Additional batteries?

I could spend $5k and get about 400V/8kWh worth of LiFePO4 batteries into the trunk. (Wouldn't actually take all of the trunk) If I went LiPo, it would actually be cheaper for the same energy storage.
This could conceivably extend range by about 30%.
I can see a zillion problems with this
But, is it doable? I imagine there's at least three technical problems:
1) How to charge these? I'd need something separate from the built-in charger.
2) How to tie into the Leaf main power? If I can match the top voltage well enough, could I parallel them? Or are large, expensive, energy converters needed?
3) How would the Leaf power control systems react to having more than expected capacity out of the battery stack?
Then there's practical problems, like cooling, and safety, and robustness, and all the rest. Given that people successfully convert gasoline cars to electrics, those should be solvable, but may also add significant extra cost.

OK, I will answer up on this one.

As a builder of several EV motorcycles, (OK not a car, but they do have the same technology on a smaller scale)
I give you points for the idea.

I have seen this type of different battery capacity/chemistry experiment added to some bikes as well as a car or two.
I am not one for squashing a project, but IMHO the effort will not be worth it, potentially dangerous and most likely
expensive for the results, if you get any.. (sorry)

Just a few points (not a zillion, but you get the idea)
The monitoring of the main battery system is set up for what is installed.
The discharge rates will be different setting up a imbalance issue.
ONE ( I have tools to prove this) mis-wire during this experiment will result in a plasma arc of epic proportion.
on and on.....

These cars are set up as a package deal monitored by a computer/controller that
does not give much room for changes....yet. :twisted:

You are more than welcome to prove me wrong. Please do a lot of homework first!

Crazy Ed

This has been done with hybrids successfully. Ingineer has powered his Leaf with a generator trailer. So I suspect this could also be accomplished.

That 8kWh of extra batteries will not give you the range gain that you expect due to the weight.. unless you are a hypermiler and then you would not need the extra range anyway

The record for range so far is 151 miles. A standard Leaf, per the EPA, will cover an area of 16,000 square miles.

Assuming the EPA 73 miles is driven as a square, I come up with about 330 square miles... How did you get 16,000?

Herm said:

That 8kWh of extra batteries will not give you the range gain that you expect due to the weight.. unless you are a hypermiler and then you would not need the extra range anyway
The record for range so far is 151 miles. A standard Leaf, per the EPA, will cover an area of 16,000 square miles.

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The added weight will tend to push you into the realm of bigger tires, suspension modifications, and such. Which increases the weight some more.

Using a different battery chemistry than what's in there is likely to give you problems because the voltages won't quite match. Then you are looking at the big expensive inverters again, to get things to match. Or you would use a scheme to have the new batteries charging up the existing batteries, but with the extra power conversion, and charging the batteries instead of using the power directly, you are then taking extra efficiency hits.

Usually, when you the "hot shot" cells (more power; think "Tesla"), or ones that can be made cheaper, you get something whose life span falls short of the ones in the car. Maybe that's OK, but the electronics now has to deal with two battery packs whose characteristics will differ as they age.

Always fun to think about, though. The best scheme would be one where you could remove all that stuff for "normal" driving.

One of the more technologically successful companies doing things around this area is Enginer.

My understanding of their product is that is has it's own battery management system and it's own charging system. It works by transferring charge to the vehicles battery rather then trying to run the vehicle directly off it's charge. I imagine there are lots of inefficiencies in this approach, but it seems like the most straight forward and safest way for a generic range extender.

I'm sure there are other ways to do this, probably more efficient and ways that could better target the LEAF - but at least it is a place to look to start to get some ideas.

I'm familiar with the plasma arcs, thanks! This came from accidentally and briefly shorting the wires on a 4S LeFePO4 pack while stripping them with a pocket knife. That blade isn't what it used to be ;-)

The nice thing with LiFePO4 is that lifetime is much better than LiPo. Also: significantly reduced explosion risk
Weight? 104 20 Ah LiFePO4 cells weigh about 58 kg, which is about the same as one additional passenger. I wouldn't need suspension or wheel mods for that, but it would reduce some of the range addition.

The different capacity/number of the cells in series shouldn't be that bad as long as you can supply the current, and can charge them separately -- whatever battery has the higher potential/voltage will provide the current, relieving the other battery. Current draw might actually be a limitation, though; LiFePO4 cells aren't really available for current draw larger than 5 times capacity, or capacity larger than 20 Ah. So, 100 amps times 400V gives 40 kW, which is less than the motor can draw. I imagine that, when parallel with the built-in batteries, this would balance out, though.
Under-voltage cut-off would be different, though.

I'd have to hook in after the BMS of the built-in cells, but before the inverter/power controller, in this thought experiment. Is the inverter in the motor end of the car, or mounted within the battery compartment below decks?

(Side note: If the charger can't even do 6 kW, why did they need that big bulk behind the back seat to mount it?)

I'm pretty sure this experiment would be a complete mess if actually attempted, but I'd still like to understand all the ways in which it would be ;-)

That's the approximate area of a circle with radius of 73 miles.

TomT said:

Assuming the EPA 73 miles is driven as a square, I come up with about 330 square miles... How did you get 16,000?

Herm said:

That 8kWh of extra batteries will not give you the range gain that you expect due to the weight.. unless you are a hypermiler and then you would not need the extra range anyway
The record for range so far is 151 miles. A standard Leaf, per the EPA, will cover an area of 16,000 square miles.

Click to expand...

Click to expand...

58kg is pretty good, what cells are you thinking about?

That seems to be the general weight of pouch-style cells. You'd need to form a hard case around them with some aluminum sheet or whatever, but that should add minimal weight.

For example, Tenergy 20 Ah 3.2V cells weigh 545 grams: http://www.all-battery.com/3.2V20AhLiFePO4RechargeableBattery-widepack-30229.aspx" onclick="window.open(this.href);return false;
Because they have tabs, you can actually stack them alternating sides up, and weld the tabs together directly, to avoid extra cabling.
Still need a small-gauge cable out from each to support balance charging and undervoltage detection, though.

I think LiPos may be even better per watt-hour: 1.4 kg for 50 Ah 3.7V: http://www.all-battery.com/polymerli-ionbattery37v50ah13212223.aspx" onclick="window.open(this.href);return false;
LiPos don't have the lifetime of LiFePO4, though, and have that explodey thing against them... I really like LeFePO4, after having used some for a hobby project.

LakeLeaf said:

One of the more technologically successful companies doing things around this area is Enginer.

Click to expand...

I'd be careful about saying they're successful. From http://priuschat.com/threads/enginer-product-quality-as-of-april-2011.91926/#post-1294825" onclick="window.open(this.href);return false; and many other posts like http://priuschat.com/threads/first-1-000-miles-tank-on-gen-iii-enginer-phev-it-has-a-bigger-thank-than-you-think.92674/" onclick="window.open(this.href);return false;, it seems the Enginer kit is pretty damned unreliable.