Voltage Sensitive Relays

[Nimrod11]

Guys,

Has anyone ever considered using a voltage sensitive relay to shut off the auxiliaries when the motor isn't running?

I've been thinking about how to make a simple circuit to shut an aux relay off when voltage is below 12.5V or so and came across such a product

http://www.iboats.com/Charge-on-the-Go- ... _id.341867 (http://www.iboats.com/Charge-on-the-Go-12V-Voltage-Sensitive-Relay-BEP-Marine/dm/view_id.341867)


This seems way over sized and is intended to charge a bank of batteries. One could use the secondary battery connection for the auxiliary loads of the bike. This would then shut off the aux when the motor is off.

Any thoughts?

[Nimrod11]

Another idea: I am not an electronics expert, but if you had a zener diode connected to a relay and reverse biased, it would shut down the relay below it's nominal voltage. So just choose a 12.5V diode. Makes sense? Any expert around?

[oxnsox]

Keep it simple and wire anything thru a relay off the aux, so when the key is in and on things work, and when it's not they don't.

You could use a VCR but what could happen is:
- What ever is connected thru the relay stays on when you are away from the bike (drawing down the battery)
- Voltage goes low on the unattended bike due to whatever is connected to the VCR drawing current. Relay operates and disconnects. Unloaded battery slowly rises in voltage. VCR senses ok volts and operates, Load on battery causes drain, VCR drops load... etc, etc,

Personally I wouldn't recommend it. The BEP unit is designed more as a saftey device for boats with more than one battery. It enables one battery (the start battery) to be dropped off line so you can restart the motor to get home. Otherwise sitting listening to tunes fishing for half a day may leave you with no enough juice in the battery.

[Nimrod11]

Thanks for the ideas. Good points...

My thought was that when the engine is running, voltage is always above 13V and below 12.5 when not. So if you had a relay that turned off when below 12.5 or so, you shouldn't get that unstable situation you mentioned.

I think my other reason was that when driving in town, voltage drops a little, to about 12.3V when my aux lights are on. If I turn the bike off in this condition, like a gas station, some times it fails to start. I just put in a new battery, so that should help, but just wondered if it would be worth shutting off all aux in these conditions.