Power Drain from 5 Pin Relay

Thread Starter

barry1441

Joined Feb 6, 2020
3
Hello, I have a 70A 5 Pin relay switched by the handbrake in a automotive vehicle. When the handbrake is on the power from the battery is fed to various electrical items, lights,USB etc. When the handbrake is off none of these items work.
The problem I have is that when the handbrake is on and all the electrical items are turned off by there switches, there is still obviously a small current draw across the coil of the relay and this over time if the vehicle is parked up causes the battery to go flat.
Any ideas or help would be appreciated.
 

dendad

Joined Feb 20, 2016
3,425
Can you supply a circuit?
And, why do you have it wired up this way?
Can you change the power feed to be driven from the ignition switch so it will not work unless the motor is running?
 

Thread Starter

barry1441

Joined Feb 6, 2020
3
Hello, I have a 70A 5 Pin relay switched by the handbrake in a automotive vehicle. When the handbrake is on the power from the battery is fed to various electrical items, lights,USB etc. When the handbrake is off none of these items work.
The problem I have is that when the handbrake is on and all the electrical items are turned off by there switches, there is still obviously a small current draw across the coil of the relay and this over time if the vehicle is parked up causes the battery to go flat.
Any ideas or help would be appreciated.
I will try upload a diagram, reason is for an approval we have on the vehicle, any non EMC tested electrical items need to turn off when vehicle in motion, we attached to handbrake so that when stopping at side of road to pick someone up it was easier to engage handbrake rather than turn off engine for lights to work
 

ebeowulf17

Joined Aug 12, 2014
3,274
Hello, I have a 70A 5 Pin relay switched by the handbrake in a automotive vehicle. When the handbrake is on the power from the battery is fed to various electrical items, lights,USB etc. When the handbrake is off none of these items work.
The problem I have is that when the handbrake is on and all the electrical items are turned off by there switches, there is still obviously a small current draw across the coil of the relay and this over time if the vehicle is parked up causes the battery to go flat.
Any ideas or help would be appreciated.
A schematic or wiring diagram would help. How exactly is the handbrake controlling the relay? Also, I assume the relay is a mechanical relay, not solid state (SSR.) If that's wrong, then an exact part number and hopefully datasheet would be helpful.

Do you need these functions to be available when the engine is off? It seems to me like the control for the relay coil shouldn't be a choice between either ignition switch OR handbrake switch. Instead it should run through BOTH of them. That way:
1) when the vehicle is in motion, functions are disabled, per your requirements
2) when stopping to pick someone up, engine can stay running and simply applying handbrake turns functions on
3) when ignition is off, no power flows through relay coil or external devices

If you do need these systems to be able to run with engine off, I don't see any way to avoid power drain through the relay coil. You can't expect the relay coil to be doing work without consuming energy. You might be able to reduce wasted power by using MOSFET based SSRs, but I'm not sure how well they'll handle electrical noise in an automotive environment, nor whether solid state switching is an acceptable cutoff device when you're dealing with regulatory requirements to shut down certain devices. The only other thing I could think to do is set up a timer that keeps the relay on only for a set amount of time after the engine stops, but then turns it off so that the wasted power consumption is limited.
 
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