EVDL Administrator via EV wrote:
Clever! I wonder though how a household GFI would handle thousands of
cycles. They're designed to be tested once a month (does anyone actually do
that?) and to shut off a few ground faults.
Its life will depend on how much current it actually has to break. They
are rated to switch 15 amps; but only occasionally (maybe 100 cycles?).
Quality is also going to be a factor -- the cheapest ones are likely to
have the shortest life.
If your charger is at the end of its charge cycle, the current will be
much lower than its bulk stage. The AC current will thus be much lower,
and the GFCI's contacts would last a lot longer.
If you're worried life, you could also use a big contactor in place of
the GFCI. They are rated for hundreds of thousands of full-load
switching cycles. In this case, you'd wire the small relay's
normally-CLOSED contact, the contactor's coil, and one of its own
normally-open contacts in series. You'd also need a pushbutton across
the contactor's normally-open contact.
To start it, push the button. This powers the contactor coil, so it
pulls in. Once pulled in, it powers the charger, AND holds its own coil on.
When the pack reaches the set voltage, the small relay pulls in. This
OPENs its normally-closed contact, which breaks power to the coil, and
the contactor turns off. Once off, it STAYS off until the next time you
push the button.
I'm not an engineer (and Lee is), but here's an early draft of the circuit
I used to shut off a 24v charger for my Electro-Ped.
http://evdl.org/images/charger_shutoff_24v.tif
Excellent! And, you get the award for having a circuit that is even
harder to read than mine. :-)
It uses the same trick I described above with a contactor and a
pushbutton. I assume the squiggle at the top right is the contactor's
coil? I'd add a freewheel diode across it. The two "3.3" are probably
3.3K resistors.
The 47uF is a good idea; it should slow down the response a bit so it is
less likely to trip on just a momentary over-voltage.
I'd move the zener diode in place of the 2.2k to the positive end of the
pack. That way, when the pack is just sitting and well below the trip
point, the circuit will draw essentially zero current.
--
If we knew what we were doing, it wouldn't be called research, would it?
-- Albert Einstein
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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