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Discussion Starter #1
I've tried searching for two days and I can't find this question on the forum. I know some folks have asked about Pb + super capacitors, but what about a little more of a compromise? How about an energy pack based on Leaf modules, say 44 for 330v pack ~20KWh, and a booster pack of 100c LiPo wired in parallel?

The searching I've done for the Leaf cells indicates they are typically around 60Ah for the newer lower mileage ones, and they can pull about 4C in the Leaf.

John Metric uses small (<100kg) LiPo packs rated at 100C for his dragsters.

If you have an energy pack of Leaf cells wired in parallel with a power pack of 100C LiPo cells, can you pull more than the 4C the Leaf cells alone would give you? Or would you just be inheriting the disadvantages of each type of battery?
 

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I saw this done with thundersky cells and LiPo, with a diode to sum the two packs. I think they were using it to demo enertrac hubs and the thundersky sagged badly, necessitating the lipo.

The diode was due to the different voltages due to chemistry. I'd be interested with identical terminal voltages as to what happens when they sag at different rates, and then attempt to rebalance against each other at high charge rates (I.e the LiPo pack may attempt to charge the lower voltage leaf cells at high rates).

Not sure what it would mean in terms of heating and lifetime.
 

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Discussion Starter #4 (Edited)
I wouldn't try to get 60AH worth of LiPo, again these will be in parallel. Ideally I would get just enough AH to give me a good 10-15 sec acceleration burst, and probably a fair range extension. I may experiment with it a little on a small scale. I'm still researching the Leaf cells, and it looks like they can do an 8C burst, which would probably be good enough for me. I will have a five speed to play with.
 

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Yes, in principle it works, and has been done with various pack types.
There is a thread on here somewhere from one of our senior contributors who built a hybrid Lipo/Lead pack for his NEV.
I will try a search.
http://www.diyelectriccar.com/forum...-lithium-hybrid-battery-experiment-74502.html
A few things I know from small scale similar packs..Lipo/18650..
Obviously voltages need to be the same..which means for you, same cell numbers in parallel, but for say
Lipo/Lifepo4 hybrids, the cell count will be different.
Maybe not so obvious though, is that you ideally want the "working voltage range". to be the same also, otherwise part of the pack will reach minimum voltage before the other part of the hybrid.
Discharge current is shared between the different hybrid sections, in proportion to the effective internal resistance of each hybrid section.

Also , those newer Leaf cells have been tested and shown to be capable of much more than 4 C, a figure of over 10C springs to mind...certainly for short bursts.
 

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How about an energy pack based on Leaf modules, say 44 for 330v pack ~20KWh, and a booster pack of 100c LiPo wired in parallel?

The searching I've done for the Leaf cells indicates they are typically around 60Ah for the newer lower mileage ones, and they can pull about 4C in the Leaf.

John Metric uses small (<100kg) LiPo packs rated at 100C for his dragsters.

If you have an energy pack of Leaf cells wired in parallel with a power pack of 100C LiPo cells, can you pull more than the 4C the Leaf cells alone would give you? Or would you just be inheriting the disadvantages of each type of battery?
It depends on what you are trying to do. If you want to drag race just use the Ampahaulic cells. If you need more power than a single leaf pack will give consider adding a second Leaf pack in parallel. This would of course double the mass of the battery but it also gives you nearly double the range and will give you double the power. The problem with adding a booster LiPo pack is the cost. There are 6S cells in each brick so to parallel with a Leaf pack you would need a minimum of 16 and at $120 each is $1920. Isn't this almost as much as a salvage Leaf pack? Sure it would give you a peak power from just the LiPo bricks of 115200 watts (154 HP) at a weight increase of 35 lbs. The load is not guaranteed to share the way you want so you would probably want to double up the LiPo for 32 packs. Now the cost of the LiPo is quite a bit higher than the cost of an additional Leaf pack.

The reason I say they wont share the way you want is because the discharge curves are the same. So your 4.5 ah liPo will only provide 4.5/60 of the current on the average. For brief shots you will see a higher loading on the LiPo pack because the internal resistance is lower but the output voltage is relative to the SOC so for more than just a few seconds the currents will average to that 4.5/60 ratio. The initial loading will be relative to the relationship of the internal resistances of the individual batteries. I would guess that with just one pack paralleled with three Leaf modules in series the relative internal resistances are going to be similar. If you have a 400 amp load initially the current will load evenly between them at about 200 amps but this will shift over the next few seconds to the other end where the Leaf pack is taking 370 amps and the LiPo pack only 30. Depending on what you want this could be ideal.
 

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Discussion Starter #7
Doug,
You're bringing excellent logic to the table! Now I just need to get my hands on some smaller batteries of each chemistry and bench test it. I appreciate every one that has shared their thoughts on this so far.
 
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