Regulate Car voltage?

[bbawkon]

Even a laptop has a power supply section built in. Most laptop power supplies are 17-19 Volts, and the actual laptop runs from much lower voltages (1.2, 3.3, 5, etc). Additionally, the actual laptop can operate from a battery that is not 17-19 Volts - usually more like 11. There are lots of switching power supplies in a laptop.

 

[MikeAusC]

. . . . Another source of nasty transients is simply turning off the blower fan. Assuming that it is a brushed DC motor, when it slowly spins to a stop, it is actually acting as a generator and may be producing some large voltage spikes. . . .

. . .and every time you switch off the Starter Motor, the energy from the 200 to 400 amps flowing in the Starter Motor coils is just itching to go somewhere, after transforming to a VERY high voltage !

People sweat over having surge suppressors on Jumper Leads when you're connecting 12 volts to 12 volts ??? If your car electronics can survive a 200 amp Inductive Load Dump, they must already have pretty good protection built in.

 

[Illum]

Also, just FYI, almost all interior lights are electronically controlled (that is how they get them to stay on a few seconds after the door is closed), so reading voltage off that may not be accurate.

Regulation in this arena might be more costly than a simple cap fed transistor that operates as a slow shutdown switch. Not surprisingly, with the power rail connected to the battery if the rectifier that bridges the alternator with the battery has no or poor filteration loops you'll get alot of wonderful readings that at times meaningless. Many times I itch to hook up my car to an oscillioscope

aside from dimming, there is also a shunt somewhere in the circuit that disconnects all loads during engine start, possibly with express intention to protect them from engine start related power spikes.

Along that line of thinking, there is a reason that a lot of switching power supply IC's are being designed to operate from voltages up to 80v or so, and that's for automotive applications. They do make it easier to reduce power dissipation and still operate over the 9v to 18v that might exist on the battery bus, as well as some of the long transient pulses.

I wish I knew of a small protection module that non-EE's could just add to their design. Until then, I'd use my earlier suggestion, and try to use a big TVS (transorb, or transient voltage suppression diode). Might want to include a fuse too, just in case. The parts don't cost all that much, and are good insurance for $20 (or more) of LEDs and current regulator circuitry.

Steve K.

Switching power supplies also comes in "HV" varieties. Since the output does not deal directly with input its just a matter of internal component sizing.

Aside from TVS's would MOVs and varisters work in this situation for protection? Harnessing the same method household surge protectors have used for years and step the claming factor by a notch

I have retrofitted LED Parking Lamps and interior lights that simply use dropping resistors - years later they are still working.

LEDs may continue to emit light years after severe phosphor decay around its die due to thermal overload, so judging from output may be an inaccurate method to measure lamp longevity. Resistors are actually a pretty good way to maintain current regulation, provided that the resistor type can maintain its tolerance over high temperatures and the LEDs [after burn-in] do not exhibit a dramatic decrease in foward voltage over time. Resistors are the most cost effective method of current regulation when the total current across a load is around 100ma or less. Even at 100ma, 3-5mm piranha leds typically are overdriven by at least 40%. For this reason many LED retrofit products parallel them in clusters. This is not a bad concept, what is bad is the cheap LEDs lack a heatsink, with the emitter thermally isolated in an epoxy dome. Even if they are driven at spec, output will diminish over time father than SMT leds.

Aren't at least some (if not all) car's circuits already regulated? It seems to me that the radio for example, must have a fairly stable voltage to work properly. And what about the GPS and all those electronic gadgets? There must be some kind of power conditioning in there... I'm just wondering.

Good point, I suspect for cars that have built in GPS, TVs, actual computers using hard drives and internet ready operate these devices over a seperate loop than what the rest of the car runs on.

It would be nice if cars offered a nice clean 12v bus for solid state devices to operate from, but I haven't heard of this happening.

12V no, but it shouldn't be very hard....

 

[Lampyris noctiluca]

There are a number of manufacturers that make transient voltage suppressors for automotive use. Littlefuse/Harris make a great range that can withstand the demands of repeated inductive load dumps etc...Heres a link, hope it helps

http://www.littelfuse.com/products/Varistors/Multilater+Varistors+(MLV)/AUML/V18AUMLA2220.html

 

[Steve K]

Switching power supplies also comes in "HV" varieties. Since the output does not deal directly with input its just a matter of internal component sizing.

I was thinking of switchers I've seen from Linear Technology and National Semiconductor. Linear Technology has this "solutions guide" that shows a car's battery bus ranging from 4v to 80v, and their products that operate over that range. National has this selection of "high voltage" switchers, but they are also limited to an 80v steady state input. Does anyone offer a simple switching regulator that will work from a 12v bus and handle higher voltages? (edit: I just noticed that National does offer some that can operate from 6v to 100v)

If you really needed to handle higher input voltages, you could try one of the LED drivers designed to operate from AC power, but then you'd have to see if it could operate from low voltages too, such as a mostly discharged 12v battery. Or for the more skilled, there's the option of designing your own, but that's beyond my area of competence.

Aside from TVS's would MOVs and varisters work in this situation for protection? Harnessing the same method household surge protectors have used for years and step the claming factor by a notch

I've seen them used, but not a lot. I think TVS's do a better job of clamping the voltage to a lower level, and I believe there is a wearout mechanism for MOVs. A review of the manufacturer's literature should clarify this. Honestly, I don't see TVS's used that much except for electronics that are subject to lighting strikes. Some of the standard automotive pulses have enough energy that it's often easier to just use a regulator designed to withstand that voltage instead of trying to clamp the voltage and absorb the energy. For a non-EE designing a home project, the easier solution is probably to just throw a few TVS's on it, a few caps, etc. and figure it's close enough.

regards,
Steve K.

 

[Illum]

Hello Steve, thanks for the clarification on National Semi's switchers. I had errorenously made the conclusion that their selection of switchers has the ability to operate over a variable input voltage. Now that I read it over, you are correct, while input can be 4-80V, it must operate under a consistent input to achieve output stability.

I mentioned TVS because negative spikes do exist, in order for bidirectional voltage suppression I know of no conventional rectifier diodes that can operate as such. Varistors is the other option, but have one disadvantage that I know of. Varistors are voltage dependent, so theretically it does not possess any current protection from motor startup.

 

[Steve K]

I mentioned TVS because negative spikes do exist, in order for bidirectional voltage suppression I know of no conventional rectifier diodes that can operate as such.

The standard solution to negative spikes is a series diode, and usually a fast recovery diode, in order to block the fast negative transients. This has the added benefit of protecting the device if someone hooks up a batttery backwards (probably when jump starting, I assume).

Varistors is the other option, but have one disadvantage that I know of. Varistors are voltage dependent, so theretically it does not possess any current protection from motor startup.

I'm not sure I understand... Any protection device is voltage dependent, isn't it? i.e. it has a high resistance until some voltage threshold is crossed, and then resistance decreases?
I probably need to review varistors a bit, as I don't recall how they stack up in comparison to TVS's, in terms of speed of response, clamping voltage level, energy handling capability, size, and cost.

regards,
Steve K.

 

[Illum]

Well, aside from voltage spikes, what about current spikes? especially the previously mentioned induction dump from the starter motor, blowfan, etc?

 

[bbawkon]

Blocking / Limiting voltage will block / limit current. See Ohms Law. Without voltage (blocked) there is no current (blocked).

For really cool blocking, see the Bourns TBU-KE parts.

 

[Steve K]

For really cool blocking, see the Bourns TBU-KE parts.

almost like a polyfuse, but faster and with a greater change in resistance? Interesting gadget.... I'll have to take a close look at these.

Another interesting series element is the Linear Technology LT4356 "Surge Stopper". It can block incoming voltages up to 80v.
Personally.... I'm not sure I'm sold on this. If 80v is the highest voltage you'll see, just buy a switching regulator rated for 80v, and save the cost (and space) of the LT4356 and the associated mosfet.
If you need this function, I'd be tempted to just build one out of a few discrete parts and a high voltage mosfet (most applications I deal with need to block 200v). Maybe the advantage of the LT4356 is that it might be faster than building a discrete version?

regards,
Steve K.

 

[Calina]

Illum and Steve, thanks to both of you for sharing your knowledge. It is always interesting to read whatever you have to say.

 

[drdunk]

I have a 2000 vw beetle that keeps blowing head lamps. I have replaced the harnesses and they keep going out every two months or so. I am trying to find a way to put some kind of voltage suppressor or voltage regulator so it does not go over 14 volts. I think that is the problem . any ideas out there

 

[Steve K]

There are various ways to regulate the voltage, but it really depends on what the actual problem is. Any idea what the voltage at the headlight is while the engine is running?

Also, what is your level of knowledge of electronics? i.e. if you were shown a schematic, could you build a design with a half dozen parts? Would you know where to buy the parts? Can you solder? Can you package a small circuit board so that it will survive the automotive environment?

 

[Jakeyb]

Never really thought about this being an issue. I've used LEDs everywhere on all kinds of equipment but their input voltage range was pretty high. I would notice a dimming on startup and a spike of brightness every once in a while but generally output was pretty consistent. Never had problems...

 

[VegasF6]

How strange, you may have a problem with your charging system.
Anyhow, A quickie fix is you can add a high current rated diode inline with each headlamp. Something like GI2401 to GI2404 for instance should give you about .8 to .9V drop.
Here are some for less than a buck.
http://www.allelectronics.com/make-a-store/item/GI2404/16A-200V-DUAL-ULTRAFAST-RECOVERY-DIODE/1.html