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I've replaced the diode assembly on my E15 charger but haven't reconnected power yet, because I want to have a better sense of what happened first.
I'm trying to figure out exactly how and why the charger failed (released smoke)
in the first place. What had been troubling me is how the "frying" happened when I closed the main disconnect, with the AC power disconnected from the charger. It looked like a few little wafts of smoke were coming from the two AC wires that power the primary
side of the transformer (the two wires going from the white connector to the primary transformer), right where the wires go into the coil. But, it's possible the smoke was coming from somewhere else and just being carried upwards. With the timer not mounted,
that is the primary area that is open to the air, for smoke to waft out.
From where the smoke was coming though it seems like it would be from a short where
those wires meet the transformer. I eventually came up with a theory of what might have happened.
With the AC power off, when you close the main disconnect switch, the diodes
normally keep any current from going through the secondary winding of the transformer (I assume their primary purpose is for rectifying, but they should also keep current from the battery from going through the secondary coil). Based on the schematic, it
looks like the negative side of the battery is tapped into the middle of that secondary coil (through CB-2), while the positive end of the battery is connected to each end of the coil through diodes, so if not for the diodes
the battery would push current through the coil.
If a diode fails
and becomes a short (which is usually what happens when a diode fails), then closing the main disconnect would put the battery across half of the secondary coil. In a steady state case that wouldn't affect the primary coil, since it would be a DC current.
But when first closing the disconnect switch, there's a sudden increase in current
through the secondary coil, which is going to induce a big current in the primary coil. What I'm wondering is if that could be what caused the smoking that appeared to come from the primary coil. Could a big induced current have melted the insulation on the
transformer wires?
Presumably CB-2 tripped since the pack would be essentially shorted, but initially
there would be that massive spike in current causing a big induced current in the primary coil.
So, the reason I haven't reconnected everything is that I'm wondering if I should
be concerned about the possibility that insulation on the transformer wires may have gotten cooked off, causing a short there.
What do you think? Does that seem like a plausible explanation of what happened?
Thanks!
Mike
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
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