calling all electrical "bright sparks"

[blue 464]

Hi, have recently fitted a thermostatic switch to my kenlowe via a relay, complete with a warning light fitted on the outlet of the relay to tell me when the kenlowe comes on, also a manual override switch connected direct to the kenlowe in case the relay fails, works fine, BUT the faster i go as the kenlowe starts to "freewheel" due to the airflow through it the warning light starts to glow, its about half brightness at 70mph.

having not paid much attention to my physics teacher 50 odd years ago I just about remember him talking about devices that only allow current to flow in 1 direction, can anybody suggest a simple cure for this please?

Dont be too technical otherwise my brain will explode!


thanks Derek

[DJT]

You want a small Zener diode in the circuit to the light. I have a small LED to indicate when the Kenlowe is running and had the same problem. I used a 8.2v Zener from Maplins (only a few pence) that does the job fine.
Dave

[Mike Stevens]

The fan, windmilling in the breeze, is acting as a generator and producing electrical power. I think your description says that the warning lamp is effectively in parallel with the fan, so it gets this electrical power and glows.

The simplest solution is a 'diode' that only lets current through one way. If this is connected only allowing current from the relay to the fan (with the lamp on the relay side of the diode), this should stop the lamp coming on when the fan is windmilling.

The diode rating must be such that it can pass the full fan current (which could be several amps) as well as not mind the reverse voltage when the fan is windmilling (easy). It must also not have too much 'leakage current' (current in the wrong direction) so that the lamp comes on when the fan is windmilling, again should be easy.

There will be plenty of diodes that will meet these specs, the problem might be in how to mount it!

I can make some suggestions if you wish... Polite ones of course.

Cheers,
Mike.

[DJT]

There was a discussion a while back on this: http://www.stag.org.uk/forum/showthr...ighlight=zener

The last post stated that the simple zener solution may not work for a filament bulb, but does for an LED.

Dave

[blue 464]

Thanks all.I will check if its a bulb light or an led and get back to you. derek

[V Mad]

No diode need; just wire the lamp to the coil side of the relay insted of the contacts.

[Mike Stevens]

No diode need; just wire the lamp to the coil side of the relay insted of the contacts.

While this wouldn't give any indication of a faulty relay, that is unlikely and the simple solutions are often the best....

Cheers,
Mike.

[blue 464]

Thanks, will try that first, derek

[blue 464]

Thanks all, changed the connection for the light to the output of the thermostat, problem solved!