3- Phase Battery charger for Hi-Lo's problem

[Anonymous]

We had a 480 3- Phase battery charger that would not go into charge cycle. This charger is at the end run of four other chargers that are all controlled from a common disconnect. At each charger in the conduit run from the disconnect we have a j-box with L1,L2, and L3 plus equip. ground wirenut connected and run to each chargers fuse panel and equip. grd. to chassis. When I checked between phases at inoperative chargers fuse panel I got these voltage readings-- L1 to L2(120 volts)--L2 to L3(240 volts)--L1toL3(240 volts) all fuses checking from top of one to bottom of the other checked good, also removed fuses checked continuity and tested good. Went to the disconnect that controlled all the chargers on this run found L1's fuse to be bad. The voltage readings here were L1 to L2(240 volts), L2 to L3(480 volts), and L1 to L3(480 volts). Though I had voltage between L1 and L2 I suspected L1's fuse and after turning off power ,removing it and testing continuity on my fluke (used wiggy for voltage checks) the fuse checked bad. Replaced fuse, problem solved. Still am somewhat foggy as to why a "weak fuse" on one phase would cause these voltage readings. Best theory I can come up with is that these chargers are not wired in the most efficient i.e. (proper) manner, basically they are series. I'm thinking the step-down transformers in each charger for contoll and monitoring voltage are effecting the line voltage. Also from what I have observed over the years no one pays too much attention to keeping the integrity of L1,L2 and L3 in any run or circuit, I am told it doesn't matter. Just trying to understand as I have only been in maintenance department a few years and we dont recieve any formal training from Ford Motor Company as we are not part of their skilled trades umbrella but are considered general maintenance. Im not totally without knowlege I know that I should have 480 between phases and 240 from any phase to ground.........RL

[imported_rlfrazee]

Wg, noticed I'm coming up guest instead of rlfrazee as author. I thought when I registered I checked the auto-log box. Do I still have to enter password and username each visit? I show up on the memberlist these darn puters are finnicky.....RL

[imported_rlfrazee]

Think I answered my own question. Went back to logon and and came up correctly after loging in.....RL

[Wgoodrich]

About a year ago I taught a class at Ford Vestion building in Indy. The union and education department provides classes of choice for union members. The students seemed to have come from maintenance department but was seeking residential design instead of industrial design. While I am qualified for both they just wanted residential. Vestion and the union contracted with me to teach the coarse for them. You might want to talk to your education department and ask if same is available in your area.

What you were experiencing is feed back through the primary windings of that or those charger units.

Lets step down to simple wiring. Take a 12/2 going to a light bulb. You have power coming in on the black and return path on the white. Take apart the return path white wire at the panel. Leave that white wire hanging in the air. Turn on power to that light fixture without a light bulb in the socket. You will find no reading of voltage between the white wire and the equipment grounding wire.

Now screw in the light bulb and test same test and you will get a voltage reading from that white to the equipment ground. This is because you are feeding voltage through that light bulb to the white wire looking for a place to go so the light bulb will light up.

Same happens in say a 240 volt water heater. You have line 1 hot wire going to one screw on that water heater element and you have line 2 hot wire going to the second screw of that same water heater element. Take one of the two hot wires off one water heater element. Test for voltage from that hot wire floating in the air to equipment ground and you will read 120 volts. Then take a voltage reading from that empty screw of that water heater element to equipment ground, you will get the same 120 volts just like that hot wire was connected by voltage back feeding through your water heater element to that empty screw. If you don't get that reading of 120 volts to equipment ground then your water heater element is burnt out. Then test from that empty screw to that first screw still connected. Here is where you get wierd volateges. If you have a minor resistant type heat element you would get 0 volts yet if you have a very heavy resistant type heat element you may get say 50 volts.

This is what you are experiencing.

Always make a habit when testing three phase to disconnect the wires from the circuit to avoid false test readings, otherwise you will get all kinds of feed back misleading you to think you have power.

What you did was leave your wires connected and when you tested for voltage you picked up voltage going through the primary wiring of your charger making you think you had power from that dead hot leg. Three phase wiring would make for a good POKER player. You get bluffed quite easy if you don't disconnect to avoid back feed misleading you.

Hope this helps

Wg

[imported_rlfrazee]

You have a very good talent for explaining electricity so that the laymen or less experienced can understand it. Didnt stop to think about feedback. For what its worth I do understand what you have said but liked your balloon theory the best so far.......Thanks RL