[Vwdiesel] glow plugs low voltage

[raymond greeley]

the inverter direction seems alittle more practicle adding of course a 
second battery just to work
the inverter when we're parked so far away from an outlet. Don't forget to 
hook up a photovoltaic
panel to charge the battery while at work on those sunny cold days.
>From: Sandy Cameron <scameron at compmore.net>
>To: vwdiesel at vwfans.com
>Subject: [Vwdiesel] glow plugs low voltage
>Date: Sun, 13 Feb 2005 22:20:53 -0500
>
>Musings from the near north
>
>I set up a haywire test set on the bench tonight to try some things.
>
>Heavy duty batt charger
>Metered Variac (variable transformer to adjust primary voltage)
>Digital volt meter
>DC ammeter
>
>2 different glow plugs, one Beru (made in Germany) straight tube with blunt 
>end,
>The other, a Bosch with the tapered tube (made in France) part # are on the
>plug, but I didn't bother reading that just yet (very tiny print vs. old
>eyes, Need the illuminated magnifier)
>
>The following figures are not absolute, but practical. Perhaps later I will
>do some more accurate measurements.
>
>Reasoning that extended time operation would likely be best done at a
>voltage/current resulting in  just barely visible redness, adjusted the
>variac to get a faint glow.
>
>3 to 4 amps, about 4 volts = 16 watts, 4 of them would be about 64 watts,
>about  that of a 60 watt light bulb. Not much compared to the common block
>heater.
>
>Typical frost plug block heater for VW is about 300 watts.
>With a thoroughly cold soaked engine to -20C, a half hour of 300 watts will
>bring the engine to a good starting temperature (start guaranteed).
>
>There was an interesting difference between the Beru and the Bosch.
>
>The Beru draws more current as the voltage is raised, more or less 
>linearly,
>while the bosch, once the voltage gets to 6 or so, any increase in voltage
>is met by a decrease in current, keeping the wattage more or less constant
>above 6 or 7 volts. As I increase the voltage, the current goes up for a
>moment, then drops back to slightly less than before. This is obviously the
>ballast trick we have recently read about on the bosch web site.
>
>At this level, from 7 volts up, the color remains about the same, quite
>bright. I really need to mount it in a large heat sink like a chunk of
>engine head to do a fair assessment, as quite a bit of the heat goes out
>through the threads into the head.
>
>Summary:
>The 115 volt block heater is about 300 watts, and is very effective, Able 
>to
>warm a COLD engine to easy starting temperature in about half an hour, and
>if left on all night, the engine will be at summer temperature in the 
>morning.
>
>The glow plugs, in normal use,  produce slightly more than 100 watts each,
>x4=400 watts
>
>Use of the glow plugs at lowered voltage (4 to 6 volts) as a head heater
>would probably be practical, if used in conjunction with synth oil to 
>ensure
>fast cranking.
>
>6 volts would probably be the max for the plugs, to avoid running them at a
>temperature high enough to cause deterioration of the iconel sheath, or
>internal resistive element
>
>The argument for 6 volts would probably be good for plugs mounted in a sink
>like the head, to prevent overheating
>
>This would result in about 100 watts total for the head,  1/3rd that of the
>block heater, and only heating the upper third of the engine (the head)
>where it will do the most good
>
>Now the how?
>
>I opened a glow plug relay to ensure there is no connection of any kind 
>from
>the glow plug rail back to the circuitry. There is not, as long as the 
>relay
>is not operated.
>
>This would permit the use of a 6 volt,  20 amp transformer (120 watts) to
>power the plugs with A/C.
>These may be found by dumpster diving (a la Hagar), or ham radio flea
>markets, but it occurs to me there are tons of 5 volt, 20 amp and up
>computer power supplies lying around everywhere. I must have half a dozen.
>Bonus, there's usually a 12 volt section , that if adjustable, could be set
>to 13.6 volts for the most perfect regulated battery float charger you 
>could
>ever ask for.  I would not suggest the power supply from a PC clone, as 
>they
>are not usually adjustable, but supplies from larger computing equipment
>that are a glut even at junkyards, would do the job.
>
>Now, what to do in the middle of a 40-acre parking lot.
>
>1. The large 6 volt battery on the glow plug rail for 3 or 4 hours, total
>16-20 amps, needs to be about 100 ampere-hours, and in addition, needs to 
>be
>a deep cycle, as an ordinary cranking battery will tolerate about 6 total
>discharge, recharge cycles before it lies down and dies....permanently
>2. There is a better way, a 12 volt, 120 ampere hour, deep cycle RV 
>battery,
>with a 400 watt inverter to get 115 volts A/C, applied to the electric 
>block
>heater for 1 hour max, will get you a toasty start, and you can recharge it
>on the way home from your alternator. Because of entropy (water runs
>downhill, but you have to push it back up, and sweat at the same time), You
>need a battery that can maintain its terminal voltage above the inverter's
>auto cut-off voltage, for the time required. This means you need battery
>capacity about twice as much as the calculated draw of the block heater for
>the required time. The fully charged RV battery will crank out the 28 amps
>needed for well in excess of the hour you need.
>
>Furthermore since batteries cannot be forced to take a complete charge in a
>short time at 13.6 volts (your alternator output, if you are lucky), you
>will have to charge the battery at home all night at a few amps to bring it
>up to full health for the next day.
>But it can (and has ) been done.
>
>This is my choice until I can get my oil burning wintermiser heater 
>installed.
>
>Some of us must park many yards, or even miles, from the nearest electrical
>outlet, (like my wilderness camp) and these tricks can help.
>
>And, of course, there is the Coleman stove, the pan full of briquettes, the
>propane lance on the block, etc. All these have been done and work.
>
>Sandy
>
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