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Old 06-11-2015, 04:18 PM   #1 (permalink)
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Default Portable parallel PHEV booster pack for the ZE2

Hi, as many of you know by now I've been brooding on a portable parallel booster pack for the 2nd gen Insight.
Note: this is no replacement for the IMA battery but an add-on.

The idea is to have a 1 kWh pack with a voltage slightly over the average voltage of the OEM pack, so it will deplete itself into that pack and force the Insight (which senses a higher than normal voltage on its pack) to use more EV support and less (like no) forced regen.
It would save fuel and give a peppier feel to the car.

I had already started a thread about it on Ecomodder (this one) but thought I'd better not make too much noise before I knew I could actually do it, so I did not start that (same?) build thread here. Yet.
After all, I cannot do this without my wife's approval.

I just told my wife I want to spend 1K on it and she basically agreed!
So, I can put the wheels in motion in earnest now. Any kind of advice is more than welcome.
See the link on ecomodder for more details.
Once things come to fruition I will definitely post about it here too though.
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Old 06-11-2015, 06:30 PM   #2 (permalink)
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there does not seem to be anyone with much experience in battery building on your thread over there.

if you build a 36S pack then it should be charged to 129.6V at a minimum with a 3.60V balance voltage on the BMS.

your statement about how a BMS will damage your battery is entirely wrong and misinformed.

if you use a 10Ah prismatic pack like the GWL then you can only expect to draw 10-20A max from it but your car will demand more when it is under load.

since the lithium will show less internal resistance to discharge, then it will provide the most current when the two parallel packs are being discharged and the nimh will recharge the lithium in between your power cycles.

but you will get more power on demand when needed. until the voltage has dropped low enuff to increase the internal resistance of the lifepo4 significantly. at that point the lifepo4 will show more internal heating. this is what shortens the life span of the lifepo4 cells.

if you use a 36S then your lifepo4 should be able to discharge down to around 80-85V if it is properly and continuously balanced by the BMS. your nimh will not go this low so much of the power stored in the lifepo4 is never useful in that case.

if you use a BMS then there is no need to use a contactor and instead you can just turn off the BMS output mosfets to shut off the pack from charge or discharge. a mosfet is a much better high voltage switch than a relay or contactor.

the headway cans will provide up to 5C of current with some significant sag, but not as bad as the winstons which really are only 2C.
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Old 06-11-2015, 10:05 PM   #3 (permalink)
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The BMS thing is my hold up too as I have 4 kilowatts in 64 x 20 amp lifepo4 cells from my old enginer kit.

Plan B was to buy a prius pack that is nickel metal and assemble a pack one stick more than the insight pack so its capacity will be used in the gen 2. Then it could be charged at home and left in the car near the oem pack.

I would use a grid charger set for a lower amp to balance the prius pack so no bms would be needed every so often.



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Old 06-12-2015, 03:08 AM   #4 (permalink)
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My reason to post it on EcoModder first was the vast experience of people there with EV builds and conversions.

Limiting the current to safe levels has always been the object, and just to be sure I will start with a big resistor in the circuit. A current limiting step-down DC converter would be great, but even if such a thing exists it will probably be too expensive to meet its ROI point ever.

I will monitor pack temperature (I have a thermometer for it ready and waiting)

My choice for LiFePO4 is no flight of fancy.
I like their relative safety; they may overheat when severely maltreated, but won't catch fire and burn.
They can be recharged over 2000 times without losing much of their capacity, even on near full cycles.

Unlike other lithium battery chemistries LiFePO4 cells keep the voltage quite steady throughout almost their entire range. For example:

This 12S pack start out at 39 Volt right from the start and keeps the voltage above 38 Volt until it has lost 80% of its charge.
The Insight IMA battery voltage hovers around 107 Volt, 1/3 of that is 35.33 Volt. This pack reaches that at about 95% of its capacity spent.
I would not want to discharge it deeper than that so it seems spot on.

I do not expect high currents to and from the parallel pack, at least not for long. The OEM pack buffers those.
Once the OEM packs voltage has been raised the current flowing from the booster pack will dwindle to less than 1C. When the Insight uses EV mode the voltage will drop, but not by as much as now because of the higher SOC and being fed from the parallel pack.
And if I can recharge the parallel pack before it is fully discharged, the OEM battery will still be in higher SOC and will not draw much current from it even from the start.

So I see no reason to use anything else than LiFePO4.

Using another NiMH hybrid pack is out of the question. That would be too heavy to be portable and takes up too much space.
Portability is a must, I will not charge the pack while it is in the car and at times I do need the space the pack would take.
The OEM NiMH pack is capable of handling the big discharge on acceleration (even better so when constantly trickle fed from its booster pack).
It does not need more NiMH.

Things to do on short notice:
Search out the right cabling, batteries, frame, docking connector (portable, right?), BMS or cell monitoring stuff, etc.

While I'm at it and to test the waters with one supplier of batteries I think about replacing my 12V battery with a 20 Ah 4S LiFePO4 block like this.

Any thoughts? I mean, "What could possibly go wrong"?
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Old 06-12-2015, 01:06 PM   #5 (permalink)
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those fake motorcycle packs have no useful BMS.

the reason you need a BMS is so that the pack can be regularly balanced by charging to full voltage.

3.65V is considered full charge, but charging over 3.60V causes the lithium to plate out away from the electrode so the lithium is depleted over time and you lose capacity.

so you want a BMS that balances at 3.60V which is where almost all BMS are designed for now that balance lifepo4.

i have plans to build a 48S lifepo4 pack from a buncha headways i still have laying around to use just like you as a parallel pack to the nimh pack. full charge would be 172.8V so i would charge to 173-174V to force the pack to balance faster when fully charged.

eventually i expect i can afford to build a C&C board using peter's stuff to be able to force the lifepo4 pack to provide power at speed. so it would b similar to a PHEV then.

i currently have a 24S 87Ah lifepo4 pack in my ZENN car that i use in parallel with a 21S 36Ah lipo pack and the 100Ah 72V SLA pack that the car has for a stock battery, except it has degraded to about 40Ah but i was able to restore some capacity of the SLA pack back up to about 55Ah.

i bot some D131 BMS with a balancing voltage of 4.18V for the lipo so i can charge both the lifepo4 and the lipo together to 87.6V which overcharges the lifepo4 to 3.65V/cell and leaves the lipo around 4.17+V on average.

i use the charge immediately so that scrubs off the higher voltage but it forces my big lifepo4 pack to balance since it is made of of recycled ping pack pouches and they need regular supervision imo.

wish i could post up pictures but they don't let me post pictures here anymore but if you wanna talk about your build over on the endless-sphere then i can post up pictures over there.
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Old 06-12-2015, 03:43 PM   #6 (permalink)
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I was looking at the bicycle packs as they are extremely portable and come with a charger; a threesome would be manageable.
But indeed I worry about the specs and quality, and they are not that cheap.

My hopes were to build a discharge cutoff when any cell should drop below say 2.8 Volt and a charge cutoff when any cell goes above 3.55 Volt.
As the pack is removable it should not be too hard to balance the cells every once in a while, should that be needed. Or I can do with charging at leisure (like 1.5 Amps) and use these to prevent overcharging the cells.

Nowadays I use Imgur for pictures and paste their ready-made BBCode in my posts.
I did use ImageShack before but somehow I could no longer access my account there (???) and Imgur turns out to be more user friendly, so no regrets.

I will look up Endless-sphere.com ? Index page soon, thanks for mentioning.
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Old 06-12-2015, 06:07 PM   #7 (permalink)
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for lithium cells you should always try to use the power from the battery at full charge. if you use the battery at less than full charge the internal resistance eats into useful power and it causes heating of the electrolyte at the SEI/electode interface with the electrolyte. this is where the gas is formed that causes the pouches to puff up.

internal resistance is a function of the population of ions to carry the current. the cell's transconductance is a function of the total number of ions that can move the current through the cell and the most free ions are available at full charge. many people think they are protecting their lithium battery by undercharging it but in fact it is just the opposite. the key is to not charge up and leave at full charge. charge up only when the charge is needed and can be discharged within a short period of time.

this is all separate from the plating out of the lithium metal away from the electrode above 3.60V for lifepo4.

so you should charge to 3.60V at least. you can discharge lifepo4 down into the 2.2V range and if you reduce the power and current flowing through the cell at these lower voltages it reduces the impact. 2.1V is generally considered to be full discharge but the cell will hit the 2V level when it is under load and then after the BMS cuts off for LVC, the cell will rebound to about 2.7-2.8V with no load present.

i never use those external image hosting websites and i never open them either because of the risk of viruses being planted in the images. google is the only hosting i would consider safe.

it is just too bad they don't allow posting pictures here.
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Old 06-12-2015, 07:09 PM   #8 (permalink)
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I guess Red the real question is what output are you expecting? Are you expecting an hour worth or extra power? That would help to size your pack. I can tell you 32 20 amp lifepo4 pouches with wires and a metal box is about 60-80 lbs. My pack if I did it would go behind the IMA box and not removed unless the car or pack is being serviced. With my enginer kit I got 3-4 hours out of 4 kilowatts. The car could use more if the converter was built heavier. So with that weight is less of an issue and with no clear cheap reliable solution for BMS as to why I would go the used prius pack route. If you can find a good bms thats not made in china that balances the cells you are good to go.



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Old 06-13-2015, 05:29 AM   #9 (permalink)
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I want a small pack, so I'd go no bigger than 10Ah. Looking for relative gains, not absolute. And I can scale up later if I wish to.
I would love to make an exception for the 20 Ah A123 pouch cells, as they are relatively light so a pack of 36 pouch cells can still be lifted out. But they are beyond my budget; they'd work great but be slow to meet their ROI.

I honestly don't expect to draw more than 5-10 Ampere on average, that should reduce my (moderately driven) fuel consumption by about 15%.
As my commute takes about 35 minutes I would not be able to deplete the cells fully in one go, and as I can charge the pack at work I will probably never have to worry about depleting cells completely. So a top balancing scheme seems best. Nonetheless, if I can have a cheap and reliable low cell voltage protection system I won't skip that.

I have not found such yet, I'll have to step up my research.
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Old 06-13-2015, 05:30 PM   #10 (permalink)
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I was using 17 amps and 117 volts on my enginer converter. It could take more, but the magic smoke would escape the converter. On average unless you try to engage EV mode I think you are fine.

I tried a few China made gizmos for BMS and the cell log 8s seemed most accurate, but has no balancing capacity. You could get 4-5 of those and program the cut off voltages and daisy chain the connector to a relay to stop charging or stop discharging when in the car in use. I just do not know the MTBF for those.

Top balancing I believe is charging each cell? For my enginer pack that has the real force cells 8 cells each of 4 20 amp cell groupings for 24 volt output. I tried a few balancing gizmos and they never got them balanced and it would quit after a while. I tried moving loads and single cell chargers around to manual balance. No luck.

It wasnt til I purchased 8 1 amp lifepo4 3.6 volt wall warts and plugging in for a week to each pack did I get all cells to the same voltage. Having 36 of those or meanwell power supplies would make for a neat display and likely cause concern from security o ra second look from someone who works with electricity.



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