[Kevin Sharpe]

I'm amazed that the Leaf does not have an active thermal management system.

The Leaf has optional battery heaters for use in cold climates.

I've been considering fixing some heat-sinks onto the additional battery packs I will add to have the wind under the vehicle help to pull away heat from the batteries.

I doubt this would help very much because each battery module has a lot of thermal mass and I don't see anyway of removing the heat easily.

Is it reasonable to assume that if I double or triple-up the battery from the original Leaf, that the strain (and heat) on the original battery would be lessened?

It's difficult to quantify the impact although I guess if you're drawing half the current then we would expect a reduction in heat build up.

Note that the latest 40kW Leafs overheat much more readily than the 24kW/30kW Leafs. You may want to factor that into your battery choice if you're convinced you have a problem with heat.

 

[Meni Menindorf]

The Leaf has optional battery heaters for use in cold climates.

I doubt this would help very much because each battery module has a lot of thermal mass and I don't see anyway of removing the heat easily.

Hey, thank you for your comment Kevin. I could be way off here, but isn't that exactly what a heat-sink is for? When you have some thermal mass with heat building up inside of it, a heat-sink can be used to remove the heat more quickly from the mass ~ just like in a CPU or GPU, which is where I'm familiar with them. The idea is to get the mass and heat in good contact with the heat-sink so the heat transfers to the sink. Then the sink is designed with a lot of surface area so that air flow is more effective at removing that heat.

I haven't gotten deep in my battery size calculations yet. . . (exactly how many 18650's can I fit under my LeSharo? ~ more on that later) . . . so I'm not sure exactly how much covering the battery box in heat-sinks would cost. . . but it's looking really expensive on Amazon. Might have to talk to my fabricator about working it into the aluminum battery box. . . But yes, I have doubt's about whether it's worth it!

It's difficult to quantify the impact although I guess if you're drawing half the current then we would expect a reduction in heat build up.

I'm hoping so ~ and hoping in general that spreading the load across several batteries would reduce the wear and tear on the system from constantly handling a larger load than it was designed for.

Can anyone with more battery knowledge chime in? If I spread the same motor-draw across two batteries in parallel, each providing the same voltage, would this reduce amp-draw on each of the two batteries individually? Does it cut the amp-draw in half? (or close to it?) Finally, would this also reduce heat build-up?

Note that the latest 40kW Leafs overheat much more readily than the 24kW/30kW Leafs. You may want to factor that into your battery choice if you're convinced you have a problem with heat.

That is a very good thing to know! I will keep this in mind when selecting an auction vehicle~

 

[MattsAwesomeStuff]

Can anyone with more battery knowledge chime in? If I spread the same motor-draw across two batteries in parallel, each providing the same voltage, would this reduce amp-draw on each of the two batteries individually? Does it cut the amp-draw in half? (or close to it?) Finally, would this also reduce heat build-up?

Think of batteries like a jug full of water.

Think of power as the rate at which water leaves the spigot on the jug.

If you using 20,000 watts, and you have 2 equally-sized batteries, it will draw 10,000 watts from each. If you only have 1, it will draw 20,000w from the 1.

Think of a single pack, if you physically chop it in half, and then electrically connect it back together... does it make a different to the power drawn? Nope.

So, two packs will be exactly half the power draw.

Lithium Ion batteries (and probably all batteries) deteriorate with age and use, so if you use them less aggressively, they'll last a bit longer.

If you use two packs that were each built to be sufficient on their own, you'll also see a very small (fraction of 1%) improvement in efficiency due to 1/4 as much heat loss in wires. But this would be equivalent to just beefing up the wires on a single pack, so, not much to gain there.

 

[Kevin Sharpe]

Hey, thank you for your comment Kevin. I could be way off here, but isn't that exactly what a heat-sink is for?

If you have a look at the Leaf battery module construction (see here) you'll see that no attempt is made to remove heat from the pouch cells. Therefore unless you're going to repackage the pouch cells with a heatsink I do not believe you will have any significant impact using a heatsink at the module level.

My advice is to run the Leaf modules as designed without cooling or use Volt/Tesla modules that have integrated liquid cooling if you are convinced heating is a problem.

exactly how many 18650's can I fit under my LeSharo?

Don't bother trying to build your own 18650 based pack. Tesla and Volt modules are much cheaper and safer.

 

[Meni Menindorf]

If you have a look at the Leaf battery module construction (see here) you'll see that no attempt is made to remove heat from the pouch cells. Therefore unless you're going to repackage the pouch cells with a heatsink I do not believe you will have any significant impact using a heatsink at the module level.

My advice is to run the Leaf modules as designed without cooling or use Volt/Tesla modules that have integrated liquid cooling if you are convinced heating is a problem.

I have seen cut-away images of the Leaf drawing heat away from the batteries and pumping it into the passenger compartment for added comfort heating. Is this only on later models? I was not sure if perhaps they had a way to divert that heat outside of the vehicle as well? I totally agree I would not want to modify the existing leaf battery~ Their system is working well enough. Can you confirm/clarify that the Leaf (even newer ones?) don't use any liquid cooling?

Don't bother trying to build your own 18650 based pack. Tesla and Volt modules are much cheaper and safer.

I have been wondering about this. It looks to me like a complete Tesla module cost break-down is . . . hard to determine. I'm seeing on eBay, a 90kWh 24V module for $700, and also a 4.5 kWh 24V module for $1250. I did some rough math and I'm guessing that I could spot-weld my own pack for about $1500 in materials that would be equivalent to the Leaf pack. This would be without a BMS. . . which I know sounds crazy, but I have been wishfully (foolishly?) thinking that since this pack would draw half (or a third, if I use 3 packs) of the amps that the Leaf originally drew from it's single pack, and if I was conscious to add some sort of heat-sink, that I would probably be safe from any overheat in my custom pack. Please talk me out of my insane idea.

 

[Meni Menindorf]

My wife and I have a bad (but oh so good) habit of off-roading just a little bit in our RV to get off the beaten path for some good boon-docking. I have been considering raising up the leaf suspension in the back of the LeSharo and adding duelies on the back to accommodate the weight of additional battery packs, and also to support our bad habits


Does anyone have any experience or knowledge about what would be required to raise the front suspension of the Leaf? Also, I'm thinking it would be prudent to replace the wheels on the Leaf with the front wheels from the LeSharo, for the weight rating on the bearings and also the tires.



Any thoughts on this?

 

[Meni Menindorf]

Think of batteries like a jug full of water.

Think of power as the rate at which water leaves the spigot on the jug.

So, two packs will be exactly half the power draw.

Lithium Ion batteries (and probably all batteries) deteriorate with age and use, so if you use them less aggressively, they'll last a bit longer.

If you use two packs that were each built to be sufficient on their own, you'll also see a very small (fraction of 1%) improvement in efficiency due to 1/4 as much heat loss in wires. But this would be equivalent to just beefing up the wires on a single pack, so, not much to gain there.

Thank you Matt! This is exactly what I'm looking for~ Any thoughts on the functionality/practicality of adding an air-cooling heat-sink to a custom designed battery pack? Not for the leaf battery, which I would probably leave untouched. . . but for a new custom pack or two that I might build?

 

[MattsAwesomeStuff]

Any thoughts on the functionality/practicality of adding an air-cooling heat-sink to a custom designed battery pack? Not for the leaf battery, which I would probably leave untouched. . . but for a new custom pack or two that I might build?

I have no experience with the packs, and experience generally trumps casual consideration, but...

I would not bother with heat-sinks or cooling.

The rate at which you're using a big pack is going to be so slow that it won't be an issue.

For example, if you have 2 hour range at highway speed, that means you're going to generate howevermuch heat it will generate, over 2 hours.

For a Tesla or something, they have performance use where they may (or may be able to) drain the battery pack in 15 minutes or something. Well now you have 8 times the heat dissipation requirements.

As long as you're looking at 1-2 hours, I can't imagine the packs would accumulate anything significant for heat. Don't sprayfoam them into a casket, but, ambient air cooling (especially while driving) is probably fine.

But again I have no practical experience, go by what someone says the cooling requirements are who've used the packs or who are more familiar with the specs and why the specs are the way they are.

...

Also, don't build your own 18650 pack.

I say that as someone building their own 18650 pack, who's been happy with the process.

Mine's on a motorbike, if it wasn't, I would just be buying a pack, it's cheaper, pre-engineered, and a bajillion times easier.

 

[Kevin Sharpe]

I have seen cut-away images of the Leaf drawing heat away from the batteries and pumping it into the passenger compartment for added comfort heating. Is this only on later models?

None of the current models (24kWh, 30kWh, 40kWh) have any active cooling and the battery is mounted in the belly of the car with little (if any) passive cooling. The next generation Leaf (60kWh iirc) will have active cooling and I suspect that's the cut-away that you've seen.

 

[Kevin Sharpe]

Please talk me out of my insane idea.

despite spending billions this still happens to Tesla's 18650 batteries

Tesla Model S fire vs 35 firefighters – watch impressive operation after a high-speed crash

 

[Meni Menindorf]

Hey AwesomeMatt,

I appreciate the comments about cooling the battery packs. I think you're spot-on!

Doing some deeper math and giving it more consideration, I now see what everyone is saying about getting prefabbed EV modules.

Kevin, do you have any experience or preference working with the Tesla modules, or Volt, or something else? Are the 5.3 kWh, 24v Tesla packs the best way to go?

I'm a little confused about working with these 24v Tesla modules. . . I would need 15 or 16 of them in series to get to the 380 volts that the Leaf operates at. . . crazy expensive! And then the Ah of the pack would be way bigger than the Leaf. . . seems like maybe not the best fit?

Would it be better to just go with the Leaf modules? 7.6V, 64Ah * 50 would get me pretty close at 380V and 24kWh. Pricing on this looks like about $5k~

I'm amazed that just the price of an equivalent 30kWh battery module is about the same price as an entire used Leaf!

 

[Meni Menindorf]

There is something I'm wondering about as I am thinking of doubling up the batteries from two different leafs. What would happen if I paired a 24kWh Leaf battery in parallel with with a 30kWh Leaf battery? Would they end up draining differently? Wearing differently? Charging differently? Is this a terrible idea? Or could it possibly work out alright?

There are a limited number of options when looking at salvage auctions so I am wondering if it might be alright to run two similar, but not identical, batteries in parallel~

Would appreciate any thoughts or feedback!

One more question. . . if I reduced the 1:7 gear ratio standard on the Leaf even further, thus lowering the top-speed, might this potentially be a better fit for a heavier vehicle like this? I've read that the Leaf has a top speed of 93 mph. I'm even considering putting two Leaf gear-boxes in series, thus rendering the top speed of the vehicle to 45 mph. . . but would this also help to relieve some strain from each gear-box, and possibly also reduce the torque required by the motor? Or reduce the wear and tear on the motor? We're not trying to get anywhere fast

 

[electro wrks]

There is something I'm wondering about as I am thinking of doubling up the batteries from two different leafs. What would happen if I paired a 24kWh Leaf battery in parallel with with a 30kWh Leaf battery? Would they end up draining differently? Wearing differently? Charging differently? Is this a terrible idea? Or could it possibly work out alright?

There are a limited number of options when looking at salvage auctions so I am wondering if it might be alright to run two similar, but not identical, batteries in parallel~

Would appreciate any thoughts or feedback!

One more question. . . if I reduced the 1:7 gear ratio standard on the Leaf even further, thus lowering the top-speed, might this potentially be a better fit for a heavier vehicle like this? I've read that the Leaf has a top speed of 93 mph. I'm even considering putting two Leaf gear-boxes in series, thus rendering the top speed of the vehicle to 45 mph. . . but would this also help to relieve some strain from each gear-box, and possibly also reduce the torque required by the motor? Or reduce the wear and tear on the motor? We're not trying to get anywhere fast

Unmatched battery packs would be a discharge and recharge nightmare to get to function properly and safely.

You need to do more homework on power transmission and gear ratios. Combining gear ratios in series multiplies the overall ratio. It does not add them. Two Leaf gear boxes in series would give 1:7 X 1:7= 1:49 not, 1:14. Think of 7 input rotations giving 1 output rotation from the first box. 7 of those rotations givies one rotation from the second box. 7 X 7=49.

 

[Kevin Sharpe]

Kevin, do you have any experience or preference working with the Tesla modules, or Volt, or something else?

I'm using Tesla models in my build (here). Damien (here) and Chris (here) are using Volt batteries.

Are the 5.3 kWh, 24v Tesla packs the best way to go?

Depends on your budget and range requirements.

I'm a little confused about working with these 24v Tesla modules. . . I would need 15 or 16 of them in series to get to the 380 volts that the Leaf operates at. . . crazy expensive! And then the Ah of the pack would be way bigger than the Leaf. . . seems like maybe not the best fit?

Tesla modules can be reworked for ~50V (see module vendors here) and therefore only 8 would be required.

Would it be better to just go with the Leaf modules? 7.6V, 64Ah * 50 would get me pretty close at 380V and 24kWh. Pricing on this looks like about $5k~

The Leaf modules are a good solution if you can live with the lack of cooling (which works fine in the Leaf). The best way to buy them is in a wrecked Leaf which will also have all the other parts you need

 

[Meni Menindorf]

Unmatched battery packs would be a discharge and recharge nightmare to get to function properly and safely.

You need to do more homework on power transmission and gear ratios. Combining gear ratios in series multiplies the overall ratio. It does not add them. Two Leaf gear boxes in series would give 1:7 X 1:7= 1:49 not, 1:14. Think of 7 input rotations giving 1 output rotation from the first box. 7 of those rotations givies one rotation from the second box. 7 X 7=49.

You are right! I should do at least a tiny-bit of homework before I start saying my crazy ideas out loud . I can't help it. . . visionary mentallity. 10,000 new ideas/day ~ most of them highly impractical. I haven't worked with gears much before so I am not that familiar with them. But I now understand the concept you are describing~ if I wanted to go from a 1:7 ratio to a 1:14, I would only need to add a 1:2 ratio gear. So . . . is the rest of my theory sound? If I have a heavier vehicle, and I don't mind if the top speed is slower, would it make less strain on the motor to gear it down a little further? For all practicality and simplicity, I will probably just leave well enough alone with the standard Leaf gear-box. . . but I was just curious if I am thinking about gear-theory correctly~


Also, thank you for clarifying about mis-matched batteries! I assumed as much, but was having wishful thinking. . . I will make sure to get a second Leaf who's battery matches my first. ie: if I get a 24kWh pack, I will make sure the second pack is also 24kWh.

 

[Meni Menindorf]

The Leaf modules are a good solution if you can live with the lack of cooling (which works fine in the Leaf). The best way to buy them is in a wrecked Leaf which will also have all the other parts you need

I have come to the same conclusion. Salvaging the battery pack from a wrecked Leaf is going to be the cheapest route~ Now I just need to find two of them with the same type of battery!

On a related note. . . I am strongly looking at a particular salvage Leaf with a smashed up trunk. I had an inspector go look at it for me and he said it looked like a light accident that only had body damage in the rear; however, he also said it won't go into gear. He postulated this was because the Leaf has an open-trunk sensor which would prevent it from shifting into gear. Anyone know about this. . . ?

Also, are there other safety systems that I will have to somehow disable in order to make the Leaf run normally after I chop-off the back half of the vehicle? Will this be workable, or substantially complicated?

 

[Kevin Sharpe]

Anyone know about this. . . ?

Lots of system faults will prevent the Leaf from moving... unfortunately I can't remember the details because it's a couple of years since I worked on that platform.

Can you post a picture of the Leaf instrument display on the vehicle you intend to purchase?

Also, are there other safety systems that I will have to somehow disable in order to make the Leaf run normally after I chop-off the back half of the vehicle? Will this be workable, or substantially complicated?

Many of your questions will have been answered in the Leaf thread (here). You'll find the thread includes a list of Leaf parts that are required

 

[brian_]

I'm a little confused about working with these 24v Tesla modules. . .

They're not really 24 volt. People seem to want battery systems to run at some multiple of 12 volts, but it doesn't work that way. Tesla Model S/X modules have 6 cell groups in series... which is 22.5 volts for the module at 3.75 V/cell (nominal).

I would need 15 or 16 of them in series to get to the 380 volts that the Leaf operates at. . . crazy expensive!

Lower-capacity Tesla Model S/X batteries had 14 modules in series; larger (100 kWh and I think 85 kWh) batteries have 16 modules in series. Yes, since (like all modern EVs) all modules are connected to each other in series, large battery capacity means that you can't use the stock modules to build a low-capacity high-voltage battery. As Kevin mentioned, some companies do modify the Model S/X modules to 12s, cutting the number of modules for a given voltage in half.

 

[brian_]

. . . if I reduced the 1:7 gear ratio standard on the Leaf even further, thus lowering the top-speed, might this potentially be a better fit for a heavier vehicle like this?

Yes.

I'm even considering putting two Leaf gear-boxes in series, thus rendering the top speed of the vehicle to 45 mph. . . but would this also help to relieve some strain from each gear-box, and possibly also reduce the torque required by the motor? Or reduce the wear and tear on the motor? We're not trying to get anywhere fast

Aside from the gearing math (which you have since figured out), it doesn't relieve the strain on the final gearing. Think of the gears in a train like links in a chain - each of them transmits the same power (everything coming out of the motor), although they are running at different speeds and therefore different torques (or loads on each tooth). If the additional reduction is after the stock Leaf gearing then the Leaf gearing would transmitting lower load at higher speed, which would be easier on the gearing.

A challenge is that there isn't any easy way to insert another stage of gearing between the existing gears and the differential. That leaves adding a gearbox on each output from the differential, either at each side of the transaxle (which would be a lot of work), or as geared hubs.

... I now understand the concept you are describing~ if I wanted to go from a 1:7 ratio to a 1:14, I would only need to add a 1:2 ratio gear. So . . . is the rest of my theory sound? If I have a heavier vehicle, and I don't mind if the top speed is slower, would it make less strain on the motor to gear it down a little further?

It would shift the motor speed and load conditions. The motor is most efficient at mid-range speed and relatively heavy load. If the change in gearing moves it from lower speeds up to a better point, and avoids maximum load (and thus maximum current for the speed), it should improve efficiency and reduce motor temperature.

It will also multiply the available torque at the wheels, by whatever reduction gearing ratio you add.

 

[Meni Menindorf]

They're not really 24 volt. People seem to want battery systems to run at some multiple of 12 volts, but it doesn't work that way. Tesla Model S/X modules have 6 cell groups in series... which is 22.5 volts for the module at 3.75 V/cell (nominal).

Yes! This makes much more sense. I think a lot of people are using these Tesla packs for DIY Power Walls and off-grid applications ~ so they are probably used to working with lead-acid.

Lower-capacity Tesla Model S/X batteries had 14 modules in series; larger (100 kWh and I think 85 kWh) batteries have 16 modules in series. Yes, since (like all modern EVs) all modules are connected to each other in series, large battery capacity means that you can't use the stock modules to build a low-capacity high-voltage battery. As Kevin mentioned, some companies do modify the Model S/X modules to 12s, cutting the number of modules for a given voltage in half.

This brings up another point I've been wondering about. The Leaf Motor (EM61) operates at 380V. What happens if I power this motor with a lower voltage battery? Say I used 12s Tesla packs and ended up with about 270 Volts? What if I got really crazy and went to 150V?



The Motor would have less power?
The Motor would get hotter?
The stock wiring would not be capable of handling the current?


I've been realizing that while 100hp petrol engine in the LeSharo is probably "under-powered," I barely ever use the full power of this engine. I would say 80% of the time I'm only using 30% of the available power. The only time I might use close to full-power is when climbing a steep hill.



This makes me wonder more crazy things. What if I used a lower power EV motor, (or wired the EM61 at a lower voltage?) and included a voltage ramper to give shorter bursts of higher power. I know there are a lot of circuits/products available out there to change voltage up or down pretty easily. I know these components get hot. Would it be possible to use one of these to provide a temporary "boost" by ramping up battery voltage for a short time?