On 2/18/2016 8:19 PM, Snuffy "Hub Cap" McKinney wrote:
"Don Y" wrote in message
...
On 2/18/2016 4:49 PM, Don Y wrote:

You can also design something to sense power being APPLIED (from the
contacts) and engage a relay coil letting the relay contacts engage the
heater load. E.g.,

C O + --+---||----- to relay coil N | T | A
+---||----- to motor circuit C T - -------------- to relay coil and
motor circuit S


I should have explained this, just in case... :

The role of the diodes is to prevent power from the batteries ON THE
"MOTOR CIRCUIT" from energizing the relay when there is NO power on the
"contacts". The second diode blocks the current from flowing right to
left (battery being connected on the right side of it) and into the relay
coil -- which would turn the relay on all the time (as long as the
batteries had power!). We only want the relay to turn on when power is
available at "contacts".

[The first diode *could* be omitted but there are some cases where it can
be of use]

Thanks for taking the time with this. I enjoy this sort of thing myself.
Relays and PLC's are a lot of fun. Will have to do some testing with
different size resistors and go with your relay method. Can't plan for
every situation, but not draining the battery is important.

Try it without the relay, first. I suspect you (or someone) can sort of
keep an eye on it to make sure it is "parked" properly while you get a
feel for how well this is working.

Granted, the heater will sap a bit of capacity from the battery while
traveling but hopefully not enough to cause the chair to stall
(those batteries are pretty substantial and I'm sure the chair is
geared way down! Probably lose more in the gear train than actually moving
the person!)