# LiFe + LiPo Hybrid pack



## arber333 (Dec 13, 2010)

I made some long drives on this configuration and i must say i am free from range anxiety. I can now drive at 120km/h without fear of being stuck on the last hill from home. 

Range is now cca 200Km at highway speeds and at least 230km at side roads speeds. I can drive trough whole Slovenia single way and expect to charge cca 5Hrs for a trip home. I do have to watch my motor temp though since amps are heavy on the motor at those speeds.

Speaking of amps... LiPo cells have really small Ri and so Amps flow to them. I noticed that at same speeds i have at least 20% greater amp gain when using regen than only on LiFe. 
When i put my SOC meter on LiFe/LiPo pack i noticed there are amps flowing even though car is stopped at the light. Batteries are equilising all the time. 
There was one time at 65% SOC i noticed my LiPo contactor was disconnecting battery. BMS has told it it was full again. I stopped and checked - true! Cells were at 4.05V and when i was braking regen forced voltage over the limit. 

I made one really long drive and at 5% SOC i noticed LiFe started to sag trough 2.65V!!! I stopeed immediately and disconnected LiFe pack manually. I drove some 25km on LiPo at 70km/h and they were still at 3.4V. It was -10%SOC!!! 
Huh that was hairy experience... I ordered another EV200 Kilovac contactor to separate LiFe pack on my whim. For driving i will primarily engage minus pole that is common to both packs and if need be i would disconnect either of pack positive lines in a way one pack will always be on. That should lengthen my range considerably.

There is only one consideration on LiPo cells. Since they are so hard, their voltage will not sag, but after 250A draw they will begin to heat up and if abuse would continue they would be internaly broken after some cycles... Not a good fate for expensive pack. I have to build some sort of current probe, to light a warning LED if current goes trough 200A.


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## JoeG (Jul 18, 2010)

Arber,
I've been following the DIY charger thread since it started and have seen the great progress you made on your version of the charger, great work!!
I've a question on the Kokam LiPo cells you have. What is their projected cycle life? I used small 1Ah-5Ah Lipo batteries in R/C helicopters and planes for years, and only got a few years, or a few hundred cycles out of them, which ever came first. Hopefully they have got the life issue solved.
Joe


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## arber333 (Dec 13, 2010)

JoeG said:


> Arber,
> I've been following the DIY charger thread since it started and have seen the great progress you made on your version of the charger, great work!!
> I've a question on the Kokam LiPo cells you have. What is their projected cycle life? I used small 1Ah-5Ah Lipo batteries in R/C helicopters and planes for years, and only got a few years, or a few hundred cycles out of them, which ever came first. Hopefully they have got the life issue solved.
> Joe


Hi

TNX, its been ups and downs with this charger, specially because i learned on the go . 
Well i also used LiPos in a few models and some airsoft guns and they are a bit strange. They dont want to end SOC! They go and go and in the end there is a phase when voltage falls down momentarily. You have to watch this. My BMS has programmed red LED that shines in my face when something is wrong with voltage per cell. 
One thing i noticed, the cells are on the order of couple 0.0X of volt balanced together and in the beggining i charged them without BMS to 145V in pack. They never went above 4.18 per cell.

Well as for life limit i dont know. I hope they will last since i will never drain them fully. 
As i noticed LiFe pack is drained first and then LiPo works on its own for some 25km at least. But i will never go lower than 3V per cell. 

You have to watch max amps though because at 250A cells start to heat up and they would degrade quickly that way.

A


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## Sunking (Aug 10, 2009)

I do a lot of RC stuff and have dozens of LiPo cells. They are great batteries with extremely high C-rates due to the very low Ri as you state. They also have extremely high cost of 10 times that of LiFeP04 cells and only get 200 to 300 cycles on them before they are ready to be shot with a .22 magnum and soaked in salt water.


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## lithiumlogic (Aug 24, 2011)

One thing i've noticed on Flashlight and Ebike forums, they use lithium cobalt 18650 or LiPo packs and obsess about taking care of the batteries by not draining below 30% or so, having a larger cell than needed etc.

The research though seems to suggest that the cell degradation happens at the top end of the charge curve for this chemistry, not the bottom. Someone here linked this US Army study where the lowest SOC they tested, 20%, showed the least calendar loss. 

LFP seem to prefer 50%, but the cell voltages of LiCo at 20% are actually pretty similar to those of LFP at 50.

Of course if you don't have a way of monitoring individual cell voltages, in a series string there is a risk of lower capacity or unbalanced cells dropping below 0% on a deep discharge, and getting damaged. 

Even so, the flashlight guys are mostly using single cell setups, so this isn't a risk. I think they're just obsessing over the problem they can control (end of discharge) rather than the one they cant (end of charge).

There are still hardly any power tools or consumer electronic devices out there where the charger allows the user to charge to less than 100% if they want. Most laptops i repair loose capacity at a rate of 30% per annum, the likes of Toshiba charge £100 for a replacement 6 cell battery. Conspiracy maybe?


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## jonescg (Nov 3, 2010)

I put a 14s3p LiPo pack (58.4 V fully charged, 15 Ah) in parallel with the 16s LiFePOf pack on the scooter. It made a huge difference - the scooter never laboured up hills and got to 60 km/h in no time. The only significant current draw between them was when I plugged them in after charging. The LiFePO4 cells settle back down to 55 V, whereas the LiPo stays at 58.4. A few volts with very low Ri makes for some warm wires, but it behaves itself before long. 40C cells can take some high currents!


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## arber333 (Dec 13, 2010)

jonescg said:


> I put a 14s3p LiPo pack (58.4 V fully charged, 15 Ah) in parallel with the 16s LiFePOf pack on the scooter. It made a huge difference - the scooter never laboured up hills and got to 60 km/h in no time. The only significant current draw between them was when I plugged them in after charging. The LiFePO4 cells settle back down to 55 V, whereas the LiPo stays at 58.4. A few volts with very low Ri makes for some warm wires, but it behaves itself before long. 40C cells can take some high currents!


Yes! I noticed it too. 42S LiFe cells were some 145V and when i charge 36S LiPo pack is at 148V but amp flow shows 20A in direction of LiPo. I can only assume because of low Ri and 20A flow my voltmeter shows higher than they really are.

While driving at first 20km distance major current flows from LiPo and then up to 20% SOC LiFe takes the burden. After that LiFe is spent and again LiPo takes over.

A


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## arber333 (Dec 13, 2010)

Crap! On my horror i got zapped today! I was measuring LiPo contacts when my hand brushed car chassis. Zap! My hand hurt for some minutes. I seem to have a leak somewhere towards chasiss GND.

I checked BMS and it was fine, although when charging it gave some strange readings from time to time.
I checked LiPo box, all good. 
So fault has to be on LiFe side. I measured 130V from + to chassis, so it has to be one - pole somewhere that is conducting...
I checked by wire and 12V bulb from + pole to GND. Light wouldnt go on but i saw sparks jumping when i touched GND. Also after some time i played like this BMS comms started to go haywire. I will put one 1A 12V ACDC module to power BMS from a different source than car. Last time i tried and it made 12VDC connected to 130VDC battery. Its only 2€!
Also i got one LiFe cell that doesnt want to charge fully in paralel with LiPo. Maybe its this one...


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## jonescg (Nov 3, 2010)

If you have a cycle analyst or some other electronic current and voltage measuring device, they often reference ground to the traction pack negative. If you have one of these, an isolating DCDC converter would fix it.


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## Sunking (Aug 10, 2009)

arber333 said:


> So fault has to be on LiFe side. I measured 130V from + to chassis, so it has to be one - pole somewhere that is conducting...


130 volts is your clue and tells you which battery it likely is.

Example if your pack is 144 volts and you are measuring 130 volts then the fault lies between cell 3 and 4, or 4 and 5 from the Negative end.

To verify take voltage measurements between chassis and inter-cell connection points at the positive end of the pack, then work your down from positive between cells until you see 0 volts. That will be the point that has faulted to chassis.

One note of thought. Those LiPo are Pouch cells right? The package is easily breached. Just wear and tear from vibrations and shifting around could wear a hole in one of the packs thin plastic wrap skins. If those LiPo's are in a metal enclosure or touching metal somewhere could have rubbed a hole through the plastic skin and making contact with one of the plates inside the battery.

EDIT NOTE:

Just a thought for all reading along. Something we have to do in industrial system when Delta power is uses is like a EV pack and the system is NOT GROUNDED. We are required to have ground fault detectors installed. It is real easy to make a GFD. All you have to do is install two light bulbs in series from positive to negative of the battery. At the junction of the series connection point you reference to ground. If the voltage of the pack is say 140 volts you use two lights rated for 140 volts. When connected each light glows dimly because they only have 70 volts across them. However if either polarity goes to ground one light goes out and the other goes to full brightness alerting you a fault has occurred.


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## arber333 (Dec 13, 2010)

Sunking said:


> We are required to have ground fault detectors installed. It is real easy to make a GFD. All you have to do is install two light bulbs in series from positive to negative of the battery. At the junction of the series connection point you reference to ground. If the voltage of the pack is say 140 volts you use two lights rated for 140 volts. When connected each light glows dimly because they only have 70 volts across them. However if either polarity goes to ground one light goes out and the other goes to full brightness alerting you a fault has occurred.


Ok, its not exactly 130V, something more... I noticed the last cell in a pack behaves strangely and never reaches full voltage if i dont push it with another charger... There is my suspect. But i cant see anything wrong with this cell. No contacts with metal walls, cable is new, huh besides strange behaviour i really cant tell. 
Oh wait! There is a contact box after last cell and here is the fuse and contactor. Hmmm... I will have to dissassemble this and see if the problem goes away.

So for GFC i should connect from + pole to - pole of my battery and put two bulbs in series with a switch? Then i would put one leg between bulbs to chassis? Like this?


+ ---------O----|----O-------/ /------ -
_____________|_
chassis gnd


tnx

A


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## arber333 (Dec 13, 2010)

Sadly i must say my LiFe pack "bought the farm last week"... 

I was experimenting with different configurations of LiFe cells vs LiPo and i was substracting or adding a cell and checking general current in the parallel network. -1 LiFe worked best during driving and general loading, but then i connected charger. No big deal here, but after 4hrs charging charger disconnected and LiFes were full. On Lipos though BMS with contactor was disconnecting them from the other pack. Seems they too were full even though overall voltage was showing normal 147VDC. 

I had 41S LiFe in paralel with 36S LiPo cells. 
So LiFe should be 3,6V per cell and LiPo should be 4.1V per cell, shouldnt be a big deal...

In effect one cell got bloated and this pushed contacts towards metal case (isolated though it was) i guess from that on each half saw full LiPo voltage... LiPos were protected by contactor but every liFe cell was literaly cooked. All cells opened valves and released electrolyte (acetone solution), one even started to smoke.
I poured water on them to cool them off. After i pulled them apart and checked, they had 4V per cell but when i shorted them there was no current. Victims of progress i guess...

Lessons learned:

1. Do not mix chemistries without safety contactors! LiPos testify to that, they are still alive...

2. It is not a good idea to charge different chemistries from the same source.

3. I should have put some hard plastic or just plywood between cells and metal casing. I couldnt have known they could bloat from the front side though!!!

4. If your cells release electrolyte it is best to wipe casing quickly with paper towels and thoroughly wash it with water and soap. Otherwise acetone fumes could damage ABS plastic in a car.

A


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