Hi everyone, I am working on a bridge saw that uses a CT which sends a signal through 2 wires to a AMP panel meter. I recently moved the control panel it is located in of the moving bridge and mounted it stationary to the floor via a steel 8x8 post. So I had to extend all the wires quite a bit to reach the cable wire chain track and then through the chain track and into the main control cabinet where all the relays, switches, computers, controllers and where the CT is located.
The 2 wires that originally sent the signal from the CT to the panel meter were about 11-12 feet in length and around 20-22 AWG. I extended the 35 wires from this control panel to the cabinet around 50 feet with this wire. http://www.zoro.com/i/G1095306/
So basically I went from 11 feet of 22 AWG to 50 feet of 18AWG and now the panel meeter reads way way low. I used my fluke amp meeter and around the same wire which passes through the CT and I get about 56 amps right at start up there but the panel meter shows only 20 or so amps. Then when its just running with no load the fluke showed about 7-8 amps and the panel meeter was on zero. I tried adjusting the screw on the front of the meter but that I found was just to hold the needle "zero" to the face place.
I realize my issue was extending the length of the wire which caused more resistance and therefore lowers the signal by the time it gets to the meter. I tried adding 2 more loops through the CT (it had 3 loops originally) This elevated the readout a tiny bit but its not reading near what it should. I read a little on this site about https://electricalnotes.wordpress.com/2011/04/16/current-transformer/ Current Transformers but there is just so much info that is way over my head and would take me years to fully understand. But I did get a few Ideas on how to correct this. One way was to take the white secondary output wire that runs to the meeter and wrap it a certain amount of turns in the correct direction to get the right ratio so the meeter reads correctly. But the type and shielded/non shielded wire all changes the math on whats needed so I am lost. There was also a part that mentioned adding a second smaller CT to the equation to get the needed ratio, which again is over my head.
The CT I have has allot of Chinese symbols and some numbers all which I goggled but didn't really get anywhere except for the "LM-0.5" and the "50/5" (50 is stamped in the metal) You can see this in these pictures. (there is also a picture of the panel meeter) http://s311.photobucket.com/user/diebog/library/Bridge saw
Only thing I know is the 50/5 is the ratio of the CT. I think the 0.5 is the accuracy? There is a "7" stamped towards the right in the picture as well as the number 200 in the middle of the pic that is printed vs stamped inside the box. So I am hoping someone could perhaps tell me what the others mean? I don't even know if its important I understand them, I just need to fix the meter not reading correctly.
So hopefully I gave all the info needed but If I missed something, just let me know. Id appreciate any and all's suggestion on how I can fix this current/signal loss going to my meter. Do I need to buy a better meter? A better or different size CT to accurately show the correct amps at the end of the 18AWG wire in the control panel? Something else?
Another tid bit of info I thought I would share, before I reconfigured the control panel on this saw the meter worked as it should. I had a mark on the 20 amp line where the manufacture of the saw said to not go over while cutting (some granite/marble/quartz cut slower or faster which effect the amps) so you just cant always go by the same speed you use on the speed control. There are some stones out there that even with the best diamond blade made the stone is so hard and dense that it has to be cut so slow because the amps just jump right up. Other stones I can cut 4 times as fast as others and the amps barely go up. So this is something I use on a daily basis and needs to be as accurate as possible. The motor it is reading is a 3 phase 30 HP electric motor. In case your curious, here is a link to a similar saw, in fact you can see how the control panel is mounted on the bridge which moves back and fourth which is real annoying and hits you in the head constantly. http://www.ebay.com/itm/NEW-Bridge-...471?pt=LH_DefaultDomain_0&hash=item2303a8d48f
It is so much nicer now that the control panel does not move with the bridge, I just gotta fix the amp signal issue.
I know my post is somewhat lengthily which I apologize for, I was just hoping to answer any questions that may arise. And again, I welcome and appreciate any thoughts or suggestions you may have.
Thanks,
Jeremy
The 2 wires that originally sent the signal from the CT to the panel meter were about 11-12 feet in length and around 20-22 AWG. I extended the 35 wires from this control panel to the cabinet around 50 feet with this wire. http://www.zoro.com/i/G1095306/
So basically I went from 11 feet of 22 AWG to 50 feet of 18AWG and now the panel meeter reads way way low. I used my fluke amp meeter and around the same wire which passes through the CT and I get about 56 amps right at start up there but the panel meter shows only 20 or so amps. Then when its just running with no load the fluke showed about 7-8 amps and the panel meeter was on zero. I tried adjusting the screw on the front of the meter but that I found was just to hold the needle "zero" to the face place.
I realize my issue was extending the length of the wire which caused more resistance and therefore lowers the signal by the time it gets to the meter. I tried adding 2 more loops through the CT (it had 3 loops originally) This elevated the readout a tiny bit but its not reading near what it should. I read a little on this site about https://electricalnotes.wordpress.com/2011/04/16/current-transformer/ Current Transformers but there is just so much info that is way over my head and would take me years to fully understand. But I did get a few Ideas on how to correct this. One way was to take the white secondary output wire that runs to the meeter and wrap it a certain amount of turns in the correct direction to get the right ratio so the meeter reads correctly. But the type and shielded/non shielded wire all changes the math on whats needed so I am lost. There was also a part that mentioned adding a second smaller CT to the equation to get the needed ratio, which again is over my head.
The CT I have has allot of Chinese symbols and some numbers all which I goggled but didn't really get anywhere except for the "LM-0.5" and the "50/5" (50 is stamped in the metal) You can see this in these pictures. (there is also a picture of the panel meeter) http://s311.photobucket.com/user/diebog/library/Bridge saw
Only thing I know is the 50/5 is the ratio of the CT. I think the 0.5 is the accuracy? There is a "7" stamped towards the right in the picture as well as the number 200 in the middle of the pic that is printed vs stamped inside the box. So I am hoping someone could perhaps tell me what the others mean? I don't even know if its important I understand them, I just need to fix the meter not reading correctly.
So hopefully I gave all the info needed but If I missed something, just let me know. Id appreciate any and all's suggestion on how I can fix this current/signal loss going to my meter. Do I need to buy a better meter? A better or different size CT to accurately show the correct amps at the end of the 18AWG wire in the control panel? Something else?
Another tid bit of info I thought I would share, before I reconfigured the control panel on this saw the meter worked as it should. I had a mark on the 20 amp line where the manufacture of the saw said to not go over while cutting (some granite/marble/quartz cut slower or faster which effect the amps) so you just cant always go by the same speed you use on the speed control. There are some stones out there that even with the best diamond blade made the stone is so hard and dense that it has to be cut so slow because the amps just jump right up. Other stones I can cut 4 times as fast as others and the amps barely go up. So this is something I use on a daily basis and needs to be as accurate as possible. The motor it is reading is a 3 phase 30 HP electric motor. In case your curious, here is a link to a similar saw, in fact you can see how the control panel is mounted on the bridge which moves back and fourth which is real annoying and hits you in the head constantly. http://www.ebay.com/itm/NEW-Bridge-...471?pt=LH_DefaultDomain_0&hash=item2303a8d48f
It is so much nicer now that the control panel does not move with the bridge, I just gotta fix the amp signal issue.
I know my post is somewhat lengthily which I apologize for, I was just hoping to answer any questions that may arise. And again, I welcome and appreciate any thoughts or suggestions you may have.
Thanks,
Jeremy