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Author Topic: How do you drop a volt or two?  (Read 6844 times)

BarryM

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Re: How do you drop a volt or two?
« Reply #25 on: December 16, 2010, 08:56:24 AM »

"NOTE: the website is temporarily unavailable and undergoing maintenace as at 30th July 2009"


I can't find the link either but I did find the above.

Barry M
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BarryM

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Re: How do you drop a volt or two?
« Reply #26 on: December 16, 2010, 08:59:07 AM »

and then I found this http://www.squirestools.com/

Never believe everything you're told.  {:-{

Barry M
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RaaArtyGunner

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Re: How do you drop a volt or two?
« Reply #27 on: December 16, 2010, 09:39:20 AM »

and then I found this http://www.squirestools.com/

Never believe everything you're told.  {:-{

Barry M

Barry M,

Thank you  O0 O0 O0
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Colin Bishop

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Re: How do you drop a volt or two?
« Reply #28 on: December 16, 2010, 06:14:29 PM »

Well, I think I may have solved the problem in a sideways sort of way and a little help from my friends.

The power resistors arrived this morning, 3 watt wirewound, 2.3 ohm, 2.7 ohm and 3.9 ohm. No single one did the trick but putting two in series did make quite a difference.

However, in the meantime Dave Milbourn of ACTion suggested that I look again at the mini cassette motors he had sent me as he had found them to be OK in this sort of situation. Although the shafts seemed to be free running, the problem turned out to be the couplings. They are nominally supposed to be 2mm but are nearer 2.3mm I think, although perhaps not actually 2.3mm as they won't fit on some of my 540 siize motors. Also the propshafts themselves are slightly under 2mm and the combiination was introducing sufficient misalignment to seriously inconvenience the mini casssette motors.

I have removed the couplings and substituted some flexible insulation tubing and both motors now run sweetly with sufficient power to move the hull along quite smartly just as Dave promised, so the sun is shining once more (actually it's snowing again  :(()

One shaft is still slightly slower than the other but a bit of fiddling about with the motor mount should hopefully fix that although it's not serious.

A couple of pics of the current setup below, one with the Action ESCs, Mixer and the Spektrum RX.

Colin
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BarryM

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Re: How do you drop a volt or two?
« Reply #29 on: December 16, 2010, 07:54:31 PM »

What's the model, Colin?

Barry M
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Colin Bishop

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Re: How do you drop a volt or two?
« Reply #30 on: December 16, 2010, 07:58:08 PM »

It's a Deans Sir Walter Raleigh Tug Tender - one of their compact kits.

Colin
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nick_75au

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Re: How do you drop a volt or two?
« Reply #31 on: December 17, 2010, 09:02:47 AM »

Great, I'm happy its worked out for you,
devil is in the details.

Cheers
Nick
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wibplus

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Re: How do you drop a volt or two?
« Reply #32 on: January 03, 2011, 10:22:02 AM »

and then I found this http://www.squirestools.com/

Never believe everything you're told.  {:-{

Barry M

Should be a law against posting candy links like this.   <*<  <*<  :police:

Just cost me a small fortune in bits I never knew I needed.   >>:-(  >>:-(   %%  %%
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Colin Bishop

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Re: How do you drop a volt or two?
« Reply #33 on: January 03, 2011, 10:31:24 AM »

Quote
Should be a law against posting candy links like this.       

Just cost me a small fortune in bits I never knew I needed.

You've got it easy! I can drive down there in under an hour and just browse.... Very expensive sometimes.

Colin
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Le Caux Deux

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Re: How do you drop a volt or two?
« Reply #34 on: January 03, 2011, 11:43:25 AM »

All this technical stuff is way over my head but maybe someone can answer a question for me on the same subject, I've just built a new tug running 2 x 12v Motors off a 7ah Battery and I've also got a small 7.2v bow thruster which at the moment runs off its own NiCad battery pack through a speed controller. To save a bit of weight (and less messing about) I'd like to run the bow thruster off my 12v battery. I know action do a unit that will drop the voltage to the right level but it does lots of other things I don't need and is quite big for the space left and cost 's. Can't I use a high wattage resistor to drop the voltage? if so what value?
I've installed a Action distributor board with 3 12v outputs 2 of which feed my motors through their P94 mixer/speed controller the other output could connect to my bow thrusters speed controller but I'm afraid I'd burn the motor out if I ran it at 12v so the plan would be to put resistors in that circuit.

Mike
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malcolmfrary

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Re: How do you drop a volt or two?
« Reply #35 on: January 03, 2011, 03:57:13 PM »

All this technical stuff is way over my head but maybe someone can answer a question for me on the same subject, I've just built a new tug running 2 x 12v Motors off a 7ah Battery and I've also got a small 7.2v bow thruster which at the moment runs off its own NiCad battery pack through a speed controller. To save a bit of weight (and less messing about) I'd like to run the bow thruster off my 12v battery. I know action do a unit that will drop the voltage to the right level but it does lots of other things I don't need and is quite big for the space left and cost 's. Can't I use a high wattage resistor to drop the voltage? if so what value?
I've installed a Action distributor board with 3 12v outputs 2 of which feed my motors through their P94 mixer/speed controller the other output could connect to my bow thrusters speed controller but I'm afraid I'd burn the motor out if I ran it at 12v so the plan would be to put resistors in that circuit.

Mike
Getting rid of 5 -ish volts is a great deal easier than losing the odd volt, although it is the same job of limiting current.  Just measure how much current the thruster takes under load, then find a 6 volt bulb that runs at about that current, insert it into a motor lead.  The bulb just acts as a resistor.  To get the resistance value, R=V/I, where R is the resistance required, V is (12 and a bit-7.2) and I is whatever you measured.  To get the power rating of the resistor, W=V*I, where W is the power in watts.  Resistors come in pre-determined values, so its usual to go for the nearest, they also come in various power ratings, good design is to take the theoretical power from the formula, multiply by 2 and go for the next rating higher.  Ultimate precision is not vital in this case, being tough enough is.  An alternative way to get a starting value is to just measure the resistance of the motor, and (bearing in mind the motor voltage and battery voltage) go for about 2/3 that value.  Or do some measuring on a bit of dead electric fire/hairdryer/toaster element.
Using a linear voltage regulator, when the required heatsink is added, it could wind up bigger than the battery you hope to replace (have a look a rathikrishna's simple speed controls - they are basic voltage regulators).  Doing it with electronics, the regulator would need to be in the +ve power supply for the ESC.
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"With the right tool, you can break anything" - Garfield
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