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

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TonyWilliams

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Joined
Feb 19, 2011
Messages
10,107
Location
Vista, California USA
What would be the best way to connect an additional battery pack to the existing main battery? Would hacking the ChaDeMo connection be the most logical access to feed DC power?

If I put a 12kWh pack together, with it's own BMS and charger, can each cell just be in series, thereby matching the 393.5v / 4.1v per cell? Is there a more advantageous voltage?
 
Don't use the CHAdeMO connector. Just tap into the big wires coming out of the traction battery. The motor only cares about voltage, and I think that goes for all the other electronics too, so if you pile up enough batteries to get to 403 volts, it should work fine. Since I don't know what I'm talking about, let me know if it works, 'cause if it does I'm gonna do it too.
 
MAJOR CAUTION WARNING

The LEAF's Battery Management System (BMS) might have enough checks to make the integration difficult or even impossible. It might think that it has a HV "leak", or ... ???.

However, even if the BMS does not object, and the car appears to work:

1. The normal cell-pair equalization process might be compromized.

2. The Low-Cell detection (to stop driving) would not include the "booster" Pack, possibly damaging cells there.

3. The High-cell detection (to stop Charging or Regen) would not protect the "booster" pack, possibly damaging cells there.

4. Connecting a 400v "booster" Pack to a half-depleated (perhaps 350v) main Pack would generally cause HUGE CURRENTS unless there was a DC-to-DC converter to act as a "charger" between the two battery packs.

No, in my opinion, there is NOT an easy, safe way to "toss in" a parallel "booster" Pack.

One might be able to "charge" 10A or so into the partially-depleated Main Pack, but the car control COULD object to something as simple as finding current flowing INTO the Traction Pack when driving and NOT doing Regen.

CAUTION:
Experinents by untrained persons can destroy the LEAF, cause a fire or explosion, or even injure or kill a person.
 
I'm really surprised that none of the companies that make kits to extend the EV rage for Prii have made a kit for the Leaf yet. Is a Leaf system more complicated than a hybrid? I would think it would be simpler? I really think that if people will pay 5-10k to extend the EV range of their hybrid, others would certainly pay the same to extend the range of there EV. Has anyone even tried? Completely agree with garygid, it should definitely be a trained individual/company who attempts this, but please someone try!!!!
 
I'll try not to stick my finger in the high voltage bits :)

So, how about if the car were stopped, turned off, and the booster battery was connected through the two high voltage cables used for the ChaDeMo connector, and the booster battery pack never exceeded 393.5 volts, can you foresee a problem with that?

Obviously, a three way switch to the battery, selecting ChaDeMo or booster battery. Now, with that simple addition, I can't imagine that the car would think anything but that it's being charged.

Having said that, obviously it's to our advantage to know the protocols and safety features of the ChaDeMo that may inhibit or regulate charging.
 
charlestonleafer said:
I really think that if people will pay 5-10k to extend the EV range of their hybrid, others would certainly pay the same to extend the range of there EV. Has anyone even tried?

I saw a 12kWh lithium manganese battery pack in a brand new Prius; very small package, 40 mile no-gas range. That's what I want in my LEAF.
 
Or what if you kept the batteries completely separate and just made a switch between the 2 packs. Almost like having the 2nd as a "reserve". If it were switched right after the batteries, before it got to any electronics, it seems like it could work?
 
You may have missed it in the LEAF Limo thread, but I asked the folks from Liberty Electric if they'd give consideration to marketing the extender pack they're developing for the limo, if aftermarket demand was sufficient and any technical limitations could be overcome. They seemed quite willing to consider the possibility.
 
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.
 
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.
 
TonyWilliams said:
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.
 
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?
 
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).
 
TonyWilliams said:
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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