Time to go to a 37 Volt electric system?

[dwightlooi]

For years, cars have relied on (nominally) 12V Lead Acid batteries. However, is it time to leave that behind?

Hybrids in general do not make economic sense to most drivers, not the Priuses of the world and certainly not the Volt. They don't make economic sense because the investment in the Hybrid power train will never be recovered for 7~13 years through fuel savings at $3 a gallon even on a Prius like vehicle. This is longer than the average ownership period for a new car buyer. This leaves the notion of owning a Hybrid something that ought to appeal only to solo car pool lane users, green image seekers, Global Warming Coolaid drinkers and people who cannot do elementary school math.

However, the advancement of battery technology leaves us wondering whether it's time to ditch the 12V electrical system. Not necessarily for reasons of fuel economy, but because 12V impedes the functionality of the vehicle and going to (let's say) 37 volts can do the following:-

• Allow the replacement of belt driven accessories with electrically driven ones (A/C, steering assist, water pumps, etc)
  
• Allow the implementation of flywheel integrated motor/generators that can start the engine (without the gearing used with 12V starters).
  

I have been advocating for the elimination of the accessory belt and belt driven accessories for some time. And, a 37 Volt electric system allows us to make that leap. Basically, the idea is that you'll dump the accessory belt, the alternator and the other traditional accessories riding on it. We are already doing electric steering, 37V makes the units more efficient. We can also run the A/C compressor electrically. The water pump can be electrical or simply driven of the camshaft. Most importantly, 37V allows you replace the flywheel of the engine with a 15mm thick motor generator which takes up practically no additional room, run all the accessories electrically and be able to start the engine without needing to kick into a really low gear drive like 12V starters. No belts means no scheduled service replacement for the belt. Getting rid of the starter and its kicker gear drive also eliminates one of the most common reasons engines fail (a failing starter gets stuck in the middle of its kick cycle). Of course, a motor generator / electric accessory setup can stop the engine at stoplights and start it seamlessly when you lift the foot of the brake pedal for idle economy without affecting HVAC function or steering effort at rest.

In short, a 12 year, 150,000+ mile maintenance free engine (minus oil changes) that is more economical, more reliable, less noisy and more compact. Also, freeing the accessory from the accessory belt in front of the engine means you have absolute freedom in where you want to place the stuff. The A/C compressor for instance can be in the rear quarter panel or unitized under the dash as part of the HVAC head unit or anywhere you want it instead of where the drive belt is.

Is the battery expensive?

Well... a Volt Li-Ion battery pack costs about $10,000. That's about 16 kWh worth of charge. A Prius's NiMH pack is about $1500 and holds about 1.3 kWh. The Honda Insight's is about 0.58 kWh and about $800. Since we are not planning on actually moving the vehicle on electric power here, all we really need is about ~0.2 kWh. That's around ~$124 using the Volt's dollar /kWH or about ~$275 using the Insight's. It's not all that expensive. Not especially since we are building in the twice traditional charge capacity so we can avoid draining the battery down too much for longevity reasons.

Is the battery big?

And, assuming we are piggybacking on the Volt's Lithium Ion technology the battery is actually going to be smaller and lighter than a typical 12V lead-acid battery. At 0.2 kWh we are holding about twice the capacity of the 12V battery, but Li-Ion is about ~200 Wh/Liter and about ~300 Wh/kg vs Lead Acid's 40 Wh/Liter and 25Wh/Kg. Hence, the battery can theoretically be about 2/5th the size and 1/6th the weight! And, if we observe good usage models like not going below a 70% discharge the battery can be good for more than 12 years and 150,000 miles.

[SAmadei]

Why 37 volts?

I recall this coming up from time to time... either 24V or 48V, but I've been skeptical. 37V or 48V would deliver a pretty good zap.

We probably should move to a higher voltage, but I imagine there will be a lot of resistance (no pun intended) and that a dual voltage (12V/37V) would be required for legacy devices and accessories.

[Drew Dowdell]

The cig lighters can be run off a step down transformer for the accessories.

[PurdueGuy]

I like the concept, but I do wonder about the cost of motor-driven accessories. Let's see, typical belt-driven accessories that would need to be motor-driven; water pump, AC, Power Steering. Depending on the setup, that could mean the cost & weight of 3 electric motors, which is likely more cost & weight than an accessory belt system. As mentioned, though, the water pump could be run mechanically, unless it can be depended on in a location outside the engine, which might ease maintenance and simplify the engine block. It might be possible to still have an accessory belt, not attached to the engine, with the AC and power steering both attached to a motor via belt (or perhaps a long-life chain instead?)

Anyway, seems like a good idea, but the details of implementation would be critical.

[SAmadei]

The cig lighters can be run off a step down transformer for the accessories.

I was actually more concerned with more devices and accessories than that. It would take a while for a lot of electrical accessories to trickle into the parts stream... and be implemented into current models... sensors, window motors, radios. Granted, some parts may run just fine at 12V or 37V, but we don't want to open ourselves to a another Ford ignition recall situation.

Of course, even a step down transformer, which can handle more wattage than a cell phone, would be a somewhat pricey piece, as its got to run more than phone chargers. It needs to run air pumps, winches, inverters... there are even cig light "jumper cables" that attempt to push a lot of power through that plug.

Then there are all the things people still wire into the fuse box... the huge car stereo market... sure, they will eventually benefit from a higher voltage, but they would be stuck with needing to provide products compatible with dual voltage for years.

What about your trailer? Do you need to convert it to 37V? That may be easy for a simple trailer which might need different light bulbs... but could be a real problem for a travel trailer... or even a larger trailer with a rechargeable braking system.

We've got so much electronics attached to cars that conversion could become a major headache. Its not 1954 (6V to 12V) anymore.

Dwight, I was thinking about the losses incurred with the belt driven engine accessories... is this really that much more than the losses incurred with electrical accessories? As someone else noted, electric motors are heavy... and would increase car weight.

Some accessories switching to electric make me nervous... water pumps, which could remain belt driven, are not as reliable in electric form... and tend to fail suddenly. I'd feel alot better if someone made a dual electric motor water pump that featured some sort of warning device should a motor fail.

[siegen]

Allow the implementation of flywheel integrated motor/generators that can start the engine (without the gearing used with 12V starters).

I think this is the next major step for traditional gasoline engines. Not only could it be used to auto-start/stop a vehicle, but it could provide assist during acceleration. That is assuming battery technology improves to where higher capacity batteries can be used in place of regular car batteries without requiring lots of extra space.

Above is either the Civic Hybrid or Insight powerplant. Honda's IMA is along these lines and I think as it improves and gets thinner, and as batteries become better, it will be a very viable option for turning all gasoline engines into hybrids without requiring any major reworking.

The orange part is the electric motor, which is sandwiched between the engine and CVT transmission. It's amazing how large transmissions are compared to modern 4-cylinder engines. Here is another image showing a closer cut-away of the electric motor.

[Drew Dowdell]

Dwight, I was thinking about the losses incurred with the belt driven engine accessories... is this really that much more than the losses incurred with electrical accessories? As someone else noted, electric motors are heavy... and would increase car weight.

Some accessories switching to electric make me nervous... water pumps, which could remain belt driven, are not as reliable in electric form... and tend to fail suddenly. I'd feel alot better if someone made a dual electric motor water pump that featured some sort of warning device should a motor fail.

Waterpumps could easily be tied into valvetrain.

Power steering pumps are already electric in many cars.

The alternator goes away because it's replaced by the regenerating flywheel.

The only thing left is the A/C, which as Dwight mentioned, can now be located anywhere in the car instead of in the front plane of the engine.

As it is, the current Ecotec serpentine belt only drives the alternator and A/C.

[dwightlooi]

I was actually more concerned with more devices and accessories than that. It would take a while for a lot of electrical accessories to trickle into the parts stream... and be implemented into current models... sensors, window motors, radios. Granted, some parts may run just fine at 12V or 37V, but we don't want to open ourselves to a another Ford ignition recall situation.

Of course, even a step down transformer, which can handle more wattage than a cell phone, would be a somewhat pricey piece, as its got to run more than phone chargers. It needs to run air pumps, winches, inverters... there are even cig light "jumper cables" that attempt to push a lot of power through that plug.

Then there are all the things people still wire into the fuse box... the huge car stereo market... sure, they will eventually benefit from a higher voltage, but they would be stuck with needing to provide products compatible with dual voltage for years.

What about your trailer? Do you need to convert it to 37V? That may be easy for a simple trailer which might need different light bulbs... but could be a real problem for a travel trailer... or even a larger trailer with a rechargeable braking system.

We've got so much electronics attached to cars that conversion could become a major headache. Its not 1954 (6V to 12V) anymore.

Dwight, I was thinking about the losses incurred with the belt driven engine accessories... is this really that much more than the losses incurred with electrical accessories? As someone else noted, electric motors are heavy... and would increase car weight.

Some accessories switching to electric make me nervous... water pumps, which could remain belt driven, are not as reliable in electric form... and tend to fail suddenly. I'd feel alot better if someone made a dual electric motor water pump that featured some sort of warning device should a motor fail.

If you take the "high wattage" stuff like the generator-motor providing engine starting (or assist) and the A/C compressor, everything else normally associated with the DC supply in a car is relatively low wattage stuff -- lights, cell phone chargers, etc. In a 37V vehicle, the power sockets in the cabin and trailer connections will still be 12V. This will be provided by a DC-DC power converter which is both very small and relatively inexpensive.

The following is a DC-DC powerboard that takes 6 to 36V input (can even be a fluctuating input) and produces steady 3.3V, 5V and 12V outputs. The total output rating is 250 watts -- plenty for most things people hook up in their cars. It also has a micro-controller on there to do fancy things like programmable shutdown delay and voltage monitoring. It is, as you can see, pretty small (about the size of 2 credit cards) and costs $75. If all you need is 12V output the board becomes even simpler, smaller and cheaper.