TheSamba.com :: View topic

Tue Apr 02, 2024 6:42 pm

I am as much a die hard strictly stock enthusiast as anyone else, so usually when anyone comes to me asking to support a "mod", I am inclined to shy away. But in this case, someone restoring a split wanted a wiring harness kit and wanted help running a 12 volt system, with 6 volt semaphores. So knowing what I know about semaphores, current draws (I am a retired electrical engineer) I quickly searched for a 1 ohm "power" resistor, and Amazon had them on my porch in a shade less than 24 hours. My customer had already paid for the harness, and the 12 volt mod resistors and I figured I would just test them, take some measurements before tossing them in the box with his shipment.

But then I realized that this might be a "Zarwerks Spy Cam" moment.

Originally I had thought about putting a dropping resistor on each sem circuit, maybe stuffing them in the sem pockets, but upon getting these resistors and realizing that they were pretty big, I came up with a better solution.

A stock semaphore, in good or better condition, draws right at about 6 amps of current at 6 volts. Math dictates that this a 36 watt power draw. It also dictates that the sem is a 1 ohm resistive load on the circuit. So the simple math is, if you want to add something to the circuit to "Drop" the voltage to the sem to 6 volts from 12 volts, you simply need another one ohm load in series to drop 6 of the 12 volts. A one ohm resistor does the trick, but before sending this solution on its way to my customer, I wanted to verify, and photograph it.

In this first couple pics, I have a restored SHO grooved semaphore connected to one of my reproduction semaphore harnesses, and an original semaphore switch. Activated with the switch, my voltage locked power supply ("CV" means constant voltage)shows it supplying 6 volts to the circuit, and it drawing 5.5+ amps from the supply. The display also shows it pulling about 33 watts of power.

In the modified circuit pics, I have added a second semaphore for no other reason than to replicate a real world circuit, and I have added the (gold colored) 1 ohm, 100 watt resistor to the input power lead on the sempaphore harness. This wire normally pics up 6 volts, switched, right off the ignition switch. The idea here was that only one resistor is needed since it can be introduced into the circuit before the semaphore Right/Left switch, and thus be able to drop the voltage into the switch. Of course only one semaphore can be activated at a time, but for what it is worth, this is a 100 watt capacity resistor and it *could* easily support two 36 watt loads.

The voltmeter in this pic is reading the voltage across the resistor and you can see that it is 5.9 volts, or very nearly half the 12 volts from the supply. But the power supply shows what is important here. I had dialed the (fixed) voltage up to 12 volts. As you can see from the readout, the current through the circuit (sem and resisitor) is still only 5.5 amps. Total power is 66 watts, 33 watts are being dissapated by the sem and 33 watts by the resistor. As far as the semphore is concerned, nothing has changed from the 6 volt system. It is not being over driven, it is not overheating.

These resistors are dirt cheap and available from Amazon for under $4. Here is the link:

https://www.amazon.com/dp/B077ZMFZM6?psc=1&ref=ppx_yo2ov_dt_b_product_details

(I bought a bunch).

While I am not really interested in selling sub $10 parts, I did solder some correctly color coded wires to them and will offer a "Convert Semaphore harness to 12 volt" option to my harness kits in the future. I have soldered some of the color correct PVC wire to the ones I bought, if you want one, PM me.

Wed Apr 03, 2024 11:07 am

My first Oval was a 55, back in 1988. I used a similar resistor but it was a ceramic resistor, 3 of them in parallel, reducing the 12V upgrade to operate the 6V solenoid. Worked great! At the time, I was dating my wife and her father was an Electrical Engineer. He designed the circuit for the semaphores. I went to Radio Shack and picked the resisters up. The next day I had working semaphores! It was so cool!

Thu Apr 04, 2024 3:16 am

Three resistors in parallel looks to be a good idea for heat dissipation, instead of just having one.

Thu Apr 04, 2024 3:27 am

like he says - 'it was so cool!' :lol:

Thu Apr 04, 2024 4:00 pm

scarabee wrote: Three resistors in parallel looks to be a good idea for heat dissipation, instead of just having one.

Just remember, that putting resistors in parallel decreases their resistance. Put two 10 ohm resistors in parallel and you will have a total of 5 ohms. The math is more complicated for three and also if they are different values, but while it would allow more power dissipation, you could quickly get into trouble if you didn't size them correctly.

Fri Apr 05, 2024 12:58 am

Yes, electronics 101...

Fri May 17, 2024 7:15 pm

A favorite MIG Rescue technique that I like. Here, a snapped off flush clutch pressure plate M8 bolt in the flywheel. This one was just over torqued, and there is no real thread corrosion/resistance. But it had to come out and there was no way to grab it. Yes, I have EZ Outs, and have used them successfully one time out of 722 tries. This MIG technique is undefeated.

In this case, I tape a rusty M8 nut over the snapped off bolt shank, then poke a hole in the tape over the nut. The idea is to get the MIG wire arc to grab the shiny bolt shank first, so a rusty nut helps out. I just shoot the MIG wire into the nut bore, and fill the void with molten metal. Let it cool just a bit, then turn the shank out with a wrench.

Fri May 17, 2024 8:17 pm

You can also use a washer, weld a blob and then add a nut and weld that to the nut inside.

Agree this is the best solution to snapped off fasteners

Sat May 18, 2024 5:56 am

Great idea. Thanks for sharing.

Sat May 18, 2024 10:59 am

This is a very good method.

In the case of a snapped off fastener with no rust locking it in place, an easyout probably would work fine. If it won't turn easily, I quit immediately. I never use them if the fastener is stuck by rust or tight interference fit though. That just doesn't work and makes things worse with the super hardened piece left in the bolt.

I have even used a worn down dremel cuttoff wheel to cut a slot for a screwdriver, but then again, only for a fastener that is not locked in place by rust.

I once broke off a 8/32 tap in a piece of cast iron I was cutting some threads into and thought I was screwed but I tapped on the end of it with a punch a few times and used some needle nose pliers to grab the flutes and it backed right out.

Sat May 18, 2024 3:21 pm

splitjunkie wrote:

In the case of a snapped off fastener with no rust locking it in place, an easyout probably would work fine.

True.

The effectiveness of the MIG method for rusted/seized shanks it the intense heat that the welding puts into them. I let them cool a bit, then apply a penetrating oil like Kroil on them. I have rescued so many "that shit's not coming out" snapped off stuff with it. I am pretty sure I have never failed. Sometimes it takes lots of donor nuts and re-welds to get it. My record for smallest is a steel M2.5 grub screw in a brass barrel.

Sat Oct 05, 2024 9:29 pm

Great thread ! .

Sun Oct 06, 2024 9:53 pm

johnshenry wrote: splitjunkie wrote:

In the case of a snapped off fastener with no rust locking it in place, an easyout probably would work fine.

True.

The effectiveness of the MIG method for rusted/seized shanks it the intense heat that the welding puts into them. I let them cool a bit, then apply a penetrating oil like Kroil on them. I have rescued so many "that shit's not coming out" snapped off stuff with it. I am pretty sure I have never failed. Sometimes it takes lots of donor nuts and re-welds to get it. My record for smallest is a steel M2.5 grub screw in a brass barrel.

I LOVE the fender washer with a nut welding regiment. But on tiny fasteners, reversible drill bits work great! You start drilling on the broken shaft as if you were going to utilize an EZ Out, BUT, when the bit catches during the drilling, it will actually twist the broken shaft out! Works great!

I have a full set of reversing drill bits, 1/32” up to 1/2”! I have used them on multiple occasions!

Tue Oct 08, 2024 8:19 am

What's wrong with drilling and tapping?

Tue Oct 08, 2024 8:53 am

Martin Southwell wrote: What's wrong with drilling and tapping?

In my experience:

Drilling and tapping: 1-127

MIG metal extraction: 74-1

Wed Oct 09, 2024 6:14 am

Fine, but not everybody has welding equipment or experience.

Wed Oct 09, 2024 7:50 am

Martin Southwell wrote: Fine, but not everybody has welding equipment or experience.

You can do it with a profi and sometimes save a lot of time. (imo, johnshenry x2)

Thu Oct 10, 2024 5:23 am

Martin Southwell wrote: What's wrong with drilling and tapping?

if you aren't perfectly centered in the hole you will have issues when you tap it.

Thu Oct 10, 2024 6:30 am

VWNate wrote: Great thread ! .

subtle =D> :lol:

Thu Oct 10, 2024 9:04 am

wagen19 wrote: Martin Southwell wrote: Fine, but not everybody has welding equipment or experience.

You can do it with a profi and sometimes save a lot of time. (imo, johnshenry x2) What is a profi?