Electrical safety concern -- grounding

[slotter]

Hi chief and thanks for your post!

I ran your tests just now and all is OK here. Got a dead short from the electrical ground pin to the metal parts and then from each plug prong to the internal metal parts, nada.

All is well here. (I hope!) :grin:

[arbycoffee]

Â…Some power supplies use common-mode rejection transformers. These are center taped. 100V is applied to the outside terminals and the ground is connected to the center tap. We use this system in high quality radio studios. It cancels out the 60 Hz hum that gets into the audio circuits.Â…

Can someone post a picture of this piece to do this meaursing on ?

Thanks in advance

[chief]

There is no picture I can post.

We are talking about machines that come wired for 100 volt operation. Not the ones that are modified with a 24 volt transformer.

The ac cord that is attached will have two prongs. Somewhere around the power supply (located on the bottom) some some of the folks here have found a cut green or yellow striped green wire.

What I was saying is, with an Ohm meter measure between the green wire and each prong on the power cord.

[logicprobe]

Chief... (as in Chief Engineer, no doubt?) :wink:
(I was going after my 1st class ticket many moons ago, till I heard about this newfangled "microprocessor" thing... and that grabbed my attention. Been focused there ever since.)

Welcome to the forum!

In the one box I've looked in, they're using a switching power supply.
I think these green wires are indeed supposed to be earth ground.
I don't think they're too worried about 60Hz leaking into the audio on these.

Good to have someone with your EE background onboard!
Don't be a stranger / lurker! We need your expertise! 8-)

[chief]

Good guess,

I was a chief engineer for over 25 years. Then became a general manager of a radio network. Now, I work for myself. I specialize in the non-commercial broadcast market, both radio & TV.

Back to the issue on hand. Just about everything today uses switching power supplies. In the post I was following, the poster measured 62 volts between ground and the chassis. I assumed that the ac input transformer was a center tap because that would generate the least amount of ac hum, that could get into the audio circuits.

_._ Walt

[Czyotto]

I have 2 Eleco Pachislo's Babel & Azteca with 100v power supply. If I do polerized grounded 3 way cord on these Pachislo's does it make a difference where the black wire (Hot) gets hooked up to? I was just going to cut the wire and do a mod like "dritz did. The 2 cords on mine are not polarized so I am guessing that it does not make a difference.

Then again I just may run a separate Green wire to the outlet grd screw. I use a remote type of switch for both to turn them on.

I really like the mod that "dritz" did on the side of his machines.

I did the Radio Shack Mod with a potentiometer, but there is not enough range. So I will get the Parts Express L-Pads again.

[cwstnsko]

On the machines I've done, there a black and a white wire in the cord. I wire them like US convention where black is hot and white is neutral, but it probably doesn't make a difference. I just feel better hooking black to black, white to white and green to green :-)

[Czyotto]

Ken (Dritz) What is that red and white wire going to the pins where the over flow bucket would go? Is that a mod for the overflow code? That is on your "picture of your 3 prong connection.

Like Arbycoffee saids "inquiring minds" want to know.

[dritz]

Those were there when the machine came in. I assume its for the over flow. Because if you connect all together it gives an error message. I assume meaning the overflow is full.

[arbycoffee]

If you have the token bucket in the machine is really making fun of you after taking all your tokens. That what mine do anyway. To fill the hoppr and token bucket around 3,000 to 3,500 tokens. It goes to show I loose a lot.

The wifes on the win cycle and I am on the loosing cycle :-(

On the thread I have been adding a ground to all my machines slowly, for safety concerns. :-)

[LaughingJim]

One thing to remember with these units is that they were originally a DC 24v setup. With DC, the life of a volt is short and hardly dangerous.

However, many transformers are inside your case. You will find transformers for the floressent lights, converting 24v into 1000+v. Aside from that, the only other transformer is the one that initially converts your 120v AC into 24v DC. The transformer should have a ground plug wired directly to it. It is bad if you feel voltage going through the transformer to the ground... even if it is through you.

That is great that it is now grounded, but you have not fixed the problem, only redirected it so it won't kill you! There is a massive electrical leak to the ground that deserves attention. Even without a ground, you should normally not feel a tingle unless there is a short.

The short that you may be getting is most likely from the cheap floressent lightbulb mount. After years of use, plastic can conduct high voltage electricity. This is due to the plastic absorbing mineral rich humidity and becomming saturated with non-mineral humidity. The quick fix is to simply use a better light fixture, instead of the cheap ABS or NYLON they used to mount the lights. You can also simply add electrical tape over the ends of the light bulbs, where the wires enter the glass.

Thier high voltage uses plastic as a dielectric bridge to the metal on the machine, heading towards the ground.

If this leak is comming from your "Installed" power converter... you may want to invest in a real power converter, not a ghetto/ancient coil transformer. (What they normally give you.)

A real, (Non-ghetto), transformer has a small initial coil, and a true circuit voltage regulator with capacitors and a quad-bridge rectifier... (That makes AC into DC.) They use less heat, and don't drain power unless they are using power. The ghetto transformers use power 24/7 while they are plugged in... a lot...

[RKnarr01]

jim do you have a pic or a link to the newer more non-ghetto transformers?

[gwarzin]

One thing to remember with these units is that they were originally a DC 24v setup. ...

...the only other transformer is the one that initially converts your 120v AC into 24v DC...

A real, (Non-ghetto), transformer has a small initial coil, and a true circuit voltage regulator with capacitors and a quad-bridge rectifier... (That makes AC into DC.) They use less heat, and don't drain power unless they are using power...

Don't ever remember seeing one designed for 24v DC. The parlors use 100v AC or 24v AC power. The transformers that are retrofitted into the 24v units do not convert 120v AC to 24vDC, they convert 120v AC into 24 v AC. The conversion to DC is done within the original power supply.

I'm just guessing here, because I haven't tried it, but I'd think anyone that takes your advice and feeds 24v DC into a device expecting to see 24v AC is taking a BIG risk. I'd like to see a full schematic of the power supply before I would be willing to try it.

BTW, the "non-ghetto" device you are describing is not a transformer, it's a power supply. By definition a transformer just changes one AC voltage to another AC voltage.

[Tulsa]

That DC reference caught my eye too.

PLEASE PEOPLE DO NOT HOOK UP DC CURRENT TO YOUR MACHINES!!!!

Unless of course purchasing power supplies is something you frequently enjoy doing.

[slotter]

But, we need to assist these ghetto transformers. The non-ghetto transformers were fortunate enough to get out. Let's not forget the ghetto ones, by all means.

[Tulsa]

Well, hooking up DC to your slot is one good way of getting a ghetto blaster!

[logicprobe]

BTW, the "non-ghetto" device you are describing is not a transformer, it's a power supply. By definition a transformer just changes one AC voltage to another AC voltage.

Yes... he MUST be talking about a switching power supply.

And PLEASE be careful about telling users to connect a ground to their TRANSFORMERS!!! Just which side of the AC on a transformer would you want them to ground???

Transformers use mutual inductance to convert one AC voltage to another AC voltage. Period. They do NOT convert AC to DC. Nor do they convert DC to AC... that would be an inverter.

Please get your technical ducks in a row before suggesting that parlors connect DC to machines... or before you suggest connecting DC in lieu of a transformer... OR before you suggest connecting a ground to ANY wire on a transformer!!!! A member following your advice may wll endanger not only their machine, but their own life and the lives of their families as well!

With DC, the life of a volt is short and hardly dangerous.

May I also suggest that a review of the fundamentals of electrical safety would tell you "Current kills"... not voltage. AC or DC... both can be potentially lethal at the right current... whether it's 120V or 24V!!! The secondary of these transformers in pachislo machines have the capability to deliver a constant FIVE OR SIX AMPERES. Depending upon skin resistance, ground contact, etc. that is more than enough to cause death!

[Lddrizzt]

LaughingJim,
Welcome to the board, I am glad you have taken an interest in our little slice of imported happiness.

That said, PLEASE GET YOUR FACTS STRAIGHT BEFORE YOU DISPENSE POTENTIALLY DANGEROUS ADVICE! oops! outside voice again.
Feel free to post any input, or advice that you want to share, but make sure you know what you are talking about first. Had you actually read the entire post we had 3 or 4 electrician types giving correct advice. Then comes the post about DC voltage, these may be toys but they do not run on batteries, we are talking houshold elctricity meaning if you screw it up bad enough ZAP goes your machine if you are lucky, god forbid that someone's child is the grounding rod attached to that newly DC converted machine.
This may sound harsh, but reality sometimes is.

Like I said earlier, welcome and enjoy your stay, but please refrain from giving advice that you obviously have no clue about.

http://users.zoominternet.net/%7Elddrizzt/voices.gif