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Daniel's EVPorsche 911 conversion
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JRP3
Hyperactive Member
I should point out that James at EVcomponents has exactly what you need, a Zilla 1000 amp High Voltage unit:
http://www.evcomponents.com/ProductDetails.asp?ProductCode=Z1K%2DHV
The nice thing about this controller, besides that it's the best DC controller in the world, is that you can hook it up to your pack at 144 volts without rewiring the batteries and see how it works, then sometime in the future if you feel the need you can rewire the pack to 288 volts and really have some fun! Yes it's expensive, but you can recoup some of the cost by reselling your used Curtis. New ones go for around $1500 so you could probably get $1200 or so for your used one.
Ah crap, it's sold, sorry for the tease.
http://www.evcomponents.com/ProductDetails.asp?ProductCode=Z1K%2DHV
The nice thing about this controller, besides that it's the best DC controller in the world, is that you can hook it up to your pack at 144 volts without rewiring the batteries and see how it works, then sometime in the future if you feel the need you can rewire the pack to 288 volts and really have some fun! Yes it's expensive, but you can recoup some of the cost by reselling your used Curtis. New ones go for around $1500 so you could probably get $1200 or so for your used one.
Ah crap, it's sold, sorry for the tease.
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Thanks to everyone: I appreciate the shift away from what I've done wrong (which I know) and back to possible solutions.
A couple of guys from the local EV club visited yesterday. Both are actively involved in conversions, and one would be willing to work on my car if I decide to ask him to.
One of them went for a ride with me. I had previously seen a peak amperage draw of 350, and then the other day I saw 400. But I'm mostly watching the road when I drive. Tim saw 460 amps briefly during acceleration, and also felt the pulsating hesitation I've mentioned. They also looked the car over.
They think the bottleneck is the battery pack. The LiFePO4 batteries have a high impedance, which limits how much current they can provide before the voltage drops too low. They think a bigger controller might help, or it might not.
But they think that the power steering and air conditioning, both of which are belt driven, are stealing considerable power. They would like to replace both with electric pumps. They say the p/s pump is taking power whether it's needed or not, and that an electric pump would only take power when I'm turning the car. And it would work when the car is stationary. They say that most folks use a 12-volt battery, with its own separate charger, to run the A/C. If the present A/C pump is taking that much power, I don't see how a 12-v battery would have enough oomph to cool the car, but they say it does.
Two days ago, we had our first hot day, and I ran the A/C (which works great) but the car would not go faster than 63 mph, and acceleration was even more sluggish than normal. So either the A/C really is taking a lot of power, or the heat was affecting the controller.
I may have mentioned this before, but it bears repeating:
I get a lot more acceleration when the car is cold than when it's hot. I wonder to what extent the Curtis is getting overheated and cutting back. Tim at first said this discrepancy was due to the higher voltage in the pack right after charging; but I've seen the same discrepancy when the car is not fully charged, but has been sitting long enough to cool off. Maybe a better controller would help even if the batteries are a bottleneck, provided the controller was less affected by overheating.
When the car is cold, the acceleration in each gear's "sweet spot" is much better than when I leave the car in 3rd. In fact, that 43 seconds was a lot of time getting from 40 to 60, and shifting would have made it accelerate better. The problem is that it's so hard to shift without a clutch. And if I shift into a high gear for acceleration, it's even harder to downshift to get back to a more efficient gear. Downshifting I have to give it just enough pedal to match the gears, and on the freeway, with a lot of traffic all around, failing to get it back into gear would be a real safety issue. I think taking out the clutch was a big mistake. Tim agrees with me. Gordy disagrees. Apparently there's no consensus on the matter among EV builders. Paul had told me the car would have so much acceleration in 4th gear that I've never shift except to back up. It probably would have had with lead batteries and a 1000 amp controller.
Perhaps my times will improve as I learn to shift the car without a clutch.
Paul never seems to be around on weekends. (His answering machine is often full on weekends.) I will try to reach him this week.
That's all for this morning.
Daniel
A couple of guys from the local EV club visited yesterday. Both are actively involved in conversions, and one would be willing to work on my car if I decide to ask him to.
One of them went for a ride with me. I had previously seen a peak amperage draw of 350, and then the other day I saw 400. But I'm mostly watching the road when I drive. Tim saw 460 amps briefly during acceleration, and also felt the pulsating hesitation I've mentioned. They also looked the car over.
They think the bottleneck is the battery pack. The LiFePO4 batteries have a high impedance, which limits how much current they can provide before the voltage drops too low. They think a bigger controller might help, or it might not.
But they think that the power steering and air conditioning, both of which are belt driven, are stealing considerable power. They would like to replace both with electric pumps. They say the p/s pump is taking power whether it's needed or not, and that an electric pump would only take power when I'm turning the car. And it would work when the car is stationary. They say that most folks use a 12-volt battery, with its own separate charger, to run the A/C. If the present A/C pump is taking that much power, I don't see how a 12-v battery would have enough oomph to cool the car, but they say it does.
Two days ago, we had our first hot day, and I ran the A/C (which works great) but the car would not go faster than 63 mph, and acceleration was even more sluggish than normal. So either the A/C really is taking a lot of power, or the heat was affecting the controller.
I may have mentioned this before, but it bears repeating:
I get a lot more acceleration when the car is cold than when it's hot. I wonder to what extent the Curtis is getting overheated and cutting back. Tim at first said this discrepancy was due to the higher voltage in the pack right after charging; but I've seen the same discrepancy when the car is not fully charged, but has been sitting long enough to cool off. Maybe a better controller would help even if the batteries are a bottleneck, provided the controller was less affected by overheating.
When the car is cold, the acceleration in each gear's "sweet spot" is much better than when I leave the car in 3rd. In fact, that 43 seconds was a lot of time getting from 40 to 60, and shifting would have made it accelerate better. The problem is that it's so hard to shift without a clutch. And if I shift into a high gear for acceleration, it's even harder to downshift to get back to a more efficient gear. Downshifting I have to give it just enough pedal to match the gears, and on the freeway, with a lot of traffic all around, failing to get it back into gear would be a real safety issue. I think taking out the clutch was a big mistake. Tim agrees with me. Gordy disagrees. Apparently there's no consensus on the matter among EV builders. Paul had told me the car would have so much acceleration in 4th gear that I've never shift except to back up. It probably would have had with lead batteries and a 1000 amp controller.
Perhaps my times will improve as I learn to shift the car without a clutch.
Paul never seems to be around on weekends. (His answering machine is often full on weekends.) I will try to reach him this week.
That's all for this morning.
Daniel
JRP3
Hyperactive Member
I haven't been able to find a spec sheet for the Hipower batteries, but I've seen some mention of them as being better than Thundersky. Thundersky cells have 3C discharge rates with 10C max. With your 100 amp cells, paralleled as 200 amp cells, that means 600 amp with 1000 amp max. Unless there is something wrong with the cells, I really don't think it's your battery pack that is the problem.
I agree with the PS pump. This is what I've been saying and where I think you'll get the most immediate improvement.
I question this as well. First of all, running the A/C with a separate motor won't save you much energy, if any. The A/C clutch is only engaged when the A/C is switched on, there should be very little drag from it when off. Second, when running the A/C, using a second motor will be less efficient than using the drive motor, and running it off a 12 volt battery charged from the main pack will be even less efficient. Most people who run a separate motor for the A/C use a motor that can run directly from full pack voltage, something like a motor from a treadmill. The best plan of action, as I see it, would be to replace the PS pump with an electric one, see how things go, then you can disconnect the A/C belt without losing power steering and see if that makes a noticeable difference even when not using the A/C.
I think the controller is overheating, if you're pulling 300-400 amps regularly on a hot day that's pushing that 500 amp controller pretty hard. In that case a more efficient controller with forced cooling and a higher amp rating, such as the Synkromotive James has, might help you out without going to higher voltage. Trying to strap some fans to your Curtis might help some.
As for the lack of clutch, that seems to be more of a personal preference and vehicle dependent. Some transmissions shift more easily without a clutch than others. As you said if you had the original higher powered controller you'd be shifting much less.
JRP3
Hyperactive Member
I just wanted to be clear that the same inefficiencies would apply to running the PS pump from a second motor and 12 volt source as the A/C, but the intermittent nature of the need for the PS pump to be running is where you pick up the efficiency. I don't know if you have a 12 volt battery on board connected to your DC/DC inverter but I think your inverter is a 40 amp unit which might be enough to power the PS pump directly. If not you'll need to add a 12 volt battery to the system as a buffer, unless there is a PS pump that can run off pack voltage.
The batteries are 1C continuous, 3C peak, and 10C spike. Richard (the battery importer) agrees with you, that the batteries should be able to do the job. The local EV guys are skeptical of that, and called HiPower a knock-off of Thundersky and say the HiPower are not as good. I'm glad to see you say they are better.
The suggestion was to run the A/C from a battery that would be charged by a separate charger from the wall, at the same time as I charge the car, not charged from the main pack. That of course would limit the amount of time it could run before draining the battery.
This makes sense to me, and Richard thinks a liquid-cooled Zilla would be the answer, if I could get one. However, the Curtis is feeding about 150 amps to the motor in steady-speed driving on the freeway at 55 or 60. It pulled up to 460 amps accelerating hard, but that was brief, and I had the pedal to the floor to see how high it would go. 250 amps is more common, and then only while accelerating. So it's not 300 to 400 regularly. Only very occasionally.
This is what the local guys said, and Richard agrees.
*****
Today I drove to Coeur d'Alene again. Since I had so much extra charge last week, I drove a bit faster today. between 55 and 60 on the way there, for 356 wh/mi, and 60 to 65 back, for 361 wh/mi. (CdA is about 1,000 feet higher than Spokane, so it's a very slight grade, up there and down back.) Overall 359 wh/mi. I used 121 ah in 49 miles.
All my wh/mi figures in earlier posts were based on a 28 kWh pack, but I realized that my pack is actually 28.8 kWh, so I'm using the new figure here. My wh/mi figures in earlier posts should be multiplied by 1.03.
I could feel the weaker acceleration from stop signs on the surface streets after getting off the freeway, but it was not too bad. I do think the controller is getting hot during the long freeway drive.
Daniel
JRP3
Hyperactive Member
To be accurate I've only read some things suggesting they are better but have no actual evidence one way or the other. More research has shown both opinions. It's also possible that earlier batches had problems and newer ones are better, this is still a developing technology after all. Do you know the manufacture date of your cells?
You'd have to figure out the HP it takes to run the A/C and figure out what sized motor you'd need to run it. I have a feeling you'd have a pretty high amp draw at 12 volts and would quickly kill a battery, but I could be wrong. You'd also have the extra weight of a good sized deep cycle battery to carry around with you, all the time.
No I don't. Sorry. I do know they were delivered to the conversion shop around the middle of December.
This was what I thought as well. Gordy thinks it would work. The trade-off is I would not lose power when cooling the car. But I am skeptical of the whole idea.
I think what I need is a 1K Zilla and the electric p/s pump.
You're smart to be skeptical. While this might be fine for a short trip to the store and home on a 'not too hot' day, I don't think it's a realistic option for routine use and long trips like you do every Sunday. Plus, you'll end up replacing 12v batteries on a regular basis from being deeply discharged and recharged.
Sure sounds like that's the place you need to start...or that Paul needs to start to make this right.
FYI, when your conversion was being done, CafeElectric had basically put production on hold indefinitely but now they seem to be going again, so it might have been a case of bad timing that the Zilla wasn't available for your conversion.
JRP3
Hyperactive Member
Exactly. Paul was using Zillas until they weren't available, then probably tried to substitute Logisystem 1000 amp controllers, but they had reliability problems, so he went with the old tried and true, but underpowered, Curtis. I believe Logisystems has fixed their problems, but I'd let others experiment with them first. The new Synkromotive looks promising, as does the new "BMF" being tested at the DIY forums.
Daniel: Thanks for posting your experiences.
I'm currently converting a 1977 Porsche 911 to electric power. http://ExplodingDinosaurs.com
A few thoughts for you:
Autocross racers often dial in some toe-out! This helps jerk the car into the turn, quickening the steering response. Toe-in makes the car the most stable, hence is the usual setting for most manufactured street cars. Zero toe (under load) is the least drag. Zero toe won't hurt your cornering per se, but the car might wander at freeway speeds. I wouldn't be afraid to try zero toe, and if the car still handles well, great, if not you've only lost the cost of an alignment to set it back to some toe-in. BTW, my Camaro with zero toe steers very stably with street tires. With race tires, it darts all over!
Going to zero camber would help range a tiny bit (much less help than toe), and would hurt your cornering and tend to wear the tire shoulders.
Are you running your tires at sidewall max pressure?
Range can have several bottlenecks -- it could be batteries or it could be the car itself. Fortunately you have a fairly easy way to see how the car is doing.
My Porsche takes about 2 kW to move slowly at steady walking speed (just multiply your measured Volts * measured Amps). Since your car is certainly heavier, it might take 3 kW or a bit more. What is your Volts * Amps to creep along at walking speeds? If that number is high, like 10 kW, it means you have a brake dragging or really bad alignment or something.
Are you driving at freeway speeds with a sunroof open or the windows down? This can increase drag by a surprising amount.
I'd be really surprised if tight motor bearings are an issue. I could easily turn my motor by hand. You could check this by pushing the car in neutral, and pushing it in 4th gear. It'll be slightly harder to push in gear, but I can hardly tell any difference on my car.
These drag things might seem nitpicky and insignificant, but remember on an ICE the motor gets more efficient under load, and you already have the "drag" of throwing away 80% of your energy as heat and needing to idle, so a little drag doesn't hurt your gas mileage much. In an electric, it gets less efficient under load, so a little extra drag can cost you alot of range.
That acceleration is pretty slow, but actually it could be about right for your system. 144 V * 500 Amps is just 72 kW nominal, or about 72 rwhp after driveline losses. Throw in some battery sag and inefficiencies, and you might be down to ~50 rwhp. Yep, that's down to VW bug or old VW diesel territory, and is on par with your acceleration numbers. It would take amazing amounts of drag to make the car that slow, so I doubt it is something dragging. The problem sounds like it is compounded by an overheating controller.
Basically, you need more voltage and more Amps. Your batteries might be the bottleneck on Amps. My humble suggestion would be to buy and install a Zilla 2k high voltage, and put in more batteries to give as high a voltage as you can (being sure to limit the output voltage to a safe number for your motor). You likely would need to respect the 500 Amp current limit still, but double voltage will improve your higher rpm power, so you can stay in a lower gear longer.
I'm currently converting a 1977 Porsche 911 to electric power. http://ExplodingDinosaurs.com
A few thoughts for you:
Autocross racers often dial in some toe-out! This helps jerk the car into the turn, quickening the steering response. Toe-in makes the car the most stable, hence is the usual setting for most manufactured street cars. Zero toe (under load) is the least drag. Zero toe won't hurt your cornering per se, but the car might wander at freeway speeds. I wouldn't be afraid to try zero toe, and if the car still handles well, great, if not you've only lost the cost of an alignment to set it back to some toe-in. BTW, my Camaro with zero toe steers very stably with street tires. With race tires, it darts all over!
Going to zero camber would help range a tiny bit (much less help than toe), and would hurt your cornering and tend to wear the tire shoulders.
Are you running your tires at sidewall max pressure?
Range can have several bottlenecks -- it could be batteries or it could be the car itself. Fortunately you have a fairly easy way to see how the car is doing.
My Porsche takes about 2 kW to move slowly at steady walking speed (just multiply your measured Volts * measured Amps). Since your car is certainly heavier, it might take 3 kW or a bit more. What is your Volts * Amps to creep along at walking speeds? If that number is high, like 10 kW, it means you have a brake dragging or really bad alignment or something.
Are you driving at freeway speeds with a sunroof open or the windows down? This can increase drag by a surprising amount.
I'd be really surprised if tight motor bearings are an issue. I could easily turn my motor by hand. You could check this by pushing the car in neutral, and pushing it in 4th gear. It'll be slightly harder to push in gear, but I can hardly tell any difference on my car.
These drag things might seem nitpicky and insignificant, but remember on an ICE the motor gets more efficient under load, and you already have the "drag" of throwing away 80% of your energy as heat and needing to idle, so a little drag doesn't hurt your gas mileage much. In an electric, it gets less efficient under load, so a little extra drag can cost you alot of range.
That acceleration is pretty slow, but actually it could be about right for your system. 144 V * 500 Amps is just 72 kW nominal, or about 72 rwhp after driveline losses. Throw in some battery sag and inefficiencies, and you might be down to ~50 rwhp. Yep, that's down to VW bug or old VW diesel territory, and is on par with your acceleration numbers. It would take amazing amounts of drag to make the car that slow, so I doubt it is something dragging. The problem sounds like it is compounded by an overheating controller.
Basically, you need more voltage and more Amps. Your batteries might be the bottleneck on Amps. My humble suggestion would be to buy and install a Zilla 2k high voltage, and put in more batteries to give as high a voltage as you can (being sure to limit the output voltage to a safe number for your motor). You likely would need to respect the 500 Amp current limit still, but double voltage will improve your higher rpm power, so you can stay in a lower gear longer.
My RangerEV is supposed to be able to do about 200amps @ 330V (~66kW). According to the meter I have in the cockpit, I rarely see it pull more than about 125amps, yet my 0-60 is only a fraction of what Daniel reports. There must be something else wrong. Gearing issues?
JRP3
Hyperactive Member
David, do you know anything about the HiPower cells? He's running 100 amp pairs in series, so he has 200 amps at 1C, 600 at 3C. Do you really think the batteries could be the bottle neck? He doesn't think he has room for more cells, and with 90 or so 100 amp cells he may be right.
Teg, I think part of the problem is the lower voltage doesn't allow the motor keep the power into the higher RPMs so he has to shift more often.
Teg, I think part of the problem is the lower voltage doesn't allow the motor keep the power into the higher RPMs so he has to shift more often.
Lots of good comments/questions to reply to:
David:
While I don't dispute what you (and others) have said about toe-in, this is a transportation car for me. It's my daily driver, replacing the Zap Xebra. So comfortable highway driving is important. Also, I am not a mechanic. I will have the alignment checked by the Porsche dealer, but I know they will not set the toe-in outside of manufacturer's recommended specs. I will ask them to set it for the minimum consistent with specs.
Sidewall max is 51 psi, and I'm running 45, but I plan on increasing it to 50. Someone pointed out that these tires expect to be driven at 120 mph, so at 70 mph (my maximum freeway speed) I could go over 51 and still be safe, but I doubt if I'd gain much by going over 50.
I have not checked my watts at walking speed. However, the car coasts very smoothly for a long distance, slowing down very gradually. So I don't think I have brake drag. I sometimes tilt the back of the moon roof up, but I almost never slide it back because the sun is too strong. I do sometimes open windows, but all my wh/mi figures posted above have been with windows closed and A/C off, and there seems to be little if any difference whether the moon roof is fully closed or tilted. (BTW I love the moon roof, because for in-town driving, where range is not an issue, the tilted-up (open toward the rear) moon roof eliminates the unpleasant wow-wow-wow that most cars produce with an open window. On the freeway I normally drive with windows closed and the moon roof cracked.
When the car goes in for some needed work, I'll ask them to spin the tires to check for motor drag. But I doubt there's any, simply because of how well the car coasts.
Your voltage and amperage calculations relating to hp are the same as one of the local guys came up with. But Richard, the battery importer, believes the batteries have the oomph needed, if the controller was more powerful. My belief is that I really need more batteries, but there really is no more room, unless I have the back seats taken out. At this point, I'd be willing to give up my back seats, since they are pretty useless, but then we're talking a lot of labor, and cost becomes an issue. Double the batteries, remove the back seats, Zilla 1K or 2K controller, replace the p/s pump with electric, and this car could cost me half again more than it already has, and contract or no contract, Paul's not going to pay for that, and I don't want to either.
Several people think the voltage is the problem. The batteries could be re-wired in series to double the voltage (and halve the amperage) but that would require new chargers. Again, a significant cost. Obviously, I think Paul should pay whatever it takes. But he may see things differently.
I spoke with him today, and he is anxious to help make the car acceptable to me. He wants me to be happy with it. He is talking to his technical people. I don't expect a quick resolution, but I'd rather take the time to try to work things out with him than rush to an adversarial posture.
My present feeling is that if I can get a Zilla, the best move would be to put it in and see what happens. I suspect that few people if any have experience with large numbers of LiFePO4 batteries in such a late-model Porsche. Most people are putting lead in older models.
There are two issues regarding the controller: One is that its acceleration cold is very lackluster. The other is that it seems to get hot and then a classic VW bug would beat it off the line. Now that I (finally) know which box is the controller, I will take its temperature the next time I have an extended drive with it. I think I can get a clear shot on it with my infrared thermometer.
I wish Tesla had gone with a more Porsche-like design, rather than the very uncomfortable Roadster design.
Daniel
David:
While I don't dispute what you (and others) have said about toe-in, this is a transportation car for me. It's my daily driver, replacing the Zap Xebra. So comfortable highway driving is important. Also, I am not a mechanic. I will have the alignment checked by the Porsche dealer, but I know they will not set the toe-in outside of manufacturer's recommended specs. I will ask them to set it for the minimum consistent with specs.
Sidewall max is 51 psi, and I'm running 45, but I plan on increasing it to 50. Someone pointed out that these tires expect to be driven at 120 mph, so at 70 mph (my maximum freeway speed) I could go over 51 and still be safe, but I doubt if I'd gain much by going over 50.
I have not checked my watts at walking speed. However, the car coasts very smoothly for a long distance, slowing down very gradually. So I don't think I have brake drag. I sometimes tilt the back of the moon roof up, but I almost never slide it back because the sun is too strong. I do sometimes open windows, but all my wh/mi figures posted above have been with windows closed and A/C off, and there seems to be little if any difference whether the moon roof is fully closed or tilted. (BTW I love the moon roof, because for in-town driving, where range is not an issue, the tilted-up (open toward the rear) moon roof eliminates the unpleasant wow-wow-wow that most cars produce with an open window. On the freeway I normally drive with windows closed and the moon roof cracked.
When the car goes in for some needed work, I'll ask them to spin the tires to check for motor drag. But I doubt there's any, simply because of how well the car coasts.
Your voltage and amperage calculations relating to hp are the same as one of the local guys came up with. But Richard, the battery importer, believes the batteries have the oomph needed, if the controller was more powerful. My belief is that I really need more batteries, but there really is no more room, unless I have the back seats taken out. At this point, I'd be willing to give up my back seats, since they are pretty useless, but then we're talking a lot of labor, and cost becomes an issue. Double the batteries, remove the back seats, Zilla 1K or 2K controller, replace the p/s pump with electric, and this car could cost me half again more than it already has, and contract or no contract, Paul's not going to pay for that, and I don't want to either.
Several people think the voltage is the problem. The batteries could be re-wired in series to double the voltage (and halve the amperage) but that would require new chargers. Again, a significant cost. Obviously, I think Paul should pay whatever it takes. But he may see things differently.
I spoke with him today, and he is anxious to help make the car acceptable to me. He wants me to be happy with it. He is talking to his technical people. I don't expect a quick resolution, but I'd rather take the time to try to work things out with him than rush to an adversarial posture.
My present feeling is that if I can get a Zilla, the best move would be to put it in and see what happens. I suspect that few people if any have experience with large numbers of LiFePO4 batteries in such a late-model Porsche. Most people are putting lead in older models.
There are two issues regarding the controller: One is that its acceleration cold is very lackluster. The other is that it seems to get hot and then a classic VW bug would beat it off the line. Now that I (finally) know which box is the controller, I will take its temperature the next time I have an extended drive with it. I think I can get a clear shot on it with my infrared thermometer.
I wish Tesla had gone with a more Porsche-like design, rather than the very uncomfortable Roadster design.
Daniel
JRP3
Hyperactive Member
There are 178 different vehicles here using lithium, including 2 under construction with with China HiPower batteries:
Battery Types
Admittedly some are bikes and scooters but you might browse through and see what others are getting from their packs.
This guy has a nice video series describing his lithium Porsche conversion:
YouTube - marionrickard's Channel
As for direct drive you'd really need a high revving AC system, or a very light vehicle with a very powerful motor.
Of course every "production" car has been direct drive. Most limited to about 80mph (until the Roadster). Direct drive is fantastic. Hard for gas-car drivers to understand that I can smoke the tires from a stop (with no clutch, mind you) in the same gear that I can cruise at 80 mph!
How do you shift into Reverse, they ask... Ha. Just spin the motor backwards. Try that with an ICE.
Daniel: Direct drive would make your problems worse. If you don't have enough power to burn rubber in 4th gear (or at least 2nd gear), you don't want direct drive. Ideally you'd still have your clutch.
EVNut: The Chrysler TEVan and the Commutavan both had multiple gear ratios. Though not a production car, the Buckeye bullet that went 315 mph had a 5 speed tranny -- that settled the debate for me!
JRP3: I don't know about his High Power cells specifically. There is a simple test, though -- how much do the cells sag under current draw? For example, a lead acid AGM pack might sag to 1/2 voltage at about 1200 Amps. That implies (12V - 6V)/1200 Amps = 0.005 Ohms of internal resistance per battery. The max power one of those batteries can deliver is (1200 Amps)^2*0.005 Ohms = 7.2 kW per battery. So Daniel, do you have some voltage sag numbers for us? In other words, voltage vs. current for several values. A good AGM pack is 3 to 5 mOhms per 12 V battery, we could caculate how powerful your pack is and see if it is the bottleneck.
TEG: I assume your Ranger is the Ford produced one with an AC motor? AC has a broad torque curve and is more efficient. Daniel with his low voltage, series motor with back EMF drop off, and possibly more voltage sag than you, his torque curve isn't as fat as yours. He could make up alot of that difference with shifting, but he can't shift quickly. I have always been impressed how AC cars could post similar 1/4 times to DC cars that were lighter and running as much as twice the current and same voltage.
EVNut: The Chrysler TEVan and the Commutavan both had multiple gear ratios. Though not a production car, the Buckeye bullet that went 315 mph had a 5 speed tranny -- that settled the debate for me!
JRP3: I don't know about his High Power cells specifically. There is a simple test, though -- how much do the cells sag under current draw? For example, a lead acid AGM pack might sag to 1/2 voltage at about 1200 Amps. That implies (12V - 6V)/1200 Amps = 0.005 Ohms of internal resistance per battery. The max power one of those batteries can deliver is (1200 Amps)^2*0.005 Ohms = 7.2 kW per battery. So Daniel, do you have some voltage sag numbers for us? In other words, voltage vs. current for several values. A good AGM pack is 3 to 5 mOhms per 12 V battery, we could caculate how powerful your pack is and see if it is the bottleneck.
TEG: I assume your Ranger is the Ford produced one with an AC motor? AC has a broad torque curve and is more efficient. Daniel with his low voltage, series motor with back EMF drop off, and possibly more voltage sag than you, his torque curve isn't as fat as yours. He could make up alot of that difference with shifting, but he can't shift quickly. I have always been impressed how AC cars could post similar 1/4 times to DC cars that were lighter and running as much as twice the current and same voltage.
