Just getting out of that terrible East Timor crisis some topic back, I found one usefull thing. The PTC heater thermistor.

The Thermistor, having a very low resistance (taking a 5 omhs at 12V) will dissipate around
28.8Watts with around 2.5Amps. When it reach it's turning value (let's suppose it's 190°F), the resistance will climb radically to some MegaOhms, leaving around 0 dissipation (the heat turns off). When the temperature goes down, it will climb again to full heating mode.
Making a regulated 190°F heater.

These things cost around a buck or two each (digikey.com) and can be lead soldered. On one spec sheet, they even stated "Can be used as diesel fuel pre-heater"!!!!!!!!!

Soldering one of these on the tip of the in-tank fuel pickup will assure the veggie is hot enough to travel trough. A bunch of them will sky-rocket the temp of veggie going trough a heat-exchanger. One smaller value one can interface dirt-cheap with a "WVO Ready" light or automatic switching system. Even for the control of a glowplug-oriented heater, it can control the relay to regulate the temperature for a lot less than a thermostat relay.

Is my assumption correct? Am I right? Is this thing sent from god to bless us all?

Anybody used these before?

-Jay, enthousiat about those PTC devices

There was some discussion about cloning the Veg-Therm product from neoteric with tech like this. Another discussion leads to farnel ptc which has some interesting (to me) ptc heaters.

How much did the digikey units cost ? Are they designed to last delivering full heat ?

Glenn

Do you have a digikey part number or catalog page for this PTC heater? I can't seem to find it...

Interesting, I like the idea of soldering one up for an in tank pickup, or one or two for a pickup wand.

Do You have the Digikey # Handy?? I need to order a couple of other things. I could throw a couple of those in to play with.

Nice to see others on this board as interested in these PTC heaters as I am!

I don't know why there's not more excitement about this -- like Jay2 said, it's like these devices were sent from heaven for SVO projects!

For anyone who's interested, here's a link to digikey that has a parts list/search screen for "PTC thermistors":

http://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=478983&Site=US&Cat=30868557

I was not able to find the same info that Jay2 was referring to, but if you poke around you can find different PTC products.

The nice thing about these units is that they are very cheap, BUT if I am reading the info correctly, they are also very small. Like less than 1/2" in size. It might take a few of them wired in parallel to generate some nice heat.

I recently took delivery of some nice PTC heaters from RS electronics:

http://www.rs-export.com

They were considerably more expensive than the digikey ones, but as you can see, they come with a metal housing, pre-soldered leads, etc.



I am going to mount one on the base of my WVO oil filter, just before the IP. The unit is about the size of a pack of Juicy Fruit, and will heat to a self-regulated temp of 100 deg C, drawing a max. of 6-7 amps peak. It will heat up my filter assembly nicely without drawing too much power.

The bad part about ordering from RS electronics was that they're in the UK, and shipping actually cost more than the parts.

If anyone does some research and can find these babies here in North America, it would be really appreciated!

This message has been edited. Last edited by: revOILutionary,

how do you find those on the site, i tried heater, ptc heater,etc. and couldnt find them. i am building my own injector pump fuel heater,using a glowplug right now, but it would sure be nice to use something self regulated.

I think that similar elements are used inside the 12V heaters that plug into your cigarette lighter. I have no idea what the temperature switchover point would be. The ones I've seen advertised say '150W' which would correspond to about 8A (I assume this is at 25C). If I had one I'd take it apart & find out...

These are very similar to ceramic heaters sold for home use (many of these use PTC ceramic elements on an aluminum heatsink). Again I'm not sure how well these would operate on automotive voltage.

I would not suggest using a PTC heating element that was designed for 120V AC ...

I don't have enough electronics background to know whether you could just wire it up for 12V DC, maybe somebody else lurking around here could answer that.

About the 12V DC accessory heaters -- yes, I totally thought the same thing. These things are basically a PTC heater, all pre-wired, etc. so all you'd have to do is take the thing apart and rig it up to your SVO system.

I've even seen these auto heaters for pretty cheap, like $30 retail ... made me wonder if it was worth it to order one just to take it apart and find out!

Check out this link and scroll to the bottom of the page to see what I mean:

http://www.caframo.com/12volt.htm

Attach the ceramic element to the housing of your IP, or your filter assembly, or your SVO tank, I dunno -- numerous possibilities! Especially for those of us with cold weather issues.

ABOUT THE PTC heater search:

On the RS website, just type "PTC heater" in the search box. Should work. The ones you're looking for are made by "European Thermodynamics".

BTW, just one thought:

I think the only draw back to these "miraculous" PTC heaters is this:

The heat isn't instantaneous. It takes a few minutes to reach rated temps. Especially in colder weather.

In terms of instant heat, the glow plug/nichrome designs of Dana and others around here are probably better.

I'm going to do a garage test in the next week of my nifty PTC packs and do a time/temperature test and see what the time vs. temp specs are. I'll let everyone know when I'm done.

I used to be an outside mirror engineer for Cadillac. We had heated mirrors, and had a standardized test where we got a calibrated amount of frost on the glass, threw voltage at the mirror and it had to clear a certain percentage of the glass in a certain mount of time in an environmental chamber at -40 C.

We used flat printed laminated PTC heaters behind the glass for this. Simple, cheap and reliable - and worked good for a single pane of glass - like most mirrors are.

Many cars have self dimming mirrors - which adds a second sheet of glass, and some electrically controlled gel in the middle. This means that the heat for the heater now has to go through this glass gel glass sandwich to get to the frost.

We were seeing that the amount of heat generated by the PTC heater was GREATER than the heat transfer capacity of the glass. Thus, the PTC would get nice and warm, but the frost wouldn't. Since the PTC had gotten warm, it started to increase resistance and shut itself down - even though the frost wasn't warm yet.

The point is that if the thermal conductivity between the element and the oil is lower, the PTC will simply match the capacity at what ever temperature it's designed to.

A non-PTC heater just puts out the same number of watts no matter what - and they have to go somewhere. If the system has a low thermal conductivity, the element will get hotter - thus increasing temperature differential until the system can keep up with the elements heat generation rate - or the element melts - whichever comes first.

In system where transient response is desired - like the initial heating of WVO - traditional heaters might be a better option. Once the material has reached steady state, an appropriately sized PTC is probably a better bet...

Eric K

The digikey parts are meant to be used as overload devices. They have a very steep temperature to resstance curve - thus they may tend to oscillate - or at least reach equilibrium allot sooner that we'd want. I doubt they have enough internal temperature capacity to function well as heaters. They MAY function well as controllers/temp sensors in a system set up for traditional heater elements. Put one in fluid flow just after the traditional heater, wire it in series, and use it as a T-stat for a more traditional heater.....

Eric K

http://dkc3.digikey.com/PDF/T042/SectF.pdf
Top of the page 936. The first one of the list is the king.

First, a small class of electronics 101 applied to PTCs.

A resistance is a passive component that will restrict current, and radiate heat. Exemples of resistances-based heater are everywhere, your water heater (electric ones) use a use resistive element to heat water, your toaster use resistive fillaments to radiate heat, your stove use a resistive element to heat, etc.

In all cases, these two formulas are to remember:
V= RI
P= V²/R = RI²
Where V is voltage (whe talk about 12 V here)
I is the current, in amps (a traditional car alternator will put out 60-100 amps total)
R is the resistance value in Ohms (Less Ohms, more heat).
P is the power in WATTS. 745 Watts aproximately makes one HP.

This watt rating is the same you see everywhere, including that 150W heater PdxWaker saw, meaning at 12V, the device has around 10 Ohms of internal resistance.

Now, these devices usually have a voltage rating. As a passive component, it's not a "operating voltage", but a continuous load, maximum voltage (usually). A toaster can but plug straight into a 12V plug, but the power will be down by a factor 100. If the same toaster is pluged into a 6000V outlet (No, there is none here), the toaster will work, but the current might be so great that it could melt the wires inside. That's why there is a max rating, but there should be no minimum one.

About AC power. Yes, as a passive element, you can use AC, but be sure to use RMS values to calculate the power dissipation and peak values to calculate maximum voltage. Exemple, in a 120V AC standart outlet, it is in fact 120V RMS with 165V peak tension. So you must chose a PTC that will operate on 165, and do the math with a V=120.

About Glow-Plugs, they are resistance too. very very small resistive values, but a resistance. I remember reading on this forums about guys who putted a continuous half-voltage to them to get 1/4 the heat while driving without hurting them too much.

Some here are wondering if these are heaters or control elements. THEY ARE BOTH!. Read this,
http://www.atpsensor.com/ptc/ptc_applications/ptc_applications.html?=ptc_appliancemag_main.html
To simplify, the resistance values can be used as a sensor when the device is heated, or the device can be put under current to produce heat.

The PTC have ONE and only one caracteristic making them interesting: They have a varying R value. Let's say whe have a 120°C (Tmax), 10 Ohms PTC. Under a 12V load, the power dissipated will be 14.4W. This will soon bring the PTC to it's Tmax rating, 120°C, where it's R value will change from 10 to 10000, and the PTC will produce a MILLION time less heat. As soon as the temps goes under, the PTC will heat again, making a regulated heater.

The glow plugs, on the other hand, will produce much more heat, but wont stop by themselves, so you have to regulate them somehow (yes, a PTC, a relay and a small transistor can regulate a glow plug easily too!).

Now, the next class: Heat transfer and thermodynamics (most of you guys know more than me!)

A resistive element produce heat. the more power, the more heat. Yes, it will take time to heat something, but it depends on the heated substance. For veggie, I guess the values must be nearby those of water, wich I recall are around 4.3j/°C/ml. (a Watt is a j/s) So, you need 4.3W to heat one mL of veggie by 1°C in a second. If you want to heat veggie from 60°C to 100°C, in a device wich the veggie pass trough in 1 sec, you will need 172W. I might be wrong on this calc. So, the time any resistive elements take to heat anything depends only of the power the device dissipate, and the energy capacity of the heated substance.

The only problem with theses is the junction temperature. Since a PTC alone is small, it won't conduct much heat as mtushmoo stated. To get around this problem, we can simply enlarge the device with heat-conductant materials, or put them dirrectly on the flow of veggie.

We can see images of "already sandwiched PTCs" some replies above. IT is a normal - digikey style - PTC, but enclose in a aluminium case for better heat transfer. The plan is there: take an aluminium plate, put a lot or heat transfer paste, put another aluminium plate on top and glue each side with Hi-Temp epoxy. You now have a high-conducting device with long surface for better transfer.

I was planning to make a device wich look like this: [BEHOLD!!! here comes my ascii talents! ]

  
   /---------------------------------------\
   | +|    +|    +|    +|    +|    +|    +| ==== <- Inlet 
====    +|    +|    +|    +|    +|    +|    |
   \---------------------------------------/

   + = PTCs
   | = walls

So each PTCs will heat, and has the WVO flow will pass around them and "cool" them, they will alway pus heat, unless it is not needed anymore, making sure they car won't explode if the device is still on while the flow stop.

A sandwich with a some of these can be soldered to a square-shaped filter to heat it, etc.

Have fun,
-Jay2.

This message has been edited. Last edited by: Jay2,

Here's the datasheet for the device you mentioned...
http://rocky.digikey.com/WebLib/Thermometrics/Web%20Data/KCxxxP-ND.pdf

It really isn't designed to be a heating element.

A better option would be these guys:
http://www.thermometrics.com/assets/images/pth.pdf

Unfortunately I couldn't find these on the digikey site. I'd love to order some up if a source can be found...

-John

Big thanks to Jay2 for the informative post.

It's nice to understand the science behind all of our garage tinkering!

Well... you sure are right. Those are not meant to be used as heating elements, but as sensors. Still, I'm pretty sure they can be used for both. with those small resistive value, the PTCs will dissipate heat, they have no other choice.

And note that the only hint it is not designed to be a heater is they state it is over-current protection, and they do not seem to exclude any use or state particularity wich could make it a "non-standard PTC". My "educated guess" is that protection is a wealthy market, and they target it. Still, I beleive thus is still a nice heater. We won't have much choice but to spend 2 bucks and check this fact out.

-Jay2

You're probably right... they should work as heaters as well. I'm wondering if you could even desolder one of the terminals and solder this side directly to an endcap of a copper pipe or to a heat sink. The pipe or heatsink could be GND for the circuit.

Also - you might want to consider an even higher impedance device if you plan on several of these in parallel. A single device will draw over 12A at 25C...

If you experiment with these please post your results. These devices could be really useful!

-John

i have been doing some research on these ptc things, they can be made to heat anything to any temp. search immersion heaters ptc, you find them. they also look like they could make very useful glowplugs, they come in sizes very close,big orders made to order. running constant, or warm up glowplugs seems to help mine out a lot,my oil immersion heater before my ip is getting my oil very hot, but it still looses at least 40f traveling through the injector pump and the exposed,metal injector lines, i can still touch them!i guess i will order a ptc 12volt defroster or heater on ebay this weekend, and tear one apart and test it for an injector line heater.i will let youall know how hot the element gets.

As I understand it the new Dodge diesel Duramax has an "Acrtic kit". This kit consist in part of a 12v (I think) fuel tank heater that is basically a glue on tank heater. This could possibly also be used to heat the injector lines maybe? Like put an aluminum or tin plate over and under the injector lines; sandwhiching them, with the duramax heater attached to the top plate. And/or.... insulate the hell out of them.

Maybe insulate the the fuel canister filter as well. I could see a cold beverage (beer can) glove thingy being modified to cover the fuel canister filter.

JMJ,
Sorry to be picky, but the Duramax is a Chevy, not a Dodge.

<i>The Thermistor, having a very low resistance (taking a 5 omhs at 12V) will dissipate around
28.8Watts with around 2.5Amps.</i>
<p>That isn't very much heat. The VegTherm (for example) produces over 10 times as much (30 amps @ 12 V)