Smoke Unit in LVTP-7 - Page 5 - RC Groups
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Feb 18, 2010, 04:03 PM
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Dan ;
Hold on to the wirewound resistors you bought ...
They might be exactly what we're looking for ...
I did some researchs about resistor and found some interesting info on Wiki....

Here's a copy of the chapter about wirewound resistor

[edit] Wirewound

Types of windings in wire resitors:
1 - common
2 - bifilar
3 - common on a thin former
4 - Ayrton-PerryWirewound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to two caps or rings, attached to the ends of the core. The assembly is protected with a layer of paint, molded plastic, or an enamel coating baked at high temperature. Wire leads in low power wirewound resistors are usually between 0.6 and 0.8 mm in diameter and tinned for ease of soldering. For higher power wirewound resistors, either a ceramic outer case or an aluminum outer case on top of an insulating layer is used. The aluminum-cased types are designed to be attached to a heat sink to dissipate the heat; the rated power is dependent on being used with a suitable heat sink, e.g., a 50 W power rated resistor will overheat at a fraction of the power dissipation if not used with a heat sink. Large wirewound resistors may be rated for 1,000 watts or more.
Because wirewound resistors are coils they have more undesirable inductance than other types of resistor, although winding the wire in sections with alternately reversed direction can minimize inductance. Other techniques employ bifilar winding, or a flat thin former (to reduce cross-section area of the coil). For most demanding circuits resistors with Ayrton-Perry winding are used.

It seems to be combining the best of the nichrome and the resistor element in one package...
I need to dig more infos as what (for example) a 12 Ohms 1/2 Watt wirewound res. would look like ( size , etc.) and try to get some for testing...

In any case I think we're on to something...

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Feb 18, 2010, 07:40 PM
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Hello Norm and Dan,I have been dealing with some I.P.issues and my router.I may have resolved this issue so I will try to catch up to you guys testing and resulting Data.Some thing came to mind about the wicks.I have a sheet of flame resistant material,it's not asbestos but has that degree of fire resistance,but it is absorbent like cotton.I will attempt to purchase some resistors tomorrow and test this materiel.I actually have a large sheet and was thinking of sending you guys a nice sized section to test in the different models you guy's have developed.Dan I will call you at 7.00pm and Normand I will send you some material if you like,just PM your address,I am sure it will be a good material because it will not become brittle after heating.Well I leave you guy's alone for three days and you re-invent the wheel,excellent work guy's,very exciting possibilities,ships,trains,planes,tanks,trucks just about every type of RC out their,the large scale semi-trucks could benefit from this kind of effeicent fogger/smoker just opens the door to better effects,Torpedo chief Had an idea to inject smoke from the devise as the Tank fires and recoils,a slot and opening hole that aligns at recoil allowing smoke to enter the barrel so as the airsoft round fires off it is followed by smoke,now how cool is that..I look forward to the discussion.Best Regards Blake
Feb 18, 2010, 07:46 PM
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I forgot to post this calculator,we use this on the lighting systems on motor cycles,Both L.E.D. and Fiber optic.
Feb 19, 2010, 10:57 AM
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latest experiment

Last night I decided to test an idea I had a while ago after viewing a video posted on this forum by Yellowshaker ...It's a video of his tiger1 using the "Creeping Death" sound module ...One thing that drew my attention when I checked their site for more info. was that they are using 2 extra battery packs to power their unit ...

Then I thought why not use an extra battery pack to power the heater element of my modified H.L. smoker ???

I used a 2000 mAh NiMH Matorro pack in a semi-proportional configaration : Where the extra pack is providing a constant power to the 12 Ohms 1/4 Watts resistor and only the speed of the fan varies with the speed of the tank ...
Since the power to the element is independant from the rest of the tank ; There's no "power drop" when I bring the throttle up ...

The running time of the tank should remain about the same ; may be a little bit shorter due to the weight of the extra pack ...
( since I am running a Pershing and have already added extra weight to the front to keep the nose down ( following the advice of members of these forums ) ; replacing that "dead weight" by a battery pack looks like a good deal ...

I connected a Volmeter at the exta pack terminals and an Ampmeter in the line to calculate the power .
I took pictures when I started ; more pictures 1 hour later ;and more 2 hours later...

Another idea came to me during the test ...
Since the groung terminals of the 2 battery packs are connected together ; why not connect the (+) terminal of the extra pack to a 2 way switch (S.P.D.T.) and have 2 modes of operation for the tanks ...

The 1st mode ("smoke") would provive the same running time than before with a lot of smoke coming from the exhausts ...

Flicking the switch would bring you to the 2nd mode ("non-smoke") ; disableing the smoke unit and connecting the extra pack in parallel with the main pack ; increasing the total capacity ; therefore extending the running time ....

Here's the pics from my test ....
Feb 19, 2010, 11:15 AM
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about that 12 Ohms 1/4 Watt resistor

Dan ;
I did that test last night without replacing that 12 Ohms 1/4 Watt element that has been in my smoker for the last 15 days....
If you calculate the power using the 1st pic : 8.44 Volts x 0.73 Amps = 6.16 Watts . I had an overload factor of 24.6 ...
When I took a Ohmmeter reading this morning ; the value was 12.4 Ohms

Tought little bugger ain't it !!!!
I plan the perform an autopsie of that element this week-end ...I want to know especially the conditin of that kevlar wick...

I'll post some pics
Feb 19, 2010, 05:53 PM
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Hello Guy's,check this out,information on different Wire wound resistors.Sax Also on this site they have a resistance builder/calculator that will produce the color of the resistors based on input information.Just makes it simple to identify resistors based on what is required,say you want 12.1ohms,the builder will show each type or color code that is available.They even offer a builder service,don't know about cost but It could be a useful vendor.Norm your battery Idea works for me in the Asiatam components tray you could stack two batteries no problem,not sure about my Jagdpanther yet as I'm following XRADS halfbreed build and using a Tamiya lower hull and hardware,still should be able to stack batteries.Sax
Last edited by SAXONDOG; Feb 19, 2010 at 06:05 PM.
Feb 20, 2010, 10:56 AM
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DanL's Avatar
Wire wound resistors in a ceramic package (see pic) - called "sand" resistors - are probably the best bet for smoker heat elements.

Here's a tidbit from the Ohmite site:

"Are Metal Film resistors superior to Wirewound Resistors?
No. In virtually every comparison we have made, and well as those published by Duncan and Colloms (1), wirewound resistors clearly outperform even the best metal film resistors. This should come as no surprise. Wirewound resistors use actual high quality metal alloy wire as a resistance element, rather than a thin, poorly-conducting vapor-deposited metal film. On the quantum level, the resistive wire of a wirewound resistor has tight molecular packing and long alloy crystals, where as the vapor deposited metal layer of a metal film resistor has large gaps between molecules and small crystals. The integrity of the signal degrades very little in an alloy wire, but significantly in the vapor deposited metal film. The only benefits of metal film resistors are size and cost, neither of which are of any significance in this context."

Carbon, metal film, etc resistors are all likely to hae a short life and have large resistance shift when heated. Strmnd - you seem to be having great luck with your 1/4 watt at high loads. Better tha my experience. I'm now using the wirewound sand resistors and see stable current (R not changing with heat). The ceramic body has some advantages over the epoxy bodies of other resistors - will not burn, rectanguar "box" geometry gives more surface area than cylinder, usually thicker/stronger leads on sand resistor and a rough surface that holds the wick securely in place (no slip/slide).

Once temp gets to the point of evaporating the fog juice, higher temp is not necessary. Better to go with a higher wattage resistor (bigger/more surface area) I think. Ideal is not to see a lot of black gunk build up quikly on the wick. So I'm focusing on designing by 1. determine battery V to be used, 2. deciding wattage to be used for element (more watts=more smoke, but less run time), 3. calculating R to get wattage desired, 4. picking a sand resistor close to that R value and at a wattage size to get an "overload factor" of about 10 or less.

Seems that smaller tank smokers are in the .5 to 1 amp at 7.1V (generally less than 10W) range because of battery type and limited size. Boat smokers are bigger, 1-2+ amp at 12V range (generally more than 10W) because of big lead acid batteries, more room, and more smoke needed given breezes on the water.

The latest set up for boats - a 10ohm, 2W sand resistor at 12V, 1.2A, is putting out a LOT of smoke. That's a 14W element running at an overload factor of only 7.

Maybe try a cooler element at lower load factor and kick up the watts just a tad to get more smoke more efficently.
Feb 20, 2010, 12:23 PM
Registered User
Congratulations Dan ;
It's another step in the right direction ...
I attribute the longivity of my resistor to the use of a kevlar wick versus cotton ...It seems that kevlar doesn't degrade as fast as cotton ; therefore providing a longer lasting cooling of the resistor ...
A combination wirewound resistor and kevlar wick might be what we're looking for ...
In any case my test was somewhat extreme ...The amount of smoke obtained is too much to be realistic in a tank ...Witch is good news...
Not only the 12 Ohms resistor made it throught but the voltage drop at the battery terminals doesn't exceed 1 Volt after running 2 hours straight ...

I plan to repeat the test using an 18 Ohms 1/2 Watts resistor ( overload factor of 6.25 ; calculated at 7.5 Volts) ...
The smoke output should be more realistic ; the resistor should last longer ; and the voltage drop should be smaller ...
It should be interesting ...
I'll keep you posted ....
Feb 20, 2010, 01:24 PM
Semper Fi
GreenAmphibian's Avatar
You guys have really taken this and run with it! I have been reading all of these posts and am impressed with what has been discovered. We should have economically feasible compact smoke units for our models that we can make ourselves soon with what is shared here!
Feb 21, 2010, 12:58 AM
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resistor autopsie

I took apart that 12 Ohms 1/4 Watts resistor I had in my smoker since Feb. 04 ...After driving it with an overload factor of 19 for 15 days straith and up to 24 for a while ; it's not a surprise that it look like charcoal ...The wick had started to carbonised and stick on the resistor ...Althou it still reads 12.4 Ohms ( still within the + or - 5% tolerance as per the gold band ) I don't think it would have last much longer ...By comparison ; the heater element in my last H.L. unit lasted 2 days ...So it's not bad at all .....

Lowering the overload factor and using wirewound resistor as suggested by DanL is the way to go ....
Feb 21, 2010, 10:51 AM
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DanL's Avatar

Fog fluid and wicks

Most of that tarry, black buildup is probably from impurities in the fog fluid. The better fog fluids use very pure water and glycol ingredients and wicks should last longer, but will still eventually gunk up. So even kevlar wicks will have to be replaced after extended run times.
I have 1/2" wide, 1/16" thick kevlar tape wick. It was only 39 cents per foot on sale (postage was almost as much as the order), so wick replacement won't break the bank...
Feb 21, 2010, 02:47 PM
Registered User
Hello Norm and Dan,as I have messaged to norm my computer crashed and I will be off-site until Wed,but it seems you guy's have worked out the resistor issues,I am going to go with the 12v system in my 1/6 scale Tiger and will build the unit based on this thread.Dan have you worked out the baffling or still testing this method? I will be missing out but will try to catch up soon.Dan it will also be Wed.before I can Send the pictures,I will send both tiger and Jagdpanther hull photos at that time.Great job guys hope to be back on Wed.Blake
Feb 21, 2010, 04:40 PM
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12 Ohms 1/4 Watts

Dan ; I have to confess I didn't follow your advice for that one : When I put that element in my smoker on Feb 04 ; I was still using glycerin as smoke fluid . When I switched to glycol last week , I didn't change the wick or anything ;
I waited for the system to get low on oil and started to refill with glycol ...When I said " that resistor has been used and abused " I meant it...
Feb 21, 2010, 05:10 PM
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last test with extra battery pack

Hi guys !!!
I decided to do another test using an extra battery pack to power the heater element of the smoker ...
Same rig that the previous test ; except for the element which is made of an 18 Ohms 1/2 Watts resistor wrapped in a kevlar wick ...
I am using "glycol fog juice " as smoke fluid ...

The test lasted almost 5 hours and I had to refill 3 times ...

Here's some pics ...
Feb 22, 2010, 12:37 PM
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DanL's Avatar

Burn Out Test

I ran a 10ohm, 2W wirewound sand resistor at 12V (1.2A, 14W) until the fluid ran out and the wick actually dried out and fluid residue in the wick was charred. Opened up the unit. The ABS box was just beginning to show surface melt around the stack port. Unwrapped the wick and the outer shell of the resistor cracked off. Inner core was still good, but the unit will fail if run to full dry.
Noticed that on this unit, 2x3" box with .75" long resistor - much bigger than the modified HL box - the wick quickly darkens in the center after short use. I tried wrapping the full width of the resistor in aluminum foil - maybe 10 layer wrap - don't go out too far and short out the leads - and retested with a new wick. Light, even browning the full width.
So, to even out the temp profile on the bigger resistor (prob not necessary on 1/2w or 1W sizes) and further moderate high T stress on the resistoe, the aluminum wrap seesm a good addition.
Here's a short clip of the smoker with two outlets.

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