Circuit Help

[PedroDaGr8]

I am unsure where to ask about this, I am looking to design a -12V circuit (or close to it, even -6V would work I guess). Unfortunately I know very little about circuit design. Chemistry I know boat loads, circuits soldering and simple stuff is about it. It needs to handle a decent number of amps. The reason is, I need to speed up the windshield wipers and I read a few places where instead of applying a ground, a -12V was appleid to the ground. Giving it a functional 24V drop. This resulted in a huge increase in speed of the wipers. Ideally, I will only turn it on using a switch, to be used in those extreme times of rain.

Edit: since it is going to a motor, extreme tightness of voltage is not needed, as right now the motor sees the typical in car fluctuations from the alternator.

Another option would be to convert 12V to 18V or so. I would try other wiper motors but I can't find any extra info and can't afford to just go willy nilly trying different ones out.

[PedroDaGr8]

Re: Circuit Help

Aww man pls someone help. Or is this harder than I realize.

[Logistics]

Re: Circuit Help

Doesn't that mean you need to install a negative 12V regulator into the system? There are positive and negative voltage regulators.

[PedroDaGr8]

Re: Circuit Help

Doesn't that mean you need to install a negative 12V regulator into the system? There are positive and negative voltage regulators.

I guess. I am not exactly sure how to go about this. I am just at a complete loss here.

[999999999]

Re: Circuit Help

A wiper motor is already running hard (hot) from 12V, you can't put 24V through it and expect it to last.

The motor may not even have separate ground lead, it may be chassis ground meaning you'd need some robust (tolerant of seasonal elements, rain, vibration, torque, etc) isolation in order to take motor ground to some lower non-ground potential. However, it's pretty likely to be getting wet (which may conduct electricity) unless entirely sealed which is a project in itself since this motor drives a moving wiper arm.

Since you have only 12V DC system, you would want a step up converter. I don't know the current such a motor uses but the converter would probably need be capable of at least a few amps. It also needs to use non-electrolytic caps due to the temp extremes possible. You could use something like a 2:3 ratio transformer rated for a few amps instead but this is lossy, larger, heavier, and probably costs more.

Frankly I think this is a bad idea, in bad rain the last thing you want to be is a beta-tester for a windshield wiper circuit. If it were only you risking your car it would be one thing but it risks your life and that of others on othe road. If higher voltage were so easy, reliable, and useful, all cars would probably already have this. Having it work ok in a test before out on the road, is no assurance your wiper motor isn't burning out faster from it and would fail when you need it. j I suppose I'm saying even if you knew how to design this yourself, even then it's a big risk.

[gonzo0815]

Re: Circuit Help

A usual wiper motor is sucking about 150w @ rated voltage. So this would be a powerful step up converter.

Aside from the problems 9999... pointed out, i think it will giving a very bad mix of switching noise problems in any susceptible circuit.
Apart from that, building devices for automotive use, is not that easy.
The environment is very very nasty, a half backed circuit would not last very long there.

If the car is not new, i would suggest to check the ground cables carefully, as this would making a huge different in available voltage at some currents.
If that is not the problem, i would suggest to get a faster, more powerful DC motor.
Check some surplus part shops, they are not very expensive there.

[999999999]

Re: Circuit Help

I'm surprised if a wiper motor draws that much current, 150W is a heck of a lot of heat for this few-cubic-inch motor to dissipate. I was suspecting more along the lines of 3A if that.

OK, I just did a brief Google Groups search and came upon one experimenter that found a Fiat wiper motor draws (@ 12V) 1.2A no-load and 11A stalled. Naturally this is no guarantee all wiper motors have same current, but I also came across brief notes that some cars had 6A or 10A fuses on the wiper motor circuit.

[hardwareguy]

Re: Circuit Help

I wouldn't modify the amount of current entering the motor. Not only could the motor fail, but the wiper gearbox could lock up or strip out as well.

Try some water beading products like RainX and a new set of high quality wiper blades.... it makes a world of difference.

[dood]

Re: Circuit Help

I use Rain-x washer fluid and high-quality blades. I rarely have to turn my wipers on high. Usually intermittant is good enough, because the water literally leaves the windshield before the wipers have a chance to swipe. The only thing I have to use wipers for is the road spray or small droplets that don't bead enough to roll off the windshield.