer to come up, or down, and therefore give the charge, or discharge, until it reaches the voltage for cutoff (ie the percentage). So therefore your battery gauge and all should function as normal.
    The bms won’t be hooked to this pack, so anything from the 2nd pack won’t be monitored by the car, so it shouldn’t trigger any warnings. Only thing will be done, is the main positive and main negative will be hooked into with this 2nd pack. So it’ll receive the charge and discharge, voltages will be the same… again just increasing capacity.
    Am I missing something or are you all not reading or understanding what I’m trying to say or explain?
    I’m not sure what would stop the system from operating just off hooking the 2nd pack to the system, with none of the bms or other hardware there. Again the IR should be good/basically the same (no faults), voltages extremely close to eachother (should be no faults), it’ll just take longer to charge and discharge… but if not, then what system, and why, would it stop it? What are you seeing that I’m not seeing, that I Havnt already have some sort of explanation to?

    as far as solar. There are some pretty dumb ones out there yes lol. But there are also some that run off the same tech as this would in the car. It wants voltages, inputs etc to be matched within its operating range. Again if I was to add a pack in parallel, it’s not going to even notice it’s there, more so it’s going to just take longer for the voltage to come up or down, because the extra capacity is there. But all those bms are working off of is the voltage of the pack, which is the same thing the car is working off of to determine battery percentage and then when to stop the charge or discharge.
     
  18. sam spade 2

    sam spade 2 Senior Member

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    Yes. For the second or third time......you are missing that the effective internal resistance of your new total pack would be roughly HALF of what the system was designed to deal with. Therefore the charging current would be greater at any given pack voltage; maybe as much as twice as much. I think it is highly unlikely that the overall system would like that at all.

    I quit. Hadn't intended to start a long drawn out debate.

    I think it is a BAD idea based on about 50 years as an Electronics Engineering Technician.
    But it is possible that I am wrong.
     
  19. Brandon Kennedy

    Brandon Kennedy Junior Member

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    im not debating, no one is? But hey assumptions are great right?
    Now explain if you have one battery that has an IR of .27mohm, and another that is .28mohm, how that is going to be significant? If you put the two together, you’ll have an average of a .275mohm pack.
    Again taking this back to solar, when you parallel a pack, the IR of the batteries is very slightly different. But it’s negligible. Even in a very sensitive environment.
    Now again for the fourth of fifth time, what is something that I Havnt been able to explain to you that you’re not listening to? Or if you give another reason and I am able to verify it’s not a problem basically, then give something that would be a problem that can’t be explained in this system or your explanation of it….
    Lithium packs have a very very small ohm difference in internal resistance, that is UNTIL it is toward its end of life, then of course it’ll start varying widely, but by then you’ve received YEARS of usage.
    Again I’m not arguing but hey, if you wanna have an attitude and say I’m not listening, then sure it’ll piss me off and I’ll throw it back at you. I’ve tried to be respectful about the questions I’ve asked, and trying to do explanations so if you don’t understand, then maybe it will help you understand.
     
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  20. bisco

    bisco cookie crumbler

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    get used to it :rolleyes: