Combining outputs of batteries through inverters, converters, or chargers

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CaliMountains
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Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

Not sure where to ask this.
Nissan Leaf gen1 battery packs purchased as cores are my cheapest choice; which I conclude by asking all my cheapest local wrecking yards. They will sell me any that don't work as a core, $500 for early Nissan 24kWh and they have not yet seen newer ones, or any random small hybrid battery. Therefore I plan to use 96 gen1 Leaf modules, paralleled at the module, using a stock BMS. However, that has a safety limit of about 160kW (two 24kWh packs), and will last longer if never pushed.

The idea:
Add a high power density plug in hybrid battery, rated as high as possible, and combine its output with a programmed amount of power from the Leaf modules. The best battery I've found so far is a 2017 Toyota Prius Prime 8.7kWh lithium ion battery, as Weber rebuilds on a video. Yet I can't find how much current it can safely produce. That battery is $1500 for a good one on ebay, so it is a fine starting point. Know any better choices for under $1500?

Easy way:
Use the Toyota battery as the main battery, with the Leaf battery wired to only charge the Toyota. That limits the car to whatever that puts out.

Hard way:
Combine the outputs of both batteries to drive the wheels. Orion's 17 page pamphlet may be nonsense. However, I would like to implement either of the dia...ah... drawings on page 17. One combines DC converters (each would have to be 100kW), and the other combines AC bus...es... but doesn't show three wires. It is not a wiring diagram. https://www.orionbms.com/manuals/pdf/pa ... trings.pdf

Questions:

Can openinverter drive two inverters at the same time, maybe given some code changes?

Can two inverters drive the same motor?

If so, can those inverters be hooked to different battery packs?

If all true, then someone could use two random batteries with one motor (like me), or one battery with two motors, or why not three of each?

What do you think of this idea?
DougEV
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by DougEV »

Just an idea from someone with no claimed knowledge.

If pack A has an useable volts output range of say 350 to 400v and has its own charging and BMS (protection and balancing) controlling its output contactor then through a power diode to a central junction. Pack B has the above but 330 to 380 range. Pack C a similar overlap. All packs individually controlled and protected with contactor and power diode to the central point.

Then none of the packs would be charged by the other due to the diodes, but all could contribute to the current to the inverter (s). As pack A sags due to current draw or reduced SOC the other packs will contribute.

However if one pack drops below it's low volt protection then it will disconnect leaving the other packs to serve from less capacity. So I guess at this point there would have to be careful management of power 'to get you home'. Maybe best if all packs have similar output volts ranges.

Comments most welcome on this !
CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

@DougEV Interesting idea and I wish it would work with discrete components, but all kinds of problems occur. Or so I'm led to believe.

By isolating the batteries and sharing only the outputs of inverters, converters, or other devices; each battery pack can have any properties: voltage, max rate of discharge, and min and max voltage for the pack or by the cell. They won't cause any current loops, leaks, or mismatches because they are completely isolated, ie are not even aware of each other. But the problem is, I do not know if inverter outputs can be ganged onto one motor or with a circuit to allow them both to run the same motor. Thus this thread.

The VCU would have to tell each inverter (or charger, converter, or other thingamabob) how much to supply, and that would need to be tuned for each installation. That's "just" a bit more code, right Mr Huebner? :) I'd love to help, but haven't coded in over 20 years. Maybe I can help down the line with debugging or testing.

What combination of current hardware or changes would make this possible?

To give a concrete example:
Any medium/large AWD vehicle, BMW X5 for Damien, VW or Audi for Johannes, a big truck or van, or a vehicle with a trailer, with a huge space allotted to batteries, Toyota/Lexus P310 (Highlander) driving half-shafts up front, L110 (RX450h transmission) driving the rear differential. Conservatively 600kW(?) but limited by the battery supply. 192 Nissan Leaf modules (four packs) for example is 1536lbs in just modules, powering only 360kW continuous, but only allow 300kW to save the batteries. The Toyota pack would need to deliver another 300kW power combined with the Leaf 300kW, for the several seconds one might drive full power; then recover for the next time you stomp on the gas hard. Or dial the Leaf pack down to 250kW and use the (Toyota?) battery for 350kW for short periods. Or combine yet more battery packs. The range for four aged Leaf packs (actually the best modules of 8 core packs) may be only 80kWh. Instead of the average EV efficiency rate of 3 miles per kwh (EV West wrote that to me once), call it 1 mile per kwh for 80 miles of spirited driving or towing. But you can drive the motor hard every day. There's a valid (okay, matter of opinion) use of that much power, and reason to pack a bunch of cheap batteries, with a strong battery up front; and need to combine the outputs. Hopefully that covers "why?"
CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

Here is one clean solution:
Single custom pack with used but selected good Leaf modules, three modules paralleled at the cell, using the Leaf BMS. That's 144 modules in one pack, about 60kWh, up to 240kW max. Tune down to 200kW max to not cook batteries. That's 1152lbs/523kg in just modules.

Most weight efficient:

The fastest land race EV in the world at the moment uses 2018-2022 Honda Insight modules because of their power density, they are Panasonic NMC with a high weight density. But relatively few are needed. There's an ebay ad from a new seller for $650 for 50 brand new modules, which works out to 1kWh, actual power output unknown to seller. I hesitate to post it, because it's the only such ad. Search "Honda Insight battery module race car" and tell me what model of modules those are? Can they be purchased new from a Panasonic distributor? There are no used ones that I can find.

A custom pack made of 50 or 100 of those new modules if the ad is legit, or 60 from a Honda, but I found none for sale, plus the instructions to safely combine outputs through inverters/converters/magic-black-boxes, it would be a cheap power increase for any diy EV!

Battery discussion starts at 9:40

CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

There's another possible way to wire this:

Could Toyota DC boost converters be used? The reason is for the complete isolation of the batteries through any available circuit. Toyota DC boost converters look like they can handle the load. Can they? That they raise the voltage might be considered a bonus.
Could this be wired use one converter for each battery/motor combination? I'm explaining by example, as it would be hard to fill it with question marks. Would the following work?

For two batteries A and B, and one motor X, boost converters needed are AX, BX.
AX and BX would share one DC bus cap and drive one inverter channel.
Takes two DC boost converters, and one inverter channel.

For batteries A and B, and motors X and Y, boost converters needed are AX, AY, BX, BY.
AX and BX would share a DC bus cap and drive one inverter channel.
AY and BY would share another DC bus and drive another inverter channel.
Takes four DC boost converters, and two inverter channels.

Edit: What other device could be used, if not converters, maybe old school magnetic transformers? 2:1 transformers are pretty common... how large would they have to be?

What about using inverters with rectified outputs as "DC Converters" to drive the normal inverters?

This could extend to more batteries or more motors.

Would this shared DC bus approach work?
CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

I found a solution using batteries and supercapacitors, but can only read the abstract:

https://ieeexplore.ieee.org/document/9432946

Any ieee members on here able to share with lay folks whether a battery and supercapacitors can be combined inexpensively enough?
Whether the ideas explained in this article can be implemented with one normal battery pack and one smaller NMC pack like the Honda modules mentioned above?
What components would be used to combine them?
That solution can be expanded to several use cases.
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by arber333 »

I remember from my Mazda days i was reading about this guy:
http://www.metricmind.com/ac_honda/main2.htm

He used siemens motor, but batteries were not yet C capable (no pun) so he found a lot of Maxwell caps...
CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

When he planned his Honda re-rebuild in September 2003, the 160 capacitors would cost him $4800 on a liquidation sale. I don't know if he built it. Maxwell has changed their products in 19 years. But now the prices have dropped dramatically, brand new cost is $9 each in quantity, such as this:

https://www.mouser.com/ProductDetail/Ma ... XMRg%3D%3D

https://maxwell.com/products/ultracapacitors/cells/

If that is the model to use, and I doubt I quickly picked the right one, it would only cost $1000 brand new for 350v of caps, if it holds at least... 10(?) seconds charge...

Anyone up to calculating how many of which new design Maxwell caps to use?
Anyone able to read the full ieee article (posted above from 2021) and give a useful synopsis of how to get the job done?
CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

Damien, Sir, Jack, Mr Bauer...
If I have to, I'll mail you a new hacksaw blade, but I can't afford private consultation for this.

You often say you don't like to repeat yourself and to go back and check previous videos. I have, extensively. I finally found maybe your only reference to this subject, and it is your current project!

Your current project, the E39 you just put in the L110 transmission, has a 24kWh Leaf pack and a 9kWh BMW 740e hybrid pack; just paralleled together. Yet the only previous references on this forum to two packs say "Don't Do It" because of a 17 page pdf by a manufacturer.
mentioned both batteries:

(2:45-3:00)
Then at 3:00 you say "We are not here to talk about batteries."

Yesterday:

(no mention, but unless you changed it, it still has the two packs)

Is this be a good place to talk about batteries? How well does that work, and how is it hooked up? What would you do differently?
If using exactly that pair of batteries, what would you suggest as to how to do it? If problems, what problems? If you "just hooked it up" and it works, then please say so.

I think a lot of people could use this trick to get their sometimes dangerously slow DIY car up to just normal. That's safety. Of course 'we always want more' and I'd like to have a Leaf battery based car go 0-60 in under 6 seconds, and to last over 60 miles with spirited driving. Seems two Leaf packs paralleled at the module with a Leaf BMS, and a second 'hybrid' battery will give both the power and range. But I've read that 'eddie currents' and other problems occur, or is that just the poorly written 17 page pamphlet by Orion?
CaliMountains
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by CaliMountains »

If no solution, what about this workaround? Switch between two modes:
1. Power the inverter with a Leaf or other weak battery pack, while charging the small NMC battery. (normal mode)
2. On high demand, power the inverter from the NMC battery alone until it discharges a given amount, and go back to mode 1.

For traffic, ten seconds would be plenty of usable capacity, with a recovery time of two minutes (these numbers were pulled directly from an unnamed orifice). Such a fast recovery time means it requires more NMC cells, but I don't know the math to size it. Maybe 5kWh of the example Panasonic/Honda NMC to get these short bursts of maybe 200kW with a fast recovery??? How would that be calculated?

What would that take?
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Re: Combining outputs of batteries through inverters, converters, or chargers

Post by johu »

Sorry to be blunt but it rings my "overthinking" bell. Even one Leaf pack won't make a car "dangerously slow". Two Leaf packs paralleled on a cell level will give you those 200 kW safely. Job done.

If, for whatever reason, you really want to throw another battery in there then charge it to the same voltage and throw it in there. No relays, diodes, or other "intelligence" needed.
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