preheater troubles

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Remember, with the transistor fully on, there will be little voltage drop across it. Therefore there will be little power dissipation. ... Little heat .

you need to bias it half way between the rails to get the most power / heat, out of it.

It's early, so I might have missed something there ! ...

Like I said on FB, a plain old power resistor would be much simpler :)

Rich

Reply to
tricky
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Not true when emitter to collector is right across the battery. 10A @

12VDC =3D 120W

not true at all without a load. I had nearly the same convo with a guy I work with. Like you, he normally thinks a transistor drives a load. What if it is the load and is operated as just a variable resistor?

paradygm shift

I'll post the heat chart from the simulator now so you can see how it'll work.

Reply to
davygrvy

I must admit, my interest is audio. Different classes of output have different heat characteristics. Usually for a fully on transistor, the power/heat is dissipated in the load. If you have no load ... then I guess you have to over current the transistor to get the same max power, for the rating of the transistor ?

However you figure it , P = VI If the transistor is shorted (fully on) then you only have the junction voltage drop to put in the equation . Therefore you cant get the full power if you stick to the max current rating .

It's been about 20 yrs since I did this thought process, but you will still have to convince me I am wrong ! LOL

A simple resistor will give you a set amount of heat without any controll needed - bar a thermistor circuit to switch it off. -

Reply to
tricky

Mine, too

Reply to
davygrvy

I think google dropped my other reply. lemme do it again.

When emitter of the heat making PNP is connected to battery plus and collector to battery minus, Vce is constant (at least to the capabilities of the battery which is good assuming start current is about 80 amps). To get a current of 1A through a transistor (Ic) you need 1/Hfe current through the base. For a 2SA1943, Hfe is about 50. Therefore, I need to pull 100mA to get 5A. 5A*12VDC =3D 60 watts of heat.

Ouch! That full capabilities of the battery. That's a crazy amount of current. You mean saturated? Doesn't get there. There's a clamp, it can't happen. Vary R11 to set the clamped base current.

Replace Q5 with a higher current type, R11, and maybe use three diodes in the clamp to get you the 300mA so you can pull 15A through Q4.

15A is 180W @ 12VDC. Do you or I need that much? Can my ignition switch handle it if I use the coil feed? I dunno yet until I make one and see what I like. I'd like to get in the car, place the key to the on position and pause waiting for maybe a minute or so while the temp comes up. Colder it is outside, longer I wait until I kick it over. Would 60 watts get the temp of the manifold from freezing to 20C in a minute? no clue until I try. 60 watts is just an initial guesstimate for me until I know better.

Naww, not tunable. well it is, but I'd have to replace a $10 (or so) power resistors compared to 2 cent resistors in a circuit board.

Reply to
davygrvy

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Reply to
davygrvy

A $3.25 2SA1943 TO-3P transistor has a 150W Pmax rating (probably for the lead size). A 50 watt Ohmite 850F2R6 at 2.6 ohms runs about $6. A transistor is still cheaper, has a smaller mounting area, and is a whole lot more tunable than a power resistor.

Reply to
davygrvy

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Doesn't Carb icing occur whilst you are driving ... not before you start the engine ! ?

Reply to
tricky

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Yup. When it happens and the car stalls, you can sit and wait it out until the heat soak has thawed the carb and manifold.

J.

Reply to
P.J.Berg

Exactly my issue. It starts fine from dead cold, but stalls after 15 seconds. runs like poo for the next five minutes. Temp of the carb base drops about 8 degrees C from ambient to just a few above freezing. preheat, now, isn't doing much work on the manifold to keep it warm with the newer exhaust. Later when the oil temp comes up, it runs fine.

must make more heat... electrically.

Reply to
David Gravereaux

On Dec 6, 2:39=A0pm, tricky wrote:

Rich, If you want, please double check my work. Grab LTSpice for free @

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load thisschematic and run the sim which will plot values over temperature.Bring the mouse over Q4, hold down the Alt key and click to plotdissipation.

Save the following as manifoldHeater.asc (between the ---- markers) using notepad or whatever

---------- Version 4 SHEET 1 1512 1024 WIRE 80 -144 -48 -144 WIRE 304 -144 80 -144 WIRE 432 -144 304 -144 WIRE 592 -144 432 -144 WIRE 880 -144 592 -144 WIRE 1056 -144 880 -144 WIRE 1184 -144 1056 -144 WIRE -48 -80 -48 -144 WIRE 304 -80 304 -144 WIRE 432 -80 432 -144 WIRE 592 -80 592 -144 WIRE 880 -80 880 -144 WIRE 1056 0 1056 -144 WIRE -48 32 -48 0 WIRE 144 32 -48 32 WIRE 432 32 432 0 WIRE 432 32 224 32 WIRE 592 32 592 0 WIRE 880 48 880 0 WIRE 992 48 880 48 WIRE 304 80 304 0 WIRE 528 80 304 80 WIRE 80 112 80 -144 WIRE 304 112 304 80 WIRE 1184 112 1184 -144 WIRE -48 160 -48 32 WIRE 16 160 -48 160 WIRE 432 160 432 32 WIRE 432 160 368 160 WIRE 880 160 880 48 WIRE 192 208 80 208 WIRE 304 208 192 208 WIRE 592 208 592 128 WIRE 640 208 592 208 WIRE 768 208 720 208 WIRE 816 208 768 208 WIRE -48 224 -48 160 WIRE 432 224 432 160 WIRE 192 240 192 208 WIRE 768 256 768 208 WIRE 144 320 112 320 WIRE 192 368 192 336 WIRE 592 368 592 208 WIRE 880 368 880 256 WIRE 768 384 768 320 WIRE -48 496 -48 304 WIRE 112 496 112 320 WIRE 112 496 -48 496 WIRE 192 496 192 448 WIRE 192 496 112 496 WIRE 432 496 432 304 WIRE 432 496 192 496 WIRE 592 496 592 448 WIRE 592 496 432 496 WIRE 768 496 768 448 WIRE 768 496 592 496 WIRE 880 496 880 448 WIRE 880 496 768 496 WIRE 1056 496 1056 96 WIRE 1056 496 880 496 WIRE 1184 496 1184 192 WIRE 1184 496 1056 496 WIRE 592 544 592 496 FLAG 592 544 0 SYMBOL npn 16 112 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL npn 368 112 M0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL pnp 528 128 M180 SYMATTR InstName Q3 SYMATTR Value 2N3906 SYMBOL res -64 208 R0 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL res 288 -96 R0 SYMATTR InstName R4 SYMATTR Value 4k SYMBOL res 416 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL pnp 992 96 M180 SYMATTR InstName Q4 SYMATTR Value D45H11 SYMBOL Misc\\battery 1184 96 R0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL diode 784 384 M0 SYMATTR InstName D1 SYMATTR Value 1N914 SYMBOL diode 784 256 M0 SYMATTR InstName D2 SYMATTR Value 1N914 SYMBOL res 736 192 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 1k SYMBOL res 416 208 R0 SYMATTR InstName R8 SYMATTR Value 8k SYMBOL res 576 464 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R9 SYMATTR Value 330 SYMBOL npn 816 160 R0 SYMATTR InstName Q5 SYMATTR Value 2N3019 SYMBOL res 864 -96 R0 SYMATTR InstName R10 SYMATTR Value 470 SYMBOL res 896 352 M0 SYMATTR InstName R11 SYMATTR Value 7 SYMBOL res 576 -96 R0 SYMATTR InstName R12 SYMATTR Value 1k SYMBOL res 240 16 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R13 SYMATTR Value 680 SYMBOL ntc_resistor -32 -96 M0 WINDOW 0 55 38 Left 2 WINDOW 38 52 76 Left 2 SYMATTR InstName U1 SYMATTR SpiceModel NTCALUGE2C90169 SYMATTR Value "" SYMBOL nmos 144 240 R0 SYMATTR InstName M1 SYMATTR Value LND150 SYMBOL res 176 352 R0 SYMATTR InstName R1 SYMATTR Value 40 TEXT 16 536 Left 2 !.op TEXT 16 616 Left 2 !.step temp -10 40 1 TEXT 408 248 Right 2 ;temp\nset TEXT 904 384 Left 2 ;max\nheat\nset TEXT 976 112 Left 2 ;*HOT* TEXT 232 -264 Left 2 ;60 watt VW intake manifold (carb base) heater TEXT -184 744 Left 2 !.SUBCKT NTCALUGE2C90169 1 2\n*

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\n.PARAM R0=3D10k\n.PARAMB=3D3984\n.PARAM TK=3D273.15\n.PARAM T0=3D25\nRP 1 2 1G\nB1 1 2 I=3DV(1,2)=/ {R0*exp(4000*(1/(TEMP+TK)-1/(T0+TK)))}\n.ENDS TEXT 536 720 Left 2 !*\n*LND150 MODEL\n*\n.MODEL LND150 NMOS (LEVEL=3D3 RS=3D150.00 NSUB=3D5.0E13\n+DELTA=3D0.1 KAPPA=3D1.O TPG=3D1 CGDO=3D2.1716E-12\n+RD=3D40.0 VTO=3D-2.0 VMAX=3D1.0E8 ETA=3D0.1\n+NFS=3D6.6E10 TOX=3D1.0E-7 LD=3D1.698E-9 UO=3D862.425\n+XJ=3D6.4666E-7 THETA=3D1.0E-5 CGSO=3D5.09E-10 L=3D10.0E-6\n+W=3D600E-6)

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Save the following as ntc_resistor.asy (between the ---- markers) Place it in %program files%\LTC\LTSpiceIV\lib\sym\

---------- Version 4 SymbolType CELL LINE Normal 16 88 16 96 LINE Normal 16 16 16 24 LINE Normal 27 24 5 24 LINE Normal 5 88 5 24 LINE Normal 5 88 27 88 LINE Normal 27 24 27 88 LINE Normal 40 40 -8 88 LINE Normal 40 24 40 40 LINE Normal 40 24 40 24 WINDOW 0 53 31 Left 0 WINDOW 38 52 60 Left 0 WINDOW 3 52 92 Left 0 SYMATTR SpiceModel NTC_R SYMATTR Prefix X SYMATTR Description Universal NTC Resistor PIN 16 16 NONE 0 PINATTR PinName A PINATTR SpiceOrder 1 PIN 16 96 NONE 0 PINATTR PinName B PINATTR SpiceOrder 2

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Reply to
davygrvy

What you are describing is not carb icing, it would never happen after

15sec, only when you actually drive the car with partly open throttle/high vacuum. The preheater tubes even when connected to a proper exhaust would not even start to get warm after 15sec.

I have not this whole thread saved and cant remember your exact carb.

It sounds like a typical auto choke issue. Have you checked setting/freedom of movement and function of the heater element working on the bi-metal spring? Also, have you checked the base setting of the butterfly itself? How about intake leaks? Gaskets, bent flanges etc.

J.

Reply to
P.J.Berg

I should have added here: With the engine off(It is stalled and won't run anyways), it takes a while for the heat soak from the heads to travel all the way up to the carb. I spent a few very very cold moments sitting stationary in my -56 in 15-20C below freezing as a youngster..

J.

Reply to
P.J.Berg

This is the kicker, the choke is working fine. Carb is a Solex (actually made by/for Kafer) 34 PICT/3 on a 1600cc dual port. Manifold isn't stock, but the same type just done in aluminum:

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I swapped the exhaust a few weeks ago. The car didn't have the problem before the exhaust swap, but temperatures here did just drop, too. The engine starts wonderfully from dead cold only to just stall 15-20 seconds later and from there on it runs like poo until the oil temp comes up.

By 'running like poo', I'll define that as if it's running on three cylinders with horrendous bog. plugs are fresh. It doesn't appear to be ignition as I've pulled plug wires while it's doing this and each I pull makes the engine run slower and even more out-of-balance. So it's not ignition.

I'm convinced I have an intense wall wetting problem I can cure with a warmer intake manifold.

Again, it runs fine when warm. I only say 'fine' cause I'm sick of the lame aircooled.net SVDA distro I've had for the past 5 years and I'm dropping in a Mallory Unilite series 47 from another motor I'm not using so I can finally tune it to a proper curve.

I will check (again) for a tight valve in the morning, but it holds a steady valve adjustment.

Reply to
David Gravereaux

Consider dual Kadrons. On each of my AVWS I run short-intake duals (One with two dual Webers, the other with dual Kadrons. No icing. Ever.

Reply to
John J Stafford

Have you got a stock Solex carb to try out?

It could very well be that the fuel metering on the replacement carb is out of whack, I'm thinking idle and transition circuit. Also make sure the base setting of the butterfly is spot on(choke 100% off, slack throttle cable, the screw on top of the long lever facing the rear -> off its stop on the carb body, screw it in until it barely touches the stop, then 1/4 turn inwards).

Make sure to check the two rubber boots/grommets(I forget the name) on the intake very carefully, have been burned there myself once.

J.

Ps. Unless the Mallory comes with a vacuum sensor i would stick to the svda dizzy.

Pps. A tight valve would only get worse as the engine heats up.

Reply to
P.J.Berg

Have you had a look here:

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J.

Reply to
P.J.Berg

Here is a page demonstrating modifying a header for stock heat riser hook up.

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I was actually looking for a different pic. I have seen somewhere, this however works the same way. If you look at some of the posts in that thread you will see the late Mr.Hoover giving his approval, that should count for something. :o)

I cant remember whether your exhaust had a header with collector behind the silencer or not.

J.

Reply to
P.J.Berg

Agreed! I'm thinking the redline K1411 kit with the Weber ICT carbs (but with manual choke)

Reply to
David Gravereaux

I may have already mentioned this, but if you use a stock muffler beware that the Venturi should be on the right side of the muffler. It is inside and you can see it if you take off the fweem pipes and peek with a flashlight. The Venturi goes over the heating pipe and 'pulls' hot air through the carb heater.

I got a Mexican muffler where the Venturi was on the WRONG SIDE.

An electrical heater puts a load on the alternator/generator, sucks horsepower. I don't even like to run with the lights on. :)

Reply to
John J Stafford

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