Don said:
Thanks for the help guys. Here is the situation. The charger I have
for my electric vehicle has one major flaw. If no output is connected
it will blow circuitry. I looked for other chargers but there are
none, which can charge up to 400V at 30A which cost around $2000.
Considering that I have already purchased the charger, and I
definitely want to protect it from blowing up, I would like to
develop a sense circuit which will ensure that no input power can be
supplied if it is not connected to a pack.
What comes to mind is the simple solution of a relay. But then again
it does not sound so simple.
Any ideas?
Hi, Don. Back in days of yore (1980s), before Potter&Brumfield T92s
ruled the earth, you would use a Potter&Brumfield PRD relay to switch
that kind of current. They've got the same contacts, but are open
frame relays with ugly black bakelite bodies. They still make 'em with
110VDC coils, and that could provide one possible solution to your
problem -- an AC coil won't cut it here.
I'm guessing that your "battery charger" is a switching power supply
with a series resistor and an in-line fuse. That would explain the
"blow up on no load" phenomenon. But I'm not too sure about the 30 amp
business. Let's see: 312V times 30 A = 9630 watts at 100% efficiency.
Don't think that's something you're just going to plug into a 120VAC
outlet, unless you've got an 80 amp service line somewhere. Or 240VAC
times 40 amps, for that matter.
But I'm hearing you say you don't want to turn on the charger, even by
accident, unless there's a battery installed in the go-cart. If your
charger is a simple one that applies a higher voltage than the battery
voltage, and then either senses current or uses a timer to determine
end of charge, or just stays on trickle charge until you unplug it, you
might want to try this circuit (view in fixed font or M$ Notepad):
'
' D1
' + >----o---->|-------------------.
' | 1K 1/2W T |
' | || ___ --- |
' o-----||-|___|-o---o o----o
' BATTERY | || R2 | SW1 |
' .-. CRY1A .-. |
' CHARGER R3 | | | | +|
' | | R1| | ---
' '-' 12K 5W'-' -
' L1 | | 312V|
' .-. C| |
' ( X ) RY1 C| |
' '-' C| |
' | | |
' - >---o--------------o----------'
'
' ||
' >----------||----.
' AUX || |
' CONTACTS CRY1B |
' |
' >----------------'
'
RY1 P&B PRD-11DY0-110
R1 12K 5WATT
R2 1K 1/2W
R3 100K
L1 NE-51
D1 85HFR60 (If=85A, PRV=600V)
created by Andy´s ASCII-Circuit v1.24.140803 Beta
www.tech-chat.de
I've made some assumptions here, which means that you can feel free to
modify things as you choose. I've assumed your battery charger is a
simple cheapie which applies a voltage higher than the battery voltage,
and either has a timer or measures current to end charge, or turns into
a trickle charger which can be left on until you're ready to use the
go-cart. This won't work for a charger that uses battery voltage
sensing. However, it shouldn't blow anything up, either. I've also
assumed that, under normal circumstances, charging current can't exceed
20A or so. (Make sure to heat sink the diode -- figure 1 watt per amp
of charging current. The specified diode is probably overkill.)
Another assumption is that you can turn on your charger with the set of
AUX contacts. That may mean leaving the charger ON/OFF switch in the
ON position, and just turning it on by switching on line voltage to the
charger. Either that or, possibly, you can finagle the wires from the
ON/OFF switch out to the auxillary contacts. Your call. I'm assuming,
of course, that you're using the appropriate HV safety precautions. A
312V battery can be fatal if handled improperly. If you don't know
what you're doing, don't do it. If you don't understand what's going
on here well enough to double-check the above and be confident it's
right, don't do it, either.
You can see from the circuit action that you have to press pushbutton
SW1 to start the charge cycle. If there's no battery, the relay won't
turn on. If the relay doesn't turn on, your charger won't turn on.
But when the charger does turn on, it also keeps the relay on, and it
will stay on until the charger is unplugged or otherwise turned off.
You have to keep the pushbutton depressed until the charger is up and
running.
A simpler circuit might be possible at the cost of leaving the relay on
after the charge cycle is complete, but that's a wasted 3.6 watts which
will tend to discharge the battery. I would guess one big diode is
worth it.
Good luck, and play safe
Chris