Extra Battery, How to Integrate with 24kWh Traction Battery?

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Here's my 'trick'

No it doesn't charge on the move, BUT if ever I ran it dead out of go juice:
I have a 5kw sine wave inverter in my boot (weighs about 12kg)
I have a 4 Ni-Cad 12v/100Ah batteries in my boot connecting to my 48vdc-240vac inverter
My evse which signals a 20a charge rate

Even if its just a coffee break I plug it in, switch inverter on, tada some more kms on the clock. Beauuuuuuuuuuuuuuuutiful.
 
^ So, making some assumptions about the depth of discharge you're allowed from those batteries and taking into account charging efficiencies, it looks like you're good for about 4Kwh? That sounds like a pretty neat setup. Would love to get some more details and pics!

Edit: Hmm...I was trying to replicate your setup. But the site I was visiting recommended only a 50% depth of discharge, in order to maximize battery life. Still, I suppose if it was only for occasional emergency use that you discharged the batteries almost completely, I would still think you'd be OK with the 400AH worth.
 
Ingineer said:
EVDrive said:
I'm still interested in adding battery capacity to my leaf. Anyone come up with a viable avenue yet?
I've proven this can be done safely and reliably, but it's not cheap or easy!

-Phil

Is $3500 for a leaf battery not cheap?

I would think if we have matched voltages that wiring directly into the mains would get you where you want to be, just use a contactor to disconnect the secondary battery to charge and suffer with a Jack Rickart style on the backup battery (not ideal) but manually workable.
 
Klutch said:
Here's my 'trick'

No it doesn't charge on the move, BUT if ever I ran it dead out of go juice:
I have a 5kw sine wave inverter in my boot (weighs about 12kg)
I have a 4 Ni-Cad 12v/100Ah batteries in my boot connecting to my 48vdc-240vac inverter
My evse which signals a 20a charge rate

I did make a "leaf plug", 100k ohm resistor from neutral to ground and hot to ground and used it for these test.

I tried this in our garage. I have an old 12v 245amp SLA (8A8D) battery connected to a xantrex prowatt 1.8kw sine wave inverter connected with 0/4 wires. I can run a 1600w heater no problem and see a voltage on the battery of 11.8. When I plug in the stock 120vac nissan evse it sits there for a about 60 seconds, then pop, the inverter trips out.

I tried the same thing with the Honda 2000i inverter genset and it hits hard after that 60 seconds, but does start charging. Much better to start with the genset not in eco mode and switch it there after the charging starts.

Having said this I doubt I will ever use the setup, just trying it out.

So my question is do larger evse not have that hard quick hit that the smaller 120 plug does? Why don't they soft start?
 
Val of EMotorWerks.com (aka valerun) has an interesting project going on over on the RAV4-EV forum. I don't think he'd mind if I linked a couple posts.

Basic theory is that he has an auxillary pack of 109 LiFePO cells (38 kWh worth) wired in parallel with the main pack.

The aux pack is top balanced with BMS and is connected to/from the main pack with a set of high current contactors.

Because the LiFePO pack has a slightly narrower voltage range than the stock pack, when discharging, the aux pack is connected up using the contactors as long as the main pack voltage and aux pack voltages are in the same range.

So the aux pack disconnects after main pack is almost full when charging (or BMS tells it to) and when discharging, it will connect the aux pack after main pack discharges enough, then disconnect once the main pack gets down around 50% SOC.

The beauty (IMO) of this approach IMO is it's simplicity as now you don't have any expensive/complex DC-DC converter to worry about - this was always a weak point in the Enginer add-on solution.

Seems like a very similar approach could be taken with the LEAF, though with a smaller pack/cells.

http://www.myrav4ev.com/forum/viewtopic.php?p=12189#p12189
valerun said:
another fun don't-do-this-at-home RAV4 hack from EMotorWerks - a 38kWHr additional pack in parallel with the main battery. Confirmed no-error operation in all modes. Will see what the onboard computer recalculates as the resulting range ;)

PS. Batteries will be covered, of course ;-)

DSC_0412.jpg

DSC_0415.jpg

http://www.myrav4ev.com/forum/viewtopic.php?p=12461#p12461
valerun said:
Kohler Controller said:
Val, Do you normally charge each pack separately, or did you just do it this time to capture individual pack recharge capacities?
only this time - for that very reason, yes ;-).

We have just built a power distribution unit to manage battery connections - see photo at https://docs.google.com/a/emotorwerks.com/file/d/0B8zi8eqgqJWod05tcEhKSG1DQ0k" onclick="window.open(this.href);return false;.

It will also handle our special battery arrangement for mobile CHAdeMO charger we will be doing a public demo on in ~2 weeks.

http://www.myrav4ev.com/forum/viewtopic.php?p=12475#p12475
valerun said:
Kohler Controller said:
I like that the RAV4EV used the AUX pack more than the main pack during its bulk discharge, thus always leaving the main pack for the bottom end where you need more accurate range estimation. I'm wondering when you bump up the AUX pack to 111 cells, if the packs will start to share more evenly, thus losing this benefit?
this will always happen due to particular shapes of discharge curves for the involved chemistries. AUX pack (LFP) has a much flatter curve relative to the Tesla pack. So almost no matter how many cells you have, you will always fully discharge the AUX before you fully discharge the Vehicle pack. With 108 cells, we have AUX discharging when 50% of the main pack is left. Moving to 111 cells would cause this to happen sooner - say, when 70% of the main pack is left.

PS. We have decided not to go to 111 cells after all. Doing so would result in difficulty to top-balance the AUX pack as no cell would reach the balancing voltage of 3.5V (CV of LFP cells we are using is 3.6V - 111 cells will have combined CV of almost 400V which is too high - we need to match native pack's CV of 382-386V). We will deal with equalizing currents through a PDU (power distribution unit) that I have shown in my previous post - it will connect the AUX pack when main pack voltage falls to AUX level and will disconnect when AUX gets discharged (based on cell-level BMS signal).
 
drees said:
Val of EMotorWerks.com (aka valerun) has an interesting project going on over on the RAV4-EV forum. I don't think he'd mind if I linked a couple posts.

Basic theory is that he has an auxillary pack of 109 LiFePO cells (38 kWh worth) wired in parallel with the main pack.

The aux pack is top balanced with BMS and is connected to/from the main pack with a set of high current contactors.

Thx for linking in! Note that the cells in the photo below are shown before the BMS installation.

We have just had the first real test of this on our ~110-mile trip to Santa Cruz (round-trip), after which the car claimed 70 miles of range remaining (in reality a bit less as only ~27% of the combined capacity was left in the packs; however, this is for a largely 80mph trip so still not bad).

We will conduct a proper 65mph test soon - from zero to depletion of both packs. Just need to design the right itinerary.

Val
 
hmm, we actually have a spare Leaf pack lying around in one of our shops so could do a similar thing to a Leaf. Extra beauty points for using the same battery chemistry so integration is further simplified.

The cells are ~550-600lbs to double the size. This is a bit of weight. Esp for a Leaf. Perhaps one could try something like Enerdels (32AH minimum capacity - hence ~1/2 of the weight for the same voltage). We have a bunch of those in our shop and Richard of Lightning can get us more. Enerdels are NMC cells and are close chemically to what Leaf is using so charging profiles are quite similar. Again, lower integration troubles. If we get a volunteer to help us work on this in either our Mountain View or Redwood City shops, this could be a project...

One can get a 50% range boost for ~$6,000 parts cost (new Enerdels from factory plus some power distribution unit similar to what we designed plus enclosure). ~300lbs. It could be made modular for ease of install / uninstall (in our RAV4 experiment, cells are in groups of 12 to be liftable at ~40kg).

Not sure if this is a viable product, though...
 
valerun said:
Not sure if this is a viable product, though...
I do think that the LEAF market would have to be for something more along the lines of 5-10 kWh - I imagine that it's a bit more price sensitive than the RAV4-EV market - not to mention that weight is more of an issue, too.

Trying to keep total weight added around 100 lbs would be nice - obviously that will limit capacity...
 
drees said:
valerun said:
Not sure if this is a viable product, though...
I do think that the LEAF market would have to be for something more along the lines of 5-10 kWh - I imagine that it's a bit more price sensitive than the RAV4-EV market - not to mention that weight is more of an issue, too.

Trying to keep total weight added around 100 lbs would be nice - obviously that will limit capacity...

don't know - IMO 5kwh has near-zero utility. 100lbs would also be near-impossible with safe type of a battery. This illustrates a problem with battery-based range extension. Seems like a good idea until one actually runs the numbers.

The only reason we are doing it to our RAV is that we will be using it for our roadside assistance pilots demonstrating car-to-car CHAdeMO charging and we need a larger pack.
 
after checking all possible things,i will end up with a fuell cell.they are working on a plug and play solution.
when ordering more items,the price can drop to 8.000.-euro(11.000.-$)

http://www.anleg.de/" onclick="window.open(this.href);return false;
http://www.76937.de/iShop/pc/index.php?route=product/product&path=59_60&product_id=52" onclick="window.open(this.href);return false;

for me it would be the best solution,so i can use the fuel cell in my electric boat,because here in euopr ,gasoline boat engines are not allowed in the most lakes.
 
valerun said:
don't know - IMO 5kwh has near-zero utility. 100lbs would also be near-impossible with safe type of a battery. This illustrates a problem with battery-based range extension. Seems like a good idea until one actually runs the numbers.
What do you think the minimum capacity is in terms of utility? For me, anyway, lots of my day trips run the to 60-80 mile range and that's simply not possible without charging on a 3-year old LEAF unless it's flat and you can drive a constant 45-50 mph at most. Yeah, 5 kWh will be not be too usable, but 10 kWh would be (assuming ~8 kWh usable, good for about 25-30 miles of range).

It seems that with the design you are using, the smarts are pretty much vehicle agnostic. You just need to adjust the battery and perhaps tweak the smart-relay-box according to parameters.
 
xado1 said:
after checking all possible things,i will end up with a fuell cell.they are working on a plug and play solution.
when ordering more items,the price can drop to 8.000.-euro(11.000.-$)

http://www.anleg.de/" onclick="window.open(this.href);return false;
http://www.76937.de/iShop/pc/index.php?route=product/product&path=59_60&product_id=52" onclick="window.open(this.href);return false;

for me it would be the best solution,so i can use the fuel cell in my electric boat,because here in euopr ,gasoline boat engines are not allowed in the most lakes.

interesting. how much capacity do you get for $11K? (the second link gives 'The page cannot be displayed because an internal server error has occurred.' when I try to click it). Also, do you know what the round-trip efficiency is? Fuel cells are notoriously inefficient, with round-trip losses of up to 60%... (i.e. you get less than half of the electricity you put in it)
 
drees said:
valerun said:
don't know - IMO 5kwh has near-zero utility. 100lbs would also be near-impossible with safe type of a battery. This illustrates a problem with battery-based range extension. Seems like a good idea until one actually runs the numbers.
What do you think the minimum capacity is in terms of utility? For me, anyway, lots of my day trips run the to 60-80 mile range and that's simply not possible without charging on a 3-year old LEAF unless it's flat and you can drive a constant 45-50 mph at most. Yeah, 5 kWh will be not be too usable, but 10 kWh would be (assuming ~8 kWh usable, good for about 25-30 miles of range).

It seems that with the design you are using, the smarts are pretty much vehicle agnostic. You just need to adjust the battery and perhaps tweak the smart-relay-box according to parameters.

I think it should be around half of the existing pack or more. That's when you not only have some meaningful range but also get some benefits important for commercial viability of the solution:
* cost of associated hardware is amortized across a bigger pack and becomes a much smaller part of the total system cost. Your $/mile of range improvement goes down quite a bit.
* 50%+ lift in range starts to *feel* serious
* The car with 1.5x+ range of the original starts to become a different type of car - with different, not possible before use cases

For example, 80% range improvement we had with our RAV4EV has allowed us to (1) go on a 110-mile round-trip to visit some business partners, (2) use the car as an energy donor in our car-2-car charging experiments, (3) give the car to our employees and not worry about them running out of range, and of course (4) brag about it being a totally different car now ;-)

Of course, a 40kwhr battery is not cheap so it makes sense only for specialized cases like ours. For mass consumer applications, I would actually develop a hitch-mounted REX unit such as BMW i3's unit (not on the trailer - directly on the hitch - similar to the bike racks). I think that would be a commercially viable product but only with a RENTAL business model.
 
The main challenge to adding a PHEV pack to the original Prius was figuring out a way to trick the Battery controller into using more battery capacity. The Prius battery controller uses a current sensor to measure amps in and out of the pack, and calculates SOC primarily based on current flow integrated over time to get Ah in and out. This is commonly called coulomb counting, and is common in NimH and Li battery systems where voltage is a poor indicator of SOC. It knows how many the Ah the battery can hold, so be counting them as they go in and out, it knows what SOC should be.

If you injected current from the second battery on one side of the current sensor, the battery controller would "count it" as current coming out of the primary pack, and when X Ah had been counted as coming out of the primary pack it would assume min SOC had been reached and start recharging. It assumed a fixed battery pack size, and didn't care that you had added more battery capacity. It would still only use the amount of Ah it expected the original battery to be able to supply.

If you injected current on the other side of the current sensor, the battery controller wouldn't "see" it, and would only count the Ah actually going out of the original pack. So far so good. Unfortunately the HV controller also measures current at the inverter / motor end, and when it saw significantly more amps arriving at that end than the battery said it was putting out, it shut down the HV system assuming a fault had occurred. Not so good.

As a result there were two common approaches to PHEV conversions.
-The budget Enginer approach was to use a dc:dc converter to inject a controlled amount of current on the motor / inverter side of the battery current sensor, keeping it low enough to keep from triggering the fault/shutdown. When not being consumed by the motor / inverter the battery controller would "count" the supplemental current as regen topping up the original battery. The downside to this approach was limited instantaneous power, meaning it couldn't always supply enough current to keep the SOC of the original pack up.
- The more expensive kits generally tapped into the battery side of the current sensor, and required a custom add on controller to either replace the original battery controller, or spoof the right CAN traffic to get the HV controller to use the extra battery capacity.

I would assume the Leaf uses a similar coulomb counting scheme for managing battery SOC, and so could have similar challenges. In general the Leaf's BMS / controller seems quite a bit smarter though, as it seems like it has the ability to adapt to changing capacity over time to account for battery degradation. It would be really interesting to see if this capability extends to revising the capacity of the battery upwards :)

For example, as I understand it the BMS already manages 2 cells in parallel at every leg of the battery stack. What would happen if you simply added a third (or third and fourth) identical cell in parallel (being careful to match them first of course)?

If the Leaf uses simple coulomb counting and a fixed capacity (or is unable to revise capacity upward) on the next charge it would simply put in the right amount of Ah to fill the original pack, and leave the new expanded pack less than full. But if it uses some sort of adaptive technique (maybe particularly on a 100% charge?) that looks for some other markers of charge completion, its possible it might just be smart enough to revise the capacity of the pack up to account for the new cells :)

Maybe it would take multiple charge/discharge cycles to get it all, but that would be really cool!

Rob
 
miscrms said:
For example, as I understand it the BMS already manages 2 cells in parallel at every leg of the battery stack. What would happen if you simply added a third (or third and fourth) identical cell in parallel (being careful to match them first of course)?

That's a great idea.

Thanks.
 
miscrms said:
As a result there were two common approaches to PHEV conversions.
-The budget Enginer approach was to use a dc:dc converter to inject a controlled amount of current on the motor / inverter side of the battery current sensor, keeping it low enough to keep from triggering the fault/shutdown. When not being consumed by the motor / inverter the battery controller would "count" the supplemental current as regen topping up the original battery. The downside to this approach was limited instantaneous power, meaning it couldn't always supply enough current to keep the SOC of the original pack up.
- The more expensive kits generally tapped into the battery side of the current sensor, and required a custom add on controller to either replace the original battery controller, or spoof the right CAN traffic to get the HV controller to use the extra battery capacity.
Rob

I am wondering what aproach did Ingineer (Phil) used with his 30kW propane turbine trailer. I recall that the idea was you could drive and charge at the same time.
 
I think there is a very good chance (95%) that it will fine to parallel a high C rate pack (with Bms and dedicated contactors) with the leaf's pack. The leaf pack will likely be lower impedance than the aux pack, so generally speaking you are safe. Simple cutoff can be implemented.

I don't think it would be dangerous to charge the auxilary in parallel since it has it's own dedicated bms and contactor.

I have 10kW (112S currently, so will take down a little bit) I want to try. I just need help finding the best place to tap. It'll be important to use heavy gauge since it's going to see load from driving.

I don't think that this will fuss with the leaf bms at all.. because the leaf treats having an aux battery as if it's going down hill or you are on the moon. that's the simplest as I can put it. It's not counting energy consumed from both packs.

EDIT: I think a dc-dc charger makes the most sense... like vals
 
Ok I am not an engineer and I might have missed this answer.

Is there possibly a safe way to link auxiliary power to the engine, so that the draw has to come through the auxiliary from the Leaf battery. Drawing power from the battery when there is not enough in the auxiliary power configuration? For example: take a cargo pod on top of the vehicle add 1 flat solar panel to the top of it. This unit is you auxiliary power with limited deep charge and power regulation. Link this into the power draw so that the Leaf pulls from here first and have the Leafs battery as the "back up" to the auxiliary. While it might not charge the Leaf battery it could extend range during lighted times. Perhaps grounding the Auxiliary through the car or even allowing excess charge to go to the 12 volt like in the SL's. I realize that by adding space you are reducing the perceived response time by the computer, but you are not messing with the regenerative monitoring or the battery in any other way. I am unsure how the computer responds to what it might label as a power leak, but I suspect it would respond as if the battery was wearing out and just keep on ticking.

I would really appreciate feedback on this. I am a new owner, but I drive a lot and the charging network in my city is far from adequate.
 
The Leaf monitors the DC power between the battery and the inverter. Only limited power can be injected there before the computer shuts down the whole car.
To use the auxiliary battery first, and bypass the DC sensors you will have to connect between the inverter and the motor. It will require another inverter. Even if you manage to sync them, I am sure that the original inverter will complain about it.

If my be easier to make the auxiliary battery power the rear wheels. you will have an all wheel drive Leaf.

Or just wait for the 60 kw battery.
 
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