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

Wed Oct 26, 2011 7:31 pm

I didn't read the Limo thread; I don't have much interest in one. Interesting on the battery issue, though. The Prius kits use the same cascade down concept that I'm proposing... that's where I got the idea from. The extra battery feeds the other.

The Limo guys are using two LEAF batteries, correct? I wonder if their setup is cascaded down, or more logically for their setup, two parallel batteries, with some switching to feed from one or the other.

Yes, the LEAF BMS would regulate the battery, just as it does now. Please enlighten me as to how the battery would know that 400 volts DC is coming from a battery in the trunk, or a ChaDeMo DC charger at 400 volts? Do you think the BMS stops working because it is receiving 400 volts?

The extra battery would have it's own BMS and charger.

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

Wed Oct 26, 2011 8:12 pm

TonyWilliams wrote:<snip>The extra battery would have it's own BMS and charger.
Ah, that would work as long as you could convince the LEAF to move while charging. I don't know what
that might take.
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mitch672
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Wed Oct 26, 2011 9:10 pm

There is at least 1 company that makes Prius PHEV kits working on this now, they are supposed to have some announcements early next year.. I can't say more than this for now, just know that its being worked on, and the head of the company I am talking about also owns a Leaf.
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TonyWilliams
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Wed Oct 26, 2011 9:14 pm

mitch672 wrote: the head of the company I am talking about also owns a Leaf.
He's going to have two soon!

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

Wed Oct 26, 2011 9:20 pm

highcountryrider wrote:
TonyWilliams wrote:<snip>The extra battery would have it's own BMS and charger.
Ah, that would work as long as you could convince the LEAF to move while charging. I don't know what
that might take.
Neither do I. But I'm convinced that this is the model I'll end up with.

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

Wed Oct 26, 2011 11:08 pm

I'd think the same interface would work for either a battery trailer
or an additional on board battery. :)
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LakeLeaf
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Thu Oct 27, 2011 12:52 am

TonyWilliams wrote:The Prius kits use the same cascade down concept that I'm proposing... that's where I got the idea from. The extra battery feeds the other.
This sounds like the Enginer kit. Seems like a very logical way to add battery capacity. One big question I would have is the efficiency of the battery to battery energy transfer. How well would that work?- especially since your energy draw is pretty large. Is there a safety that prevents you from drawing power off the pack and "charging" (or transferring power to it) at the same time?

$600/cell for additional cells?

Your add on pack would have to do it's own battery management.

If you stick them in the trunk - might need some active air flow too.

Seems like an "easier" way to start would be buying the pack from Enginer and hacking in the ChaDeMo connector. They might even help you with the process. I've written to them in the past, and they were quite happy to talk.

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

Thu Oct 27, 2011 7:21 am

I had this idea a while ago and gave it some thought.
For anyone who is interested in this, I encourage to take a good look at the service manual available online. (search the forums if you can't find it, I think a legit copy is only 20$)

Anyways, I think it should be possible to work by placing a similar voltage pack in parallel with some considerations.
There is a service cut-off switch under a panel on the floor. This disables the Leaf-pack by breaking the connection MID-PACK.
If you were to have another pack in parallel, you would have to have another service cut off switch in the same spot as the OEM one.

A DC-DC converter should not be necessary if you have the right kind of cells, the only time there would be a huge current draw is when you are connecting cells parallel to a live pack and they are not voltage matched (this would be a stupid thing to do)
As the cells drain, the CURRENT draw will shift from one pack to the other depending on which has a higher nominal voltage. (apparent voltage will be the same when they are connected in parallel)

the other issue is the aux pack would have to dis-able itself when it is drained, but then you would also have to re-enable it at the right time when charging. You would have to know EXACTLY the behavior of the Leaf pack voltage under all conditions; Driving, charging (3 levels = 3 different voltages), and what that charge curve looks like. I would use LiFEPO (lithium Iron Phosphate) batteries, these do not have a thermal run-away and do not require cooling. (they work better when warm). but you have to make sure not to over charge or over discharge, but I would have to know the maximum voltage limits of the leaf pack charge curve (probably highest with chademo charging)

I'm sure there will be an Ingineer type product out in a year or two, the answer as to why it isn't out now should be painfully obvious, it is WAY TOO EARLY. How long did it take to develop the plug-in pack for the Prius?
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garygid
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Thu Oct 27, 2011 8:24 am

The LEAF has a fairly complex, somewhat fragmented control system, along with a rather isolated Battery Pack and BMS.

Adding a Booster-Pack will not be easy, I believe. But, we will continue to struggle to understand the LEAF's inner workings (and interlocks).
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Re: Extra Battery, How to Integrate with 24kWh Traction Batt

Thu Oct 27, 2011 8:44 am

TonyWilliams wrote:Please enlighten me as to how the battery would know that 400 volts DC is coming from a battery in the trunk, or a ChaDeMo DC charger at 400 volts? Do you think the BMS stops working because it is receiving 400 volts?
I am not an expert but it was my understanding that ChaDeMo has communications protocols built in just like the J1772 system that regulate the power transfer. You would have to work within that system which means the car would be telling your battery when to supply power, hence it would act like a charger when the vehicle is stopped. For runtime parallel battery operation (charge on the go) I think you would have to bypass a number of safety systems. For one, the car won't move if it thinks something is connected to it. In other words the ChaDeMo may be a more direct connection to the main battery but it is more than just a wire going to the terminals.
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