Daniel's EVPorsche 911 conversion

[EVnut]

Daniel -

Ouch. That acceleration makes my Rav4EV seem like greased lightning.

[JRP3]

I should point out that James at EVcomponents has exactly what you need, a Zilla 1000 amp High Voltage unit:
http://www.evcomponents.com/ProductD...tCode=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.

[daniel]

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

[JRP3]

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.

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.

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.

I agree with the PS pump. This is what I've been saying and where I think you'll get the most immediate improvement.

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.

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]

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.

[daniel]

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.

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.

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.

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.

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.

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.

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.

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]

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.

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?

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.

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.

[daniel]

Do you know the manufacture date of your cells?

No I don't. Sorry. I do know they were delivered to the conversion shop around the middle of December.

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.

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.

[efusco]

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.

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.

I think what I need is a 1K Zilla and the electric p/s pump.

Sure sounds like that's the place you need to start...or that Paul needs to start to make this right.

[TEG]

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.