Apr 17, 2001, 09:44 AM
Member

# Samples of Low Voltage Cut-Off Relay Circuits

Samples of Low Voltage Cut-Off Relay Circuits

Ok, here is couple of Low Voltage Cut-Off Relay Samples

The relay is "set" by the momentary switch (shorting out the required resistor-s).

When the voltage divided across the relay coil (K) & required resistor-s (R) equals the relay's drop-out voltage, it does; shutting down the motor.

The following are crude representation of a spreadsheet (available via e-mail, cells separated by "//") and schematic.

"05"//S400
A//B//C//D
1//Number of cells//8//8
2//Drop out V//3.6//0.6
3//Relay model #//RS 275-0226//RS 275-0248
4//Coil resistance//66//320
5//Cutoff V/cell//0.9//0.9
7//Resistor wattage//0.484848485//0.016666667//((B1*1)^2)/(B4+B6)

/
(+) -----------------------+--ƒ¦/ ƒ¦------------------------------
|
K (relay)
Battery | Motor
+--+
| |
(momentary switch) S R (required resistor-s)
| |
(-) -----------------------+--+---------------------------------------

Tried to make schmatic work, but its sure not wysiwyg!

[This message has been edited by jrb (edited 04-17-2001).]
 Apr 19, 2001, 11:23 AM Member Thread OP The RS 275-248A weighs .3 oz; but I'm sure its plastic case could be change to reduce the weight further. I spent the \$4 and will try "248A" and 3.9K 1/2 watt resistor on an S400 test set-up. I'll report back on the results if there's interest.
 Apr 19, 2001, 01:46 PM Registered User Sure, let us know!
 Apr 21, 2001, 05:24 PM Member Thread OP Have done some testing. Find that the drop out voltage is 2.5 volts rather than the .6; need to pick up a 680 ohm resistor so I can complete the tests.
 Apr 24, 2001, 09:25 AM Member Thread OP A \$6 system that relay works! From testing: Coil resistance 413 ohms, drop-out voltage 2.5 volts, a smidge bigger than 2 sugar cubes. With 680 ohm resistor in series with the coil the relay set w/o problem and cut-off @ 6.7 volts – predicted @ 6.6 (.827 volts/cell). The relay also switched and survived repeated operation @ above 25 amps. Using a 1k trimmer pot (i.e. 271-280) rather than the fixed resistor as above would allow for adjustable run time/voltage cut-off. So spend \$6 @ Radio Shack buy: a 275-248A relay, a 271-280 trimmer pot, and a 275-1556 momentary push button switch (you’ll actually get 2, or you can rig something else) and you’ll have an excellent an 8 cell (7 maybe, 6 don’t think so) S400 (and probably “05”) Low Voltage Cut-Off system!
Apr 27, 2001, 08:26 AM
Montezuma, Iowa
Quote:
 Originally posted by jrb: A \$6 system that relay works! So spend \$6 @ Radio Shack buy: a 275-248A relay, a 271-280 trimmer pot, and a 275-1556 momentary push button switch (you’ll actually get 2, or you can rig something else) and you’ll have an excellent an 8 cell (7 maybe, 6 don’t think so) S400 (and probably “05”) Low Voltage Cut-Off system!
jrb,
Sounds like just what I am looking for!
Will you build me one?
Or, loan me yours so that I can see how you put it together? (I'm NOT an electrician, but I can solder)
Mike Gretz

P.S. Since asking my original question about a ideas for shutting off the motor on my speed 400 C/L airplane, I've been
pleasantly surprised at how much interest there seems to be amoung the E-Zone'ers for electric C/L. However most of the
posts went right past what I'm looking for and on to IR systems, signals through insulated lines, etc. All that's WAY too much
(heavy) for what I want. I'm looking for light and cheap. Your's sounds right!

FYI: I was flying a full house digital proportional electric control system, sending signals down 2 insulated control lines to
standard R/C servos for throttle, retracts and flaps, in my entry at the FAI Scale World Championships in 1974!!! It was the
first system of it's kind in the world - built for me by Ken Wilson (now deceased), who was an EK Logitrol repairman in
Kansas City.
 Apr 27, 2001, 09:54 AM Member Thread OP Mike, Sent you an e-mail with a couple of attachments. One being an Excel spreadsheet that does the calculations, has a picture of my relay, scan of the RS back label, and a circuit diagram. Spreadsheet is avaiable to anyone via e-mail.
Dec 23, 2001, 08:49 AM
Member