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Old 05-23-2012, 09:16 PM   #11 (permalink)
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Originally Posted by Daox View Post
I've never heard of that cell manufacturer. I have heard you can get calb cells for $1.2/ah which is the same price. They have comparable specifications and there are others using them so they're a bit more proven.
would you happen to know where you can get them at that price?

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Old 05-23-2012, 09:18 PM   #12 (permalink)
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W. Virginia safety inspection requires AS1 or AS10 safety glass for windshield.
I did not realize that... good thing I held on to the glass! Looks like I'll be putting it back in
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Old 05-24-2012, 10:47 AM   #13 (permalink)
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These are the cells that I am looking at, mostly for price... hopefully they will serve their purpose well.

160Ah, 3C, 3.2V Model: BP-HZPP-160 10.0 x 2.24 x 10.4in
I haven't heard of those cells either. The supplier does show Sinopoly, and I know they are advertising 180AH cells at 12.7 lbs and basically the same form factor as the 160AH. My cells are the 160AH, but I suspect they are actually better than that. You might want to ask that supllier about the 180 cells. That price for those 160AH cells is good. My setup keeps me very close to the 3C limitation at all times. My Soliton Jr controller maxes out at 600 amps. It would be fun to be able to dump 1000 amps for a short period of time. Most cells have a burst rating at 10C for 10 to 15 seconds. I'm finding that my car is very drivable when staying under 500 battery amps. I think if you look for a controller that can deliver 1000 amps you can have some fun, but most of the time you'll be staying under the 3C limit. Higher voltage will allow for you to deliver higher amps at higher RPMs.
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Old 05-24-2012, 11:25 AM   #14 (permalink)
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Quote:
Originally Posted by j8reign View Post
would you happen to know where you can get them at that price?

This is the place I heard of someone getting that price. He apparently bought 100 of the 100Ah cells. I got the info 2nd hand, so you're 3rd hand.

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Old 05-24-2012, 01:29 PM   #15 (permalink)
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Originally Posted by mechman600 View Post
Sounds like a great project!
My advice is that you go as high with voltage as possible within your budget. The higher the voltage, the less efficiency is lost to heat in your cables and whatnot. You can go quite high before a Warp9 turns into molten lava - something like 192V is still within reason.

Controllers do get quite pricey above 144V but many people say it is worth the investment. Keep searching the EV trading post for parts. [EV Tradin' post] - Electric Vehicle Classifieds
You can register to get alerts emailed to you when something you are looking for goes up for sale.
Best of luck!
I disagree, a DIY EV for the purpose of saving money and not creating a money hole is best operating at a LOWER voltage at LOWER amps using more or less common off the shelf parts.

Generally speaking you want your vehicle at the max reasonable speed you want to travel to draw under 200amps, preferably near 100amps.

Ideally with your pedal to the metal cruising at about 3500-4500rpms you should be at your top speed you want, have a gear or two below for mud and a gear above for special circumstances.

Every EV I have dealt with runs most efficiently (in terms of power in power out) with the pedal at WOT. AC systems and DC systems become rather inefficient at low throttle positions, enough that on a lithium setup you are loosing at least 25% out the window on PWM if you drive in that region often with a typical controller. You normally still gain range because of better aero at low speed but its still worth knowing.

Other factors such as using lead batteries is when amp draw and rate become more important than controller losses, lithium this isn't the case.

So the most effient and lowest cost EV is typically the same car. Less volts, costs less, and is less to maintain, has more parts available off the shelf new and used, but also will have less performance but be taylored to drive a specific speed most of the time and do so most efficiently.

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Old 05-26-2012, 01:31 PM   #16 (permalink)
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Originally Posted by rmay635703 View Post
I disagree, a DIY EV for the purpose of saving money and not creating a money hole is best operating at a LOWER voltage at LOWER amps using more or less common off the shelf parts.

Every EV I have dealt with runs most efficiently (in terms of power in power out) with the pedal at WOT. AC systems and DC systems become rather inefficient at low throttle positions, enough that on a lithium setup you are loosing at least 25% out the window on PWM if you drive in that region often with a typical controller.

Cheers
Ryan
Ryan,

I found your reply interesting. In particular your claim about 25% loss in efficiency when not operating at WOT. My controller, and I've seen others claim 98% efficiency. Since they use PWM to get that, I'm interested in why you think it is only 75% , not the 98%.
I would agree that picking a gearing that allows for using one gear and eliminating transmission losses is a good idea. In my 4 speed transmission, the 4th speed is straight through, so It doesn't have losses due to gear friction, but I do have losses due to the transmission oil in any gear. I drive in 4th gear whenever I can.
Since we're on the topic of efficiency I wanted point out that fast acceleration to a given speed doesn't use any more energy than getting there slower. The energy is the same, but the power required is higher. I haven't tried bringing this idea up yet because I thought it might cause some controversy. For electrics the only extra losses would be from I^2 R losses due to needing extra current, and the purcket effect which for Lithiums isn't very much. I donít know how much the I^2 R losses are, so Iím going out on a limb as far as that is concerned.
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Old 05-28-2012, 12:55 PM   #17 (permalink)
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Originally Posted by fb_bf View Post
Ryan,

I found your reply interesting. In particular your claim about 25% loss in efficiency when not operating at WOT. My controller, and I've seen others claim 98% efficiency. Since they use PWM to get that, I'm interested in why you think it is only 75% , not the 98%.
I would agree that picking a gearing that allows for using one gear and eliminating transmission losses is a good idea. In my 4 speed transmission, the 4th speed is straight through, so It doesn't have losses due to gear friction, but I do have losses due to the transmission oil in any gear. I drive in 4th gear whenever I can.
Hmm, perhaps I am 15 years out of practice but...

You need to take motor and controller as a single drivetrain unit...
98% efficiency motor and controller only occurs at WOT, below that it must be another number, AKA switching losses affect both the controller loss, motor losses and battery/conduction losses not just one or another.

I was always taught to consider a DC ev drivetrain as being roughly 85% efficient overall, it goes up to 93-98% at wot (motor/controller/wires) But if it is 85% overall and it peaks at 93-98%, what happens if you are driving at low throttle below the average?

Anyway I deal mostly with lead and forklift style DC motors but many of the AC controllers suffer the same as a DC controller when your throttle is under 50%

Depending on switching speed you can easily loose 25% of power applied through the controller & motor to switching losses when throttle is "light", where that would occur would depend on voltage, rpm, and switching speed..

On my one EV (real world) 50amps at light throttle gets me to about 18mph and no faster without wind or hills, WOT I accellerate to 30mph and level out at about 65amps, the amount of energy difference is only around 30% (out of the battery) but the power generated is greatly different, the odd part is once I get up to speed, if I let off the gas slightly so I float around 50 amps my speed only decreases slightly and holds around 24mph, this is because field strength is higher so switching losses/motor losses end up being lower (higher throttle position to push 50amps whent he motor is spinning faster)

There were composite maps of efficiency on the diyelectriccar forums of one example controller that had a very fast (efficient) switching speed at various throttle positions, even on his controller things were not as pretty getting below 50% throttle. The thing is an AC controller does not need to PWM until RPMs and power are quite low since timing can just be adjusted, so AC tends to be more efficient at lower loads but usually, though not always less efficient (a percentage or two) at wot as compared to a DC controller and good motor combo.

All this said once you get to about 75% throttle most every controller & motor combo, even a terrible one gets over 90% efficiency, it is down on 50% or less that things get murky, especially at low RPMs.

So in other words if you aren't running WOT or close to it, it isn't 98% unless you have an extremely efficient controller & motor I haven't encountered. I have never understood why people ignore the bottom 50% of the throttle in terms of efficiency.

On my EV I only try to use that area when hypermiling because I can more or less drive WOT all day without speed worries. I have considered adding a large capacitor bank to improve my low speed efficiency but I am uncertain how much affect it would have, my controllers switch rather slowly Curtis 1204/1209 but aren't real bad, just not great.

Ah well, But then again mine are old, low tech, slow and reliable.
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Old 05-28-2012, 01:37 PM   #18 (permalink)
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Thanks for the lengthy reply. I'll look into what you said about the controller. I have been assuming an 85% to 90 % efficiency for the motor, 10% loss in the drive train, and a couple of percent for the controller.
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Old 05-29-2012, 01:31 PM   #19 (permalink)
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Thanks for the lengthy reply. I'll look into what you said about the controller. I have been assuming an 85% to 90 % efficiency for the motor, 10% loss in the drive train, and a couple of percent for the controller.
What you suppose may be true on brand new AC drive, DC drive, especially older setups weren't too swift at lower rpms, the controller itself may not dissapate much but more power is lost in the motor as well in these situations, which means if RPM & throttle are too low composite efficiency can drop into the 75% area.

Normally most folks who have EVs never have so much voltage to end up in this region but you setup may be light enough and aero enough to get awefull close.

Cheers
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