Enginer PHEV Test Pilots: Mpg reports and important data

So, what happens if you don't "charge" your pack before leaving? I personally don't mind doing this, but there's no way my wife will do it. She'll want to jump in and drive.

 

I don't personally have an Enginer conversion kit, but the moral of the story is that the latest DC/DC converter that comes with the Enginer system can only transfer about 10 amps between the Enginer battery pack and the Prius OEM battery pack.

During normal drive (not EV), the vehicle uses around 10 to 15 amps during acceleration depending on how charged your battery is. If you have your headlights and air conditioning on those combined draw an additional 9 amps or so. In short, if you don't "pre-charge" your battery by letting your car sit you probably won't see very much difference in electric usage during your drive because the system can't charge fast enough.

It's one of the draw backs to the lower end conversion systems.

Andrew

 

I call BS. Pre-charging the stock battery is helpful but not absolutely necessary. What's far more important is the terrain, number stops and the speed you drive at. At this price the enginer kit is good value. People that don't actually have one should probably not report on it in a "test pilot" thread.

@cgates:

If you think you'd (or wife) find it easier to pre-charge the stock battery the night before, it works for me. I come home in the evening with 3-4 bars. I leave the car/kit on in the garage (with EV mode engaged). After watching a TV show or whatever I go down and turn it off. WARNING! Just don't forget to turn it off within the hour WARNING! I find my stock battery stays topped up overnight at 6 bars exactly where I left it.

 

I've seen this 10 amp limit on the thread a lot. Has anyone upgraded to a more capable charger? Would 20 or 30 amps be enough?

This is a good idea! Hmmm, I wonder if there's a way to remotely turn off the car. Put it on a 30 minute timer...

 

12 amps, See this post: http://priuschat.com/forums/prius-p...in-hybrid-electric-vehicle-15.html#post975836

Remote starters exist for vehicles but they might not be available for the Prius. I bet you'd still have to push a button, might as well push the button on the dash.

 

Okay, you may have a point about the test piloting part--I really don't have an Enginer conversion (though I do have sufficient experience with Enginer-like...(Enginer-esk?) systems to comment on how they work). Also, my bad--12 amps instead of 10 amps, though this still depends heavily on what the state of charge of the OEM battery is.

I am still curious though, what is your average speed during trips where you see 100+ MPG?

Andrew

 

You can install a remote starter, but you would have to leave the smart key in the car.
If you keep your car locked in a garage, that is OK, but you will also have to enable EV mode.

 

20 or 30 amps would be an improvement (I believe the old Enginer DC/DC converters were around 20 amps) but I don't believe your batteries can push that kind of current at all temperatures. Remember it has to boost the voltage from 48v to 220v so you have heat-loss and other goodies to deal with.

Hymotion uses around a 25 amp DC/DC converter, but their sitting voltage is much higher (and their batteries are substantially more powerful than the Mottcell / Thundersky). Their converter is also significantly more expensive than the one included with the Enginer system.

Andrew

 

Quote from Jack:

 

By my estimates, using two 12 amp DC/DC converters together you're probably looking at closer to 80 or 90 amps discharge from the auxiliary battery pack...assuming a 220v output voltage (which is the sitting voltage of the OEM pack at roughly 50% SOC). This would be more like 2C continuous discharge.

According to the Thundersky's own datasheet, the 40Ahr cells are only rated for a standard 0.5CA continuous discharge (yes, it's maximum discharge rating is technically 3CA but for longevity sake you don't want to approach this limit during normal discharge). It's been my experience that battery manufacturers tend to overexadurate their own datasheets to make their batteries look better than they actually are so I would take those limits to be more like the best-case scenario in a temperature controlled room.

I don't have the datasheet from Mottcell, but I'm guessing that if they are selling those cells for the same price as the Thundersky they are probably close enough in terms of performance--but I could be wrong.

I'm not trying to steal your fun here, I'm just trying to save you a headache.

Andrew

 

I'm somewhat confused -- I was under the impression after reading most of the various posts regarding plug-in conversion sets, that on drives of 20 or 30 miles whether you use the stored electricity quickly (as in trying to drive in mostly EV mode) or use it slowly in a more blended mode with the ICE and electric working together, that after the supplemental batterys are depleted and the car reverts to its normal operation, the end results are pretty much the same. That is, the amount of fuel burned is the same. If you drive the 1st 10 miles on all electric, but in the process deplete most of the stored electricty and then revert to the normal Prius operation sooner, you will then burn more fuel sooner. If you pulse and glide and use some ICE, you will burn some fuel right away, but at a reduced rate and the battery pack won't be depleted as quickly. After 20 or 30 miles, isn't the fuel burned in the 2 senarios roughly the same or am I missing something?

 

Docbooks,

I think you are asking if I drive 10 miles in EV range and 10 miles in hybrid sustain mode (OEM Prius mode) do I burn the same amount of gas as if I were to drive 20 miles in a blended mode?

Not necessarily.

That depends on three things. First, it depends on the electric strength of the blended mode. If the blended mode is using just enough electricity to lower the RPMs on the gasoline engine out of its peak range (Toyota has very carefully designed the engine so that it operates in its sweet spot as much as possible during normal conditions) then its actually possible that you end up burning more fuel using this method because the gasoline engine is most efficient under higher loads (this has been documented by Argonne national labs). If on the other hand you have a very powerful electric blended mode (such as one where you only use as much gasoline as is necessary once all available electric torque is utilized) then the gasoline engine is basically only used for small boosts. The efficiency of the engine is still dropped of course, but you're only injecting a small percentage of the fuel you'd see during normal acceleration. The stronger electric blended modes require a more powerful battery however.

Second, it depends on the temperature of the gasoline engine. If less fuel flows to the gasoline engine it will cool down much faster and it does not operate in its ideal temperature range which reduces its efficiency. Obviously, if the ICE never heats up enough it will keep burning fuel in attempts to get itself there thus fuel is wasted (this can be more than you might think). Related to this point, it also depends on ambient outside temperature. A lower outside temperature means the ICE has to work harder to heat up thus if you are using more electricity than it is expecting, it may not hit its most efficient state.

Third, it depends on the speed of the vehicle. Higher speeds means higher road resistance and higher wind resistance. Higher resistance means the vehicle has to work harder to maintain speed. The gasoline engine is most efficient when it is working hard, thus if it is told not to work as hard (because the car wants to use electric) it takes an efficiency hit thus more gas is burned.

By simply increasing the state of charge of the OEM battery, the Prius will automatically start using more electricity to prevent itself from becoming overcharged. This generally produces noticeable improvements in mileage if the charge is able to be maintained at a higher than normal rate (that is, if the auxiliary converter can keep the OEM battery charged). If it continually oscillates between a high and less than high state of charge (eg: if the converter cant keep up) then you see less of a benefit.

Hopefully that was the question you were asking and my answer was somewhat helpful...otherwise, I guess I was talking to myself =).

Andrew

 

Can you direct me to where I can find out how to calculate the discharge rates at different currents? Perhaps by limiting the discharge of multiple (2 or 3) converters you can get into the 20-25 Amp range without damaging the batteries. By the way, how much do extra converters cost?

Regarding charging the traction battery (original NiMH battery already in the car) prior to taking off for the day, is there a way to spoof the hybrid system to top it off during the first few minutes of operation (ie, always try to achieve 75-80% SOC)?

 

As for calculating discharge C rates, I did a google search and found this website: Discharge Methods
It explains pretty well how C rate discharge calculation works.

I'll have to let someone else answer about the DC DC converter cost (though I can tell you that buying a bigger converter would be significantly more expensive since they have to be rated for the maximum current transfer possible without overheating...), but as for not damaging the batteries--it comes down to how much current is being drawn from them. From the data I have collected analyzing the Thundersky 40ah cells I believe that the current 12 amp limit is probably about all that is safe to pull from them continuously without damaging them long-term (which again translates to about 45 amps on the 48v side of things). Remember you have to account for cold temperatures too. I assume Enginer has some thermistor taps to reduce current transfer in colder climates--thus your 12 amps drops significantly in the cold.

Just remember that Thundersky doesn't provide warranty's for their batteries (what's up with that?) and I don't know if Enginer steps in to fill that gap. So be careful if you start tinkering with the converters =).

As for topping the system off, the DC/DC converter is limited by hardware in how much current can pass through it to charge the OEM battery. The only way to get more current through to top it off would be to either get an additional converter (risky given the batteries used) or buy a bigger converter (expensive, or if it isn't expensive it probably should be--cheap end ones tend to overheat). Unless you were asking about using the gasoline engine to top off the battery?...

Andrew

 

Check out OTHER enginer related threads where users with more than on converter discuss technical details.

 

This may be an acceptable tradeoff. Once the traction battery is topped off, it should remain there until the enginer pack is depleted - under easy driving anyway. You'd have to have someway to stop it from trying to top off once the enginer pack is depleted, otherwise it would always run the ICE trying to peg the SOC range.

 

If you mean, how do I calculate the 48V battery current for various rates of "injected" current into the OEM battery or inverter, it's really easy. The power on the battery side will be the same as the power on the injection side of the converter, divided by its efficiency (experssed as a fraction of unity, i.e. percentage divided by 100).

For example, if you are injecting 12 A at 240 V, that's 2880 W (multiply the two numbers). Suppose the converter is 85% efficient; that would mean an efficiency (as a fraction of unity) of 0.85. So the power on the battery side is 2880 W / 0.85 = 3390 W. At this sort of current, the nominally 3.2 V cells are going to sag somewhat, let's guess to 3.1 V (it could be more like 2.8 V at low SOC). So with 16 cells, the nominally 48 V battery will sag from some 51 V to 3.1 x 16 = 49.6 V, so the battery current will be about 3390 / 49.6 = 68 A. For a 40 Ah battery (only one set), that's 68/40 = 1.7C. If you have the 4 kWh system (two 16-cell packs in parallel), that would be 0.85C for each pack (split evenly between the two).

Note that the cells have to work harder nearer the end of their charge. When ~3 kW causes the cells to sag to 2.8 VPC (volts per cell), the pack will be at 16 x 2.8 = 44.8 V, and the current will rise to 3390 / 44.8 = 76 A (1.9 C for one set).

 

Thanks for the input, and yes, that was the question I was asking. To compare apples with apples, lets say with the Enginer system that we have 2 identical cars, and that both are warmed up and that they are running on a flat surface at a steady 30 MPH and they will be traveling a distance of 50 miles. One car uses EV mode until the Enginer pack is depleted and the other car runs in blended mode until its pack is depleted. At the end of 50 miles under this scenario, wouldn't the fuel usage be roughly equivalent? I can understand on a short trip under 10 miles or so that running in EV verses blended would always be the winner. But in the scenario where you will be traveling beyond the distance that will deplete the pack regardless of which method you use, it seems that the end result (ie, energy used) would be roughly the same. Hope I'm not being too dense here.

 

Not being too dense, but you are laboring under a misconception. The Enginer pack will only deliver 10-12 amps when it's fully charged. Running EV mode, even at 30mph will deplete the OEM pack at a rate of >20 amps. Thus, the OEM pack will be depleted to the level where the ICE will kick on to recharge it LONG before your 10 miles of EV mode is over.

The most efficient way I've found to use the Enginer pack is to use a modified version of P&G where during the 'glide', you use some electric power to extend the glide as long as possible to your lower mph limit, then pulse back up to your top speed and repeat. Even then, the OEM pack will deplete faster than the Enginer pack can recharge it. Keeping an eye on your SOC and after long experience will let you know when to swap back and forth between this modified P&G and standard P&G.

 

You're not being too dense, it's a good question =). I agree with MJFrog here--it really isn't apples to apples because yes, the Enginer system cannot push EV mode for 10+ miles in a row unless you drive extremely slow and stop every so often and let it recharge. Unless you seriously change your driving habits, this isn't really practical.

It's also not apples to apples because if you do end up depleting the OEM battery during EV mode (which you likely will unless you carefully monitor the SOC bars left and cut out at the right time) in the Enginer system, the ICE has to work twice as hard to charge up the OEM battery again /and/ propel the vehicle thus fuel is wasted charging the battery because the DC/DC converter can't keep up.

As for CGate's question about using the ICE to charge the battery, the ICE is terribly inefficient at those speeds (basically idling while the car is stopped and charging it at around 20 amps). Remember, the Prius internal combustion engine is only around 31% efficient--one of the best in its class no doubt, but still, 31% efficient. Most of the energy is burned off as heat and is lost. No, you're much better off charging the OEM battery either thru the DC/DC converter (takes a long time) or directly with another charger (dangerous!).

To answer your question again DocBooks about it being roughly the same--yes it /generally/ ends up being pretty close but it really depends on the conditions already spelled out =).

Andrew