Hillhater wrote:doesnt your "bus bar" clamping system result in you having over 1000 clamped connections in series to achieve 425v ?
Hillhater wrote:Yes Ron, i saw the pictures,..thats when i realised what you had done with your "parallel" modules.
Its just that your "Bus Bars" in each parallel pack are not actually continuous bars, but a sandwich of ten tabs and ten / eleven spacers. Each side of every tab is a "working" contact face, so each pack has 40 contact faces ( 10 +ve and 10-ve tabs) each of which will be carrying your full 2000+ Amp load. It just seems you have a lot of extra joints carrying full load current.
( 40 per pack x 106 packs = 4240 EXTRA connections ! )
...Ron, what happens if ONE of those contact faces "drys" out and goes OC. ?
EVDragRacer wrote:I am not here often, so I will add a few bits of info before I go.
Each 10P 28volt module weighs about 40lbs. A bit heavier that wanted, but worth it's weight in gold when you do not have to worry about bus bar resistance and heat. Our connection method with reduce heat and resistance, while making it fairly easy to remove a 10P pack at anytime in the car without removing the pack.
The whole pack weighs around 600lbs, we have replaced the older Camaro body with a 2012 Camaro body made from fiberglass, so, the added pack weight will not make much of a difference. We estimate the car will weigh 2300lbs compared to 2650lbs last year. We will have 3000amps to launch with if we want, we will start at 2000amps and work up slowly monitoring motor temps. We have geared the car for a top speed of 170mph in the 1/4 mile, 3.25 in the rear and two GearVendors overdrives to utilize the enormous amounts of torque we have available.
Hillhater wrote:Ron, are you really going to install a BMS that monitors every one of your 1000+ cells individually ?
.... when they are paralleled in packs of 10 ??
I suspect the first indication of a dry joint will be a blown module from 2000+A all going through one or two cells in a pack.
We all need and use bolted connectors , ( much better than bullets etc) ....but every joint is a possible failure ( especially at 2000+ A ) and can be managed since usually those bolts are simply clamping 2 contact faces together.
But this design has resulted in an extra 4000+ bolted contact joints, with 20 contact faces per bolt, most of which are carrying the full load 2000A current !
A single , unitary ( solid) bus bar for each pack of 10 tabs would avoid that situation.
fechter wrote:I've always found bolted connections to be quite reliable if properly done. The ability to repair them later is also an excellent feature. Some anti-oxidant grease might help them last longer (but in a drag racer, that probably doesn't matter much). Solid copper seems like overkill, but less resistance is better. Aluminum would be much lighter. One of the real engineer types could do the math on it to see how much more loss there would be with aluminum. Aluminum does tend to corrode and make crappy connections over time.
fechter wrote:I think the silver plating is key here, along with adequate contact pressure. Silver maintains a nice low resistance connection even when tarnished.
The proof will be in the time slip.
rwaudio wrote:Hi Ron,
Nice to see you on this forum, I love your packs, but I have to agree with hillhater.
In my testing of A123 pouches my first design was a block between every tab in a 3P pack (I used aluminium but I'm going to peak at 1000A not 4000A, you may have seen my crappy pictures on diyelectriccar) the voltage drop was much higher than expected, the cells were doing just fine, but it was the hundreds of extra connections each one has a tiny resistance but you add them all up and it's significant.
This was a big enough problem in my testing that I redesigned my connection method. Instead of 7 blocks making up a 3P series connection, I now have 3 blocks, two of them being outside clamps and now only one block is between the series groups, the tabs in each 3P set are all sandwiched together.
I'm not saying your method won't work, it's going to work, and it's going to work pretty well, but I think it could work better. (not from theory, from testing)
I know you don't like A123 cells, but laser welding has nothing to do with the issues that hillhater is trying to point out.
When you get the car on the track make sure you have a logging method for the battery voltage, I would suggest something at the + and - battery terminals and not at the Shiva terminals (or the shiva itself) as there will be so much noise and ripple there it's hard to say how accurate the voltage reading would be. I'll bet you a cold Canadian beer that you experience higher sag at the battery terminals than you are expecting, and it won't be the fault of your cells it will be all of the series connections contributing to significant sag at peak current.
jonescg wrote:But hillhater, every cell tab will need to be connected to a bus somehow, and that connection will have the same issues you describe. Granted there will be fewer problems with the primary series circuit, it just means some cells won't be working as hard. If there is a problem this way, it will be very obvious and easily fixed. Depends on the application really. It's probably as good as you will get for this app. at least.
That's incorrect. It's not an issue of improperly welded connections between cells. The problem was with a welding machine that was used to build individual cells.EVDragRacer wrote:A123 has a 50 million dollar recall because their welding machine did not properly connect the cells, all their modules shorted out!