Klutch
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Thu Jan 09, 2014 4:03 am

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.

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mwalsh
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Thu Jan 09, 2014 5:56 am

^ 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.
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rmay635703
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Wed Jan 15, 2014 6:00 pm

Ingineer wrote:
EVDrive wrote: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.

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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Mon Mar 31, 2014 7:05 am

Klutch wrote: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?
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Nubo
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Mon Mar 31, 2014 8:59 am

Klutch wrote:12v/100Ah NiCD batteries ...


Where does one find such beasts?
I noticed you're still working with polymers.

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drees
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Mon Mar 31, 2014 9:41 am

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 wrote: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 ;-)

Image
Image


http://www.myrav4ev.com/forum/viewtopic.php?p=12461#p12461
valerun wrote:
Kohler Controller wrote: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.c ... EhKSG1DQ0k.

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 wrote:
Kohler Controller wrote: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).
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valerun
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Mon Mar 31, 2014 11:40 am

drees wrote: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
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Mon Mar 31, 2014 11:53 am

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...
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drees
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Mon Mar 31, 2014 11:39 pm

valerun wrote: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...
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valerun
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Thu Apr 03, 2014 12:43 am

drees wrote:
valerun wrote: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.
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