AN/VSS-3a with Beam Shots

[Augi]

Hi All,

I'm new to the flashlight game, so I decided to start big.

This is a VSS-3a that was freshly rebuilt... in he 80's? It has 3 hours on the meter.

The previous owner did the hard part and sourced all the mating connectors, including the correct square thread connector for the side of the cube.

I had to source the wire and build the cables. Wow soldering 4ga sucks...

I also built an adapter platform to mount the light to a standard machine gun mount for the top of my HMMWV.

The light draws power from the slave receptacle in the front passenger seat where they plug in jumper cables to jump start the truck.

The daylight pictures are from before I added the spade grips. The beam shots show the spades.

These trees are about 650m away.


Augi

PS The guy I bought it from has a second one he's trying to sell sans connectors located in San Diego.

 

[Augi]

I forgot to add:

Before I found this light for sale with the connectors included, I couldn't find a single list of what they all were, so I spent a while browsing Amphenol catalogs trying to figure out all the part numbers.

Here they are for reference:

Search Light 23-pin Connector
Amphenol QWL
10-107632-6S


Control Box 23-pin Connector
Amphenol 97 Series
97-3108B-32-6P


Control Box Power In
Amphenol 97 Series
97-3108B-32-5S


Remote Box Connectors
MS3106E18-1S -> Main Control Box End
MS3106E18-1P -> Remote Control Box End


Vehicle Slave Power Connector
TGC2338


And here's the wire I used:
Cable between the control box and search light and control box and remote box: MIL-W-22759/16 wire in 4ga, 8ga, 12ga, 14ga and 16ga. The insulation is white ETFE, which is shiny and slippery -> From Chief Aircraft
Power into the control box: 4ga Welding Wire -> From McMaster

Augi

 

[NoNotAgain]

Well, I've got a M923a2 truck, so it wouldn't be an issue as to powering it up nor having a stable platform.

Out of curiosity, what does he want for the second light parts?

 

[BVH]

You're off to a great start! That's a nice and clean install! Welcome to CPF!

 

[jamesmtl514]

Really cool set up.
It works so well with the HMMWV.

 

[magellan]

Wow. Nice work. Awesome set up.

The beam shots look like a light saber in the dark!

Welcome to the forum.

 

[Bill Idaho]

NoNotAgain, check how much amperage you have on your M923. Military vehicles are my hobby. (In a big way.)
I think some HMMV's have up to 400amp output, and I don't think M923's have near that much. HMMV's have up to a 400 amp alternator, whereas most M923's have only a 60 amp. Better check.

 

[Augi]

Yes, early HMMWV's had 60amp alternators unless they were shelter carriers and got 200amp or, less commonly, 400amp. It seems that they eventually standardized and all late model HMMWV's have 200amp alternators regardless.

I have a 200amp alternator in mine.

Augi

 

[BVH]

Just noticed that you're in the same area as myself. I'm down in Pismo. Where do you shine the light without drawing unwanted attention?

 

[NoNotAgain]

NoNotAgain, check how much amperage you have on your M923. Military vehicles are my hobby. (In a big way.)
I think some HMMV's have up to 400amp output, and I don't think M923's have near that much. HMMV's have up to a 400 amp alternator, whereas most M923's have only a 60 amp. Better check.

The M923a2 because of the up-dated Cummins CTA 8.3 and automatic transmission have 100 amp alternators. The first version M923 only had 35 amp versions as a carry over from the M809 series trucks before the change to a 60 amp Leece Neville.

I have 4 batteries in mine wired in parallel so it's gots lots of amps for starting.

 

[Augi]

Up

Actually I've run it for 15 minutes several times just pointing roughly upward on the street in front of my house near downtown SLO without drawing any attention.

Now that Poly is about to be back in session, I'd like to illuminate the P and see how the college kids react. I can probably reach it from anywhere in town that I can see it...

Those beam shots are off of Hwy166 near Miranda Pine camp ground.

Augi

Just noticed that you're in the same area as myself. I'm down in Pismo. Where do you shine the light without drawing unwanted attention?

 

[larryk]

Welcome to CPF. Nice clean install. Are you running the light with the engine on or off. If your running with the engine off you will be surprised how much brighter it is with the engine on and the alternator helping with voltage. If you get a chance could you measure the voltage at the battery with the engine running.
Great build, have fun.

 

[Augi]

I run the light with the engine on at idle. The voltage gauge in the dash wavers for 1/4 or 1/2 a second when energizing the light, then stabilizes at the same nominal voltage as with the light off.

I haven't actually measured the terminal voltage at the batteries tho.

You have to run at high idle for 5 or 10 seconds to get the alternator to start charging, then usually it will maintain the field at idle. I did have the field collapse once after about 20 minutes of run time. The light dimmed and the voltage gauge dropped into the yellow. I revved the engine a bit and it came back. You can really hear the engine tone change when the alternator is generating big current.

Augi

 

[larryk]

Hi Augi, the reason I would like the voltage with the engine running is because on my VSS-3 I'm using 4 14 volt AMG batteries series-parallel for 28 volts. But when the batteries are fully charged the light gets over 30 volts for a few seconds on start up. My light failed last year burning out 4 resistors and 2 power transistors. The manual states a max voltage of 28.6 I believe. I'm just wondering if the failure was caused from the short over voltage at start up
Thanks, Larry.

 

[Augi]

My truck has 2 regular car batteries in series for a nominal voltage of 24V. The alternator DC output is regulated at 28V nominal, governed by MIL-STD-1275. The standard does allow for voltage excursions for brief amounts of time. I can't remember exactly how much. You'd have to look it up, but it should be readily available. This light is designed to run on MIL-STD-1275 power. Tank or truck, the same standard applies to the 28V bus.

In any case, the alternator regulation is pretty good, and the batteries are so far below 28V that I couldn't see them spiking up.

Caps will definitely pop if you put too much voltage across them. Are they marked for their rated voltage? I would expect them to be derated quite a bit for a military application. As much as 50%. So they could be 36V or 48V caps. Then it might take another 5% or 10% before they actually fail.

For the resistors you need to look at how much wattage the part is dissipating. You can see a voltage spike, but if no current is flowing, the resistor won't be dissipating that much power and won't feel a thing.

Augi

PS Download the TM's for the light and you might find some useful circuit diagrams and troubleshooting info.

 

[NoNotAgain]

I don't have a VSS-3a yet, but my M923a2 is wired like LarryK's in that its series-parallel for two 24 volt circuits made up of 4 12 volt batteries.
Nominal voltage per battery is 13.7 volts, static and 14.2 volts running.

It's possible for the alternator to output 30 volts until the field stabilizes.

If your alternator zapped your light, I'd look at replacing the rectifier set, and make sure that your grounds are in good shape.

 

[larryk]

Thanks Augi. I meant to say 2 power transistors, I changed my post to correct this. I have all the available TM's and did repair the light. I'm not sure that little over voltage for such a brief time is what caused it. I haven't had any problems since the repair and I'm still using the same battery set up. These lights are old and maybe it failed on it's own. I guess time will tell.

 

[Augi]

Oh, that makes more sense then. I'd think you are looking at an over-current event rather than a voltage spike from the power supply.

How bad did the parts look? Any smoking craters the packages?

Sometimes this kind of thing happens if there's a short to ground in the power path, or a transistor fails closed. Then it dumps a ton of current through the parts for an extended time. They can handle short bursts, but not steady state.

Since you replaced the parts and it works now, maybe was just a fluke failure of a part.

Augi

 

[BVH]

It would be fun after all these years of guessing, to know what that actual bus system voltage is on a typical military vehicle when the VSS-3A is running steady-state both at engine idle and at say, 1500 RPM. At some point Augi, maybe you could take a couple readings and let us know?

 

[larryk]

Here is a photo of 2 of the resistors. You can see one blew out of the gold colored heat sink.