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5132 Views 25 Replies 6 Participants Last post by  helluvaengineer96
hey ya all heres some interesting e-mail that I recently had with jon at grass roots in neveda comments?

Dear Lou-ace,
I have spent a good deal of time evaluating various sources for lithium
batteries. As it turns out there are quite a few lithium battery
manufacturers. However, finding one source that is the best value for an
Electric Vehicle is daunting. After a lot of e-mails and phone
conversations we have concluded that Energetech Lithium-ion Phosphate
(LiFePO4) battery packs will give you the best value in performance,
construction, energy density, longevity, price and delivery. They use
Chinese made HiPower lithium batteries that as you may know need special
care when being charged and discharged. Therefore, special due diligence
has been exerted to find a superior Battery Management System ‘BMS’ which
will assure maximum battery life. We know the one thing that you want for
your vehicle is a reliable battery pack that will assure you years of
satisfactory driving pleasure. Energetech has been in business for 34
years and will give a full two years replacement warranty on all batteries
that are not mis-used. You will need a battery charger program for lithium
batteries I think the Zivan chargers are the best but you may have to have
yours reprogrammed.
Yours Truly,
Jon
702 2777544
www.grassrootsEV.com





> Hi Jon, lou-ace here, greetings from the northwest! I'm presently
> converting a small truck to electric ( ADc 9" motor installed, curtis
> 1231c
> controller, zivan charger, switches ect), and was planning on using trojan
> t-145
> batt. pack. I'm intriqued by your li-po battery advertised on the
> grassroot
> site. can you fill me in more on it? who makes it? is it compatible with
> conventional DC charging methods? Frankly it sounds to good to be true (
> although expensive). what track record/ history is there with this kind of
> technology? ect. rsvp to this e-mail address please. thanks........
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The 1238-7501 has a voltage shutdown at 130 volts. It seems people have based their LiFePO4 decisions on 35 or 36 batteries. 35 batteries * 3.6v = 126v maximum charge voltage or 36 batteries * 3.6 = 129.6v. Of course nominal voltage would be 35 batteries 112v and 36 batteries 115.2v. They hang higher than that off a charge and when only driven a short ways though when resting, between about 3.3v and 3.4v so usually you'd see 120v sitting idle. If you had an adjustable charger you could get an extra few cells and only charge them to 3.5 volts per cell and get 37 in there and might pull slightly more power at the higher RPM range but it probably wouldn't be enough to notice but it would a bigger difference with range. Keep in mind that 37 cells might be an issue with heavy regen current when the pack is full, which is why I'm sure people are keeping with 35 or 36 cells.
 

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I'd prefer the CALB, but TS are an option. I'd go to higher AH cells, but their increased height start making installation problematic.

Since the nominal voltage is 3.2-3.3V, i could easily charge 39 cells to 3.3 and stay below 130V. 130V/38 cells is 3.42V; well within my parameters. Like I said above, I plan to stay away from the max. capacity of the cells to increase longevity.
Charging to 3.3v is not going to give you a full cell. When you fully charge a cell I would aim for nothing less than 3.4v, at that point you still might leave a little behind and need to float the charge at that voltage a little longer at a lower voltage to ensure a full charge. Keep in mind that 39 cells will leave you with no headroom for regen. The controller shuts down at a 130v which should be the max the cells will ever reach, not the nominal voltage. The nominal rating is 108v based on lead acid cells but the max under any 'on' condition should be 130v.

helluvaengineer96, The recommended charging voltages don't really make much of a difference because its all LiFePO4 and IMHO You don't get really anything past 3.6v except for some headroom for balancing shunts to operate with if that is your mode of operation. I wouldn't base number of cells on that. There is no reason that I see to why someone would limit themselves to 34 cells because they chose TS.
 
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