# RESISTORS?



## lotsasteam (Jan 3, 2008)

I need to drop the voltage from a powerpack from 22volts 13ah to max 12 volt 2ah! The resistors i have are wirewound RS 271-135 100ohm 10 watt ,do i need 2 of them connected in series to get to that value?

Manfred Diel


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## toddalin (Jan 4, 2008)

That won't do it. The final voltage will be dependant on and vary with the load. You either need to use a voltage regulator, or a bunch of diodes with each pair of diodes reducing the voltage by 0.7 volt. Get the voltage right and don't worry about the current.


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## krs (Feb 29, 2008)

Posted By lotsasteam on 18 Feb 2010 09:44 AM 
I need to drop the voltage from a powerpack from 22volts 13ah to max 12 volt 2ah! The resistors i have are wirewound RS 271-135 100ohm 10 watt ,do i need 2 of them connected in series to get to that value?

Manfred Diel


A bit more information would help to steer you in the right direction.

- Do you want to drop both a positive and negative voltage from 22 VDC to 12 volts, or only one polarity?
- What load are you driving with the 12 volts?

- Is the load current constant or does it vary?

Any linear device that drops 10 volts at 2 amps needs to dissipate 20 watts - I would tend to look at an integrated switching regulator if you don't have to handle both plus and minus 22 VDC, otherwise a string of 3 amp diodes might be an option or even a high powered set of Zeners.


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## lotsasteam (Jan 3, 2008)

Do you want to drop a positive and negative voltage from 22VDC to 12 volts,ore only one polarity? 
I am planning to install an 276-1146 bridge rectifier bevor and then reduce the voltageto 12volt! 

The aristo revo 1rst rx will be used to regulate the smoke unit(Harbor hobby steam unit for boats 12volt 2 ah)in synchronization with the Loco speed(2nd REVO reciever)since the revo 1rst rx 
will be set to 50% speed then polarized with the bridge regulator (the smoke unit fan does not like reverse) and then the PWM voltage (which is still 22volts) needs to be reduced to max 12volt 2 ah. 

Any help will be aprechiated!!!! 

Thanks guys! 
Manfred Diel


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## Greg Elmassian (Jan 3, 2008)

you can't do it with the TE, it does not want to work at 12v... so reducing the voltage first won't work. 

Trying to reduce it after might, and as Knut said, you need 20 watts of dissipation... V=IR, so 10=2*R... R = 5 ohms.. 

As long as the load is constant you would drop the 10 volts... you need to run about 40 watts of resistor so you are not at dangerous temperatures... 

Get four 20 ohm 10 watt resistors, put them in parallel, you have a 40 watt 5 ohm resistor. 

The problem will be that at lower currents, then the voltage dropped by the resistor will not be as much, and you will be supplying higher voltage to the smoke unit... so slower "speeds" will give you back voltages over 12 volts. 

Forget it... 

Regards, Greg


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## krs (Feb 29, 2008)

Posted By lotsasteam on 18 Feb 2010 12:23 PM 
Do you want to drop a positive and negative voltage from 22VDC to 12 volts,ore only one polarity? 
I am planning to install an 276-1146 bridge rectifier bevor and then reduce the voltageto 12volt! 

The aristo revo 1rst rx will be used to regulate the smoke unit(Harbor hobby steam unit for boats 12volt 2 ah)in synchronization with the Loco speed(2nd REVO reciever)since the revo 1rst rx 
will be set to 50% speed then polarized with the bridge regulator (the smoke unit fan does not like reverse) and then the PWM voltage (which is still 22volts) needs to be reduced to max 12volt 2 ah. 

Any help will be aprechiated!!!! 

Thanks guys! 
Manfred Diel



Manfred -
I assume you want to use this smoke unit:
http://www.harbormodels.com/site08/main_pages/smoker.htm 



Are you running the engine and the smoke unit on track power or battery power?
Possible solutions would be different.


Also, when you say you would regulate or synchronize the smoke unit with the engine speed, have you checked if that can even be done with that particular unit?

ie - will the amount of smoke vary with voltage or is it more an off/on type of control since it's really meant for boats.

I don't know what the electronics of the smoke unit/fan look like - maybe just a plain heating element and a small DC motor, but it might be possible to drive it directly with the 22 volts at a 50% maximum duty cycle - I would write to the company about that and ask them.

Also ask them what they would recommend if you want to use a 22 volt PCM signal to drive the unit.

I assume nobody on MLS has tried using this smoke unit with an engine or they would have commented here.


BTW - A fellow in Austria has been experimenting with smoke units in various American diesels.
You basically want a control that generates a lot of smoke when the diesel is first started up, then also when it start to accelerate and the diesel engines rev up, but then much less smoke when the train is moving.
Don't know if you can program the Aristo unit to do that - to give that burst of voltage under those conditions.
For a steam engine you want to synchronize the smoke to the engine speed and also the load - again something that isn't required for the 'boat application', so you want to check if this smoke unit is capable of doing that before you spend your money.


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## toddalin (Jan 4, 2008)

Posted By krs on 19 Feb 2010 11:22 AM 
Posted By lotsasteam on 18 Feb 2010 12:23 PM 
Do you want to drop a positive and negative voltage from 22VDC to 12 volts,ore only one polarity? 
I am planning to install an 276-1146 bridge rectifier bevor and then reduce the voltageto 12volt! 

The aristo revo 1rst rx will be used to regulate the smoke unit(Harbor hobby steam unit for boats 12volt 2 ah)in synchronization with the Loco speed(2nd REVO reciever)since the revo 1rst rx 
will be set to 50% speed then polarized with the bridge regulator (the smoke unit fan does not like reverse) and then the PWM voltage (which is still 22volts) needs to be reduced to max 12volt 2 ah. 

Any help will be aprechiated!!!! 

Thanks guys! 
Manfred Diel




I assume nobody on MLS has tried using this smoke unit with an engine or they would have commented here.







May be a bad assumption. Many people will simply look at the thread title (some who may have tried it???) and tune out.


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## krs (Feb 29, 2008)

Posted By toddalin on 19 Feb 2010 11:56 AM 
May be a bad assumption. Many people will simply look at the thread title (some who may have tried it???) and tune out.


You're absolutely right!
There is actually another thread on this and it covers a fair amount of interesting details about this smoke unit:
http://www.mylargescale.com/Communi...fault.aspx 

One tid bit is that someone tested it at 18 volts and the current draw there was less than 1 amp.
That would make things a bit easier if the voltage only needed to be dropped four volts rather than ten.
Maybe the unit will also handle 22 volts - the manufacturer should be asked about that.

And if the current draw is 1.5 amps or less, I would use one of these inexpensive totally integrated switching regulators - that way the heat dissipation problem (and cooling required) becomes much less.

Or look at the Massoth unit which is specifically designed for our application and does provide synchronization.


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## Greg Elmassian (Jan 3, 2008)

Knut, he is trying to run it from the OUTPUT of an Aristo Revolution TE receiver, i.e. the MOTOR OUTPUT which is PWM... 

He wants to vary the amount of the smoke with the speed of the loco... by consisting them.. 

I think a better solution is to make it "chuff", but this unit is not designed for that. 

Regards, Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 19 Feb 2010 04:42 PM 
Knut, he is trying to run it from the OUTPUT of an Aristo Revolution TE receiver, i.e. the MOTOR OUTPUT which is PWM... 


Yes Greg, I realize that.
But since the Revolution will run off a 12 volt battery supply, I thought one option would be to drop the DC voltage at the input of the revolution to the 12 volt level (or 15 or 18 if the smoke unit can take that). For that one could use these tree-terminal switching regulators.

And the PWM peak output voltage would be equivalent to the DC input voltage minus the drop through the Revolution. 


If you want to drop the output PWM of the Revolution, the series diode method may be best using a few of the diode bridges - each bridge will give about a 1.4 volt drop and is somewhat independent of current.


I often find it difficult to come up with the right suggestions since one doesn't really know what the OP is really planning to do.
In this case, I think that particular smoke unit is not really the right product for the intended use.

Regards, Knut


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## Greg Elmassian (Jan 3, 2008)

I was under the impression that the revolution was marginal at 12 volts... my error maybe... 

You cannot run PWM input into a 3 terminal regulator... 

Yes, diodes are a great idea (why didn't I think of that)... 

I agree, this is not the right smoke unit, because, in my opinion, you want to find something that chuffs... 

But your idea will work... so he needs about 7 FW bridges strapped into 2 terminal devices... great idea... 

Regards, Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 19 Feb 2010 06:49 PM 
I was under the impression that the revolution was marginal at 12 volts... my error maybe... 

You cannot run PWM input into a 3 terminal regulator... 

Yes, diodes are a great idea (why didn't I think of that)... 

I agree, this is not the right smoke unit, because, in my opinion, you want to find something that chuffs... 

But your idea will work... so he needs about 7 FW bridges strapped into 2 terminal devices... great idea... 

Regards, Greg



Yes - of course you can't use a three-terminal regulator at the PWM output of the Revolution.
That's why I said: " one option would be to drop the DC voltage at the *input of the revolution* to the 12 volt level (or 15 or 18 if the smoke unit can take that). For that one could use these tree-terminal switching regulators.
In other words connect track voltage to a diode bridge to always get a positive voltage - feed that into a 3-terminal integrated switching regulator which would reduce the heat the regulator has to dissipate and then feed the output of the regulator to the input of the Revolution.

I have no clue how well (or poorly) the Revolution works with a 12 volt input, but since Aristocraft specifies at least two different 12 volt batteries as possible power sources in the Revolution manual, I would hope their product does work flawlessly with a 12 volt source.
The output of the Revolution would then be a bit less than a 12 volt PWM signal - question is: "Will the smoke unit work with a PWM input? 

The other option is to drop the PWM voltage at the output using a string of diodes or alternatively diode bridges.
The input to the smoke unit would be pretty much the same as for the first option except for the PWM voltage.

Anyone know what the output PWM frequency of the Revolution is?
I assume it's low enough so that ordinary silicon diodes will work.


Regards, Knut


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## Greg Elmassian (Jan 3, 2008)

the pwm frequency has been reported as low as 9 KHz and up to about 15-16 KHz... 

I think silicon diodes would be fine, and if they switch slow, it will further help smooth things out. 

I'd try the diodes, I think it was a great suggestion. 

I have read that people had trouble running the Revo at 12 volts... 

Regards, Greg


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## lotsasteam (Jan 3, 2008)

Looks like we are getting close to solve my "smoking problem!! 

Here is the status: the fan has ben separated from the smoke unit ,both are mounted into the Bmann K27 and are in working order,that means variable voltage applied from a transformer 8volts to 12 volts the unit smokes from low(compare to aristo smoke unit :to high up to 4 ft eyewatering plume,it really smokes!!)the fan and unit is connected through an duct tube(thin alu bent to shape and glued with paperstrips soaked in silikon(bathtub coulk+glue) the feeder wire will plug into the tender and into the control electronic(revo). 
A question on GREG: what are: 7 FW bridges and 2 terminal devices ? 

THANK YOU ! 

Manfred Diel


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## Greg Elmassian (Jan 3, 2008)

you take a full wave bridge... which has 4 terminals, hook 2 sets of 2 together (the right way) and now your full wave bridge is a 2 terminal device, dropping 1.4 volts and working in either polarity. 

If you are always feeding dc with no polarity reversal, individual diodes may be cheaper... but it's easier to find a 5 amp FW bridge than individual 5 amp diodes usually.. 

Regards, Greg


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## lotsasteam (Jan 3, 2008)

Thanks GREG! 
Just one more question? The 7 FW bridges i asume need to be hooked up in series ? Is this the right way ::: input voltage connect to the "wave symbol --- plus +minus go to the next FW /wave symbol -----Plus + Minus to the next wave symbol --and so on till 7 FW are connected? 

Manfred Diel


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