Can a first generation Prius run with no hybrid battery .. and if so,

WOW, 12 hours and no responses.

Simple answers: NO and NO.

The HV battery is an integral part of the system and is necessary for many things.
Probably the most important is: Starting the gas engine.

 

The inverter is also a functional part of the transmission. A certain fraction of the power transmitted from the engine to the wheels goes through it. The rest goes mechanically through the transmission's shafts and gears, but only if the inverter is present and doing its part. Otherwise the transmission just freewheels.

Maybe the transmission could be removed and replaced with one from a Corolla or something. I don't have any knowledge of how the mountings would line up.

 

I noticed while fixing the battery cells a weak cell causes the system to try to equalize the modules and do so by overcharging them to get them all topped up evenly, and without a fan hooked up, it gets them fairly hot, and then it goes into 'turtle' mode.

In Turtle mode, it essentially does not use the HV battery. However, it has to in order to go in Reverse, but not forward.
So it made me wonder...if heat up one of the temp sensors for the battery, it will trigger Turtle mode and that car might be driveable?

I tried to startup the Hybrid Racing League and had a few gen1 to make into rental race cars, and on the road course, you don't need reverse for sure, but also are always going more than say 20 mph, so the lack of battery power for getting up to speed isn't needed,
and so if this hack works, I could have much lighter gen1 race cars....

 

You can drive the car at highway speeds in 'limp mode', when it's gives up on the battery due to a fault, but the engine revs at high rpm the entire time and sounds like it's going to fly apart.

 

Like a lot of "can I modify X to do Y" posts I've seen on here, I think the best answer is "yes, if you really wanted to, but it would be exorbitantly difficult and counterproductive". A lot of posters shorten that to "no", which is reasonable.

I suspect, with some not-trivial modifications, you could almost get a Prius to run with the HV battery missing, without completely cutting the HV and engine ECUs out of the loop. If you can (somehow) get the HV ECU in READY, and (somehow) get the engine running, then reporting a sufficiently low SoC over CANbus ought to prevent the HV ECU from stopping the engine or trying to draw power from the (nonexistent) battery. I don't see why the hybrid system, including DC/DC and MGs, couldn't function indefinitely in this state.

You'd need a custom "battery ECU" to pull the wool over the HV ECU's eyes, but that's not too difficult: PHEV conversions already have them. A few other tricks, such as spoofing the VL signal from the inverter, are likely necessary to get to READY, but it should be possible.

The hard part is starting the engine. You might be able to fit a conventional starter motor (and suitably sized 12v), though it looks to me like you'd have to hack some chunks out of the transaxle housing, and where are you going to get a flywheel/torque damper with gear teeth? Unfortunately, that's no use because it won't spin the engine fast enough for the engine ECU to do its thing. You'd probably have to substitute your own engine ECU to make this work. I don't know if anyone's done that before, but it should be possible: the hard part is that your new engine ECU has to interface with the HV ECU over CAN, and we know pEEf already figured some of that out because their conversion tampered with that communication.

A much easier way to start the engine would be to plug rectified mains power (or...a battery) into the inverter DC bus while MG1 cranks as usual, but that fudges the problem a little.

Of course, there's no conceivable reason to do any of this. If it worked, you would have a very underpowered, very fuel-inefficient Prius, and even gentle driving would be hard on the remaining powertrain components. But is it possible? Yes, I think so.

BTW, this post is assuming gen 2, because that's what I know. It should mostly apply to gen 1 also.

 

LOL

 

Good reply

 

Buy a good used Corolla!