LiFeP04 Pack Sizing

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Digger11
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LiFeP04 Pack Sizing

Post by Digger11 »

I used the search but couldn't find the answer to this.

If I have, say $12,000 to spend on my battery pack for a heavy EV, then is there any difference in the following;

45 200ah Packs
90 100AH Packs
or even 56 160ah packs,

As the controller will limit the voltage to the motor I am thinking that maybe the higher voltage (to allow for sag) will be the most efficient ?

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woody
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LiFeP04 Pack Sizing

Post by woody »

The weight, the energy contained (kWh), and the power available (peak kW) are all about the same if the manufacturer is the same.

The difference is voltage and current.

The controller can trade battery voltage for motor current, but not the other way around.

The main factors are:
*) The controller will have an absolute maximum voltage limit, e.g. 192V (Curtis?) 450V (Tritium) 850V (Telemecanique Industrial)
*) different number and shape of the batteries may pack more or less well into the car
*) different number and size of BMS units
*) the controller can only reduce the voltage
*) chargers are available in certain voltage ranges

It is ideal to get the voltage near to the controller maximum - this means the motor can get that voltage which gives you most performance.

There is usually a small compromise to fit in with your BMS and car, e.g. your battery box may fit 44 cells perfectly, so you use 44 instead of 45.

Or your BMS may manage cells in groups of 8, so you use 216 cells instead of 220.

Or you may be planning to use multiple chargers which each charge multiple cells, e.g. a cheap 72V lithium charger does 24 cells, so you use a multiple of 24 cells.

Also you can run the cells in series/parallel e.g. 45S3P (45 series x 3 parallel) SE40AHAs may fit a lot better than a single string of SE120AHAs.

If you are using small cells (A123 / headway etc.) you will most likely need to parallel them up anyway.
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

Digger11
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LiFeP04 Pack Sizing

Post by Digger11 »

thanks Woody - nice detailed reply that I can use to analyse my proposed conversions battery requirements.

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LiFeP04 Pack Sizing

Post by eva-michael »

Depend on the nominal voltage of the motor. If it's a range, higher voltage always more torque.
For bms and charger, big version always very expensive.
I have known 120V can move a truck in maxico properly. It's a middle size Lead acid battery truck!
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antiscab
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LiFeP04 Pack Sizing

Post by antiscab »

eva-michael is right,
the more cells the more expensive the BMS.

however there is perhaps one over looked point, energy and power density is not the same across all sizes.

IIRC, the 100Ah cells are the most energy and power dense (though i haven't done a full comparison in quite some time).

btw - hard limit for a curtis 1231C is 170V (200V components, but trace inductance does bad things)

in general, just make sure that at worst case sag, the battery voltage is still above rated motor voltage.

so if using say a warp 9, its hard limit is 170v at load.
so that means if you use at least 68 cells, you won't ever run outta voltage.

Matt

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Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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coulomb
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LiFeP04 Pack Sizing

Post by coulomb »

antiscab wrote: so if using say a warp 9, its hard limit is 170v at load.
so that means if you use at least 68 cells, you won't ever run outta voltage.

Err, that would be lead acid cells then, nominal 2.0 VPC, fairly high equalisation (15 V per 12 V block of 6 cells) being 2.5 VPC, so 68 cells = 68 * 2.5 = right on the 170 V limit.

Presumably, it's a good idea to disconnect the controller when equalising just in case.
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antiscab
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LiFeP04 Pack Sizing

Post by antiscab »

no no,

lithium cells, sagged to 2.5v.
if your cells specs say they can sag to 2v, then get 85 cells.

the idea being that the system is being operated in battery current limit (max power) for as much of the accel vs speed curve as possible.

just make sure your controller can take ~306v just off charge (zilla HV, solution1, IGBT cougar, etc)

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2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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coulomb
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LiFeP04 Pack Sizing

Post by coulomb »

Oh, right; 170 was the motor upper limit, not the controller upper limit. My mistake, sorry.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

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EV2Go
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LiFeP04 Pack Sizing

Post by EV2Go »

There is a slight weight difference using the smaller batteries, 3 x 40Ah batteries will weigh slightly more than a single 120Ah due to the extra plastic.

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LiFeP04 Pack Sizing

Post by linlilinli »

dear friend,
i am linda lin,i am selling headway battery cell
we have 38120(3v10ah\8ah),38140(3v12ah),40160(3v16ah)
we can make different battery pack,like 660v50ah
if you need,please contact with me
my emial:linda19850507@yahoo.cn

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