? On voltage drop 12-6?

[chopped]

This might not be the right spot if any to ask this question, But id like to ask anyone to help me with a problem.
Problem is:
Older truck used off road .to plow. (beater,clunker,hoopty)
The problem is the heater blower motor only runs on high speed due to a burned out resistor for the lower speeds. I would like to simply be able to add another resistor of some sort or anything 'inline' in the cable to run the 12 volt blower slower. I'm thinking simply drop the voltage to maybe 6 volts or so. Nothing major .
Now the tough part, I could purchase a new resistor from a parts store to the tune of 37 dollars, but id like to go on the cheap..(open to all suggestions)
Is there any was yo simply turn the 12 volts down to 6 volts like say as a light dimmer for the house does. And that doesn't work, lol I tried it.
The main concern her is to do it on the cheap....
Thanks ahead of time, as I have seen some really good ingenious things discussed here.

 

[SnowRidge]

A power resistor of the right value should do the trick. They are available from electronics parts houses in a wide range of values for a few dollars to quite a few dollars each. The trick is determine what value you need. The resistance in ohms and the power handing capacity in watts need to be determined. To find out we need to know how much current the blower motor draws when it is operating at full speed on "12" volts. It would be helpful to know the exact voltage, but 13.2 volts is a safe bet for a running engine with a 12 volt sytem.

With the current draw information at hand, it is a simple matter to calculate the required values (ohms, watts) for the resistor. A source can then be found using Google.

Of course, if you could find out the resistance of the expensive resistor at the parts store, it would be easy to figure out a suitable wattage rating and just go from there.

Can you measure the blower current with a multimeter? You will need one with at least a 20 amp DC setting.

 

[zzvyb6]

If you only run the truck a few weeks out othe year, why not run the heater blower off a 6 volt battery or a 12 v battery that's been run down a bit? Hook it up to the main buss occasionally to get it back up to 6 volts, but hey, there are a lot of dying batteries out there. Or, get another motor and run it in series. Two fans ought to be better than one...

 

[chopped]

WOW thanks for the replies already. Actually with my limited knowledge, i thought of another thing in between , I thought a 12 volt bulb would do the trick and tried that in between but it only lit the bulb and a click in the motor.
So all i might have to do is pop another motor out of a junker here, and run them in series. Even the second one doesn't have to be in the system could be sitting on the floor next to me.
Also interesting thought on the battery I just happen to have a 6 volt battery.Thanks so much ..
I'm much interested the ''dual''' motor set up.As I have one handy.
Ill try to determine the flow .not quite sure how to test it but ill google around thanks..

 

[mbohuntr]

if your splitting the voltage to 6 volts, the resistor value will be same as the the one still in there (also the one burned up) It's the wattage that's important. get a big one.

 

[Farmerford]

An old 12V sealed beam headlight should be just about right. Start with low beam only; if the heater does not run fast enough connect the low and the high beam.

 

[capi75rs]

I'm no automotive expert, but electronics is my field of work. I'm guessing that the $37 is going to be the way to go. First is the resistor your talking about "encased" in a square plastic housing or a round tin housing? Do you know which wires are comming from the switch and going to the heater motor, and is there only one wire for the motor or a few. The problem with only putting in a single resistor, is that if a single wire is used to feed the motor you may backfeed your new resistor when you apply voltage to the other settings. This may or may not present a problem, depending on the switch. To eliminate this backfeed a proper sized diode is needed and put in the proper way. You will also need to know the resistance (Ohms) of the resistor and then purchase one that will handle the load (watts) that is needed. Here is a rundown of Ohms law which will help you.
V=voltage
I= curent (Amps)
R= resistance (Ohms)

V
------
I * R

V= I*R
R= V/I
I= V/R

Another important law that you'll need is the power law. And you thought this was going to be easy

P= power (watts)
I= current (amps)
E= voltage (volts) (some folks will forgo the E and put in V, both E and V = voltage).

P
------
I * E

P=I*E
I=P/E
V=P/I

Once you find the resistance of the resistor you'll need to convert that to current (amps) I=V/R. Example 12volts/6ohms=2amps

Now that you have both current and voltage you can get wattage, so you can get the proper sized power resistor.

E*I=P Example 12volts*2amps= 24 watts

so in our example you would need a 6 ohm 24 watt resistor.

Call the autoparts store and see if they can give you the size of the resistor, otherwise use the formulas above.

FYI the reason the light dimmer didn't work is, it is a triac that is designed for AC only operations. A diac would work though.

Hope I didn't confuse you too much and I hope your laughing and I wish you well on the repair. Even though I deal with these things daily I'd spend the $37 and get exactly what you need.

 

[mbohuntr]

Now that's a novel idea, should work!

 

[KubotaSam]

In the 1960's Chrysler products used a ballast resistor in the ignition circuit to drop the voltage going to the points. You should be able to get one at any auto parts store for under $10.00. The are a ceramic block with a resistor coil running through the center. They are very heavy duty and should work just fine for what you are trying to do. I just checked NAPA auto parts online. $4.99

 

[Travelover]

If you don't have an ammeter to check the current draw of the blower motor, you may well find it in an automotive repair diagnosis manual. Then just plug in the current into the formula provided above. Basically, you just want the resistor to draw as much current as the blower motor does now. Resistors are cheap and you can buy a bunch of them and connect them in parallel to get the wattage that you need. Use this site to calculate the total resistance:

PARALLEL RESISTOR CALCULATOR

If you can stick the resistors in the air flow of the blower, they'll cool better.

 

[Treemonkey1000]

Why not just go to the wrecking yard and pick one up. Any similar make of truck and a few years up and down from yours should work.

 

[AndyMA]

FYI the reason the light dimmer didn't work is, it is a triac that is designed for AC only operations. A diac would work though.

quote]

Curious about how you would get a diac to work in this application? As I recall a diac is a bidirectional breakover diode that typically breaks over at about 30 volts unless I don't remember my control days properly.

Andy

 

[capi75rs]

FYI the reason the light dimmer didn't work is, it is a triac that is designed for AC only operations. A diac would work though.

quote]

Curious about how you would get a diac to work in this application? As I recall a diac is a bidirectional breakover diode that typically breaks over at about 30 volts unless I don't remember my control days properly.

Andy

Andy nice catch. My mind running from AC to DC didn't think quick enough. I do stand corrected Diac in DC applications just acts like a Shockley diode, won't do him much good. Thanks for the correction.

 

[mbohuntr]

If the wattages line up,I still like the idea of the light, you can pick up a DC trap light at 55 watts for about 12 bucks.

 

[Bedlam]

So the 120 volt Light dimmer (ac) could be disected and possibley something removed to make it work?

 

[SnowRidge]

So the 120 volt Light dimmer (ac) could be disected and possibley something removed to make it work?

No. He needs a resistor of the proper value capable of safely dissipating the heat that will be generated. Nothing inside a 120V light dimmer will do that.

 

[Bedlam]

Oh ok thanks...

 

[Wayne County Hose]

Another vote for the junkyard.

 

[chopped]

Thanks all for the input. I agree the easiest would probably be the junk yard treasure but I'm aways from a yard, and I hate to get it and have it burn back out dues to another problem.
Ultimately I went with Bota Sam's idea, simply because i had an old Plymouth junk car 'in stock'.
The ballast resister on that car has four terminals, and I never knew there was a difference in the two sides . But I attached to a terminal on one end and the opposing end,a nd away it went. This still left two more terminals which I thought would be of the same resistance. but when hooked up they were less, the fan ran allot slower.At any rate I was able to patch this in and now have the two speeds.
So one problem solved but now I wonder on the two different Resistances on the dual four terminal ballast block . Could this have hindered the car (junker) back 25 years ago? Had i not hooked it up correct.?
Maybe any Plymouth guys can remember. It would be good to know lol
Oh just thought perhaps half of this is bad thus the difference in resitance on the block?

 

[mbohuntr]

I think you have a multi-position resistor. If you wish to change the voltage between the resistors, you vary the resistance. Hence you have the connections for high, med and low speeds. My guess anyway.