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D.C.-D.C. Step-Up Converters Discussed
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 Posted: Wed Feb 18th, 2015 02:36 am
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Tramcar Trev
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Various heatsinking missadventures led me to this stuff double sided thermal tape here its cut into 1" squares but it can be got in A4 sheets; http://www.ebay.com.au/itm/20pcs-25-25mm-Sticker-Square-Sided-Thermal-Adhesive-Tape-for-Heatsink-heat-sink-/291319829617?pt=LH_DefaultDomain_15&hash=item43d403d471

Very handy means usually no mechanical fastening is needed...



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 Posted: Wed Feb 18th, 2015 02:38 am
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Tramcar Trev
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mwiz64 wrote:
http://www.ebay.com/itm/with-ENABLE-DC-3-3V-3-7V-5V-6V-to-12V-Boost-Converter-Power-Supply-Step-up-Board-/271366097420 They are neat but only handle 450mA.



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 Posted: Wed Feb 18th, 2015 02:50 am
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Tramcar Trev
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Herb Kephart wrote:
The 80 - 90% efficiency means that 10 - 20% of the supplied current is dissipated as heat. Some of the ads you will notice offer ''heat sinks''. These keep the chip cooler and in marginal cases may eliminate thermal shut down.
You don't need to buy their aluminum finned extrusion, as it takes up considerable space. Any piece of thin aluminum will help, and of course the larger the better. A coat of flat black helps to shed the heat also. Be sure to put some heat conducting paste between the chip and the aluminum, what ever size you use, Beer and soda cans are a good source, and can be cut with scissors once the can is disassembled to a size dictated by the space available. Sand both sides of the metal (the inside has a clear coating) before painting with the flat black, and leave the section that will contact the chip bare, excepy for the heat compound.

http://www.ebay.com.au/itm/Gold-CPU-processor-heat-conducting-paste-gt-3-8WmK-PC-Thermal-Heat-sink-cooling-/281307590991?pt=LH_DefaultDomain_15&hash=item417f3d314f

Various size quantities, this is the smallest (and cheapest) at the present time on Ebay 

Strictly speaking this isn't necessary, but a cool chip is a happy chip.

Herb


           

We can have a really heated debate here Herb. While I agree that a cool chip is a happy chip I beg to differ on painting the heatsink. When I was involved with some students building an electric car the university did tests on the efficiency of heatsinks. Black anodising came out with the best performance followed by natural grit blasted aluminium then "mill finish" aluminium and last painted Aluminium, the single coat of paint acted as an insulator because at the interface between the paint and the heatsink there was a layer of air. Grit blasting increased the surface area by a staggering 30% over a finely machined surface... Generally the more surface area you can get the easier it is for the heatsink to dissipate the heat ergo slim people suffer the effects of heat more than portly built people...



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 Posted: Thu Feb 19th, 2015 04:51 am
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Tramcar Trev
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So getting back to the step up converters, I specifically want one for my Baldwin Tram motor, currently I use a 3 cell 6.8ah Lipo battery which gives me 9.9v but performance is not flash especially at slow speeds so I made up a 4 cell Lipo 2.2ah battery and that gives me 13.2V and the improvement is amazing but its too tight inside and 2.2ah gives me about a 45min run so one of these step up contrivances will fit in and will let me up the voltage from 9.9 to 12-13 V and let me get it all under the boiler, so to speak....

My electric cars (all use the same crappy Bachmann motor block) seem happy at 13.8 v but because the power supply is "intermittent" due to imperfect contact with the trolley wire and the rails I use one of these 1F "super Capacitors" across the Rx power bus to keep the Rx "alive". Its very realistic to have the headlights flickering but the Rx needs constant power, if it dies everything stop until it finds the signal again. The BEC on the ESC keeps it charged and it smooths out the supply of dc to the Rx...
http://www.ebay.com.au/itm/7mm-x-20mm-Radial-Electric-Farad-Super-Ultra-Capacitor-5-5V-1F-/301483815308?pt=LH_DefaultDomain_15&hash=item4631d5f18c

I have probably explained this elsewhere (maybe in the RC section)...



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 Posted: Thu Feb 19th, 2015 04:10 pm
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Herb Kephart
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Trev--

Thanks for the info on heat radiation! Very interesting that grit blasting made such a difference--

Reminded me of all the motorcycle cylinders that I painted black, thinking that I was doing the right thing.

Herb



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 Posted: Thu Feb 19th, 2015 06:35 pm
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mwiz64
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Tramcar Trev wrote: mwiz64 wrote:
http://www.ebay.com/itm/with-ENABLE-DC-3-3V-3-7V-5V-6V-to-12V-Boost-Converter-Power-Supply-Step-up-Board-/271366097420 They are neat but only handle 450mA.

How much current are you pulling? Have you ever measured it? My guess with the battery sizes people here are talking about and the duration they are getting that nearly half an amp is pretty good. Think about it, that's over 5 watts. Of course, every scale and every application has a different need.



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 Posted: Thu Feb 19th, 2015 10:37 pm
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Tramcar Trev
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mwiz64 wrote:
Tramcar Trev wrote: mwiz64 wrote:
http://www.ebay.com/itm/with-ENABLE-DC-3-3V-3-7V-5V-6V-to-12V-Boost-Converter-Power-Supply-Step-up-Board-/271366097420 They are neat but only handle 450mA.

How much current are you pulling? Have you ever measured it? My guess with the battery sizes people here are talking about and the duration they are getting that nearly half an amp is pretty good. Think about it, that's over 5 watts. Of course, every scale and every application has a different need.

In the application I'm using I have a 1.5amp stall (about 800ma running) current on the main motor and my "smoke creator" uses an amp, but it does create a lot of smoke....

Attachment: DSC_1357.JPG (Downloaded 32 times)



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 Posted: Thu Feb 19th, 2015 10:49 pm
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Tramcar Trev
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Herb Kephart wrote:
Trev--

Thanks for the info on heat radiation! Very interesting that grit blasting made such a difference--

Reminded me of all the motorcycle cylinders that I painted black, thinking that I was doing the right thing.

Herb


The coarser the grit blast the more surface area too but as you may remember to original VW beetle with the engine block that split horizontally and were air cooled and it only took a few drops of oil to leak around the joint and dust and grunge would accumulate and next thing the engine would seize....
Then there is the black car/ white car debate and black cars get hotter in the sun yes of course they do. We also busted that myth, the black car heats up a hell of a lot more quickly but gets to a point where it re radiates the heat faster than the white car which actually gets hotter than the black car but because its white the general public believe thats they are cooler on a summers day...
Black and white cars also get dirty at the same rate but the black car shows the dirt whereas the white car hides it...



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 Posted: Fri Feb 20th, 2015 12:59 am
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Huw Griffiths
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Tramcar Trev wrote: Then there is the black car/ white car debate and black cars get hotter in the sun yes of course they do. We also busted that myth, the black car heats up a hell of a lot more quickly but gets to a point where it re radiates the heat faster than the white car which actually gets hotter than the black car but because its white the general public believe thats they are cooler on a summers day...
Black and white cars also get dirty at the same rate but the black car shows the dirt whereas the white car hides it...

It's occasionally been suggested that another issue might be how well different coloured surface finishes reflect light of different frequencies.

The suggestion was something along the lines of white surface finishes reflecting enough light at visible frequencies (red ... violet) - to a similar enough extent - to appear white under sunlight.

By the time the light frequency moved down to the infra red (effectively "heat") end of the spectrum, any pigments, bases etc in any surface finishes might well behave very differently from how they might have in the visible spectrum.

I don't doubt that these differences apply just as much to bare metal - with differences depending on how the surface has been prepared (polished, grit blasted etc).

I also don't doubt that there are many people better qualified than me to comment on stuff like this.


Also of interest to me was the initial topic of this thread - voltage step up converters.

I suspect that the key issue with using these is how much current you actually need to draw out of them. This might seem like a strange statement - but I'm not sure that it is.

A couple of years back - at an engineering trade show - I was given a "white" LED torch with a step up converter (aka "Joule thief") built in (very useful it is, too).

I'm not sure how efficient it was - but it probably doesn't need to be particularly efficient.

The whole point of this device is that it allows me to drive a reasonably usable torch from 1 "AA" cell that would otherwise have been discarded. I might only get (say) an hour out of each cell - with a pretty low current driving the LED - but it's enough so I can see my way home, if I've got a bit of a walk after I get off a coach.

It's also use I would not have got out a cell that no longer had enough "juice" to do anything else - so I'm not exactly complaining if the thing isn't quite as efficient as it might be.


Would I use a similar circuit to drive anything that needs a significant current? Probably not - if nothing else, it probably wouldn't work. However, for a really low current application - where it allows me to get away with using batteries which would otherwise be completely useless - I can't think why I wouldn't wish to use something like this.

For me, the key is how much current it needs to supply - and whether I'm actually too bothered if the thing isn't quite as efficient as I might sometimes wish.


Anyway, sorry about the interruption - back to the thread.


Regards,

Huw.

Last edited on Fri Feb 20th, 2015 01:08 am by Huw Griffiths

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 Posted: Fri Feb 20th, 2015 03:09 am
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Si.
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A good rule of thumb (no pun intended) is...

...if you can hold your finger on a sinked chip...

...all is well & it will give longlife.

This is about 50c on the sink.

The junction-temp inside the chip can be 100c however.

The most significant improvement in sink performance...

...is usualy air-flow, whether forced or convection.

Vertical fins in free-air is the way to minimise sink size.

Alot of these DC-DC converters are intended for 'microelectronics'...

...rather than 'power-electronics' ie. motors.

1A load is quite a tall order without good sink AND ventilation !

(thankgoodness for thermal shutdown !)

To be honest, If I was doing this...

...I would look at different size/shape cells.

I think a properly running DC-DC converter with decent sinking...

...would take up WAY MORE room than an additional cell or two...

...and would be less efficient & probably less reliable in 'power' applications.

Cheers.

Si.



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