High Power Density Battery...Opinions?

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john
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High Power Density Battery...Opinions?

I was wondering what some of you may consider as being a suitable battery for very high power density applications? I know A123 is an obvious choice, but I was looking at something a little more economical and still decently powerful. Right now I have a pocket bike that i've converted to electric, usual swing arm extensions and what not and using 320 1/2 Saft nicad cells. These work decently well, but they seem to not be as powerful as I thought.

My setup is using a 48 volt 700 amp logisystems controller, and i would like to try and take the full benefit of it but as economically priced as possible as far as the batteries are concerned. I've considered the sub c nimh cells in RC hobby shops and such, but what other options should i look into?

john
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Re: High Power Density Battery...Opinions?

Current setup uses 320 1/2 D saft nicad cells.

andrew
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Re: High Power Density Battery...Opinions?

john, can you link to the cell spec sheet, or provide a model number? Is it the following cell:
VRE 1/2 D ?

If that is the cell you are using, than the full pack impedance will be:
40 * .01 ohms / 8 parallel strings = .05 ohms

If that is the case, then I'm not surprised why the performance is not very good. It would probably be similar out of 4 B&B HR15-12 (15ah 12v) batteries.

I would get 4 Odyssey PC680s. At about .0065 ohms impedence per battery, than the pack impedance would be about half what it is now. And, these batteries would last for a while. If you don't care so much about battery life, than SVR batteries would be an option with more power. Also, batteries plus carries some AGM batteries designed for starting that would be less expensive and deliver more power, but also probably won't last nearly as long as the PC680s.

Here is a rough calculation of max power out of each battery at 700 amps:
Existing batteries: Power peaks at 480 amps, so I'll go with 480 amps: 24v drop/.05 = 480 * 24v = 11,520 watts

Odyssey PC680s: 700 * .026 = 18.2v drop. (48v - 18.2) * 700 amps = 20,860 watts

Here's a good place for the odysseys:
http://www.remybattery.com

And for the batteries plus starter AGMs, check through their AGM listing:
AGMs from Batteires Plus
Here's one that would probably outperform the Odyssey PC680 at less cost.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

andrew
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Re: High Power Density Battery...Opinions?

BTW, I noticed the PC625s for $85 at remybattery. Those would also be a suitable option.

And, I forgot to mention that battery temperature has a huge impact on power for lead-acid. If you want your batteries to put out a lot of power, than get them hot. The best way to do this is run the bike and charge it quickly, but BEWARE of the danger of thermal runaway. It is best to use temperature compensated charging.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

john
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Re: High Power Density Battery...Opinions?

I contacted SAFT directly and they provided that same spec sheet, as I wasn't quite sure which model I had since I bought them from a local surplus store. The hawkers seem like a good choice as do the SVR's. How would these compare to hawkers and SVR's though?

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3145

If i were to use 200-300 of them, it would be close in weight to 4 of either the PC680s or SVR's, I'm just not too sure about the performance.

andrew
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Re: High Power Density Battery...Opinions?

john, it looks like they would provide a similar amount of power for the weight, but you'll need to buy some and test them as I wouldn't trust the batteryspace resistance spec.

If it held true, than a pack of 320 cells at 700 amps would provide this much power:

.005 * 40cells / 8 in parallel = .025 ohms pack resistance * 700 amps = 17.5v drop. (48v - 17.5v) * 700 = 21,350 watts. This would weigh 48 lbs for the cells alone.

I tested some of the RC packs from batteryspace. Here are my results:

7.2v R/C Batteries NiMH & NiCad

Note, that I got better performance out of the 1.7ah NiCad cell packs which have cells with a sintered electrode for more surface area. Also, I was testing the already assembled packs. If you could build your own packs, and solder copper buss bars directly to the cells, than you will get better performance. There is a slight risk of damaging cells when soldering directly to them with heat. I wouldn't buy their already tabbed batteries.

Copper buss bars and other supplies for soldering can be found here:
http://www.cheapbatterypacks.com

They also sell battery cells, but for some reason they took the performance graphs on the cells down and don't provide any information. If you decide to go with their cells, than I would definitely buy some first for testing.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

john
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Re: High Power Density Battery...Opinions?

I just really don't like the idea of going with an out dated lead design. However, it seems to be the most cost effective battery for this type of application. I started reading up on car audio batteries and found these Kinetik car audio batteries which seem to be a little better performers than hawkers. I'm not sure if there is an actual difference between the two or if it is just a re-labeled casing but it looks rather promising. Thanks for all the help so far too by the way, it really helps me narrow down my options.

(eBay Item) KINETIK CAR AUDIO BATTERY POWER CELL HC600

andrew
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Re: High Power Density Battery...Opinions?

john, I don't really understand your reasoning. There's really nothing outdated about absorbed glass matt (AGM) or lead-acid technology in general. They are used on aircraft and for military applications for high power in a small size, and high reliability. It beats anything in terms of power for cost. If you want a real high amount of power for the weight, than get the batteries hot.

The battery you link to is a re-labeled something. It might be a Genesis or Odyssey battery, but I can't be sure. The "amps" figure they put out means nothing. To get some kind of performance baseline, you'll need to find the cold cranking amps (CCA), which IIRC is a load test at 0 degrees F for 30 seconds. It is how much current the battery can deliver while maintaining a voltage above 7.2v for the entire duration. Also, the 1,000 Hz AC impedance at full charge in ohms is useful. This appears to be .007 ohms for the Odyssey PC680.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

john
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Re: High Power Density Battery...Opinions?

It's not that lead acid isn't good for racing applications, just compared to other rechargeable chemistries that are now available it doesn't have as much capacity per weight or size. For this project though it really is more about having as much acceleration and speed as possible though so it doesn't matter. I looked into the PC680's and the SVR 14ah model, is this the one that you were referring to?

http://www.electricmotorsport.com/store/ems_ev_parts_batteries_svr.php

If so is this better than the PC680 as far as performance is concerned? I was unable to find a spec sheet on this battery.

andrew
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Re: High Power Density Battery...Opinions?

That's the one. Unfortunately, I'm finding conflicting information. The following are the sources of information:

SVR Brochure: CCA listed as 250

SVR 14 page at svrbatteries.com : CCA listed as 200

That's just one helpful piece of information for performance. I can't find any 1000 hz AC impedance test data, or hot cranking amps (HCA) data, both of which Odyssey provides. The CCA listed for the PC680 is 220.

You might try a search of this from or contact mr_exon (member on this forum) I think he may have used the SVR 14s. Also might try contacting EV parts, and thundersruck-ev.com as they do drag racing and might give you an idea of how the SVR batteries compare to the Odysseys. Personally, I'd go with the Odysseys due to the better life.

BTW, john, if you really want very high power, than go to a higher voltage. You are running 48v, and the Met motor you are planning to use might have somewhere around a .055 ohm resistance (per the data here). Lets figure maximum power for various voltage minus resistive losses:

Assuming you use Odyssey PC680s (and the 1000 Hz AC impedance appears to actually be .007 ohms):

48v: .078 ohms resistance 24v/.078 = 307.7 amps (current at max power). 307.7 * 24 = 7384 watts max

60v: 30v/.078 = 384.6 amps * 30v = 11538.5 watts

72v: 36v/.078 = 461.5 amps * 36v = 16615 watts

You'd need to get Logisystems to build you another controller, and sell your existing 48v model. And the dealing with the speed may be quite a challenge which might require duel stage reduction, but I think it's definitely worth it when running higher voltages.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

frodus
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Re: High Power Density Battery...Opinions?

the comment about lead acid not having the capacity? Thats not really true, sure they're heavy, but some of the lead out there beats lifepo in how much current they can deliver (some over 7C). Some optimas can handle bursts of 500A...or more. They're a little more robust and less picky with their balancing (although it does extend their life to balance)

The only TRULY great thing about LiFePo is that its lighter, and its power to weight density is higher, but they are still more soft in discharge rates, although they do charge faster.

NiMH is likely the more stiff of all 3, having good discharge/charge capability, the only thing, is cost (like with lifepo). Plus, they're toxic.

I think you're working off assumtions about lead acid car batteries.... just be careful.. there's plenty out there made for industrial use and you CAN get a lot out of them, but size/weight is the issue, not capacity.

____________

Travis Gintz
1986 Honda VFR Conversion
www.evfr.net

john
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Re: High Power Density Battery...Opinions?

I realize that lead acid is a developed technology and is a good high discharge pulse battery, but per the size and weight it doesn't compare to other nickel and lithium chemistries in terms of wh/kg. It is much more tolerant of over discharge and balancing issues, as well as being able to take a deep discharge without too much effect. I'd really consider NIMH to be the balance between the two but these still need balancing and temperature controls. Their cycle life also isn't very good compared to A123. Lately i've been looking into flooded nicad cells just to see how they would compare to lead acid, mostly hawkers and the above mentioned svr's. The BB600 supply has long dried up, but these cells were far too large and heavy for a pocket bike the size i have. There is a few different models i found that http://www.sg-photo.com/nicad_batteries.htm did list along with the BB600's, a 14 ah model and 24 ah model that looks like it is worth pursuing. The 14 ah cell is only 5 bucks and the 24 ah is just 7 bucks. I've emailed them to see if they still have stock of these models but they haven't gotten back to me yet.

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