Re: More on DC-DC Converters

[John Wayland <dat1200@europa.com>]

Hello to All,

>I think my good friend John Wayland is baiting me again 
>to see if I'm around.

   Baiting? Me? ;-D

>Properly done, the driver can't even tell whether there 
>is a DC/DC converter or not.

      Believe me, after an hour of driving  on a cold and wet nighttime
drive in a 'conventional conversion' (not a minimalist ComutaVan)
running a powerful defogger/heater blower, strong wipers, a full
compliment of lights, and a music system to make that one hour drive
pleasant and more fun, I could easily see things getting dimmer and
slower as the miles went by and I would be very much aware that the 12
volt battery was steadily dropping in power.....I wouldn't be happy
about it, and most others would be able to notice it, too.
     Also,  having to lug around a high ahr capacity 50 lb. 12v battery
isn't the best way to do things, when just 7 lbs. of 'DC-DC /small 7 ahr
gel cell' will do the job better and save 43 lbs. of wasted weight.
 
>I just took a 10-mile drive to the airport that took 3 
>hours; at night, in the rain, with the heater on. My 
>ComutaVan uses 25 amps max. at 12v. My accessory 
>battery is 80 amp-hrs. I could have made that !@#$%^& 
>trip in the ComutaVan with no DC/DC converter and still 
>have power to spare. 

      OH, oh....BS meter is pegged! Lee, you're saying that your EV
could suck 25 amps for three hours (that's 75 ahrs) from its 80 ahr 12v
battery, with  power to spare at the end? With the wipers, blower fan,
headlights, and the brake lights on most of the time in tight and slow
traffic, that's pretty close to a 25 amp draw, too. 
       Let's see.....assuming your battery is 80 ahr @ 20 hr. rate, and
you've removed 
75 ahr @ 3 hr. rate...with 'power to spare'? Wow!!! Where can the rest
of us get these awesome batteries....the heck with using just one of
them  to power the 12v system, I want a bunch of them to power up my
EV's drive motor!
    Back to reality.....with Peukart lurking within that 80 ahr battery,
its three hour rate is probably around 50 ahrs or so. That means you
could pull about 17 amps for three hours, certainly no where close to
those 25 amps for three hours that Lee spoke of. Taking a closer look,
you couldn't even get 17 amps for three hours of 'useful 12v power', as
17 amps for three hours would result in a 100% discharge, so at the end
of that discharge, the 12v battery would have sagged to a horrible 10.5
volts.....now that's a good prescription for bright lights! It's also
not so nice for that battery's cycle life, either! 
     My guess, is that you could pull 25 amps for the first half hour,
then you'd start to see things dimming and slowing down. At the end of
an hour, the 12v battery's terminal voltage would be into the high 11's,
and at the end of 2 hours, you'd be using a towel to wipe the fogged-up
windows, and would be squinting to see past the yellowish light output
of the fading headlights, too. As you got into the third hour, you'd be
parked along side the road as the contactors dropped out and the EV left
you stranded.
      How would that same trip be with a DC-DC providing the power? The
answer is pretty straight forward...at the beginning of the trip, you'd
have crisp bright lights, and all 12v items would run in top
condition....at the end of the trip you'd have crisp bright lights, and
all 12v items would run in top condition....end of the story!
      EV builders for the most part, won't want to take the time to
disassemble the whole
donor car or truck to rewire the entire 12 volt system system so that
every 12v device performs better at lower voltage....it's so much easier
to leave the system the way it was built, and feed it with 14+ volts,
as it was designed to run on. 
      Lee argues that there is terrible waste going on...there's some
truth to that, as I pointed out in my post about the stock headlight
circuit of my Datsun pickup. However, in a full size EV conversion, the
amount of juice wasted in the factory 12v system's inefficient wiring
(not all that inefficient in many areas) is something that won't make a
'noticeable difference' in the range of an EV. And those horribly cheap
wiper motors and fan motors Lee talks about? Well, my '68 Datsun has the
original heater blower motor, still spins nicely and works great after
30 years....same for the wiper motor, too. Yes, they don't have ball
bearings (brass bushings instead), and don't use neodymium magnets
either...but they work, and they have held up very well.
           
>Headlights are designed for 12.8v. You run more voltage, >you get more light. But you also substantially shorten 
>their life. 

    Actually Lee, most all of today's headlights run quartz iodine
bulbs, and they last longer at higher voltages. In fact, talk to any
manufacturer of these bulbs (as I have done), and they'll advise you to
do the same type of hot rod wiring mods as I have done, so that their
bulbs will be hit with at least 14 volts. Talk to these same
manufacturers, and they'll also tell you that in customer's cars that
seem to go through bulbs faster than normal, in most all cases, it was
due to an under voltage condition, where the quartz bulbs ran too cool
and the recombination effect was hampered. In past cars that I've done
the hot rod wiring mods in, the quartz iodine bulbs have lasted and
lasted. Blue Meanie has had the same set of H4 bulbs, with 12 gauge
individual wires and 10 gauge power feed for the  past ten years! These
bulbs have been slammed with 14.5 volts of hot DC-DC power since
'93...not one burnt out bulb!

>If you want more light, get brighter lamps and run them 
>at the right voltage.

    This is true only if you're still in the dark ages and are running
sealed beam, non-halogen bulbs. If you take Lee's advice and get
'brighter lamps', then your talking a set of halogen bulb type
lights....once you've upgraded to halogens, take the hot rod wiring
route and give them even higher voltage to work with.

>Automotive wiper motors, fan motors, etc. all use 
>resistor controllers. 

  Sorry, wrongo! Most all automotive wiper motors have winding taps, not
resistor control. 

>A big resistor just burns up the excess voltage to run at >anything but high speed.

      Fan motors do use resistor speed control, but in the case of
heaters, it is supremely efficient, as the speed control resistor is
place in the heater fan's air flow and the resistor's heat is added to
the heat output...in a very small way, it helps to heat the vehicle. In
the heater application, that's 100% efficiency!

>And face it, how often do you use the highest speed?

    When defogging the windshield, almost all the time, as a high volume
of air does a better job of removing the fogged-up condition.

>>It should be sized so that it can run everything without 
>>a 12v battery.

>Why?

   Some of us don't find it acceptable for the important items that make
driving safer (bright headlights, taillights, turn signals, swift
wipers, strong ventilation blower, etc.)  to continuously run down lower
and lower over the driving period in an EV, as they most certainly due
when using an unassisted 12v battery.
     Lee uses his ComutaVan as an example of an EV that can get by with
a stand alone 12v battery and no DC-DC converter, and I am aware that 
there are others on the EV Discussion List who also own either
ComutaVans, ComutaCars, or Citicars, but let's be honest here....these
EVs are not known for having great ventilation and heating systems, nor
are they known for being well suited for driving in inclement weather,
nor are they known for being fitted with creature comforts and options
that many desire and want in their transportation vehicles. These are
spartan,  minimalist type EVs that are hardly comparable to a modern car
or truck. 
      If you have a more mainstream type of EV, such as a small to
midsize car or pickup with 1000-1400 lbs. of batteries for good range,
then you'll need to have higher 12v capacity than Lee is alluding to
here. Most cars and trucks produced from '80 to present, have powerful
defroster blowers that  can effortlessly clear the windshield, but these
blowers usually draw 11-12 amps on high....I don't consider this a bad
thing, rather, these powerful blowers are a godsend compared to the
wimpy blowers of the older vehicles that did a poor job of ventilating.
The total lighting system of these vehicles draw around 14-16
amps.....again, I don't consider this a bad thing, rather, newer
vehicles have safety side marker lights and more powerful headlights.
The brake lights draw 3-5 amps. The wipers draw 4-9 amps, sometimes more
if there's a second wiper in the back.....again, I don't consider this a
bad thing, rather, newer vehicles have larger windshields for better
visibility and thus, bigger wiper blades and more powerful wiper motors
that can easily sweep these big windshields in a hurry...great for those
times on the freeway when you're passing a big tractor-trailer rig that
is covering your vehicle with an ocean of water (exclusion noted for
ComutaVans, ComutaCars, or Citicars that can't even be used on
freeways). What about running a rear window electric defogger?...We're
talking about another 10-12 amps of juice. If it's an even heavier EV
with lots of batteries, you might want to add electric power
steering....we're talking 15-40 amps! What about air conditioning? Yes,
the compressor will either be powered by a high voltage motor or from
the traction motor via belt drive, but there is still the 12v current
draw of the compressor's magnetic clutch, associated relays, and
condenser cooling fans, too....these all want 12v juice.
      To the majority of those who are converting or are considering
converting  a Honda, a Nissan, a Dodge, a Chevy, or whatever mass
produced vehicle you choose, equip it with an adequately-matched DC-DC
converter/backup battery system, and say goodbye to a miserable 12v
system once and for all.

See Ya..........John Wayland