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Old 01-25-2007, 04:33 PM   #21
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You can't get the power and weight density with NiMh and they are going to cost you about 25kwh more to charge than the 50kwh you get out of them from charging losses and that ends up costing a lot in the long run. Conventional LiIon cells do have a calender life that will kill their use - I am currently evaluating a few hundred dollars worth right now because I can't seem to get enough time to build them into a EV to actually use them. Building a 50kwh pack would require about 7000 cells and I have enough trouble dealing with 70 cells. Even AltairNano has no large cell design - same problem for all Lithium cell construction - except for MIT Sadoway. Looks like the gold solution is going to be the new EEStor ultra caps with a cost about the same as Lead batteries and high power output. If they are as good as I think they are going to be, you could even add more packs for longer range and then take them out for less weight shorter trips without a power penalty because they put out so much power.
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Old 01-25-2007, 09:32 PM   #22
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Quote:
You can't get the power and weight density with NiMh
This can be compensated for with the right chassis design. The EV1 was able to fit about 1,147 pounds of NiMH which allowed about 150 kW of peak power from the battery side. Fitting a 500 lb pack into a PHEV is not out of the realm of possibility.

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and they are going to cost you about 25kwh more to charge than the 50kwh you get out of them from charging losses and that ends up costing a lot in the long run.
Yeah. Their charge efficiency isn't the greatest, but the cost per mile of Li Ions is usually going to outweigh the cost of the additional energy use from charging the NiMH.

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Conventional LiIon cells do have a calender life that will kill their use - I am currently evaluating a few hundred dollars worth right now because I can't seem to get enough time to build them into a EV to actually use them.
Unless you have a way to keep them cool while they are operating, I doubt they will last more than 5 years to 80% capacity. Otherwise, I'd expect them to lose about 2% per year. Please share your data when you are done experimenting!

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Building a 50kwh pack would require about 7000 cells and I have enough trouble dealing with 70 cells.
About what the TZero and Tesla are using!

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Looks like the gold solution is going to be the new EEStor ultra caps with a cost about the same as Lead batteries and high power output. If they are as good as I think they are going to be, you could even add more packs for longer range and then take them out for less weight shorter trips without a power penalty because they put out so much power.
A controller to drive a motor off of those things is going to be a nightmare to build. Recently, their claims have seemed to be more credible than I originally found them, but I'm not going to hold my breath waiting for them either.
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Old 01-26-2007, 06:18 PM   #23
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Ideally the EEStor caps at 300 volts charge would work well in the typical EV including the Prius as they are operating in that voltage range (285-290 volts Peak). Higher voltages will require down converters using some higher voltage semiconductors and probably are not going to be practical because of the charging issues - since 220 AC volts peaks at 360 volts when used to charge caps. Recent article seems in indicate that EEStor is capable of producing everything they claim and more as they tend to only announce proven products - they are engineers not sales/marketing people so they tell the truth. Apparently the ultracap construction process can produce very high voltage caps in the 1,200 to 3,500 volts range and possibly much higher by adjusting the insulating properties of the barium-titanate powders forming the insulation between the plates.
Entire article:
http://tech.groups.yahoo.com/group/ETList/message/6810
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Old 01-26-2007, 10:37 PM   #24
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Wouldn't the cap voltage vary wildly with state of charge? I do believe that near 50% discharge, that 300V set of caps would be somewhere around 140-160V...

If the claims are indeed true, the next hurdle for these caps is to develop in mass production the proper control system to allow them to drive a motor over their entire charge range. You don't want the caps to be restricted to operating at only 80-100% SOC in an electric car. Developing such a controller, compared with overcoming earlier battery restraints that plagued us up until NiMH were used, is probably a very simple matter.

The Zilla controllers seem to be a good candidate, able to operate anywhere from 48V absolute minimum to over 400V absolute maximum(but are suitable for battery packs of 72V-348V nominal). Just don't let the caps get discharged too much, and when they're near empty, you won't be able to make use of their full power because of the controller's voltage constraints and current limit.
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Old 01-27-2007, 08:20 AM   #25
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Yeah but by then you have used 3/4 of the energy that it contained and if you design the system to operate on a lower voltage and charge to a much higher voltage and switch it down it works. My 4 battery system charged to 60 volts and when drained was a little over 40 volts - it still ran fine just had lower top end speed.
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