Electronic 12 Volt Emergency Flasher

Hi, My VW Bus has quit flashing its turn signals and emergency flasher. The problem seems to be with the 3 terminal 30 amp relay 12 volt emergency flasher relay. I have one on order but I am just wondering if a Solid state flasher circuit could be designed to use instead.
There is 12 volt supply. Ground. and Load.
It would need to handle something like a 2 ohm (not led) rather incandescent bulb load at 12 volts with 1 second or maybe a little less on cycle.
I would love to see some design ideas Thanks:

If it's just a 3 terminal flasher unit, you can use one from just about any car built between 1975 and 1995.

You could design something, but the VW was probably new enough (after about 1970, depending on which country) that it's required to alert the driver if a bulb fails, so you would have to design that in somehow.

Thanks for the reply "Diver300" I was kind of thinking it was probably a universal flasher. I know it's load sensitive as it won't flash if a bulb is burned out. interesting thought I never considered it would have to do that but given so any design ideas would be my start to constructing one.
I was hoping it could be without mechanical relays. The original has a chip in it and a 10 uf cap and some resistors and of course the Load Mechanical Relay.

Here is a design idea but it still uses a small signal relay.

Danwvw said:

Hi, My VW Bus has quit flashing its turn signals and emergency flasher.

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Never had a VW new enough to have hazard flashers. But usually in most cars they are two different flasher units, are they in VWs? If the VW only has one, it could be the turn signal switch is bad.

Thanks for your interest, I had to check the Schematic it looks like the Emergency flasher switch E1 powers J2 the flasher relay in turn signal mode when it's off and on too for that mater when on it somehow ties all 4 lamps together So J2 is the Flasher Relay for both. For now I have the flasher relay jumpered and the turn signal do light that way just no flashing.
I'm not having any luck at all thinking of a way to use N channel Mosfets to do this a Multi-Stable Oscillator configuration would work but would need 2 separate loads.

Emergency Flasher Mode:


Turn Signal Mode:

Most old-style flasher units are in series with the lights & are not grounded.
They were typically a thermal device, using a hot wire element which expanded as it heated due to the lamp current until a contact closed.

That shorted the hot wire & resistor, bypassing them. The higher current also held in an electromagnet on the moving contact, so there was a delay before the wire cooled enough for the contact to be forced open.

The lower current through the lamps with the wire element in circuit was not enough to make them glow, but pre-heated them and extended the lamp life.

The third terminal was a second contact on a moving armature, switching power to the dashboard pilot light.

That system also gave a failed lamp warning inherently from its design, as if the total lamp current was too low, the armature would release earlier and give a shorter, faster flash timing.

This is a good diagram of that type:

rjenkinsgb said:

Most old-style flasher units are in series with the lights & are not grounded.
They were typically a thermal device, using a hot wire element which expanded as it heated due to the lamp current until a contact closed.

That shorted the hot wire & resistor, bypassing them. The higher current also held in an electromagnet on the moving contact, so there was a delay before the wire cooled enough for the contact to be forced open.

The lower current through the lamps with the wire element in circuit was not enough to make them glow, but pre-heated them and extended the lamp life.

The third terminal was a second contact on a moving armature, switching power to the dashboard pilot light.

That system also gave a failed lamp warning inherently from its design, as if the total lamp current was too low, the armature would release earlier and give a shorter, faster flash timing.

This is a good diagram of that type:

Click to expand...

To be fair, it was an extremely clever design And they have been pretty reliable over many decades.

Nigel Goodwin said:

To be fair, it was an extremely clever design

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Absolutely, it's a work of genius!

I'm not criticising in any way, just trying to put the unit function in context with the overall vehicle wiring.

Thanks for the comments but this is an electronic controlled relay one:
Here is what I have found. It seems the Flasher Chip is not listed for sale anywhere.

Also found the U634B Data Sheet but it's Obsolete too. I did find some on **broken link removed** but I would be more interested in coming up with a Solid State Relay design.

It looks like the UAA1042B and MC33193 are other dedicated flasher ICs.

Again, they are available from ebay but I can't find them in stock at any normal parts supplier.

And another - U6432B
That's listed as both TEMIC and Microchip as manufacturers..

Present vehicles must use something? Possibly a small package PIC appropriately programmed...

rjenkinsgb said:

Present vehicles must use something? Possibly a small package PIC appropriately programmed...

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Current vehicles don't have a separate flasher unit. Whatever drives the indicators, usually the Body Control Module, is just programmed to make the flash happen as needed.

Typically the direction indicators on a modern car will flash:-
When the driver signals a turn.
When the hazard lights are on
During locking and unlocking
During emergency braking, when the flashing is faster.
On cars sold in America, where the turn signals are red and are the brake lights as well, during braking.

On some cars the panel indicators will flash twice as fast if a direction indicator fails, but the remaining direction indicator flashes at the normal speed. There are also odd things like the VW track mode indicators and Land Rover / Jaguar trailer light test mode (neither of which are allowed on a moving car on the road) where the flashing is completely different.

With all those modes needed, the idea of having a "flasher unit", that just flashes, is a bit out of date.

(One 1990 car I owned had a 3 mode fasher unit. If 1 light bulb was detected, it flashed twice as fast. If 2 were detected, it flashed normally. If 3 or more were detected, it flashed normally and it lit the trailer indicator in the dashboard, to show the trailer indicator was working. I don't think that stand alone flasher units got more complicated than that before they were incorporated into more complicated control modules.)

And many new cars using the BCM as a flasher also use the radio/sound system to make the flasher sound. Many aftermarket sound systems need a seperate module to make the sound.

shortbus= said:

to make the flasher sound.

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That's what got me - I was under the impression that the "tick" was a legal requirement, so it was still a separate unit to be able to provide that feedback..

Not only the tick, it also is needed for the door chimes, and other warning sounds. The one I had to get for my truck. https://www.crutchfield.com/p_120GMOS01/Metra-GMOS-01-Wiring-Interface.html

Just found it in the wiring diagram for mine - the "tick" sounder is actually built-in to the indicator/headlamp switch unit on the steering column..



[Sorry for the sidetrack, Dan!]

Would be nice to use a micro controller. Enjoying reading what is posted above. I kept trying to figure out how to make the IRF-540 MOSFETS Flash Lamps. It was actually working so slow I didn't realize it was Flipping at first with 100 ohm resistors. With .1 ohm resistors which is where I need it to drive incandescent lamps it was flipping at 6.667 MHz.

The Replacement Flasher arrived and it works well the only problem is it makes the LED Flasher Indicators glow just a little.

Does it flash at the correct rate? It is rated for 2 or 4 bulbs at 21 W each (plus some side repeaters). I would expect it to flash faster with the smaller load that LEDs take.

You may be able to stop the LEDs glowing by putting a resistor in parallel with each side. 100 Ohms, 2 W or greater power rating would be fine.

It seems perfect! The LED's are only in the Dash indicators. It's just running the 4 21W bulbs. I am going to go through and clean my light fixtures soon and will see if it knows when a lamp is out. It's Supposed to be an OE part for the 1971 VW But it flashes at the same rate just running the turn signals as it does all 4 Emergency Flashers.

The faster flash with just one light is a deliberate feature, so it is either faster or normal, there is not a continual range of flash rates. I would not expect any difference between 2 bulbs working and 4. If you look at my earlier post about the flasher unit designed to detect the 3 lights in use when a trailer was connected, it had two distinct features (faster flashing and additional warning light).

I don't understand why the LED dashboard indicators glow. Is that when the indicators aren't in use? The conventional lights in parallel with the dashboard indicators should take away any leakage current.