Cheap DIY plug in system? decide to go with e-trailer

short answer: no it wont
Its possible someone may come up with a add on battery/ EV kit for the C but there's a good deal of engineering involved and with the tax credits/ incentives on plug in vehicles like the plugin Prius I wouldn't expect the interest as there was for the 2nd generation Prius

 

In general adding a plug-in battery to the Prius is pretty complex. A lot of work was done on this by DIYers back in the '05-'7ish time frame. It can be done, but its not cheap and takes pretty sophisticated engineering.

I assume the new ones are similar, but on the Gen 2 there were two main methods.

The first was used by the projects that grew out of the original Cal-Cars open source project. They injected the extra current on the battery side of the pack's current sensors, to avoid the DTCs and system shutdown that occurs when there is a significant imbalance measured between battery output current and inverter input current. The problem then is, that since the battery controller can't see the extra current coming into the battery it assumes all the current is coming from the original battery. When the few hundred Wh that the original battery can provide have gone out, it assumes the battery is "empty" and recharges it by running the ICE. A further complication is the hybrid controller is only really inclined to use significant amounts of electric drive when it believes the original battery is completely full. Originally this was gotten around by using an external pack that was a bit higher in voltage than it should be, which caused the battery controller to regularly think the original battery was overcharging so it would use the electric motors as much as possible. For this to work well, and to avoid really overcharging the original battery, a sophisticated controller had to be developed to connect and disconnect the extra battery under a variety of conditions by monitoring the CAN traffic. Later an even more complex controller was developed that allowed the use of a more well matched battery voltage as it tricked the controller into this higher electric drive mode by modifying messages on the CAN bus rather than yanking the battery voltage around. From there some of these projects went commercial, and continued to develop controllers that could completely replace the original controller and battery.

The other main method was the one used by Enginer. They injected the current on the inverter side of the battery current sensor, and so didn't require any complicated controller to play tricks on the battery management system. In order to do this, they used a dc:dc converter with a fairly complicated programming to provide specific amounts of current into the system based on voltage observed. Doing this, they were able to avoid tripping the DTC/shutdown condition while still providing useful amounts of supplemental current. This was a pretty touchy adjustment, and took a lot of development work. Its main downside is it could not really provide enough current for sustained electric drive. And while this approach did give decent results at a relatively inexpensive price, they were plagued by reliability problems. There is a reason why their Chinese dc:dc converters costed ~$500 while a similarly spec'd Manzanita Micro charger with an excellent reliability reputation costs $2-3k.

The early cal-cars conversions used big stacks of lead acid UPS batteries to keep development costs down. In general these performed poorly, weighed about 400lbs, and ended up only lasting about 3-6 months under these use conditions.

So yes, you can turn a regular Prius into a PHEV, but a set of deep cycle batteries and a cheap inverter are not going to cut it.

Rob

 

Great summary Rob.
Hobbit does not like the CalCars approach, to say the least.

 

I'd rather save my money for an i8.

 

one thought i had was to add motors to the rear wheels with a separate battery. then you don't have to fool around with the toyota computers.

 

Its pretty barbaric by today's standards, but it was amazing to watch it all happening at the time.

 

i think it will work. i have seen various and sundry setups like this, all working well. do some searching, you'll find them with all the technical info and pictures you want. it takes some ambition and tenacity, but it sounds like you have it.

 

no, sorry, just stuff i've stumbled across over the years. too bad about that strut. sorry to see you go with a kit, i was hoping something new might be on the horizon. the kits are just too expensive for most of us.

 

this is exciting! i can't wait to get started.

 

I wish you luck, but fear you are headed down a path that will be both expensive and disappointing.

Pusher trailers are intriguing, but have a nasty habit of becoming unstable and jack-knifing when the rear end of the tow vehicle breaks traction. The more wheels on the ground, the more rolling resistance as well. The more you disrupt the airflow off the rear of the vehicle, the more your aerodynamics will suffer as well.

You also need to consider carefully the amount power required to do the job your trying to do. A Prius requires about 9 HP to cruise at 40mph, and 19 HP to cruise at 60mph (with no wind, hills, or mechanical drag from the ICE drivetrain). The CX-9 will require about 16 HP at 40mph, and 36 HP at 60mph. HP required for acceleration is much higher, and is often what dominates intown mileage.

The cheapest way to get enough power just to cover cruising is likely going to be a basic DC brushed series wound 6.7 - 8" fork lift type motor. These run ~$1k to $2k, plus another $500- $1000 for the controller.

Lead acid is also pretty much a non-starter, given the dramatic rise in the cost of raw lead over the past decade or so. To get 10 miles of assist, you're going to need about 3.3kWh of battery. Between maintaining a reasonable DOD, and losses due to Peukert Effect, you'll be doing well to get about half the advertised AH capacity. That may still be generous.

The "cheapest" option would be something like the Trojan 12V 100Ah flooded, 6 of which would give you 72V which is probably the min acceptable. 6 * 12V * 100Ah * 50% derating = 3.6kWh which is about right if you're ok with ~ 10 miles assist. This will cost about $1200 and weigh 300 lbs. Double both if you want 20 miles of assist. If you are fairly meticulous with watering and balancing, these should last you a year or two. 12 AGMs will require less maintenance, perform better, and probably last longer but at ~1.5-2X the cost.

So for lead, you're looking at $1200-1800 for floodies or AGMs that will probably last 1-2 years.

By comparison, something like GBS Li-ion would be about $2200 for 6 * 12.8V * 60Ah * 80% derate = 3.7kWh. With regular manual maintenance you should be able to get away without a BMS at 72V. For another $144 you can add cell balancers that will help reduce maintenance. These should last 3-5 years, 1000s rather than 100s of cycles. Weight is 120 lbs.

A good wag at wiring and other incidentals is probably going to be $500-1000. Just the copper to wire for 100s of amps will be a few hundred dollars, then there's contactors, cutoffs, and control to think about.

When all is said and done, this could easily cost just as much as a PHEV conversion and will likely yield much poorer performance.

Rob

 

how goes the project?

 

looks like the gas tank but i could be wrong.

 

The main problem with floodies is they tend to have a very poor Peukert exponent. This results in greatly diminished capacity at high current draw. The stated capacity is the 20Hr Rate, which is much lower current than a typical EV application.

Here's an example of the calculation for the Trojan T-1275 12V using the numbers from their spec sheet (manufacturer numbers in bold):
20 Hr Capacity: 150Ah (7.5A for 1200 minutes)
Runtime @25A: 280 minutes (117 Ah effective capacity)
Runtime @75A: 70 minutes (87.5Ah effective capacity)
Estimated Np: 1.262
Estimated Cp: 271 Ah
Estimated Runtime at 200A: 20.3 min
Effective Capacity @200A: 67.7 Ah

So right off the bat, the high current effects reduce the pack's effective 100% DOD capacity from 12V*150Ah*6 = 10800Wh to 12V*67.7Ah*6 = 4874Wh. At 50% DOD (which should keep cycle life up in the 500-1000 range) you are down to 2.44kWh. At $1200 this is $491/kWh, plus the batteries will weigh 492 lbs, which will have some negative impact on mileage.

This is already getting close to the ~$633/kWh for the GBS Li-ion with balancers above, without even taking the longer expected cycle life and 4:1 weight advantage of the Li-ion. There are likely cheaper Li-ion options that would probably be fine for this application as well.

The ME1003 is a good motor, but its basically a big scooter motor. How much mileage improvement would you expect from strapping a vespa to your back bumper?

Running without a controller can be done, but you'll have to be pretty cautious how you use it to avoid blowing up your motor or welding your contactors. At low RPMs the motor will want to draw far more Amps than it can handle, and you'll always be switching your contactor in and out in an energized state which means it needs to be substantially oversized to have a decent life expectancy.

Rob