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pinballlooking 06-06-16 05:43 PM

Check out this project it might interest you. He is using a Tesla battery pack.

creeky 06-06-16 05:56 PM

Thx for that. Totally insane amounts of power. I'll be amazingly happy with 8 kw usable. Forget 80.

I'm on that cusp, ya? SMA and others are just starting to get high voltage DC storage/use together. What a great inverter they have. But then the added hassle of charging. Looked at it. But it's pretty much "next year."

So it'll be 48v for me. And my next install. In 5 years. When I get restless. I'll look for a 500v system.

IamIan 06-08-16 04:51 AM

1 Attachment(s)

Originally Posted by creeky (Post 50387)
BMS musings:

After some initial research: Building my own BMS is probably a bit out of my time/capability ranges. Buying one does get pricey. So right now I'm leaning towards the basic cell monitoring with the option to turn on cell balancing. From what I've read, cell balancers gone bad kill more battery packs then packs left alone.

Some relatively inexpensive made in china offerings. Can anyone check my math/understanding. My brain is a bit fuddled lately. Lot going on besides the new battery fun.

Problem: What amp BMS do I need?

If a cell leveling system fails .. yes it can cause the very problem it is supposed to prevent .. Just a question of Mean Time Before Failure (MTBF) .. OEMs like Tesla, GM , etc... all have a high enough MTBF that their electronics fail very very rarely ... soo they all use cell level balancing & Monitoring.

Basic level would be a Battery Monitoring System that sends a 'top' signal at the top of charge .. to stop from over charging .. a 'bottom' signal on discharge , to prevent over discharge ... show you the current usage volt/amp/watt .. Do cumulative AH/Wh counting ... The Ah part makes a fairly easy fuel gauge as the Ah cycle efficiency is pretty high (around ~99%).

Off the shelf example that looks at whole pack level (not cell level) for all of the above: EV-Display
w w w

(remove spaces between the w w w)

Cell level drift / imbalancing should be very slow .. a ~10 mA or so correction rate from a 24/7 device is plenty .. only need higher Amp for the main whole pack battery amps monitoring .. If you have Lithium cells going out of balance faster than that .. you have lithium cells that should be replaced.

One alternative .. that doesn't open the cell level failure risk .. is to only monitor the pack to see if there is an imbalance .. than you can manually fix/service that imbalance yourself ... that can be done very inexpensively and easily by comparing the voltages of the two half packs .. a perfectly balance pack .. the two halves should be the same voltage all the time , even under load .. if there is only a small resistance different between the two halves you can set up your comparor to have a 'fudge' factor .. like 1v or something .. only informing you if the difference between halves is greater than that .. Example of a simple circuit for that attached.

creeky 06-08-16 08:05 AM

Ian, I am trying to keep it simple. And I see plenty of evidence online that good quality lithium cells stay in balance. But, but, but. So a part of me wants to do the simple and easy thing. Perhaps I could do a similar board dividing the pack into the 6 parallel units?

Here are three BMS solution providers I have contacted.

Supower. No documentation. Few reviews that I can find. 60 bucks a board at 60 amps delivered to my home. So 360 for the base BMS.

bestekpower has some BMS with communications boards. very poor documentation which ... but good reviews amongst the EV community.

great reviews. lots of users. good documentation
They have got back to me suggesting that I run the new Q BMS. I'll have more detail on that a bit later.

IamIan 06-08-16 04:15 PM


Originally Posted by creeky (Post 50447)
Ian, I am trying to keep it simple. And I see plenty of evidence online that good quality lithium cells stay in balance.

Simple to make .. or .. Simple to use ?
At some point one of those must be chosen as more important than the other.

I assumed simple to make .. That's why I suggested the two most simple options .. Basic EV-Display type whole pack and Batt-Bridge.

Batt-Bridge type half pack comparator .. as simple and inexpensive as it gets for informing you if the cells drift out of balance .. If it happens you can manually go in to service the pack .. if it happens often .. than you can always later add the cell level BMS.

EV-Display type simple basic meter to signal whole battery Top &/or Bottom .. and do Battery Ah/Wh counting.


Originally Posted by creeky (Post 50447)
But, but, but. So a part of me wants to do the simple and easy thing. Perhaps I could do a similar board dividing the pack into the 6 parallel units?

Although it add complexity and cost .. if the MTBF rate is high enough for the cell level BMS .. Like those seen in OEM BEVs like Tesla's and such ... than it makes a lithium battery pack pretty much a 'black box' that just works , as that cell level BMS does any maintenance for you .. more complex system .. but less complex yearly maintenance/service .. ie .. less simple to make .. more simple to use.

- - - - - - - -

For parallel .. you have two main paths:
  1. Parallel Cells:
    • Pros:
      1. 1 BMS cell circuit can monitor and service all the cells in parallel.
      2. Strong individual Cells can help carry weaker cells they are paralleled to.
    • Cons:
      1. If 1 of the cells in parallel isn't just weak .. but actually goes dead .. it will take all the other cells in parallel with it.
  2. Parallel Subpacks:
    • Pros:
      1. If one cell isn't just weak but goes dead .. the BMS might be able to cut that subpack .. preventing the destruction of the others in the pack... Depending on the setup of the BMS.
    • Cons:
      1. To monitor and service each cell would require 1 BMS cell circuit for each and every individual cell.
      2. Strong individual Cells can not help carry weaker cells.

creeky 06-09-16 09:35 PM

Not much to report. Except that my head is spinning. Also:

My Morningstar Tristar-mppt-60-150 controllers can be fiddled into charging Lithium. I'm getting that straightened out. They don't like to lose power. So the HVD contactor goes on the PV input line. LVD is handled by the inverter.

You can fiddle the charge voltages by using the RTS and fooling it into thinking it's very cold out. That way the charger stops charging earlier. Hmmm.

My size of system, even at LVD, lots of power left. HVD is my real concern. And I'm planning on charging to 80% for the first while to observe. May just leave it there.

REC BMS is about 700 euros once all the bits and bobs are in. Pretty sweet solution tho.

And I'm leaning more and more to cell monitoring with manual or occasional balancing.

Anybody with a good idea for a cheap 72 (6p12s) cell monitor(s) that's accurate? And reports to a PC?

creeky 06-10-16 03:12 PM

Whoops. Let me start with the REC BMS. Not 700 Euros. 470 Euros. 700 Canadian. Whew.

And Tear Down Begins!

Can't begin to express the pleasure I derive from taking something so beautiful apart. Really put together so nicely. And all the bits and bobs are so well thought out.
Somebody's missing a tooth

Basically it was: take the connecting power cables off. Negative first! Disconnect the various control/BMS lines. Disconnect the cooling/heating hoses.

I take the smallest pack out first. So that's 2 48v packs tied together for 96. I test. The battery is at 92. It has dropped .1v since I first tested. I take the plastic cap off. Each cell tests at exactly 3.83. That's .01v lower than my initial bulk measurement (all cells together / 24).
Top popped

This also lets me know that the cells are balanced. Bonus.

I then fiddle the lock down. Wow. Nicely done. And with only one bleeding knuckle I lift the pack out. Carry it to the bench. Battery on the bench baby!
Battery on the bench!

Man. I can lift 4 kws of storage power. And look at the size. Still. I was breathing pretty hard after the lift and carry. Smile. Yes. It was because of the weight.

I'll toss in one more. The BMS. Looks like 4 sections. Two control the two 12s packs. One is the master. The other? No idea. Maybe a section for the 24 that goes unused? Or is used in the big pack. Seeing as they are modular. Guess I'll find out when I get those apart.


pinballlooking 06-13-16 02:36 PM

I love the pictures keep them coming and the great information.
Great project you have going.

creeky 06-13-16 03:55 PM

Well. My lack of electronic experience is starting to show. I slowly wander through the world of BMS, BMU, Masters and Slaves etc etc.

I have discovered I can read the cell voltages direct from the BMS wiring harness. And there's a temp wire (I hope to read).

I found a manual for the 2012 with pin out diagrams for all the harnesses. I'm hoping they don't change with the 2014. Not counting on that as the 2013/14 got an upgraded chemistry.

One thing to ponder, for those of you who are more adept, note the BMS board has no big heat dissipating resistors. Do you think chip and resistor are on the cell? The harness diagram shows 1 - temp line, 1 "low register" and 6 to 12 cell voltages lines. Nothing else.

I have learned that Chevy went with passive balancing.

So the plan(s) right now are:
- read and monitor the voltages
- balance manually as req. This gives me the advantage of reducing high cells or charging low cells. A simple RC balancer/charger might suffice.

Online reliable sources continue to point to high quality cells from LG, well maintained = very low cell drift.

b) the cost of a fancy BMS is the price of the battery pack and up. So I'm waiting to hear from China.


After some odd research I have ascertained (to a reasonable level) that the Morningstar TS-MPPT-60 will support the voltage range I need. Morningstar is now claiming on their website that the battery chemistry is supported.

Further on the RTS hack. I still don't understand it. But you can set your BMS trigger alarm to switch on a resistor on the RTS that dramatically lowers or shuts off the controller. Thus saving contactor drama or having to shut down the whole system.

The Victron inverters continue to be the leading contender. Not just the very low idle draw, but the very low LVD. 37v. Which is suitable for a battery pack where the nominal voltage is 45.6. Fully charged is 50.4. And I'm really looking at operating between cell voltages of 3.4 and 4. Or 41 to 48v. Give or take a few hundredths of a volt.

It's been a wonderful adventure. Learning something new every day. Moving along much faster than I had planned. My start date was end of September. Looking more at July sometime now. And I could start charging today.

Sorry. No pics for today.

creeky 06-14-16 09:45 PM

Right. So. I have had a lovely chat with Joe at Morningstar. On the website the controllers I have are said to support the Volt lithium chemistry.

Well. One way to find out. A back and forth with Joe. I pick voltages (conservative) that should suit the Volts charge characteristics. I download the new MS View. Very nice I must say. Input the updated values. Set the dip switches. Flash the eeprom. Easy peasy.

The controller is now reading the first of the new battery packs.

Now: One step forward and one step back ...

As I've already torn one 2x48 pack out I figured. Hey. Why not use these packs for testing. So I double check the cell voltages. 23 cells check out at 3.83 or 3.84. Cell 12, pack one, 3.68.

I will wait to charge that pack. I'm trying to either borrow a programmable charger or buy one. Next on the list I guess.

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