# Is LiFePO4x100 = to NiMHx250?



## Electron Power (Jan 2, 2013)

I have a 5.5AH NiMH battery (250 cell) that I wish to "augment" to achieve higher capacity. I was originally planning on going Li-ion, but now I am leaning towards LiFePO4, due to its lower internal resistance (less voltage drop when loaded down), and higher cycle life. I'm thinking that 100 would be the optimum of cells # to match the NiMH pack. Does that sound correct? I'm planning on using 10Ah cells, but if I could get them cheap enough, I would consider going with 20Ah cells.


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## Ziggythewiz (May 16, 2010)

What is the voltage curve and IR of your NiMH pack?


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## Electron Power (Jan 2, 2013)

Here are the specs: The pack consists of 250 5.5Ah Sanyo NiMH 'D' cells in series, for a "nominal" voltage of approximately 330. Internal resistance of the pack is about 2.1 ohms. Aah, I wanted to attach a jpg of a voltage vs SOC graph of the pack, but It isn't working. When I click on "attach files", it just highlights the words, but nothing else happens. So I will try to spell it out using less than "a thousand" words. The controller maintains the pack within the range of 310 to 350 volts. This roughly equals to a SOC of between 40% and 60%. From what I understand, limiting the variation to 20% is necessary for maintaining the long jevity of NiMH batteries. But unfortunately, this SEVERELY limits the electric range of the vehicle. You're lucky if you can squeak a mile out of it. This falls SO far short of being acceptable to me, that it is literally driving me INSANE! Mentally speaking, I can only maintain this state of mind for a limited amount of time, before SOMETHING has to give. So I have come up with a plan. The first step involves acquiring 100 AMP10 or (preferrably) AMP20 LiFePO4 cells, of the variety having the threaded stud terminals sticking out of the top, so they can be easily linked together, using aluminum bars. Of course I would also need 100 LiFePO4 charge regulators, of the BEQ1 (or equivalent) variety (1 across each LiFePO4 cell). Using these items, I will put together a battery which can be placed across (in parallel with) the stock NiMh battery in the MMH. It will be sized to fit in the rear (behind the back seats) of the MMH, sitting right on top of the stock battery. It will probably attach to the stock MC4 connectors, so it could be easily removed it extra space happens to be needed in the vehicle. I estimate that the 310-350V internal charging system would allow between roughly 10-90% SOC for the "auxiliary" battery, considering how much lower the internal resistance of the much-higher-capacity LIFePO4 battery would be. The bonus would be that it could also be charged (even more fully, to boot!) via plug-in grid power, greatly reducing "fuel" usage, and bottom line - greatly reducing the cost of operating the vehicle, which is primarily use for short trips. In order for things to start happening (I AM ready now), what I need to know is where to find the best possible deal on the 10 or 20Ah stud-terminal LiFePO4 cells and regulators. I hate to admit it, but I am on disability, so there is NFW that I could possibly afford to spend the 6K (that's more than I paid for the 06 MMH) OR MORE that the "conversion" outfits out there are charging to do what i want done. That's why I'm going - DIY!


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## Ziggythewiz (May 16, 2010)

Are you clicking the paperclip by the Add Attachment label?

What vehicle is this in?

Is 350V the resting or charge voltage when full? 

The smallest large format prismatic cells I know that are easily available are 40AHs. There are many Chinese vendors pushing 20AH cells and smaller, but I don't think anyone here has experience with those aside from the A123 pouch cells. You might check the endless sphere forums as they specialize in bikes that use smaller cells. 

Many of us don't bother with regulators (BMS) and just use some basic monitoring. A full BMS is likely to cost nearly the same as your battery pack for such small cells.


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## Electron Power (Jan 2, 2013)

There is no "paperclip" visible. Vehicle is a 2006 Mercury Mariner Hybrid (MMH) - same as Ford Explorer Hybrid (FEH) and Mazda Tribute hybrid (MTH). I believe the hybrids ran 05 through 012. For being the entry-level hybrid, they have an amazing amount of "potential". And this potential is grossly underutilized, in their stock configuration! The first, most important (and practically the ONLY), thing to "upgrade" on one of those would be the HV battery. It should be at least 10x the Wh capacity of the stock one, which is 2K. The type of cells (with the charge regulators attached) that I am looking for are the ones featured on M. Barkley's LiFePO4 battery upgrade on an electric fiero (look at photos of the battery), on flickr.com. The protruding vertical threaded stud terminals allow for the use of aluminum bars, making for nice solid cell-to-cell interconnections. Can anyone point me in the right direction for finding the best deal on a lot of 100 of them? I want to get started as soon as the shipment of cells arrives. I would even consider driving up to maybe 300 miles or so, to pick them up.


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## Ziggythewiz (May 16, 2010)

Do you already know the stuff you have to do to make it plugin?

To post image, first click Go Advanced (below the text field) then hit the paperclip dropdown:


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## Electron Power (Jan 2, 2013)

Yes, I know that "regulator" modules need to be attached to each cell for purposes of keeping the cells equalized during plug-in charging sessions. They ALSO can be seen in the photos of the batteries in the pictures that I was attempting to refer to in my last post. Show me where the best deal on the cells and regulators is, and I will pull out the credit card.


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## Ziggythewiz (May 16, 2010)

You won't catch telling someone to use any regulators. I was just wondering if you knew what else you have to hack to enable plugin charging or extending your e-drive.

As I said earlier, the smallest cells I know how to get easily in the form factor you want are 40AH. If that's what you want I'd be happy to send you my source.


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## Electron Power (Jan 2, 2013)

If 40Ah (stud terminal LiFePO4) cells is where the best bang-for-the-buck deal is happening, I guess I will go for it. But I do have fears that seeing the number quoted for 100 of them is still going to knock me out of my seat! But on the flip side, it would give me more than 20X the "usable" capacity that I currently have with the stock setup. And you are saying that the current school of thought regarding individual cell charge regulation, is that regulators are NOT really needed for plug-in charging of the pack? That is very welcome news to me, as it would eliminate the additional expense of the regulation modules, while reducing the complexity of the battery at the same time. The plug-in charging setup that I plan to build/use will charge the external battery directly. But since that battery is going to be set up for plug-n-play operation (quick connect/disconnect capability), the internal NiMH battery WILL also pick up some extra charge if the external battery is connected while it is undergoing a charge cycle. THAT should work without ANY hacks. All that is left after that, in terms of unleashing the vehicle's full electrical potential, are 2 "hacks" that I still need to get figured out. One of them involves allowing electric-only operation without the requirement of having to maintain a warmed up ICE. The other hack would be geared toward raising the upper speed limit under which electric-only operation is allowed. I personally don't mind going slow. But I do get uncomfortable knowing that I am generating road rage in the minds of the operators of the vehicles that are lined up behind me!


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## Electron Power (Jan 2, 2013)

I have been searching around on the internet for LiFePO4 cells. The options DO seem to be somewhat limited. But there DOESN'T seem to be any shortage of rip-offs for them, from what I have been reading. The best deal I have found so far for 20AH cells (assembled in china - but I suppose they ALL are), is 20 bucks apiece (that's $1/Ah, @3.3V). But I have no idea what sort of discount there would be for purchase of 100 quantity. May as well look at the cost of the battery upgrade as being around 2 grand. But if the 40s that have been mentioned can be had for under roughly 30 bucks each (in quantity of 100 - & maybe having a couple of spares on hand wouldn't be such a bad idea), I should be able to step up to what would then be 2X capacity. Let me know what the # is for 100 quantity of the 40Ah stud-terminal cells that you have access to. I AM ready to make the purchase. As far as mods go, I actually HAVE already come up with 1 that enables ICE-free operation. I'm not saying that it is the BEST approach (very "crude", actually), but I think it will work, as long as there is sufficient charge level in the battery. I accidentally stumbled upon it after purposely running out of fuel (I WAS carrying a full gas can with me), in my quest to find out what the absolute max range of the vehicle was on a full tank of fuel, before being able to go no farther. But what I actually found, was that It could indeed go farther, after it was out of fuel! When the fuel pressure sensor detects that fuel pressure is too low (like when run out), the vehicle goes into EV mode. The red triangle on the dash illuminates, and a message to pull off the road when it is safe to do so is displayed. What that suggests, is that the vehicle could be forced into ICE-free EV mode via a toggle switch wired to the fuel pressure sensor circuit which would spoof an out-of-fuel condition, when flipped on! But I believe the likelihood is high, that there probably are other signals that also could be "spoofed" in order to achieve the same goal. And I have also come up with an idea that would overcome what I see as the ONLY other obstacle that stands in-the-way of the vehicle being an all-out electric vehicle, with full ICE backup, if/when needed. I have NOT yet tested the theory, but I do plan to soon. The "other" issue involves how fast the vehicle is allowed to go, or how much current the motor is allowed to draw, when in EV only mode. There is NOT any question as to whether-or-not the electric motor itself is powerful enough. The limit for my 06 is 40mph, before the ICE is "forced" to fire up. From what I understand, the 2012 models have upgraded firmware, which among other things, allows up to 45mph, before forcing the ICE to start. The "other" things also lend towards a more aggressive strategy in keeping the ICE turned off as much as possible. I need to find out the procedure (DIY style, of course) for flashing that firmware upgrade into my 06! But anyways, even though the current EV mode limit is 40mph on my 06 (4WD version), I can only achieve about 30mph on level ground, no wind. This lends me to believe that there is also an EV mode limit on how much current is allowed to be drawn via the accelerator pedal. The yes, very crude, but also very simple, "fix" would be to spoof the current sensing/safety disconnect shunt module located in the right-rear section of the stock battery unit to allow more current to be drawn that what the system "believes" is being drawn. It probably also should be made to be "switchable". I'm sure there are also other (probably better) ways to accomplish THAT particular goal. But at the present time, THAT is what I've come up with. I'm sure that there has got to be others out there trying to accomplish the same things that I am. I would love to hear for those individuals, and any ideas that they may have in regards to modding the said line of hybrid vehicles into ones that also have full (that DOES imply plug-in) EV capabilities. P.S. I'm waiting to hear what the the rock-bottom price on 100 of those 40Ah LiFePO4 cells would be, as the mods that I have listed would be senseless to do, unless a large-capacity battery is installed. And here is the link to the (no load) voltage vs SOC chart of the stock 250 cell NiMH pack: http://www.eaa-phev.org/images/2/28/Escape_vtg_vs_soc_no_load.gif


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## Ziggythewiz (May 16, 2010)

Electron Power said:


> And you are saying that the current school of thought regarding individual cell charge regulation, is that regulators are NOT really needed for plug-in charging of the pack? That is very welcome news to me, as it would eliminate the additional expense of the regulation modules, while reducing the complexity of the battery at the same time.


To BMS or not to BMS is a huge topic of debate that when brought up creates more arguments and flame wars than rational thought.

I am in the No BMS croud, for the reasons you've mentioned. Another reason is that a BMS that is imperfectly designed or used can end up destroying your pack instead of protecting it.

I'm running a booster pack of lithium in parallel with my lead pack with no BMS and so far no monitoring other than pack voltage and AH counter. I have a JLD404 doing those and its programmed relays cut-off the lithium from the lead while charging so the lead can go on into its gas cycle without overcharging the lithium. It would also cut-off the lithium if the pack voltage got too low, but that's hardly possible the way I have it setup.

The keys to going BMS free are to:

Properly balance the cells to begin with (I use top-balancing, which is another topic for flame wars)
Stay away from the edges (I use mine from ~90-30% SOC for now)
Do basic monitoring to catch any potential problem early, such as a half pack bridge.
I still need some work on number 3 before I can really push the limits of the pack. I plan to have 2-4 DVMs on chunks of the pack so I can compare relative voltages. If they get too different I'll know to check for issues.



Electron Power said:


> All that is left after that, in terms of unleashing the vehicle's full electrical potential, are 2 "hacks" that I still need to get figured out. One of them involves allowing electric-only operation without the requirement of having to maintain a warmed up ICE. The other hack would be geared toward raising the upper speed limit under which electric-only operation is allowed. I personally don't mind going slow. But I do get uncomfortable knowing that I am generating road rage in the minds of the operators of the vehicles that are lined up behind me!


Very important stuff to figure out. Do all your extras run off electric? Power brakes, steering, etc.


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## Ziggythewiz (May 16, 2010)

I'm not aware of many discounts for 100 cells vs 1. Most Chinese distrubutors give price breaks on the order of 500 or 1000 units. 

20AH cells would certainly be the cheapest way to get your 100 cells, you just have to find a reputable supplier. Nearly everyone here uses larger cells, so we don't know much about 20AH prismatics. You could check over at the Endless Sphere forums as they deal mainly with bikes that would use smaller cells.

If you cut-off the fuel sensor or pump to force EV mode, it sounds like your hazard lights would also come on.

For the speed limit, it's probably not a current limit because you use more current when accelerating than when cruising at higher speed.


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## Ziggythewiz (May 16, 2010)

Electron Power said:


> And here is the link to the (no load) voltage vs SOC chart of the stock 250 cell NiMH pack: http://www.eaa-phev.org/images/2/28/Escape_vtg_vs_soc_no_load.gif


Do you know if they have that data in xls, csv, or txt format? It would be interesting to make an excel chart that would overlay that curve with potential LiFePO4 curves.


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## Electron Power (Jan 2, 2013)

I apologize for taking so long to respond. I don't know if the raw data in that J-peg chart is available. You may have to extract it manually. I WOULD be interested in seeing how well the NiFePO4 data would lay over onto that chart. Unfortunately, the #'s on those 40Ah LiFePO4 cells are pretty well outside of what I can work with at this time (it would practically double the amount that I already have in the vehicle). My original plan was to string together about 80, maybe 82, 18650-sized Li-ion cells. The white 5Ah ones (they have the word "Energy" printed on them - which I'm assuming is the brand name under which they are sold, but I am not sure which "OEM" brand actually makes them) can be had on ebay for about 3 bucks apiece, but the price drops down to around 2, in quantity. That means that I could go 2X the stock battery capacity for a mere 160 bucks! And 10X (to get 20KWh, using 10 cells in parallel [800 cells total]) comes out to only 1600. And I'm sure that there would be even MORE of a discount when buying a lot of say, 1000 or more! The issue that DOES get out of hand with THAT option though, is the hassle-factor. In not having the means (a spot-welder maybe?) to bond the 800 cells together in proper fashion, it is probably an understatement to say that I could easily become overwhelmed, in trying to accomplish a task of such magnitude, especially considering that I have ADHD. Maybe the reality is, that I'm NOT really ready to make a move yet, in the way of going "big-bat". I probably should commit some more time to gaining higher knowledge, before making a final decision on which way I should go.


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## Ziggythewiz (May 16, 2010)

Many 18650-sized cells are bogus, or unsafe. I'd only consider using the 'protected' ones, I think they're from Panasonic.


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## Electron Power (Jan 2, 2013)

I forgot to mention, the brakes and steering ARE electric on MY MMH, but the A/C is not. Later model years DID get an electric A/C compressor though. (sorry about my paragraph formatting not working correctly- but I'm not really sure how to fix it) And as far as running ICE-free via an out-of-fuel condition (actual or spoofed) goes, it turned out NOT to be feasible. It went into that mode recently, after I started it up one day, went down my driveway, checked my mail, and then tried to start going down the road. After going from reverse into forward, in the snow around the mailbox, the engine cut out, showing a low fuel pressure message. I assume that a drop of water froze inside of the tank, causing a temporary blockage when it got into the line. Anyways, the hazard flashers DID NOT come on. But, the max speed in that mode is only 20mph (at first), but you CAN push the pedal all the way down without kicking in the ICE, obviously. Unfortunately, it just goes downhill from there (maybe "uphill" might be the better analogy). The max allowable speed just keeps tapering down and down, until it just simply refuses to go ANY farther. The max distance it will go in that mode is only about 1/4 mile, which is well short of the distance that it can travel when in "normal" EV mode. I do believe that a current limit does exist in EV mode, because the vehicle WILL travel at up to 40mph before forcing the ICE on, but only if coasting or going down hill at anything over 30mph. It just won't give me the amount of "pedal" that I need to travel in excess of 30mph on level ground, without the ICE firing up. I have seen current (discharge) readings of up to 2/3, maybe 3/4 of "full" swing on the charge/discharge meter WHEN THE ICE IS RUNNING (assist mode). But when it is off (and I want it to stay off), the most it will take is 1/6 (maybe 1/5) of full swing on the meter.


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## Electron Power (Jan 2, 2013)

I just noticed that message that is between my last 2. I believe the ones that you are calling "bogus" are the ones with the BLUE shrink tubing on them - NOT the white. I HAVE seen some pretty ugly reviews regarding the blue cells, despite seller's claims that they are made by NCR, which IS a fairly reputable company. From what I have read, the biggest bitch that people pitch regarding them, is that they state anywhere from 3800 to 5000mAh on them, but the ACTUAL capacity of the cells is only 2200mAh. I don't think that is enough to qualify them as being all-out bogus, but rating them at 2X what they really are IS misleading, in [what I myself would consider to be] a BIG way! I have NOT been able to find anything bad said about the whites though. I recently ordered half a dozen of them for the purpose of testing then to find out if THEY really have the 5000mAh capacity that they claim to have. I will report back with the results of my findings, after testing is complete (I'll admit, my fingers ARE crossed on this one). As far as the panasonics go, I'm going to have to agree that quality wise, they are probably [among, anyways] THE best out there. I got some pan double A NiCads back in the 1970's, and a good # of them are STILL working to this day! But after checking 18650 pan Li-ion prices on ebay, I found that they cost roughly 5X as much (wow, that's ten bucks apiece!), for only about 3400mAh of capacity! That prices ME out. But regardless of HOW cheap the 18650 cells are, I'm still coming up dry on trying to think of a way to reliably bond the 800 cells together, not to mention how long it would take to do it. And what do I do if any cells need to be replaced? The LAST thing I want is to end up with a big ugly mess! And there is also the issue of Li-ion's lower peak current output capability, compared to LiFePO4 or NiMH. I'm [now back to] thinking that going with a bank of 100 (somewhere in the range of 10 to 50AH) LiFePO4 cells with stud terminals is REALLY looking like the no-brainer way that I should proceed. Even at 10Ah (totaling about 3.3KWh), I would be able to go almost 10X as far as I can go now under battery-only propulsion. Because in theory, I should be able to use practically the full capacity of the battery, instead of only 20%, that the "primary" battery allows. And being that it would be fully plug-in charged BEFORE I leave home (and possibly other places that I might be), my mileage #'s should go up considerably, from where they run currently. So if I can't locate a source for LiFePO4 cells that is let's say, half of the price that YOU can get them for, I'll just have to play the waiting game, and jump in further down on the learning curve. With all of the speculation (predictions) going on about electric vehicles being the future of personal transportation, there simply HAS to be nothing short of an 'explosion' in the production of large capacity battery cells happening RIGHT NOW, as I post this reply! I AM keeping the eyeballs open though, just in case a deal that I CAN swing right now, DOES happen to come down the pike!


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## Electron Power (Jan 2, 2013)

Hmm... Not much action on this thread since my last post. Anyways, I'm sad to report that the white "Energy" branded 18650 5000mAh cells currently being sold out of the bay are only able to manage 20-25% of there rating. In using a constant 1.05A load (roughly C/5) to test them, I was lucky to see 5-10 minutes over an hour on the best ones. Some of them couldn't even reach the 1 hour mark. If it was was ME putting MY reputation on the line, there is no way I could (in good conscience) put any # higher than about 1100mAh on them. I suppose I should have invoked the "buyer protection" clause, citing "item not as described". I don't understand why the negative feedback that should have raised up the red colored flag on the seller wasn't there. C'mon people - it simply isn't acceptable (or even right, for that matter) to let these scum-bag rip-off artists keep on propagating their scams on others, once YOU'VE got their #. Now, since paragraph separation isn't working , I'll make (yet) another consecutive post that brings us back to topic.


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## Ziggythewiz (May 16, 2010)

Electron Power said:


> I'm sad to report that the white "Energy" branded 18650 5000mAh cells currently being sold out of the bay are only able to manage 20-25% of there rating.


That's what I mean by bogus. Any good cell will provide an ah rating and the rated current at which that ah # can actually be delivered.

How do paragraphs not work? Just hit enter twice.


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## Electron Power (Jan 2, 2013)

The voltage vs SOC curve for 40Ah "Winston" brand (going by the TAN color) LiFeYPO4 cells that I found on a site which sells them as 4-cell "batteries" begins at 2.5V, which represents a min SOC of 15%, and tops out at 4.0V, which represents a max SOC of 100%. Correlating this with the V vs SOC data for the stock NiMH pack in the FEH/MMH produces a 10% discrepancy, with reference to the "Does 100 Li cells = 250 Ni cells?" question. With the FEH/MMH's normal operating voltage of 315-350 volts, the SOC for the Ni pack is 42-62%. If 100 Li cells were used, the SOC range would slide up 10%, to 52-72%. But ideally speaking, the Li pack really needs to be operating at its lowest allowable SOC range (15 -35%, in this case), so that power which is put into the pack via cheap grid charging can be fully extracted/utilized/exhausted BEFORE the 5-10x more expensive fuel-burn charging can start in. In answer to the original question (assuming that the LiFeYPO4 data that I used is on the money), it would take 110 (need 2 B multiples of 5) to equal 250 Ni cells, in terms of matching the 42-62% SOC range. But that would NOT make for optimal usage of what could easily end up being a $5,000 battery! For the LiFeYPO4 battery pack to be able to work within the optimal operational SOC range that I described (ICE charge not kick in until SOC down to 16% (2.5V/cell), and kick out at 33% (2.8V/cell), it needs to have 125 cells. I'm pretty much just figuring out the #s here as I go, and I just had a "holy sh!t" realization. In order to reach 100% SOC (4.0v/cell) on the 125 cell pack, I'm going to need a charger that is capable of putting out 500 volts!


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## Electron Power (Jan 2, 2013)

Ziggythewiz said:


> That's what I mean by bogus. Any good cell will provide an ah rating and the rated current at which that ah # can actually be delivered.
> 
> How do paragraphs not work? Just hit enter twice.





Ziggythewiz said:


> That's what I mean by bogus. Any good cell will provide an ah rating and the rated current at which that ah # can actually be delivered.
> 
> How do paragraphs not work? Just hit enter twice.


 I'm really surprised that ebay allows such scammers to operate on their "turf". They seem to imply that they try to make sure everything is on the up-and-up, but I suppose the reality of it is that that isn't always necessarily the case. And what's up with these far-easterners who claim to be so big on "honor". Well, I'm letting the world know right now - that is one of the biggest loads of BS that I've ever heard. There - I just entered about 10 carriage return/line feeds (by means of hitting enter). It looks fine when I type it, but I bet none of them will be there after the message is submitted. I've even tried entering them manually, like right here for example: ◙♪ < that is a manually entered alt10/alt13 sequence. But instead of giving me the CR/LFs that I want, it only displays the CR and LF ascii characters. Hopefully that info might help someone tell me what the problem might be.


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## Ziggythewiz (May 16, 2010)

Ebay doesn't care what people sell provided it's legal, or at least doesn't attract attention, and they get their cut. Any big sellers can buy their way out of bad ratings and you need a bunch to make any difference anyway. It's explained well here.

Most people buying batteries don't have any way to measure how much they're getting out of them, and most little batteries don't last long anyway, so no one is going to notice.

What broswer are you using? Do the CRs show up in the preview window?


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## Electron Power (Jan 2, 2013)

Man, I can't spend a whole lot more time here today. But additional research regarding LiFePO4 cells in general has started causing me to have doubts about the V vs SOC curve (it's actually a straight line, or linear - making it very easy to work with]) that I am currently using, which claims that operational range lies between 2.5V/cell (15% SOC), and 4.0V/cell (100% SOC). But I have been coming across various claims by others, which clearly diverge from those #s. There are primarily 3 different lower limit #s going around. They are 2.5v, 2.8V, and 3.0V. And there are primarily 5 different upper limit #s out there. They are 3.5V, 3.6V, 3.8V, 4.0V, and 4.2V. I remember 1 poster in particular (I don't recall exactly which site it was - may have been an e-bike site) being very adamant about not straying out of the range between 3.0V and 3.5V, IF you plan on running BMS-free! Since that IS the way I plan on running, I am VERY concerned about this! But I don't think ANY of those mentioned LiFeYPO4 cells in particular. They are the LIFe cells that have the Yttrium doped cathodes, which are likely the ones that I will end up going with. They all seem to be referring to the "plain-jane" LiFePO4 cells. Could it simply be that - I think I might possibly even have some recollection of this - the Yttrium chemistry cells actually DO have a larger voltage spread capacity, before they will incur any damage resulting from under/over voltages? Let me summarize this post by asking if the numbers that I listed at the beginning of this post are correct for LiFeYPO4 cells? Obviously, I would "unanimously" prefer not to ruin 5 grand worth of batteries. ----------OK, I'm outa here......


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## Ziggythewiz (May 16, 2010)

The LiFePO4 voltage to SOC curve is definitely not linear. It does appear so from ~ 30-80 or 90% SOC.

It's near enough to a straight line that it's very difficult to tell anything from a single cell within that range, as voltage varies with temp and current as well as SOC. You can easily see the general trend in a string of balanced cells.

The different variants of lithium phosphate will vary slightly, but not as much as the numbers you've listed. Yes, 4.2 was considered the charge peak when the cells were new and the OEMs were idiots. Now most say 3.65 for the peak charge voltage. Most cells rest ~ 3.35 or lower.

You'll have to find someone with your same brand and type to get accurate numbers, but 3-3.35 resting is typically a good operating range. I try to run mine from 3.2-3.33


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## Electron Power (Jan 2, 2013)

Ziggythewiz said:


> The LiFePO4 voltage to SOC curve is definitely not linear. It does appear so from ~ 30-80 or 90% SOC.
> 3-3.35 resting is typically a good operating range. I try to run mine from 3.2-3.33


 I actually did have a gut feeling that the straight line from 15% to 100% on that chart might not be realistic. But now having seen several OTHER charts during my unsuccessful attempts to locate that original chart that I had based all of my previous figures on, I realize that it was also grossly unrealistic in how steep the slope of the curve is, in terms of voltage vs SOC. The slope that most of the charts agree upon is WAY flatter than that first chart had me believing. I now understand why one needs not EVER allow cell voltages to stray outside of 2.75V - 3.75V, except for that first inital 1 time 4V top-balance charge. And quite a bit of safety margin & cycle life is gained by tightening down inside of 3.0v - 3.5V, or even tighter, while nary suffering any significant loss in capacity.
Now this REALLY changes things, when it comes to matching the LiFeYPO4 pack up with the stock FEH/MMH charging system. The 42-62% SOC that is maintained in the stock NiMH pack now opens WAY-THE-HELL up, on account of the LFYP cells having such a flat curve. The FEH/MMH charging system works by kicking in with a 13A CC charge when the pack voltage gets down to 315V. It continues at that charge rate until the pack voltage rises up to 365V, where it then switches down to a 1A CC charge, causing the pack voltage to drop down. When down to 350V, all charging cuts off, until the pack is discharged down to 315V again, where the cycle repeats. 
Noe if I consider 3.0V to be the lower limit, 105 cells would work. But that pushes the charge kick-down voltage up to 3.5V, for all intents and purposes covering the entire capacity of the cell. Going 115 cells would bring the (average) low end down to 2.75V, leaving no safety margin for cell voltage variances. With those considerations in mind, the ideal number of cells is dare I say, "conclusively" looking to be 110.


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## Ziggythewiz (May 16, 2010)

That CC-CC charge cycle is quite different from the typical CC-CV charge cycle for LiFePO4.

You may need to have the lithium pack cut out when it's higher or lower than you want it. If taken up to 365V, I don't think it would drop to 350V unless the current is cut-off completely.

NIMH has a voltage dip when full while LiFePO4 has an exponential spike.

I think 103-105 cells could work with a SOC ~ 20-100%, but I would restrict the pack to only connect between 30 and 90.

I don't know the LiFeYPO4 curve well enough to know how it stacks up next to vanilla LiFePO4.


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## Electron Power (Jan 2, 2013)

I may have come with something that will suffice for being able to get paragraph separation. Notice the 2 lines in my last post that I was able to cut short before they reached EOL. If it works, there will be a blank line below. 

I'm sure that the charging strategy used is intended to maintain/optimize the life/health of NiMH cells. But strangely enough, what appears to make LFYP cells the ideal replacement/upgrade candidate for NiMH, IS the fact that the narrow 20% (42-62) allowable SOC [voltage] spread required for long-term NiMH life NOW opens up to AT LEAST 70% of LFYP's capacity, where life is VERY long. That equates to 330Wh usable from only the stock N pack, vs 11,594Wh usable from a 40Ah L pack (110 [email protected]%, + N pack 20%). That's 35x the usable power man! The way I'M looking at it, it is that right THERE that just sent NiMH technology into obsolecense! 

On that 2nd point, it looks like right now there is only HOPE to go on, that the drop in charge rate from C/3 to C/40 will be enough to allow the voltage to taper down enough for charging to be able to cut out completely. Running 110 cells "might" help that situation, as the 365V charge-down point would be at a lower cell voltage, lower SOC, and thereby farther away from where cell voltage wants to spike up. If matching to the center of SOC range (the 50% SOC point) was the objective, 105 cells WOULD be the #. But for the reasoning just mentioned (and a few others) , I'm going to stick on 110 (the next "step" up from 105), as what I believe is going to be the optimum # of cells to run in the pack. My strategy of running a higher cell count, in desiring to shy farther away from the high end (100% SOC) does depend on one thing though. And that is that there IS something to work with (to take away) at the low end, as such a range "downshift" would necessitate. 

Now we come to the point where things could get very ugly. IF the charging system's voltage spread IS TOO WIDE for L cells to be able to work with, as you seem to be implying that there just might be the risk of, the complexities involved in making the pack work begin to multiply. I'm not AT ALL hip on the idea of having to install big contactor relays and things like that. One of my biggest goals involves maintaining simplicity. Since it is already a fairly complex system, one of the LAST things I want to happen, is MORE complexity added to it by ME. Right now, my brain does not even want to allow it inside of the question! If this does turn out to be an issue, the only "saving grace" that would work for me would be via the software approach. The charging profile in the traction battery module firmware would need to be modified. But for me, that is (nothing short of) a HUGE big problem. I'm going to have to confess, that software-wise, I'm probably the biggest dummy out there. I wouldn't have the SLIGHTEST idea how to fix, change, alter, modify, patch, or even hack, the control module firmware! I'm also somewhat embarrassed to admit (as I type on this computer), that I don't even KNOW anybody who I think might be able to help me out in that regard. So if this "possible issue" does end up becoming real, ugliness would be all that I could see!


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## Ziggythewiz (May 16, 2010)

Are you augmenting the NIMH pack or replacing it? 

The additional complexity to protect your pack is really not that complicated. 1 contactor, 1 programmable voltmeter. $90, maybe less.

If it were me I'd throw in an AH counter and split pack monitoring for $100 more.


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## Electron Power (Jan 2, 2013)

OK, now I feel like a REALLY big dummy for that entire last post. After finally taking the time to look more closely at the other charts that I found, it is readily apparent that the vehicle's charging system operates WAY outside of the limits that LFP cells need to be kept within. But I think I'm OK with that, since the whole idea for doing this in the first place IS to be able to run on power that is pulled from the grid, rather than having to produce it by means of burnt gasoline, because it is 5-10x lower cost. 

I'm not sure where my head was at on that last post, but I am perfectly fine with adding the all of the stuff that you suggested, with the exception of the split-pack monitoring, as that item is "already have". It IS the reason for multiples of 5 cells. (110 cell would be 5 banks of 22). In addition to the 2 "main" terminals at either end of the series string, there are 4 additional wires that need to "tap" into the battery at equal intervals within the string. It works out to 5 banks, with 66V per bank. 

My intent is to have the L pack be pigged to the N pack when the vehicle is operating, and disconnect when grid charging, or otherwise not in use. When in operating mode, it would have to be able to disconnect if needed, like when the grid charge becomes fully depleted (undervolt), and also if ICE-charge goes too high (overvolt).


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## Ziggythewiz (May 16, 2010)

Sounds good. Depending on your typical drive you may find the system rarely needing to charge off the ICE anyway.


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## Electron Power (Jan 2, 2013)

Ziggythewiz said:


> Sounds good. Depending on your typical drive you may find the system rarely needing to charge off the ICE anyway.


With the majority of my trips being roughly 5-10 miles or less, that's pretty much what I would be expecting. On the cell count question, if 100 cell drops down to less than 15% SOC before 3.15 volts per cell is reached, then it would NOT be a good idea to use ANY more cells then 100. The more I look at those charts, the more I'm beginning to think that is infact the case. Would you be in agreement with that? 

I still wonder if there is an off chance that simple direct connection to the other pack might work out OK. I HAVE actually purchased some MC4 connector pairs, for purposes of being able to manually connect/disconnect the 2 main terminals. They are rated for 1KV, but current rating of the contacts is only 30A, so I'm not sure if they will handle without becoming excessively warm . I'm not sure what type of connector to use for tap wire connections. It needs to have 4 pins & a decent voltage rating, but current rating should not be a concern, since it would only be carrying monitoring & charge balancing currents.

My (initial) grid charging strategy allows for the use of a "can't-be-more-simple" CV charger (requires a 240VAC circuit). It uses a simple bridge rectifier to convert the AC grid voltage into a steady 335VDC (unregulated, but so what?). The CV charge of 335V looks to be just about perfect, for ending up with maximum 80-85% charge in the 100 cell pack, after being plugged in overnight, or longer. 

So in the end, if this IS in fact the end (of debating the matter), the answer to the original question that began this thread, now appears to be (a resounding?) YES. Obviously, there can be no "perfect" cross-match between the different cell technologies, due to the big-time differences in their discharge curves. Given what I now know, it does appear that 100 cells probably WILL work out the best, for surviving conditions where the voltage can vary between 3.15 and 3.65 volts/cell. It also makes for easy pack vs cell voltage conversion - just adding my 1 cent (2 decimal places) on THAT one! 

I still think there is a "reasonable" possibility (to believe) that the vehicle's 92% drop in charging current concurring when 365V is reached, is sufficient to allow a dip to 350V (within a reasonable amount of time), so that charging will cut out completely. I think that maintaining the connection with the stock NiMH pack will definitely lend a lot of "weight" to making it happen. But if initial testing indicates it's not happening, then I will have no choice but to install the additional monitoring/protection hardware. I guess we'll just have to wait and see where this goes, once the pack is purchased, built, and connected to the vehicle. 

Now, it's back to finding the deal that will fly for me, on 100 40AH (threaded terminal) cells. Would you recommend buying a few extra cells for use as spares, & how many? I'm tempted to pick up an extra 4 to replace the vehicle's 12V FLA battery, also. The best deal that I can find thus far is $43 (+ a $7 what-ever-it's-for premium) per cell. That works out to 5 grand for 100 cells. But I only have around 3 to work with. Given some time, I think I could work that up to possibly 4 grand, but that is definitely where the tap goes dry. If I could secure a price of $40 per cell (quantity WOULD be in excess of 100 pieces), while finding a way to get around the $7/cell "fee" at the same time, I can picture being able to get the project started within a month. I'm even willing to drive several hundred miles each way, if THAT is what it takes to push the price down to where I need it to be. Well, maybe now is the time to start send out emails & phone calls.

BTW, is anybody aware of any "group" buys happening for large quantities of these cells, that I might be able to get in on?


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## Ziggythewiz (May 16, 2010)

100 cells could work, running 15-80% SOC, but it may work better to shift it up ~10% by using 98 cells.

If you go that route though (under 103-105 cells), keep in mind you'll lose the ability to run in parallel with the NIMH pack for a good chunk of its discharge curve unless you isolate the pack connections with a diode(s). You could still run the NIMH by itself from 365V down to 333 or wherever the lithium is resting at then latch it in down 315 and back up to 335 or so.


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## Ziggythewiz (May 16, 2010)

Oh, about the extra cells. I think it's a great idea to get 4-8 extras depending on your ACC needs. I haven't had any fail but I've only had 'em for a year or less and it's better for pack integration to have spares that are at least somewhat worn than just sitting on a shelf if you do happen to need them.


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## Electron Power (Jan 2, 2013)

Can't go 98! Would HAVE to go 95, if want less than 100. Pack [need] be split into 5 equal #'d banks (5 bank @ 20 cell/bank = 100 cell pack). So if add/remove a cell from pack, must also add/remove cell from other 4 banks in pack, so pack be stay in balance. 

I'm pretty confident at this time, that sticking on 100 is the best bet. And I'd be MORE than happy if running 315 to 365 volts maintains the SOC between 15-80%. I "could" have been incorrect about where the charging goes, AFTER the initial CC charge cuts out at 365V. It could well be a switch-down, to a 350V CV charge. But not sure what triggers THAT charge to stop (time-out maybe?). I now have some sneeking suspicion that there would NOT be ANY problems resulting from parrallizing the LYP pack directly onto the stock NiMH pack (bank-for-bank), without having to bother with any disconnect relay stuff. 

Look THIS source: http://www.alliancerenewableenergy.com/40-Ah-TS-LFP40AHA.htm?productId=1 

If order cells from factory (ie - play waiting game 2 month), NOT need pay $7 cell fee. But is rep OK? Also, anyone for group buy? Me think qty need be 500+ for get discount.


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## Ziggythewiz (May 16, 2010)

365 is too full for the cells even if they're perfectly in balance. They're full at 3.38 so if you take them up to 3.65 vpc charging, then drop to 350, that's still too high.

Haven't heard of them. I'd wonder if their TS stock is just old or what since TS doesn't exist anymore.


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## Electron Power (Jan 2, 2013)

Ziggythewiz said:


> 365 is too full for the cells even if they're perfectly in balance. They're full at 3.38 so if you take them up to 3.65 vpc charging, then drop to 350, that's still too high.
> 
> Haven't heard of them. I'd wonder if their TS stock is just old or what since TS doesn't exist anymore.



<br /><br />

Look THIS LiFePO4 charge spec: 
http://www.electriccarpartscompany....103-x-41-x-168mm-br-183-lbs--083-kg_p_54.html

<br /><br />

The spec specify CC charge until reach 3.65V, then go to CV @3.40V. Amazingly, the NiMH "20%" strategy iz zakt same, sept 4 it being 0.1V 
(per cell, @100 LiFePO4 cells) higher on the CV charge. But since the CV charge would typically terminate much sooner than if on grid charge, due to arriving at destination, that 0.1V discrepancy is really starting to smell like a blessing-in-diskize. The way I see it now, that charge profile literally COULD NOT BE any better suited to a 100 cell LiFePO4 pack. I'm actually starting to wonder if it didn't actually end up like that BY DESIGN!

<br /><br />

As for the cells being offered on the ARE site, I don't THINK they are of the TS flavor, as all of the TS cells that I have seen pictures of, were BLUE in color. And I think it was Sinopoly, that took over Thunder Sky, but I think the cells are STILL blue. To me, tan indicates WB (Winston Battery) cells. And AFAIK, THEY are the Yttrium-laced ones. But with such a fiasco going on with those chinese batteries on ebay, I'm actually VERY scared about spending thousands on ANY batteries from china. I wouldn't be able to handle that kind of loss. If I would have built an EV pack using the 18650 cells, like I was originally planning to do, I most surely would have gone postal, after finding out that the pack only had 1/5 the capacity that it was supposed to have! I can accept the idea of something being fudged up 10, maybe 20%, above what it REALLY is. But fudging 1.1Ah up to 5?? That comes out to +455% beyond reality. I don't know about anyone else, but MY mind just keeps rejecting the idea that it is OK for that to be an acceptable practice. In fact, the more I think about it, the more pissed I'm starting to become, that I live in a world in which numbers that USED to convey important information about something, have now become meaningless. I feel like I did dodge a bullet. But what do I do, now that I need 4 grand+ worth of batteries, knowing that I cannot trust the chinese? I'm serious! I WOULD like to know the answer to THAT Question.


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## Electron Power (Jan 2, 2013)

Oh gee, I just went back to the ARE site, and saw the picture of the 2 guys shaking hands. Yup, the oriental looking one IS the president of Thunder Sky Holdings, Limited. But wait a minute - his name is WINSTON Chung! Could that be a coincidence? I almost can't hardly believe it. But then, what the hell do I know? What I do know, is that I am becoming confused by it all. And that makes it quite difficult to loosen up on the very tight grip that I have on my money right now!

I'm now reconsidering the idea of simply going with 25 flooded lead acid batteries, and being DONE with it!. It WOULD be far cheaper, and less hassle also, I think.


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## Ziggythewiz (May 16, 2010)

3.65 is the max charge voltage for a single cell. If the average voltage of your string of 100 cells is 3.65V, many of them will be higher than 3.65. Also, you can't know exactly what the charge current into the lithium cells will be until you observe the cross chemistry interaction.

You don't have a CV phase if your charger only does CC and waits for the NIMH voltage to dip. With LiFePO4 it will not dip unless it drains enough from the lithium into the NIMH.

TS split into Sinopoly and Winston. TS cells were yellow, winston seems to have continued that. Sinopoly cells are mostly black and one is green. CALB sky energy cells are blue, and the new CAs are grey.

If you get cells from a reputable stateside dealer you don't have to deal with the major shipping and customs issues, but that may cost a little or a lot more.


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## Ziggythewiz (May 16, 2010)

Electron Power said:


> It WOULD be far cheaper, and less hassle also, I think.


Far cheaper now, and less hassle for the first few months. By the death of your first pack you'll be cursing yourself and by the third, your wallet.


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## Electron Power (Jan 2, 2013)

Ziggythewiz said:


> Far cheaper now, and less hassle for the first few months. By the death of your first pack you'll be cursing yourself and by the third, your wallet.


I'm debating the pros vs cons right now. In realizing how badly I would have been "taken" by the chinese, if I had purchased a large quantity of 18650 cells to build a pack, it looks like I have now picked up some sort of "phobia", in regards to sending, what for ME is BIG money, in a far-easterly direction. Given THAT, the FLA option is looking better and better. 

[paragraph formatting appears to be working now, without me having to resort to using vBulletin codes - cool]

I remember picking up a 20Ah FLA garden tractor battery from walmart for only $20. That works out to a mere 8.3 cents/Wh, as opposed at least 33.3 for LYP. Now that WAS some time ago, but if they can be STILL be had around that price level, it WILL become the deal MAKER for me, as the cost would be only 5 hundred (as opposed to 4-5 thousand), without ANY worries of getting ripped off, to be able to get in on the EV game. Granted, the pack would only have half the capacity. And cyclicly speaking, it would only last 2 years at most if recharged every day. But maybe it WOULD be a good idea to hold out 2 years on LYP technology, for it to mature, for quality to improve, for pricing to come down, and for not having to worry about getting what I am expecting to get for my money!


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## major (Apr 4, 2008)

Electron Power said:


> I'm debating the pros vs cons right now. In realizing how badly I would have been "taken" by the chinese, if I had purchased a large quantity of 18650 cells to build a pack, it looks like I have now picked up some sort of "phobia", in regards to sending, what for ME is BIG money, in a far-easterly direction. Given THAT, the FLA option is looking better and better.
> 
> [paragraph formatting appears to be working now, without me having to resort to using vBulletin codes - cool]
> 
> I remember picking up a 20Ah FLA garden tractor battery from walmart for only $20. That works out to a mere 8.3 cents/Wh, as opposed at least 33.3 for LYP. Now that WAS some time ago, but if they can be STILL be had around that price level, it WILL become the deal MAKER for me, as the cost would be only 5 hundred (as opposed to 4-5 thousand), without ANY worries of getting ripped off, to be able to get in on the EV game. Granted, the pack would only have half the capacity. And cyclicly speaking, it would only last 2 years at most if recharged every day. But maybe it WOULD be a good idea to hold out 2 years on LYP technology, for it to mature, for quality to improve, for pricing to come down, and for *not having to worry about getting what I am expecting to get for my money*!


You should worry if you expect to get 20Ah, 2 years, and daily cycling out of $20 FLA garden tractor batteries. You'll be lucky to get 10Ah, 1 year or 40 cycles.


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## Electron Power (Jan 2, 2013)

Huh, only 40 cycles? I thought flooded lead acid was good for AT LEAST 500 cycles, if they aren't too deep.

Anyways, I just sent out a request for a price quote on a Lifetech 330 volt 15Ah LiFePO4 battery. The part/item # is XPSMX-330015. That's only 37.5% of the capacity that 100 40Ah Winston/TS cells would have. But so long as the price is right (2 grand or less), that amount of capacity WILL work for me. It has a full Al-loy housing, and it supposedly does sport some sort of internal BMS.

The lifetech url is: www.battery-lifetech.com

Don't expect to find the battery on their website though. It is of the "MAX" series. But for some reason, only the "ENERGY" and "POWER" series battery packs show up on the site. Go figure THAT one out!

Do a search on the part#, and you should be able to find the specs on it. What do you think?


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## major (Apr 4, 2008)

Electron Power said:


> Huh, only 40 cycles? I thought flooded lead acid was good for AT LEAST 500 cycles, if they aren't too deep.


Maybe with the high end deep cycle FLA, but not those cheap garden tractor starting batteries. And using such cheap lead in a hybrid or plug-in would likely be counterproductive meaning you'll spend more energy hauling that mass than you can store and retrieve from the battery.


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## Ziggythewiz (May 16, 2010)

major said:


> And using such cheap lead in a hybrid or plug-in would likely be counterproductive meaning you'll send more energy hauling that mass than you can store and retrieve from the battery.


Agreed. You can't make a booster pack out of lead, you'd have to call it a ballast pack.


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## Electron Power (Jan 2, 2013)

You saying that if run FLA battery, would be nothing more than a glorified golf cart, or something like that?? Those vibes I DO pick up. 

Forget about the plumbous batteries for now, anyways. The option that I am NOW pursuing, is a complete 330V 15Ah ferrous cell pack, with aluminum housing. I did put a request in for a quote on one of them. But I'm already flooded by vibes predicting I won't like what the quote is, for the Wh rating of the pack. Will C.


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## Electron Power (Jan 2, 2013)

The week-later update: 

There has been NO RESPONSE WHATSOEVER, to my RFQ for an XPSMX-330015 330 volt 15Ah LiFePO4 pouch cell battery pack (which is already interconnected, housed, & BMS'd) from lifetech. It IS disheartening, as this appears to EASILY be the most plug-n-play solution that one could ask for. The ONLY modification required on the vehicle itself to enable such "play", is installation of the 2 "plug" wires which connect to the stock pack. It would easily be the cleanest looking setup, along with being lightweight, easily removable, swappable, and yes - even gang-able! As mentioned previously, all of this does hinge (depend) on the assumption that the 2 different technology packs are able to live together "harmoniously". The only significant effect that I can envision at this point, is that the Li pack would exert an extremely powerful influence in keeping the Ni pack voltage "in line". I'm talking about FORCING it to operate within a very tight (below 20%) SOC level, which can only INCREASE it's lifespan. Considering that the vehicle cannot even operate at all without a functioning primary pack, I think this is indeed a highly desirable trait for it to have. 

In regard to the actual # of tap wires leading from the controller unit (BMS) into the "cell bundle" within the primary pack housing, I was "highly" incorrect in stating that there were only 4 of them (divi-ing up the pack into only 5 banks). After pulling the top cover off of the HV section and subsequently looking over the (reverse-engineered) schematic diagram of the pack (provided by Hybrids Plus), 22 wires are listed. But that # does not add up, as the # of taps should be = to a # that 250 is divisible by, minus 1. Using THAT formula, the closest # would come out to 24, indicating that there has got to be some kind of error somewhere, necessitating delving deep into the cell bundle, itself. Enough said for now.


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