50+kWh of drone batteries

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skr
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50+kWh of drone batteries

Post by skr »

Hi,

I've acquired 500ish 4S drone batteries made by ATL from a drone company I used to work for. Most of them are new, but datecode goes back a few years, so there is some degradation from storage.
They should be rated 6800ish mAh, but are mostly 6000mAh. They are HV, cells are supposed to charge up to 4.35V and there are FPC heaters between the cells. Each pack can safely deliver 15-20A of current. Think of modern DJI drone batteries, but for a different ODM project. My plan is to get rid of the plastic enclosure and current BMS and make modules of 4S10P or 4S20P and then rig them in to something bigger as needed. Do trivial monitoring/balancing with custom pcb per 4S10P pack, which would serve as an internal bus bar as well.

I'm an electrical engineer with (hopefully) enough mechanical engineering skills and I have done ICE engine swaps previously so I am aware on how deep the rabbit hole will go.

I've thought about making a powerwall, but that's no fun. Given that batteries are usually the biggest expenditure (that is after time, of course) for an EV project - at least I have that avenue covered.

My country requires full certified lab tests for UN R100 compliance, which is a bit BS for one off vehicle conversion. A friend of mine is giving me Volvo 740, I was about to go get a lexus transmission, but after clarifying the legal requirements for a road legal ev swap I kind of calmed down a bit. That's tens of thousands of euros for approval documents. Most likely destructive for some sub assemblies (burining the battery with open flame, WTH)...

After studying the regulations and interviewing local companies who have done homolgation for batteries I got an idea.
Apparently R100 only applies for anything above 60V. The local road authority guy who checks all swap projects was a bit hesitant to disclose this, but after nagging him for an hour he kind of said there are no legal requirements if the battery is below 60V. Just a standard engine swap project and maybe some issues with having to prove hydraulic steering and brake vacuum pump functionality at the local race track.

I have no issues making the battery bus bars temporarily in 59.9V configuration, however under this configuration I would have to be able to reach at least 90-100km/h for those race track brake tests, which scares me a bit.

Anything else similarly fun to do with 50+ kWh of batteries?
I tried counting coulombs once
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johu
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Re: 50+kWh of drone batteries

Post by johu »

Sounds cool. Which country do you live in? You can fill it out in your profile and you might get more hints from fellow countrymen about legalities
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skr
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Re: 50+kWh of drone batteries

Post by skr »

I live in Latvia.

No one off EV swaps have been legally done here since 2018 when UN R100 came in power as told by the local road authority.

There's a company doing van conversions, but they did type approval for their batteries in a lab.
There have been discussions for the past 2 years to do a national standard with less strict requirements for one-offs, but not sure when or how it will come in to force.

To me the <60V seems like a nice loop hole to get on the road without shelling tens of k in a lab.
The question is - can I come up with at least 90km/h design without faking the voltage on the pack - do a dc>dc boost circuit for the inverter or run it in field weakening mode. I have no issues with thick bus bars being toasty running at 500+A.

I've had suggestions of just getting the car and swap registered elsewhere, but I kind of would like to get this done here out of spite. :)
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Re: 50+kWh of drone batteries

Post by MattsAwesomeStuff »

skr wrote: Wed Jun 01, 2022 10:23 pmI've had suggestions of just getting the car and swap registered elsewhere, but I kind of would like to get this done here out of spite. :)
Reddit.com/r/MaliciousCompliance

I love it. I love following the rules in unintended ways.

... What about having multiple, 60v packs, that each independently feed into an inverter?

... and inside the inverter, contactors switch them to series? Or, even just hardwired?

This is quite literally how Dewalt gets away with the "50+wh no flights allowed" rules on their ~150wh flexvolt packs. They're 3 strings of 5s that are by default in parallel, and then mechanically switched to series with a plunger to be in series with 60v for the higher voltage tools. The switch is a 6-slider 2 position switch the size of a skinny deck of cards on the whole top of the battery. In shipping, they have a piece of red plastic that the battery clips into (like it's a tool, but it's just a sleeve), that mechanically holds the plunger half way between series and parallel, electrically separating the 3 series strings inside the pack. They then call this 3 individual batteries in the same enclosure.
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Re: 50+kWh of drone batteries

Post by arber333 »

skr wrote: Wed Jun 01, 2022 10:23 pm I live in Latvia.

No one off EV swaps have been legally done here since 2018 when UN R100 came in power as told by the local road authority.

There's a company doing van conversions, but they did type approval for their batteries in a lab.
There have been discussions for the past 2 years to do a national standard with less strict requirements for one-offs, but not sure when or how it will come in to force.

To me the <60V seems like a nice loop hole to get on the road without shelling tens of k in a lab.
The question is - can I come up with at least 90km/h design without faking the voltage on the pack - do a dc>dc boost circuit for the inverter or run it in field weakening mode. I have no issues with thick bus bars being toasty running at 500+A.

I've had suggestions of just getting the car and swap registered elsewhere, but I kind of would like to get this done here out of spite. :)
We have the same problem in Slovenia now... no organization capable (or willing) to make the battery tests for HV system.
I am about the only legal HV conversion for like 4 years now :? and i had to go for TUV in Munchen.

I had thought of converting cars with 60Vdc and i just cant imagine those cars running upwards of 90km/h without transmission which is what i belive in since transmissions add another point of failure to EV simplicity.
Also you need to be aware of couple of things. DCDC converter needs to be >1kW! If you want to use H(E)PAS and servo brakes and have extra power for your lights...

Now split modules... that is a good idea. You are not twisting the law or anything. Simply sidestepping.
Imagine using Outlander or Leaf inverter and building your own "DC cover" for it. That would include a box where you would house several DC contactors which would come online every time you start the car. On top of that each battery box should NOT contain more than 60V, so it would be made of several small boxes or compartments with LV wiring comming out. Of course each should be fused!
That would require more wiring, but essentially you could assemble all voltages in one HV box from where HV would enter inverter directly.
I have just issued approval (aviation inspector) for LAK 17B sailplane with FES electric motor and 2x LiPo battery modules. They make exactly the same game with LV cabling and inox housing.
Hence that could be HV inverter with HV motor of an OEM design which allready is approved for EV use and cen be used according to UN ECE R100 R2.
That way would allow you to sidestep HV battery requirements since that is no HV battery on board.

What would your regulators say to that?
skr
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Re: 50+kWh of drone batteries

Post by skr »

Split modules seem like a good idea, thanks. I'll start with the module design. Disassembling the batteries turns out to be much more labor intensive if we're talking hundreds. With all the PCBs and enclosures I am looking at 50-55kwh @ 280-300kg, which is not bad. I am not yet sure what to do regarding the cooling aspect, but I am certain I want to be drive the heater circuit to be able to use the battery nicely in the cold climate as well.
I have thought about reusing the ATL designed BMS and I even have the docs for it, but it is a bit glitchy in some aspects. Also muxing that I2S to turn them all on at the same time would be a bit of a pain in the ass. Rewriting the firmware would be the most fitting, but given the fact that removal of the enclosure leaves the BMS board dangling I've decided of making bigger modules out of those individual drone packs and just scrap the current 4S BMS. I'll refrain from posting pics until the packs are disassembled and contain no identifying marks.
I tried counting coulombs once
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