Going on a camping trip and Prius is overloaded 900lbs. Is this going to be a problem?

Discussion in 'Gen 2 Prius Main Forum' started by Kaptainkid1, Jul 15, 2021.

  1. Kaptainkid1

    Kaptainkid1 Active Member

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    Has anyone loaded their 2nd Gen Prius on a long 1000 mile trip with 900-1000 lbs wet? Which includes 2 people and camping gear.
    I've traveled in the Prius with close to 750-800 lbs max before but never ever overloaded beyond factory spec.
    So here are mods which has push me over:
    1st a hitch bike rack 50lbs and 60lbs of bikes.
    2nd The hitch weight 35lbs.
    3rd ARB fridge 100 lbs with food.
    I'm going to drive it tomorrow unless I get reply saying it's a stupid mistake and take off 100lbs before I take off on my trip in the morning.
    So far I've read other threads and 950 lbs was heavy but people drove it no problem. They drove it slow and bottom out on speed bumps. Which I will keep in mind. My trip is pretty much flat grade whole way to mammoth except for a few steep grades. On 14hwy and the last leg going to Twin Lakes.

    I also have leaf spring helper in the rear so I feel this will help with the additional weight and keep the rear from sagging too much.

    Want hear anyone else experience on this issue.


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    #1 Kaptainkid1, Jul 15, 2021
    Last edited: Jul 15, 2021
  2. Kaptainkid1

    Kaptainkid1 Active Member

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    Delete
     
    #2 Kaptainkid1, Jul 15, 2021
    Last edited: Jul 15, 2021
  3. Kaptainkid1

    Kaptainkid1 Active Member

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    Here is leaf spring helpers. 20191230_142744.jpg 20191230_151228.jpg 20191230_151534.jpg

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  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Add extra air to your young, deeply-treaded and recently/carefully inspected tires. They'll see the worst effects of the overload so pay attention there.

    Remember to use B mode early & often on the hill descents.

    Honestly if it were me the only thing I might do differently is buying the food and water when I'm most of the way there.

    Good luck!
     
  5. sugar land dave

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    Brake early, accelerate slowly. Good luck!
     
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  6. SFO

    SFO Senior Member

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    Should be fine (famous last words). Once carried 12 (or was it 13) buckets of paint up the 101 into norcal, with a solid core rear sway installed the car handled the corners "ok". Will be interesting to see if those coil boosters hold up, how long have they been installed now?

    Without mentioning the partially obscured rear license plate, I'd be more worried about cooking the trans when hill climbing or if heavy footed and under load. Here is an older @edthefox5 reply to my question "How does a low HV battery cook a trans?" (transmission, transaxle) when embracing a long / steep hill climb or otherwise : Transaxle Failure | Page 12 | PriusChat
     
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  7. ChapmanF

    ChapmanF Senior Member

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    That Ed reply starts with some information that lots of people learned in the old days and that really was true for the kinds of motors that used to be used in simple home appliances and industrial equipment and such. The plain induction motor that's just wired across the line voltage with a switch to turn it on, and if the line voltage drops much, the motor bogs down under its load, and the current it consumes goes way up (even to several times its normal running current) and the windings may overheat and burn out. That's why we were all taught brownouts of the electrical grid can be so destructive to appliances.

    That was all true (and still is, about those kinds of equipment), but there are several ways the Prius powertrain is different.

    The motors in the Prius are actively commutated. They both have resolvers that report their exact rotor positions back to the controlling ECU to a 4096th of a revolution, there are current sensors on the windings, and the ECU is doing pulse-width modulation in real time to shape the exact voltage and current waveform it wants each winding to be getting. This is nothing like clamping a familiar appliance motor across a voltage supply and letting it draw whatever current it draws.

    Starting with Gen 2, there's even another layer of distance between the motor and the battery voltage; the inverter now contains a booster circuit to raise the voltage from the battery up to a maximum of 500 V (limit raised to 650 V in Gen 3). That allows the motors to be built lighter for the same or better power output. Just like the MG waveform shaping, the boost circuit is under the ECU's control. If the ECU has decided it wants 437½ volts right now to shape into the motor drive waveforms, that's what the booster will produce, independently of the battery voltage.

    As for the total power being handled through the powertrain, the specs for a Gen 2 are that the engine can produce 76 HP but the combined system net power is given as 110 HP, which involves counting on the battery to chip in 34 HP on top of full output from the engine. 34 HP from the battery at nominal voltage is right at the 125 amp rating of the battery's fuse, so yes, that's a practical outside limit.

    A full-capacity new battery could give you that for a shade longer than three minutes, but the car only uses the 40% of capacity between 40 and 80 percent charge. So you can get 110 system combined horsepower, but only for about a minute and a half—less than that with a tired battery.

    So let's say you start your heavy-laden Prius at the bottom of a hill, and you want to climb this hill at the maximum speed 110 HP can take you. So you mash the go pedal, and the battery will chip in 125 amps, and the engine will go to full output at 5000 rpm. (Whether 5000 rpm sounds like 'screaming' will depend on how much you've been around actual screaming engines.) There you are, going up the hill with 110 HP worth of speed.

    You'll get, at the outside, a minute and half of that, with a spanking new strong battery.

    What happens next is very simple (and if you have something like a ScanGauge or a phone app displaying the battery state of charge, you can watch it happen).

    The instant that state of charge crosses the 40% mark, the HV ECU says "that's it, no more from the battery" and you will instantly feel that you are in a 76 HP car. The engine was already at full output at 5000 rpm and it will stay there, but now that is all the power you've got, and your road speed will quickly drop to what 76 HP can haul up that grade. That is what the rest of your ascent will be like, if you still want to complete it as fast as you can.

    With respect to heating of the tranny, notice that the total power it is handling has not gone up at this point. It has dropped. For that first minute or so, it was handling the full 76 HP from the engine and 34 HP from the battery. From now to the top of the hill, it won't be handling any more than the 76 HP from the engine.

    How much of that is carried through the motors will depend on road speed. There's a magical speed where all of the power through the tranny is going mechanically and effectively none through the motors; at 5000 engine rpm and 825 rev/mile tires, that's about 123 mph. At any speed lower than that, some of the 76 HP will be going mechanically through the gearing and the rest flowing as electricity from MG1, through the inverter, and reused by MG2. At 61½ mph, the power will be evenly split, 38 HP flowing electrically and 38 mechanically.

    At still lower speeds, the motors will carry still more of the engine's power output, with the limits of the smaller MG1 coming into play first; that's why the published System Performance Curve drops below 76 HP as road speeds decrease.

    So for lower-speed travel, there is a way to see an effect like Ed described, though the reason is different.

    Suppose you're on such a steep grade with your heavy-laden Prius that 40 mph is the fastest 76 HP can haul you.

    If your battery isn't depleted, the HV ECU has options for how to give you 76 HP. For example, it could opt to give you 50 HP from the engine and 26 from the battery. The engine for 50 HP will be turning maybe 3400 rpm. The magic road speed for 3400 engine rpm is about 83 mph; 40 mph is about half that, so the engine power is taking an equal split, 25 HP through the gears and 25 through the electrics. The battery's 26 HP contribution is joining in at MG2, which is the larger motor and rated 68 HP, so 51 there isn't a problem.

    Even a strong battery starting at 80% SoC would reach 40% that way in under two minutes, and then the HV ECU runs out of options. Now the only way it can give you 76 HP is by running the engine flat out at 5000 rpm, where as we've seen the magic road speed is 123 mph, so 40 is a third of that, so the engine power is splitting 25 HP through the gears and 50 through the electrics (MG1 and MG2). That's a lot of power through the smaller MG1 (and probably more than the HV ECU would allow; Toyota hasn't published MG1's power rating, but the ECU surely knows it).

    In any event, the main thing is to be aware of when you're running the machine near its design limits; those are the especially good times to have something like a ScanGauge or phone app set up and be watching the engine coolant, MG1, MG2, and MG1/MG2 inverter temperatures.
     
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  8. PA Prius

    PA Prius Active Member

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    We did a 7500 mile trip in our '04 back in '07. Two adults, two early teens, all the camping gear, roof rack. Not sure of the e
    weight, but very likely over 800 pounds. No problems.
     
  9. Kaptainkid1

    Kaptainkid1 Active Member

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    A successful Prius Overland Trip!
    Lessons learn and tips for other overloaded Prius Overland trip plans. What I learned and what was very important for other big camping trips for fellow Prius owners.

    Know the limitations of the 2nd Gen Prius.
    I've done many camping trips and 10 in my Prius so far. 6 of the trips would classify as "Overlanding". Pushing the limitations of the car and you're self to reach your goal.

    Like the title says I ran 900lbs wet and gear going to Mammoth CA. The Prius door jam specs says 810 lbs max. I went over because I wanted all my camping supplies and friend in tow. I took out the spare tire which is 25 lbs savings and replaced it with an air pump and plugs patch kit as back up.
    I brought my ARB fridge and a back up battery to run my solar power controller and power supply in the bear box. All food supplies and food trash should be stored in the bear box which I learn the 1st night camping.
    That night I left out my stove and a bag of cooking supplies. None was food except a old dehydrated cup of noodles. At the bottom of the bag. At 2 am my friends heard noise and a black bear in our campground eating an old cup of noodles soup. The bear clawed up my cooking storage bag that I never knew was in there until he found it.
    We packed up any food fragments such as empty candy wrappers in the Prius which I was sleeping in and packed in the bear box.
    We found out the next day that 9 bears lived around Twin Lakes and they all have names and runs the campground for food often.
    We thought we were prepared the next night for bears since everything that smells like food or was food was packed away.
    Nope!!!
    The next night a bear came into the campsite again but this time the bear went to bear box and tried to open the box. The bear opened the box because we left the handle on the box door. I never knew why the door handle was on a chain and was not attached to the bear box. Now I know don't leave the handle on! They are smart and sneaky.

    The big answer can you run a 2nd Gen Prius on a long road trip with 900 lbs? Yes!
    The only issues is the power band going up hill is super slow and the rear springs can be damaged and dangerous on heavy loads. The rear springs should be address if the Prius carries heavy loads all the time. I uses spring helpers but the weight was maxing out the overall capacity of the Prius design.
    I noticed after 1 hour of driving the bikes on the rack were sliding around on the bike rack causing an unusual body roll. It felt very dangerous but I figured out I needed to strap down the bike tires and frame to the bike mount hitch. Once the bikes we're snug down the Prius drove very normal and only issue was bottoming out because of the heavy load. I was able to drive 90 mph with no unusual body roll but only drove so fast to test it out.
    It was a safe trip and I learn the maximum capacity of my Prius and wouldn't want to do that again but know it's possible.
    Screenshot_20210719-222427_Dolphin.jpg Screenshot_20210719-221240_Dolphin.jpg 20210719_162355.jpg 20210719_162333.jpg 20210719_162258.jpg 20210718_094359.jpg

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  10. black_jmyntrn

    black_jmyntrn Member

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    What are you carrying thats 900lbs? Initial estimates I thought I was at 900 but after weighing on truck scale my calculations were off.

    I did install new springs, actually i tested out 3 different sets with different spring configurations for each. I know I'm a Gen 3 but Gen 2 and 4 springs are avaliable. I'll post my results shortly if interested.
     
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