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Discussion Starter #1
Hi,


Since hydrogen fuell stations are becoming more available the next upcoming years I'm looking for some info or links on DIY fuellcell conversions.
I'd like to experiment on adding a fuelcell to an existing EV to extend the range.


What parts would it take, where to buy them, what power to expect etc.


Regards,


Paul
 

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I don't think you'll find much information about DIY fuel cell conversions, since it is far too expensive for ordinary people without massive corporate or government funding.

Parts: a complete fuel cell system - hydrogen tanks, plumbing, fuel cell with air blower etc, and control system
Where to buy: nowhere... or buy a wrecked fuel cell car and salvage parts
What power: as much as you are willing to buy and carry; the Toyota Mirai has a 114 kW fuel cell system

I have no idea where you would put all of this is in an existing EV not designed to accommodate it. It would be easier to start with a hybrid and replace the engine and supporting equipment (fuel tank, exhaust system, etc) with the fuel cell system... but even then it would be difficult to fit in a hydrogen tank of a useful size.

Prototype heavy trucks resort to a big cabinet - the height and width of the cab - mounted behind the cab to accommodate the bulk of the tanks and cells. Of course that's not an option for a car.

Decades ago there was a guy who built a fuel cell powered van (the van interior was handy because it provided lots of space for the fuel cell stacks), and he ended up installing a row of hydrogen cylinders on the roof. Scary, but it worked... and recent hydrogen fuel cell buses still put the fuel on the roof. GM made their Electrovan test vehicle in 1966, and just put huge cylinders inside the van for the liquid hydrogen and liquid oxygen that it used. With newer fuel cells (using air and compressed hydrogen) and composite fuel tanks the situation is better, but still a problem.
 

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Certainly starting with a fuel cell / battery plug-in hybrid and experimenting with it would be easier than actually converting an EV to fuel cell operation. Even replicating the Think design (starting from a regular battery Think) would be easier than modifying an arbitrarily chosen battery-only EV design.

I think the failure of the Think line - including the fuel cell prototype - provides an indication of the cost and impracticality of building them. The battery-dominant series hybrid design (popularly called a "range extender" configuration by people who don't understand that a series hybrid is) does make the whole thing more practical by minimizing the size of the fuel cell stack needed. You could ask Hydrogenics what the fuel cell unit would cost, but be ready for a shocking answer; they have a 10 kW unit intended to mount in a computer equipment rack for backup power.
 

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Discussion Starter #5
I have looked into several system setups and to keep it 'portable' I have found that i need (at least):


1 - hydrogen container/cylinder + pressure regulator

2 - FC/fuelcell stack providing DC power, for example 500W or 1000W

3 - something to connect/convert the FC DC output top the EV chargers AC input: DC/AC inverter ?

4: control logic
5: tubing

Hyundai and Toyota are using a 5.6kg/70MPa cylinder which according to them should be capable of 600km range. I cant find anything about the size and weight of that thing.


My plan at first is to have this setup run when in parking mode using the onboard charger to slowly 'refill' the battery. With a 500W unit it should charge about 10kW per 24hours/overnight when parked.
 

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3 - something to connect/convert the FC DC output top the EV chargers AC input: DC/AC inverter ?
An inverter plus the usual onboard AC-to-DC charger - both with voltage conversion steps - would work but of course would be less than ideally efficient.

The fuel cell is an inherently DC device, so charging a battery from it is a DC-to-DC conversion challenge. One straightforward solution is to use a DC-to-DC converter like those used to convert high battery voltage to 12V for vehicle accessories - some are bidirectional.

Toyota's solution is more straightforward: use a "tall" enough fuel cell stack (370 cells in series) to match the voltage of the battery. The Mirai stack runs about the same voltage as the Prius (and other Toyota hybrids), allowing them to use batteries and electronics from their production hybrids. The Prius voltage is lower than typical modern EVs, and Toyota uses a voltage booster between the battery and the inverter. If those very small fuel cell stacks can be run in series, matching their operating voltage to the battery would be feasible and would eliminate inverters and converters.
 

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Hyundai and Toyota are using a 5.6kg/70MPa cylinder which according to them should be capable of 600km range. I cant find anything about the size and weight of that thing.
Toyota's cylinders (two of them for that total of 5 kg of hydrogen capacity) are shown in various illustrations of the Mirai. The length of the forward cylinder is as long as they can fit in the car (allowing lots of space on each end presumably for safety), and the diameter is as large as they can get under the raised rear seat. The rear cylinder is much larger in diameter but shorter to fit between the rear wheel wells in what should be trunk space.

You could work out the cylinder volume if you knew the density of hydrogen at the storage pressure... but you don't need to, because there are published specs:
  • Total internal volume (l) 122.4 (60 front, 62.4 rear)
  • Hydrogen storage mass (kg) Approx. 5.0
  • Combined tank weight (kg, not including valve) 87.5

So I'm guessing roughly 25 cm diameter and 1.2 metre long for the cylinder under the rear seat and about 35 cm diameter and 70 cm long for the one in the rear.

87.5 kg of carbon fibre and polymer is a substantial pair of cylinders, but metal tanks would be much heavier. The mass of the hydrogen is trivial compared to the mass of the tanks containing it.

The capacity and range claimed by Toyota in that spec sheet are only 5 kg and 500 km, not 5.6 kg and 600 km. This two-ton mid-sized vehicle which has little trunk and only four seats is no more fuel-efficient than the cheapest gasoline-fueled car that the same manufacturer sells. The spec sheet for the Mirai is both an impressive demonstration of fuel cell output and a strong argument against fuel cell cars.

The attached illustration of the Mirai from Toyota shows both cylinders in yellow (plus the battery over the rear axle and the fuel cell stack under the front seat). If you could find a spec for the diameter of the rear brake disks you could use it for scale.
 

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My plan at first is to have this setup run when in parking mode using the onboard charger to slowly 'refill' the battery. With a 500W unit it should charge about 10kW per 24hours/overnight when parked.
That would be 10 kWh per 24 hours, or half that overnight.

I understand that operation while parked allows a smaller fuel cell stack, but I don't understand the purpose of overnight charging from hydrogen. If the vehicle is parked where electrical power is available, it would make vastly more sense to simply charge the battery from that source, rather than have someone inefficiently use electricity to produce hydrogen, then expensively transport and store the hydrogen, then inefficiently convert the energy in the hydrogen back to electricity. Is the idea to enable longer-distance travel by carrying all of the required energy as hydrogen, and using long parked times (in locations with no electrical power available) to let the fuel cell catch up? This seems like the worst-of-all-worlds scenario in which you need a large battery (more than 10 kWh) and a large hydrogen tank.
 

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I had not looked into the Hyundai fuel cell vehicles before, but I just did a quick search. One article says that the 2019 NEXO has "a range of slightly more than 600 kilometres on the highway" and "three 52.2-litre hydrogen tanks" (presumably meaning three identical cylinders or 52.2 L each). The Wikipedia article says that's 6.4 kg of hydrogen. This is a derivative of a "crossover" body style and looks like a taller vehicle than Toyota's Mirai, and it's slightly heavier, so it probably has higher aero drag and higher fuel consumption.

One of the three cylinders in the earlier ix35 (also a crossover - the Tucson) looks a lot like the rear cylinder in a Mirai, judging from a photo from an article. The photo just shows the bulge in the vehicle's floor, but I'm sure it is closely formed to the cylinder under it. Other articles confirm that this Hyundai has essentially the same cylinder configuration (two differently proportioned, fat one behind the axle) as the Mirai.

Everything available about the NEXO should be available in the Hyundai press kit, but that turns out to be almost entirely fluff. A photo from a CNet article shows the three identical cylinders under the floor and a GreenMotor article shows their relationship to other parts of the car in a cutaway.
 

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Hydrogen onboard OEM fuelcell EVs is stored at about 10,000 psig.

As a chemical engineer who has designed and operated high pressure hydrogen equipment for about 30 years, I strongly suggest that any DIY thinking about messing with hydrogen in their own vehicle, or attempting to re-fill their own DIY vehicle at a commercial H2 refilling station, back slowly away and find something else to do.
 

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In a small (Th!nk-sized) project vehicle, I assume that just one cylinder from either of these production fuel cell vehicles would potentially be a usable hydrogen store, carrying 2.1 to 2.8 kilograms of hydrogen. On the other hand, it would be hard to fit either one in and I can't imagine what it would cost to buy one, even if one shows up in salvage. Can you legally carry hydrogen at 70 MPa in a salvaged cylinder? As Moltenmetal suggests, it is probably not a good idea to try.
 

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Although hydrogen-fueled vehicles get all of the attention among fuel cell vehicles (for some very good reasons and some which are bogus), there are also fuel cells for natural gas (direct-reforming systems) and for methanol. A methanol fuel cell system could be used for a DIY project (particularly in this configuration which assumes a very low-power fuel cell stack), avoiding all issues of handling hydrogen. Of course you need methanol and no one sells that at fuel stations, but there are nearly no hydrogen stations, either. EFOY is probably the best-known supplier of methanol fuel cell systems for retail purchase.
 

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Discussion Starter #13
I understand that operation while parked allows a smaller fuel cell stack, but I don't understand the purpose of overnight charging from hydrogen. If the vehicle is parked where electrical power is available, it would make vastly more sense to simply charge the battery from that source, rather than have someone inefficiently use electricity to produce hydrogen, then expensively transport and store the hydrogen, then inefficiently convert the energy in the hydrogen back to electricity. Is the idea to enable longer-distance travel by carrying all of the required energy as hydrogen, and using long parked times (in locations with no electrical power available) to let the fuel cell catch up? This seems like the worst-of-all-worlds scenario in which you need a large battery (more than 10 kWh) and a large hydrogen tank.

I'm thinking of using the hydrogen system as an add-on. In my case I can find a public EVSE to charge but sometimes not. White more and more EV's sold everyday the use of available public EVSE becomes a problem. I dont mind leaving the EV getting its charge overnight or during daytime when parked because it is (almost) always parked for 8 - 24 hours.
 

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Discussion Starter #14
In a small (Th!nk-sized) project vehicle, I assume that just one cylinder from either of these production fuel cell vehicles would potentially be a usable hydrogen store, carrying 2.1 to 2.8 kilograms of hydrogen. On the other hand, it would be hard to fit either one in and I can't imagine what it would cost to buy one, even if one shows up in salvage. Can you legally carry hydrogen at 70 MPa in a salvaged cylinder? As Moltenmetal suggests, it is probably not a good idea to try.

Using the Th!nk is one idea just because i have a few of these available to try. On the otherhand using a bigger vehicle to carry the 'system' (like Land Rover Defender size) is also an option. There's allready a modified and road legal Tesla (called the Hesla) as proof of concept here in The Netherlands.



At this time hydrogen gas stations are work in progress and still limited to 2 or 3 but things are going to change. If you look at the near future where our local Tata Steel factory has confirmed building their own hydrogen 'factory' in 2019-2020 things might change very rapidly.
 

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Discussion Starter #15
An inverter plus the usual onboard AC-to-DC charger - both with voltage conversion steps - would work but of course would be less than ideally efficient.

The fuel cell is an inherently DC device, so charging a battery from it is a DC-to-DC conversion challenge. One straightforward solution is to use a DC-to-DC converter like those used to convert high battery voltage to 12V for vehicle accessories - some are bidirectional.

Toyota's solution is more straightforward: use a "tall" enough fuel cell stack (370 cells in series) to match the voltage of the battery. The Mirai stack runs about the same voltage as the Prius (and other Toyota hybrids), allowing them to use batteries and electronics from their production hybrids. The Prius voltage is lower than typical modern EVs, and Toyota uses a voltage booster between the battery and the inverter. If those very small fuel cell stacks can be run in series, matching their operating voltage to the battery would be feasible and would eliminate inverters and converters.

The fuel cell systems from Ballard and Hydrogenic have a 60V DC output.
I'm not sure what the minimum input voltage is of the Tesla charger but that might be an option to use as 'converter' or charger between the FC output and the higher battery voltage. Not sure if it would work by putting two smaller 5kW FC systems in series and connect their DC output as input to the Tesla 10kW charger.
 

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Depending on your computer and its browser, Kevin's post may show as just a big blank. It is an embedded YouTube video; here's the link:
https://www.youtube.com/watch?v=Y0Dz-5gLTDk

This is an automated translation of the text:
Phase 1 of the conversion of my 2CV to a hydrogen duck (a DCL'eau) is finished. Yesterday afternoon I was allowed to take him from Carl Holthausen and his men from Holthausen Clean Technology for the first time. It was (and is) great. On to phase 2: the duck is completely converted to Hydrogen. Because a duck should live on water.
The video doesn't show any of the car's hardware, other than an instrument display.
 

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Discussion Starter #19
I really wonder where they are going to install the hydrogen stuff. As it is now it just looks as an electrified Duck.
 
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