Mini battery range extender (adding more batteries)

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rmay635703

Well-known member
Joined
Jan 19, 2011
Messages
628
I have about 250 ahr of NiMH batteries enough to make a 13.2 volt or 14.4 volt battery.

I am wondering if anyone has played with the absolute limits on the 12v system.

I know on the volt a CEL occurs if battery volt exceeds 16.5 volts, the leaf I have no idea. Some creative use of diodes and a switch could keep the car from seeing an excessive voltage while charging.

The idea here is that no voltage transformations or system hacking will occur, the car shuts off the DC-DC if the voltage is above a certain threshhold, this means a battery that is slightly higher in voltage will provide the 12v current until its capacity is dimished. It appears the cut in point for the DC-DC is such that either battery would not overdischarge.

Looking it appears that a rather large chunk of juice is going out the 12v system and that a bit more passive capacity would add 1-3 kw depending on the duration of the trip. Also understand that the DC-DC loss is gone so the true gain in capacity will be slightly higher.

Not insignificant, but also very cheap and simple to add.

Let me know if you have any ideas, I am also wondering where the leaf floats the battery during driving and how low it will allow under heavy 12v draw.

Cheers
Ryan
 
It won't gain you any (appreciable) range. In fact, the added weight might actually cost you range.

Putting two 12V batteries in series gives you 24V. Putting two 12V batteries in parallel still gives you 12V but at a higher current.

Do you have a huge stereo system/subwoofer that you added so that the DC-to-DC converter is working hard?
 
aarond12 said:
Putting two 12V batteries in series gives you 24V. Putting two 12V batteries in parallel still gives you 12V but at a higher current.
The load defines the current, not the battery. You mean at a reduced internal impedance, perhaps? :mrgreen:
 
Putting a NiMH battery in parallel with a lead-acid battery sounds like a very bad idea. The different battery types have rather different voltage/charge curves, and require substantially different charging methods. The DC-DC converter would be the wrong way to charge a NiMH battery.

I am not going to take the time to try to predict the result, but I expect they would not be good.

Also, as others have noted, the load on the traction battery through the converter is determined by the total 12 volt load, a bigger 12 volt battery would just buffer more energy at that voltage, it wouldn't save any.
 
alanlarson said:
Putting a NiMH battery in parallel with a lead-acid battery sounds like a very bad idea. The different battery types have rather different voltage/charge curves, and require substantially different charging methods. The DC-DC converter would be the wrong way to charge a NiMH battery.

Not an issue the lead acid battery would either be deleted altogether or be very small and behind a diode. I am talking replacing the 12v battery with a 14.4 volt battery that keeps the DC-DC off until the battery discharges.

alanlarson said:
I am not going to take the time to try to predict the result, but I expect they would not be good.

Also, as others have noted, the load on the traction battery through the converter is determined by the total 12 volt load, a bigger 12 volt battery would just buffer more energy at that voltage, it wouldn't save any.

A bigger 14 volt battery would add capacity by removing the load from the inverter, from my measurements its 30 amps right on up so not insignificant in the least.
 
If you're looking to increase range by changing the 12v system, you're likely to be thoroughly disappointed. The single largest drain on the 12v system is the headlights. Driving from 100-0% with headlights on or off will make <1mi difference (at any reasonable speed…).

As others have said, the added weight will likely offset what little potential you had.

If you're really intent on this, replace the SLA with a 4/8 cell LiFePO4. They are made to be 100% compatible as a drop-in replacement for SLA. Not only will this double the energy capacity of the 12v battery, but it shaves off 10 lbs, instead of adding 10 lbs. They generally top out around 400 crank amps, so they're limited in use on larger ICE cars, but the Leaf only needs around 10A to drive everything on the 12v. Just be warned, the Li battery is designed to be operated under a float charge (internal PCB protects from overcharge) which the Leaf will not provide. This could lead to premature failure of the batery. (Premature in this case meaning <2 years, instead of the 5+ normal life)
 
mctom987 said:
If you're looking to increase range by changing the 12v system, you're likely to be thoroughly disappointed. The single largest drain on the 12v system is the headlights. Driving from 100-0% with headlights on or off will make <1mi difference (at any reasonable speed…).

That is not quite correct. If you look at the energy use screen you will see that turning on/off the headlights (except on the cheapest model that does not have LED) does not make that much of a difference.

rmay635703 said:
I have about 250 ahr of NiMH batteries enough to make a 13.2 volt or 14.4 volt battery.

Looking it appears that a rather large chunk of juice is going out the 12v system and that a bit more passive capacity would add 1-3 kw depending on the duration of the trip. Also understand that the DC-DC loss is gone so the true gain in capacity will be slightly higher.

Not insignificant, but also very cheap and simple to add.

Let me know if you have any ideas, I am also wondering where the leaf floats the battery during driving and how low it will allow under heavy 12v draw.

Cheers
Ryan

I have been thinking in the same lines myself.

If the "energy usage" screen displays correct usage my average power consumption on the 12v system is about 250 watts per hour. On a 2 hour drive that equals to about 500 w/h. Most of this comes from the main battery. 500 w/h is not a whole lot, but is nevertheless about 2,5% of the driving range.


I have never measured higher than 13,5v on the 12v system when driving.

My plan is to make myself a little battery pack of old 18650 cells up to around 20 volt and use a DC/DC step down to 14v. And use the 12v outlet in the car to feed in the power. This has a 20amp fuse, so this should be enough. I will also use a chip that warns me if any of the parallel cells drops below 3v.

I have not tried this yet, I do not see what can go wrong except the 20 amp fuse...

To recharge the lithium cells I will use a balance charger.
 
If you want to add range you will not do it by farting with the 12V system.
The discussion is purely academic.
Enjoy it for that, but........
Seriously?

If you want to add range, you need to add a parallel battery of the correct voltage to the traction pack.
It's simple and easily doable, and it's been done, with the right single piece of equipment.
A credit card.

Buy some leaf battery modules.
Rewire them internally so that instead of the pair-pair wiring, you wind up with all 4 cells in series.
You need half as many modules, and will wind up with a 12kw pack.
Charge it with an independent Brusa installed in the rear, and you will finally have a 100 mile Leaf!

I think about trying to buy a flood leaf with an intact battery and doing this, but too busy to fool with it.

Good luck.
 
KillaWhat said:
If you want to add range you will not do it by farting with the 12V system.
The discussion is purely academic.
Enjoy it for that, but........
Seriously?

If you want to add range, you need to add a parallel battery of the correct voltage to the traction pack.
It's simple and easily doable, and it's been done, with the right single piece of equipment.
A credit card.

Buy some leaf battery modules.
Rewire them internally so that instead of the pair-pair wiring, you wind up with all 4 cells in series.
You need half as many modules, and will wind up with a 12kw pack.
Charge it with an independent Brusa installed in the rear, and you will finally have a 100 mile Leaf!

I think about trying to buy a flood leaf with an intact battery and doing this, but too busy to fool with it.

Good luck.


Every watt counts! 2,5% is not much but still a bit. Adding a diesel heater will easily save another 3-6 kwh.

Adding 12 kwh in the boot will of course help a lot. However fiddling around with 400 volts is not for everybody.

And correct me if I am wrong, but I thought that to rewire the modules you have to open the tin boxes in each module? That seems to be a lot of work, and quite dangerous if you don't know what you are doing.
 
And correct me if I am wrong, but I thought that to rewire the modules you have to open the tin boxes in each module? That seems to be a lot of work, and quite dangerous if you don't know what you are doing.

Yes you would have to open the cans.
But the individual cells are like 3.8 volts each, so 4 of them will still be under 16 volts.
I wouldn't lick it, but otherwise should be safe.

However, I respect your caution, especially when you start hooking 20 or so of these cans together.
 
KillaWhat said:
Yes you would have to open the cans.
But the individual cells are like 3.8 volts each, so 4 of them will still be under 16 volts.
I wouldn't lick it, but otherwise should be safe.

However, I respect your caution, especially when you start hooking 20 or so of these cans together.

I am not worried about each can. I would not even worry about 400v in a stationary power pack. What I worry about is how to get this new pack insulated and safe in a moving vehicle, and make sure it gets sufficient cooling.

I am sure it can be done, but it is a lot of work, and if done incorrect: a moving disaster.

I would feel a lot safer with the cans intact in series and parallel to 100-200 volts , and a smart DC/DC.

Since we are closing in on 150 000 LEAFs world wide someone might see the potential business, but I do not have the connections nor the money to start such a venture.

Just think how much easier the life with a LEAF would be if a $ 1000 investment in the car for a DC/DC and charger would make it possible to toss in 4 suitcases with batteries to add 12 kwh. Or just add one for a 3 kwh range. Or for the possibility for a small bio-diesel generator in the booth.
 
The thing I don't get and maybe there is a reason for it, but why you can't charge while driving. If you could you could charge with pretty much any genset or battery inverter setup up to 3.3kw or 6kw depending on the onboard charger. It seems simple enough and if you could charge (or offset the use from the traction pack) at 6kw while driving that would help a bunch and make adding a genset for a long trip relatively simple.

I know this is getting in to range extending idea, but I think it would make BEV's so much more palatable to the general population if you could go to Nissan (or whomever) and rent a range extender that plugs in the back and your good to go. Would most people actually use it, probably not, but a lot of people I talk to won't go to a BEV because of that once or twice a year trip that won't work.
 
BrockWI said:
The thing I don't get and maybe there is a reason for it, but why you can't charge while driving. If you could you could charge with pretty much any genset or battery inverter setup up to 3.3kw or 6kw depending on the onboard charger. It seems simple enough and if you could charge (or offset the use from the traction pack) at 6kw while driving that would help a bunch and make adding a genset for a long trip relatively simple.

I know this is getting in to range extending idea, but I think it would make BEV's so much more palatable to the general population if you could go to Nissan (or whomever) and rent a range extender that plugs in the back and your good to go. Would most people actually use it, probably not, but a lot of people I talk to won't go to a BEV because of that once or twice a year trip that won't work.

The main reason for not being able to charge whilst driving is probably safety. You do not want to drive off with the cable still connected to the car and the wall socket. I would assume that it is possible to bypass this feature somehow, at least on the old charger, if you have the time and money since the charger is not that complex. However the old charger would you some 3,3 kw. That is really not that much from a Rex based on generator. But of course it would give you some 5 kwh extra range if travel for about an hour and a half. Lowering the speed would of course give you a bit more.

Using a Rex based on batteries does not need to go via the charger since the current is already DC, and is not limited by the chargers 3,3 kw capasity. This has already been done, but at a hefty cost. You will need the same number of cells to get the correct voltage, as well as BMS and charger. The company Ingerneer ha a clever solution to this with using a DC/DC, but they went bust.

I have been in contact with a company here in Norway that has been in touch with a major developer in Germany and their answer was clear: they can make a "box" that could be a DC/DC, BMS and charger. But they will not produce it. The reason? Nissan. Nissan is apperantly clinging to their patens, and this major german company does not want to violate their patent rights.

How great would it not be if I could buy a kit for less than $ 2000 (ideal) that would make car be able to use "plug in" modules of 2-3 kwh each (bought seperatly) up the vehicle weight limit. And at the same time getting the benefits of a "double" charger since you may use one source to charge the main battery and another to charge the REX.
 
I think the best way to go about adding range to the leaf would be building a custom rear sub frame with a small 7 or 9 inch electric motor. From what I've seen there looks like there's plenty of room down there, you could have a relatively safe sub 144V system. You'd also expand the market from offering people extra range as well as a performance boost and awd. The only thing you'd have to tap into the Nissan system for is a signal from the pedals. DC motors you only need a signal from the accelerator and AC you need to tie in the brakes, or offer full regen with lift off. You could offer a charge on a separate plug, a smaller battery would probably charge at 120v 8a in the same time the main battery takes to charge with 6.6kW or a combined system that chargers from the main J1772 hook up.

There are plenty of ready built kits out there already that would be complete with the exception of the subframe and pedal signal. If there were affordable in hub motors that would be the best solution. As an emergency back up limp home system you could probably get away with only driving one rear wheel.


If you've got extra batteries laying around and winter range is an issue the best use is probably in using them to power a radiant heat dish that's pointed just at the driver.

Second easiest thing would be to put the cars lighting on a separate 12 v system and run it off the new independent battery. You could add a switch to go from independent battery to the cars 12v. You could also do the same for things like the fan and radio. That would probably give you the most benefit with the least chance of trouble.
 
minispeed said:
I think the best way to go about adding range to the leaf would be building a custom rear sub frame with a small 7 or 9 inch electric motor. From what I've seen there looks like there's plenty of room down there, you could have a relatively safe sub 144V system. You'd also expand the market from offering people extra range as well as a performance boost and awd. The only thing you'd have to tap into the Nissan system for is a signal from the pedals. DC motors you only need a signal from the accelerator and AC you need to tie in the brakes, or offer full regen with lift off. You could offer a charge on a separate plug, a smaller battery would probably charge at 120v 8a in the same time the main battery takes to charge with 6.6kW or a combined system that chargers from the main J1772 hook up.

There are plenty of ready built kits out there already that would be complete with the exception of the subframe and pedal signal. If there were affordable in hub motors that would be the best solution. As an emergency back up limp home system you could probably get away with only driving one rear wheel.


If you've got extra batteries laying around and winter range is an issue the best use is probably in using them to power a radiant heat dish that's pointed just at the driver.

Second easiest thing would be to put the cars lighting on a separate 12 v system and run it off the new independent battery. You could add a switch to go from independent battery to the cars 12v. You could also do the same for things like the fan and radio. That would probably give you the most benefit with the least chance of trouble.


Please do not be offended, but your idea is at best "wishfull thinking".

The LEAF already has a traction motor. Why not use it? Replacing the subframe would make it ilegal is most civilized countries without a very costly testing.

Seperating the 12v system from from OEM DC/DC is also a very bad idea since a lot of the safety features is based on 12v. Even though the 12v system uses fairly little energy (less than 250 w in my car) it should be possible to eliminate the drain from the main battery by simply connecting a power supply with a higher current to the 12v system. This could even be possible by making a small battery pack with a nominal voltage of 14v connecting to the sigarett lighter with a "cut off" at 13,5 v. This would of course give up to a mile at best.

Using a different heat source than electricy from the main battery will give a lot of extra range during winter. Your idea is not very bad, but why not just install a diesel or alcohol burner? Using bio-diesel will not comprimize the Co2 emmision goals, and you can even make it yourself. Installing a used Eberspächer/Espar will keep the car warm for all passenges. And it does not need several hundred pounds of batteries installed in the vehicle.
 
TorC said:
Please do not be offended, but your idea is at best "wishfull thinking".

The LEAF already has a traction motor. Why not use it? Replacing the subframe would make it ilegal is most civilized countries without a very costly testing.

Seperating the 12v system from from OEM DC/DC is also a very bad idea since a lot of the safety features is based on 12v. Even though the 12v system uses fairly little energy (less than 250 w in my car) it should be possible to eliminate the drain from the main battery by simply connecting a power supply with a higher current to the 12v system. This could even be possible by making a small battery pack with a nominal voltage of 14v connecting to the sigarett lighter with a "cut off" at 13,5 v. This would of course give up to a mile at best.

Using a different heat source than electricy from the main battery will give a lot of extra range during winter. Your idea is not very bad, but why not just install a diesel or alcohol burner? Using bio-diesel will not comprimize the Co2 emmision goals, and you can even make it yourself. Installing a used Eberspächer/Espar will keep the car warm for all passenges. And it does not need several hundred pounds of batteries installed in the vehicle.

There are many aftermarket sub frames, modifications and kit cars all over the world. Go to DIYelectriccar.com to see what a lot of people are doing to ICE cars. People are driving with stuff like that all over the world. People drive home built kit cars too without expensive testing. Yes there will be some places in the world where you can't do that but there are many where you can. I only really know about people doing aftermarket modifications like this in Canada, the US and the UK but that alone is a pretty big market. The UK is probably the strictest and I know of many people who pass the MOT with tube front sub frames in classic minis modified for car or bike engines or even mid engine sub frames.

As far as I understand it to use the main traction motor you'd have to hack in and I don't think anyone has done that yet. I know of several places that could get a rwd sub frame up and running as quickly as I could pay for it and you can get half a leaf pack for $3k and run it as 96v for a safe 80lbft 60hp set up for another $3k. AC motor is 60lbs, 12kWh of leaf batteries is 210lbs 32"x13"x9" then whatever the new sub frame and transmission adds. That's not a lot of weight for what it adds in performance. You could easily run the system cheaper and lighter with 48v and 6kWh of batteries and a used DC forklift motor for a few hundred bucks. There's open source controllers you can build for sub 144v systems that cost a few hundred to make too.

I wasn't saying to disconnect the whole 12v system from the car, just the lights, fan and radio. The stuff that isn't involved in any safety aspect. The rest of the car could run on the stock DC/DC 12v just as it would with no lights on, no fan going and no radio on.

It wouldn't take several hundred lbs of battery to just run a heater. You can get something like this:
[/http://www.homedepot.com/p/Optimu...say he has an extra diesel or alcohol burner.
 
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