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D.C.-D.C. Step-Up Converters Discussed
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 Posted: Mon Feb 16th, 2015 07:43 am
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Tramcar Trev
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Allow you to use a single 3.3 Lion cell to boost voltage to whatever you need. Found on eBay: http://www.ebay.com.au/itm/LM2577-DC-DC-3-34V-4-35V-Digit-Step-Up-Adjustable-Power-Supply-Converter-Module-/131164010981?pt=LH_DefaultDomain_15&hash=item1e89fbf9e5 2.5A cap
http://www.ebay.com.au/itm/LM2587-DC-DC-Boost-Converter-3-30V-Step-up-to-4-35V-Power-Supply-Module-DA-/181527342570?pt=LH_DefaultDomain_15&hash=item2a43df6dea this one they claim can give 5A output....

I am going to get a couple and experiment, it would mean I could get away with a physically smaller battery but get a much higher voltage, a higher voltage means less current means less battery drain and also will give me a higher motor torque which would mean better slow speed running. Or am I wrong?
Probably not in the right place....



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 Posted: Mon Feb 16th, 2015 10:56 am
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pipopak
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I am not an electrician, but I know you can't create energy. A higher voltage (plus whatever current the module uses) means shorter battery charge life. But I am curious about the matter anyway. Jose.



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 Posted: Mon Feb 16th, 2015 02:37 pm
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Herb Kephart
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Correct Jose.

Watts, the correct measure of power available or consumed, are calculated as volts X amps.

The converter cannot be 100% efficient.

So the total available power has to be less.

But-- the converter is smaller than an additional cell if you want/need more voltage, A single, large as possible cell (misnamed battery, as a battery is a group of cells) eliminates the need for balance charging, if that is thought necessary

The linked converter has a led readout, the purpose for which isn't mentioned--I have to suspect that it reads output volts, and if so is something not needed for our purposes. In our needs, the voltage can be set by what performance is desired. I have seen on Fleabay converters that do not have the readout, which has to mean a smaller overall size, and less cost.
Herb



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 Posted: Mon Feb 16th, 2015 06:25 pm
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Dave H
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I have just bought some of these......

http://www.technobotsonline.com/pololu-step-up-voltage-regulator-1.5a-max-i-p-12v-output.html

.....to play with in OO gauge.

I'll let you know how they go! See how small they are 0.32" x 0.515"



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 Posted: Mon Feb 16th, 2015 09:34 pm
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Tramcar Trev
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Dave H wrote:
I have just bought some of these......

http://www.technobotsonline.com/pololu-step-up-voltage-regulator-1.5a-max-i-p-12v-output.html

.....to play with in OO gauge.

I'll let you know how they go! See how small they are 0.32" x 0.515"

They look the bees knees exacary what I wanted 12V from 6.6V I'll have to do some practical measurement and see If I can get away with 1.4A draw...



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 Posted: Mon Feb 16th, 2015 09:44 pm
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Tramcar Trev
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Ok I have had a bit more of a scratch around and found these sans the digital readout and they can handle 3A; http://www.ebay.com.au/itm/DC-DC-Step-up-Adjustable-Power-supply-voltage-Converter-Output-5V-35V-Module-/141051821846?pt=AU_B_I_Electrical_Test_Equipment&hash=item20d757ff16

And heatsinks to make them last longer; http://www.ebay.com.au/itm/131014795047?tfrom=141051821846&tpos=unknow&ttype=price&talgo=origal

they are not small however but much smaller than another cell...



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 Posted: Tue Feb 17th, 2015 06:10 am
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fallen
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Herb is right, there is no free lunch. If you double the output voltage you at least double the input current, so you need fewer cells but they each need bigger capacity. You do have more flexibility on the voltage supplied though.

However there is another advantage. If you have a big single cell it is easy to charge. If you have two smaller cells you need to provide for balance charging of the two cells which is slightly more complicated. This can make the installation easier.

Frank

Last edited on Tue Feb 17th, 2015 06:12 am by fallen

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 Posted: Tue Feb 17th, 2015 02:09 pm
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bobquincy
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I have been using the Pololu converters to step up 2xAA to 3.7 V. One of the smaller ones (1.2 A input) got overloaded with a motor pulling about 700 mA and would shut down until I closed the throttle for a short time. No damage done though.

Most of these are rated for input current which is the output current times the ratio of output voltage/input voltage divided by the efficiency: in my case 700 mA * (3.7/2.4) /0.8 = 1.35 A input current. I switched to one of the 2A converters and it can handle the 700 mA output.

One of the benefits is that the output voltage stays constant until the battery is really exhausted.



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 Posted: Tue Feb 17th, 2015 05:23 pm
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Herb Kephart
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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


           



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 Posted: Tue Feb 17th, 2015 07:10 pm
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mwiz64
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http://www.ebay.com/itm/with-ENABLE-DC-3-3V-3-7V-5V-6V-to-12V-Boost-Converter-Power-Supply-Step-up-Board-/271366097420



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