Enginer kit proper break-in charging cycles

Krous or anyone who knows

I have just returned to installing my Enginer kit and have a similar problem (well I dont know if its a real problem) with 1 pack.

Do you know the electrical relationship between the balancer and the charger, being an old sparky I am interested in the way it control the batteries. I have assembled it out of car and started charging before installation in car. One bank balanced perfectly (.005v) diff but the other battery pack had .7 v diff between cells.
The come down closer of course and the charger seems to turn off after a short time. There are no connection between the charger and the balancer so the charger must control its output by voltage or current.
It seems like one bank of cells are behaving like Septimus's
Any thoughs a I am going to fit them and hopefully with load and cycling the one pack will balance
David

 

They are made in China under the name "Mottcell". The kit has 32 cells.

Since my first post about this problem I have spoken to Jack Chen, who handles the Enginer PHEV conversion kits in the USA, and he will be sending me replacements for the defective cells.

He has also suggested that I try connecting the cells using the "buddy cell" method which will make the cell balancing easier.

I'm looking forward to receiving the new cells and trying the new method to connect them. Fingers crossed!

 

Could you elaborate on what this "buddy cell" method is?

 

The criteria I'm using (now) to identify a bad Mottcell is to look for a cell that alarms both at the high voltage end AND the low voltage end. This indicates very low capacity. Possibly, this means a bad connection between the paralleled wound cells inside the Mottcell case. A cell that alarms just at high voltage or just at low voltage MIGHT just be out of balance.

Jack Bradshaw

Edit: ...meant to mention, the dummy load I'm using for bench testing is an old dryer heater unit. The nichrome wire resistor measures 10 ohms as is. I've center tapped it and connected the original ends together to make a 2.5 ohm resistor. This draws about 18 amps. I posted some charge discharge curves for a good 2KWH Mottcell pack at the Enginer 2010 PHEV Technical Information thread.

 

Sure. The following is an illustration sent to me by Jack Chen:

(click on illustration to enlarge)

As you can see the method involves connecting each pair of cells in parallel and then stringing these pairs in series. Which results in the necessary 48v (if you are starting with 32 cells). Jack says that this method should result in easier balancing of the cells.

I see one other benefit of this hookup in that by pairing two cells in parallel you keep the voltage the same but double the capacity. If one of the cells fails you still have 3.0v but half the capacity. It would not take down the entire string of cells if one cell dies.

 

Sounds like a good idea. You also only need two balancers.

 

Yes, it seems only one balancer for 16 cells would be required.

I was wondering about what would happen when two cells with different voltages were connected in parallel. It seemed to me that there should be current flow from the cell with the higher voltage to the cell with lower voltage. I just tried this out today and indeed this is exactly what happens. Current flow will continue until the two cells are of equal voltage or balanced.

Oh, by the way, just FYI, my shipment of replacement cells for my 4kwh kit are being held up by FedEx - I guess because they are coming across the border - however, I am concerned about the quality of the new cells.

I have had a growing number of cells subject to over charging and over discharging. I removed the failed cells and tried to turn my pack into a 2kwh kit. This attempt unfortunately was unsuccessful since more cells started to over charge. They're falling like dominoes.

The charger's voltage output seems okay so I can only figure that the problem stems from having received a bad batch of cells.

What was your experience with charging your cells for the first time? Did they all slowly charge up together like they should?

 

They all behaved fine for the first few weeks. Then I suddenly noticed that the range dropped and I was only getting 0.8KWH per cycle. When I watched the cells I had one that alarmed at both the high end of charge and the low end of discharge (cell#16) This cell had lost capacity and was limiting the whole pack. Since the Mottcells are a package of cylindrical cells wired in parallel, I think it may be bad welds mechanically breaking down after a number of cycles.

I'm also watching 2 other cells, one of which was alarming high and the other low. These may just be examples of balancing.....

I have a few replacement cells. I'm thinking of setting the pack up as the 4KWH "buddy" system which should help keep things closer to an average cell capacity.

 

Thank you for your feedback.

Jack Chen has informed me not to continue to charge or discharge a pack with a failed cell since this may bring about the failure of other already weak cells.

I'm learning that these lithium cells can be very erratic at least until they are properly conditioned.

I am investigating the value of purchasing a type of intelligent charger/balancer/analyzer to test and properly balance my new cells before installing them into my kit. I've seen a couple that are only around $60. I think I might even be able to resurrect some of those failed cells that aren't too far gone.

Yes, I agree, I think the "buddy" pairing of cells is a superior method.

 

Let us know what you find .... they could be very usefull !

What have you seen so far ??/

 

Hello
I have installed the 4kw kit in a 02 prius I have the thundersky batteries and have installed a timer that cycles on for 3 minutes off for 57 minutes. I also have a killawatt meter I can charge up to about 2 1/2 killawatt hours without problems then I use the timer to stagger the charge so the balancers can catch up seems to be working ok. I have also ordered a 100watt lifepo4 charger it is $30 plus shipping I have not recieved it yet but I believe that will work just take longer to completely. My charger that came with my kit is labeled Li-ion Im assuming it has been reworked for lifepo4. I think the balancers are designed for a smaller amphour system and simply cant keep up with the current.
Rick

 

rickw,
Can you tell us more about the timer? Is it something you custom made?

 

I am thinking about using this system also but I was wondering if it would work if I put 4 cells in parallel then in series? Or should I just make two 48V 4KWh blocks by only putting 2 cells in parallel?

I am using a 8KWh kit in my 2010 Prius with two converters. Any suggestions?

Thanks,

Chan

 

Where can I buy the 100 watt lifepo4 charger for $30?

 

The web site LiFePo4 Chargers shows 2 smart chargers of interest -- the Thunder AC6 Smart Charger & the Sky Charger B6AC.

However, these charger/balancers seem to be intended for R/C batteries with smaller capacities but I figure that they should still work with 40Ah LiFePO4 batteries. They should just take longer to charge??

 

Interesting idea. I would think that 4 parallel cells should work in your 8kwh kit, in theory, assuming that the internal electrodynamics of the cell combination is simple (if it follows the same principles for individual cells when charging and discharging). However, that is a question for the battery experts.

Whether it would be better than 2 parallel cells, I don't really know.

I would suggest connecting 4 cells in parallel and see what happens. Check the voltage of each cell before and after leaving the pack for, let's say, 30 minutes. Assuming the voltages of each cell were all different before, they should all be relatively the same after.

Also, if you haven't already considered this, you will be needing more copper connectors to connector 4 cells in parallel than 2 cells. Right now with the standard pack configuration you have 48 copper connectors. With 2 parallel cells you will need 80 and with the 4 parallel configuration you will need 96.

 

I will give the 4 cells in parallel a try tomorrow night. You are correct about he need for more Copper connectors. Any idea on where I can buy some more?? Also I was tinkering with 2 cells in parallel this morning since I had to pull 3 bad cells from the system. I was completely lost on how to connect the balancers. Anyone have a diagram on how the balancers should be connected?

Thanks in advance.

 

Hi Eric
Its a standard digital timer I picked up at ace hardware it handles 1500watts and has 20 programmable on off times

 

This item is on ebay I have not received it yet you have to tell them when you order that its for 16 cell Lifepo4 battery pack its $19 +$28 shipping They also carry the anderson plug connector I believe the Tru power 50 is the right size so you could unplug enginer charger and plug this one directly. Im hoping that after the batteries are broken in the other charger will work ok. Im just getting tired of constantly checking for high voltage alarms.
you can also go to the sites below to check out there stuff. They gave me a better price on there anderson type plugs. There is definitly a language barrier.
This is how I told them I wanted set up. Good luck
16 Lifepo4 thundersky max 60volt charger 51.2 volt setpoint 110v 60cycle input
Welcome to Ecity Power Co., Ltd.
BMSBATTERY - The Art Of LiFePO4
This is the ebay listing number for the charger
120486936297

 

Try Jack Chen for the copper connectors. Otherwise, get some copper strips of the same thickness, cut and drill them to the proper dimensions.

As for hooking up the balancers on a pack of sixteen 4 parallel cell units. The standard hookup is as follows:

View attachment Balancer.pdf

Your hookup is the same except instead of one cell per connection you have 4 parallel cells per connection since the 4 cells connected in parallel are now the equivalent of one cell. This means that you use one balancer for 32 cells and two balancers for 64 cells.

Connect the red wire to the +ve of the first group of 4. The next wire to the +ve of the next group of 4 and so on until at the last group of 4 you connect the second last wire to the +ve and the last wire to the -ve of the same group of 4. That should work.