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Bench test of flasher unit

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JeepSaffer View Drop Down
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    Posted: 18 Sep. 2017 at 8:24am
I have so far been unable to get my flasher unit to flash.

Some background:
  1. I am running 12V
  2. I have a new 12V flasher unit from Walcks, and their aftermarket turn lever
  3. I am setting up my wiring to run my front park lights as indicators.
  4. The rears will have indicator override on the brake bulb (but I'm not that far yet)
  5. The indicator lever was properly grounded during the bench test via a dedicated ground 
I was wanting to test everything on the bench first before I installed. I hooked everything up and got 13V on the X and L terminals of the flasher when the turn lever is not switched. When I operate the lever, the park light globe lights up dimly, and I get 13V on the X terminal of the flasher and 9.5V on the L terminal of the flasher, but no flash - just a constant dim light.

I have read that the flasher needs a minimum resistive load to work properly, so I hooked up the other park light on the same circuit, and basically got the same result - both bulbs light up dimly, and I get about 9.5V on the L terminal of the flasher, with no flash.

Are the tiny park globes just too small to make the flasher unit work? If this is the case, will the rear light add enough resistance to make it work, or will I continue to have a system that does not flash?
Or is my flasher unit faulty?

1948 CJ2A #204853 in South Africa
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepSaffer Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2017 at 8:39am
Some more research has suggested that you need at least 2 x 21W bulbs connected in parallel to provide enough load for the flasher unit to work. My guess is that the two front park globes are far smaller than this. Anyone know what power they are?

I will connect up the rear globe tonight and report back on whether it makes a difference.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepSaffer Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2017 at 2:08pm
I found a great write up on the net on how thermal flashers work, including a simple circuit diagramme and a simple understanding of the maths behind the theory.

It seems that even two park lights wired together will not provide enough load to get the flasher to work. I need the larger rear light to be wired in to provide the additional load to get the flasher to work. Even then it may not be enough. I will try and crunch some numbers tonight and see what the maths says.

If you are interested, the web write-up is here:


Mike


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unkamonkey Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2017 at 3:34pm
Yes a thermal type flasher needs enough of a load to get it to work. That's why they blink at a different speed if a bulb is out. Put in some resisters or you get an electronic flasher like people had to go to when they stuffed every socket they could with LED bulbs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nobodyjeff5888 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2017 at 7:51pm
auto zone sells different flashers for your needs. I had to replace mine for the same reason. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SE Kansas 46 CJ-2A Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep. 2017 at 7:58pm
Mike is going to be hard pressed to find an Autozone in South Africa...

I would check the load on the flasher by adding the rear lamps into the system. It might also require a higher load parking lamp or a resister in the circuit.

There are types of 12 Volt flashers that will operate under variable loads.
46 CJ-2A #64462 "Ol' Red" (bought April 1969)(second owner)(12 V, 11" brakes, M-38 frame, MD Juan tub)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepSaffer Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep. 2017 at 8:10am
Quick report back as promised:

I hooked up the tail light (alone) on the flasher and it worked. So the 21W power of the single tail light has enough current draw to get the flasher to work. The 3W power of the front marker light on it's own simply does not have enough current draw to activate the flasher. Running the 3W marker light together with the 21W tail light will certainly work. 

Moral of this story: A bench test of a thermal type flasher unit is possible, but it will only work if there is enough power draw on the flasher, and a 3W marker light on it's own is not enough...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SE Kansas 46 CJ-2A Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep. 2017 at 3:48pm
46 CJ-2A #64462 "Ol' Red" (bought April 1969)(second owner)(12 V, 11" brakes, M-38 frame, MD Juan tub)

U.S. Coast Guard Chief Petty Officer(ret.)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WeeWilly Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep. 2017 at 4:45pm
I like your approach on the rebuild, it sure does save a lot of trouble shooting and tracing circuits later on. A flasher beeper alarm would also use more amps to make the flasher work better. Keep up the nice work.

    Jim
47 CJ2A (Ranch Hand) 48 CJ2A, 48 Willys truck, T3C 3782, M274 (Military Mule)
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