Tesla home battery pack and DPV battery pack Technology

[shoredivr]

Ah, hardly.

I've designed and sold rechargeable battery powered devices for 30+ years. IMO "gas gauges" are a gimmick that almost no user needs. Far better to start with more than enough battery.

If battery capacity is "mission critical" who starts with less than a full charge?

If battery capacity is "mission critical" who plans on using more than some fraction (1/2's 1/3's) of the known, proven capacity?

If battery failure (exhaustion) is life threatening who doesn't include redundancy in their planning, i.e. spare scooter, back up light etc.?

Determining useful range is of course necessary to plan, but that doesn't require real time display, it's easy to determine via data loggers or even returned capacity at time of charge.

Can detail for me exactly how real time data will change your dive planning in ways that a data logger cannot?


Tobin

Following this logic, then, SPGs are unnecessary....

 

[Pullmyfinger]

I doubt we'd be very happy getting the same benefits: try comparing efficiency between the Cuda Fury and the Genesis scooters back from the last TBM tests. Bigger batteries are great. Needing a bigger battery to deliver the same performance because you're getting the DPV equivalent of terrible gas mileage? Not great.

I will read it again.
Although, I don't recall the Fury being terrible in any aspect.

 

[Dr. Lecter]

I will read it again.
Although, I don't recall the Fury being terrible in any aspect.

It is in no way terrible - until I looked at the Genesis DPVs it was what I was planning to buy. It's a great scooter based on established technology that's just been surpassed in some respects as better designs come to market.

But the TBM numbers are quite clear that a Cuda Fury is doing less work per watt-hour than a Genesis. Put a big enough battery in it, and you'll still go further with the Cuda than with the Genesis...but then you're spending extra money and weight on making an inferior design perform the same/better. Assuming they each have the same battery, the Genesis will tow the same diver further/longer than the Cuda.

 

[cool_hardware52]

It is in no way terrible - until I looked at the Genesis DPVs it was what I was planning to buy. It's a great scooter based on established technology that's just been surpassed in some respects as better designs come to market.

But the TBM numbers are quite clear that a Cuda Fury is doing less work per watt-hour than a Genesis. Put a big enough battery in it, and you'll still go further with the Cuda than with the Genesis...but then you're spending extra money and weight on making an inferior design perform the same/better. Assuming they each have the same battery, the Genesis will tow the same diver further/longer than the Cuda.

Humm, I disagree.

Keep in mind that at the last TBM is was not possible to slow a Cuda Fury down to (IIRC) 150 fpm cruise. That means the efficiency numbers were skewed. With the new user programable motor controller Dive X sells it is now possible to select as slow a sped as you want.

Having said that why should the user care if one scooter designer selects a motor of XX efficiency and a battery of YY watthours and another designer selects a motor of with an efficiency of .95XX and a battery with 1.10YY capacity? The net result is about the same.

WRT to batteries; 18650 cells are pervasive. They are used in everything from laptops to cordless tools to Telsa Autos. Billions of cells are produced every year. That means the R&D $$ spent on 18650's is also huge. It's not chance that the capacities of 18650's has grown rapidly from ~2.0 amphour per cell to ~3.9+ in just a few years. As a designer I absolutely want to leverage the R&D $$ that Apple and Dewalt and Tesla are spending.


This is dramatic compared to large prismatic Li-Poly cells, for which there is a much smaller market.

It's also not chance that packs using many 18650's are what powers the Tesla Autos.

The specific energy (watt hours / unit mass) of packs built using 18650's is very difficult to match (impossible?) using packs built from small numbers of large prismatics.

The problem is building packs using 100's of 18650's is extremely difficult, and expensive and requires substantial investments in fixtures, and fine resistance spot welding equipment.
(Replacement costs on the welder we use is over $50K) Perhaps I should post some photos of the pile of fixtures required simply to assemble the cells in preparation for welding.

That makes soldering together a few high capacity Li-Poly cells an attractive choice for low volume applications, but by doing so the advantages of high specific energy, and massively paralleled, passive self balancing packs is lost.

The massively paralleled design we use is patented, and DSS holds the exclusive license for this technology in DPV's.

I should also mention that "active" balancing is largely ineffective for high capacity series packs produced using series strings of large capacity cells as the "balancing circuits" used for smaller batteries don't scale very well.

Oh, one last note concerning the last TBM; of all the scooters tested only the DSS Li-Ion powered scooter actually delivered *more* total watthours than we claimed to provide. Under promise and over deliver…...

Tobin

---------- Post added May 14th, 2015 at 08:09 PM ----------

Following this logic, then, SPGs are unnecessary....

SPG's are largely unnecessary. I use mine to confirm what I already know.

Let's say 1/2 way into a dive I look at my SPG and discover that I have less gas than I expected. Based on that what action do I take?

Pretty simple, some sort of gas sharing with Teammates is likely to be implemented. This of course only works because adequate predive planning insured there would be sufficient resources to complete the dive in the event of a failure.

One can easily argue that SPG's (and battery gas gauges) actually encourage additional risk taking.


Tobin

 

[Wookie]

Perhaps I should post some photos of the pile of fixtures required simply to assemble the cells in preparation for welding.

Tobin

I don't know about anyone else here, but I would freakin love to see the assembly line. Obviously without you giving up the farm with respect to things that are privileged information, If I'm ever in So Cal again, I'd be dropping by to have a look around, just so we could argue in person.

 

[cool_hardware52]

I don't know about anyone else here, but I would freakin love to see the assembly line. Obviously without you giving up the farm with respect to things that are privileged information, If I'm ever in So Cal again, I'd be dropping by to have a look around, just so we could argue in person.

Frank, if you are in town look me up.

Tobin

 

[kidsdream]

Just read this thread. A fantastic read for sure. As others have said, building small volumes of anything is a tough go - without high margins to cover your costs - materials , direct & indirect labour, SG & A, capital amortization and profit - you may not nbe around for very long.

Even with access to the a high end tool/machine shop (we build $40million of injection tools/year) and a $450million injection molding operation; I wouldn't think about building DPV's or components as a commercial endeavor.

Oh yea, went I said access, I meant I run the complete engineering and cost estimating activity for the company. We should thank guys like Tobin for even playing around with this stuff.

Jeff