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Maxwell Technologies Introduces 125-Volt Ultracapacitor Module for Heavy Hybrid and Electric Vehicles

The HTM P125 module.

Maxwell Technologies, Inc. has introduced a compact, fully integrated, 125-volt BOOSTCAP ultracapacitor module to provide an easy-to-integrate building block for scalable energy storage and power delivery solutions for heavy hybrid and electric vehicles and heavy duty industrial applications requiring up to 1,500 volts.

The new HTM BMOD0063-P125 module is based on 2.7-volt BOOSTCAP MC3000 Power cells and incorporates proprietary balancing, monitoring and thermal management capabilities to ensure industry-leading charge/discharge performance, high reliability and long operational life.

This high-performance module is designed specifically to satisfy rapidly growing global demand for ultracapacitor-based braking energy recuperation and torque assist systems for hybrid bus and truck drive trains and electric rail vehicles. It 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 charge/discharge cycles, which equates to more than 15 years of operational life.

—Dr. Richard Balanson, Maxwell President and CEO

Integrated monitoring capabilities and a highly efficient cooling configuration enable the new module to sustain continuous current of up to 150 amps with minimal temperature increase in high-temperature environments, according to Michael Everett, Maxwell Vice President and Chief Technical Officer.

The HTM BMOD0063-P125 is encased in a rugged, splash-proof, IP 65-compliant, aluminum chassis, weighs less than 50kg and measures 315x425x744mm. Up to 12 modules may be linked in series to deliver a total of as much as 1,500 volts. Maxwell also offers a complete line of standard 15- to 48-volt multi-cell pack and modules, and recently announced 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.



Bud Johns

Here's more stats....
HTM Series 125v Product Stats:
Item Performance
Nominal Operating voltage [Vdc] 125V
Maximum Operating Voltage [Vdc] 135V
Surge voltage [Vdc] 142V
Nominal Capacitance [F] 63F
Tolerance Capacitance [%] +20% / -0%
DC Series resistance [mΩ] 17.0 RT
100 Hz Series resistance [mΩ] 14.0 RT
Energy Available (Whr) 101.7 Energy Available equals 1/2C (Vnom^2 – 1/2Vnom^2) /3600
Self discharge [%of initial V] 70% 30 days RT 100V; 12 hours charge and hold
Maximum Continuous Current [A] 150A Assuming 10 degree temperature rise above ambient temperature
Max current [A] 750A (in 5 s discharge to half nominal voltage)
Lifetime 125V, RT [hours] 150,000 End of life characterized as -20% C from nominal C, or increase of 100% in ESR
Cycles 125 to 62.5 Vdc, RT [cycles] 1,000,000 End of life characterized as -20% C from nominal C, or increase of 100% in ESR
Isolation Voltage [Vdc] 4000V Maximum string operating voltage 1500V DC


What is the weight of this system? Thanks.

Bud Johns

I havn't been able to get the deminsions or weight of the modules yet. Anybody know?

Rafael Seidl

Usable energy capacity 0.1 kWh
Burst power 47-94kW (750A at 62.5-125V) for 5s
=> ~0.1 kWh transferred

(Note that the link to the detailed datasheet is broken on Maxwell's own site, so neither weight nor pricing data are available right now.)

This underlines how ultracap technology is targeted at efficient recuperative braking and burst acceleration plus engine stop/start. In other words, you can aggressively downsize the ICE and boost aggregate efficiency by always operating it at high load. This is how HDV engines are sized anyhow, making city buses, delivery trucks, garbage trucks etc. a natural fit. Sports sedans and SUVs can also benefit to some extent.

A regular battery must be also be present to ensure the vehicle can be started after having been parked for a long time. To eliminate the starter motor, the engine controls will charge up the ultracaps a little so they can power the electric motor that cranks the engine.

Towing and hill climbing have to be shouldered by the ICE alone, since ultracaps run out of juice so quickly. Don't buy one of these if you live in hilly terrain. On the plus side, ultracaps perform quite well in cold weather and do not require forced cooling.

By contrast, battery hybrids improve efficiency primarily by load leveling a somewhat larger ICE that would otherwise spend much of its time in (low) part load, all-electric cruising at low speeds and engine stop/start.

Combining ultracaps and batteries enables additional fuel economy benefits, such as PHEV designs. Deep-discharge batteries with adequate life expectancy are designed differently and are limited to moderate rated power. All-electric forklifts for indoor use are another potential application.

Reality Czech
I havn't been able to get the deminsions or weight of the modules yet. Anybody know?
It's right in front of your eyes:
The HTM BMOD0063-P125 is encased in a rugged, splash-proof, IP 65-compliant, aluminum chassis, weighs less than 50kg and measures 315x425x744mm.
Bud Johns

Thanks, reality czech! More coffee required.......


Bud, or just a wake up zap from a cap. Sorry hope you laughed... :-)

Bud Johns

Caps are great for wake up calls, for sure. I don't think you would be awake after a 1500v zap from these modules. BTW, I wonder if they would work in parallel, then there would be no limit in capacity......just a thought. For example, say you wanted to work at 250v. Series them in pairs, then parallel the pairs.


Altairnano can do the high rate and the high cycles for a lot less size and weight with lithium-ion. But Maxwell have this on the market right now....

Rafael Seidl

Bud -

yes, you can arrange banks of ultracaps in parallel. In fact, reconfiguring between series and parallel circuits on-the-fly is how you can keep system voltage in a narrower band, if your application requires that. Parallel configurations can also offer high availability through single component failures, a critical feature for safety-centric applications such as lifting equipment.

In vehicle applications, you'd normally want to choose series configurations and use power electronics to mask the variable voltage across the ultracap bank terminals from the electric motor. In addition, the engine control system must keep the current drawn from or fed into the ultracap store within rated values, which means that the rated power of the electric drivetrain path varies significantly with charge level.


63 Farads at 125V is quite a capacitor. Great to see, but I do wonder if a few young/foolish electrical or hybrid techs will get zapped by these things. The arc from a 0.1 Farad capacitor at a few hundred volts is amazing. One of these shorting out (think screwdriver across terminals) would be more like a bomb going off.


Apparently Altairnano is ready to rock with their new batteries next year. I'd love to have a EV that can go 250 miles and recharge in 10 minutes.


Michael McMillan

I shudder to think how much this costs. On one hand ultracaps are cheap compared to other capacitors, but compared to nearly any other power source they are expensive, though light weight.

a 2.7 v 35F ultracap costs about 35 dollars. At full power it takes 8 seconds to go from full to empty. if you price them in that manner, they cost about 2 dollars per watt. As a comparison, lead acid is about .5 cents per watt.

On the up side, they will last over a million cycles, and require much simpler charging circuitry.

A car manufacturer can take the speed of their car multiply that by it's weight, and purchase a ultracap which can absorb a fully loaded car's energy at 35mph.

There doesn't need to be much in the way of high voltage high amperage charging circuitry. just feed 2 amps at 600 volts off the generator into a 125 volt capacitor. The capacitor will absorb it as if it was 10 amps at 120 volts.

The cap can then be used to charge the battery bank at C/3.


It is really good to see steady progress with caps.

The hybrid concept can work much better if batteries are helped during acceleration and when capturing braking power.

That could change if batteries improve enough. But I don't expect it for a few years.


Does anyone have some news about EEstor's revolutionary capacitor?????!!!!


Nov 5th EEstor article From Austin American Statesman



1) Ban game sales

2) Subsidize diet pills

game over.

kent beuchert

With their ultra fast charge/discharge rates, I would think an electric with Altair NanoSafes would find a
capacitor like this excess baggage. Anyone know if the
Phoenix vehicles have a capacitor? I consider a product like this a stopgap or bandaid or interim "solution"
to overcome current battery limitations. I don't care for this kind of Rube Goldberg engineering, but at least its not as mentally abrasive as the Tesla's battery module's monitoring/HVAC system. That takes the cake for Germanic engineering - an ultra complicated solution of a problem that shouldn't even exist. And people wonder why German cars and their WWII tanks were so unreliable.


Diesel-electric buses currently do not shut their engines at stops when AC is running. For such applications ultracups seems to be suitable. Both Prius and last model of Civic hybrids are capable to support 10-20 minutes of AC running, so aside from prolonging battery life (due to handling high power bursts), addition of ultracups does not seems necessary. Altair NanoSafe battery does not require ultracup addition for sure, but it is still wild play. What technology will prevail and in what application – remains to be seen.


From another prespective, a bank of these w/Li-ion batteries and efficient generator could be used for direct energy weapons, namely lasers.


NessCap produce supercaps as 400Farads 2.7Volts at 20$ (1458 Joules).
It's about 1.3 cents/watt.
IT's really very competitive with batteries that need change after 500 cycles and supercaps has better conversion than batteries(90% front 80%).
Anyone can do an 'stop engine at idle' system with 5-10 of this supercaps without using battery energy, only energy from previous regenerative braking.
Why to use expensive Maxwell?
You can see one here:


Lucki, $20 for 400F-2.7v is about $50,000/kWh. That's 100x the cost of advanced batteries and is only cost competitive in applications that absolutely must have extreme high power or 500k cycle life.

Maxwell's ultracaps are about 5x cheaper than this, at least in volume. Still too expensive (and heavy) for most enery-storage applications, though.


Someone at this thread said:
"2.7 v 35F ultracap costs about 35 dollars".
But if you know where to get a supercap at about 1458 Joules at lower price (5$?), please say me.
I'm agree that supercaps are for enery-storage at short term. For example: to start engine, or help to accelerate (from previous regenerative braking), not to store all energy of an electric car.

Niels Helmoe

Have anybody heard of supercapasitors for stationary use at 1.650 volt DC railways. I would be glad of some informations if possible.

Best regards

Niels Helmø

[email protected]
Tlf. direct: + 45 82 34 63 13
Design & Development
Amerika Plads 15, 2100 Copenhagen Ø
Tlf.: + 45 82 34 00 00

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