New Plug in Conversion LiFe battery pack balancing

Hi Steve,

Connecting all your 76 cells in parallel is a simple and cheap form of manual balancing. The cells just balance by all your cells just being connected in parallel. Charging may not be necessary. It has nothing to do with top balancing.

Top balancing is automatic and is done by the miniBMS modules during charging. Top balancing is always done towards the end of charging.

There is a lot to learn.

 

I hope they give you more instructions that just the four pictures.

Looks like you're right...all cells put in parallel and charged at once as one big cell. Should work just fine. A couple comments:

1) Before you parallel all those cells together, measure every one with a DMM and make sure they are reasonably close in Voltage--"reasonably" meaning nobody is more that a few hundred mV away from the mean, which should probably be in the neighborhood of 3.2-3.3 Volts.

2) I only see one power supply. I'm not familiar with that model, but it looks to me like they have a HVC of 3.5 Volts (safely low, but high enough to get accurate balancing) set up. The 3.24 shown at the bottom is probably the output of the supply at the time the pic was taken, held below HVC by the current limit of the supply. That's not a very beefy supply, BTW. Looks like something with an output between 3-10 Amps, 20 tops.

3) Once the supply output reaches HVC Voltage, wait for the current to stabilize near zero. Once the current falls to whatever its minimum will be, you will know the leakage current of all your cells put together. If it seems unacceptably high, look for "leaky" cells and reject them if they do not meet spec.

4) After balancing, once the cells are bussed together the way they will be in the car, I would take this opportunity to cycle the pack once or twice while monitoring all Voltages during both charge and discharge. This will give you a sense of the variability between cells right out of the box, and also alert you to the presence of any cells with low capacity.

I've been meaning to respond to you for some time now about charge times. The only reason anyone should want to charge as fast as possible is because they MUST do so to keep driving RIGHT NOW--like on a long trip. On a daily basis, for everyday driving, batteries should be charged as slowly as they can while still getting sufficient charge to do their job. If they don't get to 100% SOC, all the better because that extends battery life, as do the slower charge rates. The fact is, level 1 charging is perfectly fine for most people most of the time, especially for a PHEV where range anxiety simply should not exist. If you really need level 2 charging to get the required work from your battery, try to apply it only when really necessary. Too much emphasis has been put on the "need" for charging infrastructure. For pure EV's it can become an issue, but for PHEV's I think it's a real mistake to speed charging just for the sake of having fast charging.

Hope that helps.

 

You're right that the cells will balance themselves at whatever Voltage they average to (more or less), but DO NOT skip charging and balancing at near 100% SOC. You will most likely receive your cells at somewhere between 30-50% SOC. Voltage is not a reliable indicator of SOC in this range for LiFePO4. Do yourself a favor, take them to 3.5 like PIS is recommending, and watch where the current settles. My other recs just above will take a little effort, but you will have a much better idea of where you are starting from and how these things work--critical for any DIY project, but a must for any as expensive and potentially dangerous as this one. Further, if you have any bad cells (it happens), you'll find them now when they are easy to get to and before they can lead to bigger problems that seem to come from nowhere. This is doubly important if one does not have much prior experience with batteries.

 

I don't know for sure, but I would expect your cells to come with no buss bars attached at all. Shipping lots of cells outside a pack while connected together is unecessarily dangerous. From the pics, it looks like you will need to put them on yourself for the parallel arrangement, and then again of course for the series "real world" arrangement. Perhaps you already expect this...I can't tell for sure. But geez, can't PIS be bothered to actually SAY that the cells are in parallel for their pre-assembly balance procedure? The picture is nice, but it does not tell the whole story cleanly by itself, at least not to a battery "newbie", as you seem to call yourself.

My Hymotion car is set up for level 1 only with a standard 120V AC connector. On rare occasions, I encounter situations where the only charging option available is level 2, and while it's not a deal-breaker that I can't use those stations at present, it's annoying to miss out on those charging opportunities during stops on a long trip. For that reason, I'm planning to build an adapter box like the one John (lopez) linked for you in the other thread. I'll be set up for level 1 under "normal" circumstances, but if I must use a commercial charger with J1770 connector, I'll be able to tap into that as well.

 

Charging stations in Australia are as rare as hen's teeth and then so are EVs. Reading this forum about what is available in the USA makes me feel like Australia is ten years behind the times and we are! I hope you keep us informed on your adaptor box in the appropriate thread. Maybe one day a charging station will open near me and I will then have a reason to build a adaptor box.

 

I don't think you're that far behind....I've read about smart grid stuff in Australia and wished we were making similar progress here. Charging stations are nice, but they're not a real requirement for most people. You can certainly charge at home at 240V without a J1770 connector. Your on-board charger is what limits the potential speed of charging. You may need to add a new circuit to your home's electrical panel to achieve that potential plus a GFCI for safety, but that's about as esoteric as it should ever have to get in the home.

Charging stations are fairly common in parts of CA. They are not so easy to find in most of the rest of the USA, though that is slowly changing.

 

Nickel plated Cu is probably most common. Cu is a great conductor and relatively affordable, but when naked its corrosion potential is problematic. Needs to either be "laminated" somehow or plated with something less reactive.

What's the capacity (in Ah) of your 10 kW pack, 80Ah? 0.2C is a common "gentle" charge rate for LiFePO4--that would be 16 Amps for an 80Ah pack. I would shoot for that charge rate unless you feel it will be inadequate for your typical everyday needs. The chargers you're looking at are nice because they will already run on either 120V or 240V and have increasing capability with increasing input Voltage. So, you could shoot for a charge rate of <0.2C with a 120V input. Then, if you need more charge current on a given day, you can supply the charger with 240V instead and get the faster rate with no modification needed to your car except maybe an adapter box for the different plug styles. I'm assuming whatever limits you program into the charger hold steady no matter what the input AC Voltage is.

 

Good experience in the marine environment for environmental concerns. Most people, even some really good engineers, get bit hard by missing the boat (no pun intended) in this department. Don't worry about saying anything OT to me....I'm not the only reader and tips like that are what makes reading threads like this worthwhile for newcomers.

OK, pardon my ignorance, I didn't know what PIS spec'd for a pack. That's good info. Very different from Enginer, a bit different from Hymotion. Note that the specs you quote are discharge numbers, not charge numbers. I would expect a recommended max continuous charge rate of 1C for cells like yours and a recommended charge rate of 0.2C, assuming they are comparable to RealForce cells (and the discharge numbers are similar).

Point taken, but here's my experience: There are way more charging opportunities in this world at plain old 120V outlets than at proper "charging stations". With a car like mine, that means an extension cord. With a car equipped only with a J1772 connector, that means an adapter harness with electronics. Both are theft risks. I lock my extension cord to my car and would do the same for any adapter with a $100 J1772 connector in it. I suppose the ultimate answer is to put both connectors into the car and have a switch for selecting which was in use (you would have to do this for safety reasons.) Then, you would either be able to use a charge station cable or a (relatively) inexpensive extension cord. Even at that, you will find yourself probably using the extension cord more away from home than anything else.

Time to get a bumper sticker....