Hot Rods Can we talk voltage reducer wiring, and windshield wiper park?

The "buck regulator" is using a switch mode regulator IC. That IC monitors the output voltage and adjusts the PULSE WIDTH (PWM) at a high speed for the proper output voltage. THE IC contains PWM, so this is exactly what needs to be used for your application. The voltage adjustment will control the speed of the motor. The Current adjustment should be set so that if the wiper blades get stopped for some reason, the regulator shuts down. The regulator will cycle off/on till the wiper is freed up.
Set the current adjustment to maximum setting, usually clockwise 10 turns. Then with motor running turn current adjustment counter clockwise till motor stops running. Then turn current adjustment clockwise one full turn. Run the wipers on a dry windshield and engine running. If the wipers do not operate, then turn the current adjustment clockwise till the wipers operate.
Hope this helps.

 

That should work.

 

This is making my head hurt!
I did a search for a buck convertor.
the buck converter from Amazon listed above only has a 68% positive rating.

This shows up. Ebay # 284595136197
Power converter regulator
DC 12V/ 24V
step down to DC 6V
20 A- 120W
94% efficient @ $22.91 each, free shipping
Located in Huston TX

The exact company, at the same location, also offers the same thing,
except with a 10 A 60 W
92 % efficient @ $20.11 each, free shipping.

Will either of these work?
If so, which one should I go with, the 20 a 120 w, or the 10 A 60 W?

 

Link in prior post
https://www.ebay.com/itm/284595136197

 

Gene I think I’d go with the larger unit, sounds as though it will protect to wiper motor, however they state.
Note: Can not use a long time Under the MAX. LISTED LOAD POWER.

The 20 amps at 6v should be plenty, do you know the amp draw or max amps on the wiper motor?
I see where you said 10 amps is normal, hence I would use the bigger unit if it was mine.
Dan

 

I agree with Sharpone. Even though it's rated @ 20 amps, 92% efficiency still provides over 18 amps or 108 watts. Two things to do are:
1. Wire both black wires to auto ground.
2. Mount ***embly to body metal where there is good ventilation. Make sure that the ***embly is clear of any wiring, insulation, hoses, etc.
If you want to, you can mount on firewall. Just remember to keep away from other items.

 

No, 20 amps max out is 20 amps max out. The 92% efficiency just says that says that to get 92W power out of it it has to consume 100W. At 20A and 6V out = 120W it will also turn an additional ~10W into waste heat. Still, I'd avoid running it on max load to give it a descent chance to survive, the cheap chinese stuff isn't always properly rated so keep a good safety margin.

Note that these efficiency numbers are for a specific load, the converters are usually very efficient at max load but not at low load. They have a certain constant power consumption, running on low load that becomes a significant part of the output power = poor efficiency. Still, far better than other alternatives in many cases.

Well, yes, it is true that the buck controller (and several other types) work by switching current on and off like PWM, but after that it filters it into a stable DC voltage. The PWM controller outputs a voltage switching between zero and input voltage rapidly, buck controllers output a single stable voltage.

Calling a buck regulator a PWM regulator is about as accurate as calling an internal combustion engine an electric motor, because it uses an electric spark to ignite the fuel. There's electricity involved in making the engine run, but...

 

I call it a pwm because that's main component of a Switching regulator.
Yes, there are filtering caps to smooth the ripple and the Switching frequency.
In any event, you have the right idea for the reducer.
Just make sure that when you mount the ***embly that the heatsink is not connected to car's body ground. It could be at a voltage other than ground.

 

The body of the reducer has the mounting holes. The entire car body is a vehicle ground. The car operates on a 12 volt electrical system, are you telling me the heat sink could be a higher voltage then the vehicles charging system puts out?
How do you suggest that I mount the ***embly so the heat sink is not connected to the car's body ground? I can probably mount the reducer's body on rubber pads, but if it creates as much heat as it sounds like you believe it will, won't it just melt the rubber pads? Maybe I can mount the controller's body on a raised bracket that stands away from the actual car body, does the mounting bracket need to be insulated from the vehicle ground?
There are a lot of places I can mount the reducer where it will be in air flow. It would just require longer wires to the terminals.

The original 6 volt motor was operated on a 10 amp fuse. It will be on a 10 amp fuse (unless you guys think I should run a 15 amp fuse, the wiring is new and plenty heavy enough) on the 12 volt system. I would not ever expect it to see much of anything over a 10 amp draw, a 20 am ceiling should provide more then double of what ever the motor will ever see.

 

Yeah, I got that backwards...

No, the linkage runs in the right direction, you don't know if the motor is. The problem with reversing DC motors is they're 'timed' for one direction and best efficiency. They run slower when reversed, and more importantly, draw more current and run much hotter because of the reduced efficiency. This is something that should be checked, but you'll have to pull the motor to do so, trying to apply 12V+ to the 'ground' in the car will be a dead short. If it's a permanent-magnet field motor, this can be fixed by reversing the leads to the brushes if possible. If it's a series-wound motor with electromagnetic field poles, reversing those leads will do the same thing and should be much easier.

 

Well, technically possible, but unlikely, any voltage on it is likely somewhere between 12v and ground. But the point is that if the heat sink is electrically connected at ANY other voltage then ground/zero volts, letting it come into contact with ch***is ground will cause a short circuit likely to destroy something.

Power transistors almost always have a metal back for good heat transfer, and that is connected to the transistor electrically. If the transistor is mounted directly to a heat sink the heat sink also becomes electrically connected, and letting it come into contact with anything else electrically connected is likely to damage things.
Usually there is a thin insulating disc inserted between transistors and heat sinks, this electrical insulation has a number of benefits (such as having several different transistors in different parts of the circuit on the same heat sink without short cuircuiting them to each other), but it also reduces heat transfer and increases cost, so at times it is not used.
So, basically: when in doubt, don't let heat sinks touch anything metal they're not supposed to touch.

As for mounting, if it has mounting holes, use them. It will not be hot enough to melt rubber/plastic, the electronics should give up before that temperature.

 

Years ago I used a plank of wood to isolate the radio ground from the auto body. Mount the reducer to a plank, making mounting screw heads sit below the plank on side opposite the reducer. Then use other screws to mount plank to car. Screws enter from the reducer side of plank. The wood plank could be plastic or other non-conductive material.

 

The long standing knowledge from the long standing Mopar organizations is that changing the wiper motor from a positive ground to a negative ground has no effect on the wiper function. That information has been solidly unified across many groups for many years. If the large long standing Mopar specific groups have been saying since the mid 50s that changing from the positive ground to the negative ground has no effect on the wiper motor, I'm going to take their word for it, and I have no problem repeating it as a fact.

The process of reducing the voltage from 12 volts to 6 volts has not been any where nearly as constant. simply sticking a 12 volt resister in the power wire did not give me the warm fuzzy feeling. The voltage reduction process all over the map on the Mopar groups. I have dabbled with automotive wiring for many years, I have repaired burned up automotive wiring, and have rewired cars and trucks from scratch. I came here seeking information concerning a voltage reduction process I thought would work, only to be lead around the mountain and back to the very item I was first asking about. That item reduces the voltage from 12 volts to 6 volts with a 20 amp, 120w power supply with 92% efficiency rating on a motor that has a 6 amp to 8 amp expected draw that ran on a 10 amp fuse. The unit itself says that it is not recemmended to run long periods of time at the max output, which to me means 20 amps. Its on a circuit that has a 10 amp fuse (in the old 6 volt system, and in the current 12 volt system). My automotive background tells me that if that circuit reaches 15 amps, it would blow the fuse, correct?

Help me understand what I am missing between a 10 amp 6 volt system, fuse and a 10 amp 12 volt system?

 

The only actual difference is the 12V circuit will consume twice the power as measured in watts. As converting from 6V to 12V effectively doubles the available power, that doesn't matter.

I'm not trying to be a wet blanket here, but my 30+ years in the electrical industry has proven to me time and again that ***uming things when dealing with these issues, something that appears to be a single point failure isn't always the case. It pays to check everything.

The OEM switch failed... why? Generally, when a switch fails it's from either overcurrent or overvoltage (arc suppression failure). The latter isn't an issue here; the difference between 6 and 12 volts is too small to matter. To me, this is a big red flag.

You say you've 'tested' the motor. But not at its rated voltage, which makes a difference. Electric motors are rated in HP and are sized to the load. Electrical issues internal to the motor or exterior mechanical issues that increase load will cause it to draw more current, sometimes much more. Enough to kill the switch. Applying more power with a 12v test can mask those issues... for a time. So you don't actually know if that motor is good or not. Excess current draw will also skew the resistor size, probably resulting in an over/under voltage supply to the motor when you try to apply voltage drop.

As to motor 'direction', you say it doesn't matter and you may be right. That depends on how the motor is internally wired, if it's a series-wound 'universal' type or has zero-degree timing, it won't matter.

It would be a shame to do the work and have it fail because these things weren't checked.

 

Thank you for that explanation.
I have no way to provide a 6 volt power supply without buying the reducer, or without buying a 6 volt battery.
I also have no way to test the loaded current draw on the motor.
Lets look at the options.
For about $25, I can buy the voltage reducer above with the 20 amp rating. I can't touch a 6 volt battery for that kind of money.
With the reducer wired in, and the ground pigtail grounded, I can actually install the wiper arms and blades that are already here, and run the wiper motor at a 6 volt level with a 10 amp fuse. It will either run, or it will fail immediately, or at some point in the future. When ever it fails, I can buy a used 6 volt wiper motor at the $50-$100 level (still under the cost of a 6 volt battery), or I can look into adapting a more modern 12 volt unit into the car.

 

You said you don't like Rain X, but here's a thought.
As you are putting together the wiper motor etc, clean the windshield gl*** with a couple coats of Rain X.
The wiper blades will float across the gl*** with much less effort.
I do this on my daily ride a couple times a year.

 

Here is a way of testing the motor using 12v and a 6 volt 55 watt headlight bulb.
Wire +12 volts from battery to ground side of headlight bulb. Then wire headlight bulb low beam terminal to wiper motor wire that is normally connected to the switch. The headlight bulb should reduce 12 volts to 6 volts for the wiper motor. You can put the fuse in between low beam terminal and the wiper motor wire if you like..

 

That is interesting, I would have never thought of that.
I'm not so sure there is a 6 volt headlight around here though.