[PStechPaul]

Yes, it seems like 30 of the LiPo laptop packs would be just about the same as the pack you describe. If you want, you should be able to connect the 330 volts DC to a 240V VFD and a three phase motor. You would only be able to get about 2HP (330V at 4.5A), but you might be able to control a 20-40HP motor in an EV if you run it slow and move the car in low gear. That would let you know that all your controls were working. Then you could put maybe 10 or 20 of these packs in parallel (using individual 10A fuses and 20A diodes on each), and you will be able to get reasonable power and range.

A 325V 5.5 A-Hr pack is about 1800 W-Hr, and if you can get 330 W-Hr/mile just one pack might take you 5 miles, although very slowly without any major hills.

If the Sanyo packs are 1.3 V x 250 cells, they are probably NiMH or NiCd, which will also work, but you will need the correct charger and you may not get the life and overload performance of LiPo cells. If you can get them cheap at the salvage yard, you may get an amazing bargain.

[lithiumlogic]

The idea of spot welding 18650 cells is a little frightening/intimidating to me - i can't see it becoming a mainstream option. Respect to those with the necessary skills, equipment, time and courage...

For the less able, could those plastic 18650 battery holders available all over the internet, be used for something like an ebike?

It might save a little assembly time, and sure makes swapping out bad cells easier.

The cells themselves weigh about 46g give or take.

The single cell holders that list weight are about 14g. That's 1/3 of the weight of the bare cells, and you still need a sheet of fibreglass/al to fasten them onto - really erodes the power/weight benefit.

Four cell holders do much better, 30g to hold 4 cells. That's like 7g each, now only 1/6th of the mass is going to your cell holders. But all the ones i've seen are series wired, we need parallel.

Now if someone was to make a mould for a holder that holds 9 cells across 9 cells high (81 cells) all wired in parallel, the DIY folks might be interested..

[Elithion]

Originally Posted by lithiumlogic

could those plastic 18650 battery holders be used for something like an ebike?

They certainly won't work in a car: vibrations will result in intermittent contacts.

In an electric bicycle? I don't think so either: not only vibrations, but also oxidation, as a battery in an eBike probably has less protection from the elements that one in a car.

[Ziggythewiz]

I think they'd be fine for low power uses. Most are spring loaded, so vibrations don't matter much. If they did, the fuses in my VW would be a serious issue.

The main problem would be how much power can you push through contacts designed to power an RC car or similar?

[lithiumlogic]

Heck , if they're good for an RC model they're good for anything! RC models can do 10-20C. I don't think these laptop cells are good for much more than 3C anyway..

On reflection the 4 cell holder i was admiring for weight doesn't look too secure. It's 4 cells in a row, not 2 x 2. The middle two cells look like they'd fall out if you hit a big bump.

[ev-converter]

Originally Posted by lithiumlogic

The idea of spot welding 18650 cells is a little frightening/intimidating to me - i can't see it becoming a mainstream option. Respect to those with the necessary skills, equipment, time and courage...

For the less able, could those plastic 18650 battery holders available all over the internet, be used for something like an ebike?

It might save a little assembly time, and sure makes swapping out bad cells easier.

The cells themselves weigh about 46g give or take.

The single cell holders that list weight are about 14g. That's 1/3 of the weight of the bare cells, and you still need a sheet of fibreglass/al to fasten them onto - really erodes the power/weight benefit.

Four cell holders do much better, 30g to hold 4 cells. That's like 7g each, now only 1/6th of the mass is going to your cell holders. But all the ones i've seen are series wired, we need parallel.

Now if someone was to make a mould for a holder that holds 9 cells across 9 cells high (81 cells) all wired in parallel, the DIY folks might be interested..

Why would you want to spot weld when you can solder? Since 2004 I have assembled packs for my car and others up to 32kw. It is not difficult, just takes a lot of time. You do need to know what you are doing.Tesla monitored my progress before they had their own design finished. Who knows, they may have been able to use some of my ideas in their Roadster.

[lithiumlogic]

Originally Posted by lithiumlogic

plastic 18650 battery holders...

makes swapping out bad cells easier....

Is this an important factor? Perhaps not, on reflection, but my initial instinct was that it was something i'd want.

One of the things i do at work is maintain this fleet of laptops that are between 3 months and 18 months old, and have batteries based on Sanyo cells. I've got a utility that interrogates the battery firmware and shows calendar age, cycle count and capacity, and i've done a very unofficial survey on units that came in for non battery related reasons.

About 85% of them have great batteries.... very gradual loss of capacity, or no loss at all. 18 month old batteries with 600 cycles still showing over 90% capacity. But about 15% seem to suffer from what i'd call "infant mortality". Loosing half (or more!) or their capacity in the first 6 to 30 cycles. This must be a tough thing for the manufacturer's quality control to pick up on !

But when i think about it, in an EV pack you're going to be parallelling a huge number of cells, like 80 or so. If 10 of them go bad, the other 70 will keep the show on the road. And could you imagine the amount of work to weed out the weak cells, even if you could just pop them out of a plastic holder?

[lithiumlogic]

Originally Posted by ev-converter

Since 2004 I have assembled packs for my car and others up to 32kw. Tesla monitored my progress before they had their own design finished. Who knows, they may have been able to use some of my ideas in their Roadster.

The thing that impresses me most about the Tesla pack is the thermal management . On A123's presentation trumpeting the safety benefits of phosphate chemistry, they do an experiment where they simulate a multi cell pack by wrapping a bundle of cells together in polestyrene insulation and then overcharging one of them till it explodes. Hey Presto! the heat from the burning cell has nowhere to go but into the other cells, which one-by-one cook off as well.

But Tesla and Panasonic say their pack design prevents this chain reaction. Even without the liquid cooling system, a fire in one cell does not spread. Something about the air gaps preventing any one of the neighbours absorbing too much of the heat and going into runaway itself, something about passive convection cooling air currents, and heat conduction away into the bus bars?

This is the mojo... if a DIY pack can do it without giving up too much density that is.

[Grant_NZ]

Originally Posted by lithiumlogic

...But when i think about it, in an EV pack you're going to be parallelling a huge number of cells, like 80 or so. If 10 of them go bad, the other 70 will keep the show on the road. And could you imagine the amount of work to weed out the weak cells, even if you could just pop them out of a plastic holder?

Could you weed out the bad or non performing cells with extensive testing? or before fitting them into the vehicle run them with motor and controller fixed to a bench or platform??

[lithiumlogic]

You could... at the price of putting 20 to 30 cycles on all your cells before they even go into service. Might be a one worth paying i suppose, IF the cells you are using exhibit the same behaviour as the Sanyos i have experience of. ( nested IF statements there)

Tesla do some sort of diagnostic on the battery during annual maintenance, from reading the Roadster owner forum this sometimes results in them replacing a weak "sheet" under warranty.

So this is the plan, i think

1. get a seasonal job

2. build an ev based on thousands of 18650 cells and holders.

3. assuming the holders actually work :

4. drive around all summer

5. first winter comes. spend the whole time locked in the garage testing and swapping cells tweaking crystal meth to keep going and stay awake.

6. in spring, the world swoons over your fabulous range

7. ....which the wife uses to drive my sorry ass into rehab.

8. Meanwhile Mr EV Converter with his soldered pack, still has a better Wh/kg because the dead weight of his duff cells is less than the dead weight i'm carrying around in holders. Plus he still has a job. And a wife. And all his teeth.