Genset starting circuit, help?

[rosietheriviter]

I just bought an old "Airco" welder/generator, almost an antique.  Gas engine, air cooled 2 cyclinder Kohler I think. Label KW rating is 10KW.
The recepticals are 110V AC two prong outlets and there is a 110V DC two prong outlet.  220 is accessable via a three lug connector, labeled 1, 2, 3    1 to 2=110v, 1 to 3 =220v, and 2 to 3=110v.  I plan to change out the two prong 110v outlets with three prong outlets.
I hope to ground the generator trailer frame to a copper ground stake, like my neighbor has his generator grounded.  He says I need at least 6 or 8 feet of rod driven into the ground, sounds right to me.
When I use the generator for my well pump I think the ground connector is not a concern, but when I use grounded tools or appliances on 110 volts AC, I understand the ground is extremely important.  Makes sense to me also.
I have some aerospace industry assembly experience, actually a lot, but the reason for this inquiry is that the engine starting-charging circuit is "positive ground" and I just cannot get my head around the idea of positive ground versus negative ground. 
The "silly little girl" in me is asking, am I looking at or for a problem that doesn't exist or am I just waking up at night out of boredom?

I am also watching for an 1800RPM diesel engine to install someday in the future when the gas engine dies.

Thanks all,
Rose is Rose

[xyzer]

Rose,
I'm not a electrical engineer but the 2 electrical systems are completly seperate. The positive ground engine battery system is used on some 12V systems. The british used + ground on some cars 1953 MGTD was, and I have an older John Deere tractor that is + ground. I'm not sure of the reason and maybe somone will explain why. Obviously the + ground is not used on 90% of the 12V auto systems so there must be a debate over it. But for your use the ground rod for the generator with 220V is a very good idea. 12V is not near as dangerous if a short should occur.
Dave   

[listeroidsusa1]

The difference between + ground and - ground is sinking or sourcing the voltage. This can drive you crazy if you don't realize how its set up. On a + ground system EVERYHING is hot with respect to the -. On a - ground system nothing is hot with respect to the frame unless it is switched on. A positive ground system isn't usually as safe as a negative ground system. The + ground system can do some really strange stuff to troubleshoot. My '37 plymouth had a bug that when I went over a speed bump the horn would blow and the radio and lights sometimes turned themselves on. It was a simple fix once I found the problem but troubleshooting a + ground takes an entirely different mindset than a - ground system.

[phaedrus]

The explanation for positive ground is that one end of a DC spark is hotter than the other, and the positive ground design gives a slight advantage to the crude ignition systems we used to be stuck with.

I'm not so sure the systems in the Airco are separate - I have a Hobart with a wisconsin twin in it and the field winding is the starter motor.

Grounding a genny is considered good practice, positive ground DC system or not. Suggest you get the book from Airco if you can - I was able to get the book from Hobart on mine for free - just asked 'em! The Hobart was sold in 1970, seems new enough to me...

Grounding is not always a good idea though - there are special cases when it can create problems - like on a testbench where one works through an isolation transformer, or sometimes in a welding shop - not that I am an expert, though.

[Doug]

I used to test on motors on an ungrounded delta test bench, but I always ran a bond because Capacitive coupling can still give a nastey poke even with no connection to ground.

"12V is not near as dangerous if a short should occur."

It all depends on available fault current, a small battery has a fairly high internal resistance. A large low voltage battery bank can produce hellish arcs and twist and warp things. Flamable gasses around batteries big or small are always a danger.

Doug

[rosietheriviter]

Phaedrus,
I think the welder/generator is '50s vintage, I hear that was before Miller took over.  I will continue to look for a manual, Thanks.

Doug,
I KNOW!  I've received some very painful shocks from 12VDC, and even from 5VDC!  You'd be amazed at the amperage on some of the spacecraft!  Thanks.

Since I will be frame grounding the "ground" terminal of the 110VAC receptacle, and I think the 110VDC receptacle is frame grounded on one side, I am just not able to

see the light from here.  Can I change to -ground starting circuit by changing starter and generator, or is it much more complicated than that?  If I could make that

change, I would be comfortable in believing that ignorance (on my part) is bliss.

To all, thanks,

Rose is Rose

[Doug]

Doug,
I KNOW!  I've received some very painful shocks from 12VDC, and even from 5VDC!  You'd be amazed at the amperage on some of the spacecraft!  Thanks.

Not quite sure how to take that.

I'm always getting pokes of telephones they run at a modest 48 volts and sometimes I can feel that if my fingers are damp. For some reason people feel the need to phone the line I am working on to see if I have it fixed yet and this tends to shock me with over 100 volts ( for the ringer ) that I realy don't like.

I like to try and get what ever I can to a zero energy state before working on it. I've been shocked ove rthe years ( as high as 2200 volts ) and had to rince acid and Caustic battery solutions off my hands and in one case my face so I try to offer advice based on my fear and dislike of DC.

Rather touch a live 600 volt AC line than 125 DC, DC hurts that much.

And acid in your face from a blown up cell because you shorted it out realy sucks too....

Once got a shot of an exciter went threw one hand out the other.
Felt all the muslces in my chest tighten, and right hand curled around a handle while my left hand was jerked out of the box.
I think I felt my heart spasm but obviously it kept beating because I am writing this.
Sat down and smoked hlf a pack of cigaretes and went home.
Felt some pain in my arms and chest for a few days, might have gotten a mild internal burn
I was very lucky and have been lucky a few times since but I don't think I have much reserve luck left......

Doug

[phaedrus]

When I studied electronics from a navy manual long ago I recall that the threshold for fatal shock through unbroken skin was defined by the USN as 30 volts... less if you have a cut. And of course it ain't the volts - it's the amps what killya.

[Doug]

I have a formula some place that can actualy calculate the probability of a fatailty.

Must look for that....

[rosietheriviter]

Doug,
I KNOW!  I've received some very painful shocks from 12VDC, and even from 5VDC!  You'd be amazed at the amperage on some of the spacecraft!  Thanks.
Not quite sure how to take that.
Doug

Doug,
I cut and pasted from a previous message:
I was an aerospace worker for twenty-two odd years, started on Voyager and ended up working on Endeavor.

These are NASA spacecraft that I was involved in the construction/assembly/quality control (HA!) of.

If that explains how to take that?

Rose is Rose

[phaedrus]

So, Rosie, which one of the Thiocol engineers voted to not launch, or was it lunch, eh?

Seriously that must have been a job that's given you marvelous stories. I have some good 'ns, but I bet yours are far better!

I've got a video of a high voltage linemen working on a hot 1/2 million volt transmission line - he's wearing a faraday suit, nomex and wire, hanging from a chopper in mid air...ZAP! I'll email it to you if you like. Let me know.

P

[Doug]

Doug,
I KNOW!  I've received some very painful shocks from 12VDC, and even from 5VDC!  You'd be amazed at the amperage on some of the spacecraft!  Thanks.
Not quite sure how to take that.
Doug

Doug,
I cut and pasted from a previous message:
I was an aerospace worker for twenty-two odd years, started on Voyager and ended up working on Endeavor.

These are NASA spacecraft that I was involved in the construction/assembly/quality control (HA!) of.

If that explains how to take that?

Rose is Rose

Wow.....

My contribution to life on earth and the betterment of humanity has been digging shiny rocks out of the ground.....

I hope you were not offended, I wasn't sure at first if you were serious or making light of electrical safety. No offence ment.....

When I was a young lad of about 9 I went to Ontario place and saw the "Soviet space" tour.

I pumped a Cosmonaughts hand, probably as close as I will ever come to meeting people who I thought then and still think now. For some reason ( probably wishful thinking ) I believe that may have been Alexi Leonov. Went to Florida as kid too and saw lots of cool stuff too. The shuttle hadn't flown yet but the hype and excitement were there. It was and great time to dream and be a kid....

Doug

[rosietheriviter]

So, Rosie, which one of the Thiocol engineers voted to not launch, or was it lunch, eh?
Seriously that must have been a job that's given you marvelous stories. I have some good 'ns, but I bet yours are far better!
I've got a video of a high voltage linemen working on a hot 1/2 million volt transmission line - he's wearing a faraday suit, nomex and wire, hanging from a chopper in mid air...ZAP! I'll email it to you if you like. Let me know.
P

Hi Phaedrus,

I would love to have the video but I don't know how to do it right now.  I am unable to receive in a reasonable length of time.  My dial-up speed never exceeds 24K bps and I usually get more throughput at 21.6K 
My IPS times me out after 3 hours and sometimes that is not enough for a regular Microsoft "update" to be received.

I will a little diggin' around to try to find someone you could send it to for me.

Rose is Rose

[rosietheriviter]

Durn it.

I meant to add more to the message but sent it before I was ready.  I don't have alzheimers, but I think I'm getting somezheimers.

Many aspects of the Voyager and shuttle projects were and are subject to non-disclosure agreements and a few aspects are actually classified.  Can ya believe that?

My involvement was fairly drab but I saw a lot of parts and pieces and was always amazed at the massive amounts of money spent to do some of the simplest jobs.

JPL relied on many subcontractors as did Rockwell.  My involvement with the Endeavor project ended with the rollout at Palmdale CA before transport to NASA per se.  That is, no boosters, no main tank, etc.

Rose is Rose

[phaedrus]

I thought that NASA civilian space program was 100% public by legislation. What an absurd time. Material that is obvious and public, and of course already long ago copied into Russian and, well, everybody else's records, is then made "classified" after the fact. What BS! Horse has left the barn...

Only tiny details can be kept really secret - and they seldom matter, imho.

Ever read the story about project Orion?  Bang bang bang!

I used to work for a guy who had been involved with operation fishbowl - and he told a great story about one of the gadgets atop a V-2 failing to function when triggered by radio near apogee. So there they were, waiting, wondering, while the gadget fell back and splashed. I can't confirm that story, but it's what he told me, and he was a credible guy - worked later on turbopumps for the Saturn...

Then there's the one where "It is I, Werner!" began a long night of crawling through leaking hydraulic oil, fixing leaks, under a wind-tunnel - Of course that stuff long predates the shuttle project.