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Bobcat fine adjustment; VA curve

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Bobcat fine adjustment; VA curve

Postby bosulli » Sun Feb 26, 2017 9:20 am

There are two similar threads on engine drives going and both reference the FIELDRES YouTube on SA200 VA curve and fine adjustment settings. I did not want to hijack a thread, so I am starting one just on the Bobcat 225, fine adjustment and running 7018 structural groove welds.

One poster replied to one my earlier post that the SA200 is a DC generator, and Bobcat is an AC generator, so the fine adjustment might not be the same.

This morning I re-read Bobcat manual. What I am trying to find out is the arc force difference in the fine adjustment settings, and trying to not run to hot. I practice mock up 3G structural test and 1G, and want to know what to set the machine for. Sometimes at 2nd gear and 7 fine adjustment (Miller recommended) its too hot, and getting undercut. (maybe I am moving to fast, and should slow down). If running uphill, I don't want a runny puddle, and maybe should decrease arc force\voltage. I am I over thinking this????

Also, the Bobcat manual says run 2nd gear, 7 fine adjustment for 1/8 7018, and that should be 110 A. Per my math I get 126; assuming a linear VA curve, which it is not. Here is the work behind the 126 solution. per calibration marking on the fine adjustment 1 thru 10, there should be a change of 8 amps. 7 * 8 = 56. 56 + 70 = 126A.

Thanks for taking to time to read. Any constructive input would be beneficial for the group.
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Re: Bobcat fine adjustment; VA curve

Postby MinnesotaDave » Sun Feb 26, 2017 10:44 am

Bobcats have overlapping ranges that affect arc characteristics.

As Travis, Fieldrez notes:
Using the lowest coarse adjustment allows the fine to be set higher, this increases weld voltage and makes 7018 run nicer.

Jumping up a range in coarse setting makes you reduce the fine adjustment to get the same amperage. Lower weld voltage this way and makes it harder to start rods - arc starting is noted in bobcat manual pictured below.

On the machine pictured, when the coarse range runs out of amperage, the next range higher picks it up with the fine adjust about 5.

Notice you can get 100 amps in all 3 ranges, they will not weld the same.

image.png
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Re: Bobcat fine adjustment; VA curve

Postby bosulli » Mon Feb 27, 2017 6:35 am

Thanks for the reply. That page of the manual is where I got the 110A at 2nd gear coarse adjustment, and 7 on the fine adjustment.
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Re: Bobcat fine adjustment; VA curve

Postby MinnesotaDave » Mon Feb 27, 2017 8:02 am

bosulli wrote:Thanks for the reply. That page of the manual is where I got the 110A at 2nd gear coarse adjustment, and 7 on the fine adjustment.


But that page shows 5 on fine adjustment :?:
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Re: Bobcat fine adjustment; VA curve

Postby bosulli » Mon Feb 27, 2017 1:41 pm

Oh, I see that now. Must have read over that, as on the machine they recommend a fine adjustment setting of 7. That explains why my math did not work. So, 7 would be about 116 depending on how curvy the VA curve is.
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Re: Bobcat fine adjustment; VA curve

Postby MinnesotaDave » Mon Feb 27, 2017 2:01 pm

bosulli wrote:Oh, I see that now. Must have read over that, as on the machine they recommend a fine adjustment setting of 7. That explains why my math did not work. So, 7 would be about 116 depending on how curvy the VA curve is.


7 would be about 126.

150 - 70 = 80

70 + (8)(7)
=70 + (56)
=126

As far as I know, it's assumed the amperage is linear enough to use the dial as indicated for each coarse range.
Then just dial it in as desired after welding on scrap to confirm settings.
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Re: Bobcat fine adjustment; VA curve

Postby bosulli » Tue Feb 28, 2017 12:14 pm

Thanks Dave.
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Re: Bobcat fine adjustment; VA curve

Postby bosulli » Tue Feb 28, 2017 12:15 pm

Thanks Dave.
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Re: Bobcat fine adjustment; VA curve

Postby ryanjames170 » Tue Feb 28, 2017 9:56 pm

one of my plans for this summer once i get the engine on my 2e sorted out is to play around with 6010, 7018 and 7014 to see where the sweet spots are for them.. as my 2E's manual dose not really have such a idot guide.. i kinda am planning to get a 8.5x11 lamanted with some other info related to the welder and put it on the top of the welder, as i dont really use the 2E much as i got a difrent set up i am using.. this is partly due to the 2E needing work and also its aux power is 230V and since most power tools and lights use 120V it dont end well but when you need something with balls you need it loll..

i would say this might not be a bad idea for your bobcat.. to get some rods in various sizes and types and kinda figure out what works and dont work and make note of it.. as you might figure out what works for 3/32 7018 but not use that rod again for 3 months and forget that setting and have to re figure it out...
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Re: Bobcat fine adjustment; VA curve

Postby MinnesotaDave » Tue Feb 28, 2017 10:19 pm

Does your blue star 2e have a faceplate like this where the high and low for each coarse range are shown and a fine adjust?

If yes, then pretty much the same - use the lowest coarse range possible for the amps you want so your fine control is near the top.

This will give you the highest possible weld voltage.

For vertical up or overhead you may want to go to the next range up to decrease the weld voltage - depends how you like to weld.

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