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Maxwell Introduces 390-Volt Ultracapacitor Module for Heavy-Duty Vehicles

Maxwell Technologies has introduced a rugged 390-volt BOOSTCAP ultracapacitor module to provide scalable, easy-to-integrate, energy storage and power delivery solutions for heavy hybrid and electric vehicles and heavy duty industrial applications requiring up to 1,170 volts.

The new Heavy Duty Transportation (HTM) module features enhanced integration technology and up to 2.8 times greater energy storage than earlier products.

This rugged, high-performance, module is designed specifically to meet the demanding requirements of regenerative braking systems in hybrid and electric buses, trucks, electric rail and other heavy vehicles, as well as cranes and other heavy-duty industrial applications.

—Richard Balanson, Maxwell president and chief executive officer

The new module meets or exceeds transportation industry requirements for watt-hours of energy storage and watts of power delivery per kilogram, and is designed to perform reliably through one million or more deep discharge cycles, or about 15 years of operational life for most vehicles or industrial systems. It has integrated voltage management circuitry and monitoring capabilities and highly efficient, fan-driven, forced air cooling that ensures good thermal performance at high continuous currents.

In addition to efficiently managing thermal loads under high current cycling conditions, this module is built to withstand the harsh environments, shock, vibration and extremely demanding duty cycles that are typical with heavy transportation applications. Improvements in module design and advancing cell performance through material science are enabling enhanced functionality and robustness while significantly reducing manufacturing cost.

—Michael Everett, Maxwell vice president and chief technical officer

The self-cooled HTM BMOD0018-P390 is encased in a rugged, splash- and dust-proof, IP 65-compliant, aluminum chassis. Each module is rated at 18 farads, and up to three modules may be linked in series to deliver a total of up to 1,170 volts.

Maxwell also offers standard 16-, 48- and 125-volt modules, and a Quick-Turn program that offers shipment within 14 days of receipt of a customer purchase order for custom-configured modules for applications requiring up to 540 volts.



I am ignorant in Electrical Engineering. Can anyone tel me the KWH equivalent? Is it close to 3KWH?


For some rough numbers:

Derate operating voltage to 300 V. [That's a typical derating for conventional capacitors. I don't know the manufacturer's recommended derating for this technology.]

1/2C*V^2=~800,000 Joules => 80 kW for 10 seconds per module; three times that if used in series. For stop and go delivery vehicles that's a lot of stored energy from regenerative braking. So what are the cost and physical dimensions?


Divide 800 kJ by 3600 seconds/hr to get 0.22 kWHr.
Nowhere near 3 kWHr.


Maxwells were typically around 7 Wh/kg - so if similar energy densities then each module should weigh in at around 30kg, not including casing etc.


Should be able to absorb the decelleration of a 2 ton vehicle from 30 mph to 0 ( or 40 to 0 )
Or that should be the benchmark for stop / start driving.


Kinetic energy is 1/2MV^2, so for 5000 kg at 40 mph (17.9 m/s) the energy is about 800,000 J ... or one bank of supercaps at, say, 50 kg including packaging, cooling, mounting, etc. If 50 kg of capacitors can recuperate 800 kJ a million times over its lifetime that's 222 MWHr.

Of course there are efficiency losses along the way, and this assumes the single bank of capacitors can accept energy at a very high rate (80 kW for 10 s). So call it 150 MWHr. Multiply times 100, 000+ delivery vehicles, buses, etc ... now you're talking about some significant energy savings (15,000 GWHr). Assuming 25% efficiency for the diesel engine that equates to about 350 million barrels of oil (at 1718 kWHr/barrel), worth $20B at $55/barrel, and some 280 billion lbs of CO2 (at 800 lbs/barrel).

That's a lot of energy to save, and the weight of the energy storage device isn't that much of a burden. Carrying heavy batteries around adds a lot of weight to a vehicle, which in turn is a big drag on efficiency.

Check my math ... please. And you ME types can also check my efficiency assumptions. This is admittedly a "back of the envelope" estimate.

Rafael Seidl

Energy contained in capacitor bank when fully loaded:

1/2 * C * Vmax^2 = 0.381 kWh

Energy contained when empty: Vmin = 1/4 * Vmax:

1/2 * C * Vmin^2 = 0.024 kWh

Difference: Wpot = 0.356 kWh

Figure 94% charge efficiency (true only if charging is slow enough, ~10s): 0.380 kWh at the power converter DC terminals

Figure 85% average efficiency for the power converter: 0.446 kWh at the generator AC terminals

Figure 85% average efficiency for the PM generator: 0.52 kWh at the crankshaft

Figure 94% average efficiency for the tranny and diff: 0.558 kWh where the rubber meets the road

(total efficiency wheels to ultracaps: 64%)

HDV mass fully laden: 12,000kg (medium duty truck)
Vehicle speed corresponding to 0.558 kWh: 49kph = 31mph

Total efficiency wheels-ultracaps-wheels: 64%^2 = 41%, so the vehicle can be accelerated back up to 32kph = 20 mph using recuperated energy alone, disregarding the effect of rolling resistance.

Note that this is a best case scenario, assuming the full voltage range and sufficient time for braking are available. In practice, ultracaps may indeed have to be derated in design, if only to account for the 20% or so loss in capacitance over the lifespan of the cells. Also, the power converter may not be able to handle the current at voltages as low as 1/4 Vmax.

HDVs that must operate frequently in stop-and-go traffic, ultracaps make more sense. Examples: delivery vans, city buses, garbage trucks.

An 18-wheeler (40,000kg fully laden) whose duty cycle includes a lot of hill climbing on the highway would benefit more from a battery-based hybrid system. The higher specific capacity overcompensates for the lower recuperation efficiency (~25% wheels-battery-wheels).


Its likely the old design of ultracap just bigger and thus higher capcity. The newer ultracaps can store alot more power.

Stan Peterson


I have read your posts before and throughly respect your scientific opinions. You display an ability to sort technical wheat from scientific chaff.

I recomend that you review the video presented here and feel free to comment. You can PM me if you wish.

Its time to electrify the auto fleets...


Let me try to disprove this claim of how revolutionary this module is. To do this, I will apply real electrical engineering science:
The energy stored in a capacitor is given by the formula:
E = (1/2)* C * V^2, where C is capacitance in Farads and V is the voltage across the capacitor.

From the manufacturer's data sheet for this module, the capacitance is 17.8 Farads and the max voltage is 390 V, the maximum energy that can be stored is:
E = (1/2) * 17.8 F * (390 V)^2 = 1368900 Joules

1 KW*hr(kilo-watt-hour) = 3,600,000 Joules, therefore this module can store 0.38025 KW*hr.

Now the real problem. From the manufacturer's data sheet, I obtained a mass of 165 Kg for this module, therefore the energy density is about 380.25 W*hr/165 kg = 2.3 W*hr/kg. This is extremely low for any useful energy storage devise for an EV or plug in hybrid.

How about Power density, the real strength of a capacitor? You can have 150 Amps for continuous discharge or 950 Amps for short bursts. This means that the maximum continuous power is about (150 Amp * 390 V)= 58.5 KW and the maximum peak power of (950 * 390V) = 370.5 KW. With a mass of 165 Kg, the continous and peak power density comes out to be about 0.355 KW/Kg and 2.245 KW/Kg respectively.

How does this "revolutionary module" compare with the state of the art lithium ion battery? Well, let's take Altair Nano as the standard.

Energy density = 90 W*hr/Kg (which is very poor when compared with other lithium ion batteries and yet is 39.13 times more energy dense than this capacitor module!)

Continuous Power density = 4000 W/Kg (the Maxwell module peak power density of 2245 W/Kg is lower than the battery continuous power density!)

How about the number of charges/discharges? It turns out that the Altair Nano batterys can be fully charged/discharged for 20,000 times and still retain 85% or nominal capacity. This means that over the life of the battery, a module of 165 Kg of Altair Nano batteries can store and release about:

165Kg * (85%) * 90 (W*hr/Kg)/(charge/discharge) * 20,000 Charge/discharge = 252,450 KW*hr of energy

A mid size electric car can go 4 miles for each KW*hr of energy, therefore an EV with this 165 Kg module of lithium batteries can go up to 1,009,800 miles! This far exceeds the expected milage of any car. In practice, the calendar life of the battery will reduce this number.

Conclusion: Unless there is a quantum leap in both energy density and power density, the Ultra capacitor is dead.


This is a bit premature. Ultracaps can compliment batteries because of their ability to do lots of discharges at high power density. Think launch assist combined with regenerative braking. The back of the envelope analysis that shows ultracaps having lower power densities than batteries is a bit naive and disingenuous. These are based on lab reports for maximum power bursts which certainly arent going to be recommended for general use, and it doesnt represent charging power either.

The other big point for ultracaps is efficiency. Its obvious that they'll never compete with batteries on raw energy density, but they dont have to.


Stan - Thanks for the link. IMO every thinking person should do themselves a favor and view that video. It's quite long (1h13m32s) but well worth the time.



Thanks for the analysis. 41% efficiency wheels-ultracapacitor-wheels makes things less compelling. But I'm surprised that the power converter would have such a low efficiency (85%). I thought 90+% was readily achievable at these power levels. In any case the overall round trip efficiency is still under 50%. But hey, if we can save half the breaking energy that's still quite a few barrels of oil.


Thanks for the update on the module weight. 165 kg is a lot more that I had assumed. Still, nobody (including the manufacturer's press release cited above) said this ultracapacitor was "revolutionary." I agree we're not going to make an EV or PHEV using ultracapacitors for bulk energy storage. I believe the context is stop and go driving for medium duty delivery trucks and buses. They spend much of their energy getting going, only to dissipate it as heat in the brakes.

A hybrid vehicle that has the peak power capability to capture that energy can save a lot of oil. I don't know the price for the ultracap, but I'd bet it's cheaper than a bank of Li batteries with the same power capability. And you can buy the ultracapacitor -- not true for the ALTI battery. For the future of PHEV's we all hope that will change. But if ultracapacitors can work for this application that's a positive step.

Stan & Bob,

I watched the video. It is indeed very interesting. I'm not a climate scientist, so I recognize I'm not qualified to referee the argument about global warming. But I don't need to. My son is a US Marine, and I haven't forgotten 9-11. So for personal reasons I want to save oil whether it's peaking or not, and whether CO2 causes global warming or not. Energy security crazies (like me) and global warming crazies may have very different political views, but our answers to some questions are the same.


Has anybody compared this to the hydraulic hybrids(yes I know, hydraulic/nitrogen hybrids)that UPS is testing? I believe that was quoted as having a higher wheel to pressure tank to wheel efficiency. They both seemed to be aimed at the same target, heavy duty commercial vehicles that operate in a stop and go driving pattern. Oh well test them both out and see which one comes out on top.



I veiwed the video. Very interesting. The experts involved in the video lent a great deal of credibility. They did an impressive job of putting the whole movement in context.


Supercaps are no competitor to batteries, rather complement to adsorb high currents associated with regenerative braking, prolonging battery life. From all batteries Altair Nanosafe is the last to benefit from this combination.

Maxwell supercaps are extensively used in leveling-off surges in wind turbines, as emergency energy storage in smart electricity meters, and as initial (7 seconds) power supply in un-interrupted power supply systems – before diesel generator kicks-in, and many other applications. Also supercaps are considered as the only viable option for heavy-duty hybrid vehicles, like 18-wheelers.


I believe that your estimation is a little bit on pessimistic side: regenerative braking efficiency around 50% is reported for Toyota Prius, heavy-duty supercap systems should perform better. Oshkosh Truck series hybrid military truck eliminates transmission, transfer case, driveshafts, and claims 40% improvement in fuel efficiency:


I have read a lot of comments on Swindle documentary, including from some scientists, and the only factual mistake they found is overestimation of CO2 emissions from volcanoes (political staff aside). Everything else is correct. BTW, there is another nice piece, current Congress testimony of President of Czech Republic Vaclav Klaus:


Um folks this device is made for one purpose only. To catch the energy of a big ass bis or train or other HEAVY device as is stops and fling it back into the system as it moves again.

Its NOT anything like a prius needs.

Its main selling points are likely very low cost and very low maintenance.


I'm not sure about low cost - particularly when compared to batteries in terms of $ per kWh. Also, the voltage conversion from battery to motor is much easier (read cheaper) than the expensive electronics required to convert the plummeting voltage from a capacitor on discharge.

Harvey D.


If the Toyota Prius already captures 50% of the regenerative braking energy with their slow charge NIMH batteries, regenerative braking efficiency may go up to 90% with Altair nano (or equivalent) very quick charge batteries.

This would preclude the use of super-caps for Hybrids, PHEVs and BEVs equipped with such batteries unless super-caps can extend the useful life of the on-board batteries (if it is still a problem).


One regenerative idea was to use compressing nitrogen. You could combine ultra caps with that scheme. Use the caps from above 5 mph and below use the compression, which claimed to be 70% efficient at recovering the energy. Your brake pads would sure last a long time.


Your looking at the wrong metric. They dont care about kwh they care about volts and kw. This is basicaly just a big ass electrical pogo stick. It likely doesnt even use much in controls. It prolly just catches everything it can then releases it all.

Rafael Seidl


"Supercaps are considered as the only viable option for heavy-duty hybrid vehicles, like 18-wheelers."

Volvo Trucks would presumably beg to differ:


Rafael- I read the linked article again but I still can't find the reference to Supercaps in it. The article is indeed about Volvo trucks, but where's the tie-in to Supercaps?

tom deplume

Basic electrical principles say that a generators voltage is proportional to its speed. As the vehicle slows the voltage goes down as the voltage of the ultracap goes up. Current and therefore braking force is a function of the voltage difference and at some point well before a full stop the voltages will be equal and no braking force will be available. How does this system overcome this problem???


i am new to ev's, i am very interested in building my first. i want to do it right though. can anyone tell me where to start? i want to use capacitors/lithium ion batteries, and good motors etc...

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