I already did that in my last post. Like I mentioned, a 1.5kWh A123 pack should be capable of ~50hp output from ~40lbs of batteries. Otoh, in order to get that reliably from a TS pack, I would have to go w/ ~15+kWh of batteries, which are obviously a lot heavier since the weight per kWh is more or less the same, so we're looking at a ~400lb pack.Why do you keep talking about C rates? Those are normalized discharge rates and since you (or rather we) are comparing a system that carries both high power and high energy batteries but only uses one of them at any one time versus a system that uses all high energy batteries but uses them all at the same time, you are comparing systems with different energy capacities. So you should be comparing ACTUAL current output rather than normalized (C-rating) current outputs.
That isn't the case due to the ten fold difference in consistent usable output as I mentioned in my last post. In order to get a 50hp pack from the cheaper cells, I would need to have way more lower power batteries than I want, which is prohibitive in terms of weight, aging, risk, and even cost.By using all high energy, low power batteries in the car and using them ALL at the same time you should be able to produce the same current output as the low energy, high power batteries. The combined capacity of all high energy batteries in the car rate to produce the same output current as a lower capacity, higher discharge rate battery.
Yup. Pretty much... I'm using batteries rated for 33C peak, that, at least according to the manufacturer take higher discharge rates really well in terms of lifespan, for power. And another set of batteries that doesn't seem to perform nearly as well in terms of power output at only ~3C, but are much cheaper, so I can get more energy for low power use.Basically it comes down to the fact that you can only carry so much battery weight, and assuming energy vs weight is pretty much consistent, you can only carry so much energy on your car. So what you are basically doing is shifting around normalized discharge rating of the batteries against the proportion of high energy and high power batteries in the car.
I'm not concerned about energy density, but power density, wrt weight. In this case, for roughly the same weight, there's a ~10x difference in peak power available. This means I can reach my power requirements with a ~40lb pack, and my energy requirements with a ~110lb pack, leaving me with ~250lbs less than if I used enough lower power cells to relatively safely get the same amount of power.So unless this ratio holds true:
[High Power C-rating]/[High Energy C-rating] >> [Ah of High Energy Batteries]/[Ah of High Power Batteries]
you will not gain appreciable increase in actual peak current for the added complexity by using a dual battery type "one-or-the-other" scheme rather than a single battery type "all at once" scheme.
Voltage doesn't change in the same way wrt current, at least based on what I've read. Voltage sag with TS cells is much greater than it is with A123 cells at the same C-rate.THe change of C-rating with temperature is a moot point since if it's halved for lower discharge batteries it also halves for high discharge batteries so the current output of both systems is still the same as temperature changes.
That's true, and in that case I would rather put a battery that, according to the manufacturer and anecdotal accounts, can take much higher discharge rates, in a position where it has to take much higher discharge rates, rather than try to use a battery that is rated for whatever lifespan at a much lower rate of discharge in that position, and risk wrecking it, or having it age out.Also, just in case it slipped your mind, remember that a battery rated for 10C being discharged at 10C is being worked just has hard as a battery rated at 5C being discharged at 5C.
Ah, okay a 10x different in C-ratings might warrant a hybrid system. I've never seen much more than 3x, usually 2x difference. But if you don't care about energy density then why don't you just not have the 3C batteries at all and save that weight? Replace them with empty space, not with the more 33C batteries. You obviously think you have enough energy on the 33C portion of the batteries to travel far enough without the 3C batteries or else you would be worried about energy density. You weren't gonna speed for part way and then drive like a grandma the rest of the way were you?I'm not concerned about energy density, but power density, wrt weight. In this case, for roughly the same weight, there's a ~10x difference in peak power available. This means I can reach my power requirements with a ~40lb pack, and my energy requirements with a ~110lb pack, leaving me with ~250lbs less than if I used enough lower power cells to relatively safely get the same amount of power.
More cells in parallel reduces the effective internal resistance. More cells in series will make up for the voltage lost. You're comparing different battery chemistries now and that's not as straightforward so only you can really decide that.Voltage doesn't change in the same way wrt current, at least based on what I've read. Voltage sag with TS cells is much greater than it is with A123 cells at the same C-rate.
Anyway... What kind of diode/s (in what arrangement) would I need to have a good safety net provided I had something fail and both controllers active?
The 33C batteries have ~1-1.5kWh, and since I want ~6kWh I'm probably going to add ~4-5kWh of low power batteries. That should give me ~30-40 miles of range during the low speed operating conditions I'd use EV mode with, keep the total battery costs around $4000, output ~30-50hp, and keep pack weight around 150lbs, and the system weight around ~250-350lbs.Ah, okay a 10x different in C-ratings might warrant a hybrid system. I've never seen much more than 3x, usually 2x difference. But if you don't care about energy density then why don't you just not have the 3C batteries at all and save that weight? Replace them with empty space, not with the more 33C batteries. You obviously think you have enough energy on the 33C portion of the batteries to travel far enough without the 3C batteries or else you would be worried about energy density. You weren't gonna speed for part way and then drive like a grandma the rest of the way were you?
It would mostly be for keeping speed. I would use the ~30-50hp from the A123 pack when accelerating, in conjunction with the engine and alone provided I don't need much power in the city. The ~15hp low power/high energy TS pack would be for cruising.3C discharge borders on useless in my mind for motor drives of any kind. Accelerate more smoothly unlike an SUV punk or street racer, don't rush towards stoplights only to wait, or tailgate so you constantly have to tap the brakes, and manage the transmission better to increase efficiency and lower the peak currents.
I'd definitely need to do some testing to determine what kind of voltage drop I'm looking at. Odds are the TS pack will be all series, since power output isn't maximized there. I'll have to fiddle around with parallel/series strings of the smaller A123 cells in order to figure out what kind of voltage/current I'm looking at.More cells in parallel reduces the effective internal resistance. More cells in series will make up for the voltage lost. You're comparing different battery chemistries now and that's not as straightforward so only you can really decide that.
Fuse it is! 400A/144V fuse should do fine, especially with the smaller 6.7" motor.No diodes- use a fuse for each motor driver. THat's a ridiculous amount of current flowing through those diodes which is a lot of losses. Even if the losses are insignificant to the power in the rest of the system, it's still going to introduce cooling challenges to the diodes themselves. Also remember that diodes can also fail active. Just use a fuse. Much less losses, after all, if something does go wrong to blow the fuse you aren't exactly going to be able to or want to start up the car again without doing a bunch of repairs in which case replacing a fuse will be the least of your repairs.
It really depends on where the oil comes from. Oil in the states for instance, requires a lot of energy, and extraction/transportation/refining is only at ~50% efficiency, so for most cars we're looking at ~10% efficiency give or take. Even with fossil fuel power plants at only ~30%, since we also have ~30% hydro/nukes, electrical energy generation wrt fossil fuel energy consumption is at ~50% on average, although this depends on region. Toss in EV efficiency at ~70%, and we're at ~35%. Otoh, if we got our electricity from only coal power, and our imported oil only required a lot of energy for refining, then conventional cars could be at ~15% and an EV at around 21%, so in that case there isn't a huge difference.Also, after power plant, transmission, charging losses, and motor losses EV is about the same overall efficiency as a gasoline engine, except EV has a lot more resources and energy put into producing the batteries.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?