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Old 10-18-2021, 11:09 AM   #1
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Using Nissan Leaf as detachable/drivable solar battery pack.

Hello Everyone!


My partner and I are building our bus out of a standard dog-nose international and just got the roof raise done last month, now we're moving onto our systems.



I've been back and forth deciding what kind of battery pack and solar systems I would want to use, as well as if electric would be the only other power source besides the diesel engine or if I would use propane for a stove/rv fridge etc. Ideally, I would like to use only electric for all systems other than actually driving the bus, and to use a solar/battery system for that power.



When researching batteries, and specifically using repurposed Leaf batteries, I began to wonder with its bi-directional charging if anyone has considered just keeping them in the leaf and towing it behind the bus? I know this would hurt fuel economy and would mean more tires to replace, but just to make an Li-ion battery pack of the same kW/h costs about the twice as much as just buying the whole car, and why not have a driver you can take to get groceries or visit people without having to take your whole house with you?


So this is what I'm thinking at the moment. I would have the bus wired up with its own solar/battery system, somewhere between 2.8/3.2 kw worth of panels and a bank of AGM deep cycle batteries, probably 6-8 wired for somewhere between 12v and 48v depending on what will work best once I start getting the system more fleshed out. This bank would essentially a buffer/emergency bank, used for lights and small power draw like keeping the fridge cold when the car isn't connected and it isn't getting power from solar/or being plugged into a grid.



The Leaf's bi-directional charging means that it will allow power back into the system from the car, however, this is made to be used with normal house currents, 120v or 240V AC, and while I plan to have a large inverter for being able to use normal house appliances, the leaf has to have its own inverter to use this function, which is both a waste of energy and expensive.


Essentially, I was wondering if anyone here had enough experience with the Leaf and could help answer the one question that will make such a system worth it to me; Can I use a voltage stepper, CHAdeMO charging setup, or something similar to take charge between the two different battery packs and avoid some DC to AC to DC shenanigans? Supposedly, the level 3 "fast charging" uses direct DC current, so it is made to take large DC amperage for charging and hopefully that applies to the bi-directional ability too. Failing to be able to do that, I may just rewire a pack from a wrecked leaf and throw it under the floor boards like a "normal" person.

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Old 10-18-2021, 11:27 AM   #2
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This doesn't directly address your question about the plan to tow the entire vehicle, but if you haven't seen Juan and Michelle's 3-part video series on using a Nissan Leaf battery pack in their bus it's worth watching:

RV Lithium Battery | Nissan Leaf modules in an RV Lithium Battery Beginning from this Morning
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Old 10-18-2021, 06:02 PM   #3
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I would not use any of the li-ion nominal 3.6-3.7V chemistries for this use case.

LFP only, maybe LTO.

Way too much fire risk

Boom Bad
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Old 10-18-2021, 06:16 PM   #4
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Building your own bank like Juan and Michelle is awesome and was our plan until we came across some skoolies from back east. They'd suffered a direct lightening strike and it fried the electrical system and started a battery fire. Probably just like any high amperage battery system would do in a direct strike situation.
Anyway, because they had a DIY bank they built from cells, the insurance denied their claim and it was a total loss.
So their new build has commercially built batteries and our plan changed to commercially built batteries.


YMMV
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Old 10-19-2021, 11:27 AM   #5
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I think using the whole car is an excellent plan. Especially if you were thinking about needing a small vehicle to get around.. technically you can recharge while driving if you somehow hook the brake / throttle pedal up. In that case free energy if you can sync that with when you need some bus braking.

We toyed with your idea as well since we have several electric vehicles. Did not pull thru because we wanted a 4*4 as toad for exploring..

I would keep the charging simple with your main inverter just supplying the leafs charger.. doubt that you will loose much efficiency..there is a app "leaf spy" that can monitor all functions including cell voltages thru blue tooth., Also tire pressure and so on ...some big advantages. Get some isolated DC DC converters or use the DC DC converter in the car already to keep you bus bank topped up.

Good luck,

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Old 10-19-2021, 06:27 PM   #6
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Originally Posted by joeblack5 View Post
I think using the whole car is an excellent plan. Especially if you were thinking about needing a small vehicle to get around.. technically you can recharge while driving if you somehow hook the brake / throttle pedal up. In that case free energy if you can sync that with when you need some bus braking.

We toyed with your idea as well since we have several electric vehicles. Did not pull thru because we wanted a 4*4 as toad for exploring..

I would keep the charging simple with your main inverter just supplying the leafs charger.. doubt that you will loose much efficiency..there is a app "leaf spy" that can monitor all functions including cell voltages thru blue tooth., Also tire pressure and so on ...some big advantages. Get some isolated DC DC converters or use the DC DC converter in the car already to keep you bus bank topped up.

Good luck,

Johan

Tesla also has a way to act as battery back up for a home during power outages. Same idea and I would think it would apply here. I like the idea of activating the regenerative braking too. Would have the same effect as a Telma retarder but would charge the batteries.



Maybe the Tesla could push the bus too
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Old 10-19-2021, 08:44 PM   #7
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Originally Posted by joeblack5 View Post
I think using the whole car is an excellent plan. Especially if you were thinking about needing a small vehicle to get around.. technically you can recharge while driving if you somehow hook the brake / throttle pedal up. In that case free energy if you can sync that with when you need some bus braking.
I've seen several videos of towing Teslas with other vehicles to recharge the battery, it works remarkably well. Holding the brake does not seem necessary.

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Old 10-19-2021, 10:03 PM   #8
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Interesting video. I am curious what mode the Tesla has to be in so regenerate, and can it be towed in a freewheeling mode? Also as Johan had mentioned for real world use you want it to brake(regen) only when braking is needed, and freewheel all other times. Same goes for the Leaf.
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Old 10-20-2021, 06:10 PM   #9
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First of all, someone above mentioned "free energy". THERE IS NO SUCH THING. It might seem free if you're using regen braking to provide some level of charging when braking but yo had to pay to get that speed in the first place so no, it's not free. It can however be claimed as RECLAIMED energy.
I wouldn't want to recharge a vehicle by towing it as that can't be efficient. Might work but the cost of fuel to overcome the extra drag and the mechanical and electrical inefficiencies in the system would be huge.

Now, as to the concept of using an electric car as the battery for a skoolie.......The below stats are for the 2018 Nissan Leaf.

Type Capacity Time to charge Our recommendation
Regular outlet 2.3 kW 17h00m intended for emergencies only.

EVBox 1-Phase, 16A 3.7 kW 11h00m takes longer to fully charge your car.

EVBox 1-Phase, 32A 7.4 kW 6h00m the best fit for this car!


That's a LOT of power!!!!! 40kWh to be exact. Now where are we going to get that unless we're plugged into the grid....which removes the need to use the EV as a battery.


Of course you only have to put in what you took out but still...... you're going to need a grid tie or a massive solar array bigger than our skoolies are capable of holding.

Can anyone point me to something I'm missing that would make the concept actually useable?

















.
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Old 10-25-2021, 12:25 PM   #10
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Thanks for all the replies, everyone.


The idea is to use the car as a detachable battery pack, essentially towed by a tow bar on the back. If the drive tires are being pulled, that may produce some regenerative breaking for the batters, but the idea is to charge the power with the solar, but the car is only for getting around every once in a while when needed, otherwise it is just acting as a large, self contained battery pack. Far larger than I could ever use in a day even with full electric heat in a normal winter.


I am mostly worried of efficiency with going DC to AC to DC through the panel and conventional batteries on board the bus. Joeblack5 thinks the loss wouldn't be worth worrying about, wondering what everyone's else's thoughts are on it. Ideally I'd like to straight line it from DC to DC with a voltage step up, but I don't have enough knowledge of electric cars to know how hard they have the charge system on lock down. I would imagine it is fairly hard to hack for safety reasons.


Edit: I feel like I need to mention that we're looking at the Leaf because it is one of the very few that offers bi-directional charging right now. There is plans for Tesla, but for a VERY large cost for their specific system and required powerwall.
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Old 10-25-2021, 12:35 PM   #11
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Originally Posted by HamSkoolie View Post
First of all, someone above mentioned "free energy". THERE IS NO SUCH THING. It might seem free if you're using regen braking to provide some level of charging when braking but yo had to pay to get that speed in the first place so no, it's not free. It can however be claimed as RECLAIMED energy.
I wouldn't want to recharge a vehicle by towing it as that can't be efficient. Might work but the cost of fuel to overcome the extra drag and the mechanical and electrical inefficiencies in the system would be huge.

Now, as to the concept of using an electric car as the battery for a skoolie.......The below stats are for the 2018 Nissan Leaf.

Type Capacity Time to charge Our recommendation
Regular outlet 2.3 kW 17h00m intended for emergencies only.

EVBox 1-Phase, 16A 3.7 kW 11h00m takes longer to fully charge your car.

EVBox 1-Phase, 32A 7.4 kW 6h00m the best fit for this car!


That's a LOT of power!!!!! 40kWh to be exact. Now where are we going to get that unless we're plugged into the grid....which removes the need to use the EV as a battery.


Of course you only have to put in what you took out but still...... you're going to need a grid tie or a massive solar array bigger than our skoolies are capable of holding.

Can anyone point me to something I'm missing that would make the concept actually useable?

















.
The idea is the car is going to sit and act like a large battery, and sit behind the bus on a tow bar, topped off on power 95% of the time, at night it would get a small draw depending on what we decide to use, but nothing the solar couldn't top back off the next day. For a vehicle that is only going to be used maybe once a week for short distances, I don't need the phase three for the quick charge, it is just the only charge that is direct DC, the other "phases" using AC 120 and 240v respectively. So I would never expect to get a full wattage, 30 minute charge at any point, it would just be marginally more efficient without the AC-DC phase changes. The panel power would be able to trickle charge this thing more than quickly enough for how often we plan on disconnecting and driving it, regardless of what charge phase we decide to use. And if we're driving it, then the systems (fridge mostly) on bus can be run with a smaller bank of more conventional batters while we're away.
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Old 10-25-2021, 12:40 PM   #12
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I would not use any of the li-ion nominal 3.6-3.7V chemistries for this use case.

LFP only, maybe LTO.

Way too much fire risk

Boom Bad
Oof, good to know. I didn't realize. Looks like they either stay in the insured car behind the bus, or I'm using something safer inside.
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Old 10-25-2021, 12:43 PM   #13
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Building your own bank like Juan and Michelle is awesome and was our plan until we came across some skoolies from back east. They'd suffered a direct lightening strike and it fried the electrical system and started a battery fire. Probably just like any high amperage battery system would do in a direct strike situation.
Anyway, because they had a DIY bank they built from cells, the insurance denied their claim and it was a total loss.
So their new build has commercially built batteries and our plan changed to commercially built batteries.


YMMV
Wow, I hadn't heard that. I'm sorry for them, that is terrible. I had looked at their bus videos and they were the reason I was looking at Leaf batteries too! Hopefully keeping it towed behind in the car they are supposed to come in keeps them safer and the insurance payout available if there is a problem. I may just have to use their charging system running from my DC-AC inverter to charge it to for the same reasons. They find out I hacked in my own style of DC to DC charging for it and I would bet my payout would go "bye bye" if there were a fire.
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Old 10-26-2021, 07:07 PM   #14
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Originally Posted by Topbun View Post
Wow, I hadn't heard that. I'm sorry for them, that is terrible. I had looked at their bus videos and they were the reason I was looking at Leaf batteries too! Hopefully keeping it towed behind in the car they are supposed to come in keeps them safer and the insurance payout available if there is a problem. I may just have to use their charging system running from my DC-AC inverter to charge it to for the same reasons. They find out I hacked in my own style of DC to DC charging for it and I would bet my payout would go "bye bye" if there were a fire.

TO BE CLEAR
It WAS NOT Juan and Michele's skoolie that took the hit.
I thought that was quite clear but the wording of your response made me wonder if you thought it was their rig. IT WAS NOT THEIRS.
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Old 10-29-2021, 03:34 AM   #15
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Gosh this whole concept is pretty intruiging. Several points I would like to adress. In the sailboat world to the many people considering electric drive conversions my advise is to only look at the electric motor as a form of trasmission. Its hard to beat the petrolium battery when it comes to energy storage. So if a boat owner puts electric drive in I beg keep the tanks and at least have a small diesel on board both for ac power, but for emergent dc charging. Now the same advise I would recommend to you. The rolling leaf on a tow dolly is a drivable towable remote bigger than house bank!!! Pretty cool. Of note where my mother lives in southern california (She drives a leaf) there are free charging stations with time limits, so one could get regular topping off when near grids and citys. I have to say that makes them handy cars to drive (so long as you drive from camarillo to LA and plan on two, two hour top off stops. But as I digress having the leaf as a battery bank I would hope you could have a charging capabilityon board bus. For that I would suggest a little kubota 3 banger diesel genset pushing 6 or 7k Not that you want to have to use it (especially listen to it) but would be glad to have it when the need arrives. Carry as much pannels as you can afford both finantially and or space to reduce genset run time to near zero if possible. Dc to ac to dc wow I wish I had good info to give but I dont know how to calculate parasitic losses of transforming vs voltage drop over distance with dc. Again wish to help but that is for smarter folks than me. Lastly the flat towing for regen....ouch it would be cool to be able to control regen braking remotley and this may be possible now or soon with hacks ect. However I would not advise it as the potential to overcharge is high. With my prius it recomends in manual NOT to flat tow as even in nutural it is always charging (or powering) which leads me to beleive it is permanant magnet motor. Please dont take my word for it, seek further advise to verify that point. With my bus the intention is to use above mentioned genset I have already, and plan to mount it up front hanging off front bumperet sharing engine service items with maim engine. Focus on roof raise and insulation and when bargains allow, begin lining roof with panels as I can afford. (Building house bank too) what sucks for me is battery chemistry of prius is wrong for this application, or decidedly more TEMPormental (pun intended) than I want to hassle with. I look forward to seeing this post work to a conclusion. David
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Old 10-29-2021, 11:22 AM   #16
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If you carry a genset there is no point in going to such heroic measures for big Ah storage.

You have energy on demand, both for running big loads, and charging your bank, so it can be a normal size, say 400-800Ah.

Au fond, your average daily input Ah must exceed your average daily consumption

All a bigger bank buys you is more days to spread out that averaging

less frequent but longer duration runtime
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Old 10-29-2021, 06:47 PM   #17
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Describing a battery banks capacity with only an amp hour number is meaningless without the voltage at which those amps are stored and the chemical technology of the bank.



Only WATTS or WATT HOURS can be listed singly and give any indication of the storage capacity of a battery bank.


800 amp hours at 6 volts is a mere 4.8 kWh of which only 2.4 are useable if it's lead acid tech.


At 12 volts its 9.6kWh with half (4. usable with lead acid tech.


At 24 volts it's 9.6 usable kWh with lead acid tech.


Bt regardless of the battery technology WATTS are the unit of work performed by an electrical circuit and should be the unit used to describe capacity unless volts are also given.


I teach this stuff. It's not rocket science. WATTS or Amps AND Volts. Anything else and there is no quantifiable amount of work capacity.
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Old 10-30-2021, 03:07 AM   #18
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Yes nominal voltage must be known as well as amps and Ah.

The problem with using Wh directly for capacity testing is that the Peukert effect makes results **much** more variable depending on the C-rate used.

Ah more directly relate to the actual chemical reactions inside the battery, Wh are affected much more by SoC and C-rate at that instant.

For example a LI battery might have an efficiency well over 99% using Ah but only 80% in one set of conditions, then 70% in others.

So, best to use CC load test, get your Ah capacity (if secondhand % of original also gives you SoH)

and then multiply that Ah number by nominal volts in order to publish a Wh figure.

Then the impact of Peukert's Law is much less a wild card.

Consider V and A as your "realer" foundation variables to measure, power in Watts is just a calculated value derived after the actual measurements.

more details here: https://www.rcgroups.com/forums/show...e#post42495251
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Old 10-30-2021, 03:09 AM   #19
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Of course when discussing a system with energy conversion between different voltages, the Wh are best used for comparisons and simplicity
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Old 11-02-2021, 10:19 AM   #20
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Oh, that's good to hear. I did misunderstand but still a tragedy for the other bus owners.
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