Empeg modification needed!

http://www.caraudiomag.com/specialfeatures/0307cae_42volt/

That article makes a lot of leaps of faith and has a lot of juxtaposed comments/ideas with no clear reasoning as to why these ideas/comments are linked.
[or in some cases, the article uses circular logic e.g. 36 volt electrical systems are better because 36 volt electrical systems are better].

Similarly:

In reply to:

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There are dozens of fractional horsepower motors on a car or truck. Electrically controlled mirrors require multiple motors for changing tilt and angles. Adding car sound systems, plus electronically controlled engine management systems, electric heating, ventilating and air conditioning systems has resulted in big increases in power needs. Vehicle electrical demands vary considerably by type, size and model of vehicle as well as by component. In general, it is estimated that typical vehicle electric demands doubled between 1990 and 2000. On small cars, electrical power demand has doubled from 500 watts in 1990 to close to 1 kilowatt today, going to 1.5 kilowatts by 2005 (large cars exceed 2 kilowatts and by 2005 will reach 3.5 kilowatts). Within a decade a typical vehicle's electric demand is expected to approach 10,000 watts of power.

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I fail to see the link between 36 volt car electrical systems and the bald statement that "cars todays have lots of little motors in them".

So - in the cars of the future, they'll have even more motors in them and ...?

I also note the last comment - large cars today use up to 2.5kW of electrical energy.

But will use up to 4 times this in the future [becuase of all the little motors and car audio systems presumably if you believe this article anyway] , then they say comments like "we will remove the need for mechanical devices hanging off the engine by putting motors there instead".

Most of the "loss" of energy (from that available in the fuel used as compared to the output of the engine) in a internal combustion engine is due to heat and friction, noise etc, and not just in the engine. Going to 36 volts in itself won't reduce a lot of this loss of "energy" from the fuel when its combusted in the engine as its inherent in any mechanical engine.

Going to something like a fuel-cell powered vehicle - thats a different kettle of fish - but thats not whats discussed/proposed.

Using the engine only when the car needs to is efficient - but you have to offset this "saving" with the "cost" of needing to top the batteries up again with lots of starts & stops of the engine and increased wear and tear, [versus leaving the (properly electronically controlled/tuned) engine idling for a while e.g. a traffic lights]

The biggest mechanical device hanging off any modern [and future] vehicle engine under this regime will probably end up being the Generator/Alternator needed to provide all this power to the electrical components formerly run (mechanically) off the engine. I don't see any alternative to having the alternator mechanically attached to the engine, yes maybe replacing the beltdrive with some other device might be more efficient. Most car engines already have belts/chains inside them controlling things like valve timing anyway and will probably for the foreeable future - even with 36 volt power systems, so thats not something which will "disappear" magically when 36 volt systems become commonplace.

The next largest device that uses "power" besides the alternator is the air-conditioning - it will probably be no more efficient to generate electricity from the engine via [mechanically attached] alternator and then run the air-conditioning compressor electrically than it is right now to run it mechanically.

However this change would let you run the air-conditioning when the engine is off unlike in todays cars - but unless you have larger & heavier batteries to store this power needed to run the air-conditioning compressor, then its really a zero-sum game.

And if the goal is merely to have air-conditioning that works when the engine is off, the article should say so.

If on the other hand, this change is paving the way for "hybrid' cars that use the engine only sometimes to "top up" the batteries and run the car electrically for motive power and for everything else and only sometimes mechanically for motive power, then yes a high-voltage power system is good.

But again, the article fails to say so or say/explain why its so important.

I expect the switch to 36 volts is going to happen, but I also suspect the true agenda as to why this change is "good" and for whom it is "good" is not being told at the moment - and thats what this article fails to explore in any way at all.

BTW: To answer the original posters comments about needing a Empeg conversion - the same article states that a 36 Volt to 12 volt "convertor" will be used to power existing 12 volt components as the change over to only 36 volt components will take many years to occur.
So no "empeg conversion" will be needed [within the life time of the Empeg in most liklihood].

So, is the point merely that, because motors generally draw a lot of current at 12V, we can save weight/size on conductors by using a higher voltage, and therefore lower current, for the same amount of motor "power" ?

Is it true to say that supplying power at higher voltage is more efficient than higher current?
I also seem to remember that the major manufacturers were eager to get to higher voltages as the car electrical systems get more complex etc.
But as to any overriding reason, I can't remember.
It must be my age.....

I can't really see that as being the major driving force. I would guess that the majority of the wire in a car's loom is 18ga or smaller anyway. As the number of sensors, controllers, and 'low' power extras has gone up in recent years, I'd bet that the average wire diameter has decreased, and as such the potential % savings aren't huge.
But what might be a factor is EMI and SnR ratios. Electromagnetic radiation is proportional to current, so by cutting the large currents by 3 will reduce potential EMI problems. EMI issues are becoming more prevalent - in modern cars EMI isn't just something that makes your car stereo click and whine, but something that has the potential to prevent safety-critical components (brakes, airbags etc) from working correctly.

Okay here is how i see it

Your engine has numerous parasetic loads on it these being water pump, oil pump, powersteering pump, AC compressor, belt drag, and a few others

Now the water pump is a huge compramise as it is designed to cool the engine at idle in a traffic jam in a hot climate after possibly heavy driving so it needs a real good flow at idle, now you then take the same pump and cruise along a motorway in norway with the engine running considerably faster and a huge amount more cooling from cold air and more airflow so then the water pump is running far harder than needed.

The same could be said to some extent to the oil pump.

Now dump the oil pump and water pump and drive them electrically.

Get in your car turn the key, the engine does not start but your lub oil pump starts and runs for 5 seconds pre lubing your bearings then the engine starts with nice oiled bearings and runs, the water pump is still stopped and the engine climbs in operating temperature far faster giving you better combustion and now you drive along the motorway in motorway and the water pump matchs its speed to engine and ten miles later you are in arazonia desert traffic jam your engine is idleing but the water pump is flat out you then move along a bit. You stop at the traffic lights and decide to drag race off the lights you get full engine power as your generator will switch off and your pumps and extras will run for a short period off the battery supply.

now that as far i could see would be an advantage, the dump the water pump modifcation is already very common in racing saloons.

from my point of view i think 42 volts is good

Makes a load of sense when you put it that way.

When I was coming round this morning, the business programme on radio 5 was doing a feature on a company in California set up by two English guys. They are developing some kind of much more efficient and smaller electric motor and Volkswagen have shown an interest.

That could well have a bearing on car electrics and the context of this article.

Mmm.. the heat output of an internal combustion engine is pretty much directly related to the rate of combustion == engine RPM for the most part.

My car generally varies between 1000 RPM at idle to 3000 RPM at highway speed. The water pump is therefore most needed at 3000 RPM, where it just happens to run three times as fast as at 1000 RPM! On a hot summer day, the airflow around the engine doesn't have nearly the cooling impact of the water pump (and radiator etc..), so I don't see any need to control the pump separately from engine RPM.

Until winter arrives, that is. Many days in the winter here it would be nice to have the water pump run at a much lower rate for the first half hour or so of operation. But not really, because that same water is used to heat the interior of the car, and if it circulated less, we'd freeze our butts off (well, not me.. my Subaru has electrically heated front seats!).

As for turning off the pump during engine warm up, I dunno. Most all cars have a theromostat valve to keep water from circulating outside of the engine block until it has warmed up to a certain temperature, so the pump isn't really slowing down engine warm up there. More like just evenly distributing heat around the engine block instead, so it doesn't crack open from intensely concentrated heat around the combustion chambers.

Cheers

yes for the most part heat load does vary dependant on engine rpm but when designing an engine you must account for extremes like towing a caravan with a load of fat blokes in the back seat. So your car is designed for that. So engine load and engine rpm cannot be taken as being the same you can be at full load at 3000 rpm and at half load at 5000 rpm.

By airflow i mean the airflow through the rad not round the block and 3000rpm doesn't mean 70mph all the time, you could be screaming through town up through the gears so your water pump is designed for everything which means at cruising revs it is well over rated.

As to the thermostat that is there getting in the way of a decent waterflow all the time and what would you rather have control you engine temp as a software person a lump of wax as in the modern car or a nice piece of software.

Also temperature of the engine that has alot to do with not only fuel effiecency but also emissions and liner behaviour etc but basically you need higher temps early on to light up your cat and other things.

That all sounds very logical and everything, but in what way is 42V better than 12V.
I know there is a logical reason that is elluding us!

It's going to be easier to get better sounding stereo installs. That's good enough for me

Oh yeah i never explained that bit.

Okay for any power tranmisson application be it your mains voltage or around your car or for me on a ship, the higher the vlotage you use in conducting the power the lower your losses are. Also if you use a higher voltage the conductors can be smaller since they do not have to conduct such a high amperage to move a set amount of energy

For example your nearest power station will be poducing power at about 22Kv or higher and then that goes through the overhead wires then it comes to sub stations where it gets dropped with a transformer to a lower voltge like 6.6Kv and then it travels a wee bit further and gets dropped again down to 440V (three phase) and then once it gets to the final substation they then drop it to 220 for us or 110 for you lot.

If you started at 220V at the generators the losses by the time it got to your house would be huge.

These losses come from resistance in the cables and since power is basically volts mutiplyed by amps this means to move a load of energy you need high amps or high voltage.
Now high amps heats the conductor instead of heating your house so there fore to counter this we need to drop the amps or drop the resistance. Dropping resistance implies we go for superconductors (ultra expensive) or bigger cables which ends up being to damn heavy and impracticle to run. So it is easier to drop the amps by uping the voltage.

now i could explain the advantages of three phase but it is beyond me but i know three phase is better and your car already has a three phase generator fitted just it rectifys it out as DC