The Stovebolt Site Forums The Shop Area The Electrical Bay 12 to 6V reducers for stock gauges and heater motor

Looking to see what brand, or where you guys sourced your reducers for your stock gauges. I'm considering converting my '36 but don't want to change the gauges. Want to buy something that I know works and other have had success with

Thanks
Ron

Runtz voltage drops have been the "go to" solution for 12v systems using 6v gauges forever. You can get them here. One per electrical gauge.

Thanks Bill.

You only need one for the fuel gauge sender. Years ago I went to Radio Shack and bought a big ceramic resistor, 60 Watt, its been working for 25 years now. I still use the stock amp gauges, even with A/C and electronic ignition, it hardly ever moves off center. I did notice last weekend it was charging 10-15 amps for a while, but it hasn't been driven for awhile and I had to crank to fill the carburetors. The resistor goes between the power source ( key switch ) and the fuel gauge. Keep it mounted out in the open to keep it cool, not bundled up a harness.

Joe, yes. I shouldn't have said "gauges", as I only need a reducer/resistor for the fuel gauge and one the heater motor. Other than that, I think just bulbs for the conversion.

Thanks!

The Runtz unit will not work on your heater motor. Waaaaaaaaaaaay too much current involved.

Get a 12v heater motor

They have a separate one for the heater motor.

Does the reducer go to the hot line to the heater motor? Does anything need to happen with the stock 2 speed heater switch?

Check out the instructions in this Legacy Tech Tip for 12 Volt Conversions.

Thanks for your reply. My situation is somewhat unique. The truck is already 12 volt, and the heater motor has been replaced with a 12v unit. But the motor spins at an ungodly high r.p.m. I want to put a 12 to 6v. reducer to the motor and cut the r.p.m.s. Not sure if the old switch has a reducer on it, but I think you're telling me I need that also? It makes an incredible amount of harmonics inside the cab and I want to install a radio a bit later. It would be nice to actually hear it!

Here is a voltage reducer that should work for your fan motor.
[on edit] After reading JonG's post below, this one is probably not stout enough for a fan motor. Rated at only 4 amps. Might work with a 6V motor drawing 4 amps, but who knows what your 12V fan motor is drawing. if you use it, it may let the smoke out.

Someone with more "electrical" knowledge may have to answer your question based on your motor being 12v already. Usually a modern multi-speed switch handles your speed management and I'm not sure if a Runtz reducer will have sufficient effect with your very high speed motor.

Hopefully someone else will chime in with better suggestions.

You can find a heater control switch from Kanter (kanter.com) that will handle your speed control needs. I think it is about $30 plus the cost of shipping and as I recall it is rated for 20 amps. It works using resistance wire set into a ceramic holder (so heat can be absorbed/shed). Please don't try to convert 12v down to 6v. There are significant unknowns here and at the least you will have to "dispose" of a bunch of electrons in the form of heat. If you look at any of the Chinese made fan controllers, you'll see they all have a finned heat sink on the back. Some are rated for 7 amp and others for 10 amp even though they look to me like the same unit. That amperage rating and the heat sink is to prevent the equivalent of Mount Vesuvius from happening. The heat sink gets hot and the fins shed that unwanted amperage as heat. Your fan motor...we don't know the amperage and it may be as high as 10 amps or more (a friend had one last summer we measured at 12 amps spinning with the squirrel cage mounted on it)...might not work with a 4 amp voltage reducer as some folks are selling. If it draws 10 amps and you run that through a device designed for 4 amps, well, that heat has to go somewhere. Even if your fan only draws 5 amps (and I suspect it will draw this much at the very least), you want the device to be rated for at least 50% higher than that. Good luck.

Does your heater motor happen to have three wires by any chance?
The 12 volt heater motor that is in my '50 has 3 wires. One is a ground wire, the other two are positive wires. One of them causes the fan to run like a jet engine. The other one runs it at a reasonable speed. I just hooked that one up and left the other wire disconnected.

Nope! Single wire and ground. Thanks.

Instead of installing a voltage reducer, which seems needlessly complicated, why not install a proper 4 position switch?

Off, Lo, Med, Hi

Standard Motor Products part # HS-572

I just saw Jon's reply. Do that.

Even easier is 3 speed blower motor resister block from any '60 -'70s GM car. Use one of the three to get the speed you want, mount it in the air stream to keep it cool just as GM did. You can find new ones for around $14 from any auto parts store. Splice into the your current low speed wire, and add the resistor. I used one on a Vintage Air under seat heater, I mounted it right in front of the blower wheel intake opening, nothing fancy, just one screw to hold it in the air stream. I used the biggest resistor of the three to really slow down the motor. If you are real creative, you could add an additional switch to make a 5 speed fan.

Thanks again to all who responded. I think I'm going with a 12v 3 speed switch. I'm hoping that will eliminate the need for an add on reducer. If you see smoke on the horizon call 911.

Just make certain it is rated for higher amps. Some of the switches don't tell you because they're made in China and the sellers don't know. As I mentioned a friend last summer had one of these 12v motors pulling 12 amps. The fire might warm your cab up pretty quickly. He had already burned up one control switch when he contacted me.

Just purchased at Auto Zone. Resistor block and fuse on back side. Getting ready to install in a few. I'll let everyone know if it's a thumbs up or down.

Thumbs DOWN! Just a few seconds of run time on lowest speed started producing noticeable whiffs of smoke from the resistor wire. Going to Kanter.com now as per John G.s suggestion.

That might have just been residual oil burning off the wire. If it keeps working and the smoke stops, that would confirm that's the case. As long as the wire doesn't burn in two.

Guess I'll hook it back up and try again. Thanks.

Be sure the resister in in the air stream, they need to be kept cool. What is the part number from auto zone?

Here is a suggestion that should end all and any questions. Find (or borrow) a handheld tester which includes an amperage testing option. Mine is an APPA and it will measure amps up to 20 amp (for a max of 30 seconds) but even very cheap multimeters often have a 10 amp setting. Figure out the amperage draw while the motor is running (with the fan on and mounted in the heater or air conditioner...it WILL make a difference). Follow the instructions with the tester for higher amperage measurements. Once you do this you will know for certain how many amps your motor (in operation) is drawing. Resistance wire is interesting. The way it operates is more/less as an accurate resistor. What I mean to say is a specific length of it (say for example 4 feet and 2 inches) will produce a specific resistance amount. Now if you have a "wiper" which makes contact with that wire and completes the circuit, the amount of resistance will be variable and in normal cases will go from "off" to whatever resisted measurement the wiper offers. Resistors limit the amount of current passing through them...current being different from voltage. For decades I've told people to think of voltage as the size of your arm. Think of current as the strength of your arm. Actually you might be able to "see" this happen using the ammeter in your dash. When you turn on the fan motor (engine not running) if the amp draw is higher than 10 amps, you may see the needle deflect to the negative side. It won't be necessarily accurate, but it might tell give you a relative idea. As I said before these motors are funny...especially the ones coming from China. They are not rated and we really don't have any idea how they've been made nor wound until they're tested. Good luck!

Thanks for the reply! Good info.

If you or anyone else here needs a simple (and generally fun to read) electronics explanation, you should be able to download this pdf version:

https://theeshadow.com/files/Forres...Getting%20started%20in%20electronics.pdf

Moderator Edit Note: The replies to Jon G's post have been removed now that the link works. Back to the topic at hand.

This one opened, I saved it to my downloads file. Looks interesting, getting late. I'll dive into it tomorrow. Thanks.

Good! It is the sort of thing you can read before going to sleep at night. As I said a nicely written book.

Here is a 20 amp PWM type fan control: https://www.walmart.com/ip/20A-PWM-...8V-w-Potentiometer-Knob-Switch/502729525

You would need to make a little box to hold the circuit board but it should work okay for you and the price seems pretty good.

Jon G's new link gives me a 404 error code on my desktop PC with Firefox and on my phone with Google Chrome.

Well unfortunately it looks like the link access has been blocked by the source. Anyone that was able to download a copy of the PDF may (or may not???) be able to share with others through private emails.

Jon G - Perhaps we need to remove the link and the reply post since it's no longer accessible???

The link worked from my Samsung phone.

I played around with one of these a few years ago. Neat part. I payed less than 3 bucks for it. Only problem I saw was that it controlled ground, not supply voltage. So it wouldn't work on a 1 wire fan that uses the fan motor case for ground.

Gord sent me this link.

https://theeshadow.com/files/Forres...Getting%20started%20in%20electronics.pdf

Sorry I didn't reply sooner. I think the Auto Zone unit will go in the junk pile. Going to try the one from Walmart that Jon G. suggested. Thanks for your reply.

I've had a friend (a retired computer engineer) look into this. It is either my system, the source system (which he suspects) or this platform (which he says is last on the list). He suggests I simply tell folks to use Google or whatever search engine you prefer and search for: Getting Started in Electronics by Mims in a pdf format.

Sorry for any confusion.

This is what I used on my 53 after converting to 12v.

uxcell Power Voltage Converter

Thanks for the reply! We found one on Amazon that's rated at 20A. Have a couple on order, waiting for them to show up. I'll let everyone know if it works as planned.